ABSTRACT Background/Question/Methods: Historic land-use change can reduce water quality by impair... more ABSTRACT Background/Question/Methods: Historic land-use change can reduce water quality by impairing the ability of stream ecosystems to efficiently process nutrients such as nitrogen. We present study results from streams affected by urbanization, quarrying, agriculture, and impoundments in the Chesapeake Bay watershed in Maryland and Pennsylvania, USA. Our objectives were to identify patterns among biogeochemistry, microbiology, geology, and hydrology in order to identify effective nutrient management practices for impaired streams. Results/Conclusions: 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. Prehistoric wetland sediments buried due to historic land use and mill dam impoundments, were significantly better able to support denitrification. Collectively, our results suggest that management practices that can increase organic carbon availability to microbes, increase ground water residence times, and expose buried wetland sediments may improve the nitrogen removal capacity of impaired streams.
ABSTRACT Recent evidence from the mid-Atlantic suggests that freshwater supplies are threatened b... more ABSTRACT Recent evidence from the mid-Atlantic suggests that freshwater supplies are threatened by chronic chloride inputs from road salts applied to improve highway safety. Elevated chloride levels also may limit the ability of aquatic systems to microbially process nitrate nitrogen, a nutrient whose elevated levels pose human and ecological threats. Understanding the behavior of chloride in urban watersheds where road salts are applied is critical to predicting subsequent impacts to ecosystem health and drinking water supplies. Here we report on a long-term study of water chemistry in Minebank Run, a recently restored stream in an urban watershed of Towson, MD that receives chronic chloride inputs from the 695 Beltway highway and connecting arteries. Chloride, sodium, and specific conductance were greatly elevated in the both surface water and ground water of Minebank Run, spiking in correspondence to road salt application in the winter. Chloride levels were consistently higher in ground water of the bank side of a minor roadway and downstream of the 695 Beltway. Surface water chloride levels remained elevated throughout the year apparently because ground water continued to supply surface water with chloride even after road salt application ceased. Thus, ground water may represent a chronic source of chloride to surface water, thereby contributing to the upward trend in freshwater salinity in urbanizing areas. Stream susceptibility to road salt impacts may depend upon ground water hydrology and stream geomorphology. However, geomorphic stream restoration practices widely used in the mid-Atlantic are not designed to address salinity effects. Source control of road salts may be necessary to reduce environmental risk.
ABSTRACT Background/Question/Methods: Historic land-use change can reduce water quality by impair... more ABSTRACT Background/Question/Methods: Historic land-use change can reduce water quality by impairing the ability of stream ecosystems to efficiently process nutrients such as nitrogen. We present study results from streams affected by urbanization, quarrying, agriculture, and impoundments in the Chesapeake Bay watershed in Maryland and Pennsylvania, USA. Our objectives were to identify patterns among biogeochemistry, microbiology, geology, and hydrology in order to identify effective nutrient management practices for impaired streams. Results/Conclusions: 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. Prehistoric wetland sediments buried due to historic land use and mill dam impoundments, were significantly better able to support denitrification. Collectively, our results suggest that management practices that can increase organic carbon availability to microbes, increase ground water residence times, and expose buried wetland sediments may improve the nitrogen removal capacity of impaired streams.
ABSTRACT Recent evidence from the mid-Atlantic suggests that freshwater supplies are threatened b... more ABSTRACT Recent evidence from the mid-Atlantic suggests that freshwater supplies are threatened by chronic chloride inputs from road salts applied to improve highway safety. Elevated chloride levels also may limit the ability of aquatic systems to microbially process nitrate nitrogen, a nutrient whose elevated levels pose human and ecological threats. Understanding the behavior of chloride in urban watersheds where road salts are applied is critical to predicting subsequent impacts to ecosystem health and drinking water supplies. Here we report on a long-term study of water chemistry in Minebank Run, a recently restored stream in an urban watershed of Towson, MD that receives chronic chloride inputs from the 695 Beltway highway and connecting arteries. Chloride, sodium, and specific conductance were greatly elevated in the both surface water and ground water of Minebank Run, spiking in correspondence to road salt application in the winter. Chloride levels were consistently higher in ground water of the bank side of a minor roadway and downstream of the 695 Beltway. Surface water chloride levels remained elevated throughout the year apparently because ground water continued to supply surface water with chloride even after road salt application ceased. Thus, ground water may represent a chronic source of chloride to surface water, thereby contributing to the upward trend in freshwater salinity in urbanizing areas. Stream susceptibility to road salt impacts may depend upon ground water hydrology and stream geomorphology. However, geomorphic stream restoration practices widely used in the mid-Atlantic are not designed to address salinity effects. Source control of road salts may be necessary to reduce environmental risk.
Uploads
Papers by Elise Striz