Nitrogen and phosphorus discharge from small agricultural catchments predicted from land use and hydroclimate

Excess nutrients cause eutrophication of freshwaters all over the world. Decision-support tools are needed to assess nutrient discharges from catchments. This paper used a 28-year nutrient-discharge, hydroclimate and land-use history of small rural catchments to calibrate a simple nitrogen (N) and phosphorus (P) runoff model. The N and P runoffs declined following the post-Soviet collapse of agriculture, and stabilised at low output during the 1990s and early 2000s. Introduction of the European Union Common Agricultural Policy (CAP) re-intensified the agriculture and somewhat rebounded the N and P discharges. Thus, the history of the catchment represents a broad range of land-management systems. Our objective was to explain annual nutrient runoffs from small rural catchments by five factors: hydroclimate, soil type, land-use type, fertilisation and the autumn soil-nutrient stock. Our model independently predicted the eight-year mean N and P losses from a test set of small agricultural catchments in Estonia. This shows the impact of political decisions on agricultural contamination of waters. We can suggest our robust model as a decision-makingtool for land-use management in small agricultural catchments.