The success of river restoration is often poorly quantified due to poor design, absence of proper monitoring or incomplete documentation. This study is an attempt to overcome this ex-post using the aggregating nature of the ecosystem services approach. In 8 pairs of restored reaches and their adjacent floodplains of middle-sized European rivers, we quantified as many provisioning, regulating and cultural services as possible that were of final value to humans as annual biogeochemical or –physical fluxes, or densities per year, and summed these to annual economic value normalised per area.
We separated different forms of land cover using the European harmonised land cover classification CORINE, summing per habitat type and service type. Non-market values were obtained from questionnaire surveys among inhabitants and visitors leading to a.o. willingness-to-pay estimates for restoration, water quality improvement and scenic beauty.
We found a significant difference in total ecosystem service value between unrestored and restored reaches of 1400 ± 600 € ha-1 y-1 (2500 minus 1100, p=0.03, paired t-test and regression). We analysed possible relations with 23 physical and social geographical characteristics of the floodplain and upstream catchment after reducing these to 4 principal components explaining 80% of their variance. Cultural and regulating services correlated with human population density, cattle density and agricultural Nitrogen surplus in the catchment, but not with the fraction of arable land or forest, the slope of the floodplain or mean river discharge, or GDP. We interpret this that landscape appreciation and flood risk alleviation are a simple function of human population density. Our total ecosystem service values are comparable to recent literature values from elsewhere and scale with local annual land rent with a median ratio of 3.
We conclude that our approach allows ex-post evaluation of river restoration success, and posit that restoration of middle sized rivers in Europe, by and large enhances overall societal benefit.