Influence of Human Activities on Land Use Changes and Environmental Quality of Riparian Ecosystems: "a Case Study of Saiwa Swamp Watershed, Western Kenya"

Abstract

This study focused on the Saiwa Swamp watershed in western Kenya an area with mixed farming systems. The watershed is drained by Saiwa and Sitatunga rivers that feed the River Nzoia system that flows into Lake Victoria. The watershed is the main water catchment of one of the smallest conservation areas, the Saiwa Swamp National Park (3 knr'). Saiwa Swamp National Park is conservation area and habitat to the rare and endangered sitatunga antelope (Tragelaphus spekei). As the Swamp is surrounded by farms, making it an ecological island, this threatens the very existence of this important wetland and the conservation of the sitatunga antelope. It was postulated that increase in human population and related human activities would have profound impacts on the watershed and eventually would affect Saiwa Swamp. The study, therefore, looked at the population dynamics, soils and the land use and land cover changes in the watershed. By understanding the various human activities in the watershed this would provide the pre-requisite knowledge on how to mitigate negative impacts on of the Saiwa Swamp. The study also compared the chemistry of surface water and soil sediments at specific sites along the Saiwa Swamp gradient during the dry and rainy seasons. Results from the study show significant land use and land cover changes (LULC) have taken place in the watershed in the last 3 decades since 1985. Although built-up and riparian areas covered about 0.46% and 0.81% of the watershed, these two land use types showed significant increase and a decline respectively. The LULC changes were largely attributed to socio-economic drivers including population increase and extensive agriculture. There is hence need to strengthen law enforcement on physical planning in order to reduce encroachment of natural areas such as forests and riparian zones. The study also recommends further assessment and monitoring of spatial and temporal based land use and land cover changes in Kenya. pH of surface waters was nearly neutral (mean of 7.0) during the entire study period while that of the soil sediments was acidic (4.6 to 5.0). Elements Ca, Mg and Fe recorded higher concentrations in dry season compared to the wet season. Other elements including Cu, Mn and Zn were not detected in surface water during the dry season. There was an increase in concentrations of Cu and Mn in the Swamp waters during the wet season. It appears that agrochemicals released from the surrounding farms are channelled into the Swamp thus affecting its physico-chemical status. The findings of the study showed a high percentage of the nutrients were removed from the subsurface water by plants and soils and this further emphasises their role in filtering contaminants from nmoff waters. This demonstrates the vital role of wetlands in pollution control and the need to maintain and restore wetland vegetation along riparian zones. In general, this study found that swamps played this vital role of retention of chemicals and metal elements, especially during the dry season when water flow is low and slow, and has longer residence times within the swamp to allow for filtration and mopping up of these chemicals and sediments.