Friday, August 8, 2008
Exhibit Hall CD, Midwest Airlines Center
Laura S. Craig, Program in Behavior, Ecology, Evolution and Systematics, University of Maryland-College Park, College Park, MD and Margaret A. Palmer, National Socio-Environmental Synthesis Center, University of Maryland, Annapolis, MD
Background/Question/Methods Streams in human-altered environments are often N saturated and therefore capable of delivering large fluxes of N to downstream waterways. Recently, the development of strategies to increase N removal in such degraded streams has received a great deal of attention, yet more research is needed to understand the factors that constrain N removal in these systems. We used a combination of approaches to look at the response of stream-water N concentrations to additions of limiting nutrients. In the summer of 2007, we conducted short-term injections of phosphorus (P) and dissolved organic carbon (DOC) in three, nitrogen saturated streams. And, in the fall of 2007, we completed a two-week microcosm study to look at the effects of nutrient limitation (P, DOC, and micronutrients) on N dynamics in a controlled environment.
Results/Conclusions During the field experiments both P and DOC were rapidly removed from the water column indicating a demand for these nutrients. However, responses of both ammonium and nitrate were highly variable. Often there was either no detectable change in N or there was a significant increase in nitrate; on one occasion there was a significant decrease in ammonium. Results from the microcosm experiment indicate that N removal is stimulated by the addition of limiting nutrients; however, several hours passed before we were able to measure detectable differences. These studies indicate the importance of both increased biological demand resulting from the provision of limiting nutrients and prolonged contact with the benthos on N removal in saturated systems.
