Little Manatee River Study A characterization of the watershed hydrology and investigation of water quality and nutrient/solids transport: Final report

[From the U.S. Government Printing Office, www.gpo.gov]

TTLE MANATEE RIVER STUDY

A Characterization of Watershed Hydrology
and Investigation of Water Quality
and Nutrient/Solids Transport

FINAL REPORT

Sid Flannery
Southwest Florida Water Management District

Herbert L. Windom
Feng Huan
Skidaway Institute of Oceanography

Ken Haddad
Florida Department of Natural Resources
Florida Marine Research Institute

Edited by
Gail M. Sloane
Steve J. Schropp
Fred D. Calder
Florida Department of Environmental Regulation

March 23, 11390

Funds for this project were provided by the Department of
Environmental Regulation, Office of Coastal Management using
funds made available through the National Oceanic and
Atmospheric Administration under the Coastal Zone Management
Act of 1972-1, as amended.

TABLE OF CONTENTS

EXECUTIVE SUMMARY . . . . . . . . . . . . . . . . . . . . . iii

ACKNOWLEDGEMENTS . . . . . . . . . . . . . . . . . . . . . . vi

I. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . 1
OVERVIEW OF THE LITTLE MANATEE RIVER WATERSHED PROJECT . 3

II. DESCRIPTION OF THE WATERSHED . . . . . . . . . . . . . . 5
SIZE AND TRIBUTARIES . . . . . . . . . . . . . . . . . . 5
CLIMATE . . . . . . . . . . . . . . . . . . . . . . . . 7
GENERAL RUNOFF CHARACTERISTICS . . . . . . . . . . . . . 10
GEOGRAPHIC INFORMATION SYSTEMS DEVELOPMENT . . . . . . . 16
Data Acquisition and Duality Contro . . . . . . . . 16
Data Layers . . . . . . . . . . . . . . . . . 16
Tabular attribute data . . . . . . . . . . . . 20
Quality Control and Assessment . . . . . . . . 20
Data analyses . . . . . . . . . . . . . . . . 21

III. WATER RESOURCES . . . . . . . . . . . . . . . . . . . . 23
HYDROGEOLOGY . . . . . . . . . . . . . . . . . . . . . . 23
WATER USE PERMITS . . . . . . . . . . . . . . . . . . . 24
FLORIDA POWER AND LIGHT WITHDRAWALS . . . . . . . . . . 26

IV. HYDROLOGIC CONDITIONS DURING THE STUDY . . . . . . . 30
DATA COLLECTION NETWORK . . . . . . . . . . . . . . 30
RAINFALL. . . . . . . . . . . . . . . . . . . . . . . 34
STREAMFLOW. . . . . . . . . . . . . . . . . . . . . . 37
TIDES . . . . . . . . . . . . . . . . . . . . . . . . 43

V. FRESH WATER CHEMISTRY . . . . . . . . . . . . . . . . 46

OBJECTIVES. . . . . . . . . . . . . . . . . . . . . . 46
SAMPLING AND ANALYTICAL METHODS . . . . . . . . . . . 46
OTHER DATA SOURCES. . . . . . . . . . . . . . . . . . 53
DATA REDUCTION . . . . . . . . . . . . . . . . . . . 54
Estimates of Annual Material Flux from Sub-Basins 54
Extrapolation method for estimating material
flux . . . . . . . . . . . . . . . . . . . 56
Interpolation method for estimating material
flux . . . . . . . . . . . . . . . . . . . 58

RESULTS . . . . . . . . . . . . . . . . . . . . . . 61
Water Quality Characteristics . . . . . . . . . 61
Chemical Transport from Sub-basins . . . . . . . 77
Rating curves . . . . . . . . . . . . . . . . . 77
Fluxes from Sub-basins . . . . . . . . . . . . . 79

VI. ESTUARINE WATER CHEMISTRY . . . . . . . . . . . . . . . . 85
OBJECTIVES . . . . . . . . . . . . . . . . . . . . . . . 85
SAMPLING AND ANALYTICAL METHODS . . . . . . . . . . . . . 85
DATA REDUCTION . . . . . . . . . . . . . . . . . . . . . 90
RESULTS . . . . . . . . . . . . . . . . . . . . . . . . . 92
Salinity Distributions . . . . . . . . . . . . . . 92
Dissolved Oxygen . . . . . . . . . . . . . . . . . 104
General Water Chemistry . . . . . . . . . . . . . . 112
Nutrient and Suspended Solids Distribution . . . . . 115
Dissolved Nutrients. . . . . . . . . . . . . . 115
Total Suspended Sediments and Particulate
Nutrients . . . . . . . . . . . . . . . 116
Chlorophyll, Phytoplankton and Primary
Productivity . . . . . . . . . . . . . . . . 116
Seasonal Trends for Chlorophyll
Concentrations and Phytoplankton
Composition . . . . . . . . . . . . . . 120

LITERATURE CITED . . . . . . . . . . . . . . . . . . . . . . . 128

EXECUTIVE SUMMARY

The Little Manatee watershed is located in southern
Hillsborough and northern Manatee Counties. The river generally
flows in a westerly direction discharging to Tampa Bay near
Ruskin.

Land use in the watershed was analyzed using a geographic
information system. The entire watershed comprises 57,364
hectares (224 square miles). Upland plant Communities comprise
13% of the watershed and consist of pinelands to hardwood
forests. Wetland plant communities constitute 9% of the
watershed ranging from saltmarsh to hardwood swamp. Water bodies
comprise 3% of the watershed, not including the river and its
tributaries.

The largest category under GIS land use is
agriculture/pasture/barren, which constitutes 75% of the
watershed. This category is very general, and includes urban
areas. Urban areas represent a small portion of this percentage.
This category is representative for subwatersheds except for the
Cypress Creek subwatershed which includes the urbanized Sun City
center area.

Streamflow and water quality in Carlton Branch, Dug Creek,
Cypress Creek, the Little Manatee near Fort Lonesome, South Fork,
and the Little Manatee near Wimauma were monitored during the
study period from January 19Be through January 1989.

Bi-weekly water quality sampling during the study year found
pronounced differences in water chemistry between the seven
stream stations. DOC and nitrate 'concentrations were highly
variable during the study period. Concentrations of ammonia and
phosphate were somewhat less variable and reached maximum values
between July and September. This was the approximate time of the
highest discharge.

Particulate carbon, nitrogen and phosphorus vary, in
general, with total suspended solids. The maximum or spike in
particulate substances for the Cypress Creek, Carlton Creel-.-.,
Wimauma and Ft. Lonesome chemographs occur at the same time but
are not present in the Dug Creek and South Prong chemographs.

The Fort Lonesome station was the most upstream site
monitored on the main channel of the Little Manatee River.
Generally, water quality at this site can be characterized as
highly colored, slightly acidic, with low levels of suspended
matter and moderate levels of nutrients. Mean values of color
and total dissiolved carbon were highest at this station, probably
reflecting the input of humi-z compounds leached from vegetation
and litter in the drainage basin.

iii

The site most similar to Fort Lonesome was the South Fork,
which was the only station on that branch of the river. Mean
Values of alkalinity and chloride were ranked lowest for this
station, and a number of parameters were ranked second lowest
only to Fort Lonesome (conductivity, turbidity, total suspended
solids, particulate carbon, particulate nitrogen, calcium and
sul f ate) .For some other parameters (total dissolved carbon,
ammonia, nitrate/nitrite, ortho-phosphate, and silica'.), the South
Fork was ranked near the middle of the seven stations.

Of the remaining five stream sampling stations, two sites
(LMR near WimaUMa and LMR North Fork) were on the main channel of
the river while three stations were on three tributary creeks to
the main channel. These three tributaries, Carlton Branch, Dug
Creek and Cypress Creek, all flow from north to south and enter
the Little Manatee on its-, northern bank. In general, water in
these tributaries was lower in color and more highly mineralized
than water in the main river or the South Fork. Cypress Creek
was notable for the high levels of turbidity, total suspended
solids, particulate carbon and particulate nitrogen, probably
reflecting the soil disturbance and resulting suspended load that
was generated in the sub-basin during the study. Dug Creek and
Carlton Branch had the lowest mean color values found in the
study but had the highest levels of nitrate-nitrite and silica.
It is believed that the high degree of mineralization and
dissolved constituents in these three tributaries are the result
of irrigation runoff.

The three stations on the main channel of the Little Manatee
River are Fort Lonesome, LMR North Fork, and the LMR near
Wimauma. Examination of mean water quality values for these
three stations demonstrates the increasing mineral and nutrient
content of the Little Manatee as it flows to Tampa Bay. Some
constituents, such as nitrate, silica, TSS and sulfate show
significant levels of enrichment proceeding downstream while both
particulate and dissolved phosphorus show little or no
enrichment.

Salinity distributions in the estuary showed distinct
changes in response to these changes in flow. Mean water Column
salinity was measured at four fixed locations in the river.
Salinity at the mouth cif the river remained above 20 ppt until
early September, when flood flows briefly reduced salinity to
near 5 ppt. For the remainder of the year, salinities fluctuated
between 18 and 23 ppt salinity, with slight decreases in November
and January due to storm events. Maximum observed salt
penetration was in June, near the end cif the dry season.
Salinity in the river decreased through July and AugUSt, and the
river was completely fresh except for a small salt lens at the
(nouth during a flood in early September. By late September and
through the fall, salinity distributions had returned to more

typical profiles, although a significant storm event in January
1989 freshened the river above mile five.

Dissolved oxygen concentrations in the Little Manatee River
were at high levels during most of the year but reduced to values
below 4 mg/l during much of the summer, indicating potentially
stressful concentrat ions for aquatic biota in the summer.
Differences in dissolved oxygen between surface and bottom waters
were small, however, and it does not appear that oxygen stress
occurs in bottom waters due to limited mixing. Generally, with
regard to temperature and salinity effects on water density and
stratification, the Little Manatee tends to be well mixed. There
are areas of the river, however, that appear to be sensitive to
factors that could reduce dissolved oxygen concentrations.

A progression from the upper reaches of the Little Manatee
estuary to Tampa Bay showed chemical differences indicative of a
change from nutrient-rich, low-salinity waters to phytoplankton
dominated, high-salinity waters. Nitrate-nitrite, silica,
particulate carbon, turbidity, and total dissolved carbon showed
distinct declines in concentrations from the upper reaches of the
estuary to Tampa Bay. With the exception of phosphorus, the bay
has much lower levels of dissolved nutrients (N,,Si) due
presumably to phytoplankt---)n uptake. Dissolved phosphorus
concentrations were distributed very evenly along the salinity
gradient indicating this nutrient is not limiting and is in
excess supply in the estuary. Total suspended solids were
highest in Tampa Bay, and increased with salinity in the river
due to the influence of bay water.

The Ruskin Inlet station was located in an urbanized
tributary to the Little Manatee that receives considerable
amounts of urban runoff. Of -:,.-jurse, salinity fluctuated MUCh
r@ore at this station than at the stations located on specific
salinity concentrati--nns. Nutrient cr-incentrations showed large
seasonal variation at this station due to stormwater inputs and
the rapid change from a meschaline (medium salinity) to a 1---tw
salinity environment.

ACKNOWLEDGEMENTS

Watershed management has been an elusive concept to apply in
protecting estuaries and their tributaries. One of the reasons
for this is the difficulty in obtaining physical, chemical and
biological information on a scale needed to determine system-wide
resource protection strategies.
The Little Manatee River Project demonE-:;trates that skilled
people will go beyond their routine responsibilities in
contributing to a team effort to make a large-scale Study work.
In particular, the complex field and laboratory activities, of
this project could riot have been conducted without the personal
interest and pr----fessional help from.- Quincy Wylupek, Phillip
Rhinesmith and Mark Rials of the Southwest Florida Water
Management District.
Of considerable importance to watershed -5tUdies are good
descriptions cof hydrological processes and upland features. For
assistance in providing these, special thanks are due to Dr.
Bruce Taylor, P.E. (Taylor Engineering, Inc.), and Harry Downing
(Southwest Florida Water Manaciement District). We especially
appreciate the help of Ken Butcher (United States Geological
Survey) for his promptness in collecting stream flow information
and establishing stream discharge statistics.
Funded by NOAA through the Coastal Zone Management Act, as
amended

I. INTRODUCTION

This is a report on water chemistry and hydrology in the

Little Manatee River, its tributaries, and estuary. The results

presented in this report deal mainly with characterizations of

the movement of nutrients, solids and major ions through the

system. The report also includes a brief physiographical

description, including vegetative cover, land use, soils, and,

climate to support finding on the origin, transport and removal

of chemical constituents and solids carried by the river.

This document, along with separate biological reports-

(Peebles,1989),(Rast, 1989),(Vargo, 1989)-are the result of

efforts by the Southwest Florida Water Management District

(SWFWMD), Florida Department of Environmental Regulation (FDER),

and Florida Department of Natural Resources (FDNR) to develope a

system-wide understanding of resource management needs for the

Little Manatee River basin. These reports are basic information

sources to be used in identifying man's influences on the river,

estimating possible degradation of the aquatic system, and

understanding the susceptibility of the system to future

problems.

SWFWMD, FDER and FDNR` initiated this project in response to

agency and public concern over protection of the last major river

in a relatively natural condition in the Tampa Bay system. The

protection of the Little Manatee River and estuary is a state

priority. The river, in addition to its own resource values

influences water, quality and habitat in Tampa Bay including the

adjacent Cockroach Bay Aquatic Preserve. Because of the lack of

urbanization in the basin, there is opportunity to develop a

comprehensive strategy to anticipate and prevent problems as the

basin is developed.

Activities to protect and re-establish living resources in

Tampa Bay cannot be fully effective without protecting the Bay's

tributaries and their associated wetlands. Drainage basins with

natural systems relatively intact, such as the Little Manatee

River basin should be managed as ecological and hydrological

units. This comprehensive approach is the only effective way to

ensure that proper freshwater flows and nutrient inputs are

maintained in the estuarine part of the system.

As in many coastal systems the existing information on the

Little Manatee River and estuary was not on system-wide

processes. While localized data is useful for individual

regulatory decisions, larger-scale studies that integrate

physical and chemical information are essential for judging the

susceptibility of the river to development pressures,

establishing sound management objectives and plans, and providing

development criteria for maintaining conditions that support

estuarine productivity.

OVERVIEW OF THE LITTLE MANATEE RIVER WATERSHED PROJECT

Prior to initiating the study, we consulted with local,

state and federal agency representatives to determine the extent

of existing information on the system and to help establish a

master plan and detailed sampling and analytical methods. During

discussions between the project team and persons with local

knowledge of the river, the following concerns were expressed:

1. Upstream impoundments and water diversions have

decreased the estuary's value as a fishery nursery;

2. Nutrient enrichment has resulted from agriculture

and aquaculture operations in the watershed;

3. Future development in the watershed may increase

erosion and contribute to increased sedimentation and

nutrient enrichment;

4. Land use planning agencies do not have sufficient

information to adequately protct watershed features and

natural processes; and

5. Finfish and shellfish yields have decreased.

During the prelimanary stage, the U. S. Geological Survey,

under contract with DER installed stream flow recorders on

subwatersheds in preparation for chemical and hydrological

measurements on the major system compartments.

After initial testing of field and laboratory methods,

formal work began in January 1988. The last field measurements

included in this report were taken January 1989, although

monitoring will continue on a less intensive basis.

The SWFWMD conducted the field program, the majority of the

laboratory work, and assisted in interpretation of the data.

Supplemental laboratory analyses were done by commercial

laboratory. The Department of Natural Resources Marine Research

Institute provided mapping and descriptions of land features,

land usage and drainage patterns. The Department of

Environmental Regulation provided technical assistance on

establishing methodology and interpreting chemical and physical

measurements.

II. DESCRIPTION OF THE WATERSHED

SIZE AND TRIBUTARIES

The Little Manatee watershed is located in southern

Hillsborough and northern Manatee Counties. The Little Manatee

River is about 40 miles in length with a contributing drainage

basin of about 221 square miles (Figure 2.1). Headwaters for the

river are in a swampy area of southeastern Hillsborough County.

The river generally flows in a westerly direction discharging to

Tampa Bay near Ruskin. The river channel is usually well defined

except in the most upstream areas. The lower 10 to 15 mile reach

of the river is tidally influenced.

Major tributaries to the Little Manatee River include

Cypress and Dug Creeks located in the northwestern portion of the

basin; Gully, Carlton, and Pierce Branch located in the north-

central portion; Howard Prairie Branch and Alderman Creek in the

eastern portion; South Fork in the south-central portion; and

Wildcat and Curiosity Creeks in the western portion of the basin.

Streamflow and water quality in Carlton Branch, Dug Creek,

Cypress Creek, the Little Manatee near Fort Lonesome, South Fork,

and the Little Manatee near Wimauma were monitored during the

study period from January 1988 through January 1989. Details

Little Manatee River
Drainage Basin

)C3
4
B x
E G

x
A

........ ..
F

2 X

A e USGS Streamflo sites
w gaging x z
X Rainfall stations L/5
LK
C)

Figure 2.1. Tito Little Manatee River Drainage basin.

presented in Figure 2.2. Most of the rainfall occurs during the

summer months. Tropical storms and convective thunderstorms are

the main reason for the higher precipitation rates in the summer

months.

RUSKIN AVERAGE MONTHLY RAINFALL (1976-1989)

Figure 2.2. Distribution of the monthly average annual rainfall for the
Ruskin station (1976-1989).

Another important aspect of the climate that effects runoff

is evapotranspiration. Evapotranspiration is the process whereby

incoming energy from solar radiation transforms water from a

liquid to a gaseous state. The processes involve direct

evaporation of water from moist surfaces and transpiration during

plant respiratory processes. There are two types of

evapotranspiration (ET) estimates: potential and actual.

Potential ET is the maximum ET expected under prevailing climatic

conditions assuming non-limited water availability. One of the

most accurate methods for estmating potential ET is the Penman

method. The method considers cloud cover, temperature, vapor

pressure deficits and incoming solar radiation. For the Tampa

area, the 50 percent probable potential ET is 54 inches

(Smajstrla, 1984), which is close to the average annual

precipitation for the area.

Actual ET, on the other hand, is the amount of water

transformed based upon prevailing climatic conditions and the

amount of available moisture. Actual ET is very difficult to

estimate because of its dependency on numerous factors. Such

factors include land cover, distribution of rainfall, surface

water storage, and soil percolation. Since the basin exhibits

very little ground water recharge or discharge into the aquifer

system (Aucott, 1988), the actual ET rate can be approximated by

rainfall minus runoff. If the average annual rainfall is taken

as 50.5 inches/year and the average annual runoff depth at 15.6

inches/year, the actual ET estimate is 34.9 inches/year. This

estimate is probably low because of the irrigation runoff within

the basin. The USGS has estimated actual ET in the region at 39

inches/year.

GENERAL RUNOFF CHARACTERISTICS

A one-hundred forty-nine square mile area of the Little

Manatee River watershed has been monitored for runoff at a USGS

gaging station since 1939. This USGS strean gaging station

(#02300500) is located on the Hwy. 301 bridge near Wimauma 15

miles upstream from the river's mouth. Daily records for this

site are available for a period of about 50 years which provide a

good statistical base for establishing characteristic flow

patterns for the watershed.

Average monthly discharges for the period of record

available for the Wimauma station are presented on Figure 2.3.

July through September represent the highest runoff months with

average discharges between 300 and 400 cubic feet per second

(cfs).

WIMUAMA AVERAGE MONTHLY FLOW (1939-1989)

450

400

350

300

250

200

150

100

0 JAN FEB MAR APR FEB MAY JUN JUL AUG SEP OCT NOV DEC
MONTH

Figure 2.3. Average monthly flows for Wimauma station (1939-1989).

The remaining months of the year averaged 150 cfs or less.

Pronounced low flow periods usually occur in the late spring

(May) or the late fall and early winter (November and December).

The average discharge for the 149 square mile area is 171 cfs.

In terms of depth of water over the contributing watershed, this

flow represents 15.6 inches of runoff per year. Along with the

Alafia basin, the Little Manatee basin has the largest runoff

depth of any basin located within west-central Florida (15 to 20

inches/year) (USGS, 1981).

A review of historical flow records for the Wimauma site

reveals extreme seasonal and yearly variations in discharge. The

largest instantaneous flow of record is about 14,000 cfs which

occured in June 1960. The lowest flow of record is about 0.8

cfs which occurred in December 1976. Table 2.1 represents a

duration analysis of discharges at the Wimauma monitoring

station. Between the 95 and 5 percent exceedance probabilities

flows varied between 10.0 and 708 cfs, with a median of 54 cfs.

This median flow is less than the average flow for this station

by more than a factor of three, indicating that the average

statistic is heavily influenced by brief periods of high runoff.

Based on a review of historical runoff events and the

duration analysis, it appears that the runoff hydrographs are

very peaked or ephemeral. This type of runoff pattern indicates

the absence of significant surface water storage areas that can

moderate discharges by attenuating flows. For example, the

Withlacoochee River system drains an area greater than 2000

Table 2.1. Wimauma Flow Duration Table.

Wimauma Flow Duration Table

Exceedance Exceedance
Probability Flow Probability Flow
95.0 10.5 45.0 67.5
90.0 15.6 40.0 75.3
85.0 20.0 35.0 89.3
80.0 23.6 30.0 109.7
75.0 27.2 25.0 140.3
70.0 31.9 20.0 185.2
65.0 36.6 15.0 257.2
60.0 42.0 10.0 400.6
55.0 47.4 5.0 708.3
50.0 55.3

square miles; however, the highest recorded discharge near the

mouth of that basin has been less than 10,000 cfs. This is

because the associated lakes, sloughs, and swamps in the

Withlacoochee basin provide significant attenuation of peak

flows. This is in contrast to the Little Manatee River at the

Wimauma USGS gaging station which has a drainage area of 149

square miles but a recorded peak discharge of 14,000 cfs.

During the study period several days of significant rainfall

occurred over the basin yielding a peak discharge of 9700 cfs.

This represents a discharge event with a probability of

occurrence between one-in-10 to 25 years. As previously

indicated, the largest instantaneous flow of record for the

Wimauma station was 14,000 cfs. This represents a discharge

event with a return frequency of one-in 50 years. Table 2.2

represents expected high discharges for various return intervals.

Table 2.2. Flood Flow Return Frequencies (D&M, 1975)

Return Interval Years Flow @ Wimauma

100 18,550
50 14,800
25 11,560
10 7,930
2.33 3,300

Results of low flow frequency analysis for the Little Manatee

River near Wimauma are presented in Table 2.3. This table shows

that the river has prolonged periods of low flows. For instance,

a thirty-day period of average flow less that 13 cfs has a return

frequency of every two years. The lowest daily flow of record

(0.8 cfs) has a return interval greater than one-in 20 years.

Florida Power and Light (FP&L) has a large pumping station on the

Little Manatee River that is used for make up water for their

power generating facility which went into operation in 1976. It

is expected that this withdrawal will have little impact on

exteme low flows because of withdrawal limitations by agreement.

Table 2.3. Low-Flow Frequency Wimauma

Consecutive Return Frequency in Years

Day 2 5 10 20

1 7.9 4.1 2.7 1.9
3 8.3 4.4 3.0 2.1
7 9.1 4.8 3.2 2.3
14 10 5.7 4.1 3.1
30 13 7.6 5.8 4.7

The next longest term gaging station (#02300100) within the

basin is the Little Manatee River near Fort Lonesome. The

station monitors discharge from a 31.4 square mile basin located

in the northeast section of the Little Manatee watershed which is

within the 149 square mile area monitored by the Wimauma station.

The monitoring station is located near the Hwy. 674 bridge 31

miles upstream from the Little Manatee River mouth. The station

was installed in 1963 and has been continually operated since

that time, providing about 25 years of daily discharge data.

A review of the historical flow records reveal the same

extreme variations in flow as noted at the Wimauma station. The

largest instantaneous flow of record is 3100 cfs which occurred

in September 1979. The minimum flow is zero and it occurs quite

often. Average monthly discharges for the period of record at

Fort Lonesome are presented on Figure 2.4. July through

September represent the highest runoff months with average

discharges between 50 and 80 cfs. The remaining months of the

year average from 30 to slightly below 10 cfs. Similar to the

Wimauma station, the lowest average monthly flows are observed in

the late spring and late fall. The average discharge for the

basin is 29.6 cfs. In terms of depth of water over the

contributing basin, this flow represents 12.80 inches of runoff

per year. This is significantly less than the Wimauma runoff

depth by about 20 percent. This difference in runoff depth would

indicate that the hydrologic conditions within the basins are

t- j.

FORT. LONESOME AVERAGE MOM-HLY FLOW (.1963 - 1989)

30 -
cn

U
40
3:
0
U- an -

JAN FEB MAR APR MAY JUN JUL AUG:SEP OCT NOV DEC
WONTH

Figure 2.4. Average monthly flow for Fort Lonesome station (1963-1989).

THIS
MATERIAL SUCJEC7' TC) nEVtS10tv

GEOGRAPHIC INFORMATION SYSTEMS DEVELOPMENT

The development of a GIS database is complex, dynamic and

requires data acquisition from many sources. Since the future

analyses to be conducted with GIS will quantitative, it is

imperative that cartographic integrity be maintained. This

constraint has inhibited data entry, but results of maintaining

this approach will have long-term benefits.

Figure 2.5 depicts some of the layers of data being input to

the Marine Resources Geographic System (MRGIS). These layers

represents data identified as available in map form, or that can

be generated from area photography or satellite imagery.

The base map (data layer to which all other layers are

referenced) consists of an April 1988 SPOT satellite panchromatic

image geo-referenced to 7.5 minute U.S.G.S. quandrangles in a

Universal Transverse Mercator (UTM) projection. The MRGIS data

layers are currently in raster format, although we can accept

vector data or convert raster data to vector for various analyses

or for data distribution.

Data Acquisition and Quality Control

Data Layers. Numerous problems have been encountered

generating appropriate overlays. Some data sources, problems and

solutions are depicted in Table 2.4. It should be understood

that many of these databases were not created with GIS entry in

mind and do not have the cartographic integrity of a

photogrammetrically developed map. Problems have been compounded

7E SENSING
base Map REMO I

Panchromati c REMOTE SENS ING
I ilia zi e

Land REMOTE SENSING
19
Land Cover REMOTE SENSING
1982
Land Cover REMOTE SENSING
1938

REMOTE SENSING
Soils

Elevation REMOTE SENSING

Flood Zones

Future Land REMOTE SENSING
Use

Drainage

7ransportation

Public Lands

urisdic-, '-ion&]
Tabular d ata TIJ boundaries
Water puzilliTy 'parameters
Fisheries data Hy d r ol o gy
Fla. Nptu-al Areas Inventory
Perini tted discharges
Hydrological parame-Lers 7-t-cetera
Sol Is attributes

rigure Some oC the data layers bakng im-plemented cn the
for rl)L wazershecl. 1hose Inyers cepencient c..i reMoUe
sensin3 are i)oz:ed. 1'abular datta r-o be linked to t;he cia@:a
layers are Z16c, ncz@n@l.

DaLa T-;:)e Snt!rce Problems soluLions

Base Mal) SPOT P_@ncromatic Geo-referencing to Careful selection 4)f control points
satellite data 1:24,000 USGS Quads. to reduce spatial. errors found on
USGS quads

1950/1980 FDNIR & USFOS aerial 30 Mqi@ic,-daEa rasi-_,npled to 10 mecer da@_a
],and cover Photography

1988 Land cover SPD.T Multi- spectral Statistical analyses Incorl)orate T4 satellita daLa in
satelLite imagery. difficult at 10 meter both Ole analyses phase
-spatial resolution and 1-11terpretavion phase. Use WHAP
coloi:-IR aerial lAiotography.

a i I S Soil Comer,.atiort Ser- Soils delineated on photo- Soils scientist re-cowpile soils
vice & Manatee County, based separates are not carto- maps onto 1:24,000 USGS OLIaOS. Scan
Fl. graphically accurate.

I'levation USGS Quads and Southwest 5 Et- contours from LISGS Quads Accent resolution of USCS data or
Fla. Vater Hanaoment Dis- are not adequate in a low re- di-iLize SWFORD waps
trict (SWD.119)) lief watershed. SWII@V", has (in-
digitized I & 2 ft. contours

Flood Maps Federal Emergency Manage- Cartographically inaccurate- Use 3 poi-nL trian!@ulauian to
ment Agency and very general spatially' dil&_;@ti_-e.

FLI'Lre land- 11illsborough and Manatee Cartographically inaccurata Use 3 point triangulation. Cross-
Use plans Counties and different classification reference classification system
schemes -

Aerial -].@,@_ography Time consuming interprecacion Holle
r

Ta b 1, e Sources , problems, and solutions for some of clie data
layers being entered cr, the HRGIS for rhe UIR.

by the fact that rectified SPOT data were more spatially resolved

than National Map Accuracy Standards for 1:24,000 maps, making

geo-referencing difficult and creating overlay problems at common

borders (for example, shorelines defined by soils vs. land-use

vs. flood zones). Furthermore, many data are in scales smaller

than 1:24,000, compounding overlay difficulties. This does not

present a problem if the limitations of the analyses are

understood. For example, the future land-use data, if originally

developed by the county at a 1:100,000 scale, cannot be applied

to individual zoning issues at a parcel level, but could be used

to project land-use changes over larger portions of the

watershed.

Complete watershed coverage has been built for flood zones,

future land use, and general land cover for 1988. The estuarine

portion of the watershed has land cover for 1950 and 1982

completed. The status and specific problems with several

remaining data layers are as follows:

1. Soils: Soils data have been compiled by the Soil

Conservation Service, and scan digitized for the LMR portion of

Hillsborough County. Those data are in the MRGIS and being

corrected and quality checked. Data are currently grouped by

U.S.G.S. quad. Joining the quads (edge matching) to provide a

continuous watershed coverage has proven difficult due to the

complexity of soils polygons. Soils quads for the Manatee county

portion of the watershed have been joined to form a continuous

coverage. Based on preliminary observations, it appears that

merging soils data from Manatee and Hillsborough Counties will be

challenging.

2. Elevation: The Southwest Florida Water Management

District is providing this data layer. We are currently

developing methods and formats for data transfer.

3. Drainage: This data layer is the most tedious effort

for compilation, National High Altitude Program (NHAP) photos

(1:50,000 scale) have been enlarged to 1:24,000 scale and

detailed drainage line work is being interpreted. This type of

interpretation has not been done for many areas in the U.S.,

particularly at the resolution being attempted for this program.

For example, individual drainage ditches within agricultural

fields are being identified, along with their connection to

tributaries of the watershed. This will allow better analysis of

sources of waterborne constituents and will allow network

analyses.

4. Land cover/Land use: A land cover layer has been

developed for the entire watershed by the Florida Game and

Freshwater Fish Commission in cooperatin with the Florida Marine

Research Institute (FRMI). These data are for 1987 (from Landsat

Thematic Mapper) and provide a first look at land cover from a

habitat and runoff potential. A 1988 SPOT image is being used to

complete a detailed land use coverage. The land use data are

being compiled at a 0.1 hectare resolution.

5. Watershed and Subbasins: This data layer has been

digitized from maps provided from the SWFWMD. The boundaries are

inaccurate in some areas because the basins were originally

deliniated in the 1970's. Substantial changes have occurred in

the drainage characteristics of the watershed since then.

Tabular attribute data. Tabular data, such as soils

definitions, bald eagle nesting locations, station locations and

all associated water quality or fish distribution data, permitted

effluent charges, and other digital data that represent a

singular geographic location are also required for analyses. The

biggest problem in working with these data are positional in

accuracies and data exchange formats.

Quality Control and Assessment. Data quality control and

assessment are extremely important in the generation of the GIS

layers and their tabular attributes. The two components of

concern are cartographic integrity and data accuracy (is it where

it should be and is it being called the right thing?). When

accessing databases outside the control of FMRI, these issues are

often difficult to assess prior to data entry. When we have

control, such as in the soils digitization, we have taken extreme

measures to insure cartographic integrity but can only accept the

SCS's ability to properly identify soils. In most cases accuracy

assessment of the information has nor been completed by the

parent organization. For data being developed at FRMI, such as

land use, statistical analyses of classification errors are being

conducted.

Data analyses. Numerous test analyses have been conducted on

portions of the watershed with many data layers. Only results of

analyses specific to water quality data will be presented. The

specific analyses addressed the issue of what land covers

comprise the drainage area (subwatersheds) of each seven water

quality stations. This type of information, in conjunction with

other data layer information, can be used to assess the

contribution of runoff to water quality findings. Table 2.5

summarizes the general coverage, in hectares, for each of the

water quality stations depicted in Figure 2.1. It should be

noted that subwatersheds are difined by U.S.G.S. Criteria.

The entire watershed comprises 57,364 hectares (224 square

miles). Upland plant communities comprise 13% of the watershed

and consist of pinelands to hardwood forests. Wetland plant

communities consititute 9% of the watershed ranging from saltmarsh

to hardwood swamp. Water bodies comprise 3% of the watershed,

not including the river and its tributaries.

Agriculture/pasture/barren constitute 75% of the watershed.

This category is very general, and includes urban areas. Urban

areas represent a small portion of this percentage, and will be

well defined in the detailed land use layer. In Table 2.5 this

category is representative for subwatersheds except at ST7 which

is the urbanized suncity center area.

Within each of the subwatersheds, the dominant land cover is

agriculture/pasture/barren with a high of 90% at ST2 and low of

t t h c a j. w t h mia I
i ri

V.) C`Fli t Et 1.1 E` f P &.1, E. t U V F. At S- f.1 t f i o v r a cl F..,i d c- m j. r-) t. C., db y

barren, represent i rig Ur ban and Use.

'Up I and Wetland AF r i cul t ur e
Plant Plant Pasture
Station Communities C; omrmm i t i e s Water Barren Total

ST1 624 718 208 6,577 6,127

i5i 61 1 1,848 .2,061

ST3 4,281 1,527 2.26 17,169 231,203

ST4 2,531 1,060 47 6,249 9,887

ST5 77 79 26 862 1,044

ST6 6 , 515 3 115 1,684 27,989 39,303

ST7 127 42 1,636 2 , 146
(urban)

-jo@ A G IJ-) t -.Y I' o

III. WATER RESOURCES

Local water resources in the Little Manatee River basin are

used extensively for agriculture and other consumptive purposes.

A brief summary of factors pertaining to water resource

utilization in the basin is presented below.

HYDROGEOLOGY

Most of the Little Manatee River watershed is overlain with

a deposit of undifferentiated sands that vary in thickness from

less than 25 feet along the coast to greater than 50 feet in the

eastern portions. The Bone Valley Formation, which is comprised

of a mixture of phosphatically enriched clays, limestone and

sands, underlies these sands in certain areas. The

undifferentiated sands also overlay the Hawthorn Formation which

varies in thickness from less than 200 feet to more than 350

feet. Below the Hawthorn Formation are the water bearing

limestone formations of the Floridan aquifer system. Vertical

movement of water through the Hawthorn Formation to the Floridan

aquifer, termed recharge, is slow. The estimated recharge for

the area is 0-1 inches/year (Aucott, USGS 1988).

Due to impeded vertical movement of water in the Little

Manatee watershed, the area has characteristic high water tables

and runoff potentials. Agriculturalists in the area have

maximized the utilization of the high water table condition for

some of their farming operations. For example, vegetables are

irrigated by managing the water table within close proximity of

the root zone. Soil capillarity will then pull the water into

the root zone of the crop providing a stabilized environment.

Large quantities of groundwater are required to raise and

maintain the water table due to irrigation inefficiencies.

WATER USE PERMITS

The Southwest Florida Water Management District (SWFWMD)

permits water use within a 16 county area which includes the

Little Manatee River watershed. Most of the water used within

the watershed is withdrawn from the Floridan aquifer. Figure 3.1

indicates the location of 200-plus production centers that each

withdraw 100,000 gallons per day or more. Most of the water

withdrawn is used for irrigation. As demonstrated by the density

of squares, most of the withdrawals are concentrated in the

northeastern and north-central portions of the watershed.

:zr ".0

J-)b

ILI

Viu
'YQ

@6 A I-A

Out.
ume per J@GlaL*tc tlve-r basi-Et.

FLORIDA POWER AND LIGHT WITHDRAWALS

Lake Parrish is a man-made, off-stream reservoir adjacent to

the Little Manatee River in Manatee County that was constructed

by FP&L in 1975. The reservoir is located in the south-central

portion of the basin and occupies about 4,000 acres. The storage

capacity of the reservoir is 48,000 acre-feet or 15.7 billion

gallons. The reservoir is used as a cooling source for the FP&L

electric power generating facility. A diversion channel

transports water from the Little Manatee river to pumps that

discharge into the reservoir. A Southwest Florida Water

Management agreement allows up to a 47 percent diversion of river

flows that are above 40 cfs except during the months of August

and September. During August and September, flows above 112 and

97 cfs may be diverted, respectively.

Make-up water is required to counteract losses from the

reservoir from groundwater seepage and evaporation as the result

of heat addition from the power plant and sun. The average

pumpage rate into the reservoir since construction has been 11.5

cfs or 7.4 million gallons per day. Pumping at this rate for a

year yeilds 17.2% of the total volumetric capacity of the

reservoir. The largest withdrawal amount for any year has been

4,468 millions gallons during 1987, which represents 28.5% of the

total reservoir capacity. During the 1988 study period, 2,407

million gallons of water were pumped to the reservoir.

The average pumping rate of 11.5 cfs represents 6.5 percent

of the average flow at Wimauma during the period of operation.

Monthly values of pumping to the reservoir and streamflow at the

Wimauma station are plotted for the period January 1979 to

October 1989 in Figure 3.2.a. Diversion rates during this period

are summarized by month in Table 3.1. Actual diversion

quantities are greatest in July and August while percentage flow

reductions are greatest in January and May through July.

Table 3.1. Average pumpage from the Little Manatee River
(cfs) and the percentage of flow at the LMR near
Wimauma gaging station, 1979 to 1989.

Month
J F M A M J Jy A S O N D
Pumpage (cfs)
10.9 8.2 13.1 5.0 11.3 11.1 22.9 22.3 12.9 4.7 4.8 9.1
Per cent of Flow
10.2 6.8 9.2 4.6 9.5 9.0 14.7 7.7 5.7 9.9 5.1 8.4
J F M A M J Jy A S O N D

Daily pumpage to the reservoir and daily flow rates at the

Wimauma gaging station are showm for the study year in Figure

3.2.b. Pumpage from the river was very small from January

through June 1988. Then, significant quantities were pumped from

the river from July to early September. Pumpage ceased from mid-

September through October, but resumed for a period of frequent

pumping from November 1988 through January 1989.

Since operation, FP&L's withdrawals from the river have been

characterized by intermittent withdrawals with a high degree of

short-term variation in quantities. For instance, during a 28-

day period from December 12, 1988 to January 8, 1989, pumpage

Figure 3.2. Daily and monthly (A; pumpage of water from the Little
Manatee kiver and corresponding flows at the LMR near Wima
gaging station.

pUMpRG- i AND WIMAUMA, DISCHARGE
FPLL r-
j200 - AVERAGE MONTHLY VALuEs

1000 -

Boo -

800 -

700 -
cn
U-
Soo -

LLJ 500 -

Ly
400 -

(n 300 -

200 -

100 -
o lei laz'83184 185 86187 Ile les

YEARS

z
.0

FPLL pUnppCE AND DISCHARCE AT WIMRUMR

LU
Soo 2050
DO
:D
V)

300 'U <

'00
Ln

ui
300

ZZ 0

200

150

100

DEC JFIH, FEB IIAR APR nRy JUH jUL MUC SEP OCT )I Ov DEC JAH

13EC- Be - JRK. SE

averaged 22.6 cfs or about 48 percent of the average daily flow

near Wimauma for that same period. By contrast, during the

previous twent-six day period when average daily flows in the

river were more than twice as high, pumpage averaged only 10.3

cfs or 9 percent of average flow. It is not known why these

differences in pumping rates were done by the Utility over this

short-term period. One objective of the Little Manatee River

Project is to recommend a withdrawal schedule based on

probability analysis that meets the Utility's need for make-up

water while better interacting with the inflow needs of the

downstream riverine and estaurine ecosystems.

IV. HYDROLOGIC CONDITIONS DURING THE STUDY

DATA COLLECTION NETWORK

The collection of hydrologic data is essential for

understanding the relationships of land use to runoff and water

quality in the Little Manatee River basin. For this project,

existing USGS stream gaging stations and District rainfall sites

were utilized in addition to new data collection sites

established for the study. Figure 4.1 is a map showing the

location of streamflow gaging and rainfall data collection sites

used during study year (January 1988 to January 1989). A

continuous water level was also installed at the mouth of the

river to record tide stage fluctuations.

The most downstream stream gaging station on the main stem

of the Little Manatee River (LMR) is LMR near Wimauma (station F,

Figure 4.1). The USGS has collected continuous streamflow data

at this station since 1939, giving 50 years of daily record. Two

other gaging sites in the basin, LMR near Fort Lonesome and

Cypress Creek, are part of the regular USGS stream gaging

network. The Fort Lonesome gage, with a corresponding drainage

area of 31.4 square miles, measures flow from the upper-most

reaches of the Little Manatee River basin. Data collection at

this site began in 1963, giving 26 years of record. The Cypress

Creek station, with a drainage area of 8.1 square miles, measures

'Little Manatee River
'Drainage Basin

X3
X4-
G
IX q

2 X

A USGS Streamf low gaging sites x
x Rainfall stations

Figure 4.1.. Location of stream gaging and rainfall data collection sites in the Little Hanatee River
basin during the study year (January 1988 to January 1989).

Figure 4.1. (Key)

Stream zazinz sites

A. Dug Greek
B. Cypress Creek

D. LMR South Fork

E. Carlton Branch

F. LMR near Wimauma

G. LMR near Fort Lonesome

Rainfall sites

1. Ruskin

2. Florida Power and Light

3. Fort Lonesome

4. Wimauma

5. Fort Green

6. Four Corners

flow from the smail sub-basin that includes the residential

development of Sun City Center.

Three new streamflow sites, LMR South Fork, Dug Creek and

Carlton Branch, were established for the duration of the project.

Continous streamflow at all sites was monitored by personnel of

the USGS Tampa office. These sites were established to examine

rainfall-runoff relationships in discrete sub-basins of the

Little Manatee River basin. Data collection at these three sites

began in either December 1987 or January 1988, and concluded

after the last water quality sampling trip on January 24, 1989.

The South Fork station, with a drainage area of 38.4 square

miles, measured virtually all flow from the South Fork of the

river. Carlton Branch, with a drainage area of 7.9 miles,

measured flow from a small sub-basin dominated by agriculture.

The Dug Creek site, with a drainage area of 3.6 square miles,

measured flow from a very small basin with mixed land use.

The rainfall data collection network for the study included

five stations in the existing District network (Figure 4.1).

Periods of record for these stations range from eight years

(Wimauma - 1981) to thirty-four years (Fort Green- 1955). An

additional station at the FP&L power plant was established to

measure rainfall inthe southwestern portion of the drainage

basin. Daily rainfall records were available from all the

stations during the study year. At two of these stations

(Wimauma and FP&L), recording rain gages make the examination of

hourly rainfall data for the study year possible.

RAINFALL

Monthly and total yearly rainfall amounts for the six

stations in the project area are listed in Table 4.1. Total

yearly rainfall for these stations averaged 52.6 inches, which is

near normal for the region. The yearly total of 46.6 inches for

the FP&L station in the southwestern are was somewhat lower than

totals for the other five stations which ranged from 51.2 to 56.5

inches.

Seasonal rainfall distribution in the basin during the study

period found the spring dry season and the summer rainy season to

both be somewhat exaggerated. A comprison of the bar chart of

average monthly flows for Ruskin (Figure 2.2) and the monthly

values presented in Table 4.1 shows that rainfall was near normal

at most of the stations from January through April, with a sharp

drop in rainfall occurring in late March at the beginning of the

dry season. This transition can be seen in greater detail in

Figure 4.2, where daily rainfall amounts during the study year

are shown for three of the stations (Ruskin, Fort Lonesome,

FP&L). Rainfall from mid-March to early June was particularly

low, with only 2 or 3 rainfall events of over 0.2 inches

occurring in the basin. When the summer rains began in June they

were well below normal for the remainder of the month at four of

the six rainfall stations. As a result, from late March through

June the basin experienced a pronounced dry season during which

rainfall was below normal.

---------------------------------------------------------------------

Table 4. 1. Monthly and total yearly rainfall (inches) at
stations shown in Fiqure 4.1 durinq January 1938
to January 19B9. Listed yearly totals are for
1989 only.

Rainfall (Inches)

Ft. FIDUr Ft .
Da t e F F-'?! L 13 r c;? c? n 1-: r n r s L-gneg-c-me Ruskin L) i M @:k U fn k
1/8S
F,

X2, C)

1131 8 3. a 5.4 3. 6 5 . 1 4.4 4.B
6.

4/80
1.7 C). 4 1.7 21 . I I . E,

5/ae 1. C) 1.2 C). 8 1. E.

G/eB 1.8 1.8 j 4.8 2.B 1.9 1

7/38 33 . 7 1C). 4 6.7 10. 9 G . 7 7.4

B/Be 9. B 15 . 2, 10. 5 9.8 9. E. 10. 0

9/88 13 . F, 10 . 9.4 13 . G- I j--:,. -7

10/88 1 . 0 0. a C). e 1.4 0.
1.5 1.

11/88 3.5 1

12, /1 E., S I . 1 ej C).7 0.9 C). 'D

1 . G

TOTAL -4 E-, . E. 5 F, . -5 51 1, . 15 52'.' . E,

---------------------------------------------------------------

RAINFALL AT FT.. LONESOME

4.5

2.5-
LU

J F J A 0 J

RAI N FALL AT RUSKIN.

2.6-

2.4-

2.2-

1.8

1.6

1.4

1.2

0.8

0.6

0.4

.0.2
0 LL
B J F M A M J J A S 0 N D J
Figure 4.2. Daily rainfall at three stations in or near the Little Maxiatee
River basin from December 1987 through January 1989.

RAINFALL AT FP&L

Ln
w
5 2-
Z

0.5-

J F M A M

Figure 4.2. (Continued)

In contrast to the prolonged dry season, rainfall was

abundant in the late summer. Rainfall totals were near normal

for July and above normal for August and September. Of

particular significance were a three-inch rainfall that occurred

in early August and a four-day rainfall event in early September

when a stalled frontal system dumped over ten inches of rain in

the basin. Rainfall was greatly reduced in late September,

however, and October received below normal amounts. The passage

of two frontal systems in November resulted in a basin average of

4.4 inches for the month. During December and early January

rainfall was again low, but another winter front in late January

caused two days of rain at the end of the study period.

In sum, total rainfall during the study year was near normal

but showed extreme fluctuations in short-term and seasonal

quantities, which is not unusual for west-central Florida. With

regard to the water quality aspect of the project, this pattern

was fortuitous for it allowed monitoring of the basin under a

wide range of hydrologic conditions.

STREAMFLOW

Streamflow measured at the six stream gaging sites shown in

Figure 4.1 closely followed the seasonal rainfall pattern

described above. Average monthly flows and average flows for the

study period for the six streamflow sites are listed in Table

4.2, while hydrographs of daily flows for these same stations.

are shown in Figure 4.3.

- - - - - - - - --- - - - -7 -- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
TableO4.2. Average monthly and study peric-,d streafriflc-w (cfs)
at stream gaging sites shown in Figure 4.1 during
January i9se to January 1989.

LMR u t h LMR r I t ---, 1-1 C DLkg
.Ypr ess
Da t e W i rri.-I U M @-I F*,---,I'[:: Ft. L..--tnes17ifTjPI Dr anc h C: r e c--? k C, Y. p e k

2-7.
1/ple I 121. ID 1 E3. 1 8.6 3.7

8 EI 140. 1 D. 7 1 C). '-D

3/88 G 3, 4.7.8 1 FI. 1 19. 5

4 / BE I 1 '3'. 4 11.4 -:4
1.4

5/88 50.2, 12.6 6. ID 7 1.7

6/88 @_j . 4 9.5 5 1 . 0 0. 5

7 / 39 1 1 40. 4S. 0

2C . G 13 1 . 1 7.8
S/BE3 3 7 -2 . '-2- 1 '2"j . 7 10 '3 . E,

9/ae 1120. 1 33 * 225 . 9 3 254. 'D 59.4 89. 4

1 0//BB 1 '@ -2-5 . 4 .4. 3 i'71. 9 1 8 3. 0

-7,
11/38 1339. 4 4 0 . 3-1 :2,C). 4 j 7.1

12/88 I-=@9. 0 E, 10. 1 11.5 -71

1 /G-D 1 4

----------------------------------------------------------------- @-7
Ave.- 7 E-1. 4 4G. '7, 15.

-------------------------------- --------------------------------

bUU I H f ILPM Nt:HK WIMAUMA DISCHRRGE

'4200

4000

3800

3600

3400

L)
- 1200
U.)
0
W 1000

goo
in

GOO

400

EDO

JAN FEE nAR APR nRy JUN JUL RUC SrP OCT NOV DEC JRH

JAN. 8B - JAN. 89

CYPRESS CREEK NEAR WIMRUMR DISCHRRGE

RVII MR

STT

8t5

goo

375

LL too
t -

W
130

100

0 T3

JAN FCR nAR APR nAY JUN JUL AUC SEP OC7 may DEC JAN

JAN. 88 JRH. 83

Figure 4.3. Hydrographs of daily streamflov at the stream gaging sites shown
in Figure 4.1 for the period January 1988 to January 1989.

FLOW NEAR XIMAUMA

Otto -

Soto -

1900

1600
cc
14130
u
iftoo

3600

ROD

too

DEC JAN rEl hRR APR MAY JUL uC SEP DO DEC in"

DEC. Be JAN. 89

LT. MANATEE NEAR FT-LONESOME
2100

ZDCO

1900

1800

1700

u Soo
ui Soo
700 -
C=
Soo -
L)
U) Soo -

400 -

300 -

200 -

100

DEC JAN FES MAR RPR MAIY JUN JUL RUG SEP OCT NOV DEC JAN

DEC. 88 JRN. SS

Fizure 4.3.. (Continued)
LIJ@

CARLTON BRANCH DISCHARGE

475

450

425
U)
LL
U

Ld
LD
x 150 -
cr-

L-)
100 -

50 -

J8H FES MRR AFR MRY JUN JUL RUG SEP OCT HOY OEC JMH

JRN. 88 JRN. 89.

DUG CREEK DISCHARGE

Irs
Ix

rts MO VVR MOT AW "M OCT WV IMC 4OX

Figure 4.3. (Continued)

A comparison of average flows for the study period gives a

grouping of the stations that correspons to their ranking based

on drainage basin sizes. The Wimauma site had by far the highest

average flow at 209.7 cfs, which is approximately 22 percent

greater than the long-term average for this site. The South Fork

and Fort Lonesome sites, with average flows of 61.4 and 46.2 cfs,\

comprise a middle group with intermediate drainage basin sizes

(38.4 and 31.4 square miles, respectively). The average study

period flow for the Fort Lonesome site was 56 percent greater

than the long-term average flow for this site, which is based on

25 years of record. This period of record, however, has been

characterized by a trend in below average rainfall.

Average study period flows for Carlton Branch and Cypress

Creek were nearly equal (15.5 and 15.9 cfs, respectively)

refecting their nearly equal drainage basin sizes (7.9 and 8.1

square miles). The small 3.6 square mile basin corresponding to

the Dug Creek gage yielded the smalles average flow (5.6 cfs)

for the study period.

A comparison of the hydrographs of daily streamflow values

(Figures 4.3) with the plot of daily rainfall amounts (Figure

4.2) indicates close correlation between these two variables.

Rainfall events in January, February, and March resulted in

moderate flows for all the streamflow sites. Declining flows

from April through June occurred with small peaks in flow

observed after brief rainfall events. Rainfall was somewhat

variable in the basin during July (Table 4.1) with amounts over

t~en i n~ch~e~c~E f ~a~ql I i n~g J~i~, ~n the ~P~ql~ast~ern part -~.-~,f t~qhe r n~,~-~-~. u n ~c e

r~-~,~,~-~- Y~- e a. ~s~i~@ ~e ~-~-~@ ~qi n ~s t ~i - ~e a fr~i f 1 ---1 ~w ~w ~e ~r ~e.~-~@ ~o ~qb ~s~@~, ~e r v ~e d i n J~U I ~qyt a. ~q1. 1 ~c~-~-: t: ~'~E~., t i ~:.~, n

except Dug and Cypress Creeks i~n t~qhe n~c~-rth~-~-~centr~al part ~-~-~,f the

basin where rainfall w~a~s lower. All stations ~E.~-~@xhib~qited high

~ ~qow~s ~-~id ~arti~c~qu~qlarly in early Se~ql~-~-~itember, when
~924;56;124qin early A~U~QU~qSt ~a~i p~@

~M~1~,~RX~qiMUM flc~ws~, were observed stations. The peak fl~,~nw of

~,~qD7~qF~q3C) ~cf~s at t~qhe Wim~aum~a station was over 5~q0 times greater than

the ~aver~ac~i~qe flow for this site a~nd c~c~-rresp~.~:~,nd~(-~=?d to a 1~q0- to ~'2~q5-

year fl~-~-~-~I~,~-~-~-d event. Alth~C~-U~Qh ~!~-~-~,~o~qm~e homes ~a~nd ~cther strU~Cture~s were

inundated during this September flood, ec~onc~,mic damages ~qin t~qh~e

basin were min~--~-r d~ue to the undeveloped character of the river

corridor. For the remainder of t~qhe study period, fl~ow~S at all

sites returned to low to moderate levels with brief pea~ql~.~-~-s

C~ICCLA~I~-~1~-ing during November and January ~in response tc~-~, rainfall

associated with the pas~qsa~qq~L~- of ~-:~-~-~-~-~qld fronts.

One interesting p lien omen ~-~-~,n t~qhat was observed during t~qh~e

study w~as a. ~c~qle~ar~.d~qifferen~ce in b~qase~2p~1p~1p~ levels between the ~S~ub

basi n~s~. For instance~, t~ql~-~ie.~- ~qF~'~.~-~-~,rt Lonesome gage measures flow fr~o~a~l

an area ~a1m~c~ist f~I~DUr times greater than t~qhe Branch site.

D~Uri~n~qg wet months, average m~c~-~,r~ith~ql~qy flows ~z~-~ct: F~,~-~-~~,r~,~qt L~one~s~c~.~,ME~? ~k~k~)2~r~e

~q-significantly greater than at the Branch site. F r t I ~-~j ~e

dry m~c~.~,nth~s~. ~r..April, May, June, ~qO~,~:tc~,bE~-~.~,~r, and December~q), h~c~-~'W~qev~E~--~r,

~qav~qer~qa~qc~qie flows at Fort L~qone~q'~q@~q,~q:~q,~qome ~qand ~6qB~qr~qan~qc~q-h were nearly

eC~6qjU~qE~qkI These ~qY~q'~qE~qS~qL~qAIt~qS and the water chemistry data ~2qr~q-~q-~q)r~qe~q-~qs~qe~qnt~qed in

~qI-~6qI~qi~qapt~qe~qr V indi~qc~qa~ql~ql~q.~q-~q-~qe~q- that dry flows i~qn ~0qC~q,~q-~q-~qirlt~8qon Branch~q; are

heavily supplement by runoff from farms which originate as

pumpage from groundwater sources.

TIDES

Water levels in the lower fifteen miles of the Little

Manatee River are affected by tidal fluctuations in Tampa Bay.

At the most upstream extent, this effect is very small and

restricted to periods of extremely high tides in the bay. Water

levels at the mouth of the river are largely controlled by tidal

fluctions in the bay, but periodically can be significantly

affected by high river flows.

The recording of tide stage during the study is very

important for interpreting the estuarine water chemistry and

salinity results. Therefore, a water level recorder was

installed at the mouth of the river at Shell Point and operated

by the USGS for the duration of the study. This instrument

recorded water level measurements every 15 minutes with retrieval

of these measurements plus daily mean, minimum, and maximum

values possible.

Tides at the mouth of the Little Manatee River contain a

mixture of diurnal and semi-diurnal components. On most days,

there are two high and two low tides. The high tides are of

unequal height consisting of a high-high and a low-high tide.

Low tides are similarly of unequal heights. During some periods

of the year, depending on astronomical forces, there is only one

high and one low tide daily at the mouth of the river. Water

levels and tidal fluctuations in the lower Little Manatee River

can also be affected by the action of prevailing winds on the

waters of Tampa Bay.

Based on data collected between January 1988 and January

1989, the average daily tidal range at the mouth of the Little

Manatee River was 2.47 feet. Average monthly valuesl for daily

mean tide, daily maximum, daily minimum, plus the absolute

maximum and minimum tides for each month are illustrated in

Figure 4.4. Monthly mean water levels were highest in the fall

(September through November), but the September value was

affected by the extremely high river stages during the flood in

the early part of the month. The differences between monthly

values for average daily maximum tide and average daily minimum

tide range only from 2.25 to 2.60 feet, demonstrating the small

seasonal fluctuations in daily tidal ranges at this station.

Figure 4.4. Average monthly values for daily mean tide, da 'ily minimum and
maxi-n- tide plus monthly maxim= and minimum tide at the mouth
of the Little Manatee River from January 1988 to January 1989.

+4.0-

+3.5-

+3.0-
+2.5- Maximum
+2.0-
7z
A verage Daily
+1.5 - Maxinium

+1.0-
X@z
>
z +0.5-- Mean
LU
0 -
LU
LL
-o.5

iverage Daily
minimum

--- Minimum
-2.0

-2.5

-3.0
F M A M J J A S. 0 N D J

MONTH

V. FRESH WATER CHEMISTRY

OBJECTIVES

The water chemistry program had three objectives:

1) to determine the flux of nutrients and suspended solids

contributed by each of the sub-basins of the Little

Manatee Watershed,

2) to determine seasonal variations in concentrations of

these substances in each sub-basin,

3) to evaluate the movement of these materials through the

Little Manatee estuary.

The first two objectives required an examination of water

quality in the freshwater streams of the basin. Water quality

data will be compared to land use and soils in the respective

sub-basins to document the effects of various land uses on water

quality. The third objective is addressed in the following

chapter on Estuarine Water Chemistry.

SAMPLING AND ANALYTICAL METHODS

This report on stream water quality is based primarily on

data collected between January 1988 and January 1989. During the

study year, water chemistry and physical parameters were measured

at seven freshwater stations in the Little Manatee basin (Figure

5.1). Six of these stations were located at USGS stream gaging

sites, while the seventh station was located at a site on the

Little Manatee River Freshwater
Station Locations

r
Ilk
E .7 GorN
"S
A
Az 4

It
F C
2 U.,

Bi-Weekly sampling stations

May and September sampling stations
Figure Locations Of freshwater stream sampling stations in the Little Manatee River basin.

Figure 5.1. (Key)

A,
i ,
1. Bi-weekly sampling stations and continuous USGS streamflow gaging sites
A. Dug Creek
B. Cypress Creek
C. LMR (North Fork)

D. South Fork

E. Carlton Branch

F. LMR near Wimauma

G. LMR near Ft. Lonesome

2.1 May 17, and September 21, 1988 dissolved constituents sampling
1., Dug Creek at Saffold Road

2. South Fork at Bunker Hill Road
3. Alderman Creek at S.R. 39

4. Alderman Creek at Taylor-Gill Road
5. Howard Prairie Branch at Grange Hall Road

6. Pierce Branch at Owens Road

7. Pierce Branch at C.R. 674
8. LMR Grange Hall Road
9. Carlton Branch at Sweet Loop Road
10. Carlton Branc h at Colden Loop Road

11. Unnamed Creek near U.S. 301

12. Unnamed Creek near railroad bridge

13. LMR near FP&L intake

14. Unnamed Creek near C.R. 579

15. Gully Branch
16. LMR main channel above Gully Branch

17. Carlton Branch at confluence with-J..MR

river ("C", North Fork) where streamflow can be estimated by

station differences. Sampling at these stations was done

approximately every two weeks, so 26 regular samples were

collected during the study year. At each stream sampling

station, duplicate water samples were taken at .5 m depth or at

mid-depth if total depth was less than one meter. Filtration for

separation of particulate (C, N, P) and dissolved nutrients (PO4,

NO $ NO Organic Carbon) was done in the field with filters and

filtrates kept in iced coolers for transport. Water samples for

chlorophyll analysis were kept chilled and transported to the

Department of Natural Resources Laboratory in St. Petersburg

where filtration for pigment removal was done the same afternoon.

Samples (filters) for particulate phosphorus determinations were

periodically shipped to Savannah Laboratories and Environmental

Services, Inc. (SL&ES) in Savannah, Georgia where digestion and

measurement was done. Remaining water chemistry parameters were

determined at the District Laboratory in Brooksville. Parameters

measured and the analytical methods employed are listed in Table

5.1. Also, at each sampling station, in situ measurements of

temperature, dissolved oxygen, pH, and specific conductance were

made with a Hydrolab meter at .5 m or mid-depth, depending on

water depth.

At the same stations as the bi-weekly sampling, major ion
_
species (Ca, Mg, K, Na, Fl, Cl, and HCO were measured on

duplicate samples on a monthly basis for a total of twelve

regular sampling events. In addition to regular bi-weekly and

Tab I e 5. 1. Water qualit@ parameters measured and analytical
methods for freshwater and estuarine sampling
stations during January 199B tc, January 19B9.

-----------------------------------------------------------------

Pa r a m P t e r Un i t s, Method F, c-., f P r E., n,-- c-D

Temper at t..tr e Hydr,---11 ab Hydrolab InstrUments'.

Sp E-C i f i C Um Fic-, s / c m Fly drolab Hyclrolab lnstl@Uments
n d Li :: i, a nc e

pH (field) P H U n i t s Hyd r c, 1. ab Hydrolab InstrUments

Dissolved mg/1 Hydrc.lab Fiydrc-lab Instruments
Oxygen

TUrbidity NTLJ Nep h e lcimet r ic APHA, I9P)

1:1 1 Cir Nessler tubes APHA, 19B5
FICU

Total Suspended mg/l f iItrati----n/qr.-xvirTietric APHA, 19 e!.:,
Sol i ds

TSS-vc-I at i I e mg/I Qr avi met r i c / i cin i t i on APHA, 1965-1
f r ac t i on

Part j. c ul. at e mg / 1. C-H-N analyzer Per k i n -E I mer
ar b on I n st r umen t

Par t j. C U 1 at e mg/I C-H-N analyzer Fer 1.;-. i n-E I mer
nitroaLr-n InstrUments

Particulate mg./I acid diqe=-tii--In/ EPA,
phosphorOUS colorimetric APHA, 19 8 5

mg/I -rime -ir -IA, -)C5
C tI

N 0 NI 0 m C1 / 1. c, r i m e. t r i 1z A. P i :D e5

PO MI Q / I o I or i rrEt r i c
APHA,

Si 1 ir a / 1 crD 1,--ir i met r j.;-- APHA, I 'D B 5

-----------------------------------------------------------------

C. rI t- n u

------------------------------------------------------------------

Par amet er Uni ts M e t h ---- d R e f e r e nc e

C,
C: h I C, r C, p 11 y I I a rn g / ril p e c t r h Cl fri E- t Y. i APHA, I., Pff5

*CZII. C i UM mg / 1 Atomic Absorption APHA, 19 C -5

*Magnesi UM mg/l Atomic Absorption APHA, 1-985

Po t .1 S 5 i LA (TII fnq Atomic Absorption APHA, 1985

*Sc,dium mg/l Atomic Absorption APHA, 1985

*Sulfate mg/l tUrbiclimetric APHA, 19B5

*Ch lor i d e mg/l titration APHA, 1,D e,,j

APHA, 192C7
*F1 uor i de mg/I el ec t r ode

*Ali-.-alinity (nQ/l t i t r at ion APHA, 1985

Fresh wz:tter stations only

-----------------------------------------------------------------

monthly sampling, two additional sampling trips on May 17, 1988

and September 21, 1988 were performed when major ions, dissolved

nutrients and physical parameters were measured at an additional

17 water quality stations (Figure 5.1). Duplicate samples were

not collected during these two additional sampling events except

for duplicate analyses performed as routine quality assurance.

OTHER DATA SOURCES

Other surface water quality data for the Little Manatee

River basin are available from the U. S. Geological Survey (USGS)

and the Hillsborough Environmental Protection Commission (HEPC) .

Mean values for several parameters measured by these two agencies

during 1986 to 1988 are listed in Table 5.2. Station locations,

for these data are the same as three of the stations, shown in

Figure 5.1 and follow the same nomenclature.

Table 5.2@'. Mean values for selected water chemistry parameters in
the Little Manatee River Basin recorded by the
Hillsborough County Environmental Protection Commission,
1986 and 1987. Mean values recorded for Ft. Lonesome by
the USGS during 19B6 to 19BB are also shown.

LMR near LMR LMR near
F'arameter Un j. t s W i m EA U m a F,-.,rl::*) F t: . L -:-, n P siri m cn
('HEF,i--,*) (USGS)

"@I -7 1
Spec i f ic U M h 0 S M @15 137
C:,::,ndUCtance

pH pH Units 7.5 7.4 7.4 G.e

Turbidity NTU 8 7 -1

Col,or PCU 58 65 e.-., 9

Organic nitrogen mQ/1 .96 .9C) 1 . OF, aG

NH (as N mg/1 i G 10 ---

NO &-NO -z (as N) fTIQ / 1 .57 -- .13 10

Total Phosphc-rus mg/l .4.5 .55 E-0 .54

Chlorophyll a mg/m -- -12'. 7 1. C) --

Ca. I C i U M mg/I 26 17 14

Sul f at C=' mg/1 12, a

DATA REDUCTION

The T--!,-ita @,.jere fira-A-- c-.'-,---I-smined 41- c a e r t C-tin similciritieE@ and

differences in water quality am,--,ng stations and seas,:,ns. A 11

statistical anaIysE-.,s and --,f bi-weekly dat.1 in thi5

les. T@),-E?n, the
report are based on thtlE? me,-=knE of dUPIi,:E-ktL- P --

CIE-kta k4e)-E' C--V@@klU&'L-E'd t,-' CIPtermine the relativE-., imp-r-11-ance cif

flu.,,,es (J)Utriants and fr,::,m the maj----r

S, U b b Zk S i n. si. f t. I--, e L t 41--IE-!

Branch, South Prong, Dug Creek, Cypress Creek, adn Wimauma) and to

elucidate processes influencing the transport of thesr materials

through the Little Manatee estuary.

Estimates of Annual Material Flux from Sub-Basins

The sum of the discharges recorded at the Cypress Creek

(CYPR) and Wimauma (WIMA) gaging stations represent the

approximate total fresh water and material fluxes to the Little

Manatee estuary. Thus they, along with Tampa Bay, are the major

sources of materials, such as nutrients, supplied to the esturary.

For the purpose of evaluating the relative importance of

each sub-basin, the discharges and fluxes determined from data

collected at the Cypress Creek, Dug Creek, Carlton Branch, Ft.

Lonesome and South Prong gaging stations are assumed to represent

the transports from their respective watersheds. The discharge

and flux determined from the data collected at the Wimauma gaging

station represents the influence of the intervening watershed

below the upper sub-basins (all except Cypress Creek) when the

sum of the fluxes and discharges from these are subtracted. This

part of the watershed is referred to as the Inner sub-basin (IB).

The flux or load of a chemical substance transported from

each sub-basin is simply the product of the chemical

concentration and water discharge observed at the gaging station.

Instantaneous values of flux are relatively simple to derive for

each gaging station using measured substance concentrations and

instantaneous or daily mean discharge at the time of sampling.

It is, however, much more difficult to estimate, with a high

degree of accuracy, fluxes over longer periods of time such as a

year or more since this requires long term records of

concentration (C) and discharge (Q), so that flux (F) can be

calculated by intergration using the equation:

F = _ *C Qdt (1)

It would still be easy to calculate fluxes if concentrations of

substances were constant over all variations in discharge. This,

however, is not the case since the concentrations of virtually

all substances, both particulate and soluble, vary with

discharge. Nonetheless, several approaches have been used to

calculate fluxes with limited data collected over various flow

conditions of a watershed. Generally the approaches used involve

either extrapolation or interpolation of the data. Both

approaches were used in this study and are discussed below.

Extrapolation method for estimating material flux. These

procedures attempt to extrapolate the available database by

developing rating relationships which link chemical

concentrations measured at infrequent intervals to river

discharge at the time of sampling. Rating relationships are

normally developed for sites with discharge monitorying facilities

so that the rating function may be applied to a continuous flow

record thus allowing for extrapolation of chemical concentration

(and flux) between periods of sample collection. Simple power

functions of the form:

Concentration = aQ (2)

are used to relate the concentration of a substance and river

flow, Q. Such relationships have been routinely documented by

many studies. For example, suspended sediments generally show

increased concentration with discharge following a relationship

similar to the described in equation (2) with b being a positive

number. In the case of total dissolved solids a similar

relationship is observed, but b is often negative (Figure 5.2).

Rating relationships or rating curves have been demonstrated for

many specific substances, for both natural and anthropogenically

disturbed (e.g., agricultural areas) watersheds (Nilsson, 1971;

Turvey, 1975; Walling and Webb, 1983; Walling and Kane, 1984).

Although rating relationships for total dissolved solids

often exhibit decreasing concentrations with increasing

discharge, specific dissolved substances such as nutrients often

show increases with discharge (Walling and Webb, 1984; Webb and

Walling, 1985).

Rating curves are developed by obtaining concentration data

over seasonal variations in discharge for a given watershed.

Fitting concentration data to discharge is usually accomplished

by least-squared regression techniques. This approach was

employed in this study using the individual bimonthly

concentrations of constituents and mean discharge for the station

on the day of sample collection using a log transformation of

equation (2).

Other authors (e.g., Jansson, 1985) have argued that other

methods of curve fitting are more appropriate, and in some cases

(e.g., Hall, 1970; Davis and Zobrist, 1978; Foster, 1980), the

relationship between concentrations and discharge will not be

described by a simple power function. Nonetheless, we felt that

the approach used in this study was more appropriate given the

limited data set for each station.

Many investigatiors have stressed the complexity and

variability of storm-period sediment and solute responses to

discharge (Walling and Foster, 1978; Miller and Drever, 1977;

Foster, 1978a,b; Reid et al., 1981; Dupraz et al., 1982; Webb and

Walling, 1983; Walling and Webb 1986a,b). Thus it is important

to determine concentration relationships to storm related

variations in flow. In practice, for a given watershed, separate

rating curves are developed for seasonal flow and storm related

flow. For this study data collected during storm event campaigns

are related to discharge averaged over hourly intervals also

using the least squares regression approach.

Once the rating curves were developed annual flux of a given

material by each river was calculated using the following

equation,
_n_
Flux = E aQ t (3)
i = 1

where Q, is the mean daily (hourly from storm event) discharge

recorded at the specific stream gage, n = 365 (or the number of

15 minute intervals represented by the storm event), a and b are

constants derived from the least square regression analysis of

concentration on discharge, and t is the time over which Q, is

averaged.

Interpolation method for estimating material flux. Several

interpolation procedures have been used for estimating total

loads or fluxes of materials. Five representative numerical

procedures are listed in Table 5.3. These procedures make the

assumption that the chemical concentration of a water sample is

representative of conditions in the river for the period between

sampling. These approaches essentially attempt to weight the

concentration to discharge. Because of the sometimes

considerable differences in flux values generated by the

different procedures, two were used: Methods 3 and 5. In each

case the calculations were carried out using the results from the

26 weekly samples collected between January 1988 and February

1989. Thus n = 26 and the conversion factor K was adjusted for a

discharge record of 13 months.

Aable 5.3. Interpolation methods for flux calculations.

WelhDd Numerical Procedure

n n
r- 7-
Total Load wK n

n
7-
2 'Total Load KQr
n

n
3 1 otal Load - K 7
rk

n
4 Total Load K2@ (3i0p)

n
KY, (CiOp)
5 Total Load n Cr

gal

K = Conversion Fa--tor To Take Acrount Of Period Of Record
Ci = Instantaneous Con--enlration Asso--i ated With Individual Samples
Oi = Instantaneous Discharpe At -5me CY, S=)lino
Or = Mean Disch,aroe For Period Of Rec:ord
C Mean Disc;haroe For Imerval BeTween Samples
n Number a, Sam,D:!es

RESULTS

Water Quality Characteristics

Hydrographs and chemographs for the six gaging stations

during the period of study are shown in Figures 5.2, A through F.

Dates of routine sample collection are indicated by data points

along the time axis. Time is in days starting with 1 January

1988. Compared to historical streamflow data, the sampling

appeared to capture a fairly wide range of discharge conditions.

The base flow recorded at all gaging stations is quite low.

Superimposed on this pattern are short period storm spikes. Only

one storm event, occurring during September, appears particularly

significant.

Bi-weekly water quality sampling during the study year found

pronounced differences in water chemistry between the seven

stram stations. DOC and nitrate concentrations were highly

variable during the study period. Concentrations of ammonia and

phosphate were somewhat less variable and reached maximum values

between July and September, although this varied between

sub-basins. This was the approximate time of the highest

discharge.

Particulate carbon, nitrogen and phosphorus vary, in

general, with total suspended solids. The maximum or spike in

particulate substance for the Cypress Creek, Carlton Creek,

Hydrograph and Chemographs for Ft. Lonesome Gauging Station

kv
00 0a 4
Do FLOW NH3 PC

,do CA

so 2

20 02

10
0 L 00 0
a 00 100 U10 2M 200 SM 000 400 a co too iao aw wo wo aw Am a ao go Ido 200 2w am Wo 4w

oil
oo D3. C PO4 PN
26 ad
02
20

Is 04

to
02

00 00
0 80 100 SW ZO 200 400 000 4CO
a no 100 wo aw 400 0 00 too 100 aw am 000 wo 400

04 CA
04 Pp

ob
02

062

at at
L

00
0 00
a go 100 140 2w ka am 4w 0 10,0 100 .200. 200 moo ow 4w 0 00 IW M 200 2M WO OM 400

Hydrograph and Chemographs for Carlton Branch Station

so 06 4
FLOW NH3 PC

0 00 0
0 so IM IM wo aim M 4co a no 100 lao am no Sao am 4w0no 100 wo 2w am am 400

so 08
.u DOC PO4 pN
as 04
so

C64 U

to
02 ell

CIO
0so jC0 mo wo am M 4w a so wo iao Sao 2w wo sw 4w0 so ica Mo sw Sao ow am 4w

20 0M
NO ow pp
is

am
go
10
u Q10
w ow
a& V-4@
Go 000
t

a so %a mo Sao M am no 4w a Go 100 lao wo no Sao M 400 0 w V0 M M w 4w

flydrograph"and Chemographs for Dug Creek Station

12
FLOW NH3 PC

064
4 a

2 02

010 0
a 00 IDD U10 200 200 800 OW 4M a no SOD lao 201) aw am am 4w 0 00 100 IBO 200 200 9M BM 400

20 06 as
DOC PO 4 PN
16 0B
OA
LD
LD
10 cw

CL2

0 00 00
0 00 100 MO 200 2W boo Sao 4w 0 40 100 100 2W ftO MW OW 400 0 00 Im 100 Sao 200 moo No 4w

4 415
NO3 Pp

000-

ow
0 so 100 lao am 200 9M IW 400 0 00 wo 100 sm 900 sw sw 4w w IM w wo wo w IKM
L

Hydrograph and Chemographs for South Prong Station

Da
FLOW NH3 PC
90
W 2

02
so

0 00 L I-
a w sw m 4w 0 00 IM 100 SM 200 OW OM 400 0 na wo Ina 2oo 2w am ano 4cc

so Do 025
so DOC P4 020 PN
00
20
ala

C64
010
to
C12 006
& am i @
0 00 100 UQ 200 200 SM 800 4W 0 00 too 100 200 200 sw am 4co 0 00 1w 180 goo 200 sm sm 4w

is 20
U 012- Pp

00 009-
10
ad 000-

5
03 003-

00 0 C)OO-
0 00 i0o laO 200 2130 OM 000 400 a 00 i0o 100 900 2w sw sw 4w 0 00 100 IaO SW 200 9M SW 4M
,J,j

Hydrograph and Chemographs for Wimatma Station

No 06 w
wo FLOW NH3 20 PC
wo cm

10
wo 02

41
so

0 A- 00 0
0 IM w m am am 4w a 00 lw sw 2w wo aw am 4w a 00 Ica lao 200 2m am aw 4w

so . . . .
w DO PO 4' ta- PN
20 u -

IS 04 09

00
02 -

0 00
a w w sm no 4w 0 ao too too aw 2w sw am 4w 0 00 100 lao am wo am sw am

IM I'Al
u NO 12 11 P.
AA 80 40
IQ Do

03 Q3

00
0 00
-N

0 1* lco %w No -M a 00 too wo 200 Sao aw No 4w 0 00 100 180 200 20a am sm 4w

Hydrograph and Chemographs for Cypress CreeK

FLOW 12 NH3 PC

10 4

G 2
08

0 A@ IL 00 a
0 00 lw wJD aw 2130 Sco Ono 4w a ao 100 lao am boo am 4w a 00 Im lao Roo gm goo am 4w

C64 08
20 DOC -00 PO 4' Cho - PN

to 02 G4 -

00 00
0 w w m ow wo 400 0 00 100 NO aW 2M SM NO 4W 0 w m 4w

PP
12 3 ao 06 -

09 00 -

cm 04-
03A
20
as 02

00
0 00
0 w IM m 400 0 00 too 100 aw no wo aw 400 0 Do lco 100 boo am Sm dw 4w

Wimauma and Ft. Lonesome chemographs occur at the same time but

are not present in the Dug Creek and South Prong chemographs.

Mean values for selected water quality parameters at these

sites during the study year are listed in Table 5.4. For a few

parameters (pH, turbidity, ortho-phosphorus), variation between

the stations was not large and comparison of station means for

these parameters with Duncan's multiple range test found no

significant differences (p <.05) between stations. For the

majority of the measured parameters, however, variations between

stations was large and water quality in the different sub-basins

showed clearly different characteristics. A general discussion

of water quality at these sites based on mean values is presented

below with general reference to land use and possible

cause/effect relationships.

T -,x b 1 e 5 :1 Mean valuec--, f-@,-- k4jtt*er chemisi--ry
freshwater s@: t t.. j. :, n i t t: I c--..., M ari a t e e, F,':'.:L E-@ Y

C: y P) r P S7, S LA C1 Nc., r t 1-i C: a r I t: --, n S, C-) U t h Ft
Parameter Linits- W i ff) .ik Lk M I C: r e v; --.r eek F,-T r k D r zi. nr h F o r k L ci 1*1 e S C-I fn -0

Spec i f i u (n h s '7171 4 229 3 4
C:,--l n cl u --- t /Cm

p 1-1 p H Un i t s E, . C, G1. 4 Fl. ID C, I. E3 E -_4 E, C7 C, M-

-7-
Tur b i d i t y NTLJ 7. 1 5. G 4.3 3-3 . 7

@9
Cc, I or PCU 113 78 ID 112 1 -38 116 14.2

TSS mg/1 5.1 8 . F, C:,. E. . ID 5. 9 4.1

P-a r t i c u I at c-?
- 1. 1 -j S3 1.15 .74.
C: a r b o n mQ/1 eo 1 4-5

Tot al
Di ss.::.]. ved gig / 1 15 . 7 16.7 11 . C) 14.9 9. 3 13). 8 1 B. 5
C-ar b on

Pa, r t i c u I a t, e
Ni tr ogen (TIQ 11. 11 08 00 04 C) 3,

.2-4 11 C7 08 (7 -)S
NH3 Cas N) Mg / 1 .08

NO arNO , (N' giq 1 5 5 1 . I GO I . 70 1 IF)

Par t i C U I at e
Ph osp h or US Mg 0@ C
.04 .(--)4 0,3 (-)1

.7--7 -4 -7
PO 4 (a s F" Mg/ .3-4 C)4 1 . C) 37

Sj. 1 i c a MQ
E. 4, 7.0 E, . 4. 4. e4-

-J
a M Q ri'l

C tk I C i U (T) mq/1 @9. 7 44 .9 C-1 S . 5 6 - 3 5 . E, - 2 1 - 2 1-3 14.1

El I i n j. t y
s C, a C: D gi ci./ 1. 5'ED, . 7 60. el 4 7 . r5l, E,

C: h 1 17 1. Ej p C, -:4
"D

t
Ej Fj

Si-mviple.-d mr--,nt[ily

The Fort Lonesome station was the most upstream site

monitored on the main channel of the Little Manatee River. Land

use in the drainage basin for this station is different from

other monitored sub-basins in that the primary land uses are open

space and pasture. The other sub-basins have much higher

densities of either citrus, row crops, or residential

development. In accordance with this difference in land use,

water quality at the Fort Lonesome site was distinct from the

other stations and more similar to an unimpacted, central Florida

stream. Generally, water quality at this site can be

characterized as highly colored, slightly acidic, with low levels

of suspended matter and moderate levels of nutrients. Mean

values of color and total dissolved carbon were highest at this

station, probably reflecting the input of humic compounds leached

from vegetation and litter in the drainage basin. For a number

of parameters, mean values were either ranked lowest or near

lowest for this station, with Duncan's multiple range test

grouping the station alone or with one or two other stations

depending on the parameter (conductivity, turbidity, total

suspended solids, particulate carbon, particulate phosphorus,

nitrate-nitrite, calcium, alkalinity, and sulfate). Although

further examination of soils distributions is necessary, it is

suggested that the Fort Lonesome station can be viewed as a

control, indicative of relatively unimpacted water quality in the

basin.

The site most similar to Fort Lonesome was the South Fork,

which was the only station on that branch of the river. Mean

values of alkalinity and chloride were ranked lowest for this

station, and a number of parameters were ranked second lowest

only to Fort Lonesome (conductivity, turbidity, total suspended

solids, particulate carbon, particulate nitrogen, calcium and

sulfate). For some other parameters (total dissolved carbon,

ammonia, nitrate/nitrite, ortho-phosphate, and silica), the South

Fork was ranked near the middle of the seven stations.

Of the remaining five stream sampling stations, two sites

(LMR near Wimauma and LMR North Fork) were on the main channel of

the river while three stations were on three tributary creeks to

the main channel. These three tributaries, Carlton Branch, Dug

Creek and Cypress Creek, all flow from north to south and enter

the Little Manatee on its northern bank. Land use in Carlton

Branch is primarily agricultural with extensive citrus groves and

row crops. Land use in the small basin (3.6 square miles)

upstream of the Dug Creek sampling site is mixed with low density

residential, citrus and fish farms. Cypress Creek drains an area

of residential development where there was extensive highway

construction durign the study year. Water quality for these

three tributaries to the Little Manatee were grouped together by

the multiple range test, and with a few exceptions, were ranked

1, 2, and 3 with regard to mean values for specific conductance,

alkalinity, calcium, ammonia, particulate nitrogen and

particulate carbon.

In general, water in these tributaries was lower in color

and more highly mineralized than water in the main river or the

South Fork. This degree of mineralization was particulary

reflected in high mean values for specific conductance (322 to

528 mg/1), calcium (35.6 to 66.5 mg/1) and sulfate (38.0 to 166.5

mg/1). Cypress Creek was notable for the high levels of

turbidity, total suspended solids, particulate carbon and

particulate nitrogen, probably reflecting the soil disturbance

and resulting suspended load that was generated in the sub-basin

during the study. Dug Creek and Carlton Branch had the lowest

mean color values found in the study (39 and 38 mg/1), but had

the highest levels of nitrate-nitrite and silica. It is believed

that the high degree of mineralization and dissolved constituents

in these three tributaries are the result of irrigation runoff.

High levels of silica, calcium, and sulfate are characteristic of

ground waters in the region.

As discussed in Chapter III, substantial groundwater pumping

occurs in the Little Manatee basin for agricultural irrigation.

Also, the USGS reports that runoff to Cypress Creek is

supplemented by spray irrigation in the basin. High levels of

nitrate-nitrite and ammonia in these tributaries may also result

from runoff transport of fertilizer. Upcoming investigations are

to confirm the occurrence of irrigation runoff in these

tributaries. Runoff-rainfall relationships discussed elsewhere

in this report show that baseflow levels in these creeks are

higher than the other basins and likely supplemented by

irrigation runoff.

The three stations on the main channel of the Little Manatee

River are Fort Lonesome, LMR North Fork, and the LMR near

Wimauma. Examination of mean water quality values for these

three stations demonstrates the increasing mineral and nutrient

content of the Little Manatee as it flows to Tampa Bay. Some

constituents, such as nitrate, silica, TSS and sulfate show

significant levels of enrichment proceeding downstream while both

particulate and dissolved phosphorus show little or no

enrichment. Although Cypress Creek flows into the Little Manatee

below the LMR near Wimauma site, data from near Wimauma can be

considered as indicative of the net water quality flowing to the

estuary.

Mineral and nutrient enrichment of the Little Manatee River

is also seen in the additional water quality samples that were

taken on May 17 and September 21, 1989 (see Figure 5.1). Average

values for selected water quality parameters at ten of these

stations plus average values for four of the regular stations on

the same two dates are listed in Table 5.5. The stations are

grouped according to which region of the Little Manatee drainage

basin they occur. Group A stations in Table 5.5 are located in

upper part of the drainage basin near the Fort Lonesome site.

These stations are characterized by relatively high color and low

values of specific conductance, sulfate, and at three of the four

sites, silica. Silica values were high at station 5 in Hurrah

ater quality parameters sampled on
lable 5.5. Averaqe values for w
May 17 and September .21, 19BB at select-ed stations in
Fiqure 15.1.

------------------------------------------------------------------
Circ-up A Stati. c-Ins P Statigns

St at i ---,n Lin j. t s D

S P (--- C i f i C U (n1h ---I s
Crin d U C t - c m 182.1 184 1 BE., 1 E, 5. 14 131

pH pH units. 7.( F, . 2 6.9 F, . ID E, ED

Col or FCU 140 115 1017 115 P)-7,

7, -)5
NI-6 (N:) (Tig

NO __FNO N) mg 1 62:, GO 0.,1, .22 14

P04 (P) mg/l
30 .44 3) C) .41

Silica mg/l 2.9 -,--,.5 7.4 5 . '.2 7.4

C a mg/l 19 13 7 14 15

Alkalinity mg/l 46 .4 G 44 4C) 4 33

Chloride mg/l I'D 1-, 11

Sul fate rrjQ/l 16 is 13 14 7 51

Total Dis-
sol ved mc:l 17 12. A. 17 14
Carbon

Tab 1 e 5. 5. (Cont i nued)

--------------------------------------------------------------------
2L12-
IS, -L. a r., -S f J. -L -I n

St at i on Un i t s 7 E 15 141. R I C-I

Spec i f i UMhOS/
1 -7p
C.':c,ndL.tCt. cm I I-D 31 t; S' 10 1

-7 -7
pH P 1-1 U 1-1 i t El 7 . `2 F, . 0 7.4 0. 19 --- 7. 27'

Cc. I or F'CU G7 33 7 -12 7 40 EA 1 '33 7 117 @D

W@ (N) mQ/l C)I C)I .1 01 0121 0 :2:1

NO &-NO N') mg / 1 1.7 1 . I . 4 14 E@ .71 .47

17
P0 4 ( P) mg/l .11 lB .19 .30

Si I i ca ma/l 4. 4.7 9.2 1 a 130. 8 4.2 7.(-) 7.9

C mg/l 1.8 18 41 97 87 24 40 1:0

All.--.alinity mg/l -..G 20 76 75 - 44 59 G 8

Ch I or i de Mg / 1 21. 1 17 17 16 16 15 is

6C 9
SL(l f ate mg/l is 2 G, C @.)9 17 - C)

Total Dis-
s -_-, I v e d mg El. 7 9. F, 9. 9 1 El 14 1 2'
C a r bc, n

--------------------------------------------------------------------

and m,--,derz--:kte nit'r.---ate-nit-r-ite concen 41- r a t i r i w c--, r e f 1-1 u n d a t

--itatic-ns 3 and 4 in Alderm,-trjs C'.reek.

GrIDUFj B stations are in the SOUth F,--,rl:: --,f the river,

4
EkS P)@E-Vil-'LlSlv d@'SCLASSECl. hzi- t,,,Fcter CjLAEdj.-'-\/ MCIE;t tCl the
d Ll

Fc-rt Lones-c-Ime r-rrea. TI-jerce appears to be considerable enrichment

Of the CSIDUth fcir sFvEr,-'-kl cc,rist-ituents-@

p I' C g r E2
4- -.j. i t -=incl lh-cm, up:-trc--eam

station 2 to the regular South Fork station which is just above

the north fork confluence.

Group C stations are located on Pierce Branch and Carlton

Branch which both flow into the Little Manatee North Fork.

Station 7, on the lower reaches of Pierce Branch, has water

quality similar to the upper station (#9) on Carlton Branch.

Station E, the regular sampling station on Carlton Branch,

however, has markedly higher concentrations for a number of

parameters (conductivity, silica, calcium and sulfate) probably

due to irrigation runoff to this stream. Closer investigation of

land-use in the Pierce and Carlton Branch sub-basis should

establish the water quality effects of various agricultural

practices. Group D stations are two small tributaries which

drain into the river downstream from the Carlton Branch

confluence. These stations had some of the highest levels of

specific conductance, silica, calcium and sulfate concentrations

of any sites monitored during the study, presumably due to runoff

from groundwater pumping. Interestingly, however, neither

nitrate-nitrite nor dissolved phosphorus concentrations were high

for these streams.

Group E stations are listed to show the increasing mineral

content of the north fork of the Little Manatee as it progresses

downstream between the confluences of Carlton Branch and the

south fork. In a distance of approximately four river miles,

increases are seen in conductivity and silica by near a factor of

2 and sulfate by a factor of 5. This small geographic region

will be examined in detail with regard to land-use to investigate

the causes of these water quality changes.

Chemical Transport from Sub-basins

As was discussed in the Data Reduction section, the annual

flux of dissolved and particulate nitrogen, phosphorus, and

carbon and total suspended solids were calculated using two

different approaches: extrapolation and interpolation. The first

approach is accomplished by developing rating curves and

integrating these over the annual hydrographs. Two interpolation

procedures were used to calculate annual fluxes.

Because the rating curves potentially provide information

from which other conclusions can be drawn these results will be

discussed in the next section. Following that, annual flux

estimates based on both the extrapolation and interpolation

approaches will be presented, compared and discussed.

Rating curves. The results of the least square regression

fit of the data for the various parameters to discharge are given

in Table 5.6 for each gaging station. For dissolved

constituents, significant rating curves could be established for

DOC, phosphate, total suspended solids and particulate carbon for

all of the gaging stations. Nitrate and particulate nitrogen

rating curves were significant for all gaging stations except

Carlton Branch and Ft. Lonesome, respectively. These gaging

stations had nonsignificant rating relationships for particulate

TABLE

r2 Rating Relationships for Gauging Stations*
values underlined represent non-significant relationships)

DOC N03 N"H3
a b r2 a b r2 a b r2

LONE 0.14 2.92 0.43 -0.16 -1.95 0.14 0.06 -3.37 0.01
CARL 0.28 2.41 0.44 0.09 0.41 0.01 0.35 -2.92 0.11
SP 0.22 2.47 0.42 -0.32 -0.87 0.36 0.12 -3.34 0.02
DUG 0.12 2.60 0.19 -0.15 -0.54 0.11 0.13 -2.25 0.04
WIMA 0.23 2.31 0.48 -0.07 -0.62, 0.03 -0.15 -2.60 0.05
CYPR 0.06 2.85 0.22 -0.42 -2.19 0.56 -0.18 -1.95 0.32

P04 TSS PC
a b r2 a b r2 a b r2

LONE ..0.10 -0.97 0.40 0.16 0.70 0.22 0.19 -0-79 0.24
CARL 0.31 -0.98 0.67 0.32 1.97 0.45 0.26 0.31 0.26
SP 0.20 -1.36 0.82 0.34 1.17 0.50 0.33 -0-54 0.48
DUG 0.29 -1.96 0.19 0.31 2.42 0.55 0.35 0.73 0.42
VaMA 0.18 -1.34 0.44 0.38 1.00 0.20 0.40 -0.93 0.23
CYPR 0.24 -2.98 0.30 0.21 2.42 0.28 0.23 0.46 0.36

PN PP

a b r- a b

LONE 0.13 -3.87 0.06 0.17 -4.20 0.10
CARL 0.29 -2.56 0.16 0.56 -3.01 0.35
SP 0.41 -3.51 0.41 0.18 -3.79 0.16
DUG 0.38 -1.70 0.30 0.21 -2.70 0.22
MMA 0.37 -3 ).71 0.15 0.14 -3.68 0.03
CYPR 0.26 -1.95 0.28 0.13 -2.83 0.06

Parameters listed are for the general equation: In C alnQ + b

phosphorous and all but two (Carlton Branch and Wimauma) had

non-significant relationships for ammonia.

The lack of observed significant rating relationships for

ammonia for most of the gaging stations is not surprising given

the variability of nitrification and denitrification in the

watershed.

In general, the significant rating curves for a given

parameter are similar for all gaging stations.

Fluxes from Sub-basins. The annual fluxes of dissolved

organic carbon nitrate, ammonia, phosphate; particulate carbon,

nitrogen and phosphorous; and total suspended solids from the six

sub-basins of the Little Manatee Watershed were estimated using

the three methods described in the water chemistry data reduction

section. Result of the two methods which gave the best

agreement are presented in Table 5.7. These estimates of fluxes

for each constituent for each gaging station were used to

calculate mean annual fluxes. The poorest agreement was observed

generally for the smaller sub-basins.

The total fluxes of the various constituents due to

discharges from all sub-basins are presented in Table 5.8. The

relative contributions to these fluxes from each sub-basin are

also given in this table. Fluxes of dissolved nitrogen and

particulates from Carlton Branch, Dug Creek appear

disproportionately high on the basis of comparison to watershed

size or discharge.

TABLE

Annual Flux of Dissolved and Particulate Nutrients
and Total Suspended Solids From Sub-Basins of
The Little Manatee River

Kilograms Per Year

Sub-Basins DOC N03 NH3 P04 PC PN PP TSS
xl()5 x,03 x,03 x,03 x,03 x,03 x,03 x,04

Ft. Lonesome 1 10.3 4.72 1.62 19.4 27.7 1.12 0.87 0.4
(LONE) 1) 10.8 4.30 2.34 18.9 39.4 2.11 1.36 17.2
Mean 10.5 4.51 1.98 19.2 33.5 1.61 1.12 8.8
S.D 0.4 0.30 0.51 0.3 8.3 0.70 0.35 11.9

Carlton Branch 1 1.70 21.5 0.86 5.82 20.5 1.18 0.97 11.2
(CARL) 2 2.46 30.9 1.26 7.07 31.5 2.01 1.06 16.1
Mean 2.08 26.2 1.06 6.44 26.0 1.59 1.02 13.6
S.D 0.53 6.7 0.28 0.88 7.8 0.58 0.06 3.5

South Prong 1 .10.69 15.4 2.49 22.4 72.3 4.66 1.84 41.0
(SP) 2 9.05 11.6 2.41 34.6 96.0 5.96 2.39 3.61
Mean 9.87 13.5 2.45 28.5 84.2 5.31 2.12 38.6
S.D 1.16 2.7 0.06 8.6 16.8 0.92 0.38 3.5

Dug Creek 1 0.65 3.29 0.51 0.71 10.7 0.96 0.33 5.7
(DUG) 0.69 3.73 0.67 2.08 45.2 2.99 0.58 16.5
Mean 0.67 3.51 0.59 1.39 27.9 1.97 0.45 11.1
S.D 0.03 0.31 0.11 0.97 24.4 1.44 0.17 7.7

1 '7. 1
Wimanma 1 40.6 85.0 9.57 8 7. 4 319 1 7.36 197
(WIMA) 1) 41.8 75.3 8.10 82.4 349 19.4 9.25 191
Mean 41.2 80.1 8.84 84.9 334 18.2 8.31 194
S.D 0.8 6.9 1.04 3.5 21 1.7 1.34 4

Cypress Creek 1 2.54 1.57 1.88 0.88 26.9 2.51 0.92 18.7
(CYPR) 2 2. 5 4 1.35 1.75 130 '35.3 2.92 1.61 241.2
Mean 2.54 1.46 1.82 1.09 31.1 2.72 1.27' 21.5
S.D 0.00 0.15 0.10 0.30 6.0 0.30 0.49 3.9

TABLE

Annual Material Fluxes to the Little Manatee Estuary
and Relative Contributions from Sub-Basins

Total LONE CARL SP DUG WIMA CYPR IB2
(tons/yr.) (Percent)

DOC 4370 24 5 23 2 94 6 41
N03 81.6 6 32 17 4 98 2 40
NH3 10.6 19 10 23 6 83 17 26
P04 86.0 22 7 33 2 99 1 34
PC 365 9 7 23 8 92 8 44
PN 20.9 8 8 25 9 .87 13 37
PP 9.58 12 11 22 5 87 13 38
TSS 2160 3 4 6 18 5 90 10 56
Watershed 451 19 4 27 2 95 5 52

1 Total is calculated as the sum of the fluxes measured at the Wimanma and Cypress
Creek gauging stations.
C7 0

2. IB refers to the inner basin. Fluxes are calculated as the difference between the
flux at Wimanma and the sum of the fluxes at Dug Creek, Carlton Branch, Ft.
Lonsome and South Pron,-.
3. Watershed area is in km2.

Total fluxes given in Table 5.8 are conservative estimated

of the amount of material delivered to the Little Manatee estuary

because we have not considered smaller sources of materials such

as direct surface runoff and contributions downstream of the

gaging stations. We also have not considered removal processes

that may be occurring downstream of the gaging stations.

The efficiency of material mobilization from each sub-basin

is compared in Figures 5.3 A and B. Figure 5.3 A compares the

flux of dissolved substance per unit area and Figure 5.3 B does

the same for particulate substances. These comparisons can be

used to distinguish similar watersheds and perhaps identify the

influence of different land use practices.

Q16
DOC 006
0 NH3

Q10

0
004

0,06

0
c\j 002
E 0.00
000
0) 0 100 200 300 400 6W a 100 200 300 400 600

0.4
PO Cj
X NO
:D 3 4
1 0.3
LLI_

0
OL1

0
QO 01 00
0 100 200 4W Wo 0 100 200 4W 6W

WATERSHED AREA (kM2)
Figure Flux per unit area of dissolved nutrients for sub-basins of the Little
Manatee River Watershed plotted againS t sub-basin area. Symbols are
defined below.
LONE CARL SP DUG WIMA CYPR NP

3
TSS PC

08 2

0
13
04 -

04 OL2 - 0
E
V 0 0
CLO 0
200 3W 400 600 a
100 200 300 400 600

OL20
X PN PP

C1 16
004 A
LL

CLIO

aO2 93

0
Q,OO 0100
0 200 300 4,00 60a 0 100 200 WO 400 600

WATERSHED AREA (km 2
Figure_'S_3@- Flux per unit area of total suspended solids and particulate nutrients
from sub-basins of the Little Manatee River sub-basin area. Symbol s
are defined below.

LONE CARL SP DUG WIMA CYPR NP
A

VI. ESTUARINE WATER CHEMISTRY

OBJECTIVES

An overall goal of the Little Manatee River Project was to

examine the relationships of the quality and quantity of

freshwater inflows to the ecological characteristics of the

Little Manatee River estuary. A central component of this

investigation was the monitoring of salinity and water quality

conditions in the estuary during the study year. Data collected

within the estuary were synoptic with the freshwater stream

sampling so the effects in the estuary from short term changes in

freshwater inflows could be examined.

SAMPLING AND ANALYTICAL METHODS

Estuarine water quality sampling was conducted on a bi-

weekly basis with 26 sampling events occurring during the study

year (January 24, 1988 to January 24, 1989). Sampling in the

estuary was coordinated with the freshwater sampling regime and

on 24 dates estuarine and freshwater samples were collected on

the same day. on two dates, freshwater samples were collected

the day befor the estuarine sampling.

Estuarine field sampling included a combination of two fixed

location stations and several stations which were located on

specific surface salinity concentrations (Figure 6.1). The first

fixed location station was located in Tampa Bay northwest of

marker #1, approximately 2.3 miles from the river mouth

River mlfles - Little Manatee River Estuary

GO I f
Of
q MEX11CO

RAIS KJN INUT _j
it
@j W-@Y

"t6-.

U, 41
3

LITTLE MANATEE
FtIVER

_Zn

1 Reference. locations of es-tuarinc sampling %tations in Little
Karw-tee River and Tampa Bay, Fixed locations are shown by all X
@-n Tampa Bay and Ruskin Inlet. Mileages ahown provide refe-rutter,
fo,r values listied in Table 6,1 for stations -based -on saliniry
Concentrations.
Gulf
011COX
MEX

following the boat channel. The second fixed station was located

in Ruskin Inlet, a channelized tributary to the Little Manatee

River approximately 2.5 miles upstream of the river mouth. The

locations of the remaining sampling stations were flexible and

based on the location of selected surface water salinity

concentrations on the that sampling day. For the entire study

year samples were collected at 18 ppt and 9 ppt salinity

concentrations. The 0 ppt salinity station was determined by the

location of surface water near 1000 umhos/cm specific

conductance. For the first two sampling trips, samples were

taken at the 9 ppt salinity concentration, but this station was

discontinued and for the remaining 24 trips samples were taken at

the 12 ppt and 6 ppt salinities. River mile locations were

recorded for all samples collected on salinities. The locations

of these stations during the study year are listed by rivermile

in Table 6.1, while a map of the estuary showing river mileages

is illustrated in Figure 6.1.

All estuarine water quality sampling was conducted in the

morning or early afternoon on an incoming tide. At each station,

duplicate water samples were taken from both surface and bottom

waters. Water samples for chlorophyll analyses were kept chilled

and transported to the Florida Department of Natural Resources

Laboratory in St. Petersburg where filtration of the sample for

pigment removal was done the same afternoon. As with the fresh

water samples, filtration for the separation of particulate (C,

N, and P) and dissolved nutrients (PO_ NO_ & NO_ Organic

Table 6.1. Location of Little M@rnatee Piver salinity stations and
the Tampa Bay station by rivermile. Pivermiles werc-
measured as distance from the mc-uth. Neaative numbers
indicate distance into Tampa Bay measured in the channel
from navigation marker #1. Positive numbers are
distances from the mouth toward the head of the river.

-----------------------------------------------------------------

Tampa Rus. k i n
Date Bay 113ppt 12- > p p t Gppt Oppt Inlet

1 1-71E @7* N.D. N.D. @.7 j
Ie- -/88 '1
02, / 10 0 . -31 1 N.D. N.D. 6- @ I
-2/,- 1.
A 44 4 G. 5
0 C) 9 C). 00 0 0 -1 . G, 5
1. -C.18 1 . 5j'S C1. . 1. 5
4 'C)E,
/ @.. 11 E,. 0C)
C) 4 1. 3C) 33, E, C) S . '725 S. 4 r5i
05/04- 1 . S15 'Ed, . 7 0 El. 151 C- . 33 5
05/ 18 2.55 6. IC) 7 . 223 1 C). 223
06/01 3. 70 5.65 E 3 C) 10. 46
OE/ 15 4. BC) G . 60 S.GC) 1 (). 4 5
C) F, /'29 5. 10 El. 16 9. E-0 10. 63
C) 7/14 31. 50 5. 19 8.34 9.25
0 7 /,2, B 1. 4-0 3. 50 C) 7.19
C). 0C) 24
C)S/ 10 ( . '*:' 4 15 4. *@
08/30 1 . -'23 -0.91 0. 00 3:1. 40
019/0e -2.1() T.BAy** 0-81
0 E) / * _2 1 2 T. Bay*-)@- I . 533 4. J.C) F, -25
1 C-) I I T.Bay** -0.45 '---'5
1 -0. 1.9 i . 0 C) I
11 /07 - 4-15 -1.1e 1.4-C) 4. 55
C., -) 9 -7 0 S '71
C r, 4.;_ -1
.7'. @ (') -
12-1 --1. 4F, 0. SO 7. 1,-@
12 Ok") r-., 1. 4 . E. c5
C) S

+ -7
Averaoe +(). +'7'. 1 j k-)
J
Range 0 C) 5) @-:j 8 1.
1:1 1 to S. G, C tr,

-----------------------------------------------------------------

*'Fixed location
c @.:k TZMT p
I i n i t y oriC EFit r Ekt'i, F1 I'CILAFI I t EA h" \Y S .!--,IFA t i r-1

Carbon) was done in the field with resulting filters and

filtrates put immediately on ice. Samples (filters) for

particulate phosphorus analysis were periodically shipped to

SL&ES for digestion and measurement. Remaining water chemistry

parameters were analyzed at the District Laboratory in

Brooksville. Water samples were analyzed for the parameters

listed in Table 5.1, using the methods indicated. All

statistical analyses and presentations of these data are based on

the mean of duplicate samples.

At each water quality station, vertical profiles of

temperature, dissolved oxygen, pH, specific conductance and

salinity were made at 1 meter intervals plus bottom with a

Hydrolab Surveyor II water quality meter. Also, at each station,

a light penetration profile was taken with a Li-Corr photometer

by measuring ambient (deck) and in-water light intensities at .5

meter intervals plus bottom.

Beginning with the third sampling trip (February 24, 1989),

additional measurements were made throughout the estuary for

vertical profiles of temperature, dissolved oxygen, pH, specific

conductance and salinity. These measurements were performed

during what is termed a "Hydrolab run", where numerous fixed

locations in the river were sampled within a one hour period.

After water chemistry samples were collected on an incoming tide,

Hydrolab runs were performed in the mid-afternoon on a slack,

high-tide condition. Stations for the Hydrolab run were at fixed

locations extending from the river mouth to 9.5 miles upstream,

with extra meaSUrements taken ifurthrre tAPstream during two

saffi,-)ling events. The Hydrolat? run was initiaVed to measure in

situ physical parameters throughout the estuar:y on as similar

conditions as possible. Similar sampling had been done in the

Little Manatee River by the District between 1965 -and.1987. Muc h

of the analyses regarding salinity distributions and dissolved

oxygen relationships in the river are based on the "Hydrolab

runs" made from 1985 to 19B7 plus the study year.

DATA REDUCTION

Advection-diffusion models have been used by many

investigators to interpret estuarine chemical data- (e.g., Li -and

Chan, 1979; Kaul and Froelich, 1984). Thege models use salinity

as a tracer. The distribution of a-constituent in estuarine

waters can be compared to salinity to determine whether a

substance is: 1) conservatively transpprted through the estuary,

(2) removed from the water column or (3) added to the water

column due to local input (e.g. anthropogenic, release from

sediments, etc.). These types of estuarine behaviors are

demonstrated in Figure 6.2.
L.

From the advection-diffusion models using salinity as a

Conservative tracer, the intercept of the extrapolation (or

tangen't) of the constituent-salini-It-,y curve at the high sali nity

end of the curve where change in constituent concentration with

change in salinity is constant, is defined as the apparent zero

salinity endl--4ember (AZE). It can be demonstrated mathematically

A -AZE
C:

V'2DD-
AZE C) :C:z)
iDD
U
0 D
0 10 20 3D 0 10. 20 3D

AZ&- C

IIC) 210 310
Salinity (%C))

Figure .9-M. ENamples of different estuarine behavior of trace
metals: (a) removal (after Faqueres et a!., 1978); (b)
conservative; and (c) release (Windom, unoublisbed data).

that river discharge multiplied by the difference in the observed

zero salinity concentration and the AZE value gives the rate of

removal, or release, or the constituent, per unit time, necessary

to produce the observed concentration distribution. The only

assumption required is that the concentration of the constituent

in the freshwater input is constant over the residence time of

the estuary. For the Little Manatee estuary, this assumption is

satisfied sufficiently to draw the conclusions that will be made.

Following the approach described above bimonthly data for

concentrations of dissolved nitrate + nitrite (No ), ammonia

(NH ) orthophosphate (PO ), organic carbon (DOC); total suspended

solids (TSS); and particulate carbon (PC), nitrogen (PN) and

phosphorus (PP) were plotted against salinity. The zero salinity

concentration was taken to be the mean value of the bimonthly

concentrations observed at the Wimauma and Cypress Creek gaging

stations weighted by their mean daily discharge at the time of

sampling. This value was then plotted on the constituent vs.

salinity curves for each month.

RESULTS

Salinity Distributions

Streamflow levels in the Little Manatee River typically have

large seasonal variation with resulting effects on salinity

distributions in the estuary. Streamflow characteristics for the

Little Manatee River near Wimauma based on over 50 years of

record were presented in Chapter II. In sum, the river

experiences prolonged low-low periods, usually in the spring or

fall, when daily flows average less than 50 cfs. Conversely,

brief periods of heavy rainfall rapidly increase streamflow in

the basin and short-term flows over 1000 cfs are not uncommon.

As described in Chapter IV, an unusually wide range of

streamflow levels occurred during the study year. Estuarine

water quality and salinity sampling during January through March

corresponded to medium to medium-high flow levels for the river

(71 to 429 cfs daily flows). Beginning in April, a prolonged

period of generally diminishing flows occurred which were lowest

in mid-June (15 to 20 cfs) and extended-into early July. Summer

rains began in mid-July and flows were at moderate levels for the

remainder of that month. The first high flow levels (1050 cfs)

occurred during the August 10 sampling event, and extremely high

flood flows (9720 cfs) were recorded in early September after

four days of heavy rain. Flows generally returned to low to

moderate levels for the study year, although storm events raised

flows to 414 and 493 cfs in November 1988 and January 1989,

respectively.

Salinity distributions in the estuary showed distinct

changes in response to these changes in flow. Mean water column

salinity for four fixed locations in the river are plotted by

date in Figure 6.3. Salinity at the mouth of the river remained

above 20 ppt, until early September, when flood flows briefly

reduced salinity to near 5 ppt. For the remainder of the year,

salinities fluctuated between 18 and 23 ppt salinity, with slight

MILE 0.0

01
05DEC87 14MARBS 22JUN88 30SEP88 08JAN89 18APR89

DATE

MiLE 4.23

-C@

10@

01
05DEC87 14MAR88 22JUN88 30SLP88 OSJAN89 18APR89

DATE

Figure 6,1. Mean water collmn salinities at four locations in the Little
Mar-tee River, February 24, 1988 to Janu.-a7 24, 1989.

,MILE 7.19

17
16
15
14
13
12
0-11
10
9
Zj 8
V) 7
6
5
4
3
2

0
05DEC87 14MAR88 22JUNB8 30SEPBB OBJANS9 IBAPRB9

DATE

MILE 9.53

z 5

V) 4

05DEC87 14MAR88 22JUNSB 30SEP88 OSJAN89 18APR89

DATE

Figure 6..t. (Continued)

decreases in November and January due to storm events.

Salinity at mile 4.23 (Figure 6.3b) displayed a much wider

degree of fluctuation. Salinity steadily increased in the spring

and early summer in response to the continuing dry season.

Salinity was highly variable the rest of the study year, ranging

from 9 to 3 ppt after four storm events to values above 10 ppt

during a dry spell during December and early January.

The other two stations (mile 7.19 and mile 9.53) presented

in Figure 6.3 show a similar trend with regard to salinity. Both

stations were essentially fresh in the early part of the study,

but salinity increased beginning in April and continued with the

dry season until early July. Increases in flow during the summer

rainy season reduced salinities to low levels, and for the

remainder of the year, they remained near fresh at mile 9.53 and

below 3 ppt at 7.19.

Seasonal changes in salinity distributions are also

described by longitudinal profiles of mean water column

salinities on selected dates which are presented in Figure 6.4(a-

f). As shown, salinity in the river below mile 7.19 were reduced

from February to March due to an increase in flow. The maximum

observed salt penetration is shown for June 29, near the end of

the dry season, when salinities above 20 ppt were found six miles

upstream and salinity at mile 10 was near 8 ppt. Salinity in the

river decreased through July and August, and the river was

completely fresh except for a small salt lens at the mouth during

the flood in early September. By late September and

FEE3. 24 and MAR. 22 1988

01.
0 1 2 3 4 5 6 7 8 9 10

MILE

JUN. 29 (0) and JUL.28 1988

0 1 2 3 4 5 6 7 8 9 10 1 1

MILE

Figure Longitudinal salinity, profiles for the Little Manatee River
estuary on selected dates from February 24, 1988-to Janua:ry 1989.

AUG. 10 (0) c.rid AUG. 26 198 8
,30-1

01.
0 .1 2 3 4 5 6 7 8 9 10

MILE

SEP. 08 (o) and OCT. 24 1988

0 1 2 3 4 5 6 7 8 9 10

MILE

Figure 6:-3. (Continued)

NOV. 21 ond DEC. 16 1988

V)
10

0 1 2 3 4 5 6 7 8 9 10

MILE

JAN. 1 1 ond JAN. 24 1989

0
0 1 2 3 4 5 6 7 5 9 10

MILE

Figure 6.3'. (Continued)

through the fall, salinity distributions had retained to more

typical profiles, although a significant storm event in January

1989 freshened the river above mile five.

The salinity data presented graphically above show that

salinity distribution in the Little Manatee River is highly

variable and responds to relatively small changes in streamflow.

This phenomenon is common in estuaries and much of the estuarine

biota are tolerant of widely fluctuating salinity. One approach

for describing estuarine ecological structure, however, is to

estimate the frequency that various salinities are encountered at

different parts of the river.

For the Little Manatee River Project, salinity measurements

recorded between 1985 and 1989 allow the statistical examination

of salinity-flow relationships in the estuary. In Figure 6.5,

salinity at various points in the river are plotted versus

average daily flow when the respective measurements were taken.

Predictive equations for salinity as a function of flow for these

locations are being established using linear regression analysis.

Although the relationships presented in Figure 6.5 use average

daily flow at the time of salinity measurement it is expected

that some integrated flow value, such as the preceding 5 or 10

day average flow, will give a better fit. The inclusion of a

tide stage variable corresponding to high-tide height at the time

of sampling should also increase the fit of relationships. The

development of equations using regression analysis will then be

compared to the flow duration characteristics of the river to

102

MILE 0.0

281
271
26

E25

2 4

E 23

1 9.

17
0 100 200 300 400
FLOW (cfs)

MILE 4.23

0,
0 100 200 300 400
FLOW (cfs)

Figure 6 L4'. RelAtionships of mean water colxmm salinity to same day average
flow at four locations in the Little Manatee River estuar"y.

MILE 7.19

19
18
17
16
15
14
13

10
9
8
7
6
5
4
3
2 %
1

0 100 200 300 400
FLOW (Cfs)

M I L IE- 9. 5 3

5
41
3

0 100 200 300 400
FLOW (cis)

give estimates of what frequency various salinities are

encountered at different locations on the river.

Dissolved Oxygen

Seasonal dissolved oxygen conditions in the Little Manatee

River estuary are examined in this report primarily from data

collected in the "Hydrolab runs" which were conducted on 24

sampling dates between February 24, 1988 and January 24, 1989.

These data are particularly useful because they were collected

throughout the estuary on similar conditions (mid-afternoon,

slack high tide), thus reducing possible confounding effects from

time of day or different tidal conditions. Other data which may

be important for understanding dissolved oxygen concentrations in

the estuary are the physical and chemical data collected each

trip on the incoming tide before the Hydrolab run was performed.

Dissolved oxygen (D.O.) concentrations for four locations in

the estuary during February 1988 to January 1989 are illustrated

in Figure 6.6. D.O. concentrations were typically highest and

had the least seasonal variation at the mouth of the river. D.O.

did show the expected inverse relationship to water temperature,

with highest D.O. concentrations found in the winter and lowest

concentrations in the summer. The lowest instantaneous mean D.O.

level measured at this site was near 4.0 mg/1 during the early

September flood.

D.O. concentration at mile 4.23 (Figure 6.6.) were

generally lower than at the mouth, particularly during the summer

105

MILE 0.0

E
C;

05DEC87 14MARBS 22JUN88 30SEP88 OBJAN89 18APR89
DATE

MILEE 4.23

05DE'.57 14MAROH 22JU1488 30SEP88 OBjA-NB9 ISAPR89

DATE

Figure 6 . 6, Mean water coli-m dissolved oxygen concentrations at four
locations in the Little MarLntee kiver estmary, February 24, 1988
to January 24, 1989.

MILE 7.19

05D@CV .1 4MARBS 22JU'N88 30SEPBB OBJAN89 18AP'R89

DATE

MILE 9.53

14MARE-B 22JUNBB 30SEP88 OZJAW89 I lull, R89
DATE

Figure@ (j5, (@,&jttnued)

months. Mean D.O. concentrations below 4 mg/1 were recorded on

five dates between July 14 and September 22, 1988. The

September flood actually resulted in an increase in D.O. at this

station. D.O. concentration's were more erratic at mile 7.19, but

followed a similar seasonal pattern to mile 4.23. Low D.O.

levels were observed during the summer, but D.O. concentrations

increased from the September to October samples and remained high

for the remainder of the year. D.D. concentrations showed the

most seasonal variations at mile 9.53 where levels above 10 mg/l

were recorded during May and October, 1988, but levels below 4

mg/1 Were recorded between June and September.

In sum, D.O. concentrations in the Little Manatee River,were

at high levels during most of the year but reduced to values

below 4 mg/1 during much of the summer, indicating potentially

stressful concentrations for aquatic biota in the summer.

Differences in D.O. between surface and bottom waters were small,

however, and it does not appear that oxygen stress occurs in

bottom waters due to limited mixing. Generally, with regard to

temperature and salinity effects on water density and

stratification, the Little Manatee tends to be well mixed. There

are areas of the river, however, that appear to be sensitive to

factors that could reduce D.O. concentrations. Longitudinal

profiles of salinity and dissolved oxygen concentrations are

plotted by rivermile in Figure 6.7. Profiles measured from June

through August show consistent declines in D.O. from the mouth

upstream to near miles 4.0 to 7.0, with minima often occurring

108

JUN.115,1988

30;

20 7

C6 0

3
0 1 2 3 4 5. 6 7 8 9 10 1 1

MILE
JUN-29,19881
30 9

C)
20 7
0

0'
0 2 3 4 5 6 7 8 9 '10

MILE

Figure 6 - Longitudinal profiles of mean water column salinity and dissolved
oxygen profiles in the Little Manatee River estuary, February 24,
1988 to January 24, 1989.
D

14, 19 8 8

30 1-

20 7

CL 0

Ln 10 5

01.
0 1 2 3 4 5 6 7 8 9 10 11

MILE

JUL.28,1988
301 9

20 .7

CL p

3
2 3 4 5 7 8

MILE

Figure 6.-6. (Continued)

A U 10, 9 B s

20 7
0

Ln 10 5

C) 3
0 1 2 3 4 5 6 7 8 9 10

MILE

AUG.26,1988

20 7

3
0 1 2 3 4 5 6 7 8 9 10

MILE

Figure 6.6. (Continued)

SEP. 08, 1988

C) 4 7

0
3

Ln
2

oll 3
0 1 2 3 4 5 6 9 lo@

MILE

SEP. 22, 1988

9
17
It 6
15
14
13
012 7

41
3
21
@3
0 1 2 3 4 5 6 7 8 9 .0

MILE

F i gur e @-6 (Continued)

between mile 4.0 to 6.0 These minima were found over a wide
range of salinity concentrations ranging from 8 to 22 ppt. On
several dates, D.O. increased upstream in low salinity and freshwater
reaches.

Although not shown., D.O. concentrations at the nearest

freshwater stream site (near Wimauma) did not reach the low(4

mg/1) concentrations observed in the estuary. Estuaries, because

of their tendency to retain suspended and organic matter, are

often sites of D.O. depression. Data to date indicate that the

Little Manatee River estuary does not currently have a serious

problem with low dissolved oxygen concentrations, but in many

areas of the river, conditions are borderline and further

perturbations could result in significant reductions in water

quality.

General Water Chemistry

Mean values for nutrients and other water quality parameters

for the estuarine sampling stations are listed in Table 6.2. All

the stations, except Ruskin Inlet, are arranged with salinity

reducing from left to right (from Tampa Bay to 0 ppt) so changes

along the salinity gradient can be easily Visualized. The

general water quality characteristics of the estuary are

summarized in the discussion below. Greater detail regarding the

behavior of nutrients and suspended matter in the estuary is

provided in the Subsequent section.

113

--------- ---------------------------- ------------------------

Tal.-J-4 e 6. 2. Mean values @or water chemistry parameters at
estuarine sampling stations Little Manatee
River.

Tampa Rus k i n
Parameter Uni ts PC 18 rip 12 mn 6. EPt 0 ppt Inlet
:.Iy

Mile miles -2.27 0.67 2.19 4.1'37 6.76 2.5

Salinity ppt 23.4 18.6. 12.4 6.4 0.6 10.6

Temperature OC 22.6 3 . 0 24.1 25.1 22.9 24.7

pH pH 7.3 7.0 6.9 6.8 6.7 7.2

Turbidity NTU 4.6 2.9 3.0 4.2 5.8 4.13

Color PCU 14 25 44 70 106 57

Total Sus-
pended Solids mg/l 1.9.2 10.5 8.2 8.0 7.1 10.1

Particulate
Carbon mg/l 1.18 0.84 0.91 1.25 1.30 1.46

Total Dis-
solved Carbon mg/l 6.9 7.9 9. B 11.8 14.6 11.7

Particulate
Nitrogen mg/l 0.13 0.10 0.11 0.13 0.14 0.17

NF6 (as N) mg / 1 0.04 0.08 0.09 0.08 0.07 0.07

NO 2r_NO -x-N mg/l 0.02 0.05 0.09 0.16 0.43 0.15

Particulate
Phosphorus mg/l 0.06 0.03 0.04 0.05 0.05 0.05

P04 (as P) mgll- 0.34 0.32 0.32 0.31 0.30 0.35

Silica mg/ 1 0.9 2.2 2.1 3.7 4.9 3.6

Chlor a mg/m 6.6 5.5 10.4 15.6 20.3 19.0

---------------- -------- ---------------------- --

114

The Little Manatee River estuary is really a functional unit

of a much larger estuary, Tampa Bay. The open waters of Tampa

Bay,however, are much different than the waters of its brackish

tributaries such as the Little Manatee River. The progression

from the upper reachers of the Little Manatee estuary (o ppt

station) to the Tampa Bay station showed chemical differences

indicative of a change from nutrient-rich,low-salinty waters to

phytoplankton dominated, high-salinity waters. Nitrate-nitrite,

silica, particulate carbon, turbidity, and total dissolved carbon

showed distinct declines in concentrations from the upper reaches

of the estuary to Tampa Bay. With the exception of phosphorus,

the bay has much lower levels of dissolved nutrients (N,Si) due

presumably to phtoplankton uptake. Dissolved phosphorus

concentraions are distributed very evenly along the salinty

gradient with mean values ranging between .30 and .34 mg/l

indicating this nutrient is not limiting and is in excess supply

in the estuary. Total suspended solids were highest in Tampa

Bay, and increased with salinity in the river due to the

influence of bay water.

The Ruskin Inlet station, listed on the far right of Table

6.2, was located in an urbanized tributary to the Little Manatee

that receives considerable amounts of urban runoff. Of course,

salinty fluctuated much more at this station than at the

water salinty at Ruskin Inlet ranged from 0.0 to 22.0 ppt during

the course of the study and averaged 10.6 ppt. Nutrient

115

concentrations showed large seasonal variations at this station
due to stormwater inputs and the rapid change from a mesohaline
(medium salinity) to a low salinity environment.

Nutrient and Suspended Solids Distribution
The results of the analyses of dissolved and particulate
nutrients in estuarine samples are plotted against salinity in
weighted freshwater concentration of a substance to its
concentrations at higher salinities provides a basis for judging
estuarine behavior of the substance as discussed in the data
reduction section. For this purpose, the trend in the data for
concentration versus salinity connecting weighted mean freshwater
concentration to concentration at highest salinity is interpreted
as discussed earlier. The following discussion summarizes the
behavior of the nutrients based on their estuarine distributions.

Dissolved Nutrients DOC is observed to behave
approximately conservatively throughout the year. Results
suggest that the relatively high DOC associated with fresh water
is diluted as fresh water mixes with seawater in the estuary.
Most of the year nitrate appears to be removed in the
estuary, perhaps due to uptake by microorganisms, ammonia
concentrations, however, show mid estuarine maxima indicating its
production within the estuary.

116

Phosphate concentations in the estuary suggest conservative

mixing throughout most of the year. During May and June,

phosphate appears to be removed in the estuary. Although

phosphate concentrations are mostly conservative in the Little

Manatee estuary, the relative value of the fresh water and high

salinity end-members varies. January to March fresh water

concentrations are higher than the high salinity (i.e, ocean

end-member) concentrations. This is true during July and August

as well, but during the rest of the year the high salinity mixing

end member has greater concentrations of phosphate than does the

fresh water end-member.

Total Suspended Sediments and Particulate Nutrients. Total

suspended solids increase virtually conservatively from zero to

higher salinities. This suggests that the greatest source of

sediment to the Little Manatee estuary is Tampa Bay.

Particulate carbon, nitrogen and phosphorous are

significantly torrelated (0.01) throughout the estuary,

throughout the year. While it is apparent that a large fraction

of the particulate nutrients is derived from Tampa Bay, there is

some indication that particle production, due to primary

production, may influence mid-estuarine concentrations during

June.

117

Chlorophyll, Phytonplankton and Primary Productivity

An important component of the Little Manatee River study was

an investigation of spatial and temporal patterns of primary

productivity in the estuary. Water quality parameters related to

primary production, i.e. nutrients, chlorophyll a and light

penetration profiles, were measured at each water quality

station. In addition, researchers from the University of South

Florida accompanied field crews on each trip and collected

surface-water samples for analyses of phytoplankton composition,

primary production (photosynthesis) and nutrient limitation. A

brief summary of the year one results for chlorophyll

concentrations and phytoplankton abundance and composition is

presented below. Much greater detail regarding these data, plus

the results for the primary production and nutrient limitation

analysis are contained in the report submitted by Dr. Vargo of

the University of South Florida (Vargo, 1989).

Mean annual values for chlorophyll a primary production and

total phytoplankton cells are listed in Table 26.3. Chlorophyll a

and phytoplankton cells were measured at all stations, while

primary production measurements were performed at all stations

except 6 ppt salinity and Ruskin Inlet. Because all stations

except Ruskin Inlet were consistently collected along the

salinity gradient, the results for Ruskin.Inlet are examined

separately.

118

-------------------------------- -- ------------------ --------- - --

Table 6.3 Annual mean values, for several parameters related
to primary production in the LMR and Tampa Bay,

arranged in rank-order.

Total Phytonplankton Chlorophyll a Primary Production

Rank Station Cells ml Station
ug/l Station mgCm hr

1 R. Inlet 9391.1 0% 20.3 0% 122.25

2 T.Bay 6007.0 R.Inlet 19.3 T.Bay 89.38

3 0% 4712.1 6% 15.6 12% 84.85

4 6% 4314.0 12% 10.2 18% 50.89

5 12% 3260.8 T.Bay 9.4

6 18% 2808.8 18% 7.3

-----------------------------------------------------------------

The ranking of mean values for chlorophyll a, primary

production, and total phytoplankton cells sh the moveable

salinity stations which were located in either the river or boat

Channel outside the river mouth. All three parameters were

highest at the 0 ppt station, and steadily decreased with

salinity, being lowerst at the 18 ppt station. Generally,

variation in these parameters was much greater at the low

salinity station with frequent high values indicative of

periodic algae blooms. Near the mouth of the river in higher

salinty waters, seasonal variations in phytoplankton cells,

chlorophyll a and primary production were much reduced. A more

detailed discussion of seasonal trends for these parameters is

presented in a following section.

The results for the Tampa Bay station showed an inconsistent
ranking with regard to the moveable salinity stations. This may
reflect that the fixed-location bay station was always the most
seaward, and represented a much different physical environment
from the moveable stations which were located within or near the
mouth of the river. The bay represents a high salinity (>18
ppt), wind mixed, open-water environment where substantial
phytoplankton populations are present year-round and waters are
generally low in dissolved nutrients, particularly silica and
nitrogen. Total phytoplankton cells were highest at the bay
compared to the other stations except Ruskin Inlet. Chlorophyll
concentrations, however, were comparatively low and ranked only
above the 18 ppt station. this difference in ranking for
phytoplankton cells and chlorophyll concentrations is probably
due to phytoplankton species composition in the bay, which was
ususally dominated by diatoms with low concentrations of
chlorophytes and blue-green algae. Primary production at this
site was at a moderate level, similar to the 12 ppt station.

In sum, although the bay was ranked differently for the
various parameters, a consistent pattern was observed for the bay
and river system. Phytoplankton production was high in the low-
salinity upper reaches f the estuary ad generally declined,
with reduced seasonal variations, toward the mouth of the river.
Phytoplankton production did increase, however, from the 18ppt
salinity station to the bay reflecting a transition from the
river mouth to the open-bay environment. On some dates, usually

120

T ~qi -I ~e ~qF~.~, ~I..~t ~qk ~qi ~r I I ~n ~+~1 ~E~k t: ~qi r- h ~C~@ -;I'! :I:, t ~qV~c, ~-~r ~qf ~C~:~1

i ~r~i t h ~e~. ~c~-~;t ud ~k~4 ~S I ~-D a t ~e d i r~j ~c~%~k I ~i a I-) n ~qj~.-ed t~r~qi~qL~l~ut~ar- t~,~:~-~-~-~,

~qt I ~qj. ~V~E
Little ~qlv~ql~an~at~eE~7.~. ~j.~-~t p p ~Y~' ~-x ~qj m a t ~q3. ~qy ~'~7 5 ~f ~7 ~1 ~qi ~q1. ~e ~E~-~:~@ ~up~s~itr~e~E~.~-~tm fr~c~.~m ~E~.~.~.~. ~r

~1-~1 ~@~z~:~-~.L
~f~T~i~,~.~-~.~.~i ~qu t h ~qk I r~~, I r ~1~q3. ~qt ~r e~l ~V ~C.~? d ~c~.~, ~r~- a L~-~, ~q1 e t ~-~-~. r m w a ~qt~. e r U n f

~a f t ~e~. r r a ~qi n ~s , ~qL~I U t r ~e ~c~S J ~cl ~en c~. e~.~.~- -~I~- i m e ~E-~-~. i n t h ~e I r ~i I e t a ~r e p r ~-~-D b a ~qb 1 y

relatively l~c~-ng b~e~,~-~-~,~7~kL~tSe tidal -~=~ind river ~CUrrent~s appear t~c~, be

M~LAC~-h reduced th~er~E~.~.~. to t~-h~c~.~, m~o~kin ~ch~ann~C~.~6qA. ~--~-f th~E:~-~.~, ~1-~1~VE~N~1~.

Ph~qvt~o~qpl~an~qkt~on ~c~e-~q11 c~-~D~qunt~s~-~7~. were h~qiQhe~st for this st~ati~c~-n dU~C~-~1 t~O ~an

~ab~Uncl~ance of ~qA~0qdth~O~L~.~qMh th~e m~c~-~-~-~,~an ~1~'~)~L.~If~f~)~qL~'~1p~2p~p~of

phyt~c~-~6qplan~qkt~c~in cells was twice ~qas great for Ruskin Inlet compared

to t~qf~-~-~j~e C~) ppt ~5t at ~qi on , t h ~e ~s ~e s t a ~-t ~qi c~. n ~s h a ~C~qJ ~F~, ~qi ~m ~qi I a r c h I ~I~:~- r ~-~-~-~, ~qp h ~qy I

m e a n ~s :~, f a p p i m a t e 1 y ~q2~-~4qY) U ~q / I

f
~S~qe~a~sc~qm~a~ql. Tr~qend~c~-: for Chlorophyll ~-~qF.~rn~c~entr~ati~o~n~s and ~qPh~qyt~qo~qp~ql~a~qD~qkt~qon

~qF~. m s J~ t n SL~A~rf~a~I-~C~? water ~c~i~r ~qop h~,,"Il for

~e~S~:~-tL~A~,~R~r~qj~.F~j~E ~st~a~-~1~1~-i~o~n~s: ~ar~e plotted bv d~at~-~E~-~-~.~, in ~-~qF~qi~c~l~u~r~E~:.~, ~qC-~qS. ~6q7~1~--~1 e ~F~; ~e

~s ~@~- ~-~s- -a 1 ~qi t ~7~-~t t ~qi v ~e ~q1. 1 m p ~r e ~qd ~qt~. ~.~-~D p A n ~qk t ~n a b ~L ~i n d ~@~7 ~i ~c~.~- ~i
a q u ~r

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S7A-1
ON,TAMPA BAY

.40

U20

0
05DEC87 14MAR88 22JUNBB 30SEP88 OBJAN89 18APR89

D AT I-

STATION 18 PPT

__j

10
01
05DEEC87 14MAR88 22JUN88 30SEP88 08JANB9 ISAPR89

D
A
t,

z =Station at Tarnpc Bay site

Figure 6.1g. Mean values for surface water chlorophyll a concen trations at six
stations in the Little Manatee River estuary.

STATION 12 PP-1

LD
201

110
zo,

0
05DECS7 14MARBB 22JUNBS 30SEP88 08JAN89 18APR89

DATE

a =Stction at Tampa Bay site

STATION 6 PPT

0
20

IBAPR89
05DEC87 14MAR88 22JUNBS 30SEPBB OBJAN89

Figure (Continued)
n

STATION 0 PPT

-j 40

10.

01
05DEC87 14MAR88 22JUN88 30SEP88 08JAN89 18APR89

DATE

STATION RUSKIN INLET

0 30

01.
05DEC8? 14MAR@B 22J6NBB 30SEP88 08J'AN89 18APIR89
DATF

Figure 6.0- (Continued)
n,
n.

not reflected by the chlorophyll data. Chlorophyll

concentrations were at increased levels in the early summer, but

were low during the September flood. Peak chlorophyll

concentrations occurred in late September and early October, when

the blue-green alga Schizothrix sp. reached high densities. It

is believed this blue-green algal bloom was associated with the

increased nutrients and reduced salinities in the bay following

the September flood. Chlorophyll levels returned to low values

in the following winter period.

Chlorophyll concentrations were remarkably stable at the 18

pot station, being less than 10 ug/l except during the Octover

Schizothrix bloom when this station was located at the Tampa Bay

site. With the exception of this bloom, microflagellates and

diatoms were the dominant phytoplankton groups at this station.

Chlorophyll concentrations at the 12 ppt station showed a

steady increase from winter to spring and were maximal in early

July. This July peak was due to a bloom of an unknown, naked

dinoflagellate which burst upon preservation. Chlorophyll

concentrations and phytoplankton cells were low during the

September flood and remained below 10 mg/l for the remainder of

the study. After the flood large numbers of the blue-green alga

Schizothrix were not found at this station as the bloom was

confined primarily to the waters of the bay.

The largest spatial differences between chlorophyll

concentrations occurred between 12 ppt and 6 ppt salinty

stations. Chlorophyll concentrations increased at the 6 ppt

125

station through the spring, and fluctated between 15 and 40 ug/1
from April through July. Microflagellates became relatively more
important as water temperature increased. Decreases in
chlorophyll levels and phytoplankton abundance were observed
during August and September when river flows were at high
seasonal levels. It is suggested that low residence times in the
upper estuary during high flow periods inhibited the development
of large phytoplankton populations. Values for both parameters
increased during October, and showed pronounced short-term
variations, occasionally reaching high values, during the
following fall and winter. Diatoms and microflaellates were the
dominant phytoplankton groups at this station with diatoms at
their greatest abundace during the fall and early winter. Also,
several typical freshwater species were periodically found at
this station.
Chlorophyll concentrations at the 0 ppt salinity station
showed large seasonal variations, ranging between 3.1 ug/1 and
63.8 ug/1. Chlorophyll concentrations were low in the winter of
1988, but increased to values between 15 and 40 ug/1 during April
through June. Chlorophyll returned to low values from July
through September. Phytoplankton numbers followed this same
trend and were low during the winter (January and February) and
summer, separated by high spring counts. Although temperature
effects could have been important for the winter minima, both
chlorophyll and phytoplankton were clearly lowest at this station
during periods of moderate to high streamflow, indicating that

126

phtonplanktonl populations are flushed from the upper estuary by

moderate to high flows. Chlorophyll and phytoplankton both

showed pronounced peaks when flows returned to normal in October.

The first peak was dur to a bloom of Skelotemema costatum, a

ubiquitous estuarine diatom that was distributed throughout the

river and bay. The second bloom was comprised of large numbers

of Cyclotella sp., a species that was restricted to low salinty

for the remainder of the year with periodic blooms due primarily

to diatoms or microflagellates. Freshwater chlorophytes (green

algae) were most abundant at this station but never averaged more

than 7 percent of the total phytoplankton cells. High

chlorophyll and phytoplankton values at this station were the

result of rapid algal growth in the estuary, and not imporation

from upstream, since chlorophyll values at the most downstream

freshwater stream station averaged 2.7 ug/l and never exceeded

8.6 ug/l.

Chlorophyll values at Ruskin Inlet showed a seasonal pattern

distinct from the other stations. In contrast to the other sites,

chlorophyll concentrations were high in the winter of 1988.

Chlorophyll concentrations remained between 10 and 30 ug/l during

the summer, generally being the highest values found in the

estuary during that period. Peak chlorophyll values occurred in

November due to a bloom of Skelotemema costatum. The most

notable characteristic of the phytoplanton community in Ruskin

Inlet was the almost continuous presence of chlorophytes,

127

paticularly Euglenoid flagellates, and dinoflagellates.

128

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