Water and sediment pollution of intensively used surface waters during a drought period — a case study in Central Northern Namibia

Abstract

Semiarid regions are often affected by water scarcity and poor water quality. Seasonal changes in precipitation and drought events increase the pressure of use on water bodies and their pollution. In Central Northern Namibia, a high seasonal intra- and inter-annual variability of precipitation caused a 5-year lasting drought period. In the semiarid region, ephemeral channels and water pans represent the main water source, besides the institutionalized water supply. No systematic analysis of its quality has been conducted so far. The states of the surface waters at the end of the dry season in 2017 and the end of the rainy seasons in 2018 and 2019 were characterized by the analysis of physical–chemical parameters, focusing on usability. The first results show coarse contamination of the waters, which results in high turbidity values. Salt concentrations, such as Ca2+ and Na+, greatly increased due to evaporation. Al is present in high concentrations in solid and liquid phases, which indicates direct anthropogenic pollution. Spatial differences are evident in the study area and based on the precipitation gradient, land use, and population density. The waters cannot be used as drinking water without prior treatment.

Ecotoxicological evaluation of surface waters in Northern Namibia

“…In addition to the effects on fish embryos, acute effects on algae growth could also be observed. As mentioned before, heavy metals, such as Cd, Cr, and Cu, could be detected in the investigated samples (Faulstich et al, 2023 ). These analyzed heavy metals can also influence the observed toxicological effects on algae.…”

“…Further compounds, such as pesticides (Awoyemi et al, 2019 ), flame retardants (Parsons et al, 2019 ), nanomaterials (Shaw et al, 2016 ), and heavy metals (Taslima et al, 2022 ) can also cause edema. In the analyzed samples of the Iishana, concentrations of Cd (0.5 µg/l), Cr (3.94 µg/l), and Cu (37.33 µg/l) were detected in previous studies (Faulstich et al, 2023 ). Muzungaire et al ( 2012 ) could detect 64.0 µg/l Fe and 9.0 µg/l Cu concentrations in the Kavango River.…”

“…Logan et al ( 2023 ) identified several negative impacts of nanofibers, such as increasing apoptosis and the neutrophil response for the embryonic development of fish. Microplastic fragments and fibers have been detected in the Iishana system (Faulstich et al, 2023 ) and the blood stasis as a result of neutrophilic reactions could also be detected in the tested embryos. Therefore, it cannot be excluded that nanofibers may have negatively affected the embryonic development of Danio rerio .…”

“…In general, ecotoxicological studies in ephemeral systems in arid and semi-arid regions are rare (Lahr, 1997 ). In previous studies, the water quality and microplastic pollution of the Iishana were investigated (Faulstich et al, 2022 & 2023 ). The Iishana have high turbidity values, up to 1615.4 NTU, and elevated salt concentrations, Na up to 429.0 mg/l and Cl up to 678.0 mg/l.…”

“…The Iishana have high turbidity values, up to 1615.4 NTU, and elevated salt concentrations, Na up to 429.0 mg/l and Cl up to 678.0 mg/l. Aluminum and iron were found in elevated concentrations (up to 19.3 mg/l Al and 3.9 mg/l Fe 2+ ), particularly in suspended solids and sediments (Faulstich et al, 2023 ). With this composition, the water is not suitable as potable water and must first be treated.…”