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Modeling ecohydrologic processes at Hubbard Brook: Initial results for Watershed 6 stream discharge and chemistry
Citation:
MCKANE, R. B., J. Campbell, L. Rustad, M. Stieglitz, AND F. Pan. Modeling ecohydrologic processes at Hubbard Brook: Initial results for Watershed 6 stream discharge and chemistry. Presented at Hubbard Brook Collaborators Meeting, Hubbard Brook, NH, July 07 - 08, 2009.
Impact/Purpose:
The Hubbard Brook Long Term Ecological Research site has produced some of the most extensive and long-running databases on the hydrology, biology and chemistry of forest ecosystem responses to climate and forest harvest.
Description:
The Hubbard Brook Long Term Ecological Research site has produced some of the most extensive and long-running databases on the hydrology, biology and chemistry of forest ecosystem responses to climate and forest harvest. We used these long-term databases to calibrate and apply GTHM-PSM, an ecohydrologic model that links hydrologic and biogeochemical processes in watersheds. Our goal is to develop a well-validated modeling framework for assessing the effects of changes in climate and land use on important ecosystem services, including regulation of water quality and quantity, carbon sequestration and fiber production. Here we report initial model results for stream discharge and chemistry for Watershed 6, a mature northern hardwoods forest that serves as the primary reference watershed for Hubbard Brook. There was generally good agreement between simulated and observed stream discharge and chemistry for W6, although additional improvements can be made by including more detailed snow dynamics and spatially-explicit soil data (depth, texture, flow paths, etc.). Inclusion of a simple 3-parameter snow model significantly improved simulated winter hydrographs, but further improvement can be made by incorporating a more sophisticated snow model (e.g., Stieglitz 1994) that includes snow and soil thermodynamics and effects of irradiance. This will be essential for simulating peak stream flows and soil nutrient flushing events during snowmelt in March-April. For 1995-2005, the years for which stream chemistry data were available for major dissolved forms of nitrogen and carbon (DIN, DON and DOC), the largest deviations from observed data occurred during large flushing events for years with heavy snowfall. Further model tests will be conducted after the addition of a more detailed snow model, and discussions with Hubbard Brook investigators concerning water flow paths and residence times.