Case study: Intertidal Wetlands
Intertidal wetlands:
- develop in coastal areas subject to periodic inundation by salty water
- mangrove wetlands occur in intertidal zones along tropical and subtropical coastlines, usually between 25oN and 25oS latitude.
- contain plants adapted to life in saline conditions for example, mangroves, seagrass.
- usually have large quantities of zooplankton and are thus safe areas for the smaller members of species
- are important for fishing industries (utility value), but also for biodiversity and intrinsic values.
- Coastal wetlands – in temperate areas (25 degrees N- 60 degrees N and 25 degrees S- 60 degrees S)
- Intertidal wetlands – in coastal areas of tropical regions, (specifically between 32oN-38oN)
- develop in coastal areas subject to periodic inundation by salty water
- mangrove wetlands occur in intertidal zones along tropical and subtropical coastlines, usually between 25oN and 25oS latitude.
- contain plants adapted to life in saline conditions for example, mangroves, seagrass.
- usually have large quantities of zooplankton and are thus safe areas for the smaller members of species
- are important for fishing industries (utility value), but also for biodiversity and intrinsic values.
- Coastal wetlands – in temperate areas (25 degrees N- 60 degrees N and 25 degrees S- 60 degrees S)
- Intertidal wetlands – in coastal areas of tropical regions, (specifically between 32oN-38oN)
Wetlands are areas where water is the primary factor controlling the environment and the associated plant and animal life. They occur where the water table is at or near the surface of the land, or where the land is covered by shallow water. Wetlands are defined as:
"areas of marsh, fen, peatland or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or salt, including areas of marine water the depth of which at low tide does not exceed six metres".
As such the term “wetlands” extends to a wide variety of habitat types, including rivers and lakes, coastal lagoons, mangroves, peatlands, and even coral reefs.
Why conserve wetlands?
Wetlands are among the world’s most productive environments. They are cradles of biological diversity, providing the water and primary productivity upon which countless species of plants and animals depend for survival. They support high concentrations of birds, mammals, reptiles, amphibians, fish and invertebrate species. Of the 20,000 species of fish in the world, more than 40% live in fresh water. Wetlands are also important storehouses of plant genetic material. Rice, for example, which is a common wetland plant, is the staple diet of more than half of humanity.
More and more economists and other scientists are working in the field of the valuation of ecosystem services. This is a difficult task, still full of uncertainties, but there is no other choice than to progress in this direction. Some recent studies have indicated that ecosystems provide at least US$ 33 trillion worth of services annually, of which US$ 4.9 trillion are attributed to wetlands.
The interactions of physical, biological and chemical components of a wetland, such as soils, water, plants and animals, enable the wetland to perform many vital functions, for example: water storage; storm protection and flood mitigation; shoreline stabilization and erosion control; groundwater recharge (the movement of water from the wetland down into the underground aquifer); groundwater discharge (the movement of water upward to become surface water in a wetland); water purification through retention of nutrients, sediments, and pollutants; and stabilization of local climate conditions, particularly rainfall and temperature.
Wetland values
Wetlands provide tremendous economic benefits, for example: water supply (quantity and quality); fisheries (over two thirds of the world’s fish harvest is linked to the health of coastal and inland wetland areas); agriculture, through the maintenance of water tables and nutrient retention in floodplains; timber production; energy resources, such as peat and plant matter; wildlife resources; transport; and recreation and tourism opportunities.
In addition, wetlands have special attributes as part of the cultural heritage of humanity: they are related to religious and cosmological beliefs, constitute a source of aesthetic inspiration, provide wildlife sanctuaries, and form the basis of important local traditions.
These functions, values and attributes can only be maintained if the ecological processes of wetlands are allowed to continue functioning. Unfortunately, and in spite of important progress made in recent decades, wetlands continue to be among the world’s most threatened ecosystems, owing mainly to ongoing drainage, conversion, pollution, and over-exploitation of their resources.
"areas of marsh, fen, peatland or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or salt, including areas of marine water the depth of which at low tide does not exceed six metres".
As such the term “wetlands” extends to a wide variety of habitat types, including rivers and lakes, coastal lagoons, mangroves, peatlands, and even coral reefs.
Why conserve wetlands?
Wetlands are among the world’s most productive environments. They are cradles of biological diversity, providing the water and primary productivity upon which countless species of plants and animals depend for survival. They support high concentrations of birds, mammals, reptiles, amphibians, fish and invertebrate species. Of the 20,000 species of fish in the world, more than 40% live in fresh water. Wetlands are also important storehouses of plant genetic material. Rice, for example, which is a common wetland plant, is the staple diet of more than half of humanity.
More and more economists and other scientists are working in the field of the valuation of ecosystem services. This is a difficult task, still full of uncertainties, but there is no other choice than to progress in this direction. Some recent studies have indicated that ecosystems provide at least US$ 33 trillion worth of services annually, of which US$ 4.9 trillion are attributed to wetlands.
The interactions of physical, biological and chemical components of a wetland, such as soils, water, plants and animals, enable the wetland to perform many vital functions, for example: water storage; storm protection and flood mitigation; shoreline stabilization and erosion control; groundwater recharge (the movement of water from the wetland down into the underground aquifer); groundwater discharge (the movement of water upward to become surface water in a wetland); water purification through retention of nutrients, sediments, and pollutants; and stabilization of local climate conditions, particularly rainfall and temperature.
Wetland values
Wetlands provide tremendous economic benefits, for example: water supply (quantity and quality); fisheries (over two thirds of the world’s fish harvest is linked to the health of coastal and inland wetland areas); agriculture, through the maintenance of water tables and nutrient retention in floodplains; timber production; energy resources, such as peat and plant matter; wildlife resources; transport; and recreation and tourism opportunities.
In addition, wetlands have special attributes as part of the cultural heritage of humanity: they are related to religious and cosmological beliefs, constitute a source of aesthetic inspiration, provide wildlife sanctuaries, and form the basis of important local traditions.
These functions, values and attributes can only be maintained if the ecological processes of wetlands are allowed to continue functioning. Unfortunately, and in spite of important progress made in recent decades, wetlands continue to be among the world’s most threatened ecosystems, owing mainly to ongoing drainage, conversion, pollution, and over-exploitation of their resources.
Intertidal Wetlands - Nature and rate of change
The nature of change impacting on Intertidal Wetlands refers to the types of change.
The rate of change impacting on Intertidal Wetlands refers to the speed of the change and its impacts.
Overview:
Natural changes such as salinity, tides, deposition, etc. These are gradual changes and happen over a long period of time. The ecosystem still functions more or less the same way.
Human-induced changes such as development, clearing, etc. These usually occur over a short period of time. These may completely alter the way the ecosystem functions.
The most significant change that is and will impact on Intertidal Wetlands is climate change and the associated sea level rise. It is anticipated that this will dramatically impact on the location, size and functioning of ecosystems.
Nature of change
We have discussed previously that the ecosystem is in a constant state of flux (it is always changing) as a result of weather, tides, sediment flow, etc. An example of a natural change is that changes in humidity levels in the atmosphere can cause stress in plants impacting on animals. Change under these conditions will be slow. However the most significant changes impacting on Intertidal Wetlands are human-induced changes. The following syllabus dot point will enable us to explore all the human impacts in detail. An example of a human impact is that increased nutrients from run-off and sewage can cause algal blooms affecting ecosystems severely. The most significant issue affecting Intertidal Wetlands at present and into the future is climate change and the associated sea level rise.
Impact of climate change on Intertidal Wetlands
Intertidal wetlands are under pressure from rising sea levels associated with climate change.
Previously intertidal wetlands were able to adapt to changes in sea levels by moving further inland.
The biggest hurdle to wetlands being able to adapt to change in sea level rise and move inland is the location of human development. This will be a problem particularly along the east coast of Australia.
The change in climate will also result in changed patterns to erosion, sediment deposition and salinity levels.
The distribution and abundance of mangroves and saltmarshes will change depending on the rate of sea level rise. It is thought that mangroves may initially benefit from sea level rise. In the past, mangroves have been able to deal with sea level rises by increasing elevation (moving further inland and upslope). The mangroves will invade the salt marsh areas in a struggle to find new places to survive. This will result in a decline in the size of salt marsh areas. If sea level continues to rise or accelerates, even mangroves will have difficulty
surviving.
There is a risk that Intertidal Wetlands will go locally extinct in certain area, along with the birds, fish and other wildlife reliant on the ecosystem.
Intertidal wetlands are used for a variety of human uses and have undergone dramatic changes in most areas - farmed, reclaimed, used for industry, transport and recreation, e.g. Sydney Grey Mangrove has been extensively cleared. 90% of all the grey mangrove left in Sydney is found at Towra Point.
The rate of change impacting on Intertidal Wetlands refers to the speed of the change and its impacts.
Overview:
Natural changes such as salinity, tides, deposition, etc. These are gradual changes and happen over a long period of time. The ecosystem still functions more or less the same way.
Human-induced changes such as development, clearing, etc. These usually occur over a short period of time. These may completely alter the way the ecosystem functions.
The most significant change that is and will impact on Intertidal Wetlands is climate change and the associated sea level rise. It is anticipated that this will dramatically impact on the location, size and functioning of ecosystems.
Nature of change
We have discussed previously that the ecosystem is in a constant state of flux (it is always changing) as a result of weather, tides, sediment flow, etc. An example of a natural change is that changes in humidity levels in the atmosphere can cause stress in plants impacting on animals. Change under these conditions will be slow. However the most significant changes impacting on Intertidal Wetlands are human-induced changes. The following syllabus dot point will enable us to explore all the human impacts in detail. An example of a human impact is that increased nutrients from run-off and sewage can cause algal blooms affecting ecosystems severely. The most significant issue affecting Intertidal Wetlands at present and into the future is climate change and the associated sea level rise.
Impact of climate change on Intertidal Wetlands
Intertidal wetlands are under pressure from rising sea levels associated with climate change.
Previously intertidal wetlands were able to adapt to changes in sea levels by moving further inland.
The biggest hurdle to wetlands being able to adapt to change in sea level rise and move inland is the location of human development. This will be a problem particularly along the east coast of Australia.
The change in climate will also result in changed patterns to erosion, sediment deposition and salinity levels.
The distribution and abundance of mangroves and saltmarshes will change depending on the rate of sea level rise. It is thought that mangroves may initially benefit from sea level rise. In the past, mangroves have been able to deal with sea level rises by increasing elevation (moving further inland and upslope). The mangroves will invade the salt marsh areas in a struggle to find new places to survive. This will result in a decline in the size of salt marsh areas. If sea level continues to rise or accelerates, even mangroves will have difficulty
surviving.
There is a risk that Intertidal Wetlands will go locally extinct in certain area, along with the birds, fish and other wildlife reliant on the ecosystem.
Intertidal wetlands are used for a variety of human uses and have undergone dramatic changes in most areas - farmed, reclaimed, used for industry, transport and recreation, e.g. Sydney Grey Mangrove has been extensively cleared. 90% of all the grey mangrove left in Sydney is found at Towra Point.
Intertidal Wetlands - Spatial patterns
– Coastal Wetlands: in temperate areas (25oN-60oN and 25oS-60oS)
– Intertidal wetlands: in coastal areas of tropical regions, specifically between 32oN-38oN
Consider: What are the reasons for the location of Intertidal Wetlands? (Why are they located where they are?)
- Location: Intertidal wetlands are found in coastal areas of tropical regions where air temperature, wave action, salinity levels, and sediment movements are moderated by the locational features of the estuarine environment. They exist in a band between 32°N and 38°S of the Equator.
– Coastal Wetlands: in temperate areas (25oN-60oN and 25oS-60oS)
– Intertidal wetlands: in coastal areas of tropical regions, specifically between 32oN-38oN
- Altitude: They exist within the limits of the coastal range.
- Size, shape and continuity: The area covered by intertidal wetlands is determined by the limits of the tidal range and, increasingly, by human obstructions and imposed land restrictions.
Consider: What are the reasons for the location of Intertidal Wetlands? (Why are they located where they are?)
Biophysical processes - Adaptations to natural stress
Natural stress in Intertidal Wetlands
In intertidal wetlands the majority of natural stress comes from salinity and tidal movements. The intertidal wetlands must be able to survive extreme conditions of mainly salt water at high tide, fresh water at low tide and times of flood and brackish water at other times. The saline water is a very difficult condition for plants to survive in. The grey mangrove can survive by excluding salt in the root system, salt excretion glands in the leaf, and waxy leaves to minimise water loss. However it is still vulnerable to changes in salinity levels.
Changes to tidal movements through increased run-off or altered drainage can cause the roots of mangroves to be inundated for longer than normal periods affecting their pneumatophones. It can also be pushed past its threshold level if water quality is changed. Thus even healthy ecosystems are vulnerable to change. Some species such as oysters + molluscs have been used as indicator
species, with any decline in their numbers indicating the ecosystem is under stress. A decline in nutrient levels will also affect primary productivity and thus bring about change. More e.g.s. of natural stress are: storms; global warming, increase in sea levels.
The length and intensity of the stress is important. Species such as oysters and molluscs are indicator species. This means that they can be measured and used to determine the health of the ecosystem. Ecosystem stress will be shown by a decline in the number of indicator species. Another indicator of stress is decline in primary productivity.
In intertidal wetlands the majority of natural stress comes from salinity and tidal movements. The intertidal wetlands must be able to survive extreme conditions of mainly salt water at high tide, fresh water at low tide and times of flood and brackish water at other times. The saline water is a very difficult condition for plants to survive in. The grey mangrove can survive by excluding salt in the root system, salt excretion glands in the leaf, and waxy leaves to minimise water loss. However it is still vulnerable to changes in salinity levels.
Changes to tidal movements through increased run-off or altered drainage can cause the roots of mangroves to be inundated for longer than normal periods affecting their pneumatophones. It can also be pushed past its threshold level if water quality is changed. Thus even healthy ecosystems are vulnerable to change. Some species such as oysters + molluscs have been used as indicator
species, with any decline in their numbers indicating the ecosystem is under stress. A decline in nutrient levels will also affect primary productivity and thus bring about change. More e.g.s. of natural stress are: storms; global warming, increase in sea levels.
The length and intensity of the stress is important. Species such as oysters and molluscs are indicator species. This means that they can be measured and used to determine the health of the ecosystem. Ecosystem stress will be shown by a decline in the number of indicator species. Another indicator of stress is decline in primary productivity.
Intertidal Wetlands - Human Impacts
Humans can impact on ecosystems both positively and negatively
Positive
Humans can maximise the area of healthy, functioning intertidal wetlands by minimising their impacts and by developing management strategies that protect, and where possible rehabilitate these ecosystems at risk. The following are positive ways of trying to protect or rehabilitate intertidal wetlands.
Exclusion – Those responsible for the management of wetland areas often facilitate public access to a small, designated area while restricting access to other areas. Provision of defined boardwalks and walkways is a management strategy used to restrict access to vulnerable areas, as is the issuing of permits whilst visiting Towra Point Nature Reserve.
Education – In the past, wetlands were regarded as waste-lands. Education campaigns have helped to change public perceptions and foster public support for the wetlands. Due to their location in the catchment area, education programs need to teach about total catchment management programs. Educational programs include guided tours for the general public, school visits, media liaison, information centres, conference presentations, interpretive signage, publications and facts sheets. Staff should also include education officers.
Action – too little is known about the intertidal wetland system to successfully reinstate all natural conditions. Management plans focus on the rehabilitation of the site and the removal of human-induced stresses. For example, fox and rabbit baiting, removal of weeds (at Weedy Pond).
Design – Design interventions have proved successful in minimising sources of natural stress. At Towra Point Beach, for example, there is a sandbag wall to help prevent salt water from leaking into the fresh-water Towra Lagoon.
Legislation – Legislation and regulations are used to protect Towra Point Wetlands. Conventions that Australia has signed in regard to Towra Point Wetlands are the Ramsar Convention, the Japan Australia Migratory Bird Agreement (JAMBA) and the China Australia Migratory Bird Agreement (CAMBA). Legislation that Australia and New South Wales has passed in regard to Towra Point Wetlands are the Wetlands Policy (federal govt.), the New South Wales Wetlands Management Policy (state govt. 1996) and the State and Environmental Planning Policy 14 on Coastal Wetlands.
Negative
Changed wind patterns due to high-rise near some wetland areas e.g. Bicentennial Park.
Alteration of water flows through construction of roads, dams and recla.
Removal of resources for urban and industrial land uses. These also increase turbidity and toxins in the water supplied to mangroves. (The removal can also result in changed energy flows and nutrient cycles, affecting food chains for both sedentary and migratory fauna).
Replacement of wetland areas for parks, playing fields or pasture.
Destruction of sea grasses in areas adjoining wetlands can affect energy flows and nutrient cycles as species levels will be affected.
Introduction of exotic species e.g. foxes, rabbits, sheep, cattle, pigs. – change energy flows and nutrient cycles. Birds are particularly affected, for example the Little Tern.
Indirect influences from adjacent sites e.g. weed infestation (lantana – Towra Point) – carried into the wetlands by horses from the nearby stables.
Trampling – from illegal access
Threat of oil spills - Kurnell refinery near Towra Point
Recreational horse-riding on the Reserve and unsupervised recreational use of the Reserve (eg. dog walking)
Boating - disturbs wildlife in the park, and creates pollution.
Fishing - kills fish, which affects the food chains operating within the Reserve.
Erosion of Towra Beach due to wave refraction from the Sydney Airport runway which causes the freshwater Towra Point Lagoon to become saline .
Fragmentation of the Reserve by private land ownership
Bay development in general, including the Sydney Airport runway and the oil refinery. There have also been concerns that the recently announced desalinisation plant will impact negatively on the Reserve.
Illegal rubbish dumping has occurred both in the Reserve and near the entrance. In late 2004, a large amount of dumped asbestos was discovered.
Positive
Humans can maximise the area of healthy, functioning intertidal wetlands by minimising their impacts and by developing management strategies that protect, and where possible rehabilitate these ecosystems at risk. The following are positive ways of trying to protect or rehabilitate intertidal wetlands.
Exclusion – Those responsible for the management of wetland areas often facilitate public access to a small, designated area while restricting access to other areas. Provision of defined boardwalks and walkways is a management strategy used to restrict access to vulnerable areas, as is the issuing of permits whilst visiting Towra Point Nature Reserve.
Education – In the past, wetlands were regarded as waste-lands. Education campaigns have helped to change public perceptions and foster public support for the wetlands. Due to their location in the catchment area, education programs need to teach about total catchment management programs. Educational programs include guided tours for the general public, school visits, media liaison, information centres, conference presentations, interpretive signage, publications and facts sheets. Staff should also include education officers.
Action – too little is known about the intertidal wetland system to successfully reinstate all natural conditions. Management plans focus on the rehabilitation of the site and the removal of human-induced stresses. For example, fox and rabbit baiting, removal of weeds (at Weedy Pond).
Design – Design interventions have proved successful in minimising sources of natural stress. At Towra Point Beach, for example, there is a sandbag wall to help prevent salt water from leaking into the fresh-water Towra Lagoon.
Legislation – Legislation and regulations are used to protect Towra Point Wetlands. Conventions that Australia has signed in regard to Towra Point Wetlands are the Ramsar Convention, the Japan Australia Migratory Bird Agreement (JAMBA) and the China Australia Migratory Bird Agreement (CAMBA). Legislation that Australia and New South Wales has passed in regard to Towra Point Wetlands are the Wetlands Policy (federal govt.), the New South Wales Wetlands Management Policy (state govt. 1996) and the State and Environmental Planning Policy 14 on Coastal Wetlands.
Negative
Changed wind patterns due to high-rise near some wetland areas e.g. Bicentennial Park.
Alteration of water flows through construction of roads, dams and recla.
Removal of resources for urban and industrial land uses. These also increase turbidity and toxins in the water supplied to mangroves. (The removal can also result in changed energy flows and nutrient cycles, affecting food chains for both sedentary and migratory fauna).
Replacement of wetland areas for parks, playing fields or pasture.
Destruction of sea grasses in areas adjoining wetlands can affect energy flows and nutrient cycles as species levels will be affected.
Introduction of exotic species e.g. foxes, rabbits, sheep, cattle, pigs. – change energy flows and nutrient cycles. Birds are particularly affected, for example the Little Tern.
Indirect influences from adjacent sites e.g. weed infestation (lantana – Towra Point) – carried into the wetlands by horses from the nearby stables.
Trampling – from illegal access
Threat of oil spills - Kurnell refinery near Towra Point
Recreational horse-riding on the Reserve and unsupervised recreational use of the Reserve (eg. dog walking)
Boating - disturbs wildlife in the park, and creates pollution.
Fishing - kills fish, which affects the food chains operating within the Reserve.
Erosion of Towra Beach due to wave refraction from the Sydney Airport runway which causes the freshwater Towra Point Lagoon to become saline .
Fragmentation of the Reserve by private land ownership
Bay development in general, including the Sydney Airport runway and the oil refinery. There have also been concerns that the recently announced desalinisation plant will impact negatively on the Reserve.
Illegal rubbish dumping has occurred both in the Reserve and near the entrance. In late 2004, a large amount of dumped asbestos was discovered.
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