Browsing by Author "Mangi Halima O."

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Fish productivity response to water quality variations: A case study of Nyumba ya Mungu dam, in Pangani water basin, Tanzania
(Sokoine University of Agriculture, 2023-07-24) Mangi Halima O.; Onywere,Simon M.; Kitur Esther C.;
Fish habitat degradation, such as water pollution due to the rapid expansion of incompatible land uses, is one of the noteworthy challenges to freshwater ecosystems. Elevated contents of nutrients and contaminants in water are some of the imperative challenges. Tis research was conducted to investigate the link between water qualities and fsh productivity in the Nyumba ya Mungu Dam, whose fshery potential had decreased by 95% between 1972 and 2018. Physicochemical characteristics, namely, temperature, pH, dissolved oxygen (DO), turbidity, total nitrogen, total phosphorus, chlorophyll a, and the water depth of fshing net location, were assessed following standard procedure. Fish catches per unit efort representing fsh biomass/productivity were monitored for twelve months from January to December 2019. Pearson’s correlation analysis indicated that fsh catch per unit efort was positively and signifcantly correlated with turbidity (r = 0.461, P < 0.01) and TP (r = 0.405, P < 0.01). Stepwise multiple regression model results indicated that turbidity, dissolved oxygen, and the depth of the fshing net location are the statistically signifcant predictors of fsh catch per unit efort which represented fsh biomass. Findings further indicated that the model combining turbidity and dissolved oxygen predicted a 24% change in fsh catch per unit efort, whereas turbidity, dissolved oxygen, and the depth of fshing net location contributed a 28.9% change in fsh catch per unit efort. In conclusion, fsh productivity in the NMD is limited by organic matter availability and nutrient levels that cause algae bloom occurrence. Turbidity is an indicator of organic matter availability and the efect of algae bloom on fsh productivity. Infow of nutrients to the dam nourishes the algae biomass, thus creating vicious cycles on fsh productivity as fsh species in the dam failed to take advantage of high primary production by algae.
Hydrological response to land use and land cover change on the slopes of Kilimanjaro and Meru Mountains
(Elsevier B.V., 2022) Mangi Halima O.; Onywere Simon M; Kitur Ester C.; Lalika Makarius C. S.; Chilagane Nyemo A.
Land use and cover change are closely linked to catchment hydrology characteristics. Land uses and cover determine the ability of the catchment to collect, store, and release water. The catchment water storage and flow ability affect the quantity and timing of runoff, soil erosion, and sediment transport downstream. Agriculture on of the major drivers for the changes in water flow pathways, which also causes a catastrophic shift of aquatic ecosys- tems. We assessed the impact of land-use changes on the water flow characteristics in the Upper Pangani Sub catchment using the hydrologic model Soil and Water Assessment Tool (SWAT). Land use and cover changes within the Upper Pangani Sub catchment were ana- lyzed between 1987 and 2017 using QGIS. The result shows that agriculture has expanded from 96,737 ha to 314,871 ha between 1987 and 2017. Bare land and built-up land have gained 14690 ha and 7083 ha respectively during this period. Land-use changes have af- fected the basin’s land cover. Forest has decreased from 196558 ha to 106839 ha between 1987 and 2017. Bush land cover has lost 83445 ha during this period. Bushland cover fall victim to agricultural activities, whereas forest is cleared for logging and fire incidences. Consequently, surface runoff has increased from 60.84 to 73.02 (20.6% increase) between 1987 and 2017. Sediment yield has increase from 6.9 to 12.74 ton/ha (46% increase), and groundwater recharge has decreased from 106.53 to 99.56 (6.5% decrease). It concluded that land cover transformation alters hydrology characteristics of the catchment, resulting to fast surface flow, high rate of soil erosion and low infiltration rate. It is recommended that agro-forestry should be emphasized in the catchment.