Mangaliso Gondwe | University of Botswana (original) (raw)
Papers by Mangaliso Gondwe
Environment, Development and Sustainability
Fish can be a key strategy in addressing the global food and nutrition insecurity challenges. Fis... more Fish can be a key strategy in addressing the global food and nutrition insecurity challenges. Fish nutrient data are critical for policy development targeting to reduce these problems. Despite this, much of the published studies on nutritional characteristics of fish have focused on marine ecology and there is little information on natural freshwater fish habitats like inland delta areas. This study investigated the nutrient composition of Okavango Delta fishes and their potential contribution to the recommended nutrient intake. Fish species sampled were Clarias ngamensis, Oreochromis andersonii, Schilbe intermedius, Marcusenius altisambesi, Brycinus lateralis, Barbus poechii and Tilapia sparrmanii. The nutrients analyzed were moisture, ash, proteins, Na, K, Ca, Mg, P and Zn. The small fishes (B. lateralis and B. poechii) had higher mineral content; Ca (643–968 mg/100 g), Mg (47–49 mg/100 g) and Zn (2.8–3.6 mg/100 g) compared to the larger species with average mineral content; Ca (7...
Earth System Science Data, Jul 29, 2021
Methane (CH 4) emissions from natural landscapes constitute roughly half of global CH 4 contribut... more Methane (CH 4) emissions from natural landscapes constitute roughly half of global CH 4 contributions to the atmosphere, yet large uncertainties remain in the absolute magnitude and the seasonality of emission quantities and drivers. Eddy covariance (EC) measurements of CH 4 flux are ideal for constraining ecosystem-scale CH 4 emissions due to quasi-continuous and high-temporal-resolution CH 4 flux measurements, coincident carbon dioxide, water, and energy flux measurements, lack of ecosystem disturbance, and increased availability of datasets over the last decade. Here, we (1) describe the newly published dataset, FLUXNET-CH 4 Version 1.0, the first open-source global dataset of CH 4 EC measurements (available at https://fluxnet.org/data/fluxnet-ch4-community-product/, last access: 7 April 2021). FLUXNET-CH 4 includes half-hourly and daily gap-filled and non-gap-filled aggregated CH 4 fluxes and meteorological data from 79 sites globally: 42 freshwater wetlands, 6 brackish and saline wetlands, 7 formerly drained ecosystems, 7 rice paddy sites, 2 lakes, and 15 uplands. Then, we (2) evaluate FLUXNET-CH 4 representativeness for freshwater wetland coverage globally because the majority of sites in FLUXNET-CH 4 Version 1.0 are freshwater wetlands which are a substantial source of total atmospheric CH 4 emissions; and (3) we provide the first global estimates of the seasonal variability and seasonality predictors of freshwater wetland CH 4 fluxes. Our representativeness analysis
Environment, Development and Sustainability, Jul 13, 2023
Fish can be a key strategy in addressing the global food and nutrition insecurity challenges. Fis... more Fish can be a key strategy in addressing the global food and nutrition insecurity challenges. Fish nutrient data are critical for policy development targeting to reduce these problems. Despite this, much of the published studies on nutritional characteristics of fish have focused on marine ecology and there is little information on natural freshwater fish habitats like inland delta areas. This study investigated the nutrient composition of Okavango Delta fishes and their potential contribution to the recommended nutrient intake. Fish species sampled were Clarias ngamensis, Oreochromis andersonii, Schilbe intermedius, Marcusenius altisambesi, Brycinus lateralis, Barbus poechii and Tilapia sparrmanii. The nutrients analyzed were moisture, ash, proteins, Na, K, Ca, Mg, P and Zn. The small fishes (B. lateralis and B. poechii) had higher mineral content; Ca (643-968 mg/100 g), Mg (47-49 mg/100 g) and Zn (2.8-3.6 mg/100 g) compared to the larger species with average mineral content; Ca (73-460 mg/100 g), Mg (23-35 mg/100 g), Zn (1.2-2.9 mg/100 g). The most nutrient-dense species recognized were B. poechii and B. lateralis followed by the large species, M. altisambesi. These species illustrated the potential to contribute 80-121% Ca, 32-47% Mg and 70-150% Zn of the recommended nutrient intake to children (1-9 years), pregnant women and the elderly (65 + years). The study recommends prioritizing small and some large species (M. altisambesi and T. sparrmanii) for polyculture systems, primarily for securing food and nutrition security for local communities.
The data resource consists of half hourly time series of heat (latent and sensible) and trace gas... more The data resource consists of half hourly time series of heat (latent and sensible) and trace gas (carbon dioxide and methane) fluxes obtained by eddy-covariance, gas concentrations and ancillary meteorological data (e.g. air temperature, relative humidity, pressure, photosynthetically active radiation, total incoming radiation, wind speed and direction). The data were collected at Guma Lagoon (18°57'53.01"S; 22°22'16.20"E), in the perennially flooded area of the Okavango Delta, Botswana, for the purpose of quantifying greenhouse gas fluxes over a Cyperus papyrus stand. The measurement period was 01/01/2018 to 31/12/2020. The instrumentation was installed the UK Centre for Ecology and Hydrology; monthly maintenance and data collection visits were effected by the Okavango Research Institute, University of Botswana. The research was funded through NERC grant reference NE/N015746/2 - The Global Methane Budget.
SIL Proceedings, 1922-2010, 2009
Wetland goods and services provide a means of survival for many riparian rural communities in dev... more Wetland goods and services provide a means of survival for many riparian rural communities in developing countries, particularly in the Sub-Saharan Africa. To sustain the provision of goods and services for human use, spatial and temporal variations in the quantity and quality of water in a given wetland should be adequately understood and managed. In this study we monitored the quantity and quality of surface water through the Okavango Delta for 2 years, from June 2008 to June 2010. Specifically we monitored precipitation over the Delta and surface inflow and outflow (via the Okavango and Thamalakane Rivers respectively) for water quantity, nutrients, cation and anion levels in the surface water along a river transect from Mohembo through the Delta to Lake Ngami. The study revealed that the water balance during the study period was similar to earlier reports. Most of the water inflow was via the Okavango River while surface outflow via the Boro River accounted for about 2% of total...
Agricultural and Forest Meteorology, 2021
Gap-filling eddy covariance methane fluxes: comparison of machine learning model predictions and ... more Gap-filling eddy covariance methane fluxes: comparison of machine learning model predictions and uncertainties at FLUXNET-CH4 wetlands.
Remote Sensing, 2019
Lake Malawi is an important water resource in Africa. However, there is no routine monitoring of ... more Lake Malawi is an important water resource in Africa. However, there is no routine monitoring of water quality in the lake due to financial and institutional constraints in the surrounding countries. A combination of satellite data and a semi-analytical algorithm can provide an alternative for routine monitoring of water quality, especially in developing countries. In this study, we first compared the performance of two semi-analytical algorithms, Doron11 and Lee15, which can estimate Secchi disk depth (SD) from satellite data in Lake Malawi. Our results showed that even though the SD estimations from the two algorithms were very highly correlated, the Lee15 outperformed the Doron11 in Lake Malawi with high estimation accuracy (RMSE = 1.17 m, MAPE = 18.7%, R = 0.66, p < 0.05). We then evaluated water transparency in Lake Malawi using the SD values estimated from nine years of Medium Resolution Imaging Spectrometer (MERIS) data (2003–2011) with the Lee15 algorithm. Results showed ...
Journal of Health, Population and Nutrition, 2015
Background: Some rural African communities residing along rivers use the untreated river water fo... more Background: Some rural African communities residing along rivers use the untreated river water for domestic purposes, making them vulnerable to waterborne diseases such as diarrhea. Methods: We determined water use practices and water quality, relating them to prevalence of diarrhea in communities along the Boro-Thamalakane-Boteti river system, northern Botswana. A total of 452 households were interviewed and 196 water samples collected show during February, May, September, and December 2012 in settlements of Boro, Maun, Xobe, Samedupi, Chanoga, and Motopi. Information was sought on water use practices (collection, storage, and handling) and diarrheal experience using questionnaires. Water quality was assessed for physicochemical and microbiological parameters using portable field meters and laboratory analysis, respectively. Results: All (100 %) of the river water samples collected were fecally contaminated and unsuitable for domestic use without prior treatment. Samples had Escherichia coli (E.coli) and fecal streptococci levels reaching up to 186 and 140 CFU/100 ml, respectively. Study revealed high dependence on the fecally contaminated river water with low uptake of water treatment techniques. Up to 48 % of households indicated that they experience diarrhea, with most cases occurring during the early flooding season (May). Nonetheless, there was no significant relationship between river water quality and households' diarrheal experience across studied settlements (p > 0.05). Failure to treat river water before use was a significant predictor of diarrhea (p = 0.028). Conclusions: Even though the river water was unsafe for domestic use, results imply further recontamination of water at household level highlighting the need for simple and affordable household water treatment techniques.
African Journal of Aquatic Science, 2016
The Okavango Delta depends on water quantity and quality to sustain its ecosystem services. Where... more The Okavango Delta depends on water quantity and quality to sustain its ecosystem services. Whereas many studies have been carried out on its hydrology, few have been done on water quality in the delta. Water pH, electrical conductivity (EC), dissolved oxygen (DO), turbidity, total suspended solids (TSS) and dissolved organic carbon (DOC) were monitored at 10 sites along the Okavango–Boro–Thamalakane–Lake Ngami system almost fortnightly from June 2008 to June 2010. Water quality in the delta was generally good, despite high evapotranspiration rates which would normally produce very saline waters. Electrical conductivity and water temperature increased with distance from Mohembo to Lake Ngami, the former most likely due to evapoconcentration. In contrast, pH, DO, turbidity and TSS decreased with distance from Mohembo to Boro at the lower end of the seasonal floodplain, before increasing again to Lake Ngami. Dissolved oxygen and TSS most likely declined due to biological uptake and particle sedimentation, respectively. Strong and significant relationships were observed between TSS and turbidity and between DOC and EC, indicating that turbidity and EC could be useful proxies for routine estimations of TSS and DOC, respectively, in the delta.
Wetlands Ecology and Management, 2015
African Journal of Aquatic Science, 2014
The quality of water in aquatic systems is subject to temporal and spatial variations due to vary... more The quality of water in aquatic systems is subject to temporal and spatial variations due to varying effects of natural and anthropogenic factors. This study assessed the dynamics of water quality in the Boro-Thamalakane-Boteti river system along an upstream–downstream gradient above and below Maun during February, May, September and December 2012. Temperature, conductivity, pH, dissolved oxygen, turbidity, Escherichia coli and faecal streptococci were monitored in the settlements of Boro, Maun, Xobe, Samedupi, Chanoga and Motopi along the river system. Comparisons of water quality among settlements using ANOVA and Tukey's honest significant difference test highlighted a significant decline in water quality from upstream to downstream, indicated by increases in microbial numbers and turbidity. The quality of water improved as the water level rose during the peak flooding season in September and declined thereafter. This study highlights the possible influence of human settlements and associated developments on waterbodies, and lends strong support to management efforts to maintain river water quality to ensure the suitability of the water for various ecosystem uses.
Wetlands Ecology and Management, 2013
ABSTRACT Global warming is associated with the continued increase in the atmospheric concentratio... more ABSTRACT Global warming is associated with the continued increase in the atmospheric concentrations of greenhouse gases; carbon dioxide, methane (CH4) and nitrous oxide. Wetlands constitute the largest single natural source of atmospheric CH4 in the world contributing between 100 and 231 Tg year−1 to the total budget of 503–610 Tg year−1, approximately 60 % of which is emitted from tropical wetlands. We conducted diffusive CH4 emission measurements using static chambers in river channels, floodplains and lagoons in permanent and seasonal swamps in the Okavango Delta, Botswana. Diffusive CH4 emission rates varied between 0.24 and 293 mg CH4 m−2 h−1, with a mean (±SE) emission of 23.2 ± 2.2 mg CH4 m−2 h−1 or 558 ± 53 mg CH4 m−2 day−1. These emission rates lie within the range reported for other tropical wetlands. The emission rates were significantly higher (P 4 m−2 h−1 than in floodplains (20.4 ± 2.5 mg CH4 m−2 h−1) and lagoons (16.9 ± 2.6 mg CH4 m−2 h−1). Diffusive CH4 emissions in the Delta were probably regulated by temperature since emissions were highest (20–300 mg CH4 m−2 h−1) and lowest (0.2–3.0 mg m−2 h−1) during the warmer-rainy and cooler winter seasons, respectively. Surface water temperatures between December 2010 and January 2012 varied from 15.3 °C in winter to 33 °C in summer. Assuming mean inundation of 9,000 km2, the Delta’s annual diffusive emission was estimated at 1.8 ± 0.2 Tg, accounting for 2.8 ± 0.3 % of the total CH4 emission from global tropical wetlands.
Journal of Great Lakes Research, 2011
is a great lake not only because of its large size (30,800 km 2); but also because it hosts betwe... more is a great lake not only because of its large size (30,800 km 2); but also because it hosts between 700 and 1000 fish species, mostly endemic cichlids. The fish are most abundant and more diverse in the littoral zone. Cage aquaculture in Lake Malawi started in 2004 in the nearshore waters of the southeast arm. Approximately 50 cages were operational by 2009 harvesting about 20 tons fresh fish/cage/year. In 2007, data were aggregated from cage feed and production records to produce a mass balance for carbon (C), nitrogen (N) and phosphorus (P) added to cages in the form of feed and juvenile fish for 22 production cycles. Nutrient losses from cages to the surrounding environment accounted for between 81 and 91% for C, 59 and 80% for N and 85 and 92% for P. Production strategies such as stocking density and feeding rates were also analysed to assess their effect on fish harvests and nutrient loads from the fish cages. The study showed that nutrient loads from the cages were significant and can be exacerbated by poor feed quality, overstocking, stocking of premature fish and use of lower than recommended feeding rates to grow the fish to target sizes. The inefficient production strategies necessitated longer production cycles (376 ± 42 days) and more feed usage to achieve market sizes of ≥ 300 g/fish than if generally recommended stocking and feeding rates were followed. If cage aquaculture continues to expand, it will become an important new source of nutrients, not only locally, but on a lake-wide basis.
Journal of Great Lakes Research, 2011
The initiation of cage aquaculture in the shallow southeast arm of Lake Malawi has raised concern... more The initiation of cage aquaculture in the shallow southeast arm of Lake Malawi has raised concerns about its possible impact on the surrounding environment and the highly diverse fish community. To evaluate the impact of the cage operation on the surrounding environment, observations were made over an annual cycle in 2007 at a production capacity of~200 tonnes fish/year. Impacts of the cage wastes in the water column in the vicinity of the cages were minimal despite the substantial discharges from the cages. No significant differences were observed in concentrations of dissolved and particulate nutrients (ammonia, nitrate, phosphate, particulate C,N and P), chlorophyll, chlorophyll fluorescence, dissolved oxygen, total suspended solids, Secchi depths and extinction coefficient of photosynthetically active radiation between the cage site and the control stations upstream or downstream of the fish farm. Although sedimentation rates measured in traps were higher under the cages than at control sites, the sediment flux was a small percentage of total feeds added to the cages. Apparently cage wastes were efficiently dispersed by water currents which averaged 9.3 cm/s below the fish cages. Consumption of the wastes by wild fish species which aggregated around the fish cages and their movement in the vicinity of the cages also contributed to the dispersion of the cage wastes and served to dilute impact of the cages. In combination, these physical and biological processes reduced the immediate impact of the cage farming operation and must be considered in the siting of future cage farms.
Hydrobiologia, 2007
... Planktonic nitrogen fixation in Lake Malawi/Nyasa Mangaliso J. Gondwe Æ Stephanie J. Guildfor... more ... Planktonic nitrogen fixation in Lake Malawi/Nyasa Mangaliso J. Gondwe Æ Stephanie J. Guildford Æ Robert E. Hecky ... MJ Gondwe (&) SADC/GEF Lake Malawi Biodiversity Conservation Project, PO Box 311, Salima, Malawi e-mail: mgondwe@scimail.uwaterloo.ca ...
I hereby declare that I am the sole author of this thesis. This is a true copy of the thesis, inc... more I hereby declare that I am the sole author of this thesis. This is a true copy of the thesis, including any required final revisions, as accepted by my examiners. I understand that my thesis may be made electronically available to the public.
Aquaculture, 2012
Cage culture of native tilapiine cichlids was initiated in Lake Malawi in 2004. The lake is well ... more Cage culture of native tilapiine cichlids was initiated in Lake Malawi in 2004. The lake is well known for its highly endemic ichthyodiversity, and it is estimated to have more species of fish than any other lake in the world. Consequently there is concern about the impact of cage farming operations on the wild fish communities. In 2007, high densities of diverse wild fish were observed around the cages and stable isotopes, δ 13 C and δ 15 N analyses, established that cage wastes were incorporated in the food web that supported diverse wild fishes in the vicinity of the cages. Comparison of δ 13 C and δ 15 N signals of caged and wild fish caught in 2007 in the vicinity of the fish farm and signals of fish samples caught between 1995 and 1997 before the fish farm was started in 2004 established a shift in the isotopic signatures of wild fish indicating the incorporation of cage wastes into the wild fish diet. Sedimentation of cage wastes collected in sediment traps below the fish cages was also confirmed using the δ 13 C and δ 15 N analyses. The accumulation of the cage wastes in the sediments below the cages was, however, minimal as indicated by the small differences in the isotopic ratios between the bulk sediments and some sedimentary organisms (bivalves, snails and earthworms) under the cages relative to ratios in similar organisms at control stations. The low impact of cage wastes on underlying sediments and benthic organisms was due to the rapid and efficient dispersion of the cage wastes facilitated by water currents through the fish farm which averaged 9.3 cm s − 1 as well as the consumption and subsequent dispersion of cage wastes by the large numbers of wild fishes which aggregated around the cages. This study has also shown that in Lake Malawi, fish rather than benthic organisms and plankton material may be a more sensitive monitor of the dispersion of cage wastes.
Environment, Development and Sustainability
Fish can be a key strategy in addressing the global food and nutrition insecurity challenges. Fis... more Fish can be a key strategy in addressing the global food and nutrition insecurity challenges. Fish nutrient data are critical for policy development targeting to reduce these problems. Despite this, much of the published studies on nutritional characteristics of fish have focused on marine ecology and there is little information on natural freshwater fish habitats like inland delta areas. This study investigated the nutrient composition of Okavango Delta fishes and their potential contribution to the recommended nutrient intake. Fish species sampled were Clarias ngamensis, Oreochromis andersonii, Schilbe intermedius, Marcusenius altisambesi, Brycinus lateralis, Barbus poechii and Tilapia sparrmanii. The nutrients analyzed were moisture, ash, proteins, Na, K, Ca, Mg, P and Zn. The small fishes (B. lateralis and B. poechii) had higher mineral content; Ca (643–968 mg/100 g), Mg (47–49 mg/100 g) and Zn (2.8–3.6 mg/100 g) compared to the larger species with average mineral content; Ca (7...
Earth System Science Data, Jul 29, 2021
Methane (CH 4) emissions from natural landscapes constitute roughly half of global CH 4 contribut... more Methane (CH 4) emissions from natural landscapes constitute roughly half of global CH 4 contributions to the atmosphere, yet large uncertainties remain in the absolute magnitude and the seasonality of emission quantities and drivers. Eddy covariance (EC) measurements of CH 4 flux are ideal for constraining ecosystem-scale CH 4 emissions due to quasi-continuous and high-temporal-resolution CH 4 flux measurements, coincident carbon dioxide, water, and energy flux measurements, lack of ecosystem disturbance, and increased availability of datasets over the last decade. Here, we (1) describe the newly published dataset, FLUXNET-CH 4 Version 1.0, the first open-source global dataset of CH 4 EC measurements (available at https://fluxnet.org/data/fluxnet-ch4-community-product/, last access: 7 April 2021). FLUXNET-CH 4 includes half-hourly and daily gap-filled and non-gap-filled aggregated CH 4 fluxes and meteorological data from 79 sites globally: 42 freshwater wetlands, 6 brackish and saline wetlands, 7 formerly drained ecosystems, 7 rice paddy sites, 2 lakes, and 15 uplands. Then, we (2) evaluate FLUXNET-CH 4 representativeness for freshwater wetland coverage globally because the majority of sites in FLUXNET-CH 4 Version 1.0 are freshwater wetlands which are a substantial source of total atmospheric CH 4 emissions; and (3) we provide the first global estimates of the seasonal variability and seasonality predictors of freshwater wetland CH 4 fluxes. Our representativeness analysis
Environment, Development and Sustainability, Jul 13, 2023
Fish can be a key strategy in addressing the global food and nutrition insecurity challenges. Fis... more Fish can be a key strategy in addressing the global food and nutrition insecurity challenges. Fish nutrient data are critical for policy development targeting to reduce these problems. Despite this, much of the published studies on nutritional characteristics of fish have focused on marine ecology and there is little information on natural freshwater fish habitats like inland delta areas. This study investigated the nutrient composition of Okavango Delta fishes and their potential contribution to the recommended nutrient intake. Fish species sampled were Clarias ngamensis, Oreochromis andersonii, Schilbe intermedius, Marcusenius altisambesi, Brycinus lateralis, Barbus poechii and Tilapia sparrmanii. The nutrients analyzed were moisture, ash, proteins, Na, K, Ca, Mg, P and Zn. The small fishes (B. lateralis and B. poechii) had higher mineral content; Ca (643-968 mg/100 g), Mg (47-49 mg/100 g) and Zn (2.8-3.6 mg/100 g) compared to the larger species with average mineral content; Ca (73-460 mg/100 g), Mg (23-35 mg/100 g), Zn (1.2-2.9 mg/100 g). The most nutrient-dense species recognized were B. poechii and B. lateralis followed by the large species, M. altisambesi. These species illustrated the potential to contribute 80-121% Ca, 32-47% Mg and 70-150% Zn of the recommended nutrient intake to children (1-9 years), pregnant women and the elderly (65 + years). The study recommends prioritizing small and some large species (M. altisambesi and T. sparrmanii) for polyculture systems, primarily for securing food and nutrition security for local communities.
The data resource consists of half hourly time series of heat (latent and sensible) and trace gas... more The data resource consists of half hourly time series of heat (latent and sensible) and trace gas (carbon dioxide and methane) fluxes obtained by eddy-covariance, gas concentrations and ancillary meteorological data (e.g. air temperature, relative humidity, pressure, photosynthetically active radiation, total incoming radiation, wind speed and direction). The data were collected at Guma Lagoon (18°57'53.01"S; 22°22'16.20"E), in the perennially flooded area of the Okavango Delta, Botswana, for the purpose of quantifying greenhouse gas fluxes over a Cyperus papyrus stand. The measurement period was 01/01/2018 to 31/12/2020. The instrumentation was installed the UK Centre for Ecology and Hydrology; monthly maintenance and data collection visits were effected by the Okavango Research Institute, University of Botswana. The research was funded through NERC grant reference NE/N015746/2 - The Global Methane Budget.
SIL Proceedings, 1922-2010, 2009
Wetland goods and services provide a means of survival for many riparian rural communities in dev... more Wetland goods and services provide a means of survival for many riparian rural communities in developing countries, particularly in the Sub-Saharan Africa. To sustain the provision of goods and services for human use, spatial and temporal variations in the quantity and quality of water in a given wetland should be adequately understood and managed. In this study we monitored the quantity and quality of surface water through the Okavango Delta for 2 years, from June 2008 to June 2010. Specifically we monitored precipitation over the Delta and surface inflow and outflow (via the Okavango and Thamalakane Rivers respectively) for water quantity, nutrients, cation and anion levels in the surface water along a river transect from Mohembo through the Delta to Lake Ngami. The study revealed that the water balance during the study period was similar to earlier reports. Most of the water inflow was via the Okavango River while surface outflow via the Boro River accounted for about 2% of total...
Agricultural and Forest Meteorology, 2021
Gap-filling eddy covariance methane fluxes: comparison of machine learning model predictions and ... more Gap-filling eddy covariance methane fluxes: comparison of machine learning model predictions and uncertainties at FLUXNET-CH4 wetlands.
Remote Sensing, 2019
Lake Malawi is an important water resource in Africa. However, there is no routine monitoring of ... more Lake Malawi is an important water resource in Africa. However, there is no routine monitoring of water quality in the lake due to financial and institutional constraints in the surrounding countries. A combination of satellite data and a semi-analytical algorithm can provide an alternative for routine monitoring of water quality, especially in developing countries. In this study, we first compared the performance of two semi-analytical algorithms, Doron11 and Lee15, which can estimate Secchi disk depth (SD) from satellite data in Lake Malawi. Our results showed that even though the SD estimations from the two algorithms were very highly correlated, the Lee15 outperformed the Doron11 in Lake Malawi with high estimation accuracy (RMSE = 1.17 m, MAPE = 18.7%, R = 0.66, p < 0.05). We then evaluated water transparency in Lake Malawi using the SD values estimated from nine years of Medium Resolution Imaging Spectrometer (MERIS) data (2003–2011) with the Lee15 algorithm. Results showed ...
Journal of Health, Population and Nutrition, 2015
Background: Some rural African communities residing along rivers use the untreated river water fo... more Background: Some rural African communities residing along rivers use the untreated river water for domestic purposes, making them vulnerable to waterborne diseases such as diarrhea. Methods: We determined water use practices and water quality, relating them to prevalence of diarrhea in communities along the Boro-Thamalakane-Boteti river system, northern Botswana. A total of 452 households were interviewed and 196 water samples collected show during February, May, September, and December 2012 in settlements of Boro, Maun, Xobe, Samedupi, Chanoga, and Motopi. Information was sought on water use practices (collection, storage, and handling) and diarrheal experience using questionnaires. Water quality was assessed for physicochemical and microbiological parameters using portable field meters and laboratory analysis, respectively. Results: All (100 %) of the river water samples collected were fecally contaminated and unsuitable for domestic use without prior treatment. Samples had Escherichia coli (E.coli) and fecal streptococci levels reaching up to 186 and 140 CFU/100 ml, respectively. Study revealed high dependence on the fecally contaminated river water with low uptake of water treatment techniques. Up to 48 % of households indicated that they experience diarrhea, with most cases occurring during the early flooding season (May). Nonetheless, there was no significant relationship between river water quality and households' diarrheal experience across studied settlements (p > 0.05). Failure to treat river water before use was a significant predictor of diarrhea (p = 0.028). Conclusions: Even though the river water was unsafe for domestic use, results imply further recontamination of water at household level highlighting the need for simple and affordable household water treatment techniques.
African Journal of Aquatic Science, 2016
The Okavango Delta depends on water quantity and quality to sustain its ecosystem services. Where... more The Okavango Delta depends on water quantity and quality to sustain its ecosystem services. Whereas many studies have been carried out on its hydrology, few have been done on water quality in the delta. Water pH, electrical conductivity (EC), dissolved oxygen (DO), turbidity, total suspended solids (TSS) and dissolved organic carbon (DOC) were monitored at 10 sites along the Okavango–Boro–Thamalakane–Lake Ngami system almost fortnightly from June 2008 to June 2010. Water quality in the delta was generally good, despite high evapotranspiration rates which would normally produce very saline waters. Electrical conductivity and water temperature increased with distance from Mohembo to Lake Ngami, the former most likely due to evapoconcentration. In contrast, pH, DO, turbidity and TSS decreased with distance from Mohembo to Boro at the lower end of the seasonal floodplain, before increasing again to Lake Ngami. Dissolved oxygen and TSS most likely declined due to biological uptake and particle sedimentation, respectively. Strong and significant relationships were observed between TSS and turbidity and between DOC and EC, indicating that turbidity and EC could be useful proxies for routine estimations of TSS and DOC, respectively, in the delta.
Wetlands Ecology and Management, 2015
African Journal of Aquatic Science, 2014
The quality of water in aquatic systems is subject to temporal and spatial variations due to vary... more The quality of water in aquatic systems is subject to temporal and spatial variations due to varying effects of natural and anthropogenic factors. This study assessed the dynamics of water quality in the Boro-Thamalakane-Boteti river system along an upstream–downstream gradient above and below Maun during February, May, September and December 2012. Temperature, conductivity, pH, dissolved oxygen, turbidity, Escherichia coli and faecal streptococci were monitored in the settlements of Boro, Maun, Xobe, Samedupi, Chanoga and Motopi along the river system. Comparisons of water quality among settlements using ANOVA and Tukey's honest significant difference test highlighted a significant decline in water quality from upstream to downstream, indicated by increases in microbial numbers and turbidity. The quality of water improved as the water level rose during the peak flooding season in September and declined thereafter. This study highlights the possible influence of human settlements and associated developments on waterbodies, and lends strong support to management efforts to maintain river water quality to ensure the suitability of the water for various ecosystem uses.
Wetlands Ecology and Management, 2013
ABSTRACT Global warming is associated with the continued increase in the atmospheric concentratio... more ABSTRACT Global warming is associated with the continued increase in the atmospheric concentrations of greenhouse gases; carbon dioxide, methane (CH4) and nitrous oxide. Wetlands constitute the largest single natural source of atmospheric CH4 in the world contributing between 100 and 231 Tg year−1 to the total budget of 503–610 Tg year−1, approximately 60 % of which is emitted from tropical wetlands. We conducted diffusive CH4 emission measurements using static chambers in river channels, floodplains and lagoons in permanent and seasonal swamps in the Okavango Delta, Botswana. Diffusive CH4 emission rates varied between 0.24 and 293 mg CH4 m−2 h−1, with a mean (±SE) emission of 23.2 ± 2.2 mg CH4 m−2 h−1 or 558 ± 53 mg CH4 m−2 day−1. These emission rates lie within the range reported for other tropical wetlands. The emission rates were significantly higher (P 4 m−2 h−1 than in floodplains (20.4 ± 2.5 mg CH4 m−2 h−1) and lagoons (16.9 ± 2.6 mg CH4 m−2 h−1). Diffusive CH4 emissions in the Delta were probably regulated by temperature since emissions were highest (20–300 mg CH4 m−2 h−1) and lowest (0.2–3.0 mg m−2 h−1) during the warmer-rainy and cooler winter seasons, respectively. Surface water temperatures between December 2010 and January 2012 varied from 15.3 °C in winter to 33 °C in summer. Assuming mean inundation of 9,000 km2, the Delta’s annual diffusive emission was estimated at 1.8 ± 0.2 Tg, accounting for 2.8 ± 0.3 % of the total CH4 emission from global tropical wetlands.
Journal of Great Lakes Research, 2011
is a great lake not only because of its large size (30,800 km 2); but also because it hosts betwe... more is a great lake not only because of its large size (30,800 km 2); but also because it hosts between 700 and 1000 fish species, mostly endemic cichlids. The fish are most abundant and more diverse in the littoral zone. Cage aquaculture in Lake Malawi started in 2004 in the nearshore waters of the southeast arm. Approximately 50 cages were operational by 2009 harvesting about 20 tons fresh fish/cage/year. In 2007, data were aggregated from cage feed and production records to produce a mass balance for carbon (C), nitrogen (N) and phosphorus (P) added to cages in the form of feed and juvenile fish for 22 production cycles. Nutrient losses from cages to the surrounding environment accounted for between 81 and 91% for C, 59 and 80% for N and 85 and 92% for P. Production strategies such as stocking density and feeding rates were also analysed to assess their effect on fish harvests and nutrient loads from the fish cages. The study showed that nutrient loads from the cages were significant and can be exacerbated by poor feed quality, overstocking, stocking of premature fish and use of lower than recommended feeding rates to grow the fish to target sizes. The inefficient production strategies necessitated longer production cycles (376 ± 42 days) and more feed usage to achieve market sizes of ≥ 300 g/fish than if generally recommended stocking and feeding rates were followed. If cage aquaculture continues to expand, it will become an important new source of nutrients, not only locally, but on a lake-wide basis.
Journal of Great Lakes Research, 2011
The initiation of cage aquaculture in the shallow southeast arm of Lake Malawi has raised concern... more The initiation of cage aquaculture in the shallow southeast arm of Lake Malawi has raised concerns about its possible impact on the surrounding environment and the highly diverse fish community. To evaluate the impact of the cage operation on the surrounding environment, observations were made over an annual cycle in 2007 at a production capacity of~200 tonnes fish/year. Impacts of the cage wastes in the water column in the vicinity of the cages were minimal despite the substantial discharges from the cages. No significant differences were observed in concentrations of dissolved and particulate nutrients (ammonia, nitrate, phosphate, particulate C,N and P), chlorophyll, chlorophyll fluorescence, dissolved oxygen, total suspended solids, Secchi depths and extinction coefficient of photosynthetically active radiation between the cage site and the control stations upstream or downstream of the fish farm. Although sedimentation rates measured in traps were higher under the cages than at control sites, the sediment flux was a small percentage of total feeds added to the cages. Apparently cage wastes were efficiently dispersed by water currents which averaged 9.3 cm/s below the fish cages. Consumption of the wastes by wild fish species which aggregated around the fish cages and their movement in the vicinity of the cages also contributed to the dispersion of the cage wastes and served to dilute impact of the cages. In combination, these physical and biological processes reduced the immediate impact of the cage farming operation and must be considered in the siting of future cage farms.
Hydrobiologia, 2007
... Planktonic nitrogen fixation in Lake Malawi/Nyasa Mangaliso J. Gondwe Æ Stephanie J. Guildfor... more ... Planktonic nitrogen fixation in Lake Malawi/Nyasa Mangaliso J. Gondwe Æ Stephanie J. Guildford Æ Robert E. Hecky ... MJ Gondwe (&) SADC/GEF Lake Malawi Biodiversity Conservation Project, PO Box 311, Salima, Malawi e-mail: mgondwe@scimail.uwaterloo.ca ...
I hereby declare that I am the sole author of this thesis. This is a true copy of the thesis, inc... more I hereby declare that I am the sole author of this thesis. This is a true copy of the thesis, including any required final revisions, as accepted by my examiners. I understand that my thesis may be made electronically available to the public.
Aquaculture, 2012
Cage culture of native tilapiine cichlids was initiated in Lake Malawi in 2004. The lake is well ... more Cage culture of native tilapiine cichlids was initiated in Lake Malawi in 2004. The lake is well known for its highly endemic ichthyodiversity, and it is estimated to have more species of fish than any other lake in the world. Consequently there is concern about the impact of cage farming operations on the wild fish communities. In 2007, high densities of diverse wild fish were observed around the cages and stable isotopes, δ 13 C and δ 15 N analyses, established that cage wastes were incorporated in the food web that supported diverse wild fishes in the vicinity of the cages. Comparison of δ 13 C and δ 15 N signals of caged and wild fish caught in 2007 in the vicinity of the fish farm and signals of fish samples caught between 1995 and 1997 before the fish farm was started in 2004 established a shift in the isotopic signatures of wild fish indicating the incorporation of cage wastes into the wild fish diet. Sedimentation of cage wastes collected in sediment traps below the fish cages was also confirmed using the δ 13 C and δ 15 N analyses. The accumulation of the cage wastes in the sediments below the cages was, however, minimal as indicated by the small differences in the isotopic ratios between the bulk sediments and some sedimentary organisms (bivalves, snails and earthworms) under the cages relative to ratios in similar organisms at control stations. The low impact of cage wastes on underlying sediments and benthic organisms was due to the rapid and efficient dispersion of the cage wastes facilitated by water currents through the fish farm which averaged 9.3 cm s − 1 as well as the consumption and subsequent dispersion of cage wastes by the large numbers of wild fishes which aggregated around the cages. This study has also shown that in Lake Malawi, fish rather than benthic organisms and plankton material may be a more sensitive monitor of the dispersion of cage wastes.