Ecosystem health assessment in five shallow tropical waterbodies

Abstract

Ecosystem health of five shallow tropical perennial waterbodies differing in pollution and productivity histories was evaluated by examining chemical parameters of water, biological production, and the Shannon diversity index. Samples of surface water were monitored every two weeks for pH, total hardness, chemical oxygen demand, dissolved oxygen, dissolved organic carbon, different species of nitrogen (ammonium, nitrite and nitrate nitrogen) and phosphorus (soluble reactive phosphate and total phosphorus) during the period of investigation. Net primary production of phytoplankton and abundance of zooplankton were also determined at biweekly intervals. High organic input either through bathing and domestic activities of large number of pilgrims during a 15-day annual fair in pond 2 or discharge of effluents from a brewery in pond 4 resulted in a sharper rise of net primary production than in the moderately manured fish pond (pond 3) or oligotrophic water body (pond 1). Influx of alkali from a gas factory into pond 5 was responsible for low net primary production and zooplankton abundance. The variability of net primary production in these waterbodies was primarily attributable to the variations of different species of phosphorus and nitrogen of surface water. Spatial and seasonal variability of some chemical indices such as chemical oxygen demand, dissolved oxygen and organic carbon concentrations suggested that pond 4 was more stable due to a consistent effluent discharge and pond 2 was less stable because of seasonal anthropogenic activity. The mean values of Shannon index of general diversity of zooplankton remained between 2.1 and 2.41 in pond 2 and showed the diversity pattern as in pond 1 and pond 3, whereas it remained between 1.0 and 2.0 in ponds 4 and 5, which suggested that stable chemical load throughout the year in these ponds resulted in loss of ecosystem health.