Ecological changes in the Hooghly Estuary due to water release from Farakka Barrage

A.C. Nandy, M.M. Bagchi, S.K. Majumder

Abstract



Observations on the ecological changes of the Hooghly Estuary, West Bengal, India were made for a period of two years from May 1975 to April 1977 to study the effects of freshwater release from Farakka Barrage into the system. The ecology of the Hooghly Estuary has undergone a major change after the commissioning of the Farakka Barrage on the Ganga. Additional freshwaters to the Hooghly were discharged by the Barrage on the 21st April 1975 as a low rate which raised the freshwater flow into the Hooghly estuary and changed the ecology of the system significantly. All over the estuary, the drops in salinity have been significant. The earlier recognized gradient zone has largely become the freshwater zone while the marine zone has become largely gradient zone. The physico-chemical parameters like total suspended solids, pH, total alkalinity, silicate, phosphate, and nitrate have been described. With the lowering of the estuarine salinity and increased fresh water flow, the general habitat of the biological population considerably improved. The planktonic population has shown significant improvement and the density has increased 3-5 times in different zones of the Hooghly estuarine system during 1975-77 as compared to those reported before the Farakka discharges. Some of the typically euryhaline species had shown a decline trend in the upper and gradient zone. The total landings as well as species composition in marine zone of the estuary did not show any significant changes

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