Release of dissolved organic carbon from upland peat

Abstract

This study examines the release of dissolved organic carbon (DOC) from upland peat during the period of the autumn flushing. Hydroclimatic conditions were monitored in conjunction with measurements of absorbance and the E4/E6 ratio of the stream draining an 11·4 km2 upland peat catchment in northern England. During two months of monitoring the effects of 67 separate rainfall events were examined showing that: The peat behaves hydrologically as if it were a two end-member system consisting of old, interevent, and new, event, water. Runoff is initiated by percolation excess of new water at the acrotelm-catotelm interface. The discharge of dissolved organic matter behaves like a three end-member system with the between-event water being low in DOC and storm events being characterized by two types of water. Initial runoff being characterized by new water rich in DOC that gives way to new water depleted in DOC. This transition can be ascribed to the runoff progressing from throughflow within the acrotelm progressing to saturation-excess overland flow. Depletion of DOC during storm events is accompanied by a change in the character of the DOC as the E4/E6 ratio changes. This suggests that the decrease in DOC during events is the result of exhaustion of reserves rather than changes in the flowpaths being utilized by runoff. The amount of carbon released in any event is critically dependent upon the time between events during which oxidation processes generate a reservoir of available carbon. Production of available carbon in the catchment is as high as 4·5 g C per day per m3 of peat, suggesting a turnover rate of peat of the order of 42 years.