Trophic status of Vondo and Albasini Dams; impacts on aquatic ecosystems and drinking water

The presence and levels of major nutrients in the water from Vondo and Albasini Dams and their water treatment plants have been assessed to determine trophic status of the dams and impacts on aquatic ecosystems and drinking water. Water quality parameters particularly phosphates and nitrates are critical in assessing the trophic status. Water quality parameters linked to eutrophication and agrochemicals were analyzed. Phosphate was undetectable in both dams. The nitrate levels in Albasini and Vondo Dams which were from 1.16 to 6.65 mg/L and 0.46 to 4.19 mg/L, respectively, were within and above the South African guideline for aquatic ecosystems of 2 mg/L. The raw water pH for Vondo and Albasini Dams were from 6.20 to 7.46 and 6.35 to 8.70, respectively, and were mostly within acceptable guidelines for aquatic ecosystems. The water transparency for Vondo and Albasini Dams were from 0.5 to 4.2 m and 0.4 to 0.9 m, respectively. The levels of all other water quality parameters investigated in both dams and their WTPs mostly indicate low, rarely high and no water quality problems in aquatic ecosystems and drinking water. The low levels of total suspended solids and water transparency, the pH range, low to high electrical conductivity, low to acceptable dissolved oxygen levels, acceptable to high biological oxygen demand and nitrate levels for both dams indicate oligotrophic to eutrophic states. Though oligotrophic state dominates, the mixture of trophic states has been attributed to increase in urbanization and intensive agriculture.

Keywords
Eutrophication; Oligotrophic and Eutrophic states; Physico-Chemical parameters; Water transparency