Changes in algal community structure and primary productivity of river ganga as influenced by sewage discharge

摘要

Distribution of algae, phytoplankton density, species diversity, similarity and dissimilarity indices and primary productivity, were studied for the river Ganga at four sites. To assess the effect of city sewage on algal community structure and phytoplankton primary productivity, a control site was also selected upstream, just before the river enters into the city of Varanasi. From the results obtained, it was found, that the discharge of sewage adversely affected algal community structure and phytoplankton productivity. Out of 48 genera and 138 species recorded from different algal groups, the control site (unpolluted) possessed the maximum number of genera (41) and species (119) and the least numbers of genera (26) and species (64) were reportedat the site receiving maximum sewage discharge. Chlamydomonas derenberji, C mirabilis, Hydrodictyon reticullatum, Gomphonema clevei. Anabaena spp. and Nostoc calcicola were dominant pollution tolerant algae recorded during the study. Algal community showed high degree of similarity at control site and site IV (highly polluted) possessed very low value. Usually, higher species diversity and photosynthesis were recorded during the rainy months followed by summer and winter months. The biological characteristics of river water was highly influenced by amount of sewage discharged. Analysis of variance showed the variation in phytoplankton density among the sites and the months was significant (P<0.01). Phytoplankton density and primary productivity were positively correlated (P<0.05).