Surface water quality was examined to determine spatial and seasonal variations in the Mkondoa River, in an agricultural area at Kilosa, Tanzania. Five sampling stations were chosen spatially along the river continuum to reflect a consideration of all possible activities that are capable of affecting the quality of the river water. Triplicate samples of physical water parameters were collected on a monthly basis at each station for four months from February 2015 to May 2015, covering part of the dry season (February - March) and part of the wet season (April - May). Temperature showed significant variation in both space and time (p < 0.001), while DO and BOD showed significant variation only with respect to time (p < 0.001). The pH values varied significantly (p < 0.001) temporally, but not spatially. Temperature, DO and pH showed lower mean values during the wet season relative to the dry season. In contrast, the concentration of BOD was high during the wet season and lowest in the dry season. Water quality index (WQI) indicated that water quality was fair (77±0.98) in the upstream reach of the Mkondoa, marginal (55±0.86) in the midstream reach and poor (33±0.45) in the downstream reach. There were significant relationships (p < 0.001) between physical parameters and WQI. The results suggested that the water quality of Mkondoa River is degraded towards downstream reach, and provided critical information for water resource conservation in agricultural watersheds of Tanzania.
Key words: Water quality, physical parameters, water quality index, agricultural watersheds.
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