Impact of jute retting on physicochemical profile of Chhariganga oxbow lake in Nadia district, West Bengal, India

Abstract

The present study was carried out to assess the ecosystem of the Chhariganga, an oxbow lake in eastern India to assess the pollution due to jute retting and trophic status on broader aspects for its sustainable management. The physicochemical analyses of the studied oxbow lake showed the range with annual mean values of surface water temperature in ºC (11-37, 27.64±6.56), water transparency in cm (16-106, 45.82±23.39), water pH (7.4-8.8, 8.17±0.34), DO (2.60-7.85, 4.65±1.52 ppm), BOD (1.10-6.40, 2.98±1.59ppm), COD (70-90, 79±7.38ppm), NH₄-N (0.026-0.093, 0.05±0.02ppm), NO₂-N (0.008-0.08, 0.03±0.02ppm), NO₃-N (0-2.459, 0.81±0.69ppm), OP (0.067-0.62, 0.26±0.18ppm), total alkalinity (82-165, 120±24.03ppm), total hardness (70-138, 102.62±19.60ppm), GPP (0.30-1.80, 1.25± 0.47mgC/l/day), NPP (0.15-1.38, 0.95± 0.40mgC/l/day); sediment pH (6.8-7.9, 7.53±0.34) and sediment organic carbon in % (1.87-2.89, 2.17±0.28). The highest mean values of BOD (4.59ppm), COD (86.67ppm), OP (0.50ppm), sediment organic carbon (2.29%) were observed during monsoon whereas the lowest values of oxbow lake water’s transparency (27.00cm), pH (7.84), DO (3.63ppm) and NO₂–N (0.01 ppm) contents were found during monsoon when jute retting process intensified in the oxbow lake. Compared to their values in pre-monsoon, mean values in monsoon showed an increase in BOD (182.57%) and OP content (167.64%) unlike reduction in water transparency (62.54%), GPP and NPP (both reduced by about 50%); The highest concentration of NH₄-N and NO₃-N were noticed during post-monsoon and OP during monsoon. The water transparency mean values showed sharp fall during monsoon from pre-monsoon. Physico-chemical analyses revealed that almost all parameters in oxbow lake did not show significant changes throughout the year unlike water transparency, BOD_, NO₂ and especially OP content of water which otherwise showed significant changes throughout the year.  The present semi-closed oxbow lake water was of poor to moderate quality and it was classified as oligo-mesotrophic in nutrient status with high to moderate organic pollution due to jute retting process which needs to be controlled and regulated for sustainable aquaculture in oxbow lake ecosystem.