2007 BES Annual Meeting Presentation and Poster Abstracts
Spatial and Temporal Variability of In-Stream Nitrogen Processing in a Suburbanizing Watershed
Co-Authors: Christina Tague, Lawrence E. Band, Peter M. Groffman and Stephen T. Kenworthy
Abstract: In suburbanizing watersheds, in-stream processing is a critical control on nitrogen export. We looked at the role of small streams in controlling nitrogen export from a suburbanizing watershed (Baisman Run). Results from several field-modeling studies are presented, addressing spatial and temporal aspects. For spatial aspects, we used a longitudinal (stream channel corridor) approach. We conducted short-term nutrient addition experiments in late Fall 2003 and late Summer 2004, and looked at the effect of stream size, transient storage and nutrient concentration on nitrogen uptake. Our results showed large seasonal and longitudinal differences in NH4 uptake (e.g., a seasonal shift in longitudinal patterns of NH4 uptake); these differences reflect the important role of leaf litter and other organic debris. Our results also showed reverse longitudinal trends for NH4 and NO3 uptake (negative relationship with stream size for NH4; positive relationship for NO3). The latter is a result from variation in biological uptake capacity. With uptake capacity effecting uptake kinetics, this poses constraints on using ‘static’ uptake metric relationships for scaling uptake across stream networks. For temporal aspects, we conducted a mass balance approach; we measured flow and nutrient concentrations over a wide range of flows, including extreme drought and wet conditions (Jul 2001 through Sep 2004). Our mass balance results showed that temporal variability in NO3 loss is large; proportional NO3 loss (i.e., relative to load) is significant only when flows are low. This finding is important for evaluating the effectiveness of stream restoration and other management options in reducing nitrogen export.