Vegetated buffer strips show variable capacity to reduce nutrient loading and sediment influx in ponds in two European countries

Eutrophication is a pervasive threat to freshwater ecosystems, and while the implementation of vegetated terrestrial buffer strips is increasingly promoted as a measure to reduce nutrient runoff into riverine systems, little is known on their effectiveness in protecting ponds in agricultural landscapes. We investigated the effect of buffer strip width on pond nutrient concentrations (TN, TP), the concentration of total suspended solids (TSS) and phytoplankton biomass (CHLa) using data from 34 ponds located on agricultural land in Belgium and Germany. We found a strong negative relation between buffer strip width and the concentrations of TN, TP and TSS in the German set of ponds. While even small buffer strips (5 m) can already be effective, our results also show that larger buffer strips are considerably more effective. In contrast, we did not find an association between buffer strip width and the concentrations of TN, TP and TSS in the Belgian ponds. This could be linked to differences in landscape characteristics, historical eutrophication and pond hydroperiod between both countries. In addition, we did not find evidence for an effect of buffer strips on phytoplankton biomass, which is likely reflecting the fact that, even with buffer strips, nutrient concentrations remained very high in the studied ponds.