Water Hyacinth Eichhornia crassipes (Mart.) Solms-Laubach Dynamics and Succession in the Nyanza Gulf of Lake Victoria (East Africa): Implications for Water Quality and Biodiversity Conservation

This study, conducted in Nyanza Gulf of Lake Victoria, assessed ecological succession and dynamic status of water hyacinth. Results show that water hyacinth is the genesis of macrophyte succession. On establishment, water hyacinth mats are first invaded by native emergent macrophytes, Ipomoea aquatica Forsk., and Enydra fluctuans Lour., during early stages of succession. This is followed by hippo grass Vossia cuspidata (Roxb.) Griff. in mid- and late stages whose population peaks during climax stages of succession with concomitant decrease in water hyacinth biomass. Hippo grass depends on water hyacinth for buoyancy, anchorage, and nutrients. The study concludes that macrophyte succession alters aquatic biodiversity and that, since water hyacinth infestation and attendant succession are a symptom of broader watershed management and pollution problems, aquatic macrophyte control should include reduction of nutrient loads and implementing multifaceted approach that incorporates biological agents, mechanical/manual control with utilization of harvested weed for cottage industry by local communities

Presence and distribution of mosquito larvae predators and factors influencing their abundance along the Mara River, Kenya and Tanzania

Among all the malaria controlling measures, biological control of mosquito larvae may be the cheapest and easiest to implement. This study investigated baseline predation of immature mosquitoes by macroinvertebrate predators along the Mara River, determined the diversity of predators and mosquito larvae habitats and the range of their adaptive capacity to water physico-chemical parameters. Between July and August 2011, sampling sites (n=39) along the Mara River were selected and investigated for the presence of macroinvertebrate predators and mosquito larvae. The selected sampling sites were geocoded and each dipped 20 times using standard mosquito larvae dipper to sample mosquito larvae, while a D-frame dip net was used to capture the macroinvertebrate predators. Water physico-chemical parameters (dissolved oxygen, temperature, pH, conductivity, salinity and turbidity) were taken in situ at access points, while hardness and alkalinity were measured titrimetically. The influence of macroinvertebrate predator occurrence was correlated with mosquito larvae and water quality parameters using Generalized Linear Model (GLM). Predators (n=297) belonging to 3 orders of Hemiptera (54.2%), Odonata (22.9%) and Coleoptera (22.9%), and mosquito larvae (n=4001) belonging to 10 species, which included An.gambiae s.l (44.9%), Culex spp. (34.8%) and An. coustani complex (13.8%), An. maculipalpis (3.6%), An. phaorensis (1.2%), An. funestus group (0.5%), An. azaniae (0.4%), An. hamoni (0.3%), An. christyi (0.3%), An. ardensis (0.08%), An. faini (0.07%), An. sergentii (0.05%) and 0.05% of Aedes mosquito larvae which were not identified to species level, due to lack of an appropriate key, were captured from different habitats along the Mara river. It was established that invasion of habitats by the macroinvertebrate predators were partially driven by the presence of mosquito larvae (p < 0.001), and the prevailing water physico-chemical parameters (DO, temperature, and turbidity, p <0.001). Understanding abiotic and biotic factors which favour mosquitoes and macroinveterbrate co-occurrence may contribute to the control of malaria

Effects of Land Use Types on the Levels of Microbial Contamination Based on Total Coliform and Escherischia coli counts on the Mara River, East Africa

The effects of land use types on levels of microbial contamination based on total coliforms and E. coli (faecal coliform) levels was investigated in the Mara River system, Kenya and Tanzania. Water samples were taken from five sampling sites with different land uses and the Most Probable Number (MPN) method used to determine the total coliforms. A biochemical test was done and the proportions of E. coli bacteria given per study site. The mean concentration of total coliforms was lowest at Silibwet Bridge and highest at Kirumi Bridge. However, counts of E. coli were highest at an urban site (Bomet Bridge) and lowest at a swamp site (Kirumi Bridge). Overall, the proportion (40.9%) of Eosin Methylene Blue (EMB) broth plates that produced E. coli in the study sites was higher than the WHO recommended standards of 0% per 100 ml in potable water. The results show that sections of the river with most human activity and inappropriate types of land-use contributed to high levels of coliform bacteria, particularly E. coli. This may indicate the existence of point sources of faecal contamination along the Mara River and corrective measures should be taken to control them.Keywords: E. coli, faecal coliform bacteria, land use type, most probable number, Mara River

Additional file 1: of Spatial distribution and habitat characterization of mosquito species during the dry season along the Mara River and its tributaries, in Kenya and Tanzania

Multilingual abstracts in the six official working languages of the United Nations. (PDF 673 kb