Untangling land use and climate impacts on catchment water quality: Decadal trends in catchment dissolved organic carbon export in response to wind farm development on peatland

Wind farms can help to mitigate increasing atmospheric carbon (C) emissions. However, disturbance caused by wind farm development must not have lasting deleterious impacts on landscape C sequestration. To understand the effects of wind farms on peatlands, we monitored streamwater in five catchments (5.7–31 km²area) draining Europe’s second largest onshore wind farm at Whitelee, Scotland, UK for 10 years after wind farm development that occurred in phases. Dissolved organic carbon (DOC) concentrations were measured every 2–4 weeks and DOC fluxes estimated using flow from either direct measurements in the catchments or scaled via catchment area from a nearby river flow gauge. Similar measurements were made at a nearby peatland catchment unimpacted by wind farm development that acted as the best possible reference site. Generalised additive mixed models (GAMM) were fitted to all catchments to assess differences in trends and seasonality in DOC and flow between catchments. Interactions terms allowed for the possibility of changing seasonal patterns, and temporal correlations were included in the models and formal testing using an AR(1) structure. Change points in DOC trends were identified using first derivatives of the estimated trends and compared with the timings of wind farm construction. DOC exports from the wind farm-impacted catchments are high at 17–34 g C m^-2 year^-1. The models showed increasing trends in streamwater DOC concentrations and fluxes in the wind farm-impacted catchments, with timing apparently synchronous with the development phases. In contrast, streamflows were more stable. Trends and seasonality of DOC concentrations and fluxes were different in the reference catchment during the study period. Hydrological and biogeochemical processes driving the DOC response of peatland catchments to wind farm development will be discussed, and their consequences for landscape C sequestration assessed.