African Journal of Aquatic Science

The use and protection of water resources in the uThukela River Catchment, South Africa: A review of its past, present and future

M Wade — 2024-12-28

South Africa is a water-stressed country and therefore the quantity and quality of the water resources are very important. The uThukela River is one of South Africa’s largest rivers and is a critical component of water resource utilisation in South Africa. The rich history of the catchment illustrates the various goods and services provided by the water resources. Presently developments within the catchment have resulted in various impacts to both the quantity and quality of these water resources. The aquatic ecosystem in many of the river’s reaches are deemed ecologically sensitive and important but have been modified due to various anthropogenic impacts. The reduction of flow throughout the system that impacts both the riverine life and the marine ecosystem, including the uThukela Banks and the biology of the Bight, has been addressed. This review highlights not just the socio-economic importance of the uThukela Catchment but also the aquatic ecosystem and the state of water resources in the basin. This review identifies the high priority to manage socio-economic development in the uThukela and the country by reaching a balance between resource use and protection for future sustainability.

Impact of agricultural land-use on functional feeding groups of Afrotropical Ephemeroptera, Plecoptera and Trichoptera in the Kat River, Eastern Cape, South Africa

Frank Chukwuzuoke Akamagwuna — 2024-12-28

Despite Africa experiencing a substantial rise in inadequately managed agricultural practices, studies examining the effects of these activities on the functional organisation of macroinvertebrates in tropical streams are underdeveloped. The responses of Ephemeroptera, Plecoptera and Trichoptera (EPTs) functional feeding groups (FFGs) to agricultural pollution were investigated in the Kat River, Eastern Cape, South Africa, to identify potential FFG indicators. Physicochemical parameters and macroinvertebrates were sampled from eight sites delineated into four land-use impact categories (highly impacted, HIC; impacted category, IC; moderately impacted, MIC; and least impacted, LIC) based on the percentage of agricultural land cover. The Permutational multivariate analyses of variance (PERMANOVA) results revealed land use (F = 4.2, 3.62; p < 0.05) and season (F = 2.89, p < 0.03) influenced FFGs in the river, with shredder abundances decreasing with increasing agricultural stress. Conversely, collectors, predators and scrapers were tolerant of agricultural disturbance. Nutrient variables (NO₃-N, NO₂-N and NH₄-N), canopy and depth were the critical variables that affected FFG structure in the river. Our findings provided more understanding and insights into the functional structure of EPT in relation to agricultural pollution and can contribute to developing trait-based biomonitoring tools in Africa.

Molecular evidence reveals fish-pathogenic Aphanomyces spp. (Oomycetes: Saprolegniales) on new host of the threatened seasonal cyprinodont fish Nothobranchius spp. (Teleostei: Cyprinodontiformes) in south-eastern Democratic Republic of Congo

Béla Nagy — 2024-12-28

The Aphanomyces species pose an important global threat and cause damage to aquaculture and agriculture by infecting aquatic animals and plants. Several subpopulations of the seasonal cyprinodont fish genus Nothobranchius with lesions suggestive of infection with Aphanomyces invadans, were observed in ephemeral wetland habitats of the upper Congo drainage in the south-eastern Democratic Republic of Congo. Molecular analyses on samples collected in 2023 revealed evidence of fish-pathogenic oomycetes Aphanomyces invadans and A. laevis, for the first time in the host of fish genus Nothobranchius spp. All Nothobranchius fishes in the upper Congo drainage are subject to a high level of threat and belong to one of the threatened Red List categories, due to habitat degradation of seasonal wetlands. These fishes complete their seasonal life cycle in ephemeral natural habitats. The latter makes them highly vulnerable, as such wetland habitats are often degraded by the cumulative effect of multiple human stressors which include: the cultivation of wetlands for agriculture, the abstraction of water, the expansion of urban areas and the pollution load. Evidence of infection by oomycete pathogens documented in this study, represents a critical additional threat to the unique seasonal aquatic biodiversity of the region.

Molluscicidal effects of Persicaria senegalensis on terrestrial snails Cornu aspersum in South Africa

MC Mathole — 2024-12-28

Cornu aspersum is an invasive terrestrial snail pest of the family Helicidae. In South Africa, where the snail causes significant crop losses in viticulture areas, synthetic molluscicides are used to control them. However, the latter negatively affects both those who apply it and the non-targeted organisms. Persicaria senegalensis, a plant in the family Polyganeaceae, has demonstrated molluscicidal properties against aquatic snails. The present researchers conducted a quantitative analysis of the total saponin content of the leaves, flowers, stems and roots of P. senegalensis. We evaluated the plant’s molluscicidal properties against C. aspersum using the contact assay method over a period of 24 hours. The total saponin content of P. senegalensis’s methanolic leaf, flower, stem and root extracts was found to be 254.42 ± 0.55, 188.53 ± 0.83, 155.19 ± 0.55 and 68.27 ± 0.79 mg DE/mg, respectively. The standard error LD₅₀ of methanol leaf, flower, stem and root extracts against C. aspersum were determined at 549.54 ± 158.49, 758.58 ± 107.15, 1778.78 ± 114.81 and 1819.70 ± 346.73, respectively. The mortality rate of snails exposed to doses of methanolic extracts of P. senegalensis leaves increased with increasing concentrations. P. senegalensis therefore, contains high concentrations of total saponins and molluscicidal properties against C. aspersum.

Greenhouse gas concentrations in tropical wetlands of the Cross River estuary, Nigeria

AB Andem — 2024-12-28

The Cross River estuary is a coastal wetland in the south-eastern part of the Niger Delta region of Nigeria with its hydrological cycle largely dependent on precipitation. The purpose of this study was to determine the greenhouse gas (GHG) concentrations in water from selected wetlands in the Cross River estuary. Water samples were collected from the Ikang, Anantigha and Adiabo wetlands and the major GHGs were analysed using a gas chromatography coupled to a mass spectrometer. The mean concentration levels of carbon dioxide (CO₂), nitrous oxide (N₂O) and sulphur oxide (SO₂) were measured in the water samples for both seasons. There was a significant difference in concentrations of all the greenhouse gases in the water samples for both seasons. The exceptions were: SO₂ in Adiabo, CO₂ in Anantigha and N₂O in Ikang, which showed insignificant differences for both seasons. The water CO₂ concentrations from the Adiabo wetland recorded the largest contribution of greenhouse gas levels, ranging between 6.88 ± 2.22 ppm and 11.02 ± 2.52 ppm. These levels were in the range of those reported in the Congo basin. The variation in concentrations could be due to location, hydrological characteristics, nutrient load injection or the nitrification and denitrification processes of wetlands.

A new diatom-based multimetric index (MMI-D) for ecological health monitoring in the Tropical Rift Valley Lake (Lake Hawassa, Ethiopia)

TW Gelaw — 2024-12-28

Multimetric assessment is one of the important tools for diagnosing, detecting and measuring impairment in ecosystem function in lentic ecosystems. It enhances detection capabilities across a broader variety of stressors and offers a more complete picture of ecological conditions than single metrics or biological indicators. In this context, a diatom-based multimetric index (MMI-D) has been developed to evaluate the ecological health of Lake Hawassa. Physicochemical and benthic diatom sampling was conducted at nine sites along the lakeshore, representing varying levels of human disturbance, from February to November in2015 and 2016. The sampling sites were classified a priori into three categories: minimally disturbed (three sites), moderately disturbed (three sites) and highly disturbed (three sites). This classification, was based on a clustering analysis using the percent disturbance score (PDS). Of the 24-diatom candidate metrics, only ten were chosen as core metrics for the development of MMI-D, based on redundancy analysis, reaction to environmental conditions, percent discriminatory efficiency (%DE) and box plots. The newly established MMI-D clearly distinguished between reference and non-reference sites, and between the lake’s three clusters. The MMI-D’s performance was validated using independent data sets from lakes Hawassa and Ziway and it demonstrated the best capability for discrimination between different disturbance levels. MMI-D 2-stage Least Squares (2SLS) regression analysis revealed an inverse but robust connection with the PDS, indicating its responsiveness to Lake Hawassa habitat quality degradation (n = 9, R² = 0.921, p < 0.001). The MMI-D revealed a high %DE (95.1%) and a negative but significant connection with nutrients, total suspended solids (TSS), and turbidity (R² > 0.6; p < 0.05). Generally, it can be concluded that this index is a powerful tool that could assist endusers by providing a practical method for measuring the ecological quality of Lake Hawassa.

Impact of climate change on the distribution of the invasive water hyacinth in Ethiopia

Abdulbasit Hussein — 2024-12-28

The introduction of exotic species poses one of the greatest threats to biodiversity globally. Water hyacinth is a dangerous invasive species that has harmed Ethiopia’s wetland ecology and economy. This research aims to evaluate the current distribution of water hyacinth and the impact of environmental variables on its spread, while also mapping future habitat suitability under climate change scenarios and assessing how these changes may influence the species' potential expansion. To estimate the risks of climate change to the species, a predictive model was developed from six modeling methodologies to investigate the climatic suitability of target species for the years 2050 and 2070 under two Representative Concentration Pathway (RCP) scenarios (RCP4.5 and RCP 8.5). Under the current climatic scenario, only 69.78% (789 503.8 km²) and 16.02% (181 262.8 km²) of the country is moderately and highly suitable for species dispersion and invasion respectively. The remaining 14.2% (160 620.9 km²) is unsuitable for the distribution and invasion of the species. In 2050, under the RCP4.5 and RCP 8.5, the ‘highly suitable’ range of water hyacinth is anticipated to expand by 16.35% and 15.39%, whereas the ‘moderately suitable’ area is predicted to increase by 70.81% and 71.52%, respectively. Under the RCP8.5 scenarios, compared to the current climatic conditions, in 2070 the ‘highly suitable’ region for the species is expected to increase by 11.48%. Its continuing growth would exacerbate the issue of ecological and economic crisis, cause significant economic and environmental harm and endanger the community’s way of life. In order to avert or reduce these effects, a thorough examination of water hyacinth along the two RCPs by water resource scientists and mamangers, that takes into account how climate change is affecting water hyacinth growing locations in Ethiopia, and provides a proper solution, is mandatory.

Phylogenetic diversity of Actinomycetota species isolated from waters of Lake Natron, Arusha, Tanzania

Sadikiel E Kaale — 2024-12-28

Actinomycetota are bacteria with biotechnological potential known to produce bioactive compounds in their natural ecosystems. Natural ecosystems include extreme environments such as soda lakes. Lake Natron is one of the soda lakes found in Arusha region, Tanzania. This study aimed to characterise and establish the phylogenetic diversity of the isolated Actinomycetota species that inhabit the lake waters. Results after 16S rRNA gene sequencing showed eleven genera of phylum Actinomycetota: Streptomyces, Micrococcus, Microbacterium, Gordonia, Micromonospora, Kocuria, Isoptericola, Dietzia, Arthrobacter, Nocardiopsis and Mycobacterium have been identified. Of these, Streptomyces radiopugnans, Streptomyces harenosi, Streptomyces althioticus, Micrococcus terreus and Kocuria sp. are reported for the first time in this soda lake, and this is the first time that Gordonia sp. has been reported from a soda lake in East Africa. Micromonospora sp. and Arthrobacter sp. are reported for the first time as occurring in a Tanzanian soda lake and three putative new species of Actinomycetota have been revealed. The Actinomycetota species described in this study sets a platform for future bioprospection of novel bioactive compounds from Lake Natron.

A preliminary macroinvertebrate index of biotic integrity (M-IBI) for monitoring the highland flood plain wetland ecosystems in Ethiopia

Habtamu Getnet Fetene — 2024-12-28

Anthropogenic activities have put tremendous pressure on the natural condition of wetlands. However, few studies have used indices based on benthic invertebrates to assess the effect of these pressures on wetland ecosystems. Multi-metric indices (MMIs) have been used successfully to assess freshwater ecosystems worldwide and are an important management tool, but little is known about their applicability in the wetlands of Ethiopia. In this study, we developed MMIs for wetland invertebrates to assess wetlands in Ethiopia. The wetland invertebrate assemblages were sampled from 24 sampling stations in six wetlands in the Achefer flood plains. These sampling stations included those in least affected areas and those affected by adjacent, agricultural and urban activities. Forty-one candidate metrics were initially reviewed and screened before six core metrics were selected: Taxa richness, ET taxa richness, % EOT, % Diptera, % Collector/Filterer and % intolerant taxa. Mann–Whitney U tests, Box and Whisker plots, correlation analyses, and redundant metric tests were used to assess the ability of metrics to distinguish among reference and impaired wetlands. The MMIs were robust in discriminating reference wetlands from impaired wetlands and therefore have potential as a biomonitoring tool to assess the condition of, and to guide efforts to restore, freshwater wetlands.