Location: Hydrology and Remote Sensing Laboratory
Project Number: 8042-13610-030-056-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Aug 1, 2022
End Date: Sep 30, 2023
While it is well known that wetlands facilitate the removal of dissolved nitrate through both denitrification processes and plant uptake, the ability of wetlands to retain nitrogen and thus improve water quality is heavily dependent on N transport pathways, the presence of N sources within the wetland catchment area, and the presence of appropriate “reducing” conditions to facilitate denitrification. The overall goal of the proposed research is to instrument and monitor a set of reference wetlands within the Chesapeake Bay Watershed to better our understanding of the role of wetlands in improving water quality. The proposed work is designed to reduce uncertainty in quantifying agricultural N fluxes to wetlands and to better our understanding of the extent to which these wetlands may be capturing legacy sources of N.
ARS will use MESA (metolachlor-ethane sulfonic acid)—a metabolite of the widely used herbicide metolachlor—as a novel tracer of agricultural N fluxes to wetlands, with the goal of developing better spatially explicit predictions of N sources to wetlands, of providing better estimates of the magnitudes of agricultural N reaching current and restorable wetlands, and of more accurately quantifying N removal rates and related nitrous oxide emissions. In the proposed research, ARS will be collecting metolachlor, MESA, and nitrate concentration data from agriculturally-impacted wetlands within the Chesapeake Bay Watershed. ARS will leverage a set of monitored, reference wetlands which constitute a portion of the Reference Wetland dataset maintained by Penn State’s Riparia Center for Water System Science, for which historical datasets are available. Groundwater wells will be installed to obtain depth-varying groundwater samples. In addition, for wetland surface water monitoring, grab samples will be obtained at 2-week intervals at wetland inlet and outlet sites as well as from the wetland water column. The obtained data will be analyzed to determine the extent to which wetlands adjacent to agricultural sites are receiving agricultural N runoff, and these findings will be used as a proxy to determine the level of connectivity with groundwater sources of N. MESA chirality will also be analyzed, and mixing models will be applied to provide estimates of relative amounts of “modern” vs “legacy” N reaching the study wetlands. Findings will also be used to identify wetland sites serving as major receptors of surplus agricultural N and will serve as a basis for more future work in which we will implement more intensive seasonal sampling campaigns to provide data for model development.