Fluxes of dissolved organic carbon and nitrogen to the northern Indian Ocean from the Indian monsoonal rivers

Abstract

Dissolved Organic Carbon (DOC) and Nitrogen (DON) were measured in 27 major and medium monsoonal estuaries along the Indian coast during southwest monsoon in order to understand the spatial variability in their concentrations and fluxes to the northern Indian Ocean. A strong spatial variability (∼20-fold) in DOC and DON was observed in the Indian monsoonal estuaries due to variable characteristics of the catchment area and volume of discharge. It is estimated that the Indian monsoonal estuaries transport ∼2.37 ± 0.47 Tg (1 Tg = 10¹² g) of DOC and ∼0.41 ± 0.08 Tg of DON during wet period to the northern Indian Ocean. The Bay of Bengal receives 3 times higher DOC and DON (1.82 and 0.30 Tg, respectively) than the Arabian Sea (0.55 and 0.11 Tg). Catchment area normalized fluxes of DOC and DON were found to be higher in the estuaries located in the southwestern than the estuaries from other regions of India. It was attributed to relatively higher soil organic carbon, biomass carbon and heavy rainfall in catchment areas of the rivers from the former region. It has been noticed that neither catchment area nor discharge volume of the river controls the fluxes of DOC and DON to the northern Indian Ocean. Since the total load of DOC and DON is strongly linked to the volume of discharge, alterations in the freshwater discharge due to natural or anthropogenic activities may have significant influence on organic matter fluxes to the Indian coastal waters and its impact on microbial food web dynamics needs further evaluation.