Relative Contributions of Particulate and Dissolved Organic Carbon to the Total Organic Carbon Export From a Forested Catchment.

A total of 14 storm events were sampled over a 16-month period to investigate the temporal patterns and relative contributions of POC and DOC to storm runoff from two (12 and 79 ha) nested, forested catchments in the mid-Atlantic region of USA. While the concentrations of both DOC and POC increased with storm-event discharge, the increase in POC concentrations was greater and occurred earlier on the rising limb of the hydrograph. DOC concentrations peaked at or after the discharge peak. End-member mixing analyses suggested that POC transport occurred with surface runoff delivering carbon-rich forest floor material to the stream, whereas DOC export was facilitated by surface runoff and rising groundwater that leached accumulated DOC from surface soil horizons. Peak POC concentrations decreased with closely spaced storm events whereas no such decrease in concentrations was observed for DOC. On the other hand, very large events with peak discharges exceeding 3mm/hr produced a dilution in DOC concentrations at peak flow whereas POC concentrations continued to increase. These results allude to important differences in the storage pools and leaching rates of POC and DOC. POC accounted for 84% of the total organic C flux from the watershed during storm events. Three largest events in terms of precipitation contributed to 84 % and 63 % of the storm-event exports of POC and DOC. Flow-duration analysis revealed that 90 % of POC and 75 % of DOC was exported during storm flows that were exceeded less than 10 % of the time. These results underscore the importance of POC for the total carbon flux during storm events, as well as the dominant role of large, high-intensity storm events for C flux from catchments. Large, high-intensity storm events that predicted to increase under future climate-change scenarios will likely enhance the storm-induced carbon flux from catchments.