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- Title
Seasonal Patterns of Mixing and Arsenic Distribution in a Shallow Urban Lake.
- Authors
Fung, Samantha R.; Hull, Erin A.; Burkart, Kenneth; Gawel, James E.; Horner‐Devine, Alexander R.; Neumann, Rebecca B.
- Abstract
Arsenic, a neurotoxin and carcinogen, is a legacy contaminant in the sediments of many urban lakes and poses health risks to aquatic ecosystems and lake users. Arsenic uptake into the aquatic food web is enhanced in shallow, polymictic lakes compared to deep, seasonally stratified lakes. We present the results of a 17‐month field study in Lake Killarney, a shallow, urban lake in Federal Way, Washington, USA, which examines the physical and biogeochemical mechanisms controlling arsenic mobilization and transport from sediment into lake waters, a prerequisite for arsenic uptake into the food web. In Lake Killarney, arsenic mobilization and transport into bottom waters occurred only when stratified conditions and elevated temperatures facilitated deoxygenation of bottom waters. Frequency of lake mixing varied seasonally and controlled the vertical distribution of arsenic in the water column. Convective mixing was the main contributor to elevated vertical turbulent intensity in the water column during periods of high arsenic mobilization, and thus to the upwards transport of arsenic from bottom waters. Maximum near‐surface arsenic occurred when the lakebed sediment temperature was elevated and the water column was overturning frequently. This work clarifies the mechanisms that contribute to vertical arsenic transport in shallow lakes and provides a basis for identifying contaminated systems with the physical and biogeochemical conditions that promote transport of arsenic into near‐surface water. Plain Language Summary: Arsenic, a toxic pollutant found in many urban lakes, can get taken up into the food web and make its way into fish and other animals consumed by humans. Arsenic has a larger impact on the food web in shallow lakes compared to deep lakes. To understand why this is the case, we carried out a 17‐month field study in Lake Killarney, a shallow, urban lake in Washington, USA. In this paper, we examine the processes that control the movement of arsenic from the bottom to the surface of contaminated lakes. We found that more arsenic moved out of lake sediments into bottom waters when the lakebed sediment was warm and the lake was separated into layers of different density. The frequency of lake mixing changed throughout the year and controlled how arsenic was distributed in the lake water. Highest arsenic concentrations in lake surface water occurred when the lakebed sediment temperature was elevated and the lake mixed frequently. This work clarifies the mechanisms that contribute to arsenic transport in shallow lakes and provides information needed to identify systems with conditions that lead to high levels of surface water arsenic. Key Points: In polymictic, temperate lakes, stratification and high temperatures are needed to promote anoxia and arsenic release in bottom waterConvective mixing is a key mechanism transporting arsenic from lake bottom waters to surface waters inhabited by oxygen‐requiring biotaArsenic release in shallow, temperate lakes overlaps with high primary producer growth and leads to arsenic accumulation in the food web
- Subjects
WASHINGTON (State); URBAN lakes; ARSENIC; ARSENIC in water; LAKE sediments; SEDIMENT transport; ARSENIC compounds
- Publication
Water Resources Research, 2022, Vol 58, Issue 10, p1
- ISSN
0043-1397
- Publication type
Article
- DOI
10.1029/2022WR032564