ANSWERS-2000: A Nonpoint Source Pollution Model for Water, Sediment, and Phosphorus Losses
Nutrients — nitrogen (N) and phosphorus (P) in particular — are indispensable for crop and animal production. However, used in excess they have detrimental effects on the environment and human health. Agriculture is the principal source of nutrient losses worldwide (Novotny 1999). Combating diffuse pollution from agriculture is complicated due to the temporal and spatial lag between the management actions
taken at the farm level and the environmental response (Schröder et al. 2004). Beside the correct identiﬁcation and quantiﬁcation of sources, cost-effective P mitigation requires the delineation of critical P source areas, which contribute disproportionate amounts of P to receiving waters. According to Dickinson et al. (1990), targeting and prioritizing nonpoint source (NPS) pollution control potentially could triple pollutant reduction, is ﬁnancially attractive, and minimizes the extent of area affected negatively by restrictive land practices. Modeling is essential to the implementation of cost-effective and environmentally friendly management strategies to optimize nutrient use and to reduce their losses in terrestrial ecosystems. Modeling, especially when using a distributed approach, can help prioritize critical source areas at various scales within a catchment and assess the impact of landscape factors on nutrient delivery.