Influences of land use/cover on water quality in the upper and middle reaches of River Njoro, Kenya

Abstract

Data from 10 sampling sites along the River Njoro are used to examine the contribution of nutrients from upstream land uses draining each of the sampling sites. The data also are used to assess whether both the proportion of land uses and the size of the subwatersheds account for the variability in water quality in the River Njoro watershed. Geographical Information System analysis was used to determine the spatial distribution of land-cover types and subwatersheds contributing run-off to the sampling sites in the River Njoro. Standard Digital Elevation Model-based routines were used to establish the watershed area contributing run-off to each sampling site. Water and sediment samples were collected for chemical analysis, and the nutrient levels were related to the upstream land-use types and the size of the subwatersheds. The mid-stream portion of the River Njoro (near Egerton University) accounts for the highest nutrient contributions. The percentage contribution is magnified by additions from industrial, human settlements and agricultural land uses around the University. There is a significant decrease in nutrient levels downstream, however, indicating natural purification as the river flows through an area of large-scale farming with intense, well-preserved riparian and in-stream vegetation. Steep slopes of the land upstream of Egerton University enhance erosion and nutrient losses from those subwatersheds. Mixed small-scale agricultural and bare lands contribute over 55% of the phosphorus load to the upper and mid-reaches of the River Njoro. The size of the subwatershed accounts for about 53% of the variability in the soluble phosphorus in the river. The land-use subwatershed proportions are important for characterizing and modelling water quality in the River Njoro watershed. Upland land uses are as important as near-stream land uses. We suggest that conser vation of intact riparian corridor along the river and its tributaries contributes significantly to natural purification processes and recovery of the ecological integrity of the River Njoro ecosystem.

Dynamics of ungulates in relation to climatic and land use changes in an insularized African savanna ecosystem

“…In particular, the destruction of forests in the catchment and alteration of the catchment hydrology (Shivoga et al 2007;Olang and Kundu 2011) has destroyed most of the wildlife that the catchment once supported. Wildlife were exterminated or dispersed from most parts of the catchment area due to clear felling of vast tracts of natural and plantation forests that constituted their habitats.…”

“…The average level of the lake has thus dropped from an average of 2.5 m during 1925(Vareschi 1982 to 1.01 m during 1992-2002 (Raini 2009b) and 1.50 ± 0.765 m during 2003-2011, reflecting high siltation rates. Water quality in the streams draining into the lake is deteriorating (Shivoga et al 2007), exposing wildlife to potentially dangerous agrochemical residues (e.g. pesticide residues), heavy metals, dioxins and furan and discharges of solid waste washed by storm water from Nakuru town (Odada et al 2004;Raini 2009b).…”

“…The extent of the Eastern Mau Forest to the west of the park was reduced by 28% between 1967 and 1989, largely due to excisions for human settlements. Degazettement (excision) of about 300 km 2 of plantation forest followed in 1994, with illegal felling and burning within the gazetted forest reserve further reducing the forest cover (Baldyga et al 2008;Shivoga et al 2007;Olang and Kundu 2011). In 1994, the government de-gazetted over 200 km 2 of the Eastern Mau Forest on the western divide of the catchment of the basin, a major national watershed, and the source of important streams feeding Lake Nakuru.…”

Effect of Mau Forest Clear Cut on Temperature Distribution and Hydrology of Catchment of Lakes Nakuru and Naivasha: Preliminary Study

“…There are several studies (Shivoga et al, 2007;Kitaka, Harper, Mavuti, & Pacini, 2002;Raini, 2009aRaini, , 2009bMogaka, Gichere, Davis, & Hirji, 2006) dealing with the hydrological response of catchments, river outflows, water quality and hydrological regimes of lakes. A common feature of these papers is the monitoring of land cover/use changes (Baldyga, Miller, Driese, & Gichaba, 2007) and its impact on water quality.…”

Observing Changes in Riparian Buffer Strip Soil Properties Related to Land Use Activities in the River Njoro Watershed, Kenya

“…The "free access" mentality has led to a decline in riparian services such as water quantity and water quality. The increased prevalence of downstream flooding during rainfall events due to increased runoff during the rainy season and decreased runoff during the dry season has been attributed to land use change (Baldyga et al 2007;Lelo et al 2005;Shivoga et al 2007). Better quality stream water has been observed adjacent to intact riparian buffer strips compared to stream water adjacent to little or no vegetated riparian buffer strips ).…”