NUTRIENT Fluxes And Adaptation To Environmental Dynamics By Phytoplankton In The Gulf Of Khambhat

Environmental dynamics with a view of understanding the nutrient fluxes and the factors regulating phytoplankton production, in waters off Bhavnagar, Gulf of Khambhat, were investigated during 1996-2007. The coastal waters of Bhavnagar revealed normal pH (7.97±0.12) and enhanced DO (4.81±1.47 ml/l) level. The fluctuation of salinity (29.7 ± 4.21 ppt) was due to freshwater influx through several rivers. The coastal water of Bhavnagar was characterized with poor concentration of chlorophyll a (0.76±0.34 mg/m3), high phaeophytin (1.24±0.68 mg/m3), poor species diversity of phytoplankton (0.693-1.495, av. 0.749), high SS concentration (1502.58±1038.62 mg/l) and poor irradiance (secchi depth, mean 0.11 cm), with high concentration of NO3--N (32.52 ± 12.37 mmol/l), NO2--N (2.38 ± 4.12 mmol/l), NH4+-N (2.33 ± 4.43 mmol/l) and PO43--P (9.04 ± 10.37 mmol/l). The positive significant correlation between SS and NO3--N (r=0.443, p=0.000), NO2--N (r=0.302, p=0.010) and NH4+-N (r=0.229, p=0.055) indicated that the strong currents churning out the bed sediments and eroding the shoreline and inputs through several rivers draining into the Gulf, were sources of nutrient fluxes and an enhanced concentration in the region. The presence of Thalassiosira gravida and Navicula distans continuously and Cylindrotheca closterium sometime as the major species in the coastal waters of Bhavnagar over the period of 11 years suggested their adaptation to the environmental condition of the region. Thus, the high concentration of suspended solids was the regulating factor for phytoplankton production.