https://orcid.org/0000-0002-9016-8741
ABSTRACT
Water Quality Indices (WQIs) enable researchers to combine the measurements of multiple parameters into a single unitless score of overall water quality. The Nemerow's Pollution Index (NPI) is a flexible and intuitive index that uses an ascending scale to indicate overall levels of impairment/contamination. This study demonstrates the utility of the NPI, when used in combination with site-specific water quality guidelines, to investigate correlations between land use and water quality across a sample of 58 sub-catchments located along the western, southern, and south-eastern coast of South Africa. NPI scores for the period 2013–2014 were calculated for each sub-catchment using data from South Africa's National Chemical Monitoring Programme. Land use metrics for urban, agricultural, and natural land cover were estimated from a contemporaneous national land cover map. Correlation analysis revealed statistically significant positive correlations across the sample between pollution levels and proportions of urban and agricultural land (Spearman's ρ = 0.333 and 0.621, respectively), and strong negative correlations between pollution levels and proportions of natural land cover (Spearman's ρ = –0.729). The study concludes that, when used in concert with site-specific water quality standards, the NPI is a useful tool for evaluating overall levels of impairment across a sample of water bodies.
HIGHLIGHTS
The Nemerow's Pollution Index (NPI) was used to investigate correlations between land use and water quality across a sample of catchments in South Africa.
Overall contamination levels at most sites had exceeded ecologically acceptable limits.
Urban and agricultural land covers were associated with increased levels of impairment, while proportions of natural land cover were strongly correlated with improved water quality.
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