The Influence of Peatland Drainage and Harvesting on C, N, and P Loading to Aquatic Ecosystems: A Landscape Perspective.

Boreal peatlands store vast amounts of organic matter, as a result of slowed decomposition under anaerobic conditions. Peatland drainage, including drainage for the purpose of peat harvesting, thus has the potential to affect the downstream loading of carbon (C), nitrogen (N), and phosphorous (P) - both due to altered hydrology but also due to increased peat decomposition following drainage. Impacts of peatland disturbances on downstream water quality are important to understand, and to put into context of impacts of other land uses, in order to inform decision-making. Here, we use a repeat synoptic sampling approach in 50 subcatchments near Seba Beach, AB to understand the influence of peatland drainage and harvesting on spatial and temporal nutrient dynamics in boreal watersheds. Subcatchments were selected to represent a swath of catchment sizes (<1-180 km²) and land use types including pristine and drained peatlands, forests, agriculture, and pastureland. We hypothesize that subcatchments affected by peatland drainage will disproportionately release dissolved organic C (DOC), whereas agricultural and pastureland subcatchments will disproportionately release N and P. Further, we hypothesize that the spatial pattern of nutrient sources and sinks will be stable or conserved through time because of inherent catchment characteristics such as surficial geology or water residence time. Results from this study show that drained peatlands had elevated DOC, N, and P export compared to pristine peatlands, and that drained peatlands had an important influence on the total export of DOC and N at the landscape scale, while increased peatland export of P was minor when compared to agricultural export. Overall, this study enhances understanding about the role of human disturbance in carbon and nutrient dynamics in aquatic boreal ecosystems.