The Utility of Radium as a Tracer in a River-Dominated System

Publication Title: The Utility of Radium as a Tracer in a River-Dominated System

Subject: Physical Oceanography
Coastal & Estuarine Habitat
radium; water flux; water residence time; glacial river

CSE Reference: Haag J (University of Alaska Fairbanks, Fairbanks, AK). 2022. The utility of radium as a tracer in a river-dominated system. Anchorage (AK): US Department of the Interior, Bureau of Ocean Energy Management. 20 p. Obligation No.: M20AC10016. Report No.: OCS Study BOEM 2022-045. URL: https://espis.boem.gov/Final%20Reports/BOEM_2022-046.pdf

Abstract: This project tested novel methods for tracing the flow of seawater and its dissolved constituents into, through, and out of Kachemak Bay, Alaska. Oceanographic surveys in Kachemak Bay collected radium isotope samples to assess the feasibility of creating radium budgets to characterize groundwater inputs, a potentially dominant source of freshwater, carbon, and nutrients to the Gulf of Alaska. The low concentration of 223Ra in seawater led to challenges in the collection and analysis of this isotope. Instead, we analyzed a select group of samples for longer-lived Ra. Results indicated that offshore waters that enter Kachemak Bay from the Northern Gulf of Alaska are relatively enriched in long-lived radium, violating a key assumption needed to perform residence time calculations.n Radium (Ra) has been used to trace the flux of produced water in the coastal system, but in a river-dominated system, the naturally occurring Ra from rivers may obstruct the signal of Ra from other sources. We sampled six major rivers flowing into Kachemak Bay to determine the relationship between the concentration of Ra in rivers and watershed characteristics. We found that Ra from sources other than rivers, such as groundwater, could only be detected in areas with minimal river discharge or further offshore.