Changes in dissolved organic carbon quality in soils and discharge 10 years after peatland restoration

Peatlands are large sources of dissolved organic carbon (DOC) to downstream ecosystems and DOC losses account for an important portion of peatland carbon balance. Disturbance and restoration of peatland ecosystems alters ecohydrological conditions that are likely to affect DOC chemistry in both soil water and discharge, although the direction of change and controls on DOC chemistry post-restoration remain unclear. We investigated DOC chemistry (concentration, SUVA254, E2:E3, E4:E6, pentose and hexose concentration) during the growing season (May to October) in soil and discharge of a peatland restored for 10 years and compared the results to those measured at neighboring unrestored and natural peatland sites. Controls on the spatial and temporal variability of DOC chemistry, including pH, water table, temperature, plant cover and type, and carbon dioxide and methane flux were also investigated. After 10 years, restoration increased DOC concentration in soils compared to both natural and unrestored sites. This high DOC concentration likely resulted from high plant productivity post-restoration and a mean water table position deeper than the natural site. Ecohydrological conditions were also correlated to DOC chemistry. High vascular plant cover and photosynthesis rates were correlated to lower SUVA254 and higher pentose concentration, while deeper water table position was correlated to higher E2:E3 and E4:E6. DOC concentration in discharge was lower, and E2:E3 higher, at the restored compared to the unrestored site. Differences in DOC chemistry in discharge water were minimal between the sites except when water was likely sourced from the near surface layer at the restored site, which represents new peat accumulated post-restoration. These results suggest that DOC dynamics 10 years post-restoration remain intermediate between natural and unrestored peatland.