Diurnal variations in the water quality of sewage polluted Adyar mangrove water, east coast of India

94-97Diurnal fluctuations of physico-chemical factors were studied at 2 h interval over a period of 24 h at a fixed location in the sewage polluted Adyar mangrove waters both when the mouth of the estuary was in closed and open conditions. When the water was stagnant due to sand bar formation, salinity showed no marked diel variations whereas when the mouth was in open condition salinity fluctuated widely with two peaks. When the mouth was closed, dissolved oxygen was below detection limit during the night hours but fluctuated 0.1-8.82 mg.l-1 during day time. Among the dissolved nutrients NH3-N and SiO2-Si showed high values when the mouth open and PO4-P and NO3-N were high when the mouth was closed. Total phosphorus and total nitrogen concentrations were increased when the mouth was open due to storm water inflow and during this period all the nutrients showed clear tidal variations with high values occurring during the low tide and low values during the high tide