Seasonal Water Quality Changes in Reservoirs in Different Climatic Regions of Sri Lanka

Abstract

The current study investigates the patterns of the changes of the physicochemical characteristics in 58 relatively shallow, eutrophic reservoirs of Sri Lanka during the wet (rainy) and dry seasons. These reservoirs range in values of specific conductance from 17 to over, 920 μS/cm during the dry season and 16 to over, 630 μS/cm during the wet season and can also be described as slightly alkaline, eutrophic systems. The reservoirs examined are located in four climatic regions [Arid, Dry, Galoya Basin (dry zone), Intermediate, and Highland Wet zones] of Sri Lanka that vary according to, for example, patterns of precipitation, evaporation and seasonality. Results of the study clearly indicate that the specific conductance and related variables reflect the patterns in precipitation and evapoconcentration. The highest specific conductance values are found in the Arid and Dry Zones (average concentrations of 586 and 274 μS cm-1) during the dry season, and are sequentially lower in the Intermediate and Highland Wet zones. Interestingly, reservoirs in the Gal-Oya basin (Dry Zone) also record low specific conductance with the average values 81 and 58 μS cm-1 during both dry and wet seasons. The average dissolved oxygen was higher during the dry season in all the regions except in Highland Wet Zone. The concentration and gradient of important nutrients (e.g. ammonia-N, total phosphorus and dissolved phosphorus) show marked variation during wet and dry seasons having higher values especially during the wet season. Pearson correlation analysis shows that a concentration of total phosphorus is strongly related to chlorophyll a confirming the phosphorus is the limiting factor for algal growth within the study reservoirs