The application of δ~(13)C-DIC on weathering and biogeochemical processes of carbon in rivers

The river is the important link between land and aquatic ecosystem,which takes a large of material to ocean and impacts the global carbon cycle.Here,water chemical and carbon isotopic evidence from different scale catchments in Southwest China to ascertain the chemical weathering and carbon sources as well as impacting factors.The relationship of δ~(13)C-DIC versus chemical ion ratios demonstrate that sulfuric acid derived from oxidation of pyrite is also an important agent of rock weathering in Beipan River.The result shows that around 25%of the HCO_3~- in Beipan River originated from the interaction between carbonate minerals and sulfuric acid based on the Mixing diagrams between carbonic acid weathering and sulfuric acid weathering according to the relationships between δ~(13)C-DIC and major ions.There is high carbonate weathering in the Houzhai catchment relative to other catchment,Southwest China,which is a small typical karstic catchment with the developed subterranean conduits and frequent agricultural activity.The δ~(13)C and DIC characters in Houzhai catchment are thereby considered to be mainly impacted from soil CO_2 and weathering of carbonate rocks.Meanwhile,the nitrate derived from agricultural activity might shift the δ~(13)C-DIC.Furthennore,the higher PCO_2 contents in subterranean conduits compared to that of surface stream leads to part of CO_2 evasion to the atmosphere after groundwater discharging into streams.In brief,δ~(13)C-DIC can be useful to understand the carbon biogeochemical processes in rivers,which is important to assess the weathering and global carbon cycle.