Agriculturally used Wetlands in Kenya and Tanzania: Characterization Based on Soil and Water Resources Availability
Wetlands in Eastern Africa present an important and so far largely undocumented potential in terms of area and agricultural production. This potential is linked to the availability of water and the quality of soil resources. This study characterized representative wetlands and categorizes their diversity based on soil, hydrology and socio-economic attributes. A multidisciplinary regional assessment of more than 50 wetlands and over 150 wetland subunits was conducted in 2008 and 2009 in four regions of East Africa. The wetlands were located within the major landscape units comprising (i) the floodplain in the semi-arid highlands; (ii) floodplain in the sub-humid lowlands; (iii) inland valley swamps in the humid mid-hills; and (iv) inland valley swamps in the humid highlands. Based on multivariate statistical approaches of their biophysical and socio-economic attributes, the wetlands were categorized into five cluster groups which were further differentiated based on land use intensity, soil parameters and hydrology. These cluster groups included (i) permanently flooded wetlands under extensive use with moderate C and N contents; (ii) permanently flooded swamps located in remote areas that were largely unused and had high contents in C and N; (iii) seasonally flooded wetlands under medium use intensity for upland food crops and rainfed lowland rice and which had low to moderate soil nutrient and C contents; (iv) completely drained wetlands under intensive subsistence crop production and low soil N and P; and (v) seasonally wet valley bottoms under permanent and year-round horticultural production and high input use hence high C and N contents. Thus, the permanently flooded wetland soils and those under subsistence food production with organic inputs had more C and N than seasonally flooded, completely drained and intensively cultivated wetlands.
