Pub Date : 2022-10-14DOI: 10.2989/16085914.2022.2115705
C. Palmer
{"title":"A lineage of leadership: a story in memory of Brian Allanson","authors":"C. Palmer","doi":"10.2989/16085914.2022.2115705","DOIUrl":"https://doi.org/10.2989/16085914.2022.2115705","url":null,"abstract":"","PeriodicalId":7864,"journal":{"name":"African Journal of Aquatic Science","volume":"47 1","pages":"421 - 422"},"PeriodicalIF":1.4,"publicationDate":"2022-10-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49359466","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-10-13DOI: 10.2989/16085914.2022.2109576
A. F. van der Merwe, A. Myburgh, G. Hall, A. Kaiser, S. Woodborne
Stable isotope analysis is ubiquitous as a method to investigate food-web dynamics at various scales in aquatic ecology. Most studies make use of dorsal muscle tissue, which involves lethal sampling of the fish. The sampling of muscle tissue is often followed by chemical lipid extraction pre-treatment before stable isotope analysis. In this study we tested whether stable light isotope results obtained from fin tissue were comparable to those from muscle, and we investigated whether lipid correction could be used as a substitute for lipid extraction. Various lipid correction equations were evaluated. Based on our results, we propose ethical and efficient methods of sample collection and preparation for stable isotope analysis of freshwater fish. We found that dorsal muscle and fin tissue samples could yield similar interpretations of freshwater food-web dynamics in South Africa, demonstrating that fin clippings might be more widely applied as a nonlethal sampling method for stable isotope studies. Existing lipid correction equations either over- or underestimated true lipid extracted δ13C values, therefore an amended lipid correction equation is proposed as it was successfully tested against a population of wild fish. The errors arising from existing lipid correction equations suggest that site-specific calibration should be employed.
{"title":"Validation of lipid extraction and correction methods for stable isotope analysis of freshwater food webs in southern Africa","authors":"A. F. van der Merwe, A. Myburgh, G. Hall, A. Kaiser, S. Woodborne","doi":"10.2989/16085914.2022.2109576","DOIUrl":"https://doi.org/10.2989/16085914.2022.2109576","url":null,"abstract":"Stable isotope analysis is ubiquitous as a method to investigate food-web dynamics at various scales in aquatic ecology. Most studies make use of dorsal muscle tissue, which involves lethal sampling of the fish. The sampling of muscle tissue is often followed by chemical lipid extraction pre-treatment before stable isotope analysis. In this study we tested whether stable light isotope results obtained from fin tissue were comparable to those from muscle, and we investigated whether lipid correction could be used as a substitute for lipid extraction. Various lipid correction equations were evaluated. Based on our results, we propose ethical and efficient methods of sample collection and preparation for stable isotope analysis of freshwater fish. We found that dorsal muscle and fin tissue samples could yield similar interpretations of freshwater food-web dynamics in South Africa, demonstrating that fin clippings might be more widely applied as a nonlethal sampling method for stable isotope studies. Existing lipid correction equations either over- or underestimated true lipid extracted δ13C values, therefore an amended lipid correction equation is proposed as it was successfully tested against a population of wild fish. The errors arising from existing lipid correction equations suggest that site-specific calibration should be employed.","PeriodicalId":7864,"journal":{"name":"African Journal of Aquatic Science","volume":"47 1","pages":"462 - 473"},"PeriodicalIF":1.4,"publicationDate":"2022-10-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49614891","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-10-06DOI: 10.2989/16085914.2022.2115969
S. Melaku, A. Getahun, Seyoum Mengestou, Akewake Geremew, A. Belay
The artificial propagation of commercially important fish species in Ethiopia is constrained by high mortality rate at the early stage of larval rearing and a subsequent poor growth performance during later stages. This is mainly due to absence of live feeds suited to the requirements of the larvae of the species. Although not organized, several studies have indicated that microalgae, copepods, cladocerans and rotifers are the dominant inhabitants in several water bodies that are the precursors in the larviculture of commercially important finfishes in the world. However, apart from studying the abundance and diversity of these important planktonic organisms, efforts made to culture any of them for use in the larviculture of commercially important fish species in Ethiopia is minimal. This may be due to the lack of comprehensive and organized information on the distribution and abundance of these important species in the context of their potential in aquaculture of live feeds in Ethiopia. The objective of this review is therefore to compile the available information on the abundance and distribution of the major potential live feed organisms in the Ethiopian water bodies with a special emphasis on freshwater live feed organisms currently used in larviculture of commercially important freshwater finfishes. In line with this, four potential live feeds (i.e. microalgae, rotifers, copepods and cladocerans) were included in the review. It is hoped that the review will provide baseline information for future research in the culture of economically important larval live feeds.
{"title":"Potential live feeds for larval fish culture in Ethiopia","authors":"S. Melaku, A. Getahun, Seyoum Mengestou, Akewake Geremew, A. Belay","doi":"10.2989/16085914.2022.2115969","DOIUrl":"https://doi.org/10.2989/16085914.2022.2115969","url":null,"abstract":"The artificial propagation of commercially important fish species in Ethiopia is constrained by high mortality rate at the early stage of larval rearing and a subsequent poor growth performance during later stages. This is mainly due to absence of live feeds suited to the requirements of the larvae of the species. Although not organized, several studies have indicated that microalgae, copepods, cladocerans and rotifers are the dominant inhabitants in several water bodies that are the precursors in the larviculture of commercially important finfishes in the world. However, apart from studying the abundance and diversity of these important planktonic organisms, efforts made to culture any of them for use in the larviculture of commercially important fish species in Ethiopia is minimal. This may be due to the lack of comprehensive and organized information on the distribution and abundance of these important species in the context of their potential in aquaculture of live feeds in Ethiopia. The objective of this review is therefore to compile the available information on the abundance and distribution of the major potential live feed organisms in the Ethiopian water bodies with a special emphasis on freshwater live feed organisms currently used in larviculture of commercially important freshwater finfishes. In line with this, four potential live feeds (i.e. microalgae, rotifers, copepods and cladocerans) were included in the review. It is hoped that the review will provide baseline information for future research in the culture of economically important larval live feeds.","PeriodicalId":7864,"journal":{"name":"African Journal of Aquatic Science","volume":"47 1","pages":"423 - 435"},"PeriodicalIF":1.4,"publicationDate":"2022-10-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47155072","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-10-06DOI: 10.2989/16085914.2022.2124228
A. Birkhead, Mk Reinecke, C. Brown, W. Mgoola, JK Nyirenda
The Elephant Marsh lies on the floodplain of the lower Shire River, in southern Malawi. It is both a cultivated, seasonal floodplain and a wetland, characterised by a complex mosaic of meandering channels, marshland and shallow lakes. In 2016, the Marsh was granted RAMSAR status based on a series of supporting studies, including the modelling of eco-social options for managing its ecological condition. This paper describes two-dimensional (2-D) hydrodynamic modelling using RMA2, in support of this eco-social assessment. The hydraulic model was parameterised using mostly existing data but augmented with bathymetric channel and lake surveys. Calibration and verification used water level data from the hydrometric network for the period 1999 to 2009. Generally, observed water level time-series are well replicated in the model, but there are large discrepancies prior to this period. These are due to temporal changes in hydraulic controls, mainly sedimentation, but also breaching of an embankment at the downstream end of the Marsh. Selected hydraulic-habitat variables (based on daily hydrological time-series 1976 to 2009) provide the indictors of hydrological and hydraulic change used to inform a DRIFT eco-social assessment. The Marsh displays moderate flood attenuation characteristics, but the importance of this will likely increase under continued sedimentation and predicted climate futures, which include more severe storms. The 2-D modelling contributes to an improved understanding of the Marsh’s hydraulic behaviour, particularly regarding anthropogenic influences since the early 1900s.
{"title":"The Elephant Marsh, Malawi – Part 2: two-dimensional hydrodynamic modelling in support of an eco-social assessment","authors":"A. Birkhead, Mk Reinecke, C. Brown, W. Mgoola, JK Nyirenda","doi":"10.2989/16085914.2022.2124228","DOIUrl":"https://doi.org/10.2989/16085914.2022.2124228","url":null,"abstract":"The Elephant Marsh lies on the floodplain of the lower Shire River, in southern Malawi. It is both a cultivated, seasonal floodplain and a wetland, characterised by a complex mosaic of meandering channels, marshland and shallow lakes. In 2016, the Marsh was granted RAMSAR status based on a series of supporting studies, including the modelling of eco-social options for managing its ecological condition. This paper describes two-dimensional (2-D) hydrodynamic modelling using RMA2, in support of this eco-social assessment. The hydraulic model was parameterised using mostly existing data but augmented with bathymetric channel and lake surveys. Calibration and verification used water level data from the hydrometric network for the period 1999 to 2009. Generally, observed water level time-series are well replicated in the model, but there are large discrepancies prior to this period. These are due to temporal changes in hydraulic controls, mainly sedimentation, but also breaching of an embankment at the downstream end of the Marsh. Selected hydraulic-habitat variables (based on daily hydrological time-series 1976 to 2009) provide the indictors of hydrological and hydraulic change used to inform a DRIFT eco-social assessment. The Marsh displays moderate flood attenuation characteristics, but the importance of this will likely increase under continued sedimentation and predicted climate futures, which include more severe storms. The 2-D modelling contributes to an improved understanding of the Marsh’s hydraulic behaviour, particularly regarding anthropogenic influences since the early 1900s.","PeriodicalId":7864,"journal":{"name":"African Journal of Aquatic Science","volume":"47 1","pages":"386 - 404"},"PeriodicalIF":1.4,"publicationDate":"2022-10-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48976425","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-10-05DOI: 10.2989/16085914.2022.2086845
D. Khosa, John S. Hargrove, E. Peatman, O. Weyl
Native to North America, largemouth bass Micropterus salmoides (Lacepède, 1802) were introduced in South Africa in 1928. Florida bass Micropterus floridanus (Lesueur, 1822) were introduced to enhance existing largemouth bass fisheries in 1980. While largemouth bass and Florida bass readily hybridise and produce offspring that are difficult to identify morphologically, confirmation of hybridisation requires genetic analysis. This study sought to understand: (1) the extent to which Florida bass spread within a catchment once introduced; and (2) whether a subset of samples taken from within a catchment accurately characterises hybridisation throughout the catchment. Samples were collected from the Breede River and Kowie River catchments and screened using 38 species-diagnostic single nucleotide polymorphisms to assess hybridisation. Collections from the mainstem of both rivers represented hybrid swarms, and neither pure largemouth bass nor Florida bass were observed. The absence of genetic differentiation among sampling sites suggests that hybridisation will occur throughout systems where both species are present. Hybridisation levels in dams located off the mainstem rivers were significantly variable and represented potential sources for Florida bass alleles observed within rivers. This finding, in conjunction with our limited knowledge of the distributions of the two species, suggests that applying independent management strategies to control and monitor the spread of both species may prove difficult.
{"title":"The extent of hybridisation between largemouth bass and Florida bass across two river systems in South Africa","authors":"D. Khosa, John S. Hargrove, E. Peatman, O. Weyl","doi":"10.2989/16085914.2022.2086845","DOIUrl":"https://doi.org/10.2989/16085914.2022.2086845","url":null,"abstract":"Native to North America, largemouth bass Micropterus salmoides (Lacepède, 1802) were introduced in South Africa in 1928. Florida bass Micropterus floridanus (Lesueur, 1822) were introduced to enhance existing largemouth bass fisheries in 1980. While largemouth bass and Florida bass readily hybridise and produce offspring that are difficult to identify morphologically, confirmation of hybridisation requires genetic analysis. This study sought to understand: (1) the extent to which Florida bass spread within a catchment once introduced; and (2) whether a subset of samples taken from within a catchment accurately characterises hybridisation throughout the catchment. Samples were collected from the Breede River and Kowie River catchments and screened using 38 species-diagnostic single nucleotide polymorphisms to assess hybridisation. Collections from the mainstem of both rivers represented hybrid swarms, and neither pure largemouth bass nor Florida bass were observed. The absence of genetic differentiation among sampling sites suggests that hybridisation will occur throughout systems where both species are present. Hybridisation levels in dams located off the mainstem rivers were significantly variable and represented potential sources for Florida bass alleles observed within rivers. This finding, in conjunction with our limited knowledge of the distributions of the two species, suggests that applying independent management strategies to control and monitor the spread of both species may prove difficult.","PeriodicalId":7864,"journal":{"name":"African Journal of Aquatic Science","volume":"47 1","pages":"507 - 519"},"PeriodicalIF":1.4,"publicationDate":"2022-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44248299","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-09-23DOI: 10.2989/16085914.2022.2107477
A. Joubert, C. Brown, J. King, H. Beuster, A. Greyling
DRIFT (Downstream Response to Imposed Flow Transformation) is an interactive, ecological-social process and software package to assist with environmental flow assessments and river management decision-making. It was originally developed in the 1990s and has subsequently evolved and been applied in over 50 studies in Africa, South America, Asia and Europe. Early versions provided predicted ecological responses over time to specific flow changes, while the latest version provides responses to flow and non-flow drivers as seasonal time series. Here, an ecosystem or eco-social network is built for the river, with links between driver and responder indicators, and relationships created for each link. The network and relationships are developed and entered into the software by specialists based on available data and their knowledge. A range of scenarios is explored through the predicted indicator time series, discipline and site level ecological integrity, and social well-being. While DRIFT models vary in complexity, they are all based on relatively simple fundamental principles and arithmetic. Sequential averaging and summation through the system network is used to calculate an indicator’s response to different drivers for successive seasons over time, while the discipline and site level summaries are found using weighted summation of indicator results and individual discipline results, respectively. Information from different specialist areas is therefore processed in the same way, thereby enabling coherent integration across disciplines.
{"title":"DRIFT: incorporating an eco-social system network and time series approach into environmental flow assessments","authors":"A. Joubert, C. Brown, J. King, H. Beuster, A. Greyling","doi":"10.2989/16085914.2022.2107477","DOIUrl":"https://doi.org/10.2989/16085914.2022.2107477","url":null,"abstract":"DRIFT (Downstream Response to Imposed Flow Transformation) is an interactive, ecological-social process and software package to assist with environmental flow assessments and river management decision-making. It was originally developed in the 1990s and has subsequently evolved and been applied in over 50 studies in Africa, South America, Asia and Europe. Early versions provided predicted ecological responses over time to specific flow changes, while the latest version provides responses to flow and non-flow drivers as seasonal time series. Here, an ecosystem or eco-social network is built for the river, with links between driver and responder indicators, and relationships created for each link. The network and relationships are developed and entered into the software by specialists based on available data and their knowledge. A range of scenarios is explored through the predicted indicator time series, discipline and site level ecological integrity, and social well-being. While DRIFT models vary in complexity, they are all based on relatively simple fundamental principles and arithmetic. Sequential averaging and summation through the system network is used to calculate an indicator’s response to different drivers for successive seasons over time, while the discipline and site level summaries are found using weighted summation of indicator results and individual discipline results, respectively. Information from different specialist areas is therefore processed in the same way, thereby enabling coherent integration across disciplines.","PeriodicalId":7864,"journal":{"name":"African Journal of Aquatic Science","volume":"47 1","pages":"338 - 352"},"PeriodicalIF":1.4,"publicationDate":"2022-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42680878","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-09-19DOI: 10.2989/16085914.2022.2109574
N. Libala, N. Griffin, A. Nyingwa, J. Dini
Freshwater ecosystems play a fundamental role in supporting the environment, the economy and people’s well-being. However, human development and mismanagement have degraded these ecosystems. Using network analysis, we examined the interlinkages (synergies and trade-offs) between indicator 6.6.1 (water-related ecosystems) and other Sustainable Development Goal (SDG) indicators related to freshwater ecosystems to support coherent policies and strategies for freshwater management. Research into scientific literature and reports on freshwater ecosystems and SDG indicator interlinkages was carried out in 2019 and 2020. Sustainable Development Goal custodians were also interviewed about indicator interlinkages and challenges, and the data analysed using thematic analysis. The results showed that water-related ecosystems had the highest positive interlinkages (synergies) with environmental goals, while more trade-offs were found between water-related ecosystems and social goals. Thematic analysis showed that Sustainable Development Goals (SDGs) should focus on partnerships, governance, and challenges regarding water-related ecosystems and SDG implementation. Our findings suggest that an integrated and sustainable freshwater management approach is necessary, one that is embedded within the nexus approach embodied by the United Nations 2030 Agenda for Sustainable Development.
{"title":"Freshwater ecosystems and interactions with the SDG 2030 Agenda: implications for SDG implementation in South Africa","authors":"N. Libala, N. Griffin, A. Nyingwa, J. Dini","doi":"10.2989/16085914.2022.2109574","DOIUrl":"https://doi.org/10.2989/16085914.2022.2109574","url":null,"abstract":"Freshwater ecosystems play a fundamental role in supporting the environment, the economy and people’s well-being. However, human development and mismanagement have degraded these ecosystems. Using network analysis, we examined the interlinkages (synergies and trade-offs) between indicator 6.6.1 (water-related ecosystems) and other Sustainable Development Goal (SDG) indicators related to freshwater ecosystems to support coherent policies and strategies for freshwater management. Research into scientific literature and reports on freshwater ecosystems and SDG indicator interlinkages was carried out in 2019 and 2020. Sustainable Development Goal custodians were also interviewed about indicator interlinkages and challenges, and the data analysed using thematic analysis. The results showed that water-related ecosystems had the highest positive interlinkages (synergies) with environmental goals, while more trade-offs were found between water-related ecosystems and social goals. Thematic analysis showed that Sustainable Development Goals (SDGs) should focus on partnerships, governance, and challenges regarding water-related ecosystems and SDG implementation. Our findings suggest that an integrated and sustainable freshwater management approach is necessary, one that is embedded within the nexus approach embodied by the United Nations 2030 Agenda for Sustainable Development.","PeriodicalId":7864,"journal":{"name":"African Journal of Aquatic Science","volume":"47 1","pages":"353 - 368"},"PeriodicalIF":1.4,"publicationDate":"2022-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45818183","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-09-06DOI: 10.2989/16085914.2022.2086846
Z. Makuvara, J. Marumure, L. Chapungu, J. Machingura, AH Siwela
Owing to their ability to provide a functional measure of organismal response to chemical stressors, oxidative biomarkers are useful in ecotoxicological studies to assess disturbance in aquatic environments. This study assessed the use of oxidative stress biomarkers in Oreochromis mossambicus (Peters, 1852) (Perciformes: Cichlidae) to distinguish between minimally and highly disturbed aquatic environments. A water quality index (WQI) and overall index of pollution (OIP) were used to characterize the target sites, namely the Mananda Dam (control, reference site) and Lower Mguza Dam (disturbed site). Forty male O. mossambicus samples were collected from each dam between April and August 2013. Values for the WQI and OIP indices were significantly higher for the Lower Mguza Dam than for the Mananda Dam (p < 0.05). Oxidative stress biomarker evaluation results showed that the activities of glutathione peroxidase (GPx), superoxide dismutase (SOD) and glutathione S-transferase (GST) as well as the malondialdehyde (MDA) concentration in the liver of O. mossambicus were significantly higher in fish collected from Lower Mguza Dam than those collected from Mananda Dam (p < 0.05). The activities of DT-diaphorase (DTD) and catalase (CAT) were significantly inhibited in fish from the Lower Mguza Dam, when compared to those collected from the Mananda Dam (p < 0.05). From these findings, it is evident that oxidative stress biomarkers, such as antioxidant enzyme activity and MDA accumulation, can be used to differentiate minimally and highly disturbed aquatic environments.
{"title":"Comparison of oxidative stress biomarkers in Oreochromis mossambicus in minimally and highly disturbed aquatic environments in the Matabeleland region, Zimbabwe","authors":"Z. Makuvara, J. Marumure, L. Chapungu, J. Machingura, AH Siwela","doi":"10.2989/16085914.2022.2086846","DOIUrl":"https://doi.org/10.2989/16085914.2022.2086846","url":null,"abstract":"Owing to their ability to provide a functional measure of organismal response to chemical stressors, oxidative biomarkers are useful in ecotoxicological studies to assess disturbance in aquatic environments. This study assessed the use of oxidative stress biomarkers in Oreochromis mossambicus (Peters, 1852) (Perciformes: Cichlidae) to distinguish between minimally and highly disturbed aquatic environments. A water quality index (WQI) and overall index of pollution (OIP) were used to characterize the target sites, namely the Mananda Dam (control, reference site) and Lower Mguza Dam (disturbed site). Forty male O. mossambicus samples were collected from each dam between April and August 2013. Values for the WQI and OIP indices were significantly higher for the Lower Mguza Dam than for the Mananda Dam (p < 0.05). Oxidative stress biomarker evaluation results showed that the activities of glutathione peroxidase (GPx), superoxide dismutase (SOD) and glutathione S-transferase (GST) as well as the malondialdehyde (MDA) concentration in the liver of O. mossambicus were significantly higher in fish collected from Lower Mguza Dam than those collected from Mananda Dam (p < 0.05). The activities of DT-diaphorase (DTD) and catalase (CAT) were significantly inhibited in fish from the Lower Mguza Dam, when compared to those collected from the Mananda Dam (p < 0.05). From these findings, it is evident that oxidative stress biomarkers, such as antioxidant enzyme activity and MDA accumulation, can be used to differentiate minimally and highly disturbed aquatic environments.","PeriodicalId":7864,"journal":{"name":"African Journal of Aquatic Science","volume":"47 1","pages":"499 - 506"},"PeriodicalIF":1.4,"publicationDate":"2022-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41638524","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-08-22DOI: 10.2989/16085914.2022.2093828
A. Birkhead, C. Brown, H. Bukhari, Mk Reinecke, W. Mgoola, JK Nyirenda
The Elephant Marsh lies on the floodplain of the lower Shire River, in southern Malawi. It is both a cultivated, seasonal floodplain and an area of permanent shallow lakes. The marsh is highly biodiverse, has a productive fishery and supports the livelihoods of a large human population. Chronicles and hand-drawn sketches by 19th-century explorers and subsequent travellers describing the marsh landscape were used to develop an account of the marsh’s historic hydromorphology. These anecdotal accounts are supported by Shire River outflows from Lake Malawi, inferred from observed water levels in the lake from c. 1900. Records show that the marsh has experienced regular periods of drying out, followed by periods of greater inundation than it currently experiences. Long-term hydrological trends have been accompanied by anthropogenic influences such as catchment degradation and embankment construction, which have altered sedimentation patterns in the marsh. The marsh exhibits traits of resilience to natural long-term climate change through its ability to return to a similar state during wet periods, even following prolonged dry periods. Over relatively short time frames, however, the ecology of the marsh, as described when it was declared a RAMSAR site in 2017, likely has low resistance to hydrological regimes that are sensitive to climate change. An appreciation of long-term climate and recent human-induced changes afforded a unique opportunity for contextualising its hydromorphological trends within the Anthropocene.
{"title":"The Elephant Marsh, Malawi – Part 1: reconstruction of the historic hydromorphology","authors":"A. Birkhead, C. Brown, H. Bukhari, Mk Reinecke, W. Mgoola, JK Nyirenda","doi":"10.2989/16085914.2022.2093828","DOIUrl":"https://doi.org/10.2989/16085914.2022.2093828","url":null,"abstract":"The Elephant Marsh lies on the floodplain of the lower Shire River, in southern Malawi. It is both a cultivated, seasonal floodplain and an area of permanent shallow lakes. The marsh is highly biodiverse, has a productive fishery and supports the livelihoods of a large human population. Chronicles and hand-drawn sketches by 19th-century explorers and subsequent travellers describing the marsh landscape were used to develop an account of the marsh’s historic hydromorphology. These anecdotal accounts are supported by Shire River outflows from Lake Malawi, inferred from observed water levels in the lake from c. 1900. Records show that the marsh has experienced regular periods of drying out, followed by periods of greater inundation than it currently experiences. Long-term hydrological trends have been accompanied by anthropogenic influences such as catchment degradation and embankment construction, which have altered sedimentation patterns in the marsh. The marsh exhibits traits of resilience to natural long-term climate change through its ability to return to a similar state during wet periods, even following prolonged dry periods. Over relatively short time frames, however, the ecology of the marsh, as described when it was declared a RAMSAR site in 2017, likely has low resistance to hydrological regimes that are sensitive to climate change. An appreciation of long-term climate and recent human-induced changes afforded a unique opportunity for contextualising its hydromorphological trends within the Anthropocene.","PeriodicalId":7864,"journal":{"name":"African Journal of Aquatic Science","volume":"47 1","pages":"369 - 385"},"PeriodicalIF":1.4,"publicationDate":"2022-08-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43574576","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-08-05DOI: 10.2989/16085914.2022.2094323
M. Nunes, D. Lemley, J. Adams
Primary producer responses to cumulative regulating factors were investigated in a temporarily closed microtidal estuary. We hypothesised that the phytoplankton chlorophyll-a concentration (Chl a) and invasive alien aquatic plant (IAAP) abundance would be highest during the low-flow season and that shifts in community structure would be driven by salinity and nutrient gradients. The augmented freshwater inflow limited phytoplankton Chl a (<5 µg Chl a l−1) due to low freshwater residency, while isolated instances of increased Chl a (≥10 but ≤20 µg Chl a l−1) were recorded following a brief period of mouth closure. Cyanophyceae proliferated for 67% of the study period with maximum abundance (>10 000 cells ml−1) recorded in spring owing to increased water retention. A community consisting of co-dominant Cryptophyceae, Euglenophyceae and IAAPs was recorded during winter, indicating a shared preference for slow-flowing, low-salinity (<5) eutrophic habitats. Dinophyceae was the only phytoplankton class that showed niche differentiation by favouring the mesohaline lower reaches. The homogenisation of dynamic estuarine gradients and the prevalence of nutrient-tolerant primary producers is indicative of the degraded state of this estuary as a result of consistent nutrient-enriched freshwater baseflows. The application of a multidisciplinary restoration approach is required to improve the ecosystem health.
{"title":"Flow alterations and nutrient loading reduce primary producer variability in a temporarily closed microtidal estuary in KwaZulu-Natal, South Africa","authors":"M. Nunes, D. Lemley, J. Adams","doi":"10.2989/16085914.2022.2094323","DOIUrl":"https://doi.org/10.2989/16085914.2022.2094323","url":null,"abstract":"Primary producer responses to cumulative regulating factors were investigated in a temporarily closed microtidal estuary. We hypothesised that the phytoplankton chlorophyll-a concentration (Chl a) and invasive alien aquatic plant (IAAP) abundance would be highest during the low-flow season and that shifts in community structure would be driven by salinity and nutrient gradients. The augmented freshwater inflow limited phytoplankton Chl a (<5 µg Chl a l−1) due to low freshwater residency, while isolated instances of increased Chl a (≥10 but ≤20 µg Chl a l−1) were recorded following a brief period of mouth closure. Cyanophyceae proliferated for 67% of the study period with maximum abundance (>10 000 cells ml−1) recorded in spring owing to increased water retention. A community consisting of co-dominant Cryptophyceae, Euglenophyceae and IAAPs was recorded during winter, indicating a shared preference for slow-flowing, low-salinity (<5) eutrophic habitats. Dinophyceae was the only phytoplankton class that showed niche differentiation by favouring the mesohaline lower reaches. The homogenisation of dynamic estuarine gradients and the prevalence of nutrient-tolerant primary producers is indicative of the degraded state of this estuary as a result of consistent nutrient-enriched freshwater baseflows. The application of a multidisciplinary restoration approach is required to improve the ecosystem health.","PeriodicalId":7864,"journal":{"name":"African Journal of Aquatic Science","volume":"47 1","pages":"447 - 461"},"PeriodicalIF":1.4,"publicationDate":"2022-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49236606","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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