Dynamics of Dissolved Organic Carbon (DOC) in a Stream During a Quarter Century of Forest Succession

A five-year study of DOC concentration in a stream draining a clear-cut catchment at Coweeta Hydrologic Laboratory reported lower DOC concentration and export than in a reference stream and predicted that DOC concentration would increase until it was indistinguishable from the reference stream. We now have a 25-year record of DOC concentrations to determine if that prediction was correct. Both streams exhibit a consistent seasonal pattern in DOC concentration with concentrations highest in autumn, declining through March, and increasing through the summer. Average DOC concentrations are higher in the reference stream in all months; the difference in concentration between the two streams is greatest in the growing season and least in the dormant season. The differences in DOC concentrations in the two streams were greatest in dry years and have increased as forest succession proceeded. Hence the prediction based on only five years of data was not correct. Mean annual DOC concentration changes as a function of amount of leachable organic matter in both the stream benthos and its catchment. There has been a depletion of these DOC sources during the first quarter century of forest recovery from clear-cutting resulting in lower DOC concentrations in the stream.