Towards a realistic cost and impact assessment of measures for reducing nutrient export from agricultural landscapes
Field site Dummerstorf
The field site ‘Dummerstorf’ has a size of 4.2 ha, annual discharge is 7056 m³ and the average nitrate-nitrogen concentration is 9.6 mg/L. We assumed reduction targets ranging from 30 to 90%. To reduce nitrate loads, scenario analyses were conducted for MBBR, woodchip filter and constructed wetlands. Based on a literature review and NuReDrain results, cost ranges were assessed for MBBRs (50-500 €/kg N reduction), woodchip filters (2-20) and constructed wetlands (5-95).
The nomograms above allow users to estimate expected costs for the drainage plot at specific reduction targets and costs per kg N reduction. The other way round, the nomograms can be used, for example, to define a reduction target, when a fixed budget is given.
The aim of this analysis was to calculate the costs and the impact on nitrate loads when tile-drained areas will be equipped with installations to capture waterborne nitrate. It was assumed that annual discharge of the drainage plots is 80-150 mm/yr and average nitrate-nitrogen concentrations are 3-15 mg/L. Further, we decided to implement technical solutions only for drainage plots with nitrate-nitrogen concentrations >10 mg/L. MBBRs, woodchip filters and constructed wetlands were installed at small (<2 ha), medium (2-10) and large-scale (>10) drainage plots, respectively. Reduction targets and costs were the same as for the field site in ‘Dummerstorf’.
We performed 100 runs with randomly selected values based on the defined specifications. Applying these measures would lead to a nitrate reduction at catchment scale of approx. 15%. However, it is estimated that annual costs for this 30.492 ha catchment will amount to approx. 2.5 Mio € per annum.
The presented approach allows a realistic cost-benefit assessment for policy makers at an early stage of planning and it can be applied to any region if sufficient data is available.