Effect of waste disposal on nitrate and phosphate levels in Raleting Dam, Lesotho
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Date
2025
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National University of Lesotho
Abstract
Surface water quality in urban areas is consistently declining due to the indiscriminate disposal of
both liquid and solid wastes. Identifying waste sources and factors increasing nitrate and phosphate
levels in potable water bodies is crucial for water resource managers to mitigate nutrient pollution.
This study evaluates the effect of waste disposal on nitrate and phosphate levels in Raleting Dam,
located in Mafeteng, Lesotho. Fifty-four water samples were collected from nine sampling
locations from March to May 2025. All samples were analysed using a HACH DR6000
spectrophotometer. The results indicated that domestic waste and industrial effluents are the
primary contributors of nitrate and phosphate in this reservoir, respectively. Results revealed that
all water samples had nitrate concentrations that are within the WHO acceptable contamination
threshold of 50 mg/L, with an average value of (4.200 ± 1.083) mg/L. Results also revealed that
all samples had phosphate levels exceeding the WHO acceptable contamination threshold of 0.03
mg/L, with an average value of (1.620 ± 0.740) mg/L. Higher nitrate concentration levels were
exhibited during the wet season compared to the dry season, yielding mean values of 1.987 mg/L
and 1.694 mg/L, respectively. In contrast, higher phosphate concentrations were observed during
the dry season, compared to the wet season, yielding the mean values of (1.026 ± 0.114) mg/L and
(1.003 ± 0.081) mg/L, respectively. There is, however, no positive correlation between nitrate and
phosphate levels, hence suggesting a weak relationship between these two parameters.
Historically, nitrate and phosphate levels revealed a gradual increase over time. Extensive
investigations are further required around the identified pollution hotspots to ascertain the
particular sources and facilitate the implementation of corrective actions. Findings from this study
raise awareness among water resource managers and policymakers about the significant harm caused by the indiscriminate disposal of waste in this reservoir. The study can therefore serve as a
basis from which local authorities and policymakers can formulate and implement waste
management strategies in this area. Future research should explore public perceptions of illegal
dumping and involve larger sample sizes over different periods for accurate analysis. Prioritizing
physico-chemical parameters in future studies is essential for assessing water quality for domestic
use.