Source, pattern and flux of dissolved carbon in an alpine headwater catchment on the eastern Tibetan Plateau

Abstract

Dissolved carbon (DC) transported from headwater streams on the eastern Tibetan Plateau is a crucial component of the carbon cycles in the regional river. However, the spatiotemporal variability and sources of DC in these remote headwater streams remains unclear. An investigation into dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) was conducted with high temporal resolution from a glacier terminus, a forest catchment, and the catchment outlet located on the eastern flank of Mt. Gongga, Southwest China. The results showed that (1) the mean DOC concentration at the glacier terminus (2.38 ± 0.71 mg L−1) was significantly higher than at the forest catchment (2.13 ± 0.49 mg L−1) and at the catchment outlet (2.17 ± 0.58 mg L−1), while the DIC concentration increased by 21.6% at the forest catchment and by 18.7% at the catchment outlet relative to that in the glacier terminus. (2) Compared to the monsoon season, DOC concentrations in the forest catchment decreased by 24.6% postmonsoon, and the seasonal variation of DOC concentrations was minor either at the glacier terminus or at the catchment outlet; relative to monsoon values, postmonsoon DIC concentrations increased by 14.9% and 28.8% at the forest catchment and catchment outlet, respectively. Precipitation and stream pH were identified as important factors influencing the seasonal variability of DC. (3) Silicate and carbonate weathering contributed 52.9 ± 12% and 44.4 ± 9%, respectively, to DIC generation in the forest catchment according to 13C analysis. This study provides a valuable dataset on the dynamics of DC in a region where data is sparse, which improves our understanding of DC transport in alpine regions. The unexpected spatiotemporal stability of DC suggests that less frequent rates of sampling might be adequate to estimate carbon export.