Influence of anthropogenic activities on water quality of the Kihansi River (Tanzania) and on population trends of captive Kihansi spray toads (Nectophrynoides asperginis)

Abstract

Freshwater habitats in Africa receive large amounts of pollutants that affect several aspects of aquatic biodiversity, including Kihansi spray toads (KST) (Nectophrynoides asperginis). Little information is available on the influence of anthropogenic activities on the water quality along the Kihansi River, which is the only known habitat for this species. This study focused on assessing water quality and associated changes along the Kihansi River gradient where toads are being reintroduced following their recent extinction in the wild. Water samples for testing the pH, turbidity, dissolved oxygen (DO), temperature, total dissolved solids (TDS), and conductivity were collected from the upper, middle, and lower zones. In addition, socio-economic data were collected from three villages, namely Udagaji, Mgugwe and Ukami, which cover the river zone. The population trend of KSTs in captivity was obtained from the Kihansi Captive Facility (KCF). Cultivation of crops, such as rice and maize is the dominant socio-economic activity. Temperature, pH, and DO showed significant variation among the three sampled zones (p < 0.05). Crop cultivation and agroforestry practices near the river significantly increased the pH and TDS, while reducing the DO in the water. The toads in captivity increased in number significantly by 12.77% (n = 1 410). Anthropogenic activities, such as agriculture, agroforestry and grazing affect water quality, and proper management of the Kihansi River requires the involvement of local communities to ensure the survival of the reintroduced KST.