Ecohydrology of a seasonal wetland in the Rift Valley: ecological characterization of Lake Solai

The following research describes through an ecohydrological approach, the first assessment of the ecology of Lake Solai, with a particular emphasis on the vegetation. Lake Solai is located 50 km north of Nakuru in the Rift Valley in Kenya at E36°80′–36°84′ to N00°05′–00°08′. It is a shallow lake that follows a very peculiar seasonal water regime, and that faces conflicts between agriculture and conservation water users. In the upper catchment, an overview of the agricultural practices was implemented and river water uses were identified to assess river flows. Crops/grassland and woodland/shrubland were the major land uses, covering c. 65% of the catchment. Closer to the lake, vegetation samples were collected around the lake together with samples of environmental factors such as soil and water quality. Thirteen vegetation communities were identified within four main zonations: forest, grassland, river inlet and rocky outcrop. These communities showed abundance, distribution and diversity determined mostly by the human pressures, the flooding periods and the salinity. Cynodon, Cyperus and Sporobolus genera were the most abundant. Resume La recherche suivante decrit, par une approche eco-hydrologique, la premiere evaluation de l’ecologie du lac Solai, en insistant particulierement sur la vegetation. Le lac Solai est situea 50 km au nord de Nakuru, dans la vallee du Rift kenyane, et ses coordonnees sont 36°80′–36°84E a 00°05′–00°08′N. C’est un lac peu profond qui est soumis a un regime hydrique saisonnier tres particulier et qui est confrontea des conflits entre acteurs agricoles et de conservation de la nature. En amont du bassin, une etude des pratiques agricoles a ete effectuee, puis les utilisations de l’eau identifiees pour evaluer les debits des rivieres. Les cultures/prairies et les forets/broussailles etaient les principales utilisations des terres et couvraient environ 65% du bassin versant. Plus en aval, des echantillons de vegetation ont ete recoltes le long du lac, en meme temps que des echantillons de facteurs environnementaux tels que le sol et l’eau. Treize communautes vegetales ont ete identifiees au sein de quatre zones principales: foret, prairie, riviere entrante et affleurement rocheux. Ces communautes presentaient une abondance, une distribution et une diversite qui etaient principalement determinees par les pressions humaines, les periodes d’inondation et la salinite. Les genres Cynodon, Cyperus et Sporobolusetaient les plus abondants.