Studies on the Influences of Landuse on Soil and Water Resources in Thika District, Kenya

Abstract

In the last three decades a decline has been observed in water and soil resources resulting from non-point or point source pollution. Landuse patterns may contribute to pollutants flowing into water or soil within a certain region. This study was carried out to investigate the influence of different landuse patterns on water and soil quality. Data collection was done from three major landuse .zones namely coffee, horticultural and Thika urban zone during the period September 1999 to June 2000. Twenty-one water samples were collected per each site along Chania River and levels of heavy metals were determined using x-ray fluorescence. In addition, twelve representative soil samples were collected per site along the Chania River and levels of heavy metals in soils were also determined. Heavy metal levels in water were found to be higher in the Thika urban site (Blue post) compared to coffee zone site (Egaad Estate) located upstream. However, the levels are still below the drinking water standards. With increase in the use of agrochemical inputs and soil erosion the levels of heavy metals in water or soil may increase in the future. Soil samples reflected higher levels of heavy metals than water but still within allowed limits. Statistical analysis further revealed a correlation between land use and heavy metals in river water as well as from the soil. Iron and zinc were found to be higher compared to other metals. Chania River receives agrochemical wastes from horticultural and coffee farms as it flows from Egaad coffee-estate to Bluepost. Therefore the levels of heavy metals at downstream site at Thika Blue post was found to be higher than levels at upstream site at Egaad coffee estate. For example zinc in river water was 2.9ppb and 1l.6ppb at Egaad coffee estate and Thika Blue Post respectively. The allowed limits for zinc in drinking water standards set by Kenya Bureau of Standards is 5.0Oppm To prevent increase of heavy metals in soil and water, there is need for proper landuse planning such as reduction of agrochemical inputs especially from the horticultural farms. Incorporating integrated pesticide control, agricultural extension or enhancing soil conservation methods such as afforestation would further reduce heavy metal pollution.