Water Balances

Abstract

Characterizing the nutrient cycles at the Integrated Forest Study (IFS) study sites required estimates of both nutrient inputs and nutrient outputs. To determine nutrient outputs, estimates of soil water flux had to be coupled with nutrient concentrations in soil lysimeters. However, only a few IFS sites had direct measures of soil water flux (e.g., gaged watersheds at Coweeta and Turkey Lakes), and even in these instances, water flux measurements were not directly comparable with water flux below the lowest lysimeter location. Thus, our purpose was to provide water flux estimates corresponding to lysimeter locations for the IFS sites. We used the hydrologic simulation model, PROSPER (Goldstein et al. 1974), to estimate evapotranspiration and soil water flux for several IFS study sites. A modeling approach was used because it was impractical to measure soil water flux at each site. While other hydrologic models were available (e.g., BROOK; Federer and Nash 1978), we chose PROSPER because it had been applied successfully in both hardwood and conifer forests at Coweeta (Swift et al. 1975; Huff and Swank 1985) and performed well in regional evapotranspiration assessments (USDA 1980).