Fractionation of sediment organic carbon in Hirakud reservoir: a Ramsar site in India

Sediments are natural reservoirs of organic carbon assisting in maintenance of natural carbon inventory. The present work was carried out with aims to assess the various labile (employing acid digestion method) and biochemical carbon fractions in sediments of Hirakud reservoir and study the impact of spatial variations on it. The results favor a distinct spatial influence on the distribution and concentration of various carbon fractions in sediments (p < 0.05). The average concentrations of very labile (2.09%) and recalcitrant (1.25%) fractions of total organic carbon dominated the sediments while the labile and less labile fractions shared 0.39 and 0.63% respectively. Similarly, the carbohydrate carbon (0.82 mg/g) and protein carbon (0.78 mg/g) conquered the biopolymeric carbon (BPC) with the lipid carbon being 0.67 mg/g only. While the available K and P ranged between 3.81 and 17.02, and between 6.31 and 27.57 kg/ha respectively, total nitrogen varied from 198.06 to 462.15 kg/ha. Significant spatial variations were observed concerning long-term carbon storage and productivity (eutrophic condition, BPC > 3 mg/g). The reservoir sites were mesotrophic to eutrophic in nature while the downstream displayed oligotrophic condition. Organic sediment index (OSI) value suggests that the reservoir sediment was under practically uncontaminated to moderately contaminated condition (OSI < 0.20). The principal component analysis also suggests that the carbon accumulation is primarily governed by the recalcitrant carbon fraction. Thus, it can be concluded that carbon fractions regulate the sediment quality by influencing its carbon storage, production capacity, and is affected by anthropogenic pressure along a spatial scale.