The principles of mass balance, compartment-flux diagramming, and dynamic simulation modeling are integrated to create computer models that estimate phosphorus (P) export from large-scale watersheds over long-term futures. These Watershed Ecosystem Nutrient Dynamics (WEND) models are applied to a 275,000 ha dairy-documented watershed and a 77,000 ha poultry-dominated watershed in northeastern USA. Model predictions of present-day P export loads are consistent with monitoring data and estimates made using P export coefficients. For both watersheds P import exceeds P export and P is accumulating in the agricultural soils. Agricultural and urban activities are major contributors to P export from both watersheds. Continued urban growth will increase P export over time unless wastewater management is substantially enhanced and/or rates of urban growth are controlled. Agriculture cannot rely solely on the implementation of increasingly stringent conservation practices to reduce long-term P export but mustconsider options that promote P input/output balance. The WEND modeling process is a powerful tool to integrate the diversity of activities in watersheds into a holistic framework. Model outputs are suited to assist managers to explore long-term effects of overall watershed management strategies on P export in comparison to environmental and economic goals.
Dynamic phosphorus mass balance modeling of large watersheds: long-term implications of management strategies
E. A. Cassell, R. L. Kort, D. W. Meals, S. G. Aschmann, J. M. Dorioz, D. P. Anderson; Dynamic phosphorus mass balance modeling of large watersheds: long-term implications of management strategies. Water Sci Technol 1 March 2001; 43 (5): 153–162. doi: https://doi.org/10.2166/wst.2001.0274
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