Anthropogenic Impacts of Land Use and Land Cover Changes on Mai Mahiu Ecosystem, Nakuru County, Kenya

Abstract

Land-use changes are the main cause of human and environmental problems especially in many developing countries in Africa and Asia. Study was conducted in Mai Mahiu, Nakuru County, Kenya whose aim was to assess the impacts of land-use and cover changes on the ecosystem functioning and human environment. Specific objectives were: (i) to understand the nature of land use practices (ii) to monitor impacts on soil quality; (iii) impacts on vegetation composition and structure; (iv) to examine the level of variation in the physico-chemical parameters of rivers; and (v) to assess the effect of land-use change on climatic variability. GIS technology was used to establish landuse/cover changes from 1985 to 2015. Soil samples were collected for physical and chemical analyses from five land-use practice namely; undisturbed forest, disturbed forest dominated by Croton spp., disturbed forest dominated by Tarchonanthus camphoranthus, cropland and severely grazed grassland while Transect method was used for vegetation survey. Water was sampled at four sampling stations (A, B, C and D) which are sites where the river passes through the above mentioned land-use practices and analyzed for physico-chemical parameters while climate data was used in climatic variability analysis. Analysis of variance, regressions and mean separation at 0.05 significance level were excuted on the data using GenStat 14th edition. Results showed a remarkable land-use and land-cover change between 1985 and 2015. Cropland significantly increased by 135% from 27.3 km2 in 1985 to 64.2 km2 2015 at the expense natural forest. Built-up area and roads coverage had increased by almost three times from 9.8 to 29.9 km2. Soil quality deteriorated significantly with land conversions. There were significant changes in soil bulk density (p<0.001) that ranged from 0.93 g/cm3 in undisturbed forest to 1.27 g/cm3 in severely grazed grassland, soil pH (p=0.002), soil organic carbon (p=0.008) with losses of up to 63%, and total nitrogen (p=0.005) that ranged from 0.15 to 034%. Vegetation was stratified into three layers with shrub stratum being dominant replacing the tree layer that was dominant in 1985. Physico-chemical characteristics of river water deteriorated along sampling stations, A to D in both dry and wet seasons. Water pH, temperature, turbidity and conductivity increased along sampling stations A to D (p<0.001) while flow velocity and dissolved oxygen decreased significantly (p<0.001). Chlorides, sulphates, nitrates, phosphates calcium, iron, magnesium, potassium and sodium were significantly higher (p<0.001) at stations C and D compared to stations A and B. There was no significant difference in long-term annual rainfall variability (p=0.685). Intra-annual rainfall variability was noticed in the months of March, April, May and November (p>0.001). The study concluded that land use change and modifications in Mai Mahiu have negatively affected the state of the Mai Mahiu ecosystem. For the sake of the present and future generation in the region, the study recommends restoration and rehabilitation through landscape based land-use practices, enforcement of laws and implementation of policies relevant this type of ecosystem.