Acid mine drainage (AMD) is a major concern for wetlands located in coal-bearing regions, particularly where mining activities and associated spoil material are present. In this study, a diatom-based index is proposed to detect acidification related to AMD in wetlands surrounding coal mines, with a specific focus on the principal environmental stressors associated with AMD: low pH, low alkalinity, elevated electrical conductivity (EC), and elevated sulphate concentrations. Chloride was included as a secondary indicator reflecting mine-related ionic enrichment rather than direct AMD-generating processes. A total of 87 samples were collected from 45 sites across two seasons (dry and wet) to capture spatial and temporal variation in diatom community structures. Epiphytic diatoms were sampled using standard protocols, and species composition was derived alongside environmental variables. This dataset formed the basis for multivariate analyses linking diatom community structure to environmental gradients associated with acidification. Canonical correspondence analysis (CCA) demonstrated that diatom species distributions were primarily structured along an acidification gradient driven by pH (-0.93), alkalinity (-0.79), and sulphate (0.65), with a secondary ionic gradient associated with chloride and EC. Weighted averaging (WA) was used to calculate environmental optima for species under key stressors, enabling diatom taxa to be positioned along ecological gradients. These optima were used to calculate community-weighted metrics (CWMs), which were integrated into two multimetric indices (MMIs). Redundancy analysis (RDA) of the derived indices revealed strong and consistent associations with the same environmental gradients identified in the CCA, pH (-0.91), sulphate (0.67), and alkalinity (-0.78), and clearly distinguished between acidified and non-acidified wetlands. The correspondence between CCA and RDA results indicates a hierarchical compression of ecological information from species assemblages to indices while retaining dominant environmental gradients, making the proposed MMI a practical tool for distinguishing wetland acidification under AMD influence where routine water quality monitoring is constrained.

Biomonitoring tools are constantly evolving, with South Africa being no exception. This study aims to improve the knowledge of ecological preferences and tolerances of diatom species in the Karoo and to expand upon the diatom baseline for this semi-arid area. The natural water of the Karoo has wide ranges within its chemistry – often with extremely high concentrations of dissolved salts. The diatom community composition of natural Karoo waters was sampled (n = 510). A total of 543 diatom species were recorded, but the 322 species with abundance over 1% were used in the analyses. The significant environmental drivers that potentially influence these communities included electrical conductivity, calcium, chloride, oxidised nitrogen and strontium. Multivariate analysis (CCA) revealed the three main measured variables influencing diatom community composition to be lithium, chloride and oxidized nitrogen. These were followed by sulphate, selenium, silica and scandium. Several diatom taxa (as yet unidentified) have tolerances to the extremely saline conditions of the natural springs and ground water of the Karoo.

Eunotia elliotii sp. nov. is described from an unnamed tributary of the headwaters of the Bondo River in the Republic of the Congo. The diatom community in which it was found was dominated by several other species of Eunotia with several other taxa co-occurring including Actinella, Humidophila, Luticola, Nupela, Gomphonema, Brachysira, Sellaphora, Navicula, Frustulia, Orthoseira and Pinnularia. The morphological features of the new species are studied using light and scanning electron microscopy. Eunotia elliotii can easily be distinguished from other Eunotia species by its typical valve outline with two dorsal undulations, protracted rounded apices, unevenly spaced striae and the irregular thickened silica wall, which is clearly visible under the light microscope. Under scanning electron microscopy the valve face is unevenly corrugated with striae recessed in the troughs of the corrugations. Externally, surrounding the striae, the troughs are filled with numerous small round depressions in the valve face, such structures have not been observed before in Eunotia. This taxon also has no discernable rimoportula present. Differences between the new species and morphologically related species such as Eunotia rudis and Eunotia pierrefuseyi described from the Democratic Republic of the Congo and several other similar taxa are discussed.

Species in the genus Eunotia commonly occur in waters with acidic to circumneutral pH, low nutrient content, and low dissolved salt concentrations. The genus is also commonly encountered worldwide in dystrophic habitats with high humic acid content. Taxa from this genus are considered to be sensitive to pollution and indicators of good water quality. The Democratic Republic of the Congo, with its remaining tropical forest, has many such waterbodies. Small forest streams support a great diversity of diatoms and Eunotia in particular. These water bodies are often at risk from multiple potential impacts. Documenting and describing diatom species and community structure is important to potentially show future change and aid in developing possible management strategies. Based on a number of investigations in the Yangambi Biosphere Reserve, we describe two new species of Eunotia from tropical forest streams: Eunotia tropicaesilvae sp. nov. and Eunotia marginepunctata sp. nov.

Freshwater macroinvertebrates, often used as indicators of environmental quality for freshwater ecosystems, may be compromised by microplastics (MPs). We investigated MPs occurring in benthic filter feeder, predator, and grazer macroinvertebrates collected from the catchment-independent but adjacent Olifants and Sabie rivers of Kruger National Park as duplicates. We counted 369 MPs in 376 organisms (1.0 n/organism) with a mean of 8.8 n/organism, 8.5 n/organism, and 0.16 n/organism in filter feeders, predators, and grazers, respectively. Based on MP colour, size, and morphotype, significant differences in proportional compositions between predatorial macroinvertebrates and all other macroinvertebrates in both rivers preclude predatorial macroinvertebrates as a proxy indicator for the other macroinvertebrates. Proportional compositions of MP characteristics in macroinvertebrates differed in all respects between the two adjacent rivers, except for one aspect. Microplastic morphotypes occurred in equal proportions in macroinvertebrates of both rivers, suggesting biological selection based on morphotype but not MP colour or size. We found little evidence of trophic transfer between feeding guilds. Of the six polymer types observed (n = 50), butyl and chlorobutyl dominated. Waste mismanagement, single-use plastics, inefficient wastewater treatment plants, mining, and road transportation may be the major MP pollution sources that need mitigation. Microplastics in freshwater ecosystems of nature conservation areas need more attention due to high biodiversity that may be exposed.

Plastics are manufactured for various purposes but result in microplastic pollution in aquatic ecosystems. Riverine microplastic occurrence, spatial distribution, and impact have been globally documented but not well understood in Africa. We quantified 36 984 microplastics in riverbed sediment and river water along the Olifants and Sabie rivers, Kruger National Park (KNP), South Africa. These rivers have independent catchments. The microplastic profiles (size, polymer, morphotype, and colour) differed significantly between rivers. Riverbed sediment microplastic (mostly beads) concentrations ranged between 2022 to 9971 n/kg dm, and 2237 to 27 259 n/kg dm, for the Olifants and Sabie rivers respectively. Microplastic (mostly fragments) concentrations in river water ranged between 11 to 50 n/L in the Olifants River, and 4.0 n/L to 41 n/L in the Sabie River. Polyethylene terephthalate (PET) was prevalent in sediment (39%) and water (32%). Concentrations varied along both river stretches but the expected concentration decrease downstream was not observed. This raises transboundary concerns, as all the KNP rivers cross into Mozambique and from there into the Indian Ocean. Given the pervasive plastic pollution already present, there is a need for significant upstream and in-park interventions to reduce the concentration of microplastic in rivers flowing through conservation areas.

Background and aims – Actinella species from Central Africa are only rarely reported. The acid waters from many stream and small rivers in the Congo Basin form a potential environment for species of this genus. We studied several samples from the region of Yangambi to confirm whether species belonging to this genus are present. Material and methods – Samples for diatom investigation were collected in several streams and small rivers (Moni, Ngima, and Libongo), in the tropical rainforest in the Yangambi Biosphere Reserve, Tshopo Province, Democratic Republic of the Congo. The samples were prepared to obtain permanent microscope slides for light microscopy studies using standard methods and cleaned material for scanning electron microscopy. Key results – A novel Actinella was observed in the studied samples. The taxon was compared to other species such as A. disjuncta, A. lange-bertalotii, A. modesta, A. pereunotioides, and A. pseudohantzschia, although the new species morphologically resembles most A. eunotioides, a species discovered in the Amazon basin in Brazil, and A. eunotioides var. minor, described in 1966 from the Central African Republic. The taxon observed in our material differs from A. eunotioides mainly in the valve dimensions, being much smaller, and the higher density of the marginal spines. Stria density also tends to be coarser. The valve length of A. eunotioides var. minor, on the other hand, corresponds with the smallest valves of our taxon but the valves are narrower, with a higher stria density. The ventral margin is slightly convex, while in the new taxon it is slightly concave. Moreover, in the original description of A. eunotioides var. minor, the absence of spines is mentioned, while they are present on the valves in the materials we investigated. Based on the observed morphological differences, we consider the taxon recorded in the streams and small rivers in the Yangambi Biosphere Reserve distinct from A. eunotioides and its var. minor and subsequently, we describe Actinella kufferathiana as a species new to science.

Denticula costata Hustedt was originally described from fossil material from Sumatra and later assigned to the genus Tetralunata. Although Tetralunata was thought to be endemic to Indonesia, D. costata has been reported from wetwalls from South Africa. This disparity in locality prompted us to investigate the D. costata in South Africa further. D. costata (now T. costata) specimens and the species reported from South Africa were different in size, shape, and structure of the raphe system. These differences, as well as comparisons to other Denticula species, allowed us to determine that the South African specimens have not been described previously. Valve ultrastructure, including the canal raphe, areolae with volate occlusions, and presence/structure of the septa suggest this new species belongs to the genus Tetralunata. This is the first report of Tetralunata from outside of Indonesia. Herein, we describe Tetraluanata schoemanii sp. nov. and its systematic placement close to, but separate from, Epithemia. This first report of Tetralunata from outside of Indonesia, increases our understanding of the genus range and displays a unique biogeographical pattern that warrants further investigation in the future.

The common freshwater dinoflagellate genus Peridinium includes the species P. gatunense and P. bipes, which are found globally. Despite forming a significant portion of algal communities, research on dinoflagellates in Africa is limited. This paper reports the first record of the presence of P. gatunense in South Africa, as well as the reappearance of P. bipes, which was last reported from South Africa during the 1930s. Light and scanning electron microscopy were used for species identification. Knowledge about the presence of these species is crucial because both are potential bloom-forming and associated with several problems having ecological impacts. The presence of both these species has potential in inhibiting the growth of the problematic cyanobacterium Microcystis aeruginosa, as demonstrated by previous studies. It may present a natural and effective solution for the remediation of water bodies subjected to harmful cyanobacterial blooms. These insights are crucial for proactive management of freshwater ecosystems in the country. This paper discusses the morphology, taxonomy, geographical distribution, and some ecological aspects of P. gatunense and P. bipes.

Background and aims – Diatoms from tropical Central Africa are rarely studied and documented. Waters of the Congo Basin are often acidic and thus may be dominated by diatoms from the genus Eunotia, usually found in the benthos and periphyton, but rarely in the plankton. We investigated planktonic Eunotia species from the Eunotia asterionelloides complex to determine their identity and distribution. Material and methods – Samples were collected in fishponds in the vicinity of Kisangani, D.R. Congo, from herbarium material collected from the Bonkele River, D.R. Congo, and in the Kouilou River, Republic of the Congo. These samples were prepared for diatom analysis, examined using standard methods, and documented using both light and scanning electron microscopy. Key results – Several taxa belonging to the Eunotia asterionelloides complex were observed. Taxa from this complex are recorded in literature as either E. asterionelloides or E. zasuminensis. The taxon from fishponds in the D.R. Congo was identified as E. tukanorum, previously described from Brazil. The structure of the valve outline and raphe appear similar, particularly the raphe position and length. A second species was found on aquatic macrophyte (Utricularia and Nymphaea) herbarium specimens from the D.R. Congo and a third species from the Kouilou River in the Republic of the Congo. These latter two taxa superficially resemble E. zasuminensis. Although similar in valve outline, the taxa differ morphologically. The shape of the apices in larger cells is indented to a larger degree, and the raphe differs in its structure, particularly the shape of the terminal endings. The structure and position of the rimoportula also differ. Also, one of these taxa is sometimes strongly flexed around the apical axis. Based on morphology, we consider these taxa distinct from E. zasuminensis and from each other, and thus describe Eunotia globicephala sp. nov. and Eunotia magnaparva sp. nov.

Several studies regarding the effects of excess nutrients and metals as possible causes of deformities found in diatom cells have been conducted in Europe, North America and Australia. This is the first study in South Africa which catalogued and analysed diatom deformities in detail. We assessed diatom deformities in response to a large water chemistry dataset, including pH, electrical conductivity, alkalinity, hardness, nutrients, heavy metals and radioactive elements. The freshwaters of the Karoo exhibited wide ranges in many of their environmental variables. Diatom deformities were categorised into four types (outline, raphe, striation and mixed/other), and each cell measured and photographed. Correlations and multivariate analyses between environmental variables and deformity type, as well as diatom species, were performed. A cumulative criterion unit (CCU) ratio, using South African aquatic ecosystem limits, was calculated for Al, Cd, Cu, Mn, Pb, Se and Zn to determine if the combined effect of these metals exerted any influence on the cause of deformities. No single stressor could be linked to the deformities. Instead, variables showing to be most probable to exert an influence are electrical conductivity, oxidised nitrogen, sulphate and lithium, with selenium and strontium having a lesser influence. The CCU application did not yield expected results. This could be due to the naturally highly mineralised water found in the Karoo.

The environmental risks from shale gas extraction through the unconventional method of 'fracking' are considerable and impact on water supplies below and above ground. Since 2010 the recovery of natural shale gas through fracking has been proposed in parts of the fragile semi-arid ecosystems that make up the Karoo biome in South Africa. These unique ecosystems are heavily reliant on underground water, intermittent and ephemeral springs, which are at great risk of contamination by fracking processes. Diatoms are present in all water bodies and reflect aspects of the environment in which they are located. As the possibility of fracking has not been removed, the aim of the project was to determine if diatoms could be used for rapid biomonitoring of underground and surface waters in the Karoo. Over a period of 24 months, water samples and diatom species were collected simultaneously from 65 sites. A total of 388 diatom taxa were identified from 290 samples with seasonal and substrate variation affecting species composition but not the environmental information. Species diversity information, on the other hand, often varied significantly between substrates within a single sample. Analysis using CCA established that the diatom composition was affected by lithium, oxidized nitrogen, electrical conductivity, and sulphate levels in the sampled water. We conclude that changes in diatom community composition in the Karoo do reflect the water chemistry and could be useful as bioindicators.& COPY; 2023 SAAB. Published by Elsevier B.V. All rights reserved.

The persistence of insecticides in aquatic environments is a cause of concern and to date hardly any studies have focused on the effects that DDT and deltamethrin have on non-target freshwater diatom communities. The application of diatoms in ecotoxicological studies is well acknowledged and therefore this study used laboratory bioassays to determine the effects that DDT and deltamethrin have on a monoculture of a diatom indicator species, Nitzschia palea. The insecticides affected the morphology of chloroplasts at all exposure concentrations. These effects were a maximum reduction in chlorophyll concentrations (4.8% and 2.3%), cell viability (51% and 42%), and increases in cell deformities (3.6% and 1.6%) following exposure to DDT and deltamethrin respectively. Based on the results we propose that methods, such as confocal microscopy, chlorophyll-α analysis and cell deformities are useful tools in assessing the effects of insecticides on diatoms.

Pharmaceuticals are a ubiquitous group of emerging pollutants of considerable importance due to their biological potency and potential to elicit effects in wildlife and humans. Pharmaceuticals have been quantified in terrestrial, marine, fresh, and transitional waters, as well as the fauna and macro-flora that inhabit them. Pharmaceuticals can enter water ways through different human and veterinary pathways with traditional wastewater treatment, unable to completely remove pharmaceuticals, discharging often unknown quantities to aquatic ecosystems. However, there is a paucity of available information regarding the effects of pharmaceuticals on species at the base of aquatic food webs, especially on phytoplankton, with research typically focussing on fish and aquatic invertebrates. Diatoms are one of the main classes of phytoplankton and are some of the most abundant and important organisms in aquatic systems. As primary producers, diatoms generate ∼40 % of the world's oxygen and are a vital food source for primary consumers. Diatoms can also be used for bioremediation of polluted water bodies but perhaps are best known as bio-indicators for water quality studies. However, this keystone, non-target group is often ignored during ecotoxicological studies to assess the effects of pollutants of concern. Observed effects of pharmaceuticals on diatoms have the potential to be used as an indicator of pharmaceutical-induced impacts on higher trophic level organisms and wider ecosystem effects. The aim of this review is to present a synthesis of research on pharmaceutical exposure to diatoms, considering ecotoxicity, bioremediation and the role of diatoms as bio-indicators. We highlight significant omissions and knowledge gaps which need addressing to realise the potential role of diatoms in future risk assessment approaches and help evaluate the impacts of pharmaceuticals in the aquatic environment at local and global scales.

During the study of diatom samples from a brackish estuary near the reserve headquarters of the Kandalaksha State Nature Reserve at Por’ya Guba 16 taxa belonging to the genus Navicula were found. One taxon, N. curtisternoides sp. nov., is described and compared with morphologically similar species. The type specimens of two names (N. eidrigiana and N. pseudosalinarum) were studied to verify the identifications of these taxa. Four species (N. hanseatica, N. kefvingensis, N. microcari, N. paul-schulzii) were recorded for the first time in the Murmansk Region.

This paper examines the efficacy of diatoms as bioindicators of water quality in the upper reaches of the Great Fish River following a period of reduced flow from drought conditions. Of the five sites, three were sampled three times in an 18 month period while the remaining two were sampled once. As a comparison, one headwater site within Mountain Zebra National Park, situated in the same district, was sampled. A total of 166 diatom taxa belonging to 29 genera were identified. Dominant taxa for the Great Fish River were identified as Amphora pediculus; Epithemia sorex; Nitzschia frustulum; Navicula veneta and Craticula buderi. These species, indicative of high nutrient concentrations and moderately saline to brackish conditions can tolerate low flow conditions. The Generic Diatom Index (GDI), the Specific Pollution sensitivity Index (SPI) the Biological Diatom Index (BDI) and the% Pollution Tolerant Valves (%PTV) - part of the UK Trophic Diatom Index (TDI) were used for interpretation of the results. The indices showed that this river is in poor condition. By comparison the headwater site in the Mountain Zebra National Park had Cocconeis placentula var. euglypta, Achnanthidium minutissimum and Cocconeis placentula var. lineata as dominant species and, using the same indices, the river was classified as in moderate to good condition with respect to water quality. When compared to a previous study (2010 - 2012), these sites showed a shift in dominant species indicating a change in water flow conditions and quality.