Effects of lowering nitrogen and phosphorus surpluses in agriculture on the quality of groundwater and surface water in the Netherlands

The ecological status of many surface waters in the Netherlands (NL) is poor, due to relatively high discharges of N and P from agriculture, industry and wastewater treatment plants. Agriculture is suggested to be a major source, as discharges from industry and wastewater treatment plants have sharply decreased from the 1980s onwards. Agricultural land covers more than 60% of the total surface area in NL, and most of this land is managed intensively and is intersected by a dense network of ditches (total length ∼300,000 km), streams and lakes. On average, groundwater levels are shallow to very shallow. It has been suggested that nutrient balances of agricultural land are easy to measure proxies for nutrient discharges from agricultural land, though the relationships between nutrient balances and nutrient discharges into groundwater and surface water are not well-established. Thus, we explored the effects of lowering N and P surpluses in NL agriculture on the quality of groundwater and surface waters. Effects of N surpluses in the range of 40–300 kg ha−1 yr−1, and of P surpluses in the range of 0.4–17.5 kg of P per ha per year were examined using an integrated set of mathematical models and databases.