Natural peatlands as buffers for protection of water quality in boreal forested catchments

Retention and release of nitrogen, phosphorus, organic carbon, aluminum and iron by natural peatlands were studied in forested catchments in Finland. Peatlands were capable of retaining all other elements from their through-flow waters, except iron. However, relatively large mires (>50 % of the catchment area) from the viewpoint of routing runoff from managed forests to natural peatlands as a water management option were needed for efficient retention of nitrogen and organic carbon (>30–50 % retention). In contrast, aluminium and phosphorus were efficiently retained by relatively small peatlands (5–10 % of catchment area). We conclude that natural and well-established restored peatlands may be used in operational forestry as an efficient means to decrease phosphorus and aluminium loads, but the management of nitrogen, organic carbon, and iron loads by such peatlands may not be as feasible. • Water quality impacts of natural peatlands were assessed in forested catchments. • Peatlands retained all other elements from their through-flow waters except iron. • Phosphorus and aluminium were retained by relatively small peatlands. • Efficient nitrogen and organic carbon retention necessitates large peatlands.