Limited effect of drainage on peat properties, porewater chemistry, and peat decomposition proxies in a boreal peatland

Abstract

The aim of this study was to determine the effect of drainage on peat properties, porewater chemistry, and peat decomposition proxies in an ombrogenous peatland in the Hudson Bay Lowland (HBL). We anticipated that drainage would change peatland hydrology, vegetation, and biogeochemistry, leading to an increase in peat decomposition. As indicators of peat biogeochemical change and potential proxies for peat decomposition, we compared peat porewater chemistry and in situ nutrient availability of different microforms in a pristine ombrogenous bog, with a bog that has been subject to gradual lowering of the water table by 20 to 80 cm for approximately 7 years prior to, and during, our study. We also examined the chemical composition of peat and peat leachates (organic matter) from Sphagnum and lichen-covered hummocks at each site. Nutrient availability was greater in pools at the drained bog, indicating mineralisation of the dry and bare peat surface. However, our results did not show evidence of significant peat biogeochemical change or advanced decomposition in hummocks at the drained bog, with no difference in nutrient availabilities, peat porewater chemistry, or peat leachate chemistry at the drained and pristine bog. We also found no significant difference in enzyme activity (phenol oxidases) in hummocks at each site, proposed to be an important factor for C loss from peatland ecosystems in drier conditions. Overall, the effects of drainage on peat properties, porewater chemistry, and peat chemical composition at our sites were small and varied for different vegetation-microform types. Although decomposition in drained peatlands is likely constrained by cool temperatures in the HBL, our results suggest that ecohydrological feedbacks at the microform scale may also be important in slowing decomposition in these peatlands.