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Eshleman, K.N. 2000. A linear model of the effects of disturbance on dissolved nitrogen leakage from forested watersheds. Water Resources Research 36 :3325-3335. In a Nutshell: Problem - Patterns of dissolved nitrate-N leakage from five gaged, mid-Appalachian watersheds display considerable temporal and spatial synchrony with outbreaks of defoliation by the gypsy moth larva ( Lymantria dispar ). What - A simple, linear systems model (analogous to a unit hydrograph) was used to test the hypothesis that annual nitrate-N leakage could be explained by convolving a unit nitrogen export response function ( UNERF ) with the proportion of each watershed defoliated in a particular year. Findings - Results of the study showed that the UNERF models, parameterized by deconvolution of annual time series of nitrate-N export using linear programming or a least squares method, were minimally biased and explained large percentages (38-98%) of the total variation in annual nitrate-N export from the watersheds. Despite their neglect of explicit spatial data and ecosystem non-linearities, the lumped empirical models are reasonably robust and appear to be potentially useful for purposes of regionalization. |
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