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Biogeochemistry and Hydrology in Streams Impacted by Legacy Sediments and Urbanization: Implications for Stream Restoration
Citation:
Mayer, P., Ken Forshay, S. Kaushal, M. Langland, D. Merritts, AND R. Walter. Biogeochemistry and Hydrology in Streams Impacted by Legacy Sediments and Urbanization: Implications for Stream Restoration. Presented at EPA Region 3 Legacy Sediment Workshop - Franklin and Marshall College.
Impact/Purpose:
Invited presentation for the EPA Region 3 Legacy Sediment Workshop at Franklin and Marshall College in Lancaster, PA. May 9-10, 2012.
Description:
The groundwater–surface water interface, consisting of shallow groundwater adjacent to stream channels, is a hot spot for nitrogen removal processes, a storage zone for other solutes, and a target for restoration activities. Characterizing groundwater-surface water interaction (GSI) is difficult because of physical obstacles to sampling. Furthermore, urbanization and land-use change, including the impacts of legacy sediments, can impair water quality by negatively influencing GSI. We present study results from various monitoring approaches that reveal GSI and biochemical patterns in heavily impacted urbanizing streams in the Chesapeake Bay watershed including Big Spring Run (BSR) in Pennsylvania and Minebank Run (MBR) in Maryland. Our objectives were to identify patterns among biogeochemistry, microbiology, geology, and hydrology in order to identify effective nutrient management practices for impaired streams. Results showed that chemistry and hydrology were related spatially and temporally at the groundwater/surface-water interface. Water table fluctuation controlled subsurface redox conditions which dictated nitrogen dynamics. Low water tables due to reduced stream flow created redox conditions that were more conducive to microbial removal of nitrogen. Multiple, corroborating measurements of microbial activity confirmed that subsurface sediments were actively removing nitrate nitrogen, especially when more organic carbon was available for microbial respiration. Mass spectrometry results suggested that removal of nitrate in ground water via denitrification was limited by carbon availability and that relatively small inputs of organic carbon corresponded to large reductions in ground water nitrate, especially where agricultural inputs of nitrogen were high. Additionally, prehistoric wetland sediments buried due to historic land use and mill dam impoundments, were significantly better able to support denitrification. Our data showed that there is con