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A MODEL OF ESTUARY RESPONSE TO NITROGEN LOADING AND FRESHWATER RESIDENCE TIME
Citation:
Dettmann, E H. AND H A. Walker. A MODEL OF ESTUARY RESPONSE TO NITROGEN LOADING AND FRESHWATER RESIDENCE TIME. Presented at Estuarine Research Federation '99, New Orleans LA, September 25-30, 1999.
Description:
We have developed a deterministic model that relates average annual nitrogen loading rate and water residence time in an estuary to in-estuary nitrogen concentrations and loss rates (e.g. denitrification and incorporation in sediments), and to rates of nitrogen export across the seaward boundary. We assume that a constant fraction of the average mass of nitrogen in the water column is permanently removed annually by these internal processes. Model results are compared to field data for a broad range of estuaries of varying characteristics, and to interannual variations of water quality in the Potomac Estuary under a range of nutrient loading rates and water residence times. Results show strong relationships between freshwater residence time and the fractions of nitrogen that are exported, denitrified, and permanently incorporated into sediments. Year-to-year changes in average nitrogen concentrations in the Potomac Estuary are a simple function of nitrogen loading and freshwater residence time. The model lends itself to classification of estuaries according to the sensitivity of their response to nitrogen loading.