Biosphere: The interactions with the biosphere with other components of the biophysical environment in intertidal wetlands include, but are not limited to, the atmosphere’s contribution to the climatic conditions required to support intertidal wetlands; the hydrosphere’s contribution to the slightly alkaline conditions necessary for same plants and animals; and the lithosphere’s water logged characteristics, which are necessary for the distinctive flora and fauna of the intertidal wetlands.
As well as the biophysical interactions, which affect intertidal wetlands, we need to take into account the dynamics of weather and climate; the geomorphic, hydrological and biogeographical processes relevant to the ecosystem; and the way the ecosystem adjust to natural stress.
Changes in geomorphological and hydrological processes can result in ecosystems being placed at risk. The intertidal wetland receives a large amount of sediment from the upper catchments everyday. The rate of deposition is increased to a harmful level if soils are left exposed, especially during periods of heavy rainfall. Increased levels of turbidity can lead to deterioration in the health of the wetlands. In the case of Bicentennial Park wetlands, the straightening of Powells Creek directed a large proportion of the runoff away from the mangrove forest. On one hand, this reduced the impact of elevated turbidity levels of the wetland. On the other hand, it significantly reduced the natural deposition of soil on the floor of the mangrove forest. Overall, this “shielding effect” can have a detrimental impact on the mangroves as it interferes with the processes of the intertidal wetlands succession.
Human impacts on intertidal wetlands of Homebush Bay:
Atmosphere: A human modification of the atmosphere in the intertidal wetlands includes the changing of wind patterns caused by the inappropriate location and design of buildings to the wetlands and walkways within them. The implementation pf policies that regulate construction near a wetland are a positive step in the management of this problem. The high levels of humidity found within wetlands are an example of the interaction between the atmosphere and hydrosphere. Any alteration to water flows will affect humidity levels. The interaction between the atmosphere and the lithosphere includes the hydrogen sulfide produced by the water-logged soils of the mangrove ecosystem.
Hydrosphere: The straightened and mainly concrete-lined storm water channel of Powells Creek is an example of the way which the levels of dissolved oxygen can be altered by modifications to the hydrosphere. Water loses dissolved oxygen when it absorbs heat from the concrete walls and base of the channel. Urban and industrial land uses with in the Powells Creek catchments have contributed to increase levels of turbidity. Toxic chemicals and oil spills from vessels using Sydney Harbour are another constant threat.
Lithosphere: The construction of bund walls changed the hydrology of the site by modifying (reducing and redirecting) the flow of water. The reduction in flow has affected soil moisture in the mangroves. This has the potential to elevate levels of acid sulphate, damaging the health of the mangroves and adversely affecting the decomposer organisms that recycle minerals essential to the functioning of the ecosystem.
Biosphere: As already noted, the atmosphere gases necessary for plant and animal growth maybe be altered by pollution. The wide spread death of marine organisms with in these wetlands has been associated with the dumping of toxic chemicals in the catchments waterways.
The use of intertidal wetlands ecosystems by humans can be described by degrees of modification to natural vegetation.
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Removal: Areas of intertidal wetlands have been cleared to accommodate residential and industrial land use, transport facilities and waste-disposal sites.
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Replacement: Areas of intertidal vegetation have been replaced with a managed system of pasture. Homebush Bay was the site of the state Abattoir for most of the twentieth century.
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Utilisation: Salt marshes were modified and exploited as salt pans in the early eighteen hundreds, and for recreation in contemporary times.
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Conservation: The remnant natural vegetation of the intertidal wetlands ecosystem has been preserved for conservation and scientific purposes. The deliberate modification of natural process has bee minimised, but there may be indirect impacts from the land use activities on adjacent or nearby sites.
Throughout the world there is growing recognition that people must accept responsibility for protecting and managing ecosystem, especially those considered to be at risk. Increasingly, the environmental impact on human activity is being judged in terms of its ecological sustainability.
Four broad approaches to the management to ecosystems can be identified:
Preservation: Refers to the protection of the habitat (or of a species) in its existing form. It often involves the prevention of all human activities in the area being protected.
Conservation: Involves the plans used of natural resources in an effort to minimise waste of environmental damage.
Exploitation: Occurs when an ecosystem’s resources are used irrespective of the ecological consequences. Ecosystems are often destroyed, or reduced in extent, as a result of this exploitation.
Utilisation: Involves the replacement of an ecosystem with a human-made environment that is capable of providing a sustainable yield. Sustainably managed commercial agriculture is and example of Utilisation.
The reasons for managing and protecting ecosystems include:
- The maintenance of genetic diversity- Genetic diversity of intertidal wetlands should be valued and protected. Each of the organisms plays an important role in nutrient recycling.
- Utility value (both and current and potential)- The wetlands have been used in Australia’s past, (and are still being used in many developing countries) for the production of wood for construction and heating purposes and the harvesting of marine life. Once these resources have been used, the land is often reclaimed for agricultural, industrial and residential purposes.
- Intrinsic value- the intrinsic value of wetlands has often been ignored in the human orientated exploitation of these ecosystems for economic returns. Today Homebush Bay is being protected for its intrinsic value and uses are limited to those that do not exploit disrupt the components of the ecosystem.
- Heritage value- Natural areas, including wetlands are an important part of our natural heritage and can provide and insight into ways people lived in the past- especially the historical or cultural significance to past communities.
- The need to allow natural change to proceed- the area protected must be large enough to allow the evolutionary process to operate as they would in nature. Although Bicentennial Park Preserved the larger standing mangrove stands on the Parramatta River, it is still to be seen whether its size and linkages, modified prior to management, will be large enough to support natural change. The existence of buffers of park land on the southern and western sides, the relatively good resources and management available to it and co-ordination to decision makers in the wider catchments may be of assistance in providing a context in which natural change is able to proceed.
In conclusion, the biophysical interaction contributes to the unique characteristics of intertidal wetlands. The impact of humans on the intertidal wetlands has had both a positive but mainly negative affect.
