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




TD                            U.S. DEPARTMENT OF COMMERCE NOAA
                            COASTAL SERVICES CENTER
                            2234 SOUTH HOBSON AVENUE
" 'J b                  -:CHARLESTON , SC 29405-2413




                          DISSOLVED OXYGEN VARIABILITY

      I  Duc 3 ti~IN THE UPPER JAMES RIVER ESTUARY





                             *f  :     by

                                Bruce J. Neilson






                   A Report to the Piedmont Regional Office

                          Virginia Water Control Board




                                  March 9, 1990

 I

                             P:.Ao'-,, ::t -Y   of  "',' Library



         Virginia Institute of Marine Science/School of Marine Science

                    The College of William & Mary in Virginia

                           Gloucester Point, VA  23062



                      This report was produced, in part, through
     TD                financial support from the Council on the
      387    S:Environment pursuant to Coastal Resources
      .J36   i        Program Grant No. NA88AA-D-CZO91 from the
         N45'  0      National Oceanic and Atmospheric
     N45
               N5  0Administration.,
     1990
     c.2      :                                _  : __
    If: 


















                   TABLE OF CONTENTS



  I. INTRODUCTION ..1............................ 

 II. CONTEXT ................................... 2

III. CONDITIONS IN 1989 ........................ 10

 IV. DISCUSSION ............................... 20

 V. RECOMMENDATIONS .......................... 24

        REFERENCES ................................ 27

I~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


        APPENDICES

   Temperature variations ......................... 29

   Dissolved oxygen variations

        June 23 - 30 ............................... 35

        July 14 - 20 .............................. 42

        July 24 - 27  .... 48

        August 7 - 10 ............................. 54

        August 21 -24 ........................... 59

        September 6 -1 .......................... 65










                          3i













I.  INTRODUCTION



   A mandate of the Virginia Water Control Board (VWCB) is

to ensure that state water quality standards are met.

Necessary steps towards this goal are (1) gathering data,

(2) examining the data to understand existing conditions and

the processes at work, and (3) designing and implementing

appropriate water quality management plans and actions to -

protect water quality.

    During the summer of 1989, the Piedmont Regional Office

of the VWCB conducted a field study that focused on the

dissolved oxygen (DO) regime in the tidal freshwater portion

of the James River. The purpose of the present study is to

examine those data to better understand the extent, causes,

and effects of variability in dissolved oxygen

concentrations, with particular attention given to whether

the state's water quality standards were met. And, of

course, the implications of the study findings for water

quality management plans are of interest as well.












II. CONTEXT

   Water quality in the tidal James River has been studied on

a number of occasions. During 1983 and 1984, a large and

comprehensive study was undertaken under the leadership of the

Richmond Regional and Crater Planning Districts. The

monitoring, in fact, continued through 1985.  The data from

those studies, reported by Weand & Grizzard (1986a and b),

were used to re-calibrate a water quality model of the estua-ry

(HydroQual, 1986). Some information from those studies will

be used to provide the spatial context for the present study.

Time scales for natural variations in water quality also will

be discussed.

    Spatial patterns:  Wastewater discharges in the vicinity

of Richmond and near Hopewell greatly influence water quality

conditions in the tidal James.  In order to illustrate

"typical" spatial patterns, the longitudinal variation in

water quality on September 27, 1983 is presented in Figure 1.

(This figure has been taken from HydroQual's report {1986} and

includes both field measurements and model predictions.)  The

concentrations of orthophosphorus and ammonia-nitrogen both

increase rapidly below the fall line at Richmond in response

to the wastewater discharges, and then decrease in the

downriver direction.  As the ammonia is oxidized, the

concentration of nitrite-nitrate-nitrogen increases. The



                               - 2 -


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                         too.

                      ea.
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                   -J
                          40...

                   Co    20.              s

                          0.    II i          
                          120.    100.     80.      60.     40.      20.      0.

                         0.50

             I~~~~~~~~~~~~~~~~I
                            04   TOTAL--
                               OETRITAL
                         0.30_

                         0.20.

                    CD                    S
                    C 0.10         t

                         0.00
                           120.    100.     80.      60.     40.      20.      0.

                         0.50

                         0.40.

                    0.  .0.30..

                    o    .0.20.
                    I-     -
                    CD 0.10                  ï¿½

                         0.00                                B , I 
                           120.    100.  s0.         60.      40.     20.      0.

                          2.50

                          2.00.          S

                          1.50..

                          1.00..

                          0.50 00


                           120.    100.     80.      60.     40.      20.      0.


                                                  RIVER MILE


                        FIGURE 7-14A. JAMES RIVER VERIFICATION, SEPTEMBER 27, 1983
                                        CHLOROPHYLL-A AND PHOSPHORUS



             Figure 1. Field observations and model predictions.
                          (From HydroQual, 1986)



                                                   -3-







                             2.00

                                   TOTAL - - -
                        or   1.50..
                                   DETRITAL -
                             1.00 -

                       C.,
                       z
                             0.50.
                       o                      -
                             0.00     I   j~I(     II   I 
                               120.  - 100.      80.  s 0.         40.      20.        0.

                             2.00-


                          SI 1.50_..

                             1.00.           S

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                               120.     100.     80.      60.      40.       20.       0.




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                        -




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                               i20.     100.     8s.       60.      40.      20.       0.

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                                    a~~~oa _~~~~




                           I- 1.00.. 

                             0.00     I        I
                               120.  too.         80.      60.      40.      20.       0.

                                                      RIVER Nil E
                           FIGURE 7-14C-  JAMES RIVER VERIFICATION, SEPTENBER 27, 1983
                                                   NITROGEN SERIES


          Figure 1 ~Coit--;-jued).   Field observations and model predictions.
   3                                  ~~~~~~~~~(From HydroQual, 1986)


                                              -4-
 I~~~~~~~~~Jo 











                                                             TOTAL-- 

                  -    15.0..                              G~~~~~~~~~ETRITAL


             0~~~~~~~~~~~~



       o 120.0to.s.                         6..0 



       0   0S



          50..



          80...

        0 .

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       120





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            120.   too.    so.    so.                  40.        20.         0 .

                                           GIVER MILE

                 FIGURE 7-14E. JAMES RIVER VERIFICATION, SEPTEMBER 27, 1983
                            CBOD, CHLOROPHYLL-A, DISSOLVED OXYGEN





Figure I (Continued)~. Field observations and model predictions.
                          (From HydroQual, 1986)













      field data suggest an initial peak downriver of the Richmond

      discharges with a second peak at about river mile 75, with

      this latter peak presumably due to Hopewell discharges. The

      model, however, shows a single peak at the more downriver

      location.

          The nutrients support algal growth which also peaks at

       about river mile 75 on this date. It is interesting to note

       that the long-term oxyen demand (carbonaceous biochemical -

       oxygen demand at 40 days or CBOD40), does not jump up near

       Richmond, presumably because the level of BOD. removal at the

       Richmond plants is quite high.  The BOD profile, however,

       shows a maximum at about the same location as the chlorophyll

       maximum. When algae die, decomposition of this organic matter

       increases the oxygen demand; presumably the CBOD and

       chlorophyll profiles are quite similar because decomposition

       of dead algae exerts a significant BOD load.

           The BOD discharged from the wastewater treatment plants is

       oxidized in the river, decreasing ambient DO concentrations.

       The DO deficit is counterbalanced by natural reaeration and by

       the oxygen resulting from algal photosynthesis.  The DO

       profile shows a discernible DO sag below Richmond with general

       recovery by about Hopewell. Downriver of Hopewell there is a

       second DO sag. The shape of the DO sags will vary with river

       flow; during periods of high runoff, the two sags will merge.



                  *f~~~~- 6 -6

:I:          :                 














   The 1989 field study focused on the reach of the river

between Hopewell and the Chickahominy River, or about river

mile 50 to river mile 75. Many of the stations used in the

earlier studies were used in the 1989 survey.




    Time scales of variability:  Water quality conditions in

general and dissolved oxygen concentrations in particular show

a pronounced annual variation.  The solubility of oxyger in 

water decreases as water temperature increases.  During the

winter, the river water can absorb more oxygen; the saturation

concentration at 5 C is 12.77 mg/l (milligrams'per liter;

APHA, 1985).  During the summer, the solubility is greatly

reduced; at 25 C the saturation concentration is 8.26 mg/l.

For this study, the longer term variation is not an important

consideration.  Water temperatures for June through September

1989 were always above 25 C and ranged to about 30 C (see

Figure 3). Saturation concentration at 30 C is 7.56 mg/I, or

less than 10 % below the 25 C value.

    Dissolved oxygen concentrations also vary on time scales

of hours. If there is a longitudinal gradient in DO, then the

oxygen concentrations at a fixed point will vary with the

tides. For example, the DO sag will move up and down the

river with tides. At any point along the sag then, the DO

record will exhibit tidal variability, perhaps with higher DO




                              - 7 -













concentrations near times of high tide and minimum DO

concentrations near times of low tide. If there were no

longitudinal gradient, the DO would remain constant with time

as well.

    If there are abundant aquatic plants, and usually this

means planktonic algae in the tidal James, then there can be a

diurnal variation in oxygen as well. When there is sunlight

and nutrients are available, the algae grow; oxygen is a -

byproduct of photosynthesis. Algal respiration, on the other

hand, consumes oxygen. During periods of growth, there is a

net production of oxygen.  During the night and other periods

of no growth, there is a net uptake of oxygen by the algae.

The end result is a daily variation of DO with minimum

concentrations typically occurring just before dawn and peak

DO's occurring in late afternoon. Data from June of 1989

suggest that both the tidal and diurnal signals exist in the

DO records (Figure 2).  At the beginning of the deployment,

the tidal signal at Buoy 69 was reasonably strong (two peaks

per day), but towards the end of the deployment, the diurnal

variation was stronger (one peak per day). At Buoy 76, the

tidal signal remained strong throughout the deployment with

two peaks every day. Peak DO concentrations differed towards

the latter part of the deployment, with every other peak being

relatively similar. For example, the eighth and tenth peaks








                                                            .  -7
            ~~~~~~~~~~~~~~ply-                                         I ..


I
I
     '"-'

                                 IB 69-



                                                           -Buoy 69
                                                       +------ -Buby 76
         '2; 24               4~          1c~                               144    1Ba 1 Z
                           TI'- E ,hou,      - bi,,        c'' -  JiF,  25 )
I



            Figure 2. Short term variations in dissolved oxygen concentrations at
                       IBuoys 69 and 76 in the tidal James River.










           ~~I~~~~~
I-9

I













were more similar to each other than either was to the ninth

peak.

    Intermediate time scales, say days to weeks, also are

important and often result from meteorological features.

River flow responds to local events and to those occurring in

the drainage basin upriver.  Fronts, storms and cloud cover

all can affect algal growth as well.






 III.      CONDITIONS IN 1989

    The field surveys had two major elements-. Hydrolab data

sondes, equipped to measure and record temperature,

conductivity, pH, and dissolved oxygen concentrations, were

deployed at six locations for six periods.  Each deployment

lasted several days to a week. The first deployment began on

June 23rd and the last deployment ended on September 11th.

    Typically at the beginning and end of each deployment,

river surveys were conducted to monitor physical conditions

(temperature, pH, and-DO). Water samples were collected and

analyzed for nutrients, chlorophyll a, and other constituents

once during each deployment.

    Water temperatures were above 25 C during the entire study

period (see Figure 3 for two examples and the appendix for all

six temperature records). Variability tended to be greater at



                             - 10






                                 Y     74AT - TEMPERAURE

I! 
  I    ï¿½1~~~~~~~~~~~~~~~~-
         I~~~~~~~I


IU
         *  25--






                                 eBUOY 107   TEMPERATURE

          cr,
           2*  L S--


I:


             25--


              22-f                     ~
               5G1J     180       200      2ï¿½0       240
 3;                                JULIAN DAY    1969

            Figure 3. Temperature variations at Buoys 74' and 107.













upriver locations; for example, at Buoy 107 the temperature

dropped nearly 5 C during the second deployment. The reduced

temperature swings at the downriver locations are to be

expected, because the large volume of water in the lower

reaches of the river responds slowly to solar heating and to

cooling events..

    Dissolved oxygen concentrations, on the other hand, tended

to be higher and to vary less at the most upriver station (See

the record for Buoy 107 in Figure 4).  One can note large

short-term variability (tidal and diurnal variations of 1 mg/1

or more) and also large intermediate-term variations, such as

the general rise in DO concentrations at Buoy 74 during the

first deployment of the datasondes.

    The river flow across the falls at Richmond followed a

pattern of generally decreasing flows with intermittent high

flows lasting several days (See Figure 5).  The lowest flow

for the summer occurred on September 12 (Julian day 255) and

was 2,574 cubic feet per second (cfs).  In many summers, the

river flow is below 2,000 cfs for weeks or months, but this

was not the case in 1989.  Thus, the river flow pattern was

somewhat typical, but the entire record was elevated relative

to most summers.

    Two of the river surveys will be examined in some detail

in an attempt to understand processes at work.  First, we will




                             - 12-





                                           GUOY 7-4 - OTTOIv  LC0-



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                                                JLLIAN DAY    1 9 LEI

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                  U  160     1~0        200      z20         240
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     25060--                              D                                    O

                                     Flow at PiChmrend

     K  2060--





   C  15006--





      3 ?OUO    0                                0       -& ID      0, & 
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                  o~~a~~    c3EEj3F 5K       EEL~ 0~               C-6E

           I1,70 1-Jo,10                            2.QQ          2O           2~0
                                        Julion  doN"  1989







       Figure 5.  River flow near Richmond.  (Diamonds just above x-axis
                 indicate river survey dates. Bands of diamonds above
                 that indicate periods when datasondes were deployed.)



                                   -14-













look at conditions on August 10 (Julian day 222) and then look

at conditions on June 28 (Julian day 179).

    August 10, 1989:  River flows decreased from 6,109 cfs on

August 4th (Julian day 218) to 3,297 cfs on August 13 (Julian

day 225); the flow on August 10th was 3,783 cfs. In other

words, flows were decreasing, relatively constant and

moderately low. Records for the weather station at Richmond

airport show 1.55 inches of rain on August 10, but none -in-the

preceding seven days. Dissolved oxygen conditions in the

river did not vary significantly between the early morning and

late afternoon surveys (See Figure 6).  Both ptofiles showed

DO decreasing from about 7.5 mg/l near Hopewell to about 6.5

mg/1 at Buoy 74, and back to about 7.5 mg/l at Buoy 69.

    Chlorophyll a concentrations averaged about 58 ug/l at the

four upper stations (Buoys 107, 91, 86 and 76) but only 34

ug/l at the two lower stations (Buoys 69 and 74).  For the

upper stations, two of sixteen readings were above 70 ug/l and

half of the observations were greater than 60 ug/l. There was

little difference between early morning and late afternoon

values, perhaps because of cloud cover associated with the

rainfall.

    June 28, 1989:  River flows decreased from 11,485 cfs on

June 23rd to 3,889 cfs on July 5th; the flow on June 28 was

6,802 cfs. For reference purposes, the long term (40+ years)













mean annual flow at Richmond is on the order of 7,500 cfs.

Thus, this hydrograph brackets the mean annual flow but is

above typical average flows for June. The hydrograph is not

nearly as "peaky" as the other storm events in the 1989

record.  Rainfall of more than 2 inches was reported for

Louisa on June 20th, and Buckingham on June 21st-.  At the

Richmond airport, 0.57" fell on June 23rd, 0.01" on June 26,

and traces on June 24 and June 27.  No rainfall was reported-

for any Eastern Piedmont weather station on June 28.

Nonetheless, this "storm" (or some other events occurring at

that time) did have an appreciable effect on water quality.

    Peak dissolved oxygen concentrations were recorded at

Buoys 91 and 86 and minimum DO's at Buoy 69, with about a 3

mg/l difference between the maximum and minimum station

averages (See Figure 6).  DO concentrations in late afternoon

tended to be about a half a milligram per liter (or more)

higher than those observed in the early morning. The mean

chlorophyll a concentration increased from 27 ug/l in the

morning to 35 ug/l in the afternoon.  Peak chlorophyll

concentrations were at Buoys 91, 86, and 76 (Mean for the

three stations was 37 ug/l in the morning and: 47 ug/l in the

afternoon).  Concentrations at Buoy 107 were in the same range

as those at Buoy 69 and 74 (18 ug/l in the morning and 23 ug/l

in the afternoon).



                             - 16-










     I i~~~~~~~~~:

      I~~~~~~~~~~~~~~~~~~~7













*   ~   16      .    .    .        .    .I










                                               71.












* ~ ~      F gr 6. Lo~,tuia    p rfiles ofdsovd xgn  June 28; 1998(otm
                                    and August 10, 1989 top). Dashed~llnes idicate early mornin
                               obsrvtinssoidlins ndcat   aeatrnnrsls
            - -  .            .            t                    ï¿½~~~~~~~~1





. :






               d    It is relevant to note that both the early morning and the

           late afternoon DO measurements at Buoy 69 were below 5 mg/I,

           suggesting that the daily average was below the 5 mg/i

           standard.  The measurements from the datasonde show that

           oxygen concentrations below 4 mg/l were observed throughout

           the first half of the deployment (Figure 7).  During the first

           half of the deployment, two DO peaks occurred each day (tidal

           signal), but during the second half, there was only one peak

           per day (diurnal signal) and DO concentrations tended to

           increase. The daily average concentration was below 5 mg/i

           from June 23rd through the 28th (see Table 1) and the minimum

           values were well below 4 mg/1 from the 23rd through the 27th.

           Clearly, neither water quality standard was met during this

           several day period.



                   Table 1.  Dissolved oxygen concentrations (in
                             mg/l) at Buoy 69, June 1989.


                   Date      Minimum Value          Daily Mean Value

                    23            3.70                   4.11  
                    24           -3.54                   4.12
                    25            3.43                   3.94
                    26            3.42                   3.95
                    27            3.62                   4.17
                    28            4.00                   4.57


           0 I0  if     *  Less than 24 hours record.










 I:





II i


                                E'OTTC'n  DC,  AT  BeLIY  69


I                                                             1i 4

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                                               191
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                     Figure 7   Short trmvaria ioni islved oxgncnenrtosa












         IV.    DISCUSSION

                Implicit in the concept of planning is preparation

       for some specific goal or goals. In many studies, including

       the water quality management planning for the upper tidal

       James River, the goal is for water quality standards to be met

       during some "worst case".  Often the "worst case- scenario" has

       included, among other specifications, river flows at the

       "7Q10" level.  "7010" denotes the lowest flow which occurs--

       over a seven consecutive day window and occurs once during a

       ten year time period.  Implicit in use of this concept is the

       idea that shorter term violations might occur rwore frequently

       than once very ten years and that violations that lasted

       longer than seven days might occur less frequently than once

       every ten years.

           Field data from the summer of 1989 suggest that there may

       be a number of "worst case scenarios" for dissolved oxygen in

       the upper tidal James.  In particular, it appears that certain

       hydrographs can degrade water quality significantly. One must

       ask whether the mid-June event was one which has greater,

       lesser, or roughly equal probability as the 7Q10 river flow.

       One approach towards treating point sources and non-point

       source pollution equitably would be to select design scenarios

       with comparable probabilities.





                                     - 20

I                               








I ::




              Further study of the mid-June event is needed to ascertain

          the reasons why this combination of events resulted in

          violations of both DO standards. At this time, there is

          nothing to indicate that this "storm" was peculiar or out of

          the ordinary. Further investigation is needed to determine

           (1) where the rainfall occurred, (2) the amount and intensity

          of the rainfall, (3) the degree to which the quality of the

          water flowing over the falls deteriorated relative to          -

          preceding and following periods, (4) solar radiation during

          the period when the DO standards were violated, and (5)

          whether any other circumstances affected water' quality.

              A second problem illustrated by the 1989 data is that of

          excessive nutrient enrichment and associated high standing

          stocks of algae.  Conditions on August 10, 1989 approximate

          the low flow conditions incorporated in many model

           simulations. For these conditions, the DO concentrations were

          well above the state standards, and presumably this was due in

           part to the large standing stock of algae in the river.  At

           Buoy 107, chlorophyll a concentrations were over 70 ug/l in

           the early morning and 58 ug/l in the late afternoon.  The

           magnitude of the diurnal variation in DO at this station was

           more than 2 mg/l (Figure 8).  While it is clear that the DO

           standards were met, it is not as evident that this situation

           is an appropriate foundation for a water quality management



         I~~~~~~~~~~-21
                                        - 21 -









I,~~~~~~~~~

I~~~~~~~~~~
I 13-


      I               BUOYi~ 1C7 - BOlT~t~vl DO0






                                       A~~~~~~~~~~~~ ;,
       :-                                     i






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    -r 
       I~ 24
       E~~~~TM   (hu  ;  ~r~Aui~ 
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           I~~~~~~~~~~~~~~~
            I~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  0'            //                        "      '


       I                                  i "
                              II
             i~~~~~i



                                ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~,,'4
                           '_~~~~TIME(hus egins August: .,'')


         Figure 8. Short term variations in dissolved oxygen concentrations
   ï¿½  ~~~~~    at Buoy 107 during early August 1989.



















                                 -22 -













          plan. When the Water Control Board was considering adoption

          of nutrient standards, a technical advisory panel was

          convened. These individuals recommended that a river be

         classified as nutrient enriched if chlorophyll a

          concentrations exceeded 25 ug/l. Early water quality

          management plans for the Potomac River estuary were based on a

          chlorophyll a maximum of 25 ug/1 as well. It is the author's

          opinion that this is an area which warrants continued

          attention.  Further, it is unlikely that any knowledgeable

          scientist would consider chlor ophyll a concentrations in the

  I-~ 50 to 75 ug/l range as being anything but "high".  Most would

          likely suggest that nutrient control measures were called for.

          Further field observations are needed to assess this

          situation.  These should include deployment of data sondes for

          more than a few days, so that the resulting time series can be

          "decomposed" into tidal and diurnal signals.  Having longer

          records should help give insight on the relationship between

          DO variations and other factors such as cloud cover, river

         3  flow, and algal populations.















          *1~~~~~~~~~ -23


I                             :












           V.    RECOMMENDATIONS

            For the past decade and longer, water-quality management

        in the upper tidal James has emphasized the need to reduce BOD

        loads to the river in order to maintain dissolved oxygen

        concentrations at or above state standards.  The 1989 data

        suggest that the water quality planning must explicitly

        incorporate nonpoint sources of pollution in the future,

        because a modest hydrograph in mid-June produced water quality

        well below the two DO standards.  Other data reinforce the

        perception that nutrient enrichment is a problem that also

        demands attention.  Accordingly, the following recommendations

        are offered for consideration.



        1.  Estimate the likelihood that a decrease in algal growth

            could result in substandard DO conditions.

            Additional analysis of the 1989 data is needed to

        determine if (a) the longitudinal DO gradient can be related

        to the range of variation in DO at tidal time periods, and

        (b) the magnitude of the diurnal variation can be related to

        mean chlorophyll concentrations or other factors. In order to

       Icomplete this exercise, it may be necessary to have longer

        time series that are available from the 1989 deployments of

        the data sondes.






   * ;     ; 0            0            -;24-


:I      ;0:S.                                         S   













     Additional water quality model simulations should be made

  to determine how DO and chlorophyll concentrations vary with

  solar radiation.  At this time, the method by which diurnal

  variations can be estimated using a tidal-average model is not

  clear.




  2.  Assess methods to incorporate point and non-point sources

      into a single water quality management approach.

      It seems clear to the author that nonpoint sources of

  pollutants can and do affect water quality in' the James River.

  Further study of the late June hydrograph is. neded to ensure

  that this was not some "freak event".  If it turns out to be a

  relatively common occurrence, then one must conclude that

  water quality standards are violated frequently.  At present

  there are no widely accepted procedures that explicitly

  include both point and nonpoint sources of pollution in

  management scenarios. It appears that this difficult task

  must be addressed.




  3. Plan for a new, time-variable or "real time" model of

      water quality in the tidal James.

      The water quality studies of the early 1980's provide an

  excellent data base for the near term.  At some point

3  development, expansion of sewered areas, and other factors



      ;I- 25










       will result in-sufficient change that the water quality
       management plan must be re-examined. At that time, the water
       quality model should be upgraded to include real-time
       variations in water quality. With this capability, both
       short-term variations in dissolved oxygen and the river
       response to transient, nonpoint source loadings-can be
       examined with greater ease and certainty.   It is not suggested
       that such studies begin immediately, but rather that the model
       upgrade be incorporated in such studies whenever they occur.




























                                         -26-
I;0:                                                     

       I~ ~ ~~                                          ;   



   I~::                              

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   I:





   I~~~~~









*~                                      -026 -














REFERENCES


American Public Health Association, 1985.  "Standard Methods for
     the Examination of Water and Wastewater", 16th Edition.

HydroQual,  Inc., "Water Quality Analysis of th-e James and
     Appomattox Rivers", A Report to the Richmond Regional and
     Crater Planning District Commissions, October 10, 1986.

Weand, Barron L. and Thomas J. Grizzard, 1986a, "Final Report:
       1984-85 Monitoring", April 1986.

Weand, Barron L. and Thomas J. Grizzard, 1986b,   "Final -Report:
       Summer and Fall 1985 Monitoring", July 1986.




























                              27
I~~~~~~~~~~~~  


















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       DATE DUE



















GAYLORD No. 2333 jPtTED INU1SA.


















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