Dissolved carbon and silica fluxes from Kali, Sharavati and Sita-Swarna rivers, Southwestern India

Spatio-temporal behaviour of dissolved organic carbon (DOC), inorganic carbon (DIC) and silica (DSi) along the salinity gradient of three south-west Indian monsoonal estuaries are presented. This study showed both conservative and non-conservative behaviour of DOC along the salinity gradient under varying physico-chemical conditions. The gross flux of DOC arriving at the estuary from the rivers was estimated as 0.9 × 10⁹ g/yr for Sita-Swarna river, 4.2 × 10⁹ g/yr for Sharavati river and 5.6 × 10⁹ g/yr for Kali river. Similarly, the net fluxes of DOC estimated beyond the estuarine zone was 5.5 × 10⁹ g/yr (Sita-Swarna), 8.0 × 10⁹ g/yr (Sharavati) and 7.7 × 10⁹ g/yr (Kali). This indicates that these estuaries are the sources of organic carbon to the ocean. The DIC linearly increased towards the higher salinity with net fluxes of 38 × 10⁹ g/yr (Sita-Swarna), 75 × 10⁹ g/yr (Sharavati) and 97 × 10⁹ g/yr (Kali). The combined DIC flux of Sita-Swarna, Sharavati and Kali rivers is ~8% of the total DIC fluxes received from the west flowing rivers of India, to the Arabian Sea. The DSi showed a biogenic removal of 80–85% in all the studied estuaries. From this study it is concluded that the west flowing river estuaries are net sources of DOC and DIC and net sink for DSi. Consideration of the role of west flowing rivers of peninsular India is important for the better understanding of the carbon dynamics in the river-estuary-ocean boundary.