Twenty scientists representing seven LTER sites and other research stations met on June 17-19, 1992 in Denver, Colorado to discuss ecological and hydrological applications of watershed modeling. Organized by Hank McKellar (North Inlet LTER). and George Leavesley (U. S. Geological Survey), the workshop was designed to familiarize participants with a range of models that conceptualize hydrologic systems. Such models offer a common framework to explore intersite differences in biogeochemical routing on hillslopes and in channels, nutrient dynamics, and hydrological and ecological responses to disturbances, including climate and land-use change.
The four models presented represent different ways to conceptualize the linkages and spatial distribution of hydrologic processes over the landscape. PROSPER is a model of atmosphere, plant. and soil moisture relations without spatial resolution. TOPMODEL, a physically based hydrologic model, utilizes the variable source area concept in which a watershed is composed of saturated and unsaturated zones or cells defined by topography and soil hydraulic characteristics. Precipitation-Runoff Modelling System (PRMS) is a distributed parameter model which analyzes the watershed as a mosaic of hydrologic response units (HRUs) characterized by slope, aspect, vegetation, soil, and elevation. The Modular Hydrologic Modelling System (MHMS) is a modeling environment that permits combinations of process modules to be assembled to characterize different landscapes and climatic regimes. MHMS offers the promise of a common model framework to explore how different conceptualizations of hydrologic processes affect model behavior.
Workshop participants also considered the role of hydrologic modeling and research among LTER sites. Studies of fluxes of water, sediment, nutrients, energy. and organic and inorganic solutes and their effects on ecological systems are a common theme of research at most LTER sites. Understanding differences in the paths, rates, and patterns of water movement which drive many of these fluxes represents an important area for intersite comparison. Also emphasized was the importance of characterizing the wide range of LTER sites in terms of common gradients, such as the residence time of water in the system or recharge to runoff ratios.
Several key areas for intersite comparisons were identified, examining
- The strength of hydrologic coupling between landscape elements
- Linkages between hydrologic and ecologic processes
- Relations between hydrologic fluxes and disturbances
- The importance of hydrologic processes in increasing sensitivity of sites to environmental change.
Workshop participants also agreed to raise the visibility of hydrologic science and modeling within the LTER Network, and to increase awareness in the broader geophysical community of the opportunity for collaboration at the diverse LTER sites.
For more information: Gordon Grant (H. J. Andrews LTER), USDA Forest Service, Pacific Northwest Research Station, Forestry Sciences Laboratory, 3200 Jefferson Way, Corvallis, Oregon 97331, 503-750-7329, gGrant@LTERnet.edu.