LAND USE/COVER CHANGE PATTERNS IN HIGHLAND ECOSYSTEMS OF LAKE BUNYONYI CATCHMENT IN WESTERN UGANDA

Land use and cover changes influence the livelihood and degradation of fragile ecosystems. The extents of these changes in pattern were investigated in Lake Bunyonyi Catchment which lies in the South Western Highlands of Uganda. The dynamics and magnitude of land use and cover changes were assessed using Landsat (TM/ETM+) satellite images and collection of socio-economic data through interviews. The images were processed and analysed using the mean-shift image segmentation algorithm to cluster and quantify the land use and cover features. The study noted that in the assessment period 1987-2014, the small-scale farmlands, open water and grasslands remained quasi constant; while the woodlots followed a quadratic trend, with the lowest acreage experienced in 2000. The tropical high forests and wetlands cover types experienced significant decline over the years (P<0.05). Patches of small-scale farmlands, woodlots, and wetland interchangeably lost or gained more land dependant on climate variability. Even though the tropical high forest lost more than it gained, it only gained and lost to small scale farmland and woodlots; while grassland mainly lost to small scale farmland and woodlots.L\u2019occupation du sol et les changements de couverture influencent la subsistance et la d\ue9gradation des \ue9cosyst\ue8mes fragiles. La tendance des niveaux de ces changements \ue9taient \ue9valu\ue9e dans le basin versant du lac Bunyonyi qui relie les r\ue9gions montagneuses du Sud-Ouest d\u2019Ouganda. Les dynamiques et l\u2019 envergure d\u2019utilisaton de la terre et les changements de couverture \ue9taient \ue9valu\ue9es en utilisant les images du satellite Landsat (TM/ETM+) et la collecte des donn\ue9es socio-\ue9conomiques \ue0 travers des interviews. Les images \ue9taient trait\ue9es et analy\ue9es en utilisant l\u2019algorithme de segmentation de passage-moyen-d\u2019image pour grouper et quantifier les occupations du sol et les caract\ue9ristiques de la couverture. L\u2019\ue9tude a montr\ue9 que dans la p\ue9riode d\u2019\ue9valuation de 1987-2014, la petite \ue9tendue de terres cultivables, l\u2019eau libre et les prairies sont demeur\ue9es quasi constantes; tandis que les terres bois\ue9es ont suivi une tendance quadratique, avec la plus petite superficie observ\ue9e en l\u2019an 2000. Les grandes for\ueats tropicales et les zones humides ont exp\ue9riment\ue9 un d\ue9clin significatif au cours des ann\ue9es (P<0.05). Les petites parcelles de terres agricoles, les terres bois\ue9es, et les zones humides indistinctement ont perdu et gagn\ue9 plus de terres d\ue9pendamment de la variabilit\ue9 climatique. Bien que la grande for\ueat tropicale aie perdu plus qu\u2019elle en a gagn\ue9e; elle a seulement perdu de tr\ue8s petites \ue9tendues de terres agricoles et bois\ue9es; alors que les prairies ont principalement perdu de tr\ue8s petites \ue9tendues de terres agricoles et bois\ue9es

Runoff, Soil and Nutrient Losses from Major Agricultural Land-use Practices in the Lake Victoria Basin, Uganda

Soil degradation by water erosion is recognized to be a major agTicultural and environmental probkm in the Lake Victoria basin. The objective of this study was to quantifY runoff, soil and nutrient losses from major agricultural land-use types (Annual crops, banana, coffee and degraded rangelands) and assess the efficiency of contour bunds ·in reducing these losses in two selected micro-catchments of the Lake Victoria Basin. The experiment was conducted on 13 runoiT plots or 15 by 10 m. Each land-usc type was replicated three times, except banana. Contour bunds were hand constructed I wo years after establishment of runoff plots, at 20-m spacing interval. Before the establishment of contour bunds, the average annual runoff ranged between 3 I 5. 47 and 2438.92 m3 ha' 1/yr, with relatively higher amount of rainfall water loss on rangelands compared to banana and colfee (p=0.022). The avarage annual soil loss ranged from 27.7 to 86.7 t/ha/yr, with higher soil loss on annuals compared to banana and coffee (p=0.038). Seasonal soil losses contributed for more than 75% of the annual losses for all agriculrural land-use. while seasonal runoff contributed the same proportion only for banana and rangelands (p<0.05). Eroded sediments had relatively high nutrient concentrations than the remaining soils, and varied with land-use and /or seasons (p<0.05). The amount ofN, P, K and organic matter (OM) lost through erosion was relatively high, and varied with seasons (p<0.05). The establishment of contour bunds increased OM, Ca and Na content in eroded sediments. while it decreased total OM, TN losses for all land-use types except on rangelands where they increased one year afler. These exports from agricultural land play a major role in the nutrient enrichment of rivers and open bodies. •Key words: Pollution, Sustainability, Farming system, Land-use, Soil nutrient losses