Ecosystem Case Study: Towra Point Nature Reserve
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Towra Point Nature Reserve is a nature reserve of 3.86 km² located within the Sutherland Shire, NSW, Australia. It is a Ramsar site (or wetland of international importance), as it is an important breeding ground for many vulnerable, protected, or endangered species. There is also a Towra Point Aquatic Nature Reserve in the surrounding waterways.
Contents |
Spatial Patterns and Dimensions
- 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.
- Altitude: They exist within the limits of the coastal range.
- Size/shape 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.
Biophysical Interactions
The ways in which the four spheres interact is critical in determining the extent and nature of intertidal wetlands.
- Atmosphere: Microclimates are created e.g. air temperature higher in salt marshes than mangroves; minimal wind movement in mangroves; humidity is generally high; gases are created via the lithosphere e.g. sulfide and nitrogen.
- Hydrosphere: Salinity levels vary with tides and floods water movement is slowed by vegetation. Biosphere adds to store of nutrients in the water.
- Lithosphere: Small soil particle size; soil is often of a clay mix; vegetation adds to the organic nature of the soils; salinity level of the soil varies with rainfall.
- Biosphere: High faunal diversity – low flora diversity, but are highly adapted to the conditions presented by the other spheres.
The distribution and types of species are affected by all of the above.
Dynamics of Weather and Climate
The distribution of mangrove + salt marsh species is largely determined by temperature and rainfall. Precipitation affects the height of the water table, proximity of fresh water, photosynthesis, respiration etc. – processes essential to the functioning of the wetland community. The migratory and sedentary terrestrial fauna is affected by rainfall and the availability of fresh water.
Geomorphology and Hydrological Processes
The geomorphological and hydrological processes combine to create intertidal wetlands. The deposition of silt in the lower coastal regions is essential to the development of intertidal wetlands. Changes to these processes can result in ecosystems being placed at risk –
- Rising Sea Level – rises and falls in sea level will obviously affect the nature and location of wetlands. The rise in sea level from the last Ice Age has affected the nature, shape and position of coastlines.
- Weathering – The intertidal wetland is where large amounts of weathered material accumulate. This alluvial material, and the organic material from vegetation results in nutrient-rich soils. (the grey mangrove produces 600 tonnes of leaf material per 1 cm squared a year)
- Soil formation - The nature of the soil reflects the parent material, topography, climate, and vegetation of the area. They are usually grey in colour; poorly drained and rich in organic matter. The soil often smells strongly of sulfide compounds. Mangroves cope with the unstable nature of the soils by having shallow, widespread root systems.
Due to the lack of oxygen within the soil, mangroves have developed specialised structures to facilitate the absorption of oxygen into their root systems.
- Erosion – the position of wetlands in sheltered bays makes these areas of accumulation/deposition rather than erosion. The role of wetlands as flood mitigators means that they are able to absorb floodwaters and release them slowly to minimise erosion. However, some erosion will occur after storms and salt marshes may be ‘scarred’ as a result of trampling.
Biogeographical Processes
Intertidal wetlands provide an excellent example of invasion, modification and succession. The invasion and succession process is the establishment of seagrasses. These help stabilise sediment and increase sediment capture rates. The trapped sediment gradually develops into mud flats. Mud flat organisms (crustacea etc.) become established encouraging other life forms to live there - this will change the organic composition of the soils. The mangroves establish themselves in the shallower water upslope from the mudflats. Mangroves further stabilise sediment and over time increase the soil level. This results in less tidal movement and the development of salt marshes. (succession) The salty nature of the soil means it can only be tolerated by special types of grasses e.g. saltbush, rush and sedge. There is also changing species diversity in each succession. In the salt marshes there is greater species diversity, nutrient recycling, and niche specialisation making it one of the most productive ecosystems on Earth.
In Summary:
Open water + productive vegetation are breeding grounds for insects that attract birds + amphibians.
Wet mud + silt contain worms, crustaceans + molluscs.
Plants use solar energy in photosynthesis to fix carbons + accumulate energy. Nutrient cycles + food webs can be complex and intricate.
Dead tissue is broken down quickly + recycled.
Adjustments in Response to Natural Stress
In intertidal wetlands the majority of natural stress comes from salinity + 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, + 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 Nature and Rate of Change Which Affects Ecosystem Functioning
- Changes in humidity levels in the atmosphere can cause stress in plants impacting on animals. However change under these conditions will be slow.
- Increased nutrients from run-off and sewage can cause algal blooms affecting ecosystems severely.
- Intertidal wetlands are used for a variety of human uses + have undergone dramatic changes in most areas - farmed, reclaimed, used for industry, transport + recreation.
e.g. Sydney Grey Mangrove has been extensively cleared. 90% of all the grey mangrove left in Sydney is found at Towra Point.
Impacts due to Human Induced Modifications
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.
- 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.
Traditional and Contemporary Management Practices
Traditional Management Strategies
The traditional objectives for the management of wetland areas were built around the use of wetland resources for food, shelter and tools. Grey Mangrove wood, for example, was used to make shields, shells were made into fishing hooks; and marine animals were used for food.
Contemporary Management Strategies
- Identify management goals and objectives: Today management plans for wetlands focus on the preservation and sustainable use of sites for recreation, conservation and education purposes. This may involve some exclusion zones but many areas are open to recreational and educational activities.
- Define management unit and boundaries: The “management unit” for many intertidal wetlands is often difficult to define because of the large number of stakeholders. For example the Towra Point wetland has input from National Parks and Wildlife Services, NSW Fisheries, Sutherland Shire Council, Friends of Towra Point and recreational users.
- Develop and implement management plans: An intertidal wetland is a dynamic system. As our knowledge of ecosystems has increased community attitudes have changed. Communities are now demanding that these ecosystems are protected and effectively managed.
Care has been taken to develop management plans that are both realistic and flexible. They need to take into account scientific and technological advances, changing social and political attitudes and variations in the level of funding. Management plans also need to be consistent with Australia’s international obligations (most pertinently JAMBA, CAMBA and RAMSAR).
External links
- Sutherland Shire Environment Centre - Towra Point (the virtual tour is excellent)
- National Parks
- Wetlands Help Line - Towra Point
- Ramsar factsheet (PDF)
- Sydney University Excursion
- NSW Fisheries - Towra Point Aquatic Nature Reserve
- Towra Point at Wikipedia
- This page is a stub and is incomplete.
- Why not add to it? Don't be intimidated - we welcome all contributions!
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