Cases of water related diseases due to metal pollution are increasing over the global. The condition is serious to most of developing countries as a results of industrialization and population growth. Dissolved and particulate trace elements influence drinking water, aquatic ecosystem health and climate change. Mt. Kilimanjaro is one of the sources of water and icon in Africa but miss studies on dissolved and particulate metals. Therefore, this study was conducted to investigate geochemistry, distribution and yield of dissolved and particulate metals from Mt. Kilimanjaro to Indian Ocean. Surface water was sampled in rainy season and analyzed by high resolution inductively coupled plasma mass spectrometry in State Key Laboratory of Estuaries and Coastal Research. Health assessment revealed that level of Aluminium, iron, vanadium and Manganese in some stations were above recommended level, that can pose health impact to human and aquatic ecosystem. Correlation of Cobalt, Copper, Manganese and Vanadium with dissolved silicate, sulphate, calcium and dissolved organic carbon indicates that these elements were predominantly found in silicate, sulphide, carbonate and organic bounds. Positive relation between magnetic susceptibility with Copper and zinc reflects that magnetic susceptibility can be used as indicator of Copper and Zinc pollution. Rock weathering and anthropogenic activities were main sources of metals whereas redox reactions, pH, temperature and dissolved organic carbon were some of biogeochemical factors influencing level of metals. The basin transported more elements in particulate than dissolved form. Yield from Pangani River to Indian Ocean was lower than most of other rivers in East Africa.

Global croplands, pastures, and human settlements have expanded in recent decades. This is accompanied by large increases in energy, water, and fertilizer consumption, along with considerable losses of biodiversity. In sub-Saharan Africa, policies are implemented without critical consideration; e.g., agricultural expansions impair ecosystem services. We studied land use/cover and the associated rate of change for four time epochs, i.e., 1991, 2001, 2011, and 2021. This employed remote sensing and GIS techniques for analysis, while future projections were modeled using cellular automata and the Markov chain. The kappa coefficient statistics were used to assess the accuracy of the final classified image, while reference images for accuracy assessment were developed based on ground truthing. Overall change between 1991 and 2021 showed that major percentage losses were experienced by water, forest, woodland, and wetland, which decreased by 8222 Ha (44.11%), 426,161 Ha (35.72%), 399,584 Ha (35.01%), and 105,186 Ha (34.82%), respectively. On the other hand, a percentage increase during the same period was experienced in cultivated land, built-up areas, and grasslands, which increased by 659,346 Ha (205.28%), 11,894 Ha (159.93%), and 33,547 Ha (98.47%), respectively. However, this expansion of thirsty sectors has not reversed the increasing amount of water discharged out of the Kilombero River catchment. We recommend the promotion of agroforests along with participatory law enforcement and capacity building of local communities’ institutions.

Global projections show that increases in agriculture water productivity (AWP) by 30 and 60% in rain-fed and irrigated agriculture, respectively, are required to ensure food security in the period 2000–2025. In sub-Saharan Africa, attempts to understand AWP has seen a lamping of input values which paints an unrealistic picture of AWP. We employed the residual imputation method to isolate the marginal productivity value of water in six paddy farming systems viz. the conventional transplant and flooding system (CTFS), the system of rice intensification (SRI), and the Kilombero Plantation Limited (KPL) mechanized system. Findings showed that AWP for rainfed CTFS is 0.39 Kg/m³ or 0.003 US$/m³, irrigated CTFS (0.30 Kg/m³ or 0.002 US$/m³), rainfed SRI (0.68 Kg/m³ or 0.08 US$/m³), irrigated SRI (0.52 Kg/m³ or 0.06 US$/m³), rainfed KPL (0.33 Kg/m³ or 0.05 US$/m³), and irrigated KPL (0.68 Kg/m³ or 0.11 US$/m³). This shows that rainfed systems have good AWP, especially physical ones. We recommend a rollout of rainfed SRI to secure local food security and downstream ecosystem services. In addition, groupings of farmers will assist in optimizing resources, stabilizing markets, and prices for the better economic value of water (US$/m³). Adoption of SRI will require intensive demonstration that needs public financing. In addition, revamping the KPL off-taker arrangement with small-holder farmers could also be a good PPP anchor.

Reservoirs are important for flood control, production of hydroelectric power, fishing, water harvesting and storage. Climate is changing, population and anthropogenic activities are increasing which increase sedimentation rate to most of reservoirs reducing their capacity. With climate change in mind water are becoming scarce resources which need proper storage when available and suitable flood control in areas with unpredicted rainfall. Furthermore, energy demand is increasing with population growth suggesting a need of sustainable management of dams so as to control flood, produce more hydroelectric power and store water to use in dry season. Sedimentation is one of the factors influencing storage capacity of the reservoir. Understanding sedimentation rate, source of sediment and carryout proper management measures is one among of the important methods to preserve dams. 137Cs and 210Pb are important radionuclides for investigating sedimentation rate. The method has been used for more than two decades in developed countries with less use in developing countries. In this study a sediment core was sampled at the centre of Nyumba ya Mungu reservoir in Tanzania, the samples were then transported to China for processing and analysis. High-purity Germanium detector was used for analysis. The results showed that rate of sedimentation in the reservoir ranged from 0.21 to 0.65 cm/year with more sediment coming from Kikuletwa than Ruvu tributary. The range is comparable to most of reservoir in tropics of developing country. Proper utilization of this method can bring sustainable management of water, save communities from flood disaster and increase production of electricity.