Soil pH was determined using a pH meter. In this case, six distinct land use activities were identified along based on their dominant land uses and characteristics. Generally there is a variation in land use activities from upstream to downstream. Upstream is dominated by indigenous forest characterized by dense network of trees and bushes with little human disturbance. From the edge of the forests towards midstream, the land opens up to a rich upland agricultural area of extensive and intensive farming characterized by tea plantation and few human settlements. Moving downstream, grazing and mixed agricultural farming predominate with more permanently settled small scale farmers and urban set-up with high population and economic activities.Upstream riparian vegetation was least disturbed with native vegetation present on both sides of the river, intact canopy and with continuous woody vegetation along the riparian zone, dense ground cover and river banks in natural condition.
Midstream riparian vegetation is in poor condition characterized by isolated woody vegetation, limited ground cover and disturbed banks. In addition there is a high disturbance of the riparian zone by stock or through the intrusion of exotic species, although some native species remain. Valley vegetation is clearly agriculture with native vegetation clearly disturbed and with a high percentage of introduced species present. Downstream riparian vegetation is severely disturbed on both sides as indicated by reduced and absence of riparian vegetation.During the study period, significant differences were observed in Water pH and Total Nitrogen between sampling sites. Tukey’s test showed that the mean water pH at upstream sampling site differed significantly from that recorded at downstream of Chemosit river. Along Kipsonoi river, the mean water pH differed significantly between midstream and Downstream sampling sites. In both rivers, the mean value for water pH ranged from 6.9 to 7.2 . However these values fall within the pH range associated with most natural waters of 6.5 to 8.5 . Most ecosystems are sensitive to changes in pH while certain organisms prefer different ranges of pH . The reported land use activities in SWMF do not seem to modify the pH of the water. Indeed soils and land use activities affect the proportion of major ions in water bodies and hence the water pH . On the other hand, along Chemosit river significant differences were observed in total nitrogen between upstream and midstream sampling sites and between upstream and downstream along Kipsonoi river, respectively.
The high Total Nitrogen concentrations of 6.7 mg/l and 5.7 mg/l observed midstream of the two rivers could be associated with adjacent urban and agricultural land use activities. According to agricultural activities can lead to an increased flux of nitrogen into water bodies while use of fertilizers on agricultural land has been associated to high nutrient levels at such sites . Further, total suspended solids, potassium, total phosphorous, cadmium, lead and copper did not however show any significant differences. Total Suspended Solids were highest midstream on both rivers. This variation could be associated to the different land use activities reported for these sites, run-off from agriculture, soil erosion as well as in- stream activities such as car washing. Presence of indigenous forests, absence of agricultural activities, intact riparian zones characterized by dense vegetation explain the low levels of Total Suspended Solids in the upstream of the two rivers . However total suspended solids in SWMF ranged from 24 – 84 mg/l which is below WHO limits of 1000 mg/l of suspended solids of drinking water. Total phosphorous concentrations increased downstream with the highest concentration recorded at midstream and lowest at upstream on both rivers. Natural concen-trations of phosphorous in surface waters usually range from 0.005 to 0.02 mg/l, while the Environmental Protection Agency recommends a 0.1 mg/l for aquatic systems to prevent accelerated eutrophication . Low concentrations of total phosphorus recorded upstream of Chemosit and Kipsonoi rivers is linked to the undisturbed dense network of trees.
In undisturbed forested areas, streams are believed to have good water quality with low concentration of nutrients . The dense riparian vegetation within the forest land use are effective buffers in filtering out most of the nutrients from the surface run-off . These findings mirror previous studies that concluded that water quality is greatly linked to land use in a catchment and confirms several studies that have shown agriculture and urban land use as a primary predictor for nitrogen and phosphorous in stream water . The amount of heavy metals represented by Cd, Cu and Pb did not differ significantly across sites and their concentration did not follow any trend from upstream to downstream. These results agree with previous study that metal concentrations at sites located relatively high up in the catchment were comparable to, or higher than concentrations of these metals downstream. These values are linked to effluent discharge, agricultural and urban run-off, washing and bathing activities by local inhabitants and livestock access to the rivers. In addition degradation of the forest cover and other anthropogenic activities going on inside the forest, atmospheric deposition and geology weathering are potential sources of these metal ions . The low soil pH upstream might be due to the presence of slightly higher organic carbon content in the soil. Variability in total organic carbon along the two river systems is linked to the reduction in organic material being returned to the soil system due to decreasing vegetation cover downstream and oxidation of soil organic matter as a result of continuous cultivation along the riverbanks, uncontrolled grazing and browsing, loss of organic matter by water erosion and removal of green materials.
These results are in agreement with other studies that reported that the soil organic content differed with different land use types . The higher organic matter content upstream may be attributed to a higher accumulation of organic matter due to high inputs from root biomass . Variability in total nitrogen is linked to difference in soil organic matter content, intensities in cultivation and erosion, application of manures, pesticides and fertilizers rich in nitrogen content in the soils.In this study , soil pH ranged between 4.42 and 5.56, implying the soils are strongly acidic and suitable for tea production which was consistent with previous studies carried out in tea plantations . Soil pH was lowest in soils obtained Upstream on both rivers, with significant differences across the sampling sites. Tukey’s test showed that soil pH at upstream differed significantly from soil pH recorded midstream and downstream of Chemosit and Kipsonoi rivers.