Paper No. 4
Presentation Time: 8:45 AM
DISSOLVED TRACE ELEMENTS AND REE'S IN A HUMID TROPICAL RIVER BASIN, NETHRAVATI RIVER, SOUTHWESTERN INDIA
This study presents the time series data on dissolved trace elements and REE in the Nethravati river basin, a small humid tropical river basin in the southwestern India. The river basin drains Archean silicate basement (Dharwar Craton) such as granite gneisses, charnockites and metasediments. The surface area of the river basin is 4540km2 and the river discharges 388 m3s-1 water and 14x105 tons of sediments. The study aims to improve our understanding on chemical weathering process and elemental transport in the humid tropical river basins. The data shows that the trace elements and REEs exhibit strong seasonal variations, with higher concentrations during rainy season and lower concentrations during dry season for minor elements, heavy metals and dissolved organic carbon. In contrast, the actinide and lanthanide element such as U, Th and REE respectively follows the discharge variation closely. In order to understand the geochemical processes and associated elemental redistribution in the fluvial environment, the correlations between physicochemical parameters and metal elements were performed. Unlike other organic rich river basins, the relationship between dissolved organic carbon and metal cations are statistically insignificant. Whereas, the dissolved oxygen concentration variation is having significant relationship with redox sensitive metals such as Fe, Mn, Ba, V, Cr, Co, As, Mo and Ce. The pH and ionic concentration mediated sorption reactions are having dominant control over the dissolved transport of REE and heavy metals (Ni, Co, Cu and Cr). There is a negative Ce anomaly in the dissolved phase whereas, there is a positive Ce anomaly (Ce/Ce*) in the particulate and bed sediments. The variation in Ce anomaly in dissolved phase is negatively correlated with dissolved oxygen and the variation in Ce anomaly in particulate phase is positively correlated with dissolved oxygen. This suggests that the observed Ce anomaly is mainly because of redox processes in the river basin.