The contribution of submerged macrophytes and macroalgae to nutrient cycling in the Great Brak Estuary
- Authors: Human, Lucienne Ryno Daniel
- Date: 2013
- Subjects: Nutrient cycles -- South Africa -- Great Brak Estuary , Microalgae -- South Africa -- Great Brak Estuary , Estuarine ecology -- South Africa -- Great Brak Estuary
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10364 , http://hdl.handle.net/10948/d1021102
- Description: An ecological reserve study by the Department of Water Affairs on the Great Brak Estuary stated that there was a need to determine how much nitrogen and phosphorus was flowing through the estuary as well as how effective the macroalgae were at removing N and P. The objective of this study was to investigate the physico-chemical characteristics in the estuary and the influence of these on the submerged macrophytes and macroalgae. A nutrient budget for the estuary was developed in order to quantify the contribution of the submerged macrophytes and macroalgae relative to other contributing sources. The Wolwedans Dam located 3 km upstream from the estuary has reduced the amount of freshwater flow to the estuary by as much as 56 percent. The estuary has been allocated 2 x 106 m3 per annum of freshwater (ecological reserve) that is used to breach the mouth once or twice a year in spring or summer. Even though this water has been made available it is not sufficient to flush the estuary. Reduced flushing has led to an accumulation of organic matter and degradation in the water quality. Physico-chemical measurements between September 2010 and July 2012 showed that dissolved oxygen values were generally below 6 mg l-1. The average NH4+ concentration in the estuary was 7 μM and increased with depth to 12 μM at 2 m depths. Concentrations >45 μM were found in February and April 2011 at the 5 m deep hole at 3.4 km upstream. Negative correlations between dissolved oxygen and NH4+ during November 2010, February 2011, April 2011 and July 2011 (r = -0.68; -0.67; -0.63; -0.96) indicated that remineralisation of organic matter had occurred. Soluble reactive phosphorus (SRP) followed a similar trend to the NH4+ and was generally below 1 μM in the water column for most months, and had peaks at 1.0 km and 3.4 km in the bottom water. The abundance of submerged macrophytes and macroalgae below the N2 bridge were mostly influenced by mouth state and river inflow. During the closed phase the dominant macroalga Cladophora glomerata had an area cover ranging from 3000 to 6000 m2 while Zostera capensis and Ruppia cirrhosa covered an area of 2000 to 3500 m2 and 1500 to 2900 m2, respectively. After an artificial breach in February 2011, water drained out of the estuary leaving the alga stranded on the marshes and as the flood tide entered the macroalga was once again redistributed in the lower reaches. The alga utilised the available nutrients in the water column and expanded its area cover from 35000 m2 in February 2011 to 64000 m2 in March 2011. However, after the floods in June 2011, Cladophora glomerata had been washed out of the system while the submerged macrophytes responded positively extending their area cover. By comparing the artificial breach with the natural breach, and the effect on the estuary, an important observation was highlighted. Increasing the current allocated ecological reserve, and using a larger volume of water to breach the mouth artificially, would result in better scouring of sediment and associated organic matter out of the estuary. This would enable better oxygenation of the water column, reduce remineralisation and minimise algal blooms.
- Full Text:
- Date Issued: 2013
- Authors: Human, Lucienne Ryno Daniel
- Date: 2013
- Subjects: Nutrient cycles -- South Africa -- Great Brak Estuary , Microalgae -- South Africa -- Great Brak Estuary , Estuarine ecology -- South Africa -- Great Brak Estuary
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10364 , http://hdl.handle.net/10948/d1021102
- Description: An ecological reserve study by the Department of Water Affairs on the Great Brak Estuary stated that there was a need to determine how much nitrogen and phosphorus was flowing through the estuary as well as how effective the macroalgae were at removing N and P. The objective of this study was to investigate the physico-chemical characteristics in the estuary and the influence of these on the submerged macrophytes and macroalgae. A nutrient budget for the estuary was developed in order to quantify the contribution of the submerged macrophytes and macroalgae relative to other contributing sources. The Wolwedans Dam located 3 km upstream from the estuary has reduced the amount of freshwater flow to the estuary by as much as 56 percent. The estuary has been allocated 2 x 106 m3 per annum of freshwater (ecological reserve) that is used to breach the mouth once or twice a year in spring or summer. Even though this water has been made available it is not sufficient to flush the estuary. Reduced flushing has led to an accumulation of organic matter and degradation in the water quality. Physico-chemical measurements between September 2010 and July 2012 showed that dissolved oxygen values were generally below 6 mg l-1. The average NH4+ concentration in the estuary was 7 μM and increased with depth to 12 μM at 2 m depths. Concentrations >45 μM were found in February and April 2011 at the 5 m deep hole at 3.4 km upstream. Negative correlations between dissolved oxygen and NH4+ during November 2010, February 2011, April 2011 and July 2011 (r = -0.68; -0.67; -0.63; -0.96) indicated that remineralisation of organic matter had occurred. Soluble reactive phosphorus (SRP) followed a similar trend to the NH4+ and was generally below 1 μM in the water column for most months, and had peaks at 1.0 km and 3.4 km in the bottom water. The abundance of submerged macrophytes and macroalgae below the N2 bridge were mostly influenced by mouth state and river inflow. During the closed phase the dominant macroalga Cladophora glomerata had an area cover ranging from 3000 to 6000 m2 while Zostera capensis and Ruppia cirrhosa covered an area of 2000 to 3500 m2 and 1500 to 2900 m2, respectively. After an artificial breach in February 2011, water drained out of the estuary leaving the alga stranded on the marshes and as the flood tide entered the macroalga was once again redistributed in the lower reaches. The alga utilised the available nutrients in the water column and expanded its area cover from 35000 m2 in February 2011 to 64000 m2 in March 2011. However, after the floods in June 2011, Cladophora glomerata had been washed out of the system while the submerged macrophytes responded positively extending their area cover. By comparing the artificial breach with the natural breach, and the effect on the estuary, an important observation was highlighted. Increasing the current allocated ecological reserve, and using a larger volume of water to breach the mouth artificially, would result in better scouring of sediment and associated organic matter out of the estuary. This would enable better oxygenation of the water column, reduce remineralisation and minimise algal blooms.
- Full Text:
- Date Issued: 2013
Reeds as indicators of nutrient enrichment in the East Kleinemonde Estuary
- Authors: Human, Lucienne Ryno Daniel
- Date: 2009
- Subjects: Estuaries -- South Africa -- Eastern Cape -- East Kleinemonde Estuary , Nutrient cycles -- South Africa -- Eastern Cape -- East Kleinemonde Estuary
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10615 , http://hdl.handle.net/10948/1252 , Estuaries -- South Africa -- Eastern Cape -- East Kleinemonde Estuary , Nutrient cycles -- South Africa -- Eastern Cape -- East Kleinemonde Estuary
- Description: The release of nutrients (nitrogen and phosphorus) via land clearing, application of fertilisers, discharge of human waste and combustion of fossil fuels, is one of the most harmful effects of anthropogenic stresses on aquatic environments. This study investigated the use of reeds as indicators of nutrient input to estuaries. Small estuaries such as the oligotrophic East Kleinemonde where the research was mostly conducted are sensitive to nutrient enrichment from septic tanks, stormwater runoff and fertiliser application to lawns in close proximity to the estuary. Nutrient concentrations were sampled at different positions, in the groundwater, at the water’s edge, in the reed bed and in the main estuary channel at five sites in the East Kleinemonde Estuary. The NH4+ and SRP concentrations showed a definite trend as concentrations decreased from the groundwater or water’s edge into the main estuary channel. Groundwater introduced nutrients to the estuary which were then taken up by the fringing reeds (Phragmites australis (Cavinelles) Trinius ex Steudel). The water column nutrients were either below detectable limits or in very low concentrations. Low TOxN concentrations were consistently found at the different sites and probably resulted from P. australis assimilating N-TOxN for growth more efficiently than N- NH4+. The roots, rhizomes, stems and leaves of the reeds were measured for δ15N as an indicator of nutrient enrichment as nitrogen stable isotope analysis of plant tissue is an effective method for assessing and monitoring septic tank and other anthropogenic inputs. All plant parts for the three sampling sessions at Site 1 (mouth region) in the East Kleinemonde Estuary had significantly higher δ15N signatures (~20 percent) than the leaves at Site 5 (upper reaches). These differences were related to the surrounding land-use of the East Kleinemonde catchment, where the lower part of the estuary has moderate to low residential development and the upper reaches are utilized mainly for livestock farming. The high δ15N signatures at Site 1 were attributed to septic tank wastewater and stormwater run-off entering the estuary. Nutrient enrichment also influenced the morphology of the reeds. Reed biomass, height and stem density was significantly higher at Site 1 compared to Site 5. Similar studies were conducted in August 2008 in the Sundays Estuary and October 2008 in the nearby Mtati and Mpekweni estuaries to see if the results were similar. iii The same patterns were found where the groundwater NH4+ and SRP concentrations were higher than the estuary channel in the Mtati and Mpekweni estuaries. In the Mpekweni and Sundays estuaries Phragmites australis leaves had high δ15N signatures (10 and 11 percent) similar to that of Site 1 in the East Kleinemonde Estuary. Lower signatures (-2 to +4 percent) were found in the Mtati Estuary. This sampling site was sheltered by a bridge with a steep slope and the concentrations were similar to Site 3 and 5 in the East Kleinemonde Estuary where the derived nutrient was the result of stormwater runoff or fertilisers. Density and biomass of reeds in the Sundays and East Kleinemonde (Site 1) estuaries were similar and this could be related to different nutrient sources, agricultural return flow and septic tank input respectively. Reeds in the Sundays Estuary were significantly taller than in the other estuaries which showed that factors such as shelter and salinity also influence reed growth and therefore morphology alone would not be a good indicator of nutrient enrichment. Indicators of nutrient enrichment are important as the status of temporarily open / closed estuaries in South Africa is threatened by deteriorating water quality. Measurements of the water column may provide an inaccurate assessment of water quality whereas macrophytes are outstanding potential indicators of nutrient enrichment as they are widely distributed, abundant and long-lived. The findings from this study indicate that δ15N concentrations in reeds can be used to indicate nutrient loading.
- Full Text:
- Date Issued: 2009
- Authors: Human, Lucienne Ryno Daniel
- Date: 2009
- Subjects: Estuaries -- South Africa -- Eastern Cape -- East Kleinemonde Estuary , Nutrient cycles -- South Africa -- Eastern Cape -- East Kleinemonde Estuary
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10615 , http://hdl.handle.net/10948/1252 , Estuaries -- South Africa -- Eastern Cape -- East Kleinemonde Estuary , Nutrient cycles -- South Africa -- Eastern Cape -- East Kleinemonde Estuary
- Description: The release of nutrients (nitrogen and phosphorus) via land clearing, application of fertilisers, discharge of human waste and combustion of fossil fuels, is one of the most harmful effects of anthropogenic stresses on aquatic environments. This study investigated the use of reeds as indicators of nutrient input to estuaries. Small estuaries such as the oligotrophic East Kleinemonde where the research was mostly conducted are sensitive to nutrient enrichment from septic tanks, stormwater runoff and fertiliser application to lawns in close proximity to the estuary. Nutrient concentrations were sampled at different positions, in the groundwater, at the water’s edge, in the reed bed and in the main estuary channel at five sites in the East Kleinemonde Estuary. The NH4+ and SRP concentrations showed a definite trend as concentrations decreased from the groundwater or water’s edge into the main estuary channel. Groundwater introduced nutrients to the estuary which were then taken up by the fringing reeds (Phragmites australis (Cavinelles) Trinius ex Steudel). The water column nutrients were either below detectable limits or in very low concentrations. Low TOxN concentrations were consistently found at the different sites and probably resulted from P. australis assimilating N-TOxN for growth more efficiently than N- NH4+. The roots, rhizomes, stems and leaves of the reeds were measured for δ15N as an indicator of nutrient enrichment as nitrogen stable isotope analysis of plant tissue is an effective method for assessing and monitoring septic tank and other anthropogenic inputs. All plant parts for the three sampling sessions at Site 1 (mouth region) in the East Kleinemonde Estuary had significantly higher δ15N signatures (~20 percent) than the leaves at Site 5 (upper reaches). These differences were related to the surrounding land-use of the East Kleinemonde catchment, where the lower part of the estuary has moderate to low residential development and the upper reaches are utilized mainly for livestock farming. The high δ15N signatures at Site 1 were attributed to septic tank wastewater and stormwater run-off entering the estuary. Nutrient enrichment also influenced the morphology of the reeds. Reed biomass, height and stem density was significantly higher at Site 1 compared to Site 5. Similar studies were conducted in August 2008 in the Sundays Estuary and October 2008 in the nearby Mtati and Mpekweni estuaries to see if the results were similar. iii The same patterns were found where the groundwater NH4+ and SRP concentrations were higher than the estuary channel in the Mtati and Mpekweni estuaries. In the Mpekweni and Sundays estuaries Phragmites australis leaves had high δ15N signatures (10 and 11 percent) similar to that of Site 1 in the East Kleinemonde Estuary. Lower signatures (-2 to +4 percent) were found in the Mtati Estuary. This sampling site was sheltered by a bridge with a steep slope and the concentrations were similar to Site 3 and 5 in the East Kleinemonde Estuary where the derived nutrient was the result of stormwater runoff or fertilisers. Density and biomass of reeds in the Sundays and East Kleinemonde (Site 1) estuaries were similar and this could be related to different nutrient sources, agricultural return flow and septic tank input respectively. Reeds in the Sundays Estuary were significantly taller than in the other estuaries which showed that factors such as shelter and salinity also influence reed growth and therefore morphology alone would not be a good indicator of nutrient enrichment. Indicators of nutrient enrichment are important as the status of temporarily open / closed estuaries in South Africa is threatened by deteriorating water quality. Measurements of the water column may provide an inaccurate assessment of water quality whereas macrophytes are outstanding potential indicators of nutrient enrichment as they are widely distributed, abundant and long-lived. The findings from this study indicate that δ15N concentrations in reeds can be used to indicate nutrient loading.
- Full Text:
- Date Issued: 2009
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