Biodiversity characteristics of small high‐altitude tropical man‐made reservoirs in the Eastern Rift Valley, Kenya

Abstract

The biodiversity characteristics in eight small (0.065-0.249 km 2 ) public man-made reservoirs in the central part of the Eastern Rift Valley, Kenya, were studied between 1995 and 1998. A total of 71 phytoplankton species belonging to approximately 50 taxa were identified. Chlorophytes and cyanobacteria dominated the crop. The dominant taxa included Botryococcus, Syunura, Microsystis, Anabaena, and Cosmarium. A total of over 40 zooplankton species were identified. The community was composed mainly of crustacea, rotifers and protozoa. The most dominant group was Keratella but Brachionus and Nauplius were equally abundant. The diversity and abundance of benthic invertebrates was not high, and only 18 species were identified throughout the study period with the range of species number being 1-7 per reservoir. The benthic fauna was mainly composed of Lumbriculidae and Chironomid worms. A total of six monthly bird counts found an average of 60 birds per reservoir, and a total of 49 species was identified. Ducks, geese and coots dominated the waterfowl, especially during the dry season. Largescale breeding by Black-headed Heron (Ardea melanocephala) and Little Egret (Egretta garzetta) was observed in one of the sites, and other species were also breeding in the reservoirs. The population of waterbirds in reservoirs was closely related to the biomass of benthic invertebrates, and the findings of the study indicate that the structure and dynamics of life forms within small man-made reservoirs can serve as excellent sensors and indicators of the state of watershed health.

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

“…Impoundments and hydropower plants impact adversely on rivers and their resultant reservoirs (Kiplagat et al 1999, Mwaura et al 2002, Gunkel et al 2003, Mwaura 2006. The effects include the interruption and blocking of nutrient flows (Welcomme 1985) and the alteration of pH, electrical conductivity and dissolved oxygen levels (Kiplagat et al 1999, Kemdirim 2005, Mwaura 2006).…”

Limnochemistry and Biological Characteristics of Small High Altitude Reservoirs in a Sub-Tropical Region, Nyanga, Zimbabwe

“…In comparison with a similar studies carried out in Kenya on eight small high altitude lakes (Mwaura et al 2002) and in Chile (Mühlhauser et al 1995), the Nyanga reservoirs have lower nutrient loads, and significantly higher water transparency and lower turbidity. Temperatures in Kenya ranged from 15 -21 o C while the temperatures measured in Nyanga during sampling were all below 15 o C. Dissolved oxygen levels were at 100% saturation in the Nyanga reservoirs but much lower oxygen levels ranging from 23.4 -33.6% were measured in the Kenya reservoirs with even periods of oxygen depletion.…”

“…No explanation was given for this and it is not clear if these differences were caused by high altitude or the fact that they are on a different river system or because of differences in water chemistry. High altitude lakes are very diverse and examples of studies elsewhere include Andean lakes in South (Mühlhauser et al 1995;Jorge et al 2009); high altitude regions of Africa such as Kenya (Mwaura et al 2002) and Ethiopia (Elizabeth et al 1992); and alpine lakes (Mosello 1984); and even including lakes in the Himalayas (Tartari et al 1998). The local differences among high latitude lakes make it difficult to make generalisations, and therefore each system has to be studied.…”

Spatial variability in woody species richness along altitudinal gradient in a lowland-dryland site, Lokapel Turkana, Kenya

“…It is computed from the species present in a sample and takes account of both rare and common species without giving extra weight to either. This index has previously been used in vegetation studies in Kenya (Mwaura 1992(Mwaura , 2004. The ShannonWeiner index was calculated using the following equation according to Harris et al (1983):…”