Location: Watershed Physical Processes ResearchTitle: Long-term metal and arsenic mobility between wetlands and lakes_variable histories within the same floodplain Author
|Surbeck, Cristiane - University Of Mississippi|
|Davidson, Gregg - University Of Mississippi|
Submitted to: Applied Geochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/5/2018
Publication Date: 7/5/2018
Citation: Surbeck, C.Q., Davidson, G.R., Wren, D.G. 2018. Long-term metal and arsenic mobility between wetlands and lakes_variable histories within the same floodplain. Applied Geochemistry. 96. 244-251.
Interpretive Summary: Sediments stored in lakes represent a valuable archive that can be used to reveal the erosion history of watersheds, and they can also be used to study the movement of contaminants attached to soil particles. A portion of the soil that is moved down gradient during runoff events is deposited in lakes, and the rate at which sediment accumulates is proportional to the rate of erosion from the surrounding land. The result is that lake sediments can be used, after finding the age of the sediments using radioisotope methodology, to study the history of both erosion and contaminant movement in watersheds. Wetlands have long thought to provide a buffer to lakes, meaning that they adsorb contaminants and prevent them from entering lakes. This study shows that, while wetlands may initially removing contaminants from runoff, there is evidence that the wetland may slowly release the captured contaminants over time. The final result is that lakes have higher levels of certain contaminants than their attached wetland areas. This result is important for understanding the fate of pesticides in agricultural watersheds, as well as for understanding how lake-wetland systems exchange contaminants.
Technical Abstract: Short-term studies of wetlands show that wetlands scavenge non-point source pollutants, thereby mitigating the pollution of downstream water bodies. However, there are few long-term studies that demonstrate this effect. This study provides a wealth of data demonstrating that there is variable long-term mobility of metals and arsenic in wetland-lake systems. More than 900 samples were analyzed from 14 sediment cores collected from six wetland-lake systems in the same floodplain. Cores were analyzed for a suite of trace elements (As, Co, Ni, Pb, Zn reported), organic content, clay content, and water content. 210Pb and 137Cs were used to find sediment age, facilitating comparison of element concentrations in contemporaneous wetland and lake sediments. In all six systems, sediment-laden water passes through the wetland before settling into the lake. In three of the systems, element concentrations were consistently higher in lake sediments, indicating a history of remobilization of wetland elements and subsequent deposition in lake sediments. Results in the other three lakes were variable, documenting unique long-term histories of element mobility and sequestration in otherwise similar systems.