CHARACTERIZING PHYSICO-CHEMICAL PROPERTIES OF DEMBI RESERVOIR WATER IN RELATION TO FISH PRODUCTION, SOUTHWEST ETHIOPIA

Abstract

As water regulates fish’s life functions such as feeding, swimming, breeding, digestion, and excretion; the change in water quality and availability due to existing natural or anthropogenic activities can adversely affect its production. Physico-chemical water quality characteristics provide important information about the suitability of water for fish production. Thus, the objective of this study was to determine the physico-chemical characteristics of Dembi reservoir water in relation to fish production. The study was conducted during dry season (February, 2019). Water samples were collected in triplicate from selected 10 sampling stations of the reservoir water using manually prepared water sampler made from polyvinyl chloride (PVC) tube. Depth integrated sampling technique was employed to take water samples for physico-chemical characteristics analysis. From the selected 14 physico-chemical characteristics, four (temperature, electrical conductivity (EC), pH and dissolved oxygen (DO)) were tested onsite using a multi-system HQ4d electronic meter (probe), whereas the rest 10 water quality parameters were tested in the laboratory. The result showed that the current average depth of the dam was 5.6±1.61 m. The overall mean value of turbidity (26.4±0.44 FTU), temperature (26.7±0.36 °C), conductivity (51.0±1.14 μS cm-1), pH (7.7±0.07), DO (4.6±0.12 mg L-1), total hardness (22.2±0.51mg L-1), nitrate (NO3-N) (5.4±0.48 mg L-1), nitrite (NO2-N) (0.3±0.11 mg L-1), ammonia (NH4-N) (2.1±0.06mgL-1), total Phosphorus (3.0±0.16 mg L-1), soluble respective phosphorus (PO4-P) (1.7±0.27mgL-1), total alkalinity (52.5±0.91mgL-1), calcium (4.2±0.11 mg L-1), and BOD5 (2.7±0.24 mg L-1) were recorded at the reservoir water. There was a significant difference (P<0.05) in all physicochemical characteristics among 10 sampling sites of the reservoir water. The recorded values of all physico-chemical characteristics, except NO2-N, NH4-N, and PO4 -3–P, were found within the recommended standard limit for fish production. Nutrient loss and leaching from agriculture land, coffee processing station, municipal solid waste dumping site and residential wastes were responsible for the increase in those characteristics. The change in reservoir water depth and increase in nutrients shows the presence of sediment siltation and nutrient enrichment. Therefore, proper watershed management practices and waste management should be carried out for sustainable water quality maintenance and fish production.