Impact of Market Gardening on Surface Water Reservoirs in Burkina Faso - Impacts of current agricultural practices around the reservoir of Toukoumtouré, Nariarlé basin, on natural phytoplankton communities.

Sammanfattning: An evaluation of the ecological status of 23 small water reservoirs in Burkina Faso was made in 2004 by IRD (Institut de Recherche pour le Développement), Large dominance of cyanobacteria in some of the reservoirs was one of the signs of an imbalance in the ecology of the water (Cecchi et al. 2005). This led to a further investigation in 2005 and an assumption that the dominance of cyanobacteria was due to the high anthropogenic pressure, in particular the intense agriculture around the water bodies (Leboulanger et al. in prep). Further studies proved to be needed to find out the actual cause of the abundance of cyanobacteria and the mechanisms for water quality deterioration. IMPECA is a project running for two years with the intention to collect information about agricultural practices around the reservoirs. Agricultural methods, added pesticides, water and fertilizers are going to be studied. In addition, the possible impact of added xenobiotics on plankton is going to be investigated. This study is a pilot study for the project IMPECA, the first of this kind in Burkina Faso. The intention of the study is to try out a working procedure that will be used later in the project. Agricultural methods and added xenobiotics are investigated by a questionnaire survey, by visual investigation, and by GPS area measurements. Measurements of the impact of relevant xenobiotic application on the photosynthetic activity on phytoplankton communities are also made in the laboratory. The working procedures were slightly modified during the study. Irrelevant questions were discarded and more appropriate questions were added. The cultures that were dominating the year 2006-2007 were scallion and eggplant. The cultures differed in the time it took for the plants to get ready. People chose what plants to cultivate according to the availability of land, the availability of money and experience. There was a big variation in the amount of pesticides and fertilizers added on the fields. The dominant pesticides were Lampride and Lambda Super. Lampride showed no measurable negative effect on the growth of phytoplankton. A possible method of deciding the LOEC on phytoplankton with the instrument phyto-PAM was suggested.