Role of blanket bog condition in stream dissolved organic carbon export

Abstract

The degradation of peatlands across the UK and Ireland has led to rising concentrations of dissolved organic carbon (DOC) in surface waters. This can have implications for the treatment of water supplies. While catchment management strategies to improve water quality, such as peatland restoration, aim to reverse these trends and thereby reduce treatment costs, relationships between DOC generation and land use require further clarification. DOC levels recorded in discharge from relatively intact areas can be used to establish realistic restoration targets. To investigate the relationships between DOC concentrations in streams draining intact areas and adjacent disturbed areas, a year-long integrated hydrological and water quality monitoring program was conducted along a 2.2 km stretch of a first-order stream draining a blanket peat-covered catchment in the Ox Mountains, Co. Sligo, Ireland. Groundwater level monitoring operated continuously at 15 catchment locations in contrasting hydrological settings. Combining the results of continuous stream discharge measurements with groundwater level monitoring permitted event-based water quality sampling at three locations along the stream’s course; this allowed assessment of how changes in DOC concentrations and fluxes varied with land use, moving from the stream’s headwaters, downstream. Data from five water quality sampling events distributed over the course of one-year (December 2023 to November 2024) revealed that DOC fluxes draining the 107 ha catchment of the stream’s headwaters varied between 8.7 mg/m2 and 144 mg/m2. By contrast, DOC fluxes rose consistently going downstream. Results from the final 21 ha interval, (reflecting a substantially more degraded area) showed that fluxes from a formerly afforested peatland ranged from 27 mg/m2 to 907 mg/m2. The results indicated that DOC fluxes are affected by both peatland condition and seasonal variation.