Evaluation of the spatial and seasonal variations in the Dissolved Carbon Export of a non - perennial tropical river, Cauvery, Southern India

Abstract

The role of rivers in global carbon cycles are important, especially in regard to the dissolved carbon dynamics and its variability for shorter period timescales. The contribution of non - perennial rivers on global carbon cycle has not been understood clearly, where the environmental controls on dissolved carbon in such rivers is not yet defined. Hence, the objective of the present study is to assess the seasonal and spatial variations of dissolved carbon export in a non-perennial river, Cauvery, India. The river water and the adjacent groundwater samples were collected along the river at 28 locations on quarterly basis from 2013 to 2021. The samples were analysed for pH, temperature, major ions, DIC, DOC, nutrients and 13C-DIC. The DIC concentrations were low at the locations near to the origin of the river, whereas it was vice-versa for DOC concentrations. The  source of DIC  was  due to both geogenic and biogenic, where the weathering of rocks majorly influences the DIC concentration. The silicate weathering is significant during the wet periods, whereas carbonate weathering was dominant during dry periods. The soil organic carbon along with microbial process, autrotrophic production influences the DOC concentration. The transport of dissolved carbon was high during monsoon periods and was very less during dry seasons due to lower discharge and damming.  It is estimated that the Cauvery river accounts about 5% of total DIC and 1% of total DOC transported to the Bay of Bengal from the rivers. Hence, the study implies that the seasonal variation of carbon exports in the rivers should be accounted in carbon budgets.