Nutrient Distribution and Bioavailability in a Tropical Microtidal Estuary, Southwest India

ABSTRACT Renjith, K.R.; Joseph, M.M.; Ratheesh Kumar, C.S.; Manju, M.N., and Chandramohanakumar, N., 2016. Nutrient distribution and bioavailability in a tropical microtidal estuary, southwest India. This study estimates the spatial and seasonal variations of phosphorus and nitrogen fractions in the surface sediments of Cochin Estuary to assess their bioavailability and the factors governing biogeochemical distribution. Seasonal variations of the dissolved nutrients suggest that phosphorous buffering activity is very high in the estuary, and there could be a nitrogen limitation in the absence of any external input. Iron-bound and calcium-bound inorganic fractions were the major forms of sedimentary phosphorus in the central estuary. Upstream regions were characterised by higher proportions of organic phosphorus, mainly as alkali-soluble fractions. Bioavailable fractions ranged from 2.61% to 90.43% of total phosphorus and show a significant increase during the lean pre-monsoon period. This increase, which ...