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Health and Environmental Effects Research

Biogeochemistry model developed by WED scientist to be evaluated

Dr. Bob McKane of NHEERL's Western Ecology Division (WED) has collaborated with the Georgia Institute of Technology and the Marine Biological Laboratory to develop an eco-hydrology modeling framework that is intended to meet emerging risk assessment objectives more closely than other currently available models. This model framework links a suite of spatially-distributed, process-based models to address the effects of changes in climate, land use and other interacting stressors on multiple ecosystem services: production of food and fiber, carbon sequestration, regulation of water quality and quantity, reduction of greenhouse gases (CO2, N2O, NOx), and regulation of sources and sinks of reactive nitrogen (Nr) within watersheds. A central model in this framework is GTHM-MEL, a spatially-distributed eco-hydrology model that links a land surface hydrology model (GTHM, the Georgia Tech Hydrologic Model) with a terrestrial biogeochemistry model (MEL, the Multiple Element Limitation model). GTHM-MEL was designed to improve upon many existing models by reducing data/parameterization needs and complexity, while at the same time increasing abilities to predict more precisely at variable temporal and spatial scales. For the hydrologic component, the GTHM model is typically applied using 30 x 30-meter landscape units, although user-defined units of any size and shape are possible (m2 to km2). GTHM requires calibration of just three parameters to simulate evapotranspiration, infiltration, and surface and subsurface runoff (Pan et al. 2007). The model review process will be organized by Virginia Houk at EPA's National Health and Environmental Effects Research Laboratory in Raleigh, NC. The review team will be composed of scientists external to EPA who are experienced with developing and using biogeochemistry models. The reviewers will meet in Corvallis to receive an overview of the model from Dr. McKane, then will use the model in a variety of applications, comparing it with other existing models before returning to Corvallis to submit and discuss their reports of the evaluation.

Expected outcome: The model evaluation process will determine the suitability of GTHM-MEL for current EPA risk assessment needs, with particular emphasis on ecosystem services at the watershed and basin scales. Most existing models are relatively one-dimensional, in that they are used to predict processes and behaviors of only a single hydrologic or biocheochemical process or variable. Existing models generally are less precise, not scale adjustable and require more data for parameterization than GTHM-MEL was designed to be. If GTHM-MEL performs as expected across a range of scales, land uses, climates and vegetative covers, it will have important and broad applications for EPA's Ecosystem Services Research Project efforts, and will provide the ability to "scale out" from plots and transects to first through fifth order watersheds. This is a potentially valuable tool to inform scientists and policy makers about environmental and ecological processes important to EPA's policy and regulatory missions.

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