Rates of CO2 efflux and changes in DOC concentration resulting from the addition of POC to the fluvial system in peatlands

Abstract

Fluvial systems are increasingly recognised as sites of carbon processing, particularly in peatlands, where high quantities of particulate organic carbon (POC) enter the stream network during storm events. However, the fate of this POC and potential transformations to dissolved and gaseous phases are poorly understood. Here, a series of mixing experiments are undertaken, using particulate organic matter (POM) and streamwater derived from an eroding peat catchment to simulate high quantities of material entering the fluvial system during storm event. Solutions were monitored for CO2 release and changes in dissolved organic carbon (DOC) concentration. The role of microbial versus physical processes, and the influence of the initial streamwater pH and DOC concentration were also investigated. Results show that the addition of POM to the system leads to high rates of CO2 release, particularly within the first 24 h. The key control on rates of CO2 release is the initial DOC concentration of the streamwater used, with highest rates of CO2 release from solutions with the lowest initial DOC concentration. Rates of DOC production were lower, with average increases in the region of 0.8 mg/l over 24 h. There is evidence to suggest that rates of DOC increase are also influenced by initial streamwater DOC. The rapid rates of CO2 release from the fluvial system indicate that significant carbon loss to the atmosphere is possible, representing ‘hot moments’ upon the addition of POC to the fluvial system, whereas locations where POC residence times are long will be ‘hot spots’ of carbon transformation.