Biogeochemical facsimile of the organic matter quality and trophic status of a micro-tidal tropical estuary

• Published in: Environmental earth sciences 2013-09, Vol.70 (2), p.729-742
• Main Authors: Renjith, K. R, Joseph, Manju Mary, Ghosh, Prosenjit, Habeeb Rahman, K, Ratheesh Kumar, C. S, Chandramohanakumar, N
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Anthropogenic factors; Biochemical composition; Biochemistry; Biogeochemistry; Biogeosciences; Biological and medical sciences; Brackish; Carbohydrates; carbon; Chemical contamination; Chemical pollution; Earth and Environmental Science; Earth Sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Environmental Science and Engineering; Environmental testing; Estuaries; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; Geochemistry; Geology; Hydrology/Water Resources; Isotope geochemistry; Isotope geochemistry. Geochronology; Lipids; monsoon season; nitrogen; Nutrients; Organic matter; Original Article; Pollution, environment geology; Primary production; primary productivity; proteins; Sea water ecosystems; Seasonal variations; sediments; stable isotopes; Studies; Synecology; tannins; Terrestrial Pollution; Trophic status; Water column
• ISSN: 1866-6280; 1866-6299
• DOI: 10.1007/s12665-012-2159-0

Seasonal studies were carried out from 21 stations, comprising of three zones, of Cochin Estuary, to assess the organic matter quality and trophic status. The hydographical parameters showed significant seasonal variations and nutrients and chlorophylls were generally higher during the monsoon season. However, chemical contamination along with the seasonal limitations of light and nitrogen imposed restrictions on the primary production and as a result, mesotrophic conditions generally prevailed in the water column. The nutrient stoichometries and δ ¹³C values of surficial sediments indicated significant allochthonous contribution of organic matter. Irrespective of the higher content of total organic matter, the labile organic matter was very low. Dominance of carbohydrates over lipids and proteins indicated the lower nutritive aspect of the organic matter, and their aged and refractory nature. This, along with higher amount of phytodetritus and the low algal contribution to the biopolymeric carbon corroborated the dominance of allochthonous organic matter and the heterotrophic nature. The spatial and seasonal variations of labile organic components could effectively substantiate the observed shift in the productivity pattern. An alternative ratio, lipids to tannins and lignins, was proposed to ascertain the relative contribution of allochthonous organic matter in the estuary. This study confirmed the efficiency of an integrated biogeochemical approach to establish zones with distinct benthic trophic status associated with different degrees of natural and anthropogenic input. Nevertheless, our results also suggest that the biochemical composition alone could lead to erroneous conclusions in the case of regions that receive enormous amounts of anthropogenic inputs.