Browsing by Author "Machiwa, John"

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    Spatial and temporal variations of trophic state conditions of Lake Bunyonyi, south‑western Uganda
    (Applied Water Science, 2023) Saturday, Alex; Lyimo, Thomas J.; Machiwa, John; Pamba, Siajali
    The study was conducted to assess the spatial and temporal variations of the trophic state condition of Lake Bunyonyi between October 2019 and September 2020. Secchi depth (SD), total phosphorus (TP) and chlorophyll-a (Chl-a) concentration were measured to aid the quantification of trophic state condition of the lake using Carlson trophic state index (CTSI). The trophic state index (TSI) values based on SD, TP and Chl-a values were 60.82 ± 5.35, 68.99 ± 11.04 and 61.74 ± 7.51, respectively. March 2020 recorded the highest mean CSTI value (70.14 ± 4.04), while in September 2020, the lowest mean value (58.03 ± 6.22) was obtained. Based on CTSI values, the lake was eutrophic in both dry and wet seasons albeit with differences in the values. The eutrophic state of the lake is possibly attributed to nutrients inflow into the lake via runoff and drainage from farmlands. The negative value of TSI-Chl-a–TSI-TP deviation pointed out that the lake is not phosphorus limited, while the positive TSI-Chl-a–TSI-SD mean deviation value revealed the effect of Chl-a and TP on the lake’s transparency. The study recommends the necessity to develop guidelines for the trophic status monitoring of Lake Bunyonyi since results suggest the deteriorating lake condition.
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    Spatio‑temporal variations in physicochemical water quality parameters of Lake Bunyonyi, Southwestern Uganda
    (SN Applied Sciences, 2021) Alex, Saturday; Lyimo, Thomas J.; Machiwa, John; Siajali, Pamba
    The current study was carried out to examine the spatial and temporal variations of physicochemical water quality parameters of Lake Bunyonyi. The observations were made on the surface water of Lake Bunyonyi for 1 year to determine the water quality. The basic 12 variables used to determine the quality of water were measured monthly at nine stations. Water temperature, dissolved oxygen (DO), turbidity, electric conductivity (EC), pH and Secchi depth (SD) were measured in the field, while parameters like total nitrogen (TN), total phosphorus (TP), nitrite-nitrogen (NO2-N), nitrate-nitrogen (NO3-N), soluble reactive phosphorus (SRP) were determined following APHA 2017 standard guidelines for physicochemical analysis. Taking into account standard guidelines for drinking water by the Uganda National Bureau of Standards (UNBS) and the World Health Organization (WHO), the water quality index (WQI) was used to determine the water quality. Temperature, DO, pH, turbidity and EC did not differ significantly among the study stations (p > 0.05) but showed significant temporal variations among the study months (p < 0.05). Likewise, TN, TP, NO2-N, NO3-N and SRP did not differ significantly among the study stations (p > 0.05) but showed significant temporal variations among the study months (p < 0.05). The WQI values ranged from 28.36 to 49 across and from 28.2 to 56.2 between study months with an overall mean value of 36.9. The measured water quality variables did not exceed the UNBS and WHO standards for drinking water in all months and at all stations. According to these values, the water quality of Lake Bunyonyi generally belongs to the ‘good’ class in terms of drinking water quality based on the WQI classification. The study findings are fundamentally important for policy makers in setting guidelines for effective lake management.