Dissolved organic carbon production and runoff quality following peatland extraction and restoration

Abstract

We examined dissolved organic carbon (DOC) production and quality in a cutover (extracted) and restored peatland in eastern Québec through a combined laboratory DOC production study and an accompanying field DOC runoff quality study. Both temperature and substrate were significant for explaining variability in net DOC production rate in both short (5 days) and longer term (25 day) laboratory incubations. Moss ( Sphagnum spp. and Polytricum spp.) produced the least amount of DOC, with initial release rates of 0.02–0.35 mg DOC g −1 d −1. Shrubs, and to a lesser extent herbaceous vegetation, showed an initial high release of DOC followed by a decrease. Peat from the restored site had significantly higher longer-term DOC production rates than the cutover site. Humic acid (HA) was more likely to be produced by shrub and herbaceous plant material than by peat, mosses and straw. The hydrophilic (HPI) fraction of the DOC increased at higher temperatures. Despite differences in the surface cover of available substrate (e.g. vascular vegetation, moss, and straw), there was no difference in the quality of DOC exported from the cutover and restored sites. However, hydrological and biogeochemical controls were apparent in temporal variability of DOC quality in discharge. DOC exported during snowmelt and most storm events was high in HPI with little contribution from HA. Since contact time between water and soil is limited during these high flow periods, larger more hydrophobic HA molecules are less likely to be mobilized. Higher export of HA in summer compared to spring and autumn suggests that polycondensation and increased vascular plant productivity are important for controlling seasonal patterns of DOC export quality. As various substrates produced different amounts and quality of DOC, it is likely that the DOC quality exported from the restored site will continue to change as the new vegetation community develops. DOC production rates and DOC quality should be considered when developing a plan to control DOC runoff/export from managed peatlands.