Water quality and influence of interpolation procedure on visualization of selected parameters in a headwater stream, in Ayepe-Olode, southwestern Nigeria

Abstract

The aim of this study was to examine the concentrations of certain physio-chemical variables in a headwater stream in a growing commercial and semi-urban area in southwest Nigeria, and examined the procedure for modeling dispersion, using different interpolation methods: nearest point, kriging and moving average. Result showed that although the stream is vulnerable to contamination by the palm oil processing activities around the area, it also receives contaminants from other non-source points that were not investigated in this study. It also indicated that the different point interpolation methods did not produce similar results; e.g. whereas the values of conductivity were interpolated to vary as 120.1 – 219.5 µScm^-1 with kriging interpolation, it varied as 105.6 – 220.0 µScm^-1 and 135.0 – 173.9 µScm^-1, with nearest point and moving average interpolations, respectively. Also, whereas the computed variogram model produced the best fit lines with Gaussian model, the Spherical model was assumed default for all the distributions in selected GIS software, such that the value of Nugget was assumed as 0.00, when it actually varies with data locations distribution. Conclusively, procedure of estimating spatial variation always produce results that are influenced by data distribution and model assumptions, and as such the data characteristics rather than GIS software’s defaults are appropriate for consideration in geospatial evaluation.