Assessment of phosphorus retention efficiency of blanket peat buffer areas using a laboratory flume approach

Abstract

Large areas of upland blanket peat were afforested in the UK and Ireland before the importance of the riparian buffer areas was realized. These forests are now reaching harvestable age. In order to reduce the possible negative impact of harvesting activities on receiving water bodies, the creation of buffer areas along receiving water courses prior to the clear-felling of the main plantation has been proposed. In this study, laboratory flumes were used to assess the dissolved reactive phosphorus (DRP) retention efficiency of the vegetated and non-vegetated blanket peatland buffer areas under different hydraulic loadings. In addition, a mini-buffer approach is proposed and tested with flumes. The idea with mini-buffers is to keep P on site and reduce P transportation from harvest residues. In the grassed flumes, the DRP removal efficiencies gradually decreased from 80% to 40% and 30% to 18% when the hydraulic loadings increased from 49 to 123mmh−1 and 256 to 444mmh−1, respectively. In the non-grassed flumes, the DRP removal was about the same as for the grassed flumes when the hydraulic loading was 49mmh−1 but was significantly less when the hydraulic loadings increased to 123, 256 and 444mmh−1. The mini-buffer method could retain 88–95% (with seeded grasses) and 54–62% (without seeded grasses) of added DRP under different inflow DRP concentrations (between 0.5 and 3mgDRPL−1). After ending the overland flow experiment, the water extractable phosphorus (WEP) and pore water P concentrations in the non-grassed flumes were significantly higher than the grassed flumes, indicating a higher risk of subsequent P release from non-grassed buffer areas after ending of P-rich overland flow. Our results indicated that the overall P retention capacity of the normal buffer areas in blanket peat catchments is low due to frequent occurrence of high flow events that significantly reduce buffer P retention efficiency. In contrast, the mini-buffer method could be a feasible means of increasing onsite P retention. This study is of particular interest currently as large areas of upland blanket peat forests without buffer areas in the UK and Ireland are being harvested or scheduled to be harvested in the near future.