Dissolved inorganic nutrients, organic matter and stable nitrogen isotopes as indicators of human impact in two contrasting estuaries in West Bengal, India, during winter monsoon

Abstract

The present study consists of the analyses of dissolved inorganic nutrients (NH4 , NO3 , NO2 , PO4 , Si(OH)4), dissolved organic nitrogen (DON), particulate nitrogen, particulate organic carbon, amino acids and δ15N of particulate nitrogen and NO - from Hooghly and Matla estuary. Hooghly estuary was sampled at 2 stations, at Kolkata and ca. 60 km downstream. Mangrove 3-

dominated Matla estuary was investigated along a N-S transect. Dissolved inorganic nitrogen, PO4

and DON concentrations

were low, especially for the Hooghly site at Kolkata. Human influence, however, was revealed by the more labile nature and elevated concentrations of amino acids in Kolkata. Release of nutrients from particulate matter during estuarine transport

resulted in higher NO -

and PO 3-

concentrations downstream Kolkata. In Matla estuary no human influence was detected and

nitrogen fixation was observed.