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Water quality degradation of urban rivers has become a serious constraint to the sustainable development of big cities in sub-Saharan Africa, and few systematic quantitative studies have been conducted on this issue. Here, we studied three main urban rivers: Mzinga River, Kizinga River, and Msimbazi River in Dar es Salaam, the largest port city on the west coast of the Indian Ocean. The spatial and temporal changes of the physicochemical parameters including DO, pH, oxidation–reduction potential (ORP), electrical conductivity (EC), total dissolved solids (TDS), turbidity, total nitrogen (TN), total dissolved nitrogen (TDN), dissolved inorganic nitrogen (DIN), chemical oxygen demand (CODMn), total phosphorus (TP), total dissolved phosphorus (TDP), soluble reactive phosphate (SRP), and water quality index (WQI) were investigated. The results showed that the middle and lower reaches of the three rivers were severely polluted with N (nitrogen) and P (phosphorus) with pollution increasing from the upstream to the downstream. WQI results showed that the water quality of Msimbazi River was in the "poor" category and fluctuated temporally and spatially. Principal component analyses (PCA) implied that redox status and N were the main factors affecting the water quality of the rivers. Unregulated discharges of untreated municipal and industrial wastewaters were the main drivers of water quality degradation in the rivers. Rapid urbanization characterized by population explosion and the small handicraft industry aggravated the situation. Source control and end treatment are urgently needed to prevent the water quality of the urban rivers in Dar es Salaam from deteriorating further. [ABSTRACT FROM AUTHOR]

Phosphorus discharge in urban household consumption system has an important impact on the urban ecological environment, especially the surface water environment. In this study, a framework and its accounting model of phosphorus flow analysis in urban household consumption system by means of SFA (substance flow analysis) was constructed. Based on the accounting model, the flow of phosphorus in the urban household consumption system of Dar es Salaam was described quantitatively, and the results demonstrated: (1) the total phosphorus input, stock and output of urban household consumption system in Dar es Salaam were 4874t of P, 59t of P and 4815t of P, respectively. In terms of system input of phosphorus, residents' food consumption had a decisive impact on the system's phosphorus input (4765t of P, 97.76%), while the contribution of detergent to the phosphorus input of the system was small. In terms of system phosphorus output, human feces and urine phosphorus output accounted for the majority of the total system phosphorus output (2313t of P, 48.04%). The total phosphorus output of domestic garbage, wastewater and food processing loss were 1464t of P (30.41%), 561t of P (11.65%), 477t of P (9.90%), respectively. (2) There were 2314t of P discharged into surface water through human feces and urine and domestic wastewater, which had a negative impact on the prevention and control of surface water pollution. 34t of P came from scattered garbage storage and 315t of P came from centralized garbage storage due to limited treatment capacity of waste treatment plant. Centralized storage and decentralized storage increased the risk of further phosphate loss. (3) Accelerated urbanization, rapid economic development and low sewage treatment capacity would cause more phosphorus loss, and Dar es Salaam faced great challenges in P discharge reduction and pollution control. Finally, we proposed policy recommendations for P discharge reduction including the guidance to the reasonable dietary structure with low phosphorus, the promotion of cleaning products with less phosphorus and no phosphorus, and the construction of garbage treatment and sewage treatment infrastructure. [ABSTRACT FROM AUTHOR]