This study reviews selected physical and biotic responses of the St Lucia estuarine system to the recently implemented management approach of re-establishing the connection between the uMfolozi River and the St Lucia Estuary. This connection was severed in the 1950s to reduce high sediment inputs into the estuary, depriving the estuarine system of freshwater, as the management approach was to keep the river and estuary separate. In 2012, after a prolonged period of drought, the uMfolozi River was reconnected with the estuary. This brought freshwater into the system and prevented desiccation of Lake St Lucia under prolonged drought conditions. However, the reconnection came at the cost of excessive sediment accumulation in the St Lucia Estuary and Narrows, as well as the compaction of that sediment due to the prolonged closure of the mouth for over a decade. As saline water has not penetrated Lake St Lucia following the resumption of marine connectivity through the St Lucia Estuary in January 2021, the estuarine lake may soon be prematurely transformed into a freshwater coastal floodplain wetland. Modifications of the current management approach are urgently required to postpone this scenario.

This study provides an assessment of the hydrogeochemical processes influencing shallow groundwater quality in the Lefock watershed (crystalline area, Cameroon). Seventeen groundwater samples were collected in May 2021 during the rainy season. These samples were analysed for their physical characteristics and major ions composition. The result showed values within the WHO safe limits, except for pH which is acidic (below the lower limit of 6.5) for 94% of the samples and Fe2+, HCO3 − and NO3−, whose concentrations are above the WHO (2017) limit for 12%, 88% and 12% of the samples respectively. Conventional hydrogeochemical diagrams, water quality assessment indices, and multivariate statistical analysis showed that the main factors influencing groundwater chemistry in the study area are silicates weathering, leaching of the unsaturated zone of the saprolite, leaching of atmospheric pollutants by rainwater and anthropogenic contamination. The spatial distribution of NO3 −, Na+ and piezometric levels implies that groundwater is spatially influenced by land use, saturated zone of saprolite aquifers and groundwater flowpath directions. These results provide useful information for groundwater management in a semi-urban environment with heterogeneous aquifers and, in particular, the need to consider groundwater flowpath and land use stratification when planning groundwater management strategies.

Lake Victoria is a vital source of drinking water for millions, necessitating continuous monitoring of chlorophyll-a (Chl-a) concentrations to assess its trophic status and support sustainable water resource management. This study aimed to provide a scalable, cost-effective alternative to traditional in situ monitoring, which is limited in spatial and temporal coverage. Sentinel-2A imagery, integrated within the Digital Earth Africa (DE Africa) Platform, was used alongside the optimised Ocean Color 3 (OC3) algorithm to estimate Chl-a concentrations in Suguti Bay. Validation using 13 in situ samples collected between March 2018 and June 2019 showed strong agreement with satellite- derived data (R 2 = 0.97, RMSE = 1.23µg l−1, NSE = 0.97). Results revealed elevated Chl-a levels reaching up to 100 µg l−1, and frequent harmful algal blooms (HABs) between 2016 and 2024, indicating significant eutrophication. Spectral analysis consistently showed higher green than blue reflectance, aligning with Chl-a characteristics. Spatial analysis identified the southeastern bay as a hotspot, likely influenced by runoff from the Nyasangu River and anthropogenic pressures. These findings emphasise poor water quality and the urgent need for targeted nutrient management. Overall, this study demonstrates that combining Sentinel-2A and DE Africa offers a reliable, replicable framework for inland water quality monitoring in Africa.

Rapid human population growth and industrial activities along coastal areas have intensified anthropogenic contamination in water, sediment and edible fauna, posing public health risks. Mangrove ecosystems act as pollutant sinks, increasing the likelihood of heavy metal accumulation in aquatic organisms. This study examines heavy metal contamination and bioaccumulation in crabs (Callinectes amnicola) and snails (Tympanotonos fuscatus) from mangrove ecosystems along the Bayelsa coast, Nigeria. Water, sediment, crab and snail samples were collected from three stations and analysed using flame atomic absorption spectrophotometry for lead (Pb), cadmium (Cd), nickel (Ni), arsenic (As), zinc (Zn) and copper (Cu). Biota-sediment accumulation factor (BSAF) analyses for crabs revealed significant bioaccumulation of Ni, As and Zn, particularly in highly contaminated stations. The target hazard quotient (THQ) suggested low immediate health risks for human consumers. Ongoing monitoring and pollution control measures are essential to mitigate potential long-term exposure risks and protect public health and ecosystem integrity.

This study documents the diversity and spatio-temporal distribution of crustaceans from three perennial rivers (Beshir, Kalte and Olbiyawa) that flow through an urban area in Wolaita Sodo town, southern Ethiopia. Field data and laboratory-based spatio-temporal scale studies were employed for both biological and physico-chemical parameters. Water samples were collected twice monthly between November 2019 and February 2020 at three locations from each river. Identification of species was completed to genus using suitable laboratory procedures and appropriate keys. In total, 32 genera of crustaceans were identified of which 14 belonged to the sub-class Copepoda, 13 to Cladocera and 5 to Ostracoda. The copepods dominated (59.37%) followed by the Cladocera (35.81%) and the Ostracoda (4.82%), whereas highest total densities were found in the Olbiyawa River (7 186.67 ± 2.64 ind. l−1). The Shannon−Wiener’s diversity index (Hʹ), Margalef’s richness index (e) as well as Pielou’s evenness index (J) for the diversity and population density of crustaceans were high during months with souring temperatures in addition to low rainfall, steady chemical components and availability of prey. Results also indicated that both the diversity and density of the crustacean populations in the Beshir River were significantly lower than the Kalte and Olbiyawa Rivers. The Beshir River had lower levels of dissolved oxygen, electrical conductivity, total dissolved solids and chloride concentration, while pH and temperatures were consistent with the other two rivers. The diminutive distribution of crustaceans as well as the degrading water quality parameters in the Beshir River could be due to heavy anthropogenic stress including the dumping of town domestic and industrial effluents.

Ecosystem threat status (ETS) and ecosystem protection levels (EPLs) are headline indicators that can assess freshwater ecosystems at a country-wide scale. A spatial layer of freshwater, inland wetland ecosystem types of South Africa was combined with a range of spatial data sets to model their ecological condition. The ETS and EPL of each ecosystem type were determined using the area of that type in good ecological condition relative to a biodiversity target, which represented 20% of the total area of that ecosystem type. Thresholds were applied to distinguish four ETS categories ranging from Least Concern to Critically Endangered, and four EPL categories ranging from Not Protected to Well Protected. A total of 79% of the 135 of South African inland wetland ecosystem types were found to be threatened, of which 83 (62% of the number of types) are Critically Endangered, 12 (9%) are Endangered, 12 (9%) are Vulnerable and 28 (21%) of Least Concern. Of the 135 inland wetland types, 61% were Not Protected, with 6% being Well Protected, 3% Moderately Protected, and 30% Poorly Protected. Protected and Ramsar sites hosted only 7% of the total area of inland wetlands, which means that the Aichi Biodiversity Target 11 for 2020 (17%) was not met.

Land-cover change is the leading cause of habitat loss globally. The extent of estuarine habitat loss and land-use pressures are understudied in South Africa, particularly in the numerically dominant temporarily closed estuaries. Remote sensing techniques are effective tools for monitoring estuarine habitat loss, and the type and intensity of anthropogenic influences that derive from land-use, such as water quality deterioration. This study quantified land-use/land-cover within and adjacent to 57 temporarily closed estuaries in KwaZulu-Natal, on the subtropical east coast of South Africa, to investigate spatio-temporal land-use trends over the past four decades. Urban and agricultural land-use pressures were high in the estuarine functional zone and adjacent ecotones (32.1% and 52.1% transformed, respectively). The rate of land-cover change has stabilised, following a decline in transformation over time due to the withdrawal of cultivation from some wetland areas. There was, however, evidence of land-use intensification between the 1980s and 2018 as former agricultural land was progressively developed for urban or peri-urban use, and sand mining was identified as an important local land-use. High intensity sand mining, continued urban expansion and the introduction of urban land-uses in rural areas will intensify local land-use pressures, leading to further declines in regional estuary health.

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.

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.

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.