Olifants River Research Articles

Assessment of river health using benthic macroinvertebrates in the Dwars River, Olifants Water Management Area, Limpopo province, South Africa

The study assessed the impact of water and sediment quality on benthic macroinvertebrate assemblages in the Dwars River, a tributary of the Olifants River, Limpopo province, South Africa. Physico-chemical variables, heavy metals and macroinvertebrates were collected using standard methods. A multivariate analysis, Canonical Correspondence Analysis (CCA), was used to examine the macroinvertebrate community structure. Based on the selected physico-chemical variables and metal concentrations assessed, the water quality and sediment quality are deteriorating mainly in the downstream areas. The number of taxa and the Average Score per Taxon (ASPT) were significantly different between sites and seasons, with more taxa recorded in the upstream section of the river and in winter. A higher proportion of sensitive and high-scoring taxa (Ephemeroptera, Plecoptera and Trichoptera) were recorded in upstream and midstream sites and in winter. The CCA analysis showed an association of heavy metal concentration in the sediment with the distribution of macroinvertebrate taxa tolerant to poor water quality in the downstream section of the river. Because of the potential impacts of rapid economic development in the catchment, regular monitoring of the river is recommended, to detect potential river health problems early.

Using heavy metal pollution indices to assess water quality of surface and groundwater on catchment levels in South Africa

The Olifants River catchment has been adversely affected by anthropogenic land-use activities over the last decade. This study aims to determine the variation in surface and groundwater concerning heavy metal pollution. The collection of surface and groundwater was performed at three different land-use locations, namely, wastewater treatment works effluent (WWTW), acid mine drainage effluent (AMD), and borehole water (B·H.). These locations were located in the Mpumalanga and Limpopo provinces of South Africa. A total of 15 samples, five from effluent and water samples, were collected during the summer (October 2019). Several parameters were measured to see if the effluent and water was safe for drinking and irrigation purposes. The values of pH and Turbidity were within the permissible limit of the South African guidelines, while electric conductivity exceeds the limit. The samples were analyzed for heavy metals using the inductively coupled plasma-mass spectroscopy process. The results revealed that Cu, Ni, Zn, and Ba were all within the South African National Standards prescribed by the Department of Water and Sanitation's drinking and irrigation limits. At the same time, Fe and Mn exceeded the limit. The metals concentrations observed were non-significant (p > 0.05). The data obtained were used for statistical analysis and applying a heavy metal pollution index (HPI) and metal index (MI). Analysis of variance showed that all metals, Cu, Fe, Ni, Mn, Zn, and Ba, express statistically significant values (p < 0.05). The Heavy metal pollution index based on six selected heavy metals indicated that more than 75% of the area does not have good water quality, whereas less than 35% was suitable. However, these values at all stations were below the critical importance of 100. Furthermore, this study highlights that infants, children, and adults consuming water from the contaminated boreholes were exposed to significant amounts of metals. However, the health risk index values of less than 1 indicate a relative absence of health risks associated with the consumption of contaminated water. The health risk assessment like chronic daily intake (CDI) and hazard quotient (H.Q.) was calculated based on heavy metal concentrations. The values for CDI were found in the order of Ba > Zn > Ni > Cu and Fe for infants, children, and adults, and the values for heavy metals in water samples indicating no health risk.

Temporal and spatial variations of organochlorine pesticides (OCPs) and phthalates affecting the quality of water and sediment from Loskop Dam, South Africa

Organochlorine pesticides (OCPs) and phthalates are amongst the most emphasized man-made environmental contaminants, due to their prevalence, persistence and potential to induce adverse effects in organisms. In addition to prevailing industrial and domestic activities, their presence in the environment is exacerbated by leaching from associated materials, run-off and emissions. The Loskop Dam in the Mpumalanga Province, South Africa, is located on the Olifants River, which flows through a hub of industrial and agricultural activities. Research aimed at monitoring the levels of OCPs and phthalate contamination in South Africa, particularly in the Olifants catchment, has been limited and is restricted to short-term monitoring. In this study, the spatial and temporal variations of 21 OCPs and 7 phthalates in water and sediments from Loskop Dam were evaluated over a 3-year period (2015–2017). Annual average OCP levels ranged from 0.013±0.006 to 0.36±0.13 μg/L in water and from below the limit of detection to 2.4±1.2 µg/kg in sediments. Phthalates were present at average concentrations ranging from 0.023±0.041 to 2.1±1.5 μg/L and 20±0.63 to 55±6.9 µg/kg in water and sediments, respectively. The levels of OCPs and phthalates were greatest in autumn, attributed to higher input sources and concentration effects due to lower water levels. Phthalates were present at greater quantities at the inlet, while OCP accumulation was observed at the upper reaches of the dam. This may be an indication of the differences in input sources and translocation of these compounds, related to the topography of the dam and variability in water flow rates. These findings are important in highlighting the environmental and health concerns that may arise in the Olifants catchment area. After considering the outcomes of this study, we propose the implementation of regular and stringent monitoring strategies, which include surveys of OCPs and phthalates for Loskop Dam and similar water systems globally.

Spatial distribution patterns of benthic macroinvertebrate functional feeding groups in two rivers of the olifants river system, South Africa

Benthic macroinvertebrates play a vital role in ecosystem functioning, such as nutrient cycling, primary production, decomposition and material translocation. A study was done to determine the functional feeding groups (FFGs) distribution along two streams of the Olifants River System, South Africa. There were longitudinal differences of the functional groups but were more pronounced in the Dwars River than in the Spekboom River. Collector-gatherers and collector-filterers were the most abundant groups recorded in both rivers. The least abundant groups were the shredders and scrapers in both rivers. The highest abundance of shredders in both rivers was at upstream sites (DS1 and SS1), more scrapers were found at midstream sites (DS3 and SS2), collector-gatherers and collector-filterers increased in the downstream (SS4) of the Spekboom River and predators were nearly constant in relative abundance at all sites. The relative abundance and richness of the FFGs did not conform completely to the river continuum concept (RCC). This could be related to the degradation of the catchment resulting from human activities which affected the quality of the water.

The Bio-Ecology of the Grapevine Leaf Miner, Holocacista capensis (Lepidoptera: Heliozelidae) in the Western Cape, South Africa

The lepidopteran leaf-mining larvae of Holocacista capensis were recorded on the outskirts of Paarl (Western Cape), South Africa, in 2012 for the first time. Thought to have local origins, the moth has been recorded on many grape varieties in South Africa since. In order to develop appropriate management strategies, aimed at maintaining effective control of the pest in commercial vineyards, various aspects of the pests′ ecology must be known. The current study provided morphological characteristics associated with wing and abdominal colouration, which can be used to discern between male and female moths using a stereo microscope. The seasonal cycle of larvae and adults throughout a grapevine growing season was established. The leaf miner was detected in the three grape areas surveyed (Berg River, Hex River and Olifants River). Areas in the grape producing regions of the Western Cape that are heavily impacted by the leaf miner include Paarl, Riebeeck Kasteel, Tulbagh, Piketberg and Wellington. Moth and larval abundances were observed to reach considerably high numbers in February. Live larval abundances decreased from the middle of March, whilst adult abundances were only seen to drop in early April. This study aimed to assist towards the development of appropriate management strategies against the pest.

Groundwater resource exploration & development – Focus on groundwater to support surface water supply in the Lower Olifants River, South Africa

Many South-African towns in the Western Cape Province are dependent on surface water resources to satisfy the ever-increasing water demand. In recent years, the effects of climate change on the environment has challenged these areas continually and recently led to calls for major changes in water management. The Lower Olifants River Water Management Area experienced an extreme drought that persisted from 2016 to 2018, which led to the need for development of groundwater resources. The local economy of the Lower Olifants River is dependent on water releases from the Clanwilliam and Bulshoek Dams, located within the Olifants River Syncline (ORS), where ‘megafault’ zones form preferred flowpaths for groundwater in the Table Mountain Group (TMG) aquifers. The Lower Olifants River Water User Association (LORWUA) was mandated to proceed with the exploration and development of these aquifers to supplement the existing water use of the LORWUA. This will be available during periods of less rainfall and therefore increase the security of the water supplied. The groundwater project aimed at exploring and developing the fractured rock aquifers of the Peninsula (Op) and Skurweberg (Ss) Formations contained within the TMG. Through a high-level desktop assessment, remote sensing investigations and geophysical ground surveys, several target areas and drilling priorities were identified to obtain high borehole yields that access the resource in proximity to existing surface infrastructure. The projected water need from the groundwater resource was 8.6 million cubic metres per annum (Mm3/a). Faults/structure zones were the main hydrogeological targets, with drill target depths of structures planned for intersection deeper than 100 m below ground level (mbgl). Down-hole camera work and initial aquifer testing concluded that deep geological contact zones are prone to collapse when flow is induced in water-bearing fractures. This indicated the need for production borehole construction, even prior to aquifer testing for yield estimates. A major concern still to be resolved is the availability of water in storage and the realistic expectations of the well field over time. Although individual borehole testing provided information on the properties of specific water-bearing structures, long-term monitoring will provide a better understanding of the aquifer in response to abstraction and recovery in times of rest. The operating rules for the conjunctive use of the well field developed, with the existing surface water scheme, is still to be defined and modelled for optimisation, pending long-term monitoring.

Spatial distribution of heavy metals in the Ga-Selati River of the Olifants River System, South Africa

ABSTRACT The Ga-Selati River is subjected to different forms of pollution from mining, industrial and agricultural activities, and human settlements. The objectives of the study were to assess heavy metal pollution and to determine possible sources of pollutants in the river. Water and sediment samples were collected and analysed for the following selected metals: arsenic (As), chromium (Cr), iron (Fe), manganese (Mn), nickel (Ni) and zinc (Zn) using sequential Inductively Coupled Plasma-optical emission spectrometry (ICP-OES). The enrichment factor (EF) and geo-accumulation index (I geo) were used to determine the level of metal pollution in the sediment. The results indicated that Cr and Ni were the most accumulated elements in the sediments, and the midstream sites (S4 and S5) showed a much higher pollution level than the upstream and downstream sites. The main sources of pollutants were mining, wastewater/sewage and agricultural discharges. This may pose a serious threat to the river and health risk to the nearby rural communities, which rely on the river, especially for drinking water. Proper management strategies to reduce pollution is therefore necessary.

A Systemic Analysis of the Environmental Impacts of Gold Mining within the Blyde River Catchment, a Strategic Water Area of South Africa

Exploratory modelling of the impact of gold mining on groundwater in a strategic water area of South Africa was undertaken. A systems dynamics (SD) model was developed to simulate the impact of gold mining on water quality, focusing on groundwater contamination risk, within the context of competing developmental priorities around water resource development and the socio-economic gains from gold mining. The model also identified interventions to minimise the impacts by the year 2040. The study area was the Blyde River Catchment (BRC), which is part of the Olifants Water Management Area in South Africa. This area is an important contributor, currently and in the future, to freshwater flows and groundwater in the Olifants River Catchment, which is one of South Africa’s most economically important catchments. The model development process included a causal loop diagram­–based problem conceptualisation, followed by the drawing of stock-flow diagrams and the determining of model parameters based on a combination of background literature, data from environmental impact assessments, and from the national Department of Water and Sanitation. The model showed the potential environmental risks of gold mine wastewater production and interventions to minimise these risks. The most effective intervention identified to reduce the risk of groundwater contamination was the development and use of synthetic-lined tailings dams. The baseline simulation result of sulphate loading of 5430 t/year can be reduced by 3070 t/year to give a simulated sulphate load of 2270 t/year in 2040 using this intervention. In comparison, the simulated wastewater recycling intervention only reduced the sulphate load to 4630 t/year and the wastewater treatment interventions to 3420 t/year. This project contributes to the exploratory modelling of an understudied region of the Olifants River Catchment that is a crucial provider of freshwater flows to the Olifants, which is threatened by increasing gold mining in the upper BRC. The SD model highlighted the importance of protecting the dolomitic aquifers in the BRC for the long term sustainability of the catchment, which is particularly important if groundwater development occurs.

Assessing the effect of tagging and the vulnerability to predation in tigerfish (Hydrocynus vittatus, Castelnau 1861) in a water-stressed system using telemetry methods

Increase in anthropogenic pressures on freshwater ecosystems, globally and locally in South Africa, has made it difficult to meet environmental flow requirements and maintain these systems. The Letaba-Olifants catchment is one such example, where the upstream water demands place pressure on the river downstream as it flows through the Kruger National Park. We used the activity rates of Hydrocynus vittatus as a line of evidence to assess (1) the effects of telemeter tagging on their activity rates in three potential post-tagging recovery periods and (2) their vulnerability to predation and the causality related to the environmental stressors placed on the river catchment in the Olifants River Gorge, Kruger National Park, South Africa. We determined H. vittatus activity rates as locomotive movement using radio telemetry methods linked remotely to an online data management system. We telemeter tagged nine individuals from 08 May to 28 June 2018. However, only seven fish were successfully tracked for the duration of our study, and two individuals moved out of range of the remote network shortly after release and could not be located. The tagged H. vittatus individuals were found to have reduced activity at least within the first 7 days after tagging compared with the time after that. The results showed that three individuals were preyed on by predators after the tagging procedure recovery period. This coincided with abnormal low flow conditions, where the Letaba River ran dry. African fish eagles Haliaeestus vocifer were the only confirmed predator, whilst predation by other species was also evident.Conservation implications: Monitoring of H. vittatus using telemetry is a viable tool to use when assessing environmental stressors in remote locations. The abnormally low water levels in the Olifants and Letaba Rivers (cessation of flow in the Letaba River) during our study may have compromised the predator avoidance strategies of tagged H. vittatus and may further be affecting the viability of the H. vittatus populations in Kruger National Park. The synergistic effects of natural and anthropogenic stressors impact negatively H. vittatus populations and potentially other aquatic biotas.

Preliminary Assessment of Chemical Elements in Sediments and Larvae of Gomphidae (Odonata) from the Blyde River of the Olifants River System, South Africa.

Benthic macroinvertebrates and sediments can act as good indicators of environmental quality. The aim of this study was to assess the accumulation of chemical elements in the Gomphidae (Odonata) collected in the Blyde River. Seven sites were sampled for river sediments assessment and five sites for larvae (naiads) of Gomphidae bioaccumulation analysis. The tissue samples were analysed using inductively coupled plasma optical emission spectrometry (ICP-OES). The results showed high levels of all of the tested elements except Cd in the sediment. The mean concentrations of As, Cu and Cr exceeded the standard guideline values, whereas Pb and Zn were below the standard guideline values. In the insect body tissue, the concentrations of most elements were higher than in the sediments. The elements with the highest concentrations were Mn, Zn, Cu, and As. The bioaccumulation factor (BF) showed a tendency for bioaccumulation for almost all of the selected elements in the insect. The BF value was high for Cu, Mn, Sb, and Zn (BF > 1). The high concentrations of elements in the insect body tissue may pose a risk to fish that consume them, and subsequently to humans when fish from the river are consumed. It is therefore important to monitor the river to reduce pollution to prevent health risks in humans, especially in communities that rely on the river for water and food.

Macroinvertebrates assemblages in the Spekboom River of the Olifants River System, South Africa

Macroinvertebrates assemblages in the Spekboom River of the Olifants River System, South Africa

Climate change impact on water availability in the olifants catchment (South Africa) with potential adaptation strategies

Increasing population and economic growth has intensified water supply pressure on the Olifants River Basin causing it to become water-stressed. Climate change is expected to aggravate existing water supply challenges in the basin if urgent interventions are not implemented. This study evaluates the impacts of climate change on water availability and demand in the Olifants River Basin of South Africa, and assesses to what extent a combination of management strategies can mitigate current and longer term impacts using the Water Evaluation and Planning (WEAP) model. The results demonstrated by the two projected climate change scenarios (RCP4.5 and RCP8.5) showed a rise in temperature of approximately 1 °C–4 °C, and a decrease in precipitation of 5%–30%, as compared to the baseline climate of 1976–2005. Results also showed that pressure on water supply due to increased economic activities and a decline in streamflow will increase unmet water demand by 58% and 80% for the mid and end century periods respectively. Results further revealed that the combination of management measures proposed by decision makers is expected to decrease future unmet water demand from 1006MCM to 398MCM, 1205MCM to 872MCM and 1251MCM to 940MCM for reference, RCP4.5 and RCP 8.5 scenario respectively. The study therefore concludes that the combination of management strategies provides a much better and more efficient solution to water scarcity issues in the basin, compared to a reliance on a single strategy.

Pollution shapes the microbial communities in river water and sediments from the Olifants River catchment, South Africa.

Human activities such as agriculture and mining are leading causes of water pollution worldwide. Individual contaminants are known to negatively affect microbial communities. However, the effect of multifaceted pollution on these communities is less well understood. We investigated, using next-generation sequencing of the 16S rRNA genes, the effects of multisource (i.e., fertilizer industry and mining) chronic pollution on bacterial and archaeal communities in water and sediments from the Olifants River catchment, South Africa. Water samples showed less microbial species diversity than sediments and both habitats displayed different microbial communities. Within each of these habitats, pollution had no effect on alpha diversity but shaped the microbial composition and taxonomy-based predicted functions. Certain prokaryotic taxa and functional groups were indicative of different degrees of pollution. Heterotrophic taxa (e.g., Flavobacterium sp.) and sulphur-oxidizing bacteria (i.e., Thiobacillus sp.) were indicators of pollution in water and sediments, respectively. Ultimately, this information could be used to develop microbial indicators of water quality degradation.

The Impact of Exotic Tamarix Species on Riparian Plant Biodiversity

This study investigated the impact of exotic Tamarix species on vascular plant biodiversity in riparian ecosystems in the Western Cape Province, South Africa. Vegetation was sampled, using 5 m wide belt transects, along the Leeu, Swart, and Olifants riparian areas, which had varying invasion intensities. Each transect was split into three zones (Zone 1: 0–15 m; Zone 2: 15–35, and Zone 3: &gt;35 m), which were identified at each site based on species composition across each riparian zone. Woody plant species were identified, counted, and their heights measured within the transects that were laid out from the waterpoint (Zone 1) outwards (Zone 2 and 3). Herbaceous aerial cover (HAC) was determined subjectively and objectified using the Walker aerial cover scale. Leeu River had the highest species richness (Dmg = 2.79), diversity (H′ = 2.17; −lnλ = 1.91; N1 = 8.76 and α = 4.13), and evenness (J′= 0.80). The Swart River had the lowest species richness, which declined from Dmg = 1.96 (Zone 1) to Dmg = 1.82 (Zone 3). Exotic Tamarix species ranked in the top three most abundant woody vascular plant species along the Swart and Olifants rivers, where they ranked first and third, respectively. The Jaccard’s and Sorenson’s coefficients of similarity indicated that species differed greatly between the different sites, x¯ &lt; 27% for both indices. The indices also indicated that the Swart River had the lowest level of species distinctness between zones (x¯ &gt; 80%) while the Leeu River had the highest level of species distinctness (x¯ &lt; 50%) between the different zones. These findings suggest a possible displacement of herbaceous and woody tree species by exotic Tamarix invasion, inter alia, a decrease in ecosystem functions and services associated with the loss in biodiversity, as well as significant bearings on the agricultural ecosystem by reducing the faunal diversity such as crop pollinators, inter alia.

Occurrence, distribution, spatio-temporal variability and source identification of n-alkanes and polycyclic aromatic hydrocarbons in water and sediment from Loskop dam, South Africa

In this study, the spatial and temporal variations in the levels of C8-C40 n-alkanes and 18 polycyclic aromatic hydrocarbons (PAHs) in water and sediment from Loskop Dam (Mpumalanga Province South Africa), were investigated between 2015 and 2017. In addition, their sources, which have not been well defined, were also studied over the period. This water body is sourced from a historically contaminated water body, the Olifants River, which flows through areas where a range of industrial and agricultural activities take place. Mass crocodile and fish mortalities have been recorded in this aquatic system, and contamination by organic pollutants were highlighted as a contributing factor. The total average n-alkane concentrations in water and sediments ranged from 0.574±00811 to 18.8±1.39 µg/L and 4760±243 to 30700±906 µg/kg, respectively. Similarly, PAHs were detected at total average concentrations of between 0.150±00494 and 49.8±6.86 µg/L in water and 61.6±5.95 to 2618±300 µg/kg. n-Alkane and PAH diagnostic ratios indicated a mixture of sources of these compounds, attributed to terrestrial, submerged and floating plant material, as well as petrogenic and pyrogenic combustion. Inlet, middle and upper segment site clustering was observed with non-metric multidimensional scaling (NMDS) and hierarchical cluster analysis (HCA), mainly driven by the prevalence of PAHs at the inlet sites and n-alkanes in the upper reaches. By using indicator compounds, the sources of contamination could be predicted. The strategy described here can be applied to any water body for continuous long-term monitoring of pollutant levels and to identify sources attributing to water pollution.

A histological evaluation of pansteatitis-affected Mozambique tilapia, Oreochromis mossambicus (Peters 1852), from different geographical locations in South Africa.

Pansteatitis is the leading cause for the decline in Nile crocodile populations and the sporadic mortality of fish in the Olifants River System, South Africa. To determine the prevalence of this disease in lentic systems, Mozambique tilapia, Oreochromis mossambicus, were collected from Lake Loskop, Lake Flag Boshielo, Phalaborwa Barrage and Lake Luphephe-Nwanedi. The former three impoundments are located within the main stem of the Olifants River, while the latter, which is geographically isolated and situated in the Limpopo River System, served as a reference site. Mesenteric adipose, liver, serosa of the swim bladder, gill and the skeletal muscle of fish sampled were examined for gross and microscopic evidence of pansteatitis. Microscopically observed changes were used to statistically compare pansteatitis prevalence between samples and sites. Based on histopathological evaluation, the adipose tissue in the liver, swim bladder serosa and coelom from severely debilitated individuals showed the most significant pathological changes. Lesions indicative of steatitis were observed in fish collected from Lake Loskop (75%), Lake Flag Boshielo (22%) and Lake Luphephe-Nwanedi (15%). Further investigation is warranted to understand the pervasiveness and mechanisms driving pathological changes of pansteatitis at Lake Flag Boshielo, Phalaborwa Barrage and Lake Luphephe-Nwanedi.

Polysaccharides Based Adsorbent Used for the Assessment and Modeling of Metals Ions in Olifant’s River Catchment, South Africa

The Olifants River in South Africa, is well known to be one of the most polluted rivers in Southern Africa. Water quality issues in the River Catchment are known catchment are known to be primary related to salinity, eutrophication and acid mine drainage. This study aimed to assess the efficiency removal of metal ions in effluent wastewater from a domestic wastewater treatment plant (WWTW), borehole (BH) water contaminated by agriculture and mining activities and acid mine drainage (AMD) effluent from a abandon coal mine. To determine the treatment performance of the adsorbent, the water samples physicochemical parameters; pH, EC, turbidity and COD were measured. The pH and turbidly were within the range while EC and COD values did not fall within the standard discharge limit of industrial effluent by the DWF (1996).The use of shrimp chitosan product cross-linked with glutaraldehyde as an adsorbent was first tested on a certified reference material before applying it to the wastewater, obtained shows exceptional adsorption properties of up to 80% for these elements at concentration above 10 mg/L. However, no reliable results were obtained for samples with less than 1 mg/L. Statistical evaluation of the results at 95% confidence interval using the t-static test shows a standard deviation of ± 7% of the experimental results. Mathematical Modelling employed, results showed AMD effluent presented the power law process, while WWTW effluent, presented a decay process. Finally, for BH we obtained a normal distribution and a mathematical model was employ using the initial condition.

Soil salinity and moisture content under non-native Tamarix species

This study investigated, soil salinity and moisture content under the exotic Tamarix in the Olifants River, South Africa, where they predominantly occur. Soil electro-conductivity (EC) was mapped using the electromagnetic induction (EMI) device (EM38 sensor), in three transects laid along the river from as close to the water source outward towards the bank of the River at 50 m apart. This was supported by three soil EC and moisture measurements from each of the three transects at a soil depth of 0–100 cm at intervals of 10 cm using soil EC meter and Amplitude Domain Reflectometry (ADR) sensor, respectively. The highest salt concertation (3,000 mS/m or 19,500 ppm) was found at a depth of 30–40 cm under the dense Tamarix species. The highest soil moisture (20–40%) was also found at the same depth under the Tamarix, suggesting a hydraulic lift of water to the top 30–40 cm, where the Tamarix fine roots for water absorption occur. It also confirms that the distance from water point and Tamarix plant density affect salt leaching depth and amount of litter decomposition, respectively, which is the main source of salt deposition in soil.

Climate change adaptation in rural South Africa: Using stakeholder narratives to build system dynamics models in data-scarce environments

ABSTRACT The need for innovative systemic approaches for managing water resources that integrate natural and human dimensions is well established. Although systemic, participatory modelling has been shown to support stakeholder involvement and integrated analysis, the uptake within acrimonious, data-scarce contexts – especially in the developing world – is limited. This study details a process designed to address challenges facing the lower Olifants River Catchment in South Africa, including deteriorating water quality, data paucity and stakeholder conflict. Narratives and quantitative data were used to build a system dynamics (SD) model, ResiMod, within a participatory process. The paper demonstrates how narratives can inform, and be informed by, iterative model development whilst integrating scientific data. The approach facilitated an exploration of perceptions of causality, connections between stakeholder sectors, and mitigatory actions for responding to climate-change impacts on biodiversity. This offers a promising approach to support improved communication and learning in disputed, data-scarce contexts.

Monitoring the silver carp invasion in Africa: a case study using environmental DNA (eDNA) in dangerous watersheds

Biodiverse habitats are increasingly subject to an intensification of anthropogenic stressors that may severely diminish species richness. Invasive species pose a dominant threat to biodiversity and biosecurity, particularly in biodiversity hotspots like Kruger National Park, South Africa. The invasive silver carp, Hypophthalmichthys molitrix, was introduced into the Olifants River and may experience range spread owing to favorable environmental conditions. Intensive monitoring protocols are necessary to effectively manage invasions of species like silver carp. Unfortunately, tropical and sub-tropical aquatic systems are difficult to monitor using conventional methods (e.g., netting, electrofishing and snorkeling) owing to a range of factors including the presence of dangerous megafauna. Conservation of such systems may be advanced by the adoption of novel methods, including environmental DNA (eDNA) detection. Here, we explore the utility of environmental DNA (eDNA) to conduct safe, reliable and repeatable surveys in dangerous watersheds using silver carp as a case study. We conducted eDNA surveys at 12 sites in two neighbouring watersheds, and determined that the species has expanded its range within the Olifants River and to the south in the Sabie River. Expansion in the former is consistent with the presence of suitable spawning conditions. We discuss the implications of this survey for biodiversity monitoring in similar aquatic systems in the tropics and advocate an integrative approach to biomonitoring in these ecosystems.