Bioavailable dissolved organic matter and its spatio-temporal variation in a river dominated tropical brackish water Lagoon, India

Abstract

Bioavailable dissolved organic carbon (B_DOC), nitrogen (B_DON) and their degradation rate constants were measured for the Chilika Lagoon, India. Long-term laboratory incubation experiments (90 days) were conducted at a constant temperature (25 °C) to quantify the bioavailable dissolved organic matter (DOM) and the possible degradation rate coefficients. The results showed that 41 ± 12% of dissolved organic carbon (DOC) and 47 ± 17% of dissolved organic nitrogen (DON) were B_DOC and B_DON respectively, with their stoichiometry found to be higher than the Redfield ratio. A first order exponential non-linear fitting routine was used to estimate pool sizes. The degradation rate constant (k) for the B_DOC varied from 0.127-0.329 d^-1 and B_DON from 0.043-0.306 d^-1 during the study period. Half-lives of the B_DOC and B_DON ranged from 2.1-5.4 and 2.2-15.9 days, respectively. Overall, the results showed that a fraction of the labile DON was transported from the lagoon to the adjacent coastal sea.

Keywords: Bioavailability; Degradation; Degradation rate coefficients; Dissolved organic carbon; Dissolved organic nitrogen; Mineralization.