Assessing the Impact of land-use types on the groundwater quality: a case study of Mid River Njoro Catchment, Kenya

Abstract

The study assessed the impact of land-use types on the groundwater quality of the mid River Njoro catchment, Kenya.Groundwater samples were collected from eight boreholes between theperiod of October 2017 to February 2018 and analyzed for pH, temperature,electrical conductivity, dissolved oxygen, nitrate, ammonium, andtotal phosphorus. These parameters were used to calculate the GroundwaterQuality Index (GQI) value of the study area. The concentrationmaps (“primary maps I”) were constructed using Kriging interpolationof ArcGIS software from the seven groundwater quality parameters.The “primary maps I” were standardized with the KEBS and WHOstandards to the “primary maps II” for ease of integration into a GISenvironment. The “primary maps II” were then rated and weightedusing a polynomial function to generate “rank maps” before calculatingthe GQI using spatial analyst tools of ArcGIS software. The land usemap was prepared from a high-resolution Google earth satellite imageryof 2015. The mean GQI values for the different land use polygons werecalculated and compared using GIS techniques. The GQI ranged from68.38 to 70.92, indicating a high groundwater quality of mid RiverNjoro catchment. The major land-use types identified include settlementarea, forest cover, agricultural land and mixed area. The agriculturalland dominated the study area, followed by settlement area, forest coverand finally mixed area. The mean GQI value in each land use typevaried minimally and this could be because of the diffuse nature of theland use types of the study area. Settlement area had low GQI, followedby agricultural land, mixed area and the forest cover had the highestmean GQI value, which corresponds to good quality of groundwater.Even though the variation is insignificant in this particular study, itsomehow indicates the adverse effects of different land use on the qualityof groundwater