Baltimore Ecosystem Study Institute of Ecosystem Studies

2010 BES Annual Meeting Presentation and Poster Abstracts

Spatial Scaling of Biogeochemical Hot Spots and Hot Moments: A Hydroecological Modeling Approach
Duncan, Jonathan
Co-Authors: Jonathan Duncan, Larry Band, Peter Groffman

Abstract: Nonpoint source nitrogen pollution is a major environmental concern in the Chesapeake Bay and we lack the predictive understanding of nitrogen cycling necessary for optimal watershed management. Management strategies have focused on riparian buffers as a way to promote nitrogen removal via denitrification; although nitrification and mineralization have been shown to turn riparian zones into net sources of nitrate. This appears to be the case in Pond Branch, the 40 ha forested reference watershed. Streamwater nitrate concentrations at the outlet exhibit seasonal peaks during summer low flows. Longitudinal samples along the stream show increasing concentrations in the downstream direction throughout the year. These patterns suggest that there is a seasonal source of nitrate, presumably within the riparian zone. Mineralization, nitrification, and denitrification depend on soil moisture, oxygen, and substrate availability. These processes are highly heterogeneous in space and time. This poster examines processes within contrasting patches riparian zones and adjacent hillslopes by measuring proximal drivers of denitrification: soil moisture and soil oxygen levels. In situ sensor data is complimented by seasonal soil cores that are used to determine net mineralization, microbial respiration, and the flux of N2 and N2O Preliminary data suggest that riparian hollows or low spots have significantly higher flux of N2 suggesting that these zones are hotspots of denitrification. However, the sequence of wetting and drying through seasonal timescales may lessen the impact of these hotspots. Sensor and core data will be used to calibrate a spatially distributed hydro-ecological model that accounts for nitrogen cycling processes and hydrologic transport. We present a preliminary approach of discretizing the landscape into hillslope and contrasting riparian areas in order to predict catchment level export patterns.