September 2, 2020
Dr. Tsz-Ki Martin Tsui (Biology) received new funding from the Department of Energy for the project “How does mercury methylation respond to intensive forest management and the creation of anoxia in floodplain soils?”
Mercury (Hg) is a global pollutant due to long-range atmospheric transport and deposition. Forest ecosystems have been considered as Hg sinks through dry foliar uptake of gaseous elemental Hg(0). However, forest management practices, which are designed to protect or enhance the delivery of ecosystems services, may elevate Hg contamination by altering hydrology, soil properties, and vegetation composition.
To understand the influences of intensive forest management on Hg cycling, the researchers propose a 2-year exploratory study to examine the concentration and speciation of Hg in a paired experimental watershed in the lower Atlantic coastal plain on the Santee Experimental Forest in South Carolina.
A unique watershed-scale study to consider intensive forest management (clear-cut followed by prescribed fire to support longleaf pine restoration) is being implemented in 2020; this study emulates practices that are anticipated across 2×106 ha in the southeastern United States. Researchers hypothesize that the clear-cut processes (as the initial phase of longleaf pine restoration) increase the amount of labile organic matter from forest slash and increase water table level due to decrease in water demand of vegetation, which will lead to the creation of anoxic soil conditions, promoting microbial Hg methylation, resulting in highly toxic methylmercury (MeHg). It is known that MeHg can bioaccumulate and biomagnify in the aquatic food webs, leading to unsafe levels of MeHg in fish for human consumption.
To test the researchers’ hypothesis, they will examine (1) pools and fluxes of Hg and MeHg in different compartments of both treatment and reference watersheds, (2) assess the flow paths across the watershed to examine zones of methylation (i.e., hotspots), (3) measure the abundance of the Hg methylation gene in soil and water, and (4) determine the composition of organic matter in soil and water to document the temporal changes before, during, and after the intensive forest management process.
The project will thus help better understand biogeochemical hotspots of Hg within watershed and the impacts of land management on MeHg production, both of which are not well understood. The work will result in new knowledge on Hg cycling that can be transferred to other Hg-affected watersheds, and can inform watershed resource and forest managers if and how Hg pollution can be mitigated or decreased. The work will also complement the ongoing Hg Science Focus Area (SFA) research within the Hg-contaminated East Fork Poplar Creek (EFPC) watershed at the Oak Ridge National Laboratory by demonstrating the linkage between forest disturbance and aquatic Hg pollution.