Deposition of phosphorous to open land and forests in Sweden

Abstract

Deposition of phosphorus (P) is important for the nutrient supply to forests and open land but also contributes to the eutrophication of surface waters. Deposition to open land can be measured as bulk deposition while deposition to forests cannot be measured directly, due to internal circulation of P within forest canopies. This study aimed to quantify the total deposition of P to open land and forests in Sweden. The contribution from dry and wet deposition to the deposition to open land was investigated with bulk deposition sampling equipment placed under and outside a roof. The difference with and without the roofs was small and inconsistent. It was concluded that the deposition of P to open land occurred mostly as dry deposition. To estimate the dry deposition of P to coniferous forests, surrogate surfaces consisting of Teflon string samplers were used positioned under roofs. Co-located measurements of dry deposition to forests and bulk deposition to open land at ten different sites across Sweden showed that P deposition was up to five times higher for forests compared to open land. The highest deposition of P to the open land and forests was found for the inland of southern Sweden. This geographical pattern implied only a small contribution from transboundary sources of P outside Sweden. The deposition of P during 2017–2023 was on average 78 g ha⁻¹ yr⁻¹ to open land in north and 240 g ha⁻¹ yr⁻¹ in inland south Sweden. Corresponding deposition to forests was 120 and 730 g ha⁻¹ yr⁻¹.