Biogeochemical fluxes of carbon and nitrogen from Chilika lake East Coast of India

Abstract

Studies on biogeochemical cycling and fluxes of carbon and nitrogen in Chilika lake, Asia s largest brackish water lake on the east coast of India revealed for the first time a strong seasonal and spatial variability associated with the salinity. The lake was studied during both monsoon (July, 2005 and July-August, 2006) and premonsoon (May, 2006 and March-April, 2007), in 35 selected locations, including the 11 major rivers and two tidal locations. the biogeochemical processes and budgets of carbon, nitrogen and phosphorus were constructed through seasonal observations and modeling. The water residence time of Chilika Lake varied seasonally from ~7 days during monsoon to 120 days during premonsoon. The residence times of nutrients (C, N and P) varied with the water exchange rates and were about twice longer than the water residence time. Riverine inputs and lake distributions of nutrients varied both in time and space based on the seasonal sampling. The non-conservative fluxes and#916;DIN, and#916;DIP, and#916;DIC and and#916;DOC from the lake varied seasonally, where monsoonal fluxes were predominant and strong compared to the premonsoon. and#916;DIN and and#916;DIP was positive during monsoon and negative during premonsoon. and#916;DIC was positive during monsoon and negative during premonsoon, while and#916;DOC was negative during both monsoon and premonsoon. During monsoon, the DIC removal (2.06 Gg C d-1) from the lake is equivalent to the riverine influx (2.05 Gg C d-1) and in addition, almost 2.00 Gg C d-1 of CO2 evaded to the atmosphere as DIC at the air-sea boundary. The present study indicates that the Chilka lake is an important region for biological transformation of organic carbon and nitrogen to inorganic form and its export to the atmosphere. Therefore, the biogeochemical study of lake ecosystem and the fluxes of CO2, CH4 and N2O is highly essential to introvert its significant contribution in the global context. newline