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Stream Restoration to Manage Nutrients in Degraded Watersheds
Citation:
MAYER, P. M. Stream Restoration to Manage Nutrients in Degraded Watersheds. Presented at The Legacy Sediment Work Group, Lancaster, PA, November 19, 2009.
Impact/Purpose:
Study results of two streams (Minebank Run and Big Spring Run) affected by urbanization, quarrying, agriculture, and impoundments in the Chesapeake Bay watershed in Maryland and Pennsylvania, USA
Description:
Historic land-use change can reduce water quality by impairing the ability of stream ecosystems to efficiently process nutrients such as nitrogen. Study results of two streams (Minebank Run and Big Spring Run) affected by urbanization, quarrying, agriculture, and impoundments in the Chesapeake Bay watershed in Maryland and Pennsylvania, USA are presented. The purpose of these studies is to identify patterns among biogeochemistry, microbiology, geology, and hydrology that identify effective Best Management Practices for managing nutrients in 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 (denitrification). Measurements of microbial activity confirmed that subsurface sediments were actively removing nitrate nitrogen, especially when more organic carbon was available for microbial respiration. Nitrate nitrogen also was lower in groundwater where more dissolved organic carbon was available. Mass spectrometry results suggested that removal of nitrate in ground water 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. Sediment deposition from historic mill dams buried prehistoric wetland sediments that were significantly better able to support denitrification. Results suggest that Best Management Practices that increase organic carbon availability to microbes, reduce stream flow, and expose buried wetland sediments may improve the nitrogen removal capacity of impaired streams.