The impact of peatland drain-blocking on dissolved organic carbon loss and discolouration of water; results from a national survey

Peatlands are important terrestrial carbon stores but their environmental degradation has led to concerns of increased carbon loss. Many peatlands have been drained using open ditches and this practice has been associated with enhanced dissolved organic carbon loss and water discolouration. Recent peatland restoration schemes have therefore included the blocking of peatland drains as a strategy for environmental improvement. However, it is not clear whether drain-blocking consistently reduces dissolved organic carbon loads and water discolouration because many peats undergo significant physical and chemical change when they are disturbed. Previous studies investigating the impact of drain-blocking on water colour and dissolved organic carbon have been restricted to a limited spatial and temporal research framework. This study combines an extensive UK-wide survey of blocked and unblocked drains across 32 study sites and intensive monitoring of a peat drain system that has been blocked for 7 years. Dissolved organic carbon concentrations and water discolouration were significantly lower in blocked drains: the mean dissolved organic carbon concentration of water sampled from blocked drains was 28% less than that sampled from unblocked drains. However, this pattern was not consistent at all sites. At the intensive monitoring site no significant differences could be observed in total dissolved organic carbon flux from the fully instrumented blocked and unblocked drains: the blocked drain exported 31,592 kg km2 yr1 and the unblocked drain 30,123 kg km2 yr1. Results from bi-weekly grab samples from other drains at the intensively monitored site, however, did conform to the general national pattern of lower dissolved organic carbon and discolouration in blocked drains. The results demonstrate that drain-blocking can be an effective management strategy for reducing DOC loss and water discolouration in disturbed peat catchments. The caveat remains, however, that there will be a number of sites where no significant change will occur.