Scaling of increased dissolved organic carbon inputs by forest clear-cutting – What arrives downstream?

Abstract

Summary Forest clear-cutting has been found to significantly increase concentrations of dissolved organic carbon (DOC) in boreal first-order streams. Here, we address the questions of (1) how the additional inputs of DOC by upstream forest harvesting affect downstream locations within a stream network and (2) what catchment area has to be harvested to cause a significant downstream increase in DOC concentration. We combined the use of primary data from a paired-catchment experiment, clear-cut history of a nested stream network derived from satellite images with a mixing-model approach in order to quantify the importance of upstream clear-cuts on two downstream sites with different catchment sizes. Modeled [DOC] agreed well with the measured concentrations in the smaller, 8.7 km 2 catchment located above a larger wetland area, but discrepancies occurred for the larger 22.9 km 2 catchment located downstream of the wetland. Estimates of the critical area ( A critical ) needed to be harvested to cause a significant impact on downstream DOC concentrations was quantified to be 11% for p p A critical . We suggest that the estimates of A critical could be used in sensitive river networks to provide harvesting-thresholds. The latter could be implemented into forest planning that includes considerations of the negative impact of clear-cutting on water quality.