Ecological Assessment of Freshwater Ecosystem of River Soan and its Tributaries

Abstract

Assessment of freshwaters has been carried out worldwide to determine the ecological health of freshwaters however few attempts have been made in Himalayan region. A bioassessment approach based on fish diversity has been proposed in present study to develop the regional criteria for index of biotic integrity (IBI). A detailed account of spatio temporal dynamics has also been provided for different ecological components of freshwater ecosystem of River Soan, in western Himalaya. Samples were collected at 26 sites during pre and post monsoon seasons in 2008. Water and sediment samples were analyzed for alkalinity, chlorides, orthophosphates, nitrates, ammonia, total phosphorous (TP), total nitrogen (TN), ammonia- nitrogen, sulphates, COD and metals like Ca, Na, Mg, K, Fe, Cu, Cd, Pb, Ni, Cr, and Zn. Sediment samples were also analyzed for organic matter and texture analysis. Different ecological indices like WQI (Water Quality Index), TSI (Trophic State Index), Igeo (Index of Geoaccumulation), and EF (Enrichment Factor) were used to assess water and sediment quality. Pollution sources of different contaminants were identified through Principal Component Analysis (PCA) and source apportionment of these sources was carried out through Absolute principal component scores using multiple regression method (APCS- MLR). Spatio temporal trends in water were analyzed through Discriminant function analysis (DFA). Phytoplankton growth in River Soan was assessed in relation to nutrient enrichment and different hydro-physical factors like temperature, drainage area and velocity of water through regression analysis. Spatio temporal trends in fish assemblage were analyzed through multi response permutation procedures (MRPP) and NMDS (non-metric multidimensional data scaling) ordination technique. An index of biotic integrity (IBI) was developed to assess the ecological health of river. Candidate metrics were analyzed for efficiency to discriminate degraded sites from non-degraded ones and redundancy analysis. Water quality as determined by WQI was found to be relatively least degraded during the pre-monsoon season whereas poor water quality was noted at sewage draining sites. Ni, Pb and Cd concentrations were found to be higher than permissible limits. Spatial variations in water were largely attributed to alkalinity, orthophosphates, nitrates, ammonia, salinity, and Cd while seasonal variations were caused by COD, DO, pH, Cu, Cd, and Cr. Results revealed that heavy metals in water were largely added through industrial activities and sewage wastes, macro elements through urban runoff, mineralization and sewage waste, nutrients through agriculture runoff and sewage waste whereas organic pollution was mainly caused by sewage waste and urban runoff. Trophic conditions of river were classified as eutrophic at upstream, super trophic at midstream and hypertrophic at downstream. Regression analysis identified that drainage area and temperature were the best predictors of phytoplankton biomass. Heavy metals were relatively high in sediments during post monsoon. Different geoaccumulation indices indicated significant to moderate contamination of Cd, Ni, Cu, and Cr in river sediments which were mainly contributed by sewage, agrochemical runoff and industrial activities. Organic matter, sediment pH, weathering of rocks, and particle size played an effective role in distribution of metals in sediments. A total of 22 species were collected during the survey among which Barilius pakistanicus, Puntius ticto, Crossocheilus diplochilus and Labeo dero were distributed throughout the river stretch. Maximum fish diversity was recorded at suburban part of midstream whereas poor diversity was recorded at its urban part. Results revealed that major spatio temporal variations in fish assemblage were caused by thermal gradient and hydrological changes. Proposed IBI was based on five metrics namely total number of fish individuals and the proportions of omnivore individuals (excluding intolerant species), intolerant individuals, herbivore individuals (excluding benthic species) and non-native individuals. Proposed index was able to distinguish varying degrees of human impact on ecological integrity of river and suggested that poor ecological conditions in river were generally related to the drainage of urban sewage and habitat fragmentation. The restoration and effective management of ecological conditions of River Soan is needed to cope with risk caused by deteriorative human processes. Current findings suggest the conservation of physicochemical habitat of aquatic assemblages through implementation of effective waste management measures and restoration of natural flow regimes in the river. Findings of this dissertation will be helpful in future attempts to restore and conserve the ecological integrity of regional flowing water resources. Keywords: Soan River, IBI, heavy metals, sediments, WQI, PEC quotient, fish diversity, geo-accumulation index, enrichment factor, phytoplankton, trophic state index (TSI)