Comparison of nutrient input loading and riverine export fluxes in large watersheds

An input-output mass balance watershed model was developed and tested on ten large benchmark watersheds in the northeastern United States. Inputs of chlorides, sulfates, potassium, phosphorus, and nitrogen were calculated from published census data on population, wastewater discharges, land use, air emissions, agriculture, forestry, and transportation. Attenuation factors were selected for the inputs, (for example, air deposition, fertilizer, point source discharges) and the average annual riverine export flux for the watersheds was calculated for the period from 1900 to 1995. Historic chlorides, sulfates, potassium, phosphorus and nitrogen river export fluxes were independently calculated for each watershed using long term monitoring data obtained primarily from the USGS and public water supplies. A comparison of the attenuated watershed inputs and the monitored output river flux suggests that it is possible to obtain reasonable estimates of watershed export fluxes from existing landscape input data. The above methodology was applied to two major tributaries of the Hudson River and the results are described. Input-output models which can simulate long term historical changes in riverine fluxes based on inputs rather than on land use types will be useful for the development of effective and efficient nutrient control programs on a watershed basis.