Assessment of the Impact of Industrial Effluents on the Quality of Irrigation Water and Changes on Soil Characteristics (a Case of Kombolcha Town)

With the ever increasing demand on irrigation water supply, farmlands are frequently faced with utilization of poor quality irrigation water. In many parts of Ethiopia, wastewater, which are disposed to wells, ponds, streams and treatment plants, are used as a source of irrigation water as well as for drinking (Alemtsehaye, 2002). But, the continued application of poor quality irrigation water can reduce the yield of farmlands. Water quality for agricultural purpose is determined on the basis of the effect of water on the quality and the yield of the crops, as well as, the effect on the characteristic changes in the soil (FAO, 1985). The most commonly encountered soil problems used as a basis to evaluate water quality are those related to the salinity, water infiltration rate, toxicity and a group of other miscellaneous problems (Richardson, 1954; Wilcox, 1966).

Kombolcha is one of the few towns in Ethiopia with a relative greater number of large-scale manufacturing plants including Textile Factory, ELFORA-Meat Processing Factory, Tannery, BGI-Brewery Factory, Steel Product Industry and Flour Factory. On top of this, the town is selected to be an industrial town by Amhara National Regional State of Ethiopia, which indicates the industrial development and its associated pollution risk will increase in the future. The existing industries have been discharging their wastes into the surrounding environment, in particular to the near by river. According to the local woreda agriculture office, more than 25,000 farmers are diverting the effluent contaminated rivers water to irrigate about 2695 ha of farmlands in order to grow different crops including cereals, vegetables and fruits (Kalu Woreda Agricultural Office, 2006). In addition, the latest report from the local agricultural administration office explains that despite the fact that many farmers and enterprises have used the local rivers for irrigation since long time ago; no study has been conducted yet on the chemistry of the polluted river water for its irrigation suitability (Kalu Woreda Agricultural office, 2007). In Kombolcha, perhaps the most important factor in predicting and managing farmland soil is the quality of irrigation water being used.

The main intention of the study is to provide concrete information on the magnitude of the industrial liquid wastes and help farmers and policy makers to take the necessary corrective measures on time. The impact of industrial liquid wastes on the irrigation water quality  was assessed  by examining  the concentrations of Na+, Ca2+, Mg2+, BO3-3, CO3=, HCO3-, Cl- and values of pH and SAR in the polluted irrigation rivers water through laboratory analysis. Soil samples were also taken to assess the quality of the irrigation water effect on the irrigated farm soils properties.

MATERIAL AND METHODS

פרסום

Location of Study Area

The study area is found in the town of Kombolcha which is located on the north central part of Ethiopia placed immediately south east of Dessie in the Amahara region at 11o06’ north latitude and 39o45’ east longitude. River Borkena crosses the town emerging from the east and running to the west direction. In its way all through the town, it receives effluents indirectly through its tributaries rivers named Worka and Leyole. Most of the factories are found closely together in the middle of the town near by the tributary rivers of Borkena.

פרסום

Methods Samples of irrigation water and farmland soils were collected in three phases with in the irrigation period of the study area. Acceptable standard methods and instrumentations were followed during sample collection procedures. Sampling site selection: Based on the outlining of the irrigation sites and waste disposal points, three areas were selected to take water and soil samples viz a farmland at the above the effluent points (control) which was irrigated by effluent free (freshwater of River Borkena) water and two farmlands below the effluent points which were irrigated by effluent contaminated rivers water (River Leyole and River Worka). The mean values of the parameters in the control fresh irrigation water source and the effluent contaminated water of the other water sources were compared with the widely accepted standards set by FAO. The soil samples of the respective irrigated farmlands were also considered to assess the extent of the impacts of the effluent contaminated irrigation water on the characteristics the soils. The chemical parameters that have been measured in the diverted irrigation water were also determined from the soil samples of the selected irrigated farmlands. Both surface and subsurface soil samples were taken once from the fresh water irrigated farmland (control or background) at the upper and three times from the effluent mixed irrigated farmlands at the lower of the effluent points through out the irrigation period of the study area. TDS, ESP and SAR were computed following the formulas stated in FAO soil bulletin 42. Chlorides, nitrogen-nitrate, sulfate, chromium and some samples of phosphate were found to be below the detection limit in the first phase samples analyses.

Water samples: 9 water samples were taken from January 2007 to June 2007. The sampling frequency was in three phases throughout the irrigation season. In first pha

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