Eerste River Research Articles

Evaluating input data sources for isotope‐enabled rainfall‐runoff models

AbstractIsotope‐enabled models provide a means to generate robust hydrological simulations. However, daily isotope‐enabled rainfall‐runoff models applied to larger spatial scales (>100 km2) require more input data than conventional non‐isotope models in the form of precipitation isotope time series, which are difficult to generate even with point station measurements. Spatially distributed isotope data can be circumvented by isotope‐enabled climate models. Here, we evaluate the hydrological simulations of the J2000‐isotope enabled hydrological model driven with data from corrected and un‐corrected isotope‐enabled global and regional climate models (isotope‐enabled global spectral model [IsoGSM] and isotope‐enabled regional spectral model [IsoRSM], respectively) compared with 1 year of measured reference station and a yearly average precipitation isotope input for a pilot site, the data‐scarce sub‐humid Eerste River catchment in South Africa. The models driven by all input products performed well for upstream and downstream discharge gauges with Nash Sutcliffe efficiency (NSE) from 0.58 to 0.85 and LogNSE of 0.66 to 0.93. The simulated δ2H stream isotopes using the reference J2000‐iso and J2000‐isoRSM were good for the main river with a stream Kling Gupta efficiency (KGE) of between 0.4–0.9 and the top 100 Monte Carlo simulations varying by around 5‰ for δ2H. For smaller tributaries the model was unable to capture the measured stream isotopes due to biased precipitation isotope inputs. Adjusting the J2000‐iso with a bias corrected IsoRSM improved the stream and groundwater isotope simulation and outperformed the model driven by an average yearly precipitation isotope input. Differences in simulated hydrological processes were only evident between the models when evaluating percolation with unrealistic simulations for the standard J2000 model. While the regional climate model is computationally more intensive than its global counterpart, it provided better stream isotope simulations and improvements to simulated percolation. Our results indicate that isotope‐enabled climate models can provide useful input data in data scarce regions for hydrological models, where improved water management to address climate change impacts is needed.

Anthropogenic Effects on Bat Activity and Diversity along the Eerste River, South Africa

Anthropogenic Effects on Bat Activity and Diversity along the Eerste River, South Africa

Occurrence of contaminants of emerging concern in the Eerste River, South Africa: Towards the optimisation of an urban water profiling approach for public- and ecological health risk characterisation

The study evaluated the presence and fate of various contaminants of emerging concern (CECs) from a South African wastewater treatment works (WWTW) and surface waters located around an urban setting. A total of 45 CECs were quantified from nine sampling locations over an 11-month period. Daily loads (g/day) of the target analytes in the WWTW showed persistence of some CECs, along with population-normalised daily loads (mg/day/1000inh) of pharmaceuticals and drugs of abuse (DOA) that were estimated for the first time in the study area. Multiple chemical markers were recorded in river water located upstream of the WWTW discharge throughout the study period, suggesting a high degree of diffuse pollution from urban communities in the study area that are not connected to sewage networks or where sanitation services are limited. The potential of using defined surface water locations to perform community-wide substance use profiling for non-sewered communities was also explored. Environmental risk characterisation for the WWTW effluent and surface waters throughout the study period provided multiple risk quotients (RQ) for the target list of CECs spanning over various sentinel trophic levels. High risk profiles (RQ > 1.0) with a frequency of exceedance (FoE) larger than 75 % were recorded for several CECs in both WWTW effluent and surface water locations that suggest potential long-term ecological health risk impacts of pollution hotspot areas in the river catchment situated around the urban area. We present challenges in surface water quality within the study area that is relatable, or may even present more challenging, in other low- or middle-income country (LMICs) settings. The study also highlighted some challenges and limitations associated with the much-needed application of wastewater-based epidemiology (WBE) intervention in non-sewered communities that can inform on public health and communal substance use profiles of the entire urban setting.

Spatiotemporal urban water profiling for the assessment of environmental and public exposure to antimicrobials (antibiotics, antifungals, and antivirals) in the Eerste River Catchment, South Africa.

Antimicrobial agent (AA) usage, excretion, and persistence are all important factors in association with the occurrence and dissemination of antimicrobial resistance. Urban water profiling was utilised in the Eerste River catchment (South Africa) to establish AA usage in a region where comprehensive prescription records were not readily available and where portions of the community did not have sufficient access to sanitation. This technique enabled the environmental exposure to be quantified throughout the catchment area and the identification of contamination hotspots. Monitoring occurred over a 11-month period. 812 samples were processed using UPLC-MS/MS for the quantitation of 56 antimicrobials and 26 of their metabolites. Spatiotemporal trends were established, with consideration to community behaviour, seasonal changes, and physiochemical properties of the analytes. The Eerste River samples collected upstream from the town of Stellenbosch had the lowest AA loads (<4 g/day), unafflicted by industrial presence and with only small impact from farming activities. This was followed by sites downstream from a wastewater treatment plant (serving 178K people). The measurement of low AA loads (influent: 500-800g/day and effluent 50-100g/day), indicates a high efficiency of wastewater treatment, allowing for an effective reduction of AA and a lower environmental burden. This is compared to river sites that receive untreated waste from communities in informal settlements (6-12K people) that are not connected to the sewer infrastructure (with AA levels accounting for 100-600g/day). Temporal trends exhibited reduced daily loads during the summer to early autumn (Nov-May). This is likely due to seasonal patterns in community health and/or notable changes in rainfall and temperatures at the sampling locations throughout the year. However, weather patterns are also important to consider - particularly for the river sites. South Africa has notable rainfall and temperature seasonality. Antiretrovirals (ARV), emtricitabine and lamivudine, were the most prevalent drugs throughout the monitoring campaign, followed by tuberculosis drugs and sulfonamides. ARVs were, however, effectively reduced via wastewater treatment processes (>97%). This was also the case for beta-lactams, nitrofurantoin, and trimethoprim. The treatment efficacy for other drugs was more variable, that did not appear to have temporal significance.

Introducing a flat ontology into landscape research: a case study of water governance experiments in South Africa.

ContextContemporary resource management paradigms within the developed world build on an understanding of human agency as ontologically distinct from the mode of existence of plants and animals. Because of this perspective, which gives priority to human agency, policies typically take their point of departure with human societies and associated ecosystems deemed of particular value.ObjectivesAs an alternative to this worldview, social theorists have introduced what is known as “flat ontology”, where all beings are bestowed equal rights to negotiate their existence. To explore the implications of introducing such an understanding into landscape management, a participatory planning process for water allocation was developed and tested in a case study in the Eerste River Catchment in South Africa.MethodsThe planning process was mediated using the approach “politics of nature” (PoN), which aims to operationalize flat ontology to renegotiate water allocation based on the needs of all beings instead of the desire of a subset of humans. PoN allowed participants to playfully co-develop a common ontology and value-set. Data documenting these processes were collected digitally and analysed.ResultsResults indicate that the approach engendered a rethinking of key relationships between human agency and ecosystem functionality, illustrating a potential for PoN-approaches to be deployed for governance of complex landscapes.ConclusionsOn the basis of experiments using PoN-methodology in the context of watershed management, it is discussed how the introduction of a flat ontology in landscape research, could inspire new ways of designing and intervening with collaborative resource management processes.Supplementary InformationThe online version contains supplementary material available at 10.1007/s10980-021-01374-9.

Investigating the effect of the Vula Mobile app on coordination of care and capacity building in district health services, Cape Town: Convergent mixed methods study.

BackgroundCoordinating care is a defining characteristic of high quality primary care. Currently, very little is known about coordination of care in South Africa’s primary care setting. The Vula Mobile app was introduced in 2018 to assist with referring patients from primary care facilities to the Eerste River District Hospital (ERDH) emergency centre. The aim of this study was to evaluate the use of the app and its effect on coordination of care and capacity building of staff.MethodsConvergent mixed methods were used with quantitative data collected from hospital records and the Vula Mobile database, and with qualitative data collected from health professionals in primary care and the district hospital.ResultsOut of 13 321 patients seen in the emergency centre of the district hospital over the 6-month study period, only 1932 (14.5%) of the patients were referred with Vula. Most of these referrals were accepted (85.5%). Sometimes, advice was given to (35.0%) or additional information was requested (27.4%) from the referring doctor. There was little use of Vula in providing other feedback (0.6%). The introduction of the Vula app led to a decrease in the number of inappropriately referred patients (6.7% to 4.2%, p = 0.004). Doctors using the Vula app perceived that it improved care coordination and had the potential for useful feedback.ConclusionVula improved coordination of patients referred from primary care facilities in the Metro Health Services to the district hospital, but missed the opportunity to support continuing professional development and learning. Utilisation of the Vula app should be increased and its potential to provide feedback should be enhanced. Attention should be given to reducing the number of patients self-referred or referred without using the Vula app.

Modelling the impact of climate change on the flow of the Eerste River in South Africa

This research investigated the impact of climate change on the Eerste River, which is the primary source of water for the Stellenbosch Municipality and the agricultural sector in the surrounding areas of Stellenbosch Town, South Africa. Climate data projected by 11 Global Circulation Models (GCMs) of the Coupled Model Intercomparison Project - Phase 5 enforced by Representative Concentration Pathways 4.5 and 8.5, was statistically downscaled to reflect the “near” (2022–2057) and “far” (2058–2093) future periods, respectively. The ensemble mean of these GCMs outputs for the near and far future periods was compared to that of the present-day period which was accepted as the period between 1983 and 2018. This was done to determine the climate change signal, which was then transferred onto the observed precipitation and evaporation data of the present-day period. The climate change induced data, as well as land use and water demand analysed data, were then used as input to the Pitman Model, which is the conceptual semi-distributed hydrological model, for the simulation of the impact of climate change on the flow of the Eerste River. The results showed that climate change is expected to increase evaporation between 6% and 15% and, at the same time, causing rainfall to decrease between 2% and 8% in the future periods. This future climate is anticipated to cause a reduction in available water of between 8% and 18%, potentially triggering an increase in irrigation demand of between 12% and 29% in the future periods with a possible failure to meet the municipal water abstractions expected in the far-future period. Therefore, this research suggests increasing the capacity of existing farm dams and the promotion of water demand management practices to curb the potential impact of climate change on the available flow of the Eerste River.

Record of Blue tilapia Oreochromis aureus (Steindachner, 1864) in the Eerste River catchment, Western Cape province, South Africa

Oreochromis aureus was imported from Israel into South Africa in 1959 but data on its current status in South Africa are lacking. Genomic DNA was extracted and the COI gene amplified at the South African Institute for Aquatic Biodiversity. The identity of the sequences and specimens was determined using the Barcode of Life Data Systems and GenBank. Morphological and genetic assessment demonstrated that 11 specimens collected from two farm dams in the Eerste River System, Western Cape province, were Oreochromis aureus. A MaxEnt model compiled using global distribution, rainfall and temperature data predicted that large areas of southern Africa were climatically suitable for this species, indicating considerable invasion debt in southern Africa. As a result, surveys to assess for the extent of the invasion in South Africa and eradication of existing populations, if feasible, are recommended management actions.

Genetic and Morphological Characterization of Freshwater Shrimps (Caridina africana Kingsley, 1882) Reveals the Presence of Alien Shrimps in the Cape Floristic Region, South Africa.

Morphological identification and molecular data (mtDNA COI) were used to resolve the taxonomic identity of a non-native freshwater shrimp in the Cape Floristic Region (CFR) of South Africa and to evaluate levels of genetic diversity and differentiation in the species' core natural distribution. The species was morphologically and genetically identified as Caridina africana Kingsley, 1882, whose main natural distribution is in the KwaZulu-Natal (KZN) Province, more than 1200 km from the point of new discovery. Subsequently, sequence data from natural populations occurring in seven rivers throughout KZN showed the presence of nuclear copies of the mtDNA COI gene (NUMTs) in 46 out of 140 individuals. Upon removal of sequences containing NUMTs, levels of genetic diversity were low in the alien population (possibly as a consequence of a bottleneck event), while varying levels of genetic diversity and differentiation were found in natural populations, indicating habitat heterogeneity, fragmentation and restricted gene flow between rivers. Following the present study, the alien shrimp has survived the Western Cape's winter and dispersed into a nearby tributary of the Eerste River System, hence posing an additional potential threat to endangered endemics. Understanding the biology of this alien species will aid detection and eradication procedures.

Perfluorooctanoate and perfluorooctane sulfonate in South African river water

This study examined the prevalence of perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS) in river water samples (n = 56) and suspended solids (n = 5) from three major Western Cape rivers, in South Africa. Solid phase extraction (SPE) followed by liquid chromatography combined with electrospray tandem mass spectrometry (LC-MS/MS) using an analytical method developed in ISO 25101 (2009), PFOS and PFOA concentration in river water and in suspended solids from the rivers was investigated and quantified. From the results, PFOA and PFOS were detected in all the river water samples and were found in concentrations up to 314 and 182 ng/L for Diep River; 390 and 47 ng/L for Salt River; and 146 and 23 ng/L for Eerste River, respectively. In suspended solids, concentrations for PFOS and PFOA were 28 and 26 ng/g for Diep River; 16 and less than limit of detection for Eerste River; and 14 and 5 ng/g for Salt River, respectively. Some of these concentrations are higher than those previously reported in similar studies in various countries, and this suggests there is a cause for concern, in the Western Cape, South Africa, particularly in catchments where river and ground water is drawn for agricultural purposes in the province.

Plant communities along the Eerste River, Western Cape, South Africa: Community descriptions and implications for restoration

Riparian plant communities fulfil many functions, including the provision of corridors linking protected areas and other zones of high conservation value. These habitats across much of South Africa’s Cape Floristic Region, especially in the lowlands, have been heavily impacted and degraded by human activities. There is increasing interest in the restoration of degraded riparian zones and the ecosystem services they provide to enhance the conservation value of landscapes. Previous studies of riparian vegetation in the Cape Floristic Region focused on pristine headwater systems, and little is known about human-impacted communities that make up most of the riparian vegetation in downstream areas. More information is needed on the composition of these plant communities to establish a baseline for management intervention. The riparian zone of the Eerste River in South Africa’s Western Cape province provides a good opportunity to study the features of riparian vegetation along the entire gradient, from pristine vegetation in a protected area through different levels of human-mediated degradation. Riparian vegetation was surveyed in 150 plots along the entire length of the Eerste River (ca. 40 km). Data were analysed using the vegetation classification and analysis software package JUICE. Final groupings were plotted onto a two-dimensional detrended correspondence analysis plane to check the position of the communities in the reduced multidimensional space. Ten distinct plant communities were identified, including several novel communities dominated by alien plant species. Descriptions of each plant community are presented. Diagnostic, constant and dominant species are listed and the major structural and ecological characteristics of each community are described.Conservation implications: Major changes to hydrological and soil properties, nutrient dynamics and disturbance regimes and plant species composition along sections of the riparian zone mean that restoration of many of these habitats to their historic condition is not feasible. However, several native plant species that provide key ecosystem services persist in and adjacent to transformed communities, offering substantial opportunities for restoration to achieve certain goals.

Online Appendix: Plant communities along the Eerste River, Western Cape, South Africa: Community descriptions and implications for restoration

Online Appendix: Plant communities along the Eerste River, Western Cape, South Africa: Community descriptions and implications for restoration

Distribution and management of Acacia implexa (Benth.) in South Africa: A suitable target for eradication?

This study is the first detailed assessment of an invasion by Acacia implexa (Benth.) (screw-pod wattle) anywhere in the world. Approximately 30000 A. implexa individuals were found spread over about 600ha (a condensed canopy area of ~96ha) in three geographically distinct populations, all in the Western Cape, South Africa. Population structures indicate rapidly increasing populations at all sites, with vegetative suckering dominating over reproduction by seed. Populations appear capable of rapidly densifying if given the opportunity, creating monocultures and even out-competing other invasive acacias. Although seed viability is high (~60%), there is relatively low recruitment from seed, likely as a result of high seed predation (with some previous estimates of up to 100% seed loss). While high seed mortality may suggest limited rates of spread (populations are at most 1km from initial plantings at two of the sites), seeds appear to be able to disperse along roads and watercourses (in particular plants are now established about 5km down the Eerste River from the putative initial planting site in Stellenbosch). This suggests that the extent of all three populations could increase much more rapidly in the future. Formal risk assessment and bioclimatic niche modelling indicate that this species has the potential to invade large parts of South Africa, particularly in coastal regions. Given the current limited distribution, the potential threats posed and the success of control to date, we consider eradication a feasible and desirable management goal. The estimated cost of clearing established stands was ~ZAR 700000, but given the strong ability of A. implexa to resprout, proper control and follow-up would be essential to prevent re-establishment of dense stands and further spread. A systematic eradication programme over the next decade will cost an estimated ZAR 1.5million, giving a total eradication cost of ZAR 2.2million. We support the proposed listing of the species as category 1a under the National Environmental Management: Biodiversity Act, and suggest that the species should not be introduced to other countries without clear and comprehensive contingency plans.

The implementation of a battery of in vivo and in vitro bioassays to assess river water for estrogenic endocrine disrupting chemicals

Previous research has shown that accurate evaluation of environmental water samples for estrogenic activity requires a panel of in vitro and in vivo bioassays, which are based on different molecular and cellular action mechanisms. In the current study, a test battery containing four assays was used to analyze water from the Eerste River, South Africa for estrogenicity. Three sites were used for analysis, namely Jonkershoek (control site situated in the mountains at the origin of the Eerste River), sewage effluent from Stellenbosch sewage treatment works and Spier site (sampling site on the Eerste River downstream from Stellenbosch). Estrogenicity was determined using an estrone enzyme linked immuno sorbent assay (ELISA), estrogen induced proliferation of human breast cancer adenocarcinoma cells (MCF-7) also known as the E-SCREEN, estrogen induced suppression of estrogen receptor alpha protein expression (ER-α) in MCF-7 cells (ERα assay) and by monitoring estrogen induced vitellogenin (VTG) synthesis in juvenile Oreochromis mossambicus (VTG assay). Low concentrations of estrone (ranging between 1.4 and 2.2 ng/l) near the detection limit of the assay were detected in samples collected from Jonkershoek. Water from this site shows no estrogenicity in the E-SCREEN, ERα assay or VTG synthesis bioassay. The estrone concentrations in the sewage effluent extracts, as well as Spier site extracts, ranged between 14.7 and 19.4 ng/l. The assays using ERα induction by the MCF-7 cell line, MCF-7 proliferation and in vivo VTG synthesis by juvenile tilapia showed that these samples are estrogenic. The results obtained for the assays in the battery are comparable.

Viticultural terroirs in Stellenbosch, South Africa. I. The identification of natural terroir units

&lt;p style="text-align: justify;"&gt;&lt;strong&gt;Aims&lt;/strong&gt;: A natural terroir unit (NTU) can be defined as a unit of land that is characterized by relatively homogenous topography, climate, geological substrate and soil. The mapping of NTUs is the first stage of data acquisition in a terroir study. This study aimed to identify NTUs using a Geographic Information System and to characterize the Stellenbosch Wine of Origin District using existing digital information at the scale of a wine producing district.&lt;/p&gt;&lt;p style="text-align: justify;"&gt;&lt;strong&gt;Methods and results&lt;/strong&gt;: The study area is bordered by mountains, situated close to the Atlantic Ocean and bisected by the Eerste river valley, resulting in notable spatial variation of all climatic parameters. The geology is complex due to the high degree of tectonic movement and mixing of parent material. Terrain morphological units, altitude, aspect and soil type were used as primary keys/variables for the identification of NTUs. Each of the identified units was further described with respect to the extent of the expected sea breeze effect and, for certain of the soil types, the associated parent material. A total of 1389 NTUs were identified in the Stellenbosch Wine of Origin District.&lt;/p&gt;&lt;p style="text-align: justify;"&gt;&lt;strong&gt;Conclusions&lt;/strong&gt;: Many of the natural terroir units identified for the Stellenbosch Wine of Origin District are of a size that is not economically or practically viable.&lt;/p&gt;&lt;p style="text-align: justify;"&gt;&lt;strong&gt;Significance and impact of the study&lt;/strong&gt;: The natural terroir units should be grouped into larger, more manageable and thus more viable terroir units using data relating their viticultural and oenological potential. This task will be addressed in subsequent companion papers.&lt;/p&gt;

The Screening of River Water for Immunotoxicity Using an In Vitro Whole Blood Culture Assay

The acquired immunity consists of two pathways namely the humoral immunity that defends the host against extracellular pathogens such as bacteria and the cell-mediated immunity that defends the host against intracellular pathogens such as Mycobacterium tuberculosis and viruses and also against cancers. The aim of this study is to determine the effects of river water collected from pristine and contaminated sites along the Eerste River, South Africa on inflammation, humoral and acquired immune pathways. Hydrophobic extracts were prepared from water collected at contaminated and pristine sites. Inflammatory activity was determined by measuring interleukin (IL)-6 levels synthesized by whole blood after incubation with the extracts. For determining the effects on acquired immunity, phytohemagglutinin stimulated whole blood from healthy volunteers was incubated with extracts. The effect on humoral immunity was determined using IL-10 as biomarker, while interferon-gamma was used as biomarker for cell-mediated immunity. The results obtained show that water from the sites downstream from human activity induced IL-6, a biomarker of inflammation. Extracts collected from a site downstream from an informal housing settlement suppressed biomarkers of both humoral and cell-mediated immunity. Water from sites impacted by human activity can potentially suppress the acquired immune system and this can pose a health risk to people using this water source. Studies must be done to investigate the long-term effects of the contaminated water on animals in vivo.

Impact of a dam on benthic macroinvertebrates in a small river in a biodiversity hotspot: Cape Floristic Region, South Africa

Suitable reservoirs and monitoring methods are needed to manage scarce water supplies in dry countries. We assessed here the impact on aquatic macroinvertebrates of the only dam on the Eerste River, which runs through the heart of a biodiversity hotspot, the Cape Floristic Region, South Africa. The dam and associated activities, were the only forms of disturbance in this otherwise pristine area. We sampled over 20,000 macroinvertebrate individuals and illustrated some categorical effects of the impoundment and its effects on macroinvertebrate assemblages. Macroinvertebrate species diversity below the dam was only half of that in the pristine catchment area above the dam. Furthermore, Ephemeroptera, Plecoptera and Trichoptera diversity and abundance dropped to almost zero as a result of the impoundment. In contrast, the abundance of the Diptera family Chironomidae increased substantially below the dam. These changes in macroinvertebrate diversity mirrored those recorded in biologically less diverse areas, but are of major concern in this biodiversity hotspot with its rich endemic fauna. We conclude that such an impoundment, while important for human welfare, results in a high price being paid in terms of loss of local biodiversity.

Phylogeny predicts larval biology in a wood-mining chironomid (Diptera: Chironomidae)

The previously unknown larva of Elpiscladius capicola Harrison & Cranston (Diptera: Chironomidae: Orthocladiinae), predicted by postulated phylogeny to be associated with aquatic immersed leaves or wood, has been found. The larva is xylophagous, and occurs in a limited area of the Western Cape, in the Eerste River and Leopard's Kloof stream in the Hottentots Holland mountains. Association with E. capicola is assured by a distinctive (pharate) pupa visible within one mature larva, and the co-occurrence of larvae and diagnostic pupal exuviae in soft immersed wood. The characteristic mentum of Elpiscladius resembles that of Xylotopus Oliver, a Nearctic wood-mining genus, but other features including the dorsal head sclerites and the simple SI seta differ. Although phylogeny predicted the larval biology, addition of 17 larval features for Elpiscladius to that data matrix destroyed the relationship with Austrobrillia Freeman, reducing the Brillia group essentially to a polytomy. Larvae of Elpiscladius co-occur with the immature stages of an undescribed species of Stenochironomus (s.s.) Kieffer. Both these rare xylophagous taxa indicate clean flowing waters with intact native riparian vegetation, and thus can be regarded as biodiversity and environmental conservation indicators.

An epidemiological investigation of the African horsesickness outbreak in the Western Cape Province of South Africa in 2004 and its relevance to the current equine export protocol

African Horsesickness (AHS) is a controlled disease in South Africa. The country is divided into an infected area and a control area. An outbreak of AHS in the control area can result in a ban of exports for at least 2 years. A retrospective epidemiological study was carried out on data collected during the 2004 AHS outbreak in the surveillance zone of the AHS control area in the Western Cape Province. The objective of this study was to describe the 2004 outbreak and compare it with the 1999 AHS outbreak in the same area. As part of the investigation, a questionnaire survey was conducted in the 30 km radius surrounding the index case. Spatial, temporal and population patterns for the outbreak are described. The investigation found that the outbreak occurred before any significant rainfall and that the main AHS vector (Culicoides imicola) was present in abundance during the outbreak. Furthermore, 63% of cases occurred at temperatures < or = 15 degrees C, the Eerste River Valley was a high risk area, only 17% of owners used vector protection as a control measure and 70% of horses in the outbreak area were protected by means of vaccination at the start of the outbreak. The study revealed that the current AHS control measures do not function optimally because of the high percentage of vaccinated horses in the surveillance zone, which results in insufficient sentinel animals and the consequent failure of the early warning system. Alternative options for control that allow continued export are discussed in the paper.

Uptake and distribution of lead (Pb) and cadmium (Cd) in the freshwater crab, Potamonautes perlatus (Crustacea) in the Eerste River, South Africa

The uptake and distribution of lead (Pb) and cadmium (Cd) in thefreshwater crab, Potamonautes perlatus in the Eerste River,South Africa were studied seasonally over two years by comparingconcentrations in crabs, water and sediment in two localities, one upstream and one downstream from the town of Stellenbosch. Lead and cadmium concentrations in whole crabs of different sizeclasses as well as concentrations in various organs and tissues were determined by atomic absorption spectrometry. Data on physical, chemical and bacteriological features are also presented. The mean Zn concentration in the sediment of the downstream locality (77.5 ± 38.4 μg g-1) was significantly higher than in the less polluted upstream locality(44.7 ± 32.8 μg g-1) whilst the manganese concentration of the sediment was significantly higher in the upstream locality. The gonads (mean Pb 23.4, range 0.1-125.0 μg g-1; mean Cd 5.3, range 0.1-22.2 μg g -1) and carapace (mean Pb 23.4, range 0.7-327.6 μg g-1; mean Cd 4.0, range 0.4-18.5 μg g-1) contained thehighest concentrations of both metals irrespective of season orlocality. For both Pb and Cd significant differences (p < 0.05, Student's t-test) were found between the metal content of different organs. The gonads had the highest and the digestiveglands the lowest concentrations of both heavy metals.Results indicated that anthropogenic activities did not influencesediment and water concentrations significantly. Smaller crabs accumulated more lead and cadmium than larger crabs with all crabs having significantly higher concentrations than both waterand sediment. No significant differences in mean concentrationsof lead and cadmium in whole crabs or organs were found between the two localities. Although body loads for both metals did notreflect prevailing environmental levels of these metals reliably,the crabs may still be used to monitor bioavailability over time.