Review on the Water Quality Status of Lake Hawassa, Central Rift Valley Lakes, Ethiopia

Water Quality Characteristics of Lake Hawassa

Large amounts of sewage and industrial effluent dumped into the lake as a result of population growth, industry, and urbanization have considerably added to the lake’s pollution [13]. We suggested several papers for investigation to a number of technical publications on water quality for a lake called Hawassa that have been presented at the research level. According to Melaku H, et al. [12] the concentration of metals of lake Hawassa was manganese (0.83 mg/L), Z (5.75 mg/L), Cr (0.22 mg/L), PO43- (1.31 mg/L), and BOD 5 (BOD5, 68.7 mg/L) exceeded WHO standard that could be due to point sources pollution from ceramics, textile, plastics, leather tanning, and food processing industries located near the rivers and streams that end up into the lake. According to Worako W [5], the Tikurwuha River Inlet has the highest average concentrations of Zn (0.317 mg/L), Fe (0.18 mg/L), Copper (0.046 mg/L), and Mn (0.489 mg/L) (Tables 1-3).

Compared to the ocean or sea and rivers, lakes are particularly vulnerable to pollution because of their size and proximity to the community. Lake Hawassa is threatened by a variety of point and non-point pollution sources, including land development, urban storm water runoff, agricultural runoff, and industrial waste from the ceramics, dye, plastics, and food processing industries. Additionally, according to Worako W [5], the lake in Hawassa was unfit for domestic use or drinking without treatment. These were caused by the water’s severe impairment, which included bacteriological indicators including Total coliform (11 883 MPN/100 mL) and Fecal coliform (99.69 MPN/100 mL) that were over WHO, USEPA, and EU recommended standard values for F (12.8 mg/L), Na (331.14 mg/L), BOD (117 mg/L), COD (48.73 mg/l), and K (70 mg/l). The elevated concentrations of bacteriological parameters and low clarity of the lake make it unsuitable for recreational uses. In general, Worako W [5] concludes that the lake water is highly contaminated and may not fit for drinking and recreational uses but with some great care it is good for irrigation and aquatic life. Melaku H, et al. [12] quantified that the concentration of metals such as manganese, zinc, chromium, and nutrients like phosphate, BOD5 was found above the recommended WHO standard for drinking purposes and this could hurt aquatic life and humans and animals that use the lake water for various purposes. Elevated levels of these metals and nutrients could be due to point source pollution from ceramics, textile, plastics, leather tanning, and food processing industries located near the rivers and streams that end up into the lake. Menberu Z, et al. [10] used three water quality index methods to see the quality of Lake Hawassa, such as weighted Arithmetic index (WAWQI), Canadian Council of Ministers

of the Environment water quality index (CCME WQI), and Bascarón water quality index, were used to compare the water quality of the Lake Hawassa. Found as the Hawassa Lake water quality was poor as per the weighted arithmetic and modified Bascarón methods. They conclude that the lake required mitigation measures to control Eutrophication and pollutants inflow. The lake was under the hypertrophic stage as per the standard based on the results of Secchi depth and nutrient concentration. The current study showed the lake being unfit for all purposes as per the WAWQI range (> 100). According to the physicochemical and biological parameters, of the lake, it requires mitigation measures to control Eutrophication and pollutants inflow [10]. Agumassie T [14] stated that the effluent contains severe toxic organic and inorganic compounds and this, in turn, can damage the aquatic biota including fishes. Based on the report of Lake Hawassa textile factory, the effluent contains high COD (3 times higher), and TDS (19 times higher); moreover, PO3- 4 (39 times higher) was recorded in the textile effluent compared to the maximum permissible limit standardized by the Environmental Protection Agency.

Spatio-Temporal Variation

An increasing temporal trend was observed for Heavy metals Fe, K, Mg, Cr, Zn, and Cu. Whereas; Cu and Zn contents were above the recommended limits used only aquatic life. However, According to Worako W [5] except Mn, Cu, and Zn other metals such as Cd, Cr, Pb and Ni are within the permissible limits to all designated water uses. The concentration of heavy metals in the lake was relatively high at the Inlet of Tikurwuha River due to point sources of pollution from Hawassa textile factory and other factories which discharge their waste directly into this river. The concentration of metals such as manganese, zinc, chromium, and nutrients like phosphate, BOD5 was found above the recommended WHO standard for drinking purposes and this could hurt aquatic life and humans and animals that use the lake water for the various purposes [12]. Abebe Y, et al. [15] identified three saltation zones the northern, eastern, and western parts of the lake Hawassa bed representing their respective parts of the lake watershed. These zones were most probably linked with the anthropogenic factors of farming and urban development contributing to the lake’s morphometric dynamics.

The pH level was somewhat acidic (5.85) and below the (WHO, 2004) guidelines at the SLW5 (Fikir Hayik Marsh) sampling location (stagnant water near the lake). Turbidity of the lake water was higher than (WHO, 2004) standard for drinking purposes. This may be attributed to the dissolution of carbon dioxide and nutrients created by bacterial decomposition of food waste and sewage waste around the lake. The highest value of turbidity was also recorded at SLW5 (177 ± 3.21 NTUs) followed Melaku H, et al. 2 [12]. Lower values of TDS below the WHO (2004) limits were observed at the SLW5 sampling site and could be due to the dilution effect from the inflow of water during the sampling periods of a small rainy season. A high concentration of sulfate at the SLW4 (Fikir Hayik) sampling site could be related to the discharge of sulfate-containing municipal sewage and surface runoff that contain organic fertilizers from agricultural activities or due to the variability of the distribution of soluble sulfate salts in the sampling sites. The lowest nitrate concentration was recorded at SLW5 Fikir Hayik Marsh) (2.83 ± 0.03mg/L) mg/L) sampling site showing that the sampling site was relatively less polluted by nitrogenous materials.

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According to Adimasu WW [16] in all sampled sites the value of K+ was beyond the permissible limits for drinking and irrigation water use WHO. An elevation of potassium in the lake indicates the effect of hospital effluents, septic system effluents, and other anthropogenic activities besides the natural sources. Water quality of the lake was highly impaired on the town side of Hawassa that’s due to inlets of various factories effluents like Hawassa textile factory, sisal factory, soft drink factory, ceramic factory, and sewage as well as regional Hawassa referral hospital effluents. The lake is affected by both point and non-point sources of pollution besides the natural factors. Lencha SM, et al. [11] found the average pH value of the Lake Hawassa is 8.5 for this study and comparative observations were made in Lake Hawassa with previous studies and showed an increment from the results of Worako W [5]. The increased pH values are mainly due to the consumption of dissolved carbon dioxide by the autotrophic biomass in the upper layer of the eutrophic lake. The most heavily polluted site was MS10 (Fikerhayk recreation center), MS7 (Amora-Gedel), and MS8 (Gudumale) where there are hotels, restaurants, cafés, boating activities, maximum human intervention, and also there was a small fish market around that site Lencha SM, et al. [11] (Figure 2).

The findings revealed that the water quality of rivers in the upper catchment namely Wesha, Hallo, Wedessa, and Tikur-Wuha (middle part), and Lake Hawassa was generally unsuitable for drinking, aquatic life, and recreational purposes. However, the rivers possessed excellent water quality and Lake Hawassa water quality was good for irrigation purposes. Therefore, the cumulative result of WA WQI for drinking, aquatic life, and recreational uses showed that the environmental situation has become worse in the last few decades, Hence, Lake Hawassa watershed has been polluted and frequent monitoring of the watershed is necessary for proper management. The findings Lencha SM, et al. [11] announced that the lake is suffering from various deficits, high nutrient concentrations, ammonia toxicity and oxygen depletion. The high COD and BOD values are partly due to direct emissions but also to the growth of organic matter in the lake water. Its degradation leads to reduced DO levels or even anaerobic conditions in deeper layers.