Performance assessment of six bias correction methods using observed and RCM data at upper Awash basin, Oromia, Ethiopia

Selecting a suitable bias correction method is important to provide reliable inputs for evaluation of climate change impact. Their influence was studied by comparing three discharge outputs from the SWAT model. The result after calibration with original RCM indicate that the raw RCM are heavily biased, and lead to streamflow simulation with large biases (NSE = 0.1, R2 = 0.53, MAE = 5.91 mm/°C, and PBIAS = 0.51). Power transformation and linear scaling methods performed best in correcting the frequency-based indices, while the LS method performed best in terms of the time series-based indices (NSE = 0.87, R2 = 0.78, MAE = 3.14 mm/°C, PBIAS = 0.24) during calibration. Meanwhile, daily translation was underestimating simulated streamflow compared with observed and considered as the least performing method. Precipitation correction method has higher visual influence than temperature, and its performance in streamflow simulations was consistent and significantly considerable. Power transformation and variance scaling showed highly qualified performance compared to others with indicated time series value (NSE = 0.92, R2 = 0.88, MAE = 1.58 mm/°C and PBIAS = 0.12) during calibration and validation of streamflow. Hence, PT and VARI methods were the dominant methods which remove biasness from RCM models at Akaki River basin.

Microbial Risk Assessment of Vegetables Irrigated with Akaki River Water in Addis Ababa.

Background: Consumption of vegetable plays important role in human health. Above 60% of Addis Ababa, vegetable demand is covered by smallholder farmers who grow various vegetables by using the Akaki River as their main water source for irrigation. However, applying faecally contaminated water for irrigation could expose fresh vegetable consumers to many health problems. Therefore, this study aimed to evaluate the microbial contamination of irrigation water and freshly produced vegetables. The study assessed the quality of Akaki river water and vegetables. Fresh vegetables including Ethiopian Kale, Lettuce, Cabbage, and Spinach were collected from 14 farmlands, irrigated with Akaki River water, in the dry and wet seasons. Using standard methods, analysis of E.coli, Non-E.coli, Total coliform, fecal coliform, and Total Aerobic Plate Count were done among the Akaki River water and vegetables. Result: The finding of the study indicated that all fresh vegetables were contaminated with total coliforms, fecal coliforms, and Total aerobic in the dry and wet seasons. The overall mean count of E. coli and Non-E. Coli from water samples were 2.09 and >3.48 log10 CFU 10 mL−1. The mean count of TC, FC, and TAC on sampled vegetables were 3.22, 1.37, and 4.72 in the dry season, and 3.87, 2.57, and 5.09 log10 CFU per gram in the wet season, respectively.Conclusion: The Akaki River has been contaminated with non-E. Coli & E. coli coliforms and did not meet the WHO guideline criteria for safe irrigation. The microbial contamination of vegetables was found high and exceeded the HACCPTQM and ICMSF limit values for safe consumption. This calls for farmers and the consumer has to insist on properly processed/stored/sliced fresh vegetables needs to be aware.

Selection of Optimum Pollution Load Reduction and Water Quality Improvement Approaches Using Scenario Based Water Quality Modeling in Little Akaki River, Ethiopia

The collective impacts of rapid urbanization, poor pollution management practices and insufficient sanitation infrastructure have driven the water quality deterioration in Little Akaki River (LAR), Ethiopia. Water quality modeling using QUAL2Kw was conducted in the LAR aimed at selecting the optimal water quality improvement and pollution load reduction approaches based on the evaluation of five scenarios: modification of point sources (PS) load (S1), modification of nonpoint sources (NPS) load (S2), simultaneous modification of PS and NPS load (S3), application of local oxygenators and fish passages using cascaded rock ramps (S4), and an integrated scenario (S5). Despite the evaluation of S1 resulting in an average load reduction of Biochemical Oxygen Demand (BOD) (17.72%), PO4-P (37.47%), NO3-N (19.63%), the water quality objective (WQO) in LAR could not be attained. Similarly, though significant improvement of pollution load was found by S2 and S3 evaluation, it did not secure the permissible BOD and PO4-P pollution load in the LAR. Besides, as part of an instream measure, a scenario evaluated using the application of rock ramps (S4) resulted in significant reduction of BOD load. All the individual scenarios were not successful and hence an integration of scenarios (S5) was evaluated in LAR that gave a relatively higher pollutant load reduction rate and ultimately was found a better approach to improve pollution loads in the river. In conclusion, pollution load management and control strategy integrally incorporating the use of source-based wastewater treatment, control of diffuse pollution sources through the application of best management practices and the application of instream measures such as the use of cascaded rock ramps could be a feasible approach for better river water quality management, pollution reduction, aquatic life protection and secure sustainable development in the LAR catchment.

Little Akaki River sediment enrichment with heavy metals, pollution load and potential ecological risks in downstream, Central Ethiopia

Addis Ababa City’s river ecosystem is under extreme pressure as a result of inappropriate practices of dumping domestic and industrial wastes; thus, threatening its ability to maintain basic ecological, social and economic functions. Little Akaki River which drains through Addis Ababa City receives inorganic and organic pollutants from various anthropogenic sources. Most of inorganic pollutants such as toxic heavy metals released into the river are eventually adsorbed and settle in the sediment. The objective of this study was to evaluate the enrichment levels, pollution load and ecological risks of selected heavy metals (Zn, Cr, Cd and Pb) using various indices. The mean concentrations of heavy metals in Little Akaki River sediment were: Zn (78.96 ± 0.021–235.2 ± 0.001 mg/kg); Cr (2.19 ± 0.014–440.8 ± 0.003 mg/kg); Cd (2.09 ± 0.001–4.16 ± 0.0001 mg/kg) and Pb (30.92 ± 0.018–596.4 ± 0.066 mg/kg). Enrichment factor values indicated that sediments were moderate to significantly enriched with Zn and Cr; moderate to very highly enriched with Pb, and very highly enriched in all sampled sites with Cd. Geo-accumulation index and contamination factor values indicated that the sediments were moderate to very highly contaminated with toxic Cd and Pb. The decreasing order of pollution load index (PLI) in downstream was: (S9) > (S4) > (S8) > (S3) > (S6) > (S10) > (S5) > (S2) > (S7) > (S1). PLI and hierarchical cluster analysis revealed that the highest pollution load occurred in the lower course of the river (S9) which may be due to metals inputs from anthropogenic sources. The ecological risk (RI = 350.62) suggested that the contaminated Little Akaki River sediment can pose considerable ecological risks of pollution. The concentrations of Zn, Cr, Cd and Pb in Little Akaki River sediment surpassed eco-toxicological guideline limits of USEPA (threshold effect concentration) and CCME (Interim Sediment Quality Guidelines). Thus, the contaminated sediments can pose adverse biological effects on sediment dwelling organisms.

Little Akaki River Sediment Enrichment with Heavy Metals, Pollution Load and Potential Ecological Risks in Downstream, Central Ethiopia

Background: Addis Ababa City’s river ecosystem is under extreme pressure as a result of inappropriate practices of dumping domestic and industrial wastes; thus, threatening its ability to maintain basic ecological, social and economic functions. Little Akaki River which drains through Addis Ababa City receives inorganic and organic pollutants from various anthropogenic sources. Most of inorganic pollutants such as toxic heavy metals released into the river are eventually adsorbed and settle in the sediment. The objective of this study was to evaluate the enrichment levels, pollution load and ecological risks of selected heavy metals (Zn, Cr, Cd and Pb) using various indices.Results: The mean concentrations of heavy metals in Little Akaki River sediment were: Zn (78.96 ± 0.021 - 235.2 ± 0.001mg/kg); Cr (2.19 ± 0.014 - 440.8 ± 0.003 mg/kg); Cd (2.09 ± 0.001-4.16 ± 0.0001mg/kg) and Pb (30.92 ± 0.018 -596.4 ± 0.066 mg/kg). Enrichment factor values indicated that sediments were moderate to significantly enriched with Zn and Cr; moderate to very highly enriched with Pb, and very highly enriched in all sampled sites with Cd. Geo-accumulation index and contamination factor values indicated that the sediments were moderate to very highly contaminated with toxic Cd and Pb. The decreasing order of pollution load index (PLI) in downstream was: (S9) > (S4) > (S8) > (S3)> (S6) > (S10) > (S5) > (S2)> (S7) > (S1). PLI and hierarchical cluster analysis revealed that the highest pollution load occurred in the lower course of the river (S9) which may be due to metals inputs from anthropogenic sources. The ecological risk (RI =350.62) suggested that the contaminated Little Akaki River sediment can pose considerable ecological risks of pollution.Conclusions: The concentrations of Zn, Cr, Cd and Pb in Little Akaki River sediment surpassed eco-toxicological guideline limits of USEPA (threshold effect concentration) and CCME (Interim Sediment Quality Guidelines). Thus, the contaminated sediments can pose adverse biological effects on sediment dwelling organisms.

Little Akaki River Sediment Enrichment with Heavy Metals, Pollution Load and Potential Ecological Risks in Downstream, Central Ethiopia

Background: The Addis Ababa City’s river ecosystem is under extreme pressure as a result of inappropriate practices of dumping domestic and industrial wastes; thus, threatening its ability to maintain basic ecological, social and economic functions. Little Akaki River which drains through Addis Ababa City receives inorganic and organic pollutants from various anthropogenic sources. Most of inorganic pollutants such as toxic heavy metals relased into the river are eventually adsorbed and settled in the sediment. The objective of this study was to evaluate the enrichment levels, pollution load and ecological risks of selected heavy metals ( Zn, Cr, Cd and Pb) using various indices .Results: The mean concentrations of heavy metals in Little Akaki River sediment were: Zn (78.96±0.021 - 235.2 ±0.001mg / kg); Cr (2.19±0.014 - 440.8±0.003 mg / kg); Cd (2.09±0.001-4.16 ±0.0001mg / kg) and Pb (30.92±0.018 -596.4±0.066 mg / kg). Enrichment factor values indicated that sediments were moderate to significant enrichment with Zn and Cr; moderate to very high enrichment with Pb, and very high enrichment in all sampled sites with Cd. Geo-accumulation index and contamination factor values indicated that the sediments were moderate to very high contamination with toxic Cd and Pb. The decreasing order of pollution load index (PLI) in downstream was: (S9) > (S4) > (S8) > (S3)> (S6) > (S10) > (S5) > (S2)> (S7) > (S1). PLI and hierarchal cluster analysis revealed that highest pollution load occurred in the lower course of the river (S9) which may be due to metals inputs from anthropogenic sources; hence, its quality was deteriorated showing that the site is polluted. The ecological risk (RI =350.62) suggested that the contaminated Little Akaki River (LAR) sediment can pose considerable ecological risks of pollution.Conclusions: The concentrations of Zn, Cr, Cd and Pb in Little Akaki River sediment surpassed eco-toxicological guideline limits of USEPA (threshold effect concentration) and CCME (Interim Sediment Quality Guidelines). Thus, the contaminated sediments can occasionally pose adverse biological effects on sediment dwelling organisms. Thus, measures must be taken to regulate discharge of untreated wastes into river and surrounding environment.