Abstract
There is an increased human population along the catchment area of river Rwizi who are engaged in various activities with potential to contaminate river Rwizi especially along the streams. Studies have been done to examine the physico-chemical quality of the mainstream river Rwizi in Mbarara Municipality. However, the comprehensive source of contamination may be beyond the municipality and yet the streams have not been investigated to substantiate their contribution on quality degradation of the river and this formed the basis of the study. This study determined the physico-chemical parameters of streams draining into river Rwizi. Raw water was purposively selected from streams in the upstream, midstream and downstream sections of the river. Water samples were analyzed for 15 physico-chemical parameters including dissolved oxygen (DO), colour, turbidity, total suspended solid (TSS), total iron (Fe), phosphates (PO3-4), alkalinity, magnesium (Mg), calcium carbonate (CaCO3), temperature, pH, ammonium (NH+4), electrical conductivity (EC), chloride (Cl) and nitrates (NO3). The water samples were analyzed following the standard methods of American Public Health Association and standard operating manual (1985). The obtained values were also compared with the international Environmental Protection Agency (EPA, 2001) guidelines for water quality and the National Environment Management Authority (NEMA, 1999) standards for waste water. The results showed that most of the streams in the downstream generally recorded the highest levels (p i.e. bus park stream (temperature, 27.6°C; colour, 431.17 TCU; TSS, 99.33 mg/l; alkalinity, 468.33 mg/l; Mg, 121.89 mg/l; CaCO3, 588.67 mg/l; Cl, 333.33 mg/l), Kikutu stream (turbidity, 123.58 NTU; EC, 698 μs/cm; DO, 55.73 mg/l; PO3-4, 12.85 mg/l), Kakyeka upper (pH, 10.52; NH+4, 46.67 mg/l), Rwentondo (Fe, 3.44 mg/l) and Kakyeka GBK (NO3, 10.83 mg/l). Most of the parameters downstream were higher than the EPA guideline (temperature, 25°C; colour, 20 - 150 TCUs; TSS, 50 mg/l; alkalinity, 400 mg/l; Cl, 250 mg/l; DO, 5 mg/l; PO3-4, 0.5 - 0.7 mg/l; pH, 5.5 - 9.0; NH+4, 0.2 - 4 mg/l; Fe, 0.2 - 2.0 mg/l) and NEMA standards (colour, 300 TCUs; Mg, 100mg/l; DO, 5mg/l; PO3-4, 10 mg/l; pH, 6.0 - 8.0). On the other hand, the streams in the upstream registered the lowest values of the parameters i.e. Kibimba (temperature, 17.28°C; EC, 31 μs/cm; PO3-4, 0.24 mg/l), Kasharara (colour, 15.17 TCU; TSS, 2.5 mg/l; pH, 6.23; alkalinity, 19.67 mg/l; DO, 9.99 mg/l; Mg, 4.41 mg/l; CaCO3, 23.17 mg/l) and Karungu (turbidity, 7.02 mg/l; Fe, 0.12 mg/l). Calcium carbonate hardness of the waters ranged from soft to excessively hard across the stream. The variations of the parameters detected in the streams in the downstream could reach adverse conditions if no intensive measures are taken to regulate the different anthropogenic activities within the catchment of river Rwizi.
Highlights
Safe water and sanitation are services of great concern globally and have been listed as number six among the recently established sustainable development goals (SDG) [1]
The results showed that most of the streams in the downstream generally recorded the highest levels (p < 0.05) of the physico-chemical parameters followed by the midstream and lastly the upstream
Temperature is vital to aquatic organisms because they depend on certain temperature ranges for their optimal health
Summary
Safe water and sanitation are services of great concern globally and have been listed as number six among the recently established sustainable development goals (SDG) [1]. According to World Health Organisation, (WHO) approximately 748 million people, mostly from rural poor settings, cannot access improved water supply sources [2]. The poor communities find themselves with fewer options for water supply including natural tributaries like rivers and streams. Rivers and streams are very susceptible to contamination, because of their shallow aquifers [3] and may not be safe. The water sources are often exposed to contamination from industrial and animal wastes which make them unfit for human and animal health. It is important to carry out a study on the physicochemical composition of river Rwizi and its streams. The interactions of both the physical and chemical properties of water play a significant role in composition, distribution, abundance, movements and diversity of aquatic life forms [4] [5] [6] [7]. Temperature, dissolved oxygen, pH, turbidity, water transparency and current affect riverine fish ecology [8] and fish move away from alkaline waters when pH levels approach 9.06 - 10.0 [9]
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