Leaching of solutes from an intensively managed peat soil to surface water

In many peat land areas in The Netherlands target concentrations for nitrogen (N) and phosphorus (P) in surface water are exceeded. A considerable, but poorly quantified, fraction, of the N and P loading of surface water in these areas originate from the subsoil. Waterboards, responsible for the water management, are currently exploring options to improve surface water quality, whilst sustaining agricultural production. Therefore, insight into dynamics of nutrient pools in peat soils is required. The aim of this study was to measure concentration profiles (0-12 m) of the soil solution in an intensively managed grassland on peat soil and to explore the effects of a rise in surface water level on N and P loading of surface water, using budgeting approaches and two dimensional simulation modeling. The concentration profiles of N, P and Cl reflect by the presence of nutrient-rich anaerobic peat and a nearly impermeable marine clay in the subsoil. Concentrations of N, P and Cl tended to increase with depth till about 6 m and then decreased. In the top soil, inputs of N and P via fertilizers and animal manure were only partly retrieved in the soil solution, suggestion that biogeochemical processes, uptake and lateral transport processes had a dominant influence on dissolved N and P. Exploring scenario simulations showed that major drainage fluxes passed through the peat layer that transported nutrients to adjacent surface water. Raising surface water levels with 20 cm suppresses this kind of nutrient loading of surface water by more than 30%, but nutrient rich peat layers will remain persistent as a potential source of nutrients in surface water in many peat polders in the western part of The Netherlands.