Abstract

study was conducted to understand the intra- and inter-seasonal variability of dissolved oxygen and
nutrients inatropical monsoon estuary (Zuariin Goa, India). We adopted a dual sampling approach with
(a) daily or alternate day sampling at a fixed location in the mid-estuarine zone and (b) longitudinal
transect sampling from fresh water end to mouth during spring and neap tides of each month for about a
year. Multivariate statistical analyses of oxygen and nutrients were carried out to evaluate the
hypotheses: (i) biogeochemical processes chiefly regulate their variability and (ii) anthropogenic inputs
lead to material accumulation in the estuary. Multivariate statistical analyses helped identify the
controlling factors of the oxygen and nutrient variability. Our results significantly revealed (i) physical
forcings (freshwater discharge and tidal circulation, the seals of a cilitate sedimentary releases) are more
important than biogeochemical processes in determining oxygen and nutrient variability in the water
column and (ii) the monsoon driven regular annual flushing makes the system resilient to human
interference as the Zuari estuary returns to normalcy by post monsoon every year. Our study identified
the significance of subsurface discharges in transporting mining effluents from the river basin. Results
also suggest that extrapolation of controlling factors of biogeochemical variables at a fixed location to the
entire estuary is untenable since the relative dominance of forcings vary in time and space in the estuary.