Modeling phosphorus dynamics in ecosystems: Mass balance and dynamic simulation approaches

Phosphorus (P) export from agriculture is a major cause of eutrophication in many lake ecosystems. Human activity, hydrology, and physicochemical and biological processes that store, transform, and transport P, define P export patterns over time and space. We suggest that an ecosystem paradigm is useful to holistically view P dynamics within complex watersheds. An ecosystem model of a dairy agricultural system was created within a hierarchical compartment-flux structure of a conceptual watershed ecosystem. Mass balance calculations with our Agriculture Ecosystem model (AEP model) describe P dynamics for the farm system, which are driven by the amount of P stored in agricultural soils and system management practices. Longterm P dynamics respond predominately to human interventions in watersheds and define conditions for future generations, Model simulations suggest that long-term environmental protection programs should incorporate the notions of P sustainability into management decisions. Dynamic simulation modeling is a valuable paradigm for understanding how complex watersheds process P and for developing management perspectives and public policy to achieve goals of environmental quality as well as economic and resource sustainability.