Water Resources Research Act Program

Details for Project ID 2007MS61B

Natural Enhanced Transport of Agricultural Pb and As Through Riparian Wetlands

Institute: Mississippi
Year Established: 2007 Start Date: 2007-03-01 End Date: 2009-08-31
Total Federal Funds: $49,476 Total Non-Federal Funds: $99,723

Principal Investigators: Gregg Davidson

Project Summary: Riparian wetlands are commonly believed to act as chemical buffer zones for non-point source pollutants because they serve as sinks for sediment and particulate matter entrained in surface flows. While short term reductions in contaminant flux have been documented in flows exiting wetlands, the long term fate of non-degradable or persistent chemicals in wetlands is not well known. Previous work at Sky Lake in the Delta region of Mississippi suggests that Pb and As in pesticides that reached the perimeter wetland in the early 20th century were eventually flushed from the wetland and into the lake. Large Pb and As concentration spikes are now found in sediments in the open-water environment at depths representing deposition during the late 1920�s and early 1930�s, but no contemporaneous spikes are found in the wetland sediments. The hydrology of Sky Lake suggests that Pb and As did not bypass the wetland. Rather, it is likely that Pb and As were initially deposited in the wetland and later remobilized by successive flooding and aeration events. The proposed study is designed to determine if other lake-wetland systems in the Delta contain a similar history recorded in their sediments, and to better understand how contaminants may be remobilized after deposition. Sediment cores will be collected from three Delta lakes surrounded by wetland riparian zones and adjacent to agricultural land that has been under tillage for at least 75 years. Sediment cores will be collected from the open water and wetland environments, dated using 210Pb and 137Cs, and analyzed for trace element concentrations including Pb and As. Sequential extractions will be carried out on select sediment intervals that represent background and elevated Pb concentrations to determine if higher concentrations are associated with a more mobile source material that might account for remobilization and transport out of a wetland.