Spatial and seasonal variation of lake water quality: Beseka in the Rift Valley of Oromia region, Ethiopia

摘要

Nowadays, freshwater pollution is an environmental crisis caused mainly by anthropogenic activities. The water quality deterioration of Lake Beseka which is located in the Ethiopian portion of the East African Rift Valley is associated with rapid expansion of that lake that is not fully understood yet. This water quality impairment is the major cause of severe shortage of water supply for human consumption, irrigation use, and public health problems in that area. Hence, this study aimed to investigate the physicochemical and metal concentrations of Lake Beseka and evaluate the impact of the spatio-temporal variation on the water quality. Water samples were collected from six sampling sites during the dry and wet seasons. The concentration ranges for physicochemical parameters evaluated were: temperature (25-40 °C), electrical conductivity (EC) (1407-3321 ps/cm), turbidity (28.5-63.0 NTU), total dissolved solids (TDS) (740-1598 mg/L), pH (7.47-10.86), NO_3~--N (0.30-16.69 mg/L), PO_4~(3-)-P (0.03-13.00 mg/L), SO_4~(2-) (10.00-70.00 mg/L), Cl~- (0.00-200.00 mg/L), F~- (0.40-3.80 mg/L), K (0.30-2.40 mg/L), Mg (0.40-2.46 mg/L), Ca (0.40-3.80 mg/L) and Fe (0.40-3.80 mg/L). For several parameters investigated, the result showed some significant differences (p < 0.05) among the six water samples during both the rainy and dry seasons, except for turbidity, EC, NO_3~--N, PO_4~(3-)-P, SO_4~(2-) and Cl~-. The values of many water quality parameters exceeded the WHO water quality guidelines for drinking water. Furthermore, the water is not suitable for irrigation due to extremely high values of pH (10) and other parameters dominating in salt lakes. This deteriorated water body has the potential to interfere with the natural function of the ecosystem by affecting human health in the area. Hence, to upgrade water quality to meet public health and environmental safety, implementation of suitable water treatment technologies is a crucial agenda to use Beseka lake water.