Role of environmental factors on nitrogen fixation rate in a tropical estuary (southwest coast of India)

Abstract

Nitrogen fixation is one of the key biogeochemical processes that regulate the availability of biologically active nitrogen to the natural environments; however, ecological control of this process is still unknown. This study reports the variations of N2 fixation rate in the water and sediment environments of an estuary (southwest coast, India) as a function of environmental factors controlling this process. The N2 fixation rate was measured in-situ in the surface water and sediments by acetylene reduction assay. The N2 fixation rate was relatively high in surface water (1.07 ± 0.54 nmol N L−1 h−1) than in the sediment environment (0.27 ± 0.13 nmol N g−1 h−1) and showed spatial variation. A significant seasonal disparity in the fixation rate was elucidated in water and sediment environments (P<0.01). Further, the results demonstrate that, rate of N2 fixation correlated positively with pH (p<0.05), dissolved inorganic phosphate (p<0.05) and temperature (p<0.01), while negatively correlated with dissolved oxygen (p<0.01), dissolved inorganic nitrogen (p<0.05) and nitrogen: phosphorous ratio (p<0.05). These data emphasizes the significance of environmental factors affecting on N2 fixation process on anthropogenically disturbed aquatic ecosystem.