Ex-ante assessment of costs for reducing nitrate leaching from agriculture-dominated regions

In sandy regions of the Netherlands, current agricultural practices result in high nitrate concentrations in the upper groundwater, endangering water resources. A methodology to estimate costs of region specific solutions is applied to a groundwater protection area. It requires that for existing farms in the region variants of management are described that differ in nitrogen surplus. Costs of variants relate to investments and losses in income due to changes in farm management additional to those required by existing legislation. The expected nitrate concentration for each combination of variant and groundwater class is calculated from nitrogen and precipitation surplus and a leaching fraction. A linear programming model indicates the optimal spatial allocation of variants such that desired regional and sub-regional nitrate concentrations are reached at minimum regional costs. In the case study, current land use is grouped into non-dairy farms and various types of dairy farms and non-agricultural land use. Management variants are described for most of these groups. The LP model was used to analyze the effect of the following conditions: (a) the scale at which the tolerated maximum NO 3 concentration is effectuated; (b) the level of this maximum; (c) the hydrological situation; (d) the way farms are grouped; and (e) the biophysical situation of farms. Total regional costs show a negative, but not necessarily linear, relation with the resulting regional nitrate concentration. This relation is strongly influenced by the actual situation regarding management at the farms and the groundwater table depths in the region. For each region a specific cost–benefit relation might apply. Higher groundwater tables result in strongly reduced costs for required changes in farm management. Depending on costs and physical feasibility, measures that result in a higher groundwater table could therefore be used in addition to or replacement of measures at farm level. Calculated costs are influenced by the method of grouping of farms into farm types, the largest effect due to differentiating intensities of production. Differences between farms need therefore be considered when analyzing possibilities for and costs of measures to reduce nitrate leaching. Political decisions, specifically about the scale at which the maximum nitrate level should be effectuated (farm-type or region) also have a strong effect on the cost–benefit relation. Requiring all farm types to comply with a g