ASSESSMENT OF NUTRIENT LOADING AND WATER QUALITY IN A TROPICAL WETLAND

Abstract

Water resources have been associated with the development of human civilization from historical time period. Excessive and improper use of agrochemicals in crop fields and unscientific agricultural activities in catchment area can cause a serious threat in wetland ecosystem. The present study has been done to determine nutrient loading and water quality of surface water in a tropical wetland and suggested applicable management strategies for long term use of wetland. For this purpose, various physico-chemical parameters and heavy metal content in water and sediment samples were investigated spatially and seasonally during the time period of two years. Carlson Trophic status index and Gaardner and Gran method were used to determine trophic status and productivity of wetland respectively. Multivariate statistical techniques, principal component analysis (PCA) /Factor analysis (FA), cluster analysis (CA) were computed to determine relationship between parameters and their influence on water quality with possible contamination sources in wetland respectively. Area distribution within the study area was determined by using polygon feature in google earth map which revealed that permanent green belt persisted throughout the study period with varying water level and vegetation growth in different seasons. A significant variation among physico-chemical parameters, nutrients and heavy metals, was observed seasonally whereas minimum variations were investigated spatially in water and sediments of wetland. Seasonal trend for major pollutants in wetland observed with their decreasing concentration as premonsoon > monsoon > post-monsoon confirming that excessive evaporation from wetland surface will concentrate the water with inorganic salts and nutrients. Contamination from catchment area and backflow water of drain no 8 (in monsoon) notably influences various physico-chemical properties of sediments as well as water in wetland. Also agrochemicals like number of pesticides contribute different types of heavy metals in wetland systems which further declined quality of water and sediments and bioaccumulate in various biotic species within wetland. The growth of submerged vegetation helped in improving water quality by adding photosynthetically-produced oxygen to water and by filtering the suspended impurities. But, the addition of wastewater from adjoining villages and runoff from nearby fields has resulted in increased concentration of nutrients (phosphates and nitrates) and heavy metals in monsoon season. Since these chemical species cause eutrophication and impart toxicity, respectively, the health of ecosystem and aquatic life is affected adversely. Besides preliminary investigation of physico-chemical parameters along with nutrient and vi

heavy metal concentration, distinct approaches were implemented to assess the pollution status of wetland water and sediment in research area. For this purpose, various water quality indices, heavy metal pollution index (HPI); heavy metal evaluation index (HEI); degree of contamination (Cd); and water quality index (WQI) were incorporated to define suitability of water in irrigation and aquatic use. Results obtained during the analysis classified water appropriate for irrigation and aquatic life except the regions adjoined to rural habitation. Various metal pollution indices viz. enrichment factor (EF), contamination factor (CF); degree of contamination (DC), pollution load index (PLI), geo-accumulation index (Igeo), sediment pollution index (SPI) in sediments were analysed to determine degree of contamination along with their sources of origin either natural or anthropogenic. Sediments were found minimum to significantly enriched with Cd, Cr, Zn, Ni, Cu and Pb, heavy metals, indicate their anthropogenic source of origin wherein Cd possessed high geo-accumulation index except all other studied heavy metals. Degree of contamination below total number of studied heavy metals, confirms their decreased contamination in wetland sediments. Based on Sediment Pollution Index, sediments were found low to moderately contaminated with SPI in range between 0 to 2, indicating natural source of origin. Also well defined seasonal changes in primary productivity were observed with increased trend from monsoon to post-monsoon and then pre-monsoon. Carlson Trophic Status Index classified water of Bhindawas wetland in hypereutrophic category. In order to avoid further degradation and declining wetland water quality and to eventually restore the beneficial uses of the wetland, proper management strategies including reduced agro-chemicals (fertilizers and pesticides) use in catchments should be exercised or adopted. Also proper rules and guidelines should be prepared for the trophic status of freshwater bodies in the nation by making bottom-up-down discussion.