Factors controlling organic matter composition and trophic state in seven tropical estuaries along the west coast of India.

To understand the organic matter (OM) sources and trophic states, spatial and seasonal (post-monsoon and pre-monsoon) variation in sedimentary OM compositions was investigated in seven tropical estuaries of the state of Maharashtra along the central west coast of India. Based on the result of cluster analysis, estuaries were segregated into two distinct groups: Northern Maharashtra and Southern Maharashtra owing to dissimilarity in OM characteristics potentially constrained by geomorphology and catchment properties. Enrichment of C and major biochemical compounds (lipids, carbohydrates and proteins) in the middle zone of most estuaries highlighted towards the addition of allochthonous OM. Results of principal component analysis highlighted the similar source of OM in most of the estuaries during both seasons and their distribution largely constrained by grain size change. The benthic trophic state indicated the prevalence of eutrophic state in the middle zone of the investigated estuaries, which may be sporadic and dependent upon anthropogenic activities in the study area.