Coastal land

2011

 

For further information, see Chapter 5: Land.

Urban settlements and our population are concentrated along the eastern, south-eastern and south-western coastal fringes of Australia. This area overlaps, and sometimes conflicts, with the areas most suitable for intensive agriculture (i.e. higher rainfall zones within 200 kilometres of the coast and where the floodplains of major rivers provide the most fertile soil). Land managed for nature conservation is located primarily in central and northern Australia, and in the forested ranges of the east and south-west of both mainland Australia and Tasmania.

2.3.1 Major trends

Some major trends in land use that are relevant to coastal Australia include:

  • continuing urban expansion in both capital cities and major regional coastal cities (see also Chapter 10: Built environment)
  • continuing expansion of the conservation and Indigenous estates (see also Chapter 6: Marine environment, and Chapter 8: Biodiversity)
  • continuing decline in the area of native forest managed for wood production and a corresponding increase in the extent of native forest managed for conservation, much of which is found in coastal ranges (see Chapter 5: Land)
  • changes in flows from rivers into estuaries and coastal environments, due to increased extraction of water for agricultural and urban use, and to drought over the past decade in many areas (see Chapter 4: Inland water)
  • growth of mining developments in the north-west of Australia (see Chapter 6: Marine environment), which is increasing the number of people accessing coastal environments for recreation, warranting monitoring of its impacts
  • improvements in land management practices in many (but not all) areas, which have reduced the flows of sediments and chemicals to the coast that were characteristic of major rainfall events in the past (see Chapter 4: Inland water).

2.3.2 Factors affecting coastal land-use change

Growing Australian and global populations will demand more food and fibre, and expanding settlements and infrastructure will continue to impact on the environment. Economic growth places more demands on natural resources, as well as generating financial resources and new technologies for environmental management. The changed climate regimes and sea level rise associated with global warming are expected to place new pressures on both the natural environment and primary production systems. All of these factors will affect coastal ecosystems, but particular pressure will come from the interaction between sea level rise and human settlements.

2.3.3 Acid sulfate soils

Acid sulfate soils occur naturally in both coastal (tidal) and inland or upland (freshwater) settings. When disturbed, sulfides within the soil react with oxygen in the air, forming sulfuric acid.2 Coastal development for tourism, towns and agriculture has disturbed large areas of acid sulfate soils, with significant environmental, economic and social costs to coastal communities. Adverse impacts of acid sulfate soils in coastal lowlands include:

  • poor water quality (e.g. dissolved metal contaminants, low pH, reduced oxygen levels)
  • direct killing of fish, or fish becoming more vulnerable to pathogens
  • loss of critical habitat areas, aquaculture production, fish stocks, wetland biodiversity and amenity
  • acid erosion of infrastructure
  • the need for rehabilitation of disturbed areas.3

The public health implications of disturbing acid sulfate soils are not well understood. However, acidified coastal wetlands may provide predator-free habitat for species of mosquito that transmit arboviruses (e.g. Ross River virus). Acid dust mobilised during ploughing and construction activities may cause dermatitis and eye irritation.3

Risk mapping in various locations around Australia has lacked consistency and contained many large gaps. In collaboration with the National Committee for Acid Sulfate Soils, the Commonwealth Scientific and Industrial Research Organisation (CSIRO) developed the Atlas of Australian Acid Sulfate Soils, which has now been incorporated into the Australian Soil Resource Information System.a

Local and state governments around Australia have produced policies, plans and guidelines for managing the risks of acid sulfate soils. At a national scale, the National Water Quality Management Strategy4 provides guidelines on water management, including management of acid sulfate soils; the National Strategy for the Management of Coastal Acid Sulfate Soils5 assists in coordinated management; and the handbook Managing acid and metalliferous drainage6 provides guidance on best-practice management for an Australian context.

2.3.4 Changes in native vegetation and habitat

Chapter 5: Land, and Chapter 8: Biodiversity discuss data on declines in native vegetation around Australia and its significance for biodiversity conservation. The greatest reductions in native vegetation extent have been in eastern, south-eastern and south-western Australia (Figure 11.2). Impacts on the coastal strip are highly variable around Australia’s coastline, ranging from very heavily cleared, with less than 10% remaining, in parts of Victoria and South Australia, through 31–50% remaining in large parts of the south-western and north-eastern coastal areas, to 71–100% remaining for most of northern Australia.

Natural coastal habitat systems, including the coastal swamp systems (such as those dominated by Melaleuca, Casuarina, saltmarsh and mangrove species) and the submerged wetlands (such as mudflats, seagrasses and algal beds), play a major ecological role in the lives of marine fish and invertebrates. These habitat systems provide breeding, feeding and nursery grounds for many species of fish and invertebrates, as well as rich feeding grounds for migratory waders and other shorebirds.7

Coastal urban development (especially canals), catchment development, marinas, breakwaters, island reclamation projects, coastal and nearshore mining and dredging, harbours and shipping channels all have impacts on the ecology of coastal habitats. For example, coastal dune vegetation and natural beaches may be replaced by housing, hard surfaces and beach groynes. In places, entirely new forms of habitat may be created, such as low-energy harbours with surrounding rock walls, which attract a different suite of marine species.

Coastal development happens in an incremental way, making it difficult for local or state planning authorities to assess the cumulative impact of specific development proposals. One consequence of coastal development is a reduction in the abundance of native vegetation and the breakdown of connectivity among remnant habitat patches.

To obtain a coarse assessment of changes in vegetation, the Environmental Resources Information Network unit in the Australian Government Department of Sustainability, Environment, Water, Population and Communities compared the current mapped extent of major (native) vegetation groups (MVGs) around Australia’s mainland coast with their modelled extent before European settlement (i.e. pre-1750) (Figure 11.3). In this analysis, the ‘coastal strip’ was defined in three different ways: 10 kilometres, 50 kilometres or 100 kilometres inland from the high water line. To examine impacts on lowland vegetation separately from impacts on mountains, separate analyses were run for map components lying below 20 metres above sea level, components below 50 metres above sea level and components regardless of elevation. Figure 11.3 shows the data for vegetation below 50 metres elevation and for two widths of coastal strip. The broad conclusions hold for the other combinations, which are available on the State of the Environment website.b

In the 10-kilometre coastal strip (where most coastal settlements fall), most MVGs, apart from Acacia shrublands and Callitrus open woodlands, occur at more than 50% of their pre-1750 extent; several are above 80% (Figure 11.3). This conclusion should be regarded with caution as MVGs are very broad groupings and may include ecosystems that are far more reduced than the average for the MVG. Furthermore, these figures are for the nation’s coastline overall, much of which (especially in northern Australia) has not been affected by urban development. Therefore, the decline of two MVGs to less than 50% of their pre-1750 level and of five MVGs to below 60% suggests that major clearing has occurred around coastal settlements. This is supported by the state of the environment reports by the states and territories.

The extents of reservation for 9 of the 23 MVGs are below 10% of pre-1750 extent, and a further 4 are at or below 15% (see Chapter 8: Biodiversity for a discussion of targets for the National Reserve System). This represents a large risk to the ecosystems within these MVGs, given the pressure on Australia’s coasts.

For several MVGs, a greater proportion of pre-1750 extent remains in the 100-kilometre coastal strip than in the 10-kilometre strip (Figure 11.3). This indicates that clearing of these MVGs (e.g. Acacia open woodlands) has been more intense near the coast than further inland. For most other MVGs, the differences are small; for three, there is 5–10% less remaining in the 100-kilometre strip, suggesting that a little more clearing has occurred inland.

Although many mangrove swamps have been lost to coastal development, particularly as a result of land reclamation near urban areas and estuarine flood mitigation programs, at the national level we still retain around 96% of mangrove area. Most of this is in pristine areas of the Northern Territory, Cape York and the Kimberley. However, even though large coherent areas of such ecosystems remain and are highly valued, many small areas of fringing mangroves have been lost from estuaries (particularly on the east coast). This will have significant ecological impacts on locally dependent species and ecological functions, such as connectivity, that contribute strongly to the resilience of coastal ecosystems. Some loss of fringing mangroves occurs across all regions. For example, substantial areas of mangroves fringing the water’s edge have declined along the Pilbara coast of Western Australia, probably as a result of local developments, changes in hydrodynamics and climate change impacts. These losses are hard to detect—trends in area coverage shown in the coarse-scale national statistics may significantly underestimate the extent of the ecological impact from the loss of fringing mangroves.

Change in area of vegetation is only one type of measure; more information is needed on how ecological processes have changed and little such information is currently available.

2.3.5 Invasive species

We deal with invasive species only briefly here, as most of the invasive species associated with coasts have invaded marine environments and are discussed in detail in Chapter 6: Marine environment (see also Section 2.4.3).

Introduced weeds and pest species have contributed to national reductions in biodiversity and marine, estuarine and coastal productivity. Many of the weeds that threaten native species and ecosystems across Australia have impacts on coastal areas. Two weeds that have particular impacts on coastal dune systems are bitou bush (Chrysanthemoides monilifera ssp. rotundata) and boneseed (C. monilifera ssp. monilifera). These species displace native vegetation, are highly invasive and have potentially high economic and environmental impacts.8-9 Weeds are a particular problem in peri-urban areas (between the outer fringes of urban centres and rural areas) as they are easily transported by high rates of traffic and people who are unaware of necessary precautions; as well, some inexperienced or temporary residents in coastal areas may practise poor weed control (see Section 2.7.3).10

Feral animals like foxes and cats are particularly active around human settlements because of the ready abundance of food.

Native species can have similar effects to invasive species when they move rapidly outside their usual range, threatening species that normally live in a particular environment. Such movements occur when native species are spread by birds, other animals or people, all of which are very active along Australia’s coastal strip, both on the land and in the water. Unusual movements of native species also occur as habitat changes (e.g. with increasing sea temperature). An example in south-east Australia is the expansion of the range of the sea urchin Centrostephanus, which is denuding coastal reefs in Victoria and Tasmania with subsequent impacts on biodiversity and recreational and commercial fishing.11

Cork S (2011). Coasts: Coastal land. In: Australia state of the environment 2011, Australian Government Department of the Environment and Energy, Canberra, https://soe.environment.gov.au/science/soe/2011-report/11-coasts/2-major-issues/2-3-coastal-land, DOI 10.4226/94/58b659bdc758b