The increased proliferation of benthic marine cyanobacteria of the Lyngbya genus in many tropical and subtropical systems worldwide is a concern due to the detrimental impacts these blooms can have on ecosystems, local economies and public health. While increasing nutrient loads from anthropogenic sources/activities has been hypothesised as the main cause, evidence to support this is limited. This hypothesis was explored by investigating blooms of the toxic, benthic cyanobacterium Lyngbya majuscula in a sub-tropical shallow coastal embayment (Moreton Bay) in southeast Queensland, Australia—where blooms have increased in frequency and severity. More specifically, the thesis aimed to investigate the role of nutrients in the physiology and growth dynamics of L. majuscula in Moreton Bay through examination of three main research questions. Examination of the spatial and temporal variations in the growth and nutritional status of L. majuscula in Moreton Bay (Research Question 1) was investigated by tracking natural summer blooms in northeastern Moreton Bay (Deception Bay) over two successive years. Detailed field observations, extensive biomass and tissue nutrient sampling (every 10–14 days) and a three-dimensional model were used to map the change in areal extent, biomass and tissue nutrients over the course of the blooms. The results demonstrated the innate ability of L. majuscula to rapidly spread and generate massive amounts of biomass, with the peak biomass calculated at 5057 tww in the 2005–2006 and 10 213 tww in the 2006–2007 seasons. A sequence of phases showing differing appearance, biomass growth and tissue nutrient changes were identified and documented. The role of nutrients (individually and collectively) in the enhancement of L. majuscula growth (Research Question 2) was investigated using a combination of comprehensive laboratory experiments (filament growth, 14C-bicarbonate uptake rate and biomass increase) and in-situ field experiments. Addition of nutrients to the water column were shown to promote prolific L. majuscula growth in the laboratory; this was confirmed in field experiments at two locations in Moreton Bay—showing nutrients can be a major causal factor in bloom formation. Additions of phosphorus (macronutrient) and iron (required for photosynthesis and nitrogen-fixation) caused the greatest stimulation of L. majuscula in both laboratory and field experiments. The form of iron was shown to be important —organically complexed iron (FeEDTA) was substantially more effective in promoting L. majuscula growth under laboratory conditions than inorganic iron (FeCl3). This is important as FeEDTA mirrors the naturally occurring iron organic complexes (which increase the solubility of iron) in waters from the region. The effect of nitrogen additions was more complex—likely due to the capacity of L. majuscula to fix atmospheric nitrogen reducing reliance on an inorganic nitrogen source. In the high light conditions experienced in this study, L. majuscula appeared to acquire nitrogen: (i) directly from the dissolved inorganic nitrogen in the water column—evidenced by a positive response to the nitrogen treatments; and, (ii) through enhanced nitrogen-fixation rates when iron and/or phosphorus were added in the absence of nitrogen—inferred from a substantial increase in the total nitrogen content of the L. majuscula biomass (nitrogen-fixation was not measured directly). The main sources of naturally occurring nutrients likely to promote L. majuscula blooms in Moreton Bay (Research Question 3) were investigated using laboratory experiments, soil and water analyses, and GIS-based modelling. The potential for groundwater/surfacewater from different vegetation, soils, geology and landuses within the study area catchments to stimulate L. majuscula response (14C-bicarbonate uptake rate) was tested in laboratory bioassays. Areas with acid sulfate soils (ASS), Melaleuca vegetation, pine plantations and Casuarina on ASS all had waters that enhanced L. majuscula growth. To investigate causal agents, bioassay response data and water analyses were subject to multiple regression and correlation analysis; this confirmed the importance of iron, phosphorus and nitrogen to L. majuscula growth and the roles of low pH and dissolved organic carbon, the latter two appearing to influence the chemical state and enhance the solubility of nutrients to L. majuscula. This information was incorporated into a GIS-based model to identify areas of hazard which were most likely to supply/export nutrients to Moreton Bay. These hazard maps, with further local verification, will be used as planning and decision support tools to assist government and landuse managers to limit the mobilisation and transport of key nutrients to potential bloom sites. The results from this thesis demonstrate that a precautionary approach to limit phosphorus, iron, nitrogen and dissolved organic carbon to waterways is necessary; otherwise the magnitude of L. majuscula blooms is likely to increase in Moreton Bay as coastal development intensifies with the predicted population increase. The thesis findings provide strong support for the hypothesised link between nutrients and the increased proliferation of Lyngbya and other benthic cyanobacteria blooms and are likely to be applicable to other areas where environmental conditions are suitable for their growth.

The increased proliferation of benthic marine cyanobacteria of the Lyngbya genus in many tropical and subtropical systems worldwide is a concern due to the detrimental impacts these blooms can have on ecosystems, local economies and public health. While increasing nutrient loads from anthropogenic sources/activities has been hypothesised as the main cause, evidence to support this is limited. This hypothesis was explored by investigating blooms of the toxic, benthic cyanobacterium Lyngbya majuscula in a sub-tropical shallow coastal embayment (Moreton Bay) in southeast Queensland, Australia—where blooms have increased in frequency and severity. More specifically, the thesis aimed to investigate the role of nutrients in the physiology and growth dynamics of L. majuscula in Moreton Bay through examination of three main research questions. Examination of the spatial and temporal variations in the growth and nutritional status of L. majuscula in Moreton Bay (Research Question 1) was investigated by tracking natural summer blooms in northeastern Moreton Bay (Deception Bay) over two successive years. Detailed field observations, extensive biomass and tissue nutrient sampling (every 10–14 days) and a three-dimensional model were used to map the change in areal extent, biomass and tissue nutrients over the course of the blooms. The results demonstrated the innate ability of L. majuscula to rapidly spread and generate massive amounts of biomass, with the peak biomass calculated at 5057 tww in the 2005–2006 and 10 213 tww in the 2006–2007 seasons. A sequence of phases showing differing appearance, biomass growth and tissue nutrient changes were identified and documented. The role of nutrients (individually and collectively) in the enhancement of L. majuscula growth (Research Question 2) was investigated using a combination of comprehensive laboratory experiments (filament growth, 14C-bicarbonate uptake rate and biomass increase) and in-situ field experiments. Addition of nutrients to the water column were shown to promote prolific L. majuscula growth in the laboratory; this was confirmed in field experiments at two locations in Moreton Bay—showing nutrients can be a major causal factor in bloom formation. Additions of phosphorus (macronutrient) and iron (required for photosynthesis and nitrogen-fixation) caused the greatest stimulation of L. majuscula in both laboratory and field experiments. The form of iron was shown to be important —organically complexed iron (FeEDTA) was substantially more effective in promoting L. majuscula growth under laboratory conditions than inorganic iron (FeCl3). This is important as FeEDTA mirrors the naturally occurring iron organic complexes (which increase the solubility of iron) in waters from the region. The effect of nitrogen additions was more complex—likely due to the capacity of L. majuscula to fix atmospheric nitrogen reducing reliance on an inorganic nitrogen source. In the high light conditions experienced in this study, L. majuscula appeared to acquire nitrogen: (i) directly from the dissolved inorganic nitrogen in the water column—evidenced by a positive response to the nitrogen treatments; and, (ii) through enhanced nitrogen-fixation rates when iron and/or phosphorus were added in the absence of nitrogen—inferred from a substantial increase in the total nitrogen content of the L. majuscula biomass (nitrogen-fixation was not measured directly). The main sources of naturally occurring nutrients likely to promote L. majuscula blooms in Moreton Bay (Research Question 3) were investigated using laboratory experiments, soil and water analyses, and GIS-based modelling. The potential for groundwater/surfacewater from different vegetation, soils, geology and landuses within the study area catchments to stimulate L. majuscula response (14C-bicarbonate uptake rate) was tested in laboratory bioassays. Areas with acid sulfate soils (ASS), Melaleuca vegetation, pine plantations and Casuarina on ASS all had waters that enhanced L. majuscula growth. To investigate causal agents, bioassay response data and water analyses were subject to multiple regression and correlation analysis; this confirmed the importance of iron, phosphorus and nitrogen to L. majuscula growth and the roles of low pH and dissolved organic carbon, the latter two appearing to influence the chemical state and enhance the solubility of nutrients to L. majuscula. This information was incorporated into a GIS-based model to identify areas of hazard which were most likely to supply/export nutrients to Moreton Bay. These hazard maps, with further local verification, will be used as planning and decision support tools to assist government and landuse managers to limit the mobilisation and transport of key nutrients to potential bloom sites. The results from this thesis demonstrate that a precautionary approach to limit phosphorus, iron, nitrogen and dissolved organic carbon to waterways is necessary; otherwise the magnitude of L. majuscula blooms is likely to increase in Moreton Bay as coastal development intensifies with the predicted population increase. The thesis findings provide strong support for the hypothesised link between nutrients and the increased proliferation of Lyngbya and other benthic cyanobacteria blooms and are likely to be applicable to other areas where environmental conditions are suitable for their growth.

The increased proliferation of benthic marine cyanobacteria of the Lyngbya genus in many tropical and subtropical systems worldwide is a concern due to the detrimental impacts these blooms can have on ecosystems, local economies and public health. While increasing nutrient loads from anthropogenic sources/activities has been hypothesised as the main cause, evidence to support this is limited. This hypothesis was explored by investigating blooms of the toxic, benthic cyanobacterium Lyngbya majuscula in a sub-tropical shallow coastal embayment (Moreton Bay) in southeast Queensland, Australia—where blooms have increased in frequency and severity. More specifically, the thesis aimed to investigate the role of nutrients in the physiology and growth dynamics of L. majuscula in Moreton Bay through examination of three main research questions. Examination of the spatial and temporal variations in the growth and nutritional status of L. majuscula in Moreton Bay (Research Question 1) was investigated by tracking natural summer blooms in northeastern Moreton Bay (Deception Bay) over two successive years. Detailed field observations, extensive biomass and tissue nutrient sampling (every 10–14 days) and a three-dimensional model were used to map the change in areal extent, biomass and tissue nutrients over the course of the blooms. The results demonstrated the innate ability of L. majuscula to rapidly spread and generate massive amounts of biomass, with the peak biomass calculated at 5057 tww in the 2005–2006 and 10 213 tww in the 2006–2007 seasons. A sequence of phases showing differing appearance, biomass growth and tissue nutrient changes were identified and documented. The role of nutrients (individually and collectively) in the enhancement of L. majuscula growth (Research Question 2) was investigated using a combination of comprehensive laboratory experiments (filament growth, 14C-bicarbonate uptake rate and biomass increase) and in-situ field experiments. Addition of nutrients to the water column were shown to promote prolific L. majuscula growth in the laboratory; this was confirmed in field experiments at two locations in Moreton Bay—showing nutrients can be a major causal factor in bloom formation. Additions of phosphorus (macronutrient) and iron (required for photosynthesis and nitrogen-fixation) caused the greatest stimulation of L. majuscula in both laboratory and field experiments. The form of iron was shown to be important —organically complexed iron (FeEDTA) was substantially more effective in promoting L. majuscula growth under laboratory conditions than inorganic iron (FeCl3). This is important as FeEDTA mirrors the naturally occurring iron organic complexes (which increase the solubility of iron) in waters from the region. The effect of nitrogen additions was more complex—likely due to the capacity of L. majuscula to fix atmospheric nitrogen reducing reliance on an inorganic nitrogen source. In the high light conditions experienced in this study, L. majuscula appeared to acquire nitrogen: (i) directly from the dissolved inorganic nitrogen in the water column—evidenced by a positive response to the nitrogen treatments; and, (ii) through enhanced nitrogen-fixation rates when iron and/or phosphorus were added in the absence of nitrogen—inferred from a substantial increase in the total nitrogen content of the L. majuscula biomass (nitrogen-fixation was not measured directly). The main sources of naturally occurring nutrients likely to promote L. majuscula blooms in Moreton Bay (Research Question 3) were investigated using laboratory experiments, soil and water analyses, and GIS-based modelling. The potential for groundwater/surfacewater from different vegetation, soils, geology and landuses within the study area catchments to stimulate L. majuscula response (14C-bicarbonate uptake rate) was tested in laboratory bioassays. Areas with acid sulfate soils (ASS), Melaleuca vegetation, pine plantations and Casuarina on ASS all had waters that enhanced L. majuscula growth. To investigate causal agents, bioassay response data and water analyses were subject to multiple regression and correlation analysis; this confirmed the importance of iron, phosphorus and nitrogen to L. majuscula growth and the roles of low pH and dissolved organic carbon, the latter two appearing to influence the chemical state and enhance the solubility of nutrients to L. majuscula. This information was incorporated into a GIS-based model to identify areas of hazard which were most likely to supply/export nutrients to Moreton Bay. These hazard maps, with further local verification, will be used as planning and decision support tools to assist government and landuse managers to limit the mobilisation and transport of key nutrients to potential bloom sites. The results from this thesis demonstrate that a precautionary approach to limit phosphorus, iron, nitrogen and dissolved organic carbon to waterways is necessary; otherwise the magnitude of L. majuscula blooms is likely to increase in Moreton Bay as coastal development intensifies with the predicted population increase. The thesis findings provide strong support for the hypothesised link between nutrients and the increased proliferation of Lyngbya and other benthic cyanobacteria blooms and are likely to be applicable to other areas where environmental conditions are suitable for their growth.

The increased proliferation of benthic marine cyanobacteria of the Lyngbya genus in many tropical and subtropical systems worldwide is a concern due to the detrimental impacts these blooms can have on ecosystems, local economies and public health. While increasing nutrient loads from anthropogenic sources/activities has been hypothesised as the main cause, evidence to support this is limited. This hypothesis was explored by investigating blooms of the toxic, benthic cyanobacterium Lyngbya majuscula in a sub-tropical shallow coastal embayment (Moreton Bay) in southeast Queensland, Australia—where blooms have increased in frequency and severity. More specifically, the thesis aimed to investigate the role of nutrients in the physiology and growth dynamics of L. majuscula in Moreton Bay through examination of three main research questions. Examination of the spatial and temporal variations in the growth and nutritional status of L. majuscula in Moreton Bay (Research Question 1) was investigated by tracking natural summer blooms in northeastern Moreton Bay (Deception Bay) over two successive years. Detailed field observations, extensive biomass and tissue nutrient sampling (every 10–14 days) and a three-dimensional model were used to map the change in areal extent, biomass and tissue nutrients over the course of the blooms. The results demonstrated the innate ability of L. majuscula to rapidly spread and generate massive amounts of biomass, with the peak biomass calculated at 5057 tww in the 2005–2006 and 10 213 tww in the 2006–2007 seasons. A sequence of phases showing differing appearance, biomass growth and tissue nutrient changes were identified and documented. The role of nutrients (individually and collectively) in the enhancement of L. majuscula growth (Research Question 2) was investigated using a combination of comprehensive laboratory experiments (filament growth, 14C-bicarbonate uptake rate and biomass increase) and in-situ field experiments. Addition of nutrients to the water column were shown to promote prolific L. majuscula growth in the laboratory; this was confirmed in field experiments at two locations in Moreton Bay—showing nutrients can be a major causal factor in bloom formation. Additions of phosphorus (macronutrient) and iron (required for photosynthesis and nitrogen-fixation) caused the greatest stimulation of L. majuscula in both laboratory and field experiments. The form of iron was shown to be important —organically complexed iron (FeEDTA) was substantially more effective in promoting L. majuscula growth under laboratory conditions than inorganic iron (FeCl3). This is important as FeEDTA mirrors the naturally occurring iron organic complexes (which increase the solubility of iron) in waters from the region. The effect of nitrogen additions was more complex—likely due to the capacity of L. majuscula to fix atmospheric nitrogen reducing reliance on an inorganic nitrogen source. In the high light conditions experienced in this study, L. majuscula appeared to acquire nitrogen: (i) directly from the dissolved inorganic nitrogen in the water column—evidenced by a positive response to the nitrogen treatments; and, (ii) through enhanced nitrogen-fixation rates when iron and/or phosphorus were added in the absence of nitrogen—inferred from a substantial increase in the total nitrogen content of the L. majuscula biomass (nitrogen-fixation was not measured directly). The main sources of naturally occurring nutrients likely to promote L. majuscula blooms in Moreton Bay (Research Question 3) were investigated using laboratory experiments, soil and water analyses, and GIS-based modelling. The potential for groundwater/surfacewater from different vegetation, soils, geology and landuses within the study area catchments to stimulate L. majuscula response (14C-bicarbonate uptake rate) was tested in laboratory bioassays. Areas with acid sulfate soils (ASS), Melaleuca vegetation, pine plantations and Casuarina on ASS all had waters that enhanced L. majuscula growth. To investigate causal agents, bioassay response data and water analyses were subject to multiple regression and correlation analysis; this confirmed the importance of iron, phosphorus and nitrogen to L. majuscula growth and the roles of low pH and dissolved organic carbon, the latter two appearing to influence the chemical state and enhance the solubility of nutrients to L. majuscula. This information was incorporated into a GIS-based model to identify areas of hazard which were most likely to supply/export nutrients to Moreton Bay. These hazard maps, with further local verification, will be used as planning and decision support tools to assist government and landuse managers to limit the mobilisation and transport of key nutrients to potential bloom sites. The results from this thesis demonstrate that a precautionary approach to limit phosphorus, iron, nitrogen and dissolved organic carbon to waterways is necessary; otherwise the magnitude of L. majuscula blooms is likely to increase in Moreton Bay as coastal development intensifies with the predicted population increase. The thesis findings provide strong support for the hypothesised link between nutrients and the increased proliferation of Lyngbya and other benthic cyanobacteria blooms and are likely to be applicable to other areas where environmental conditions are suitable for their growth.

The increased proliferation of benthic marine cyanobacteria of the Lyngbya genus in many tropical and subtropical systems worldwide is a concern due to the detrimental impacts these blooms can have on ecosystems, local economies and public health. While increasing nutrient loads from anthropogenic sources/activities has been hypothesised as the main cause, evidence to support this is limited. This hypothesis was explored by investigating blooms of the toxic, benthic cyanobacterium Lyngbya majuscula in a sub-tropical shallow coastal embayment (Moreton Bay) in southeast Queensland, Australia—where blooms have increased in frequency and severity. More specifically, the thesis aimed to investigate the role of nutrients in the physiology and growth dynamics of L. majuscula in Moreton Bay through examination of three main research questions. Examination of the spatial and temporal variations in the growth and nutritional status of L. majuscula in Moreton Bay (Research Question 1) was investigated by tracking natural summer blooms in northeastern Moreton Bay (Deception Bay) over two successive years. Detailed field observations, extensive biomass and tissue nutrient sampling (every 10–14 days) and a three-dimensional model were used to map the change in areal extent, biomass and tissue nutrients over the course of the blooms. The results demonstrated the innate ability of L. majuscula to rapidly spread and generate massive amounts of biomass, with the peak biomass calculated at 5057 tww in the 2005–2006 and 10 213 tww in the 2006–2007 seasons. A sequence of phases showing differing appearance, biomass growth and tissue nutrient changes were identified and documented. The role of nutrients (individually and collectively) in the enhancement of L. majuscula growth (Research Question 2) was investigated using a combination of comprehensive laboratory experiments (filament growth, 14C-bicarbonate uptake rate and biomass increase) and in-situ field experiments. Addition of nutrients to the water column were shown to promote prolific L. majuscula growth in the laboratory; this was confirmed in field experiments at two locations in Moreton Bay—showing nutrients can be a major causal factor in bloom formation. Additions of phosphorus (macronutrient) and iron (required for photosynthesis and nitrogen-fixation) caused the greatest stimulation of L. majuscula in both laboratory and field experiments. The form of iron was shown to be important —organically complexed iron (FeEDTA) was substantially more effective in promoting L. majuscula growth under laboratory conditions than inorganic iron (FeCl3). This is important as FeEDTA mirrors the naturally occurring iron organic complexes (which increase the solubility of iron) in waters from the region. The effect of nitrogen additions was more complex—likely due to the capacity of L. majuscula to fix atmospheric nitrogen reducing reliance on an inorganic nitrogen source. In the high light conditions experienced in this study, L. majuscula appeared to acquire nitrogen: (i) directly from the dissolved inorganic nitrogen in the water column—evidenced by a positive response to the nitrogen treatments; and, (ii) through enhanced nitrogen-fixation rates when iron and/or phosphorus were added in the absence of nitrogen—inferred from a substantial increase in the total nitrogen content of the L. majuscula biomass (nitrogen-fixation was not measured directly). The main sources of naturally occurring nutrients likely to promote L. majuscula blooms in Moreton Bay (Research Question 3) were investigated using laboratory experiments, soil and water analyses, and GIS-based modelling. The potential for groundwater/surfacewater from different vegetation, soils, geology and landuses within the study area catchments to stimulate L. majuscula response (14C-bicarbonate uptake rate) was tested in laboratory bioassays. Areas with acid sulfate soils (ASS), Melaleuca vegetation, pine plantations and Casuarina on ASS all had waters that enhanced L. majuscula growth. To investigate causal agents, bioassay response data and water analyses were subject to multiple regression and correlation analysis; this confirmed the importance of iron, phosphorus and nitrogen to L. majuscula growth and the roles of low pH and dissolved organic carbon, the latter two appearing to influence the chemical state and enhance the solubility of nutrients to L. majuscula. This information was incorporated into a GIS-based model to identify areas of hazard which were most likely to supply/export nutrients to Moreton Bay. These hazard maps, with further local verification, will be used as planning and decision support tools to assist government and landuse managers to limit the mobilisation and transport of key nutrients to potential bloom sites. The results from this thesis demonstrate that a precautionary approach to limit phosphorus, iron, nitrogen and dissolved organic carbon to waterways is necessary; otherwise the magnitude of L. majuscula blooms is likely to increase in Moreton Bay as coastal development intensifies with the predicted population increase. The thesis findings provide strong support for the hypothesised link between nutrients and the increased proliferation of Lyngbya and other benthic cyanobacteria blooms and are likely to be applicable to other areas where environmental conditions are suitable for their growth.

The increased proliferation of benthic marine cyanobacteria of the Lyngbya genus in many tropical and subtropical systems worldwide is a concern due to the detrimental impacts these blooms can have on ecosystems, local economies and public health. While increasing nutrient loads from anthropogenic sources/activities has been hypothesised as the main cause, evidence to support this is limited. This hypothesis was explored by investigating blooms of the toxic, benthic cyanobacterium Lyngbya majuscula in a sub-tropical shallow coastal embayment (Moreton Bay) in southeast Queensland, Australia—where blooms have increased in frequency and severity. More specifically, the thesis aimed to investigate the role of nutrients in the physiology and growth dynamics of L. majuscula in Moreton Bay through examination of three main research questions. Examination of the spatial and temporal variations in the growth and nutritional status of L. majuscula in Moreton Bay (Research Question 1) was investigated by tracking natural summer blooms in northeastern Moreton Bay (Deception Bay) over two successive years. Detailed field observations, extensive biomass and tissue nutrient sampling (every 10–14 days) and a three-dimensional model were used to map the change in areal extent, biomass and tissue nutrients over the course of the blooms. The results demonstrated the innate ability of L. majuscula to rapidly spread and generate massive amounts of biomass, with the peak biomass calculated at 5057 tww in the 2005–2006 and 10 213 tww in the 2006–2007 seasons. A sequence of phases showing differing appearance, biomass growth and tissue nutrient changes were identified and documented. The role of nutrients (individually and collectively) in the enhancement of L. majuscula growth (Research Question 2) was investigated using a combination of comprehensive laboratory experiments (filament growth, 14C-bicarbonate uptake rate and biomass increase) and in-situ field experiments. Addition of nutrients to the water column were shown to promote prolific L. majuscula growth in the laboratory; this was confirmed in field experiments at two locations in Moreton Bay—showing nutrients can be a major causal factor in bloom formation. Additions of phosphorus (macronutrient) and iron (required for photosynthesis and nitrogen-fixation) caused the greatest stimulation of L. majuscula in both laboratory and field experiments. The form of iron was shown to be important —organically complexed iron (FeEDTA) was substantially more effective in promoting L. majuscula growth under laboratory conditions than inorganic iron (FeCl3). This is important as FeEDTA mirrors the naturally occurring iron organic complexes (which increase the solubility of iron) in waters from the region. The effect of nitrogen additions was more complex—likely due to the capacity of L. majuscula to fix atmospheric nitrogen reducing reliance on an inorganic nitrogen source. In the high light conditions experienced in this study, L. majuscula appeared to acquire nitrogen: (i) directly from the dissolved inorganic nitrogen in the water column—evidenced by a positive response to the nitrogen treatments; and, (ii) through enhanced nitrogen-fixation rates when iron and/or phosphorus were added in the absence of nitrogen—inferred from a substantial increase in the total nitrogen content of the L. majuscula biomass (nitrogen-fixation was not measured directly). The main sources of naturally occurring nutrients likely to promote L. majuscula blooms in Moreton Bay (Research Question 3) were investigated using laboratory experiments, soil and water analyses, and GIS-based modelling. The potential for groundwater/surfacewater from different vegetation, soils, geology and landuses within the study area catchments to stimulate L. majuscula response (14C-bicarbonate uptake rate) was tested in laboratory bioassays. Areas with acid sulfate soils (ASS), Melaleuca vegetation, pine plantations and Casuarina on ASS all had waters that enhanced L. majuscula growth. To investigate causal agents, bioassay response data and water analyses were subject to multiple regression and correlation analysis; this confirmed the importance of iron, phosphorus and nitrogen to L. majuscula growth and the roles of low pH and dissolved organic carbon, the latter two appearing to influence the chemical state and enhance the solubility of nutrients to L. majuscula. This information was incorporated into a GIS-based model to identify areas of hazard which were most likely to supply/export nutrients to Moreton Bay. These hazard maps, with further local verification, will be used as planning and decision support tools to assist government and landuse managers to limit the mobilisation and transport of key nutrients to potential bloom sites. The results from this thesis demonstrate that a precautionary approach to limit phosphorus, iron, nitrogen and dissolved organic carbon to waterways is necessary; otherwise the magnitude of L. majuscula blooms is likely to increase in Moreton Bay as coastal development intensifies with the predicted population increase. The thesis findings provide strong support for the hypothesised link between nutrients and the increased proliferation of Lyngbya and other benthic cyanobacteria blooms and are likely to be applicable to other areas where environmental conditions are suitable for their growth.

The increased proliferation of benthic marine cyanobacteria of the Lyngbya genus in many tropical and subtropical systems worldwide is a concern due to the detrimental impacts these blooms can have on ecosystems, local economies and public health. While increasing nutrient loads from anthropogenic sources/activities has been hypothesised as the main cause, evidence to support this is limited. This hypothesis was explored by investigating blooms of the toxic, benthic cyanobacterium Lyngbya majuscula in a sub-tropical shallow coastal embayment (Moreton Bay) in southeast Queensland, Australia—where blooms have increased in frequency and severity. More specifically, the thesis aimed to investigate the role of nutrients in the physiology and growth dynamics of L. majuscula in Moreton Bay through examination of three main research questions. Examination of the spatial and temporal variations in the growth and nutritional status of L. majuscula in Moreton Bay (Research Question 1) was investigated by tracking natural summer blooms in northeastern Moreton Bay (Deception Bay) over two successive years. Detailed field observations, extensive biomass and tissue nutrient sampling (every 10–14 days) and a three-dimensional model were used to map the change in areal extent, biomass and tissue nutrients over the course of the blooms. The results demonstrated the innate ability of L. majuscula to rapidly spread and generate massive amounts of biomass, with the peak biomass calculated at 5057 tww in the 2005–2006 and 10 213 tww in the 2006–2007 seasons. A sequence of phases showing differing appearance, biomass growth and tissue nutrient changes were identified and documented. The role of nutrients (individually and collectively) in the enhancement of L. majuscula growth (Research Question 2) was investigated using a combination of comprehensive laboratory experiments (filament growth, 14C-bicarbonate uptake rate and biomass increase) and in-situ field experiments. Addition of nutrients to the water column were shown to promote prolific L. majuscula growth in the laboratory; this was confirmed in field experiments at two locations in Moreton Bay—showing nutrients can be a major causal factor in bloom formation. Additions of phosphorus (macronutrient) and iron (required for photosynthesis and nitrogen-fixation) caused the greatest stimulation of L. majuscula in both laboratory and field experiments. The form of iron was shown to be important —organically complexed iron (FeEDTA) was substantially more effective in promoting L. majuscula growth under laboratory conditions than inorganic iron (FeCl3). This is important as FeEDTA mirrors the naturally occurring iron organic complexes (which increase the solubility of iron) in waters from the region. The effect of nitrogen additions was more complex—likely due to the capacity of L. majuscula to fix atmospheric nitrogen reducing reliance on an inorganic nitrogen source. In the high light conditions experienced in this study, L. majuscula appeared to acquire nitrogen: (i) directly from the dissolved inorganic nitrogen in the water column—evidenced by a positive response to the nitrogen treatments; and, (ii) through enhanced nitrogen-fixation rates when iron and/or phosphorus were added in the absence of nitrogen—inferred from a substantial increase in the total nitrogen content of the L. majuscula biomass (nitrogen-fixation was not measured directly). The main sources of naturally occurring nutrients likely to promote L. majuscula blooms in Moreton Bay (Research Question 3) were investigated using laboratory experiments, soil and water analyses, and GIS-based modelling. The potential for groundwater/surfacewater from different vegetation, soils, geology and landuses within the study area catchments to stimulate L. majuscula response (14C-bicarbonate uptake rate) was tested in laboratory bioassays. Areas with acid sulfate soils (ASS), Melaleuca vegetation, pine plantations and Casuarina on ASS all had waters that enhanced L. majuscula growth. To investigate causal agents, bioassay response data and water analyses were subject to multiple regression and correlation analysis; this confirmed the importance of iron, phosphorus and nitrogen to L. majuscula growth and the roles of low pH and dissolved organic carbon, the latter two appearing to influence the chemical state and enhance the solubility of nutrients to L. majuscula. This information was incorporated into a GIS-based model to identify areas of hazard which were most likely to supply/export nutrients to Moreton Bay. These hazard maps, with further local verification, will be used as planning and decision support tools to assist government and landuse managers to limit the mobilisation and transport of key nutrients to potential bloom sites. The results from this thesis demonstrate that a precautionary approach to limit phosphorus, iron, nitrogen and dissolved organic carbon to waterways is necessary; otherwise the magnitude of L. majuscula blooms is likely to increase in Moreton Bay as coastal development intensifies with the predicted population increase. The thesis findings provide strong support for the hypothesised link between nutrients and the increased proliferation of Lyngbya and other benthic cyanobacteria blooms and are likely to be applicable to other areas where environmental conditions are suitable for their growth.

The increased proliferation of benthic marine cyanobacteria of the Lyngbya genus in many tropical and subtropical systems worldwide is a concern due to the detrimental impacts these blooms can have on ecosystems, local economies and public health. While increasing nutrient loads from anthropogenic sources/activities has been hypothesised as the main cause, evidence to support this is limited. This hypothesis was explored by investigating blooms of the toxic, benthic cyanobacterium Lyngbya majuscula in a sub-tropical shallow coastal embayment (Moreton Bay) in southeast Queensland, Australia—where blooms have increased in frequency and severity. More specifically, the thesis aimed to investigate the role of nutrients in the physiology and growth dynamics of L. majuscula in Moreton Bay through examination of three main research questions. Examination of the spatial and temporal variations in the growth and nutritional status of L. majuscula in Moreton Bay (Research Question 1) was investigated by tracking natural summer blooms in northeastern Moreton Bay (Deception Bay) over two successive years. Detailed field observations, extensive biomass and tissue nutrient sampling (every 10–14 days) and a three-dimensional model were used to map the change in areal extent, biomass and tissue nutrients over the course of the blooms. The results demonstrated the innate ability of L. majuscula to rapidly spread and generate massive amounts of biomass, with the peak biomass calculated at 5057 tww in the 2005–2006 and 10 213 tww in the 2006–2007 seasons. A sequence of phases showing differing appearance, biomass growth and tissue nutrient changes were identified and documented. The role of nutrients (individually and collectively) in the enhancement of L. majuscula growth (Research Question 2) was investigated using a combination of comprehensive laboratory experiments (filament growth, 14C-bicarbonate uptake rate and biomass increase) and in-situ field experiments. Addition of nutrients to the water column were shown to promote prolific L. majuscula growth in the laboratory; this was confirmed in field experiments at two locations in Moreton Bay—showing nutrients can be a major causal factor in bloom formation. Additions of phosphorus (macronutrient) and iron (required for photosynthesis and nitrogen-fixation) caused the greatest stimulation of L. majuscula in both laboratory and field experiments. The form of iron was shown to be important —organically complexed iron (FeEDTA) was substantially more effective in promoting L. majuscula growth under laboratory conditions than inorganic iron (FeCl3). This is important as FeEDTA mirrors the naturally occurring iron organic complexes (which increase the solubility of iron) in waters from the region. The effect of nitrogen additions was more complex—likely due to the capacity of L. majuscula to fix atmospheric nitrogen reducing reliance on an inorganic nitrogen source. In the high light conditions experienced in this study, L. majuscula appeared to acquire nitrogen: (i) directly from the dissolved inorganic nitrogen in the water column—evidenced by a positive response to the nitrogen treatments; and, (ii) through enhanced nitrogen-fixation rates when iron and/or phosphorus were added in the absence of nitrogen—inferred from a substantial increase in the total nitrogen content of the L. majuscula biomass (nitrogen-fixation was not measured directly). The main sources of naturally occurring nutrients likely to promote L. majuscula blooms in Moreton Bay (Research Question 3) were investigated using laboratory experiments, soil and water analyses, and GIS-based modelling. The potential for groundwater/surfacewater from different vegetation, soils, geology and landuses within the study area catchments to stimulate L. majuscula response (14C-bicarbonate uptake rate) was tested in laboratory bioassays. Areas with acid sulfate soils (ASS), Melaleuca vegetation, pine plantations and Casuarina on ASS all had waters that enhanced L. majuscula growth. To investigate causal agents, bioassay response data and water analyses were subject to multiple regression and correlation analysis; this confirmed the importance of iron, phosphorus and nitrogen to L. majuscula growth and the roles of low pH and dissolved organic carbon, the latter two appearing to influence the chemical state and enhance the solubility of nutrients to L. majuscula. This information was incorporated into a GIS-based model to identify areas of hazard which were most likely to supply/export nutrients to Moreton Bay. These hazard maps, with further local verification, will be used as planning and decision support tools to assist government and landuse managers to limit the mobilisation and transport of key nutrients to potential bloom sites. The results from this thesis demonstrate that a precautionary approach to limit phosphorus, iron, nitrogen and dissolved organic carbon to waterways is necessary; otherwise the magnitude of L. majuscula blooms is likely to increase in Moreton Bay as coastal development intensifies with the predicted population increase. The thesis findings provide strong support for the hypothesised link between nutrients and the increased proliferation of Lyngbya and other benthic cyanobacteria blooms and are likely to be applicable to other areas where environmental conditions are suitable for their growth.

Coastal wetlands dominated by mangroves provide important ecological services to the coastal zone, many of which are associated with tidal inundation . In this study I investigated whether all coastal wetlands provide similar ecosystem services, or whether these varied depending on their geomorphological setting and the eutrophication level of the floodwater. Sampling was conducted over two years with significantly different levels of rainfall over six estuaries in Southeast Queensland, Australia. Sediment, nutrient and carbon exchange were investigated in tidal and riverine estuaries dominated by mangrove forests. The estuaries selected also comprised a gradient from low mesotrophic to low eutrophic. Spatial variation within the coastal wetlands was also investigated, comparing nutrient exchange in the low and high intertidal cyanobacteria mat . To assess sediment exchange, I measured retention of total suspended solids and sedimentation rates. Additionally, in order to assess the origin of sediment deposited in mangroves, glomalin, a novel terrestrial soil carbon (C) tracer, was used. Nutrient and C exchange were quantified by comparison of concentrations of soluble reactive phosphorus (SRP), nitrogen oxides (NOx--N), ammonium (NH4+) total organic carbon (TOC) and dissolved organic C (DOC) in water entering and leaving the mangroves during complete tidal cycles (3 tidal cycles in 6 estuaries for 2 years). Finally, the biogeochemical function of the cyanobacteria mat was measured through experiments investigating nitrogen fixation (N) and nutrient exchange in the extensive mats in the Exmouth Gulf, Western Australia. My results show that the seaward fringe mangrove retains the majority of sediment entering the wetland during a tidal cycle accounting for 52.5 ± 12.5 % of the total sedimentation (fringe mangrove + scrub mangrove + saltmarsh/ cyanobacteria mat). Geomorphological setting had a stronger influence on spatial patterns of deposition than on sedimentation rates. Riverine mangroves had more homogeneous distribution of sediments across the intertidal zone than tidal mangroves, where most sedimentation occurred in the seaward fringe mangrove zone. The presence of glomalin in sediments, and thus the relative importance of terrigenous sediment, was strongly influenced by geomorphological setting. Glomalin was primarily delivered to riverine mangroves and deposited within the scrub mangrove zone, while tidal mangroves received less glomalin during tidal inundation and most of it was deposited within the fringe mangrove zone. Overall, NOx--N concentrations decreased in the floodwater after flooding the coastal wetland, suggesting that these ecosystems act as sinks of dissolved NOx--N during tidal inundation. In average, NOx--N concentrations in the floodwater decreased 28 %. Additionally, during periods of high rainfall the decrease in nutrient concentrations was more pronounced, and not only NOx--N but also SRP and NH4+ concentrations decreased to up to 51 % and 83 %, respectively. My results suggest that rainfall enhances nutrient removal by coastal wetlands in the region. Geomorphological setting also affected nutrient removal. Riverine mangroves received stronger nutrient pulses, which resulted in strongest rates of nutrient removal during tidal inundation. Nutrient removal was closely related to the nutrient concentration of the floodwater: high nutrient removal occurred when floodwater was rich in nutrients. The C entering the wetland in the floodwater was mainly composed of DOC and its exchange did not vary among sites with differing geomorphological setting. However, DOC exchange was strongly affected by the water quality of floodwater inundating the coastal wetland. DOC concentrations were higher in the flood compared to the ebb tide in sites flooded by water high in C, NH4+ and SRP, suggesting DOC import. Contrary, DOC concentrations were lower in the flood compared to the ebb tide in sites flooded by water high in C, NH4+ and SRP, suggesting DOC export. The high intertidal cyanobacteria mat was important in regulating N fluxes in coastal wetlands. In the arid Exmouth Gulf, where cyanobacteria mats are abundant, nitrogen fixation rates were 4.9 ± 3.2 nmol cm-1 h-1. Cyanobacteria mats also removed N from the floodwater in the form of NOx--N (0.47 ± 0.45 g m-2 h-1) and NH4+ (0.31 ± 0.02 g m-2 h-1). N fixation and nutrient removal from the floodwater was highly variable spatially and temporally. N fixation rates were highest during the day in the mat situated at low tidal elevations. Overall, I found that the material exchange in coastal wetlands is variable within the coastal zone as a result of natural factors, such as geomorphology, vegetation composition and rainfall. But material exchange in wetlands is also affected by anthropogenic factors, particularly eutrophication. From all these factors, eutrophication of the floodwater appears to be the most critical, shifting the mangrove function from a DOC source to a nutrient and DOC sink. Approximate thresholds of nutrient and C concentrations in the floodwater that are likely to trigger shifts in ecosystem function in coastal wetlands in Southeast Queensland, and thus in the ecosystem services they provide, are 0.02 mg L-1 of SRP, 0.04 mg L-1 of NH4+ and 7.5 mg L-1 of DOC.

Coastal wetlands dominated by mangroves provide important ecological services to the coastal zone, many of which are associated with tidal inundation . In this study I investigated whether all coastal wetlands provide similar ecosystem services, or whether these varied depending on their geomorphological setting and the eutrophication level of the floodwater. Sampling was conducted over two years with significantly different levels of rainfall over six estuaries in Southeast Queensland, Australia. Sediment, nutrient and carbon exchange were investigated in tidal and riverine estuaries dominated by mangrove forests. The estuaries selected also comprised a gradient from low mesotrophic to low eutrophic. Spatial variation within the coastal wetlands was also investigated, comparing nutrient exchange in the low and high intertidal cyanobacteria mat . To assess sediment exchange, I measured retention of total suspended solids and sedimentation rates. Additionally, in order to assess the origin of sediment deposited in mangroves, glomalin, a novel terrestrial soil carbon (C) tracer, was used. Nutrient and C exchange were quantified by comparison of concentrations of soluble reactive phosphorus (SRP), nitrogen oxides (NOx--N), ammonium (NH4+) total organic carbon (TOC) and dissolved organic C (DOC) in water entering and leaving the mangroves during complete tidal cycles (3 tidal cycles in 6 estuaries for 2 years). Finally, the biogeochemical function of the cyanobacteria mat was measured through experiments investigating nitrogen fixation (N) and nutrient exchange in the extensive mats in the Exmouth Gulf, Western Australia. My results show that the seaward fringe mangrove retains the majority of sediment entering the wetland during a tidal cycle accounting for 52.5 ± 12.5 % of the total sedimentation (fringe mangrove + scrub mangrove + saltmarsh/ cyanobacteria mat). Geomorphological setting had a stronger influence on spatial patterns of deposition than on sedimentation rates. Riverine mangroves had more homogeneous distribution of sediments across the intertidal zone than tidal mangroves, where most sedimentation occurred in the seaward fringe mangrove zone. The presence of glomalin in sediments, and thus the relative importance of terrigenous sediment, was strongly influenced by geomorphological setting. Glomalin was primarily delivered to riverine mangroves and deposited within the scrub mangrove zone, while tidal mangroves received less glomalin during tidal inundation and most of it was deposited within the fringe mangrove zone. Overall, NOx--N concentrations decreased in the floodwater after flooding the coastal wetland, suggesting that these ecosystems act as sinks of dissolved NOx--N during tidal inundation. In average, NOx--N concentrations in the floodwater decreased 28 %. Additionally, during periods of high rainfall the decrease in nutrient concentrations was more pronounced, and not only NOx--N but also SRP and NH4+ concentrations decreased to up to 51 % and 83 %, respectively. My results suggest that rainfall enhances nutrient removal by coastal wetlands in the region. Geomorphological setting also affected nutrient removal. Riverine mangroves received stronger nutrient pulses, which resulted in strongest rates of nutrient removal during tidal inundation. Nutrient removal was closely related to the nutrient concentration of the floodwater: high nutrient removal occurred when floodwater was rich in nutrients. The C entering the wetland in the floodwater was mainly composed of DOC and its exchange did not vary among sites with differing geomorphological setting. However, DOC exchange was strongly affected by the water quality of floodwater inundating the coastal wetland. DOC concentrations were higher in the flood compared to the ebb tide in sites flooded by water high in C, NH4+ and SRP, suggesting DOC import. Contrary, DOC concentrations were lower in the flood compared to the ebb tide in sites flooded by water high in C, NH4+ and SRP, suggesting DOC export. The high intertidal cyanobacteria mat was important in regulating N fluxes in coastal wetlands. In the arid Exmouth Gulf, where cyanobacteria mats are abundant, nitrogen fixation rates were 4.9 ± 3.2 nmol cm-1 h-1. Cyanobacteria mats also removed N from the floodwater in the form of NOx--N (0.47 ± 0.45 g m-2 h-1) and NH4+ (0.31 ± 0.02 g m-2 h-1). N fixation and nutrient removal from the floodwater was highly variable spatially and temporally. N fixation rates were highest during the day in the mat situated at low tidal elevations. Overall, I found that the material exchange in coastal wetlands is variable within the coastal zone as a result of natural factors, such as geomorphology, vegetation composition and rainfall. But material exchange in wetlands is also affected by anthropogenic factors, particularly eutrophication. From all these factors, eutrophication of the floodwater appears to be the most critical, shifting the mangrove function from a DOC source to a nutrient and DOC sink. Approximate thresholds of nutrient and C concentrations in the floodwater that are likely to trigger shifts in ecosystem function in coastal wetlands in Southeast Queensland, and thus in the ecosystem services they provide, are 0.02 mg L-1 of SRP, 0.04 mg L-1 of NH4+ and 7.5 mg L-1 of DOC.