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Coastal wetlands (mangrove, tidal marsh and seagrass) sustain the highest rates of carbon sequestration per unit area of all natural systems1,2, primarily because of their comparatively high productivity and preservation of organic carbon within sedimentary substrates3. Climate change and associated relative sea-level rise (RSLR) have been proposed to increase the rate of organic-carbon burial in coastal wetlands in the first half of the twenty-first century4, but these carbon-climate feedback effects have been modelled to diminish over time as wetlands are increasingly submerged and carbon stores become compromised by erosion4,5. Here we show that tidal marshes on coastlines that experienced rapid RSLR over the past few millennia (in the late Holocene, from about 4,200 years ago to the present) have on average 1.7 to 3.7 times higher soil carbon concentrations within 20 centimetres of the surface than those subject to a long period of sea-level stability. This disparity increases with depth, with soil carbon concentrations reduced by a factor of 4.9 to 9.1 at depths of 50 to 100 centimetres. We analyse the response of a wetland exposed to recent rapid RSLR following subsidence associated with pillar collapse in an underlying mine and demonstrate that the gain in carbon accumulation and elevation is proportional to the accommodation space (that is, the space available for mineral and organic material accumulation) created by RSLR. Our results suggest that coastal wetlands characteristic of tectonically stable coastlines have lower carbon storage owing to a lack of accommodation space and that carbon sequestration increases according to the vertical and lateral accommodation space6 created by RSLR. Such wetlands will provide long-term mitigating feedback effects that are relevant to global climate-carbon modelling.
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Sequestro de Carbono , Carbono/metabolismo , Água do Mar/análise , Áreas Alagadas , Carbono/análise , Sedimentos Geológicos/química , História Antiga , Oceanos e MaresRESUMO
Managing coastal wetlands is one of the most promising activities to reduce atmospheric greenhouse gases, and it also contributes to meeting the United Nations Sustainable Development Goals. One of the options is through blue carbon projects, in which mangroves, saltmarshes, and seagrass are managed to increase carbon sequestration and reduce greenhouse gas emissions. However, other tidal wetlands align with the characteristics of blue carbon. These wetlands are called tidal freshwater wetlands in the United States, supratidal wetlands in Australia, transitional forests in Southeast Asia, and estuarine forests in South Africa. They have similar or larger potential for atmospheric carbon sequestration and emission reductions than the currently considered blue carbon ecosystems and have been highly exploited. In the present article, we suggest that all wetlands directly or indirectly influenced by tides should be considered blue carbon. Their protection and restoration through carbon offsets could reduce emissions while providing multiple cobenefits, including biodiversity.
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Estuaries in South Africa are very important for biodiversity conservation and serve as focal points for leisure and tourism activities. The organophosphate flame retardants (OPFRs) levels in these aquatic systems haven't been documented in any studies as of yet. Due to the negative effects of persistent organic pollutants in South African estuaries, we examined the occurrence of eight OPFRs in sediments of two estuaries by studying their spatiotemporal distribution, season variation, and ecological risks. The Sundays Estuary (SDE), a semi-urbanized agricultural surrounding system, recorded an ∑8OPFR concentration in sediments that ranged from 0.71 to 22.5 ng/g dw, whereas Swartkops Estuary, a largely urbanized system, recorded a concentration that ranged from 0.61 to 119 ng/g dw. Alkyl-OPFRs were the prevalent homologue in both estuaries compared to the chlorinated and aryl groups. While TBP, TCPP, and TCrP were the most abundant compounds among the homologue groups. There was no distinct seasonal trend of ∑8OPFR concentration in either estuary, with summer and autumn seasons recording the highest concentrations in SDE and SWE, respectively. Ecological risks in the majority of the study sites for the detected compounds were at low (RQ < 0.1) and medium levels (0.1 ≤ RQ < 1) for certain species of fish, Daphnia magna and algae. However, the cumulative RQs for all the compounds had ∑RQs ≥1 for most sites in both estuaries, indicating that these organisms, if present in both estuaries, may be exposed to potential ecological concerns due to accumulated OPFR chemicals. The scope of future studies should be broadened to include research areas that are not only focus on the bioaccumulation patterns of these compounds but also find sustainable ways to reduce them from these estuarine environments.
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Monitoramento Ambiental , Estuários , Retardadores de Chama , Sedimentos Geológicos , Estações do Ano , Poluentes Químicos da Água , Sedimentos Geológicos/química , Sedimentos Geológicos/análise , Poluentes Químicos da Água/análise , África do Sul , Medição de Risco , Retardadores de Chama/análise , Organofosfatos/análise , Organofosfatos/toxicidade , AnimaisRESUMO
The long-term health of many South African estuaries is impacted by pollutants entering these systems through industrial and agricultural runoff, sewage outfalls, contaminated storm water drainage, flows from informal settlements, and plastic materials in marine debris. Uncontrolled inputs combined with poor environmental management often result in elevated levels of persistent organic pollutants (POPs) in affected estuaries. Data on POPs research from 1960 to 2020 were analysed in terms of their sources, environmental investigations, and health implications. The outcome showed polychlorinated biphenyls (PCBs) and per- and poly-fluoroalkyl sulphonates (PFASs) to exceed the US EPA health advisory levels for drinking water. Concentration of organochlorine pesticides (OCPs) in water were below the WHO limits, while those in fish tissues from most estuaries were found to be below the US FDA limits. Although environmental compartments in some estuaries (e.g. Rooiels and uMngeni estuaries) seem to be less contaminated relative to other marine systems around the world, many others were polluted and critically modified (e.g. Durban Bay, Swartkops, Sundays, and Buffalo systems). Due to inconsistent monitoring methods coupled with limited data availability, temporal trends were unclear. Of the 290 estuaries in South Africa, 65 were prioritised and recommended for POPs evaluation based on their pollution sources, and a monitoring strategy was defined in terms of sampling. Government policies to curb marine pollution need to be enforced to prevent chronic contamination that leads to water quality deterioration and loss of ecosystem services.
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Poluentes Orgânicos Persistentes , Animais , Ecossistema , Exposição Ambiental/análise , Monitoramento Ambiental/métodos , Estuários , Hidrocarbonetos Clorados/análise , Praguicidas/análise , Plásticos , Bifenilos Policlorados/análise , Hidrocarbonetos Policíclicos Aromáticos/análise , África do Sul , Poluentes Químicos da Água/análiseRESUMO
Organophosphate pesticides (OPPs) are persistent in the environment, but little information is available on their bioaccumulation in seagrass. In this study, the seagrass - Zostera capensis was collected from Swartkops Estuary in South Africa to investigate the bioaccumulation of OPPs from contaminated sediments and the water column. This plant was chosen because it grows abundantly in the estuary's intertidal zone, making it a viable phytoremediator in the urban environment. Extraction was performed by the QuEChERS method followed by GC-MS analysis. The mean concentration of ∑OPPs ranged from 0.01 to 0.03 µg/L for surface water; 6.20-13.35 µg/kg dw for deep-rooted sediments; 18.79-37.75 µg/kg dw for leaf tissues and 12.14-39.80 µg/kg dw for root tissues of Z. capensis. The biota-sediment accumulation factors (BSAFs) were greater than one, indicating the potential for Z. capensis to bioaccumulate and intercept the targeted pesticides. A weak insignificant correlation observed between log BSAFs and log Kow indicates that the bioaccumulation of OPPs in tissues of Z. capensis were not dependent on the Kow. Eight of the selected pesticides had root-leaf translocation factors (TFr-l) greater than 1, indicating that Z. capensis can transport these chemicals from roots to leaves. The results from this study implies that this plant species can clean up OPP contamination in the environment.
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Praguicidas , Poluentes Químicos da Água , Zosteraceae , Monitoramento Ambiental , Estuários , Sedimentos Geológicos , Organofosfatos , Praguicidas/análise , Poluentes Químicos da Água/análiseRESUMO
Since the addition of polybrominated diphenyls and organochlorine pesticides (OCPs) to the world banned list, toxic organophosphate contaminants (OPCs) such as organophosphate flame retardants and organophosphate pesticides have been, respectively, used as substitutes. These chemicals are reported to be more toxic than their halogenated counterparts. It is rare to find a study that focuses on visualising the publication trends of these chemical classes. In this study, we employed a bibliometric model to systematically map research activities between 1990 and 2018 using OPC articles retrieved from the WoS and Scopus databases. A total of 1090 articles were retrieved from the hybrid databases with an article/author and author/article ratio of 0.33 and 3.02, respectively. Articles on OPC studies were positively correlated with the number of years (r2 = 0.96; y = 0.23x2 - 3.82x + 27.90) suggesting an increase in the number of articles on this subject in future. The USA ranked first in terms of articles (n = 245) and citations (n = 12,922) followed by China and India (203 and 89 articles, respectively). Articles from China and the USA had strong collaboration with other countries. Research priorities and top author keywords included pesticides (n = 112), organophosphate (n = 83) and acetylcholinesterase (n = 60) and were also well represented in keywords-plus. Developed countries had higher outputs compared to developing countries. It was observed that from our thematic literature classifications, human toxicity, ecotoxicological impacts, and environmental monitoring of OPCs were of greater importance to scholars, thus indicating the direction of future research. Futuristic studies need to foster partnership with policymakers, journalists, consultants, farmers, artisans and community workers on OPC research. This will not only enhance scientific communication and community engagement but will also increase the awareness of these pollutants to the general public.
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Bibliometria , Poluentes Ambientais , Organofosfatos , Publicações Seriadas/estatística & dados numéricos , Animais , China , Bases de Dados Bibliográficas , Monitoramento Ambiental , Poluentes Ambientais/análise , Poluentes Ambientais/toxicidade , Retardadores de Chama/análise , Retardadores de Chama/toxicidade , Humanos , Índia , Organofosfatos/análise , Organofosfatos/toxicidade , Praguicidas/análise , Praguicidas/toxicidade , Publicações Seriadas/tendênciasRESUMO
Mangrove habitats support taxonomically diverse benthic communities, yet their effects on microphytobenthos remain understudied. This study investigated the benthic diatom community structure of 17 microtidal mangrove estuaries situated along the east coast of South Africa. High sediment organic content (≤ 18.1 %) and clay fraction (≤ 17.5 %) measured in the Avicennia marina and Rhizophora mucronata habitats favoured diverse communities (H' > 3) and the presence of unique benthic diatom species such as Gyrosigma balticum. The habitat complexity and stabilisation provided by the mangrove forests served as microrefugia for colonisation of benthic diatoms. Taxa displayed a broad range of nutrient tolerance, with some nutrient tolerant species (e.g., Halamphora acutiuscula, Navicula clausii, Navicula gregaria, and Navicula radiosa) dominating the communities in the Mbashe and Mnyameni estuaries. The presence of these nutrient tolerant taxa in relatively pristine systems serves as an early warning for possible anthropogenic nutrient enrichment.
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Biodiversidade , Diatomáceas , Estuários , Áreas Alagadas , Rhizophoraceae , Avicennia , África do Sul , Monitoramento Ambiental , Ecossistema , Sedimentos GeológicosRESUMO
While anthropogenic pollution is a major threat to aquatic ecosystem health, our knowledge of the presence of xenobiotics in coastal Dissolved Organic Matter (DOM) is still relatively poor. This is especially true for water bodies in the Global South with limited information gained mostly from targeted studies that rely on comparison with authentic standards. In recent years, non-targeted tandem mass spectrometry has emerged as a powerful tool to collectively detect and identify pollutants and biogenic DOM components in the environment, but this approach has yet to be widely utilized for monitoring ecologically important aquatic systems. In this study we compared the DOM composition of Algoa Bay, Eastern Cape, South Africa, and its two estuaries. The Swartkops Estuary is highly urbanized and severely impacted by anthropogenic pollution, while the Sundays Estuary is impacted by commercial agriculture in its catchment. We employed solid-phase extraction followed by liquid chromatography tandem mass spectrometry to annotate more than 200 pharmaceuticals, pesticides, urban xenobiotics, and natural products based on spectral matching. The identification with authentic standards confirmed the presence of methamphetamine, carbamazepine, sulfamethoxazole, N-acetylsulfamethoxazole, imazapyr, caffeine and hexa(methoxymethyl)melamine, and allowed semi-quantitative estimations for annotated xenobiotics. The Swartkops Estuary DOM composition was strongly impacted by features annotated as urban pollutants including pharmaceuticals such as melamines and antiretrovirals. By contrast, the Sundays Estuary exhibited significant enrichment of molecules annotated as agrochemicals widely used in the citrus farming industry, with predicted concentrations for some of them exceeding predicted no-effect concentrations. This study provides new insight into anthropogenic impact on the Algoa Bay system and demonstrates the utility of non-targeted tandem mass spectrometry as a sensitive tool for assessing the health of ecologically important coastal ecosystems and will serve as a valuable foundation for strategizing long-term monitoring efforts.
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Matéria Orgânica Dissolvida , Poluentes Ambientais , Ecossistema , Estuários , Baías , Rios/química , Agricultura , Preparações FarmacêuticasRESUMO
This study assessed the tissue distribution, dietary intake, and potential health risks of eight OPPs in Pomadasys commersonnii (Spotted grunter) and Mugil cephalus (Flathead mullet) from the Sundays and Swartkops estuaries in South Africa. The highest concentration in fish tissues was found in muscles of M. cephalus (178 ± 80.4 ng/g ww) and P. commersonnii (591 ± 280 ng/g ww) from Sundays Estuary. The ∑6OPPs concentration in muscles from both fish species was higher in muscles than in the gills with fenitrothion dominating the distribution profile. Results from the path analysis indicate that lipid, weights, and length of the fish species do not influence the concentration of OPPs in the studied fish species. The calculated hazard ratios, which represent the non-carcinogenic risks, were less than one for all OPPs, indicating that the concentration of OPPs detected in fish muscles had negligible consequences on human health.
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Inseticidas , Praguicidas , Smegmamorpha , Poluentes Químicos da Água , Animais , Humanos , África do Sul , Estuários , Monitoramento Ambiental/métodos , Distribuição Tecidual , Poluentes Químicos da Água/análise , Peixes , Inseticidas/análise , Compostos Organofosforados/análise , Medição de Risco , Ingestão de Alimentos , Organofosfatos/análise , Praguicidas/análiseRESUMO
Rapid urbanisation and industrialisation have placed increased pressure on the ecosystem health of urban estuaries. Sustainable drainage systems (SuDS) are globally accepted practices for managing the water quality of stormwater and effluent discharged into urban systems. The Swartkops Estuary in South Africa is a heavily urbanized estuary that has a long history of pollution, specifically trace metal contamination, originating from industrial sources and urban wastewater. Using a novel SuDS treatment train, the physical characteristics (total suspended solids), macronutrients (orthophosphates, nitrate, ammonium), trace metals (As, Cd, Hg, Fe, Pb, Cu), and E. coli concentrations were measured monthly for one year, both before and after the treatment train. The treatment train consisted of five interconnected 500 L plastic tanks for sedimentation, filtration (sand and stone), biodegradation and floating wetlands. Results indicate that the SuDS treatment train provided an efficient method in reducing the pollution load to this urban estuary, by reducing macronutrient concentrations by 76 %, trace elements concentrations by 74 % and faecal bacteria counts (E. coli) by 80 %.
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Metais Pesados , Poluentes Químicos da Água , Estuários , Poluentes Químicos da Água/análise , Monitoramento Ambiental/métodos , Ecossistema , Escherichia coli , Metais Pesados/análise , Sedimentos GeológicosRESUMO
Wetland plants are naturally exposed to high metal concentrations, and often have mechanisms to prevent metal toxicity. This study compared metal concentrations in seagrass (Zostera capensis) and salt marsh (Spartina maritima, Salicornia tegetaria) - to determine their niche as metal sinks. Samples were collected in each season over a year at five sites in the estuary and analysed using a Total X-Ray Fluorescence (TXRF) spectrometer. Spartina maritima and S. tegetaria accumulated in their roots, and displayed little translocation to leaves (BCF = 1-14; TF[leaf/root] < 1). Contrastingly, Z. capensis showed high uptake to its leaves (TF[leaf/root] = 1-8; Mn, Zn, Cr, Pb, Ni, Cu). Spartina maritima and S. tegetaria were identified as good phytostabilisers (BCF > 1, TF[leaf/root] < 1). Compartmentalization was unique to each species, and considering their ecosystem service importance, more plant species should be analysed to estimate their ecological value for management purposes.
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Metais Pesados , Áreas Alagadas , Ecossistema , Estuários , África do Sul , Metais Pesados/análise , Poaceae , Plantas , Biodegradação Ambiental , Monitoramento AmbientalRESUMO
Eutrophication-driven harmful algal blooms (HABs) can have secondary effects on larval fishes that rely on estuaries as nurseries. However, few studies worldwide have quantified these effects despite the global rise in eutrophication. This study presents a novel approach using biochemical body condition analyses to evaluate the impact of HABs on the growth and body condition of the larvae of an estuarine resident fish. Recurrent phytoplankton blooms of Heterosigma akashiwo occur in the warm-temperate Sundays Estuary on the southeast coast of South Africa. The response in body condition and assemblage structure on larval estuarine roundherring (Gilchristella aestuaria) was measured in conjunction with bloom conditions, water quality and zooplanktonic prey and predators. Larvae and early juveniles were sampled during varying intensity levels, duration and frequency of hypereutrophic blooms. This study demonstrated that extensive HABs could significantly impact larval roundherring, G. aestuaria, by decreasing larval nutritional condition and limiting their growth, resulting in poor grow-out into the juvenile phase. Poor condition and growth may likely affect recruitment success to adult populations, and since G. aestuaria is an important forage fish and zooplanktivore, poor recruitment will hold consequences for estuarine food webs.
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A focused diagnosis of ecosystem health in two South African estuaries (Kromme and Gamtoos) was conducted. Four pollution indices were used, i.e., geoaccumulation (Igeo), ecological risk (RI), contamination factor (CF) and pollution load index (PLI), to assess toxicity levels of metal contaminants in relation to background values. The Igeo results (11.1 %) can be classified as contaminated, with Cd, the only element with high values in both estuaries. Likely sources (herbicides, pesticides) of Cd are used in the agricultural dominated catchments. There was a high concentration of Mn (13.4 ± 2.51 and 12.3 ± 1.13 µg·g-1) and Fe (1289 ± 243 and 1291 ± 130 µg·g-1) at site 4 for Gamtoos and Kromme estuary respectively compared to the other metal elements. Although results indicate low metal contamination, with increasing global anthropogenic pressure, continuous monitoring should be prioritised to assist in managing estuarine systems that support a wide range of socio-economic and ecosystem services.
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Coastal saltmarshes provide globally important ecosystem services including 'blue carbon' sequestration, flood protection, pollutant remediation, habitat provision and cultural value. Large portions of marshes have been lost or fragmented as a result of land reclamation, embankment construction, and pollution. Sea level rise threatens marsh survival by blocking landward migration where coastlines have been developed. Research-informed saltmarsh conservation and restoration efforts are helping to prevent further loss, yet significant knowledge gaps remain. Using a mixed methods approach, this paper identifies ten research priorities through an online questionnaire and a residential workshop attended by an international, multi-disciplinary network of 35 saltmarsh experts spanning natural, physical and social sciences across research, policy, and practitioner sectors. Priorities have been grouped under four thematic areas of research: Saltmarsh Area Extent, Change and Restoration Potential (including past, present, global variation), Spatio-social contexts of Ecosystem Service delivery (e.g. influences of environmental context, climate change, and stakeholder groups on service provisioning), Patterns and Processes in saltmarsh functioning (global drivers of saltmarsh ecosystem structure/function) and Management and Policy Needs (how management varies contextually; challenges/opportunities for management). Although not intended to be exhaustive, the challenges, opportunities, and strategies for addressing each research priority examined here, providing a blueprint of the work that needs to be done to protect saltmarshes for future generations.
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Conservação dos Recursos Naturais , Ecossistema , Áreas Alagadas , Mudança Climática , Elevação do Nível do MarRESUMO
Tidal marshes store large amounts of organic carbon in their soils. Field data quantifying soil organic carbon (SOC) stocks provide an important resource for researchers, natural resource managers, and policy-makers working towards the protection, restoration, and valuation of these ecosystems. We collated a global dataset of tidal marsh soil organic carbon (MarSOC) from 99 studies that includes location, soil depth, site name, dry bulk density, SOC, and/or soil organic matter (SOM). The MarSOC dataset includes 17,454 data points from 2,329 unique locations, and 29 countries. We generated a general transfer function for the conversion of SOM to SOC. Using this data we estimated a median (± median absolute deviation) value of 79.2 ± 38.1 Mg SOC ha-1 in the top 30 cm and 231 ± 134 Mg SOC ha-1 in the top 1 m of tidal marsh soils globally. This data can serve as a basis for future work, and may contribute to incorporation of tidal marsh ecosystems into climate change mitigation and adaptation strategies and policies.
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Nutrient pollution is facilitating the encroachment of invasive aquatic plants in various water bodies globally. This study investigated seasonal aquatic macrophyte responses in two temporarily closed estuaries with different nutrient inputs. Consistent effluent discharge from the upstream wastewater treatment works (WWTW) facilitated the establishment of numerous freshwater invasive alien aquatic plants (IAAPs) in the uThongathi Estuary. IAAPs (Myriophyllum aquaticum, Pistia stratiotes and Pontederia crassipes) were only displaced from the estuary after high flow events (>5 m3 s-1). In the less polluted uMdlotane Estuary nutrient pulses (>1 mg/L DIN) associated with high rainfall changed the aquatic macrophyte composition. The nutrient tolerant non-rooted Ceratophyllum demersum outcompeted the rooted submerged macrophyte Stuckenia pectinata. Species composition changed in response to flow and nutrient inputs, with the exception of emergent macrophytes, such as the grass Echinochloa pyramidalis, that remained consistent in cover and distribution in the uMdlotane Estuary. This study demonstrated that aquatic macrophytes are more responsive to nutrient inputs in unimpacted estuaries compared to consistently nutrient-rich systems where flow is an important driver of IAAPs community dynamics. Many temporarily closed estuaries are subjected to nutrient pollution from WWTWs and restoration efforts such as diversion of discharges to constructed wetlands needs urgent implementation.
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Eichhornia , Estuários , Espécies Introduzidas , Nutrientes , Dispersão VegetalRESUMO
Worldwide seagrass populations are in decline, calling for urgent measures in their conservation. Glyphosate is the most widely used herbicide globally, leading to increasing concern about its ecological impact, yet little is known about the prevalence or impact of glyphosate on seagrasses. In this study, we investigated the effect of sublethal glyphosate exposure on the endangered seagrass, Zostera capensis, to identify effects on growth, photosynthetic pigments and leaf morphology as measures of seagrass fitness. Seagrasses were exposed to a single dose of a commercial glyphosate formulation-ranging between 250 to 2,200 µg/L. After three weeks, the median leaf area decreased by up to 27%, with reductions of up to 31% in above ground biomass (p < 0.05). Photosynthetic pigment concentration showed no significant difference between groups. The observed effects on biomass and leaf area were seen at glyphosate levels below the regulatory limits set for surface water by several countries and may negatively affect the long-term resilience of this ecosystem engineer to additional stressors, such as those associated with climate change and anthropogenic pollution. As such, glyphosates and other herbicides that are washed into estuarine and marine ecosystems, pose a significant threat to the persistence of seagrasses and are important factors to consider in seagrass conservation, management and restoration efforts.
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Herbicidas , Zosteraceae , Herbicidas/toxicidade , Ecossistema , Fotossíntese , GlifosatoRESUMO
This study investigated the nutrient removal efficiency of a constructed wetland (CW) piloted to treat urban runoff before entering an estuary. Physico-chemical, dissolved inorganic nutrient (DIN and DIP), and stormwater inflow volume data were measured. The CW removal efficiency of DIN was negligible (5% uptake), while it acted as a consistent source of DIP (68% efflux) to the receiving estuarine waters. There was low water residency within the small CW (0.8 ha) that has been compounded by a 10-fold increase in flow volume since 2016. The surface area of the CW would need to be increased to 46 ha to cope with current daily inputs (ca. 6300 m3 d-1). The lack of maintenance (e.g., macrophyte harvesting, sediment desludging) has reduced nutrient uptake and increased autochthonous inputs. The conversion of an abandoned saltpan into an extension of the CW has been considered to manage the high flow volume and remove nutrients.
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Estuários , Áreas Alagadas , Nitrogênio/análise , Nutrientes , Fósforo/análiseRESUMO
The seasonal variation, spatial distribution, and ecological risks of thirteen organophosphate pesticides (OPPs) were studied in the Sundays and Swartkops estuaries in South Africa. Ten pesticides were detected in surface water samples from both estuaries, while all OPPs were detected in sediments. The highest concentration of OPPs (18.8 µg pyrazophos L-1) was detected in surface water samples from Swartkops Estuary, while 48.7 µg phosalone kg-1 dw was the highest in sediments collected from Sundays Estuary. There was no clear seasonal pattern in OPPs occurrence in surface water from both systems. However, their occurrence in sediments was in the following order: winter > autumn > summer > spring, perhaps indicating major pesticide input in the winter seasons. Results from ecological risk assessment showed that pyraclofos and chlorpyrifos (CHL) in surface water from both systems are respectively likely to cause high acute and chronic toxicity to fish (risk quotient - RQ > 1). For sediments of both estuaries, the highest acute and chronic RQs for fish were calculated for isazophos and CHL respectively. The majority of the detected OPPs in sediments posed potential high risks to Daphnia magna from both systems. These results suggest that these aquatic organisms (fish, and Daphnia), if present in the studied estuaries, can develop certain forms of abnormalities due to OPP exposure. To this end, proper measures should be taken to reduce OPP input into the estuarine systems.
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Clorpirifos , Inseticidas , Praguicidas , Poluentes Químicos da Água , Animais , Daphnia , Monitoramento Ambiental/métodos , Estuários , Peixes , Sedimentos Geológicos , Compostos Organofosforados , Praguicidas/análise , Medição de Risco , Rios , Estações do Ano , África do Sul , Água , Poluentes Químicos da Água/análiseRESUMO
Halophytes in estuaries are effective sinks of carbon, nitrogen, and phosphorus. Blue carbon (BC) is carbon stored in coastal habitats such as mangroves, salt marshes and seagrass. The objectives of this study were to firstly assess the biomass and sediment C stocks in salt marsh (Spartina maritima and Salicornia tegetaria) and seagrass (Zostera capensis) habitats of the Swartkops Estuary, South Africa. Secondly, we applied the nutrient pollutant indicator (NPI) to assess the nutrient status of the estuary. Six replicate sediment cores of 1 m (summer) and 0.5 m (winter) per plant species were collected at six sites. Six replicates for biomass of each species were harvested at each site during summer and winter. Biomass and nutrient dynamics showed that there were distinct seasonal differences in the magnitude of C, N, and P stored in the plants. The sediment was the dominant C pool and differed spatially with creek sites storing more C. Out of the three species, S. maritima stored the most C (224 ± 19.1 Mg C ha-1 in sediment, 16.7 ± 1.2 Mg C ha-1 in biomass), followed by S. tegetaria (207 ± 3.5 Mg C ha-1 in sediment, 4.3 ± 0.4 Mg C ha-1 in biomass) and Z. capensis (180 ± 18.4 Mg C ha-1 in sediment, 2.1 ± 0.7 Mg C ha-1 in biomass). The N:biomass ratios were low in both seasons for Z. capensis, S. maritima and S. tegetaria (0.08, 0.02 and 0.04, respectively) indicating consistent eutrophic conditions in the estuary. Resultantly, the plants displayed a significantly lower below-ground standing biomass highlighting the potential variations of BC storage in eutrophic estuaries.