Impact of vegetation harvesting on nutrient removal and plant biomass quality in wetland buffer zones

Fertiliser use in agriculture increases the non-point pollution of waters with nitrogen (N) and phosphorus (P). Wetland buffer zones (WBZs) are wetland ecosystems between agricultural lands and water bodies that protect surface waters from non-point source pollution. We assessed how vegetation harvesting within WBZs impacts their N and P removal efficiency, nutrient uptake by plants and their biomass quality. We surveyed vegetation of a spontaneously rewetted fen along a small river in Poland, and analysed plant biomass, its nutrient contents and nutrient-leaching potential and the water chemistry. Total N removal reached 34–92% and total P removal 17–63%. N removal was positively related to the initial N concentration, regardless of mowing status. We found a high N removal efficiency (92%) in the harvested site. Vegetation of mown sites differed from that of unmown sites by a higher water-leached carbon and P contents in the biomass. We found that vegetation harvesting may stimulate the overall N removal, but may increase potential biomass decomposability, which eases the recycling of plant-incorporated nutrients back to WBZ. Thus, mowing should always be followed by the removal of biomass. Neglecting already mown WBZs may temporarily lower their nutrient removal efficiency due to potentially faster decomposition of plant biomass.