Physico-Chemical Quality of Lake Kyoga at Selected Landing Sites and Anthropogenic Activities

摘要

Lake Kyoga, one of the great African lakes in Uganda is facing an increasing pressure from human activities yet there is limited information on water quality of the lake. Therefore this study determined selected physico-chemical parameters of Lake Kyoga at some landing sites (Kayei, Acholi inn, Waitumba, Masindi port) and anthropogenic activities (boat dock, waste site, garden, fishing). The parameters included temperature, pH, water flow rate, dissolved oxygen (DO), nitrite (NO_2~-) and phosphate (PO_4-P). The American Public Health Association (APHA) and Water Watch Australia protocols, standard meters, Merck's rapid test kits and timing of a float were used to measure the parameters. The results showed that the mean temperature, pH, DO, NO_2~- and PO_4-P significantly (p < 0.05) varied across the anthropogenic activities. On the other hand, only temperature, pH and flow rate varied significantly (p < 0.05) across the landing sites. Lake Kyoga water flow rates were the fastest at Masindi port (0.031 m/s) and the least in Waitumba (0.021 m/s) governed by river inflow and surface vegetation cover. The mean pH (6.73 - 7.15) and DO (10.15 - 13.50 mg/l) of the lake at all the study sites were within the Environmental Protection Agency (EPA) standard values of 5.5 - 8.5 and >9.0 mg/l respectively. These mean pH and DO values reflect more or less neutral waters which are equally well saturated with oxygen at all the landing sites. However, areas close to the waste sites had the least oxygen levels (10.15 mg/l) followed by gardens (11.82 mg/l) while fishing areas were the most saturated with oxygen (13.50 mg/l). On the other hand, temperature (25.06℃ - 25.76℃) and NO_2~- (0.13 - 0.49 mg/l) levels in the study sites were above EPA standards of 25 ℃ and <0.03 mg/l respectively signifying warmer waters and sewage pollution at the sites. Fortunately, the NO_2~- levels were within the EPA drinking water guideline of 0.5 mg/l. The orthophosphates (PO_4-P) were high- est in the waste sites (0.35 mg/l), followed by gardens (0.24 mg/l) and least in the fishing areas (0.12 mg/l). However, phosphates in the form of P_2O_5were higher than the EPA standard value (0.5 mg/l) at Kayei (0.55 mg/l) and Acholi inn (0.55 mg/l) landing sites as well as at waste sites (0.80 mg/l) and gardens (0.55 mg/l) pointing to high nutrient (phosphorus) input at these sites. The high concentrations of nitrites in Lake Kyoga at the investigated anthropogenic activities and landing sites plus phosphate amounts close to waste sites and gardens including Kayei and Acholi inn landing sites call for vigilance in protection of Lake Kyoga through optimized planning. Hence, National Environment Management Authority should ensure proper sewage management in Lake Kyoga catchment to avoid discharge of untreated sewage into the lake. The authority should also regulate waste dumping and cultivation around the lake so as to reduce nutrient (phosphorus) enrichment.