Understanding the Impact of Intensive Horticulture Land-Use Practices on Surface Water Quality in Central Kenya

Abstract

Rapid expansion of commercial horticulture production and related activities contribute to declining surface water quality. The study sought to understand the impacts on select rivers in Laikipia and Meru, production hotspots. The specific aims were (1) to identify prevailing surface water quality by examining variations of 14 physico-chemical parameters, and (2) to categorize measured surface water quality parameters into land use types highlighting potential pollutant source processes. Water samples were collected in July and August 2013 along 14 rivers in the study area. The data were analyzed using principal component analysis (PCA) and discriminant analysis (DA). Principal components (PCs) explained 70% of the observed total variability of water quality, indicating a prevalence of heavy metal traces (cadmium, phosphate, and zinc). These were linked to the rigorous use of phosphate fertilizers and copper-based agrochemicals in intensive farming. DA provided four significant (p < 0.05) discriminant functions, with 89.5% correct assignment enabling the association of land use with observed water quality. Concentrations of dissolved solids, electro-conductivity, and salinity spiked at locations with intensive small-scale and large-scale horticulture. Understanding the impacts of intensive commercial horticulture and land use practices on water quality is critical to formulating ecologically sound watershed management and pollution abatement plans.

Impact on Water Quality of Nandoni Water Reservoir Downstream of Municipal Sewage Plants in Vhembe District, South Africa

“…At this particular sample point, there is a major tarred road (R524) and the stormwater waste may account for contaminates at the Mvudi upstream sample point. The presence of nitrates may be due from diffuse pollution from farming activities, which is supported by the study of Muriithi and Yu [38]. The stormwater may also account for high total dissolved solids and, correspondingly, with high electrical conductivity, that were observed at the Mvudi upstream point.…”

“…The presence of ions (cations and anions) may account for the electrical conductivity and total dissolved solids. These research findings suggest origins downstream may be associated mostly with the Vuwani sewage plant and agriculture [37][38][39]. The sewage plant receives mostly sewage influent mainly associated with domestic use from Dzwerani, Mathule, and Khumbe villages, Khumbe poultry farm, and the Vuwani military base.…”

“…PC3 accounted for 15.6% of the variation (Table 4) and was associated strongly with pH, nitrate, total coliform, and rainfall, and weak association with chloride, which represented the natural Mvudi river system and the subsistence farming that is practiced in this section of the river ( Figure 4). The presence of nitrates may be due from diffuse pollution from farming activities [38]. …”

Agricultural Expansion and Intensification in the Foothills of Mount Kenya: A Landscape Perspective

“…Nonetheless, it remains unknown whether the intensification of water use will have long-term impacts on the groundwater table, be it in the highlands or in the Merti aquifer downstream. Furthermore, intensive small-and large-scale farming is impairing the water's quality, as it affects the physico-chemical properties of surface waters [16,[74][75][76]. Muriithi and Yu [16] took water samples in the study area and examined several physico-chemical parameters.…”

“…In the Mount Kenya region, substantial agricultural expansion driven by population growth, in combination with recurring cycles of drought, has since the late 1990s been causing conflicts both between upstream and downstream water users and between pastoralists and farmers [12,14]. The more recent expansion of horticultural agribusinesses in the same area is further increasing pressure on limited natural resources, particularly water and land [15][16][17].…”