Effect of an impoundment on nutrient dynamics in the Kihansi River, Tanzania

Abstract

The impact of the Kihansi Dam on electrical conductivity, pH, temperature and dissolved oxygen in the Kihansi River was assessed in 2005 after 85% of the original river flow had been diverted to the Lower Kihansi power plant. The results are compared with the data obtained in 1995 before the dam was constructed. Primary production and nitrogen and phosphorus concentrations from sites upstream and downstream of the dam as well as in the reservoir were compared. Phosphorus fractions were determined in the reservoir's sediment. Electrical conductivity and pH values were higher in 2005 than in 1995, whereas oxygen concentrations were lower. Primary production, nitrogen and phosphorus concentrations were lower at stations downstream of the dam than at upstream stations. High fractions of iron-and manganese-bound phosphorus in the reservoir sediment suggest a potential for phosphorus retention. Concentrations of nitrogen and phosphorus along the Kihansi River were higher during the dry season than in the wet season. These results contribute to the documented baseline data on environmental changes in tropical river systems after flow diversion and reservoir development.

Hydrological and anthropogenic influence in the Gilgel Gibe I reservoir (Ethiopia) on macroinvertebrate assemblages

“…The phosphate concentration and the turbidity of the water downstream from the dam were reduced by 67 and 83%, respectively, when compared to the upstream river water. This is in agreement with a study by Ideva et al (2008) in Tanzania, where these authors indicated that concentrations of nitrate and phosphate drastically decreased downstream compared to a site upstream from the dam. Alterations of the nutrient content in the downstream part may affect the primary production of the river system (Ideva et al 2008).…”

“…This is in agreement with a study by Ideva et al (2008) in Tanzania, where these authors indicated that concentrations of nitrate and phosphate drastically decreased downstream compared to a site upstream from the dam. Alterations of the nutrient content in the downstream part may affect the primary production of the river system (Ideva et al 2008). Electrical conductivity in the downstream part increased by 210% compared to the upstream site.…”

“…Electrical conductivity in the downstream part increased by 210% compared to the upstream site. This is much more than in a Tanzanian reservoir, where the conductivity increased by 38% (Ideva et al 2008). …”

Influence of Reservoirs on the Concentration of Nutrients in the Water of Mountain Rivers

“…In the world literature, the studies on the influence of storage reservoirs on the chemical composition (including nutrients concentrations) of rivers are focused both on single and numerous reservoirs localised in various regions, diversified in terms of physical and geographical characteristics [4,[6][7][8][9][10][11][12]. Mountain regions show high temporal and spatial diversification of all hydrological processes [13][14][15].…”

Conserving Rivers and Their Biodiversity in Tanzania

“…The project was closed on the Kihansi River in 2000 and diverted an estimated 85% of the river's flow. Studies have shown subsequent changes in water quality and community composition of wetland plants and amphibian species, most notably the endemic Kihansi Spray Toad (Nectophrynoides asperginis), whose only known habitat is the humid areas created by the spray of the original waterfall at the dam site [68,69]. Once the dam was closed and began operations, this spray habitat disappeared and an international captive breeding and reintroduction effort to save the toad from extinction was launched.…”