University of Maryland ESSIC Faculty Website at:
Research focuses on the ecology and biogeochemistry of watersheds and aquatic ecosystems, primarily through long-term
studies. Research interests include: land use and climate impacts on water resources, urban watershed restoration, long-term trends in stream chemistry, human-impacted biogeochemical cycles, and applications of geochemical tracers to ecosystem ecology.
2010 - Present
Earth System Science Interdisciplinary Center
Department of Geology
University of Maryland College Park
2005 - Present
Adjunct Assistant Professor
University of Maryland Baltimore County
2005 - 2010
University of Maryland Center for Environmental Science
2003 - 2005
Institute of Ecosystem Studies
Land use change, air pollution, and ecological effects of organic nutrients in aquatic systems - Nitrogen and phosphorus are elements necessary to the creation and persistence of life. Organic forms of N and P can comprise a substantial proportion of the total N and P in surface waters. Yet, the cycling of organic N and P has been poorly incorporated into existing paradigms due to the common assumption that they are not biologically available. Our work shows that biologically reactive forms of organic N and P are generated in great quantity across gradients of land use in the Chesapeake Bay watershed. Although not typically quantified, these forms appear to be an important supply of nutrients to a diversity of aquatic ecosystems.
Restoration of denitrification in coastal watersheds - Urbanization leads to predictable changes in the hydrologic and geomorphic properties of stream channels. One common alteration is the routing of water to deeper flow paths caused by channel incision and lowering of the water table. This results in transport of nitrate-rich groundwater (from pollution sources) that can circumvent active zones of denitrification. Our work investigates the effects of large-scale hydrologic manipulation on restoration of denitrification rates in a coastal watershed by direct measurement of N 2 , N 2 O, and NO gases in the field using 15 N tracer techniques.
Increased salinization of fresh water due to suburban and urban growth - Chloride concentrations are increasing at a rate that threatens the availability of fresh water in the northeastern U.S. We observed chloride concentrations up to 25% the concentration of seawater in streams of Maryland, New York, and New Hampshire during winters, and chloride concentrations up to 100 times greater than forest streams during summers. Our work shows that mean annual chloride concentration increases as a function of impervious surface and can exceed tolerance for freshwater life in suburban and urban watersheds. Widespread increases in roadways and deicer use are now salinizing fresh waters, degrading habitat for aquatic organisms, and impacting large supplies of drinking water for humans. We are investigating the effects of increasing salinity on ecosystem function in waters draining developing landscapes.
Tracing N sources and transformations along flow paths - Quantification of the transport of anthropogenic N from dispersed sources has relied primarily on mass-balance estimates. This approach, however, does not allow sources to be discriminated along flow paths. We have modified and tested a technique that uses 15 N isotope signatures in algae and aquatic food webs to identify and quantify N from domestic wastewater to streams in the Colorado Rockies. Annual estimates from N isotope ratios (corrected for natural background variations across seasons) were similar to mass balance estimates obtained from routine measurements of discharge and major N fractions in stream water. We are now using this technique to delineate N sources and transformations in streams at the Baltimore LTER site affected by differential land use and at the Hubbard Brook LTER site.
Climate change, urbanization, and export of carbon from eastern rivers - Fluvial export of carbon may be sensitive to increasing atmospheric CO 2 and changes in land use. There are temporal and spatial increases in organic carbon across streams draining gradients of land use in the Chesapeake Bay watershed. We are in the process of quantifying and characterizing major fractions of carbon in streams and rivers of the Chesapeake Bay watershed and investigating the relationship between dynamics of organic carbon and changing patterns in watershed development by humans. Particular emphasis is being placed on estimating sources, quality, and transformations of organic carbon in surface waters and investigating its ecological significance to food webs.