Composition of sedimentary organic matter in Thrissur Kole wetland, southwest India

Spatio-temporal distribution dynamics of various biochemical components in Thrissur Kole wetland were analyzed to assess the quality of organic matter (OM) and trophic status. Thrissur Kole wetland forms part of the Vembanad wetland system, located on the southwest coast of India. Surface sediment samples were collected from sixteen sites during the pre-monsoon (February 2019) and monsoon (August 2019) seasons. Concentration of biochemical parameters displayed the trend as follows: total carbohydrates > total protein > tannin and lignin > total lipids. Intermediate values of C/N ratios [average: 17.15 ± 0.86 (pre-monsoon), 9.81 ± 0.42 (monsoon)], indicated a mixed origin of OM. The occurrence of high tannin and lignin content substantiated terrestrial vascular plant input to the wetland ecosystem. Elevated levels of PRT were due to anthropogenic inputs via aquaculture activities and guano of birds. Majority of the sites exhibited lower values of protein to carbohydrate ratios (< 1) revealed the occurrence of aged sedimentary OM. Lower values of total lipid to total carbohydrate ratio (< 1) indicated lower nutritional quality of the OM. Lower % contribution of labile OM to total OM, lower biopolymeric carbon to total organic carbon ratio and lower algal contribution to the biopolymeric carbon suggested that a bulk fraction of OM exists as refractory. Based on protein and carbohydrate content, biopolymeric carbon and algal contribution to biopolymeric carbon, trophic state of the wetland system was evaluated as hypertrophic which implies deterioration in ecosystem health.