Abstract
This work aimed at studying the changes in the vegetation structure and soil components at upstream and downstream areas of Alaqiq dam. A total of 169 species belonging to 124 genera and 47 families were recorded from the area. The upstream zone had 123 species, 98 genera, 41 families while downstream zone had 101 species, 81 genera, 35 families. Poaceae was the dominant family in the study area with 14 genera and 19 species. Therophytes and chamaephytes were the most common life forms indicating a typical desert life-form spectrum. TWINSPAN classified the studied sites into two main groups; the near upstream site represented the first group while the other three sites combined together in the second group. JACCARD'S similarity value revealed that there was a high similarity between far downstream and near downstream sites. Diversity values of Simpson, Shannon-Wiener and Margalef demonstrated that the two near sites of the dam were more diverse than the two far sites. The soil of the study area was not saline (0.18-0.86 dS/m), slightly alkaline (pH, 8.46-8.62), contained 307.7-667.8 mg kg(-1) nitrogen and very poor in phosphorus content (< 0.001 mg kg(-1)). The upstream area had high amount of nitrogen (667.8 mg kg(-1)) and water (21.47%) contents as compared with the downstream area. This result suggested that the nitrogen and soil water contents strongly influenced the distribution of plants at both areas of the dam. The trace and toxic elements were found in the soil at unpolluted level.