Export of particulate organic carbon by the mountainous tropical rivers of Western Ghats, India: Variations and controls.

ABSTRACT

Transport of organic carbon by small mountainous rivers is essential, but the poorly constrained component of the global carbon cycle. In the current research, we sampled and analyzed particulate organic carbon (POC) contents from 70 sizeable tropical coastal rivers, draining the Western Ghats (WG) of India. This study aimed to investigate the spatiotemporal variability in POC contents, to estimate flux and to identify environmental controls on POC sources and transport characteristics across the region. The averaged value of organic carbon (OC) in the particulate samples is 3.24%, and the mean POC concentration is 2.86 mg l-1. We classified the samples based on total suspended matter (TSM) classes for source appropriation. Litter/riparian (42.5%) pools are the largest source of organic matter, followed by autochthonous (36%) and soil (21.5%) for the WG region. However, locally autochthonous sources contribute exceptionally to POC pools, indicating a favorable environmental condition for the growth of algae and phytoplankton. Land-use & land-cover, climate, topography, and sediment erosion seems to be determining the local variability in sources to POC pools and fluxes. The POC export rates suggest that within the region, the POC yields of the Deccan Trap (DT) and the Western Dharwar Craton (WDC) blocks are about two times higher than that of the Southern Granulite Terrain (SGT) region. With POC yield of 7.0 g m-2 yr-1, this region exports 0.79 Tg C (~ 0.5% of the global POC) to the Arabian Sea annually. The POC flux of the WG region (covering 0.25% of Asia's land area) is approximately 1.0% of Asia's riverine POC flux to the ocean.