Abstract
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.
Highlights
Agricultural activities, combustion of fossil fuels and other impacts related to a growing human population have significantly altered the cycles of elements controlling the primary production of ecosystems (e.g. Steffen et al, 2015; Battye et al, 2017)
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 wetland buffer zones (WBZs)
The study area is located in central Poland, in the Ciechanowska Upland physico-geographical mesoregion (Solon et al, 2018) situated in the central part of the North Mazovian Lowland—an undulating plain characterised by moraines and kame hills; it is a typical agricultural land interspersed with a few forest clusters (Fig. 1a)
Summary
Agricultural activities, combustion of fossil fuels and other impacts related to a growing human population have significantly altered the cycles of elements controlling the primary production of ecosystems (e.g. Steffen et al, 2015; Battye et al, 2017). Increased food demands and fertiliser use are the causes of a growing rate of non-point pollution of waters with nitrogen (N) and phosphorus (P). WBZs can capture and remove nutrients through several mechanisms, including biological (microbial denitrification, plant uptake), chemical (precipitation of P), physical (sedimentation) and biochemical (humification during decomposition of organic matter), and all these processes can be further influenced by vegetation management (Zak et al, 2019). The impact of plant uptake and biomass harvesting (i.e. mowing and removal of aboveground shoots) on the nutrient export remains, understudied. Harvesting can enhance water purification in WBZs because it removes the labile N and P that would otherwise be partially released after plant’s death at the end of the growing season. Rewetted riparian fens (i.e. minerotrophic peatlands) constitute an important type of WBZs and, due to legacies of drainage and agricultural use, as well as nutrient input from agricultural land, they are often
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