Coastal land

2016

Terrestrial pollution

Terrestrial pollution occurs when solid or liquid waste is deposited on land or underground, and has the potential to contaminate soil and groundwater. It directly affects terrestrial habitats, but can also have flow-on effects on coastal waterways and marine habitats when contaminants are transferred from land to aquatic environments (Allinson et al. 2014). Because of the concentration of human activities near the coast, a disproportionate amount of coastal land is polluted compared with the rest of Australia. Two major types of terrestrial pollution on Australian coasts are landfill and chemical pollutants.

Australia generates a large volume of domestic waste, and much of this ends up as landfill. In 2013, Australians generated 647 kilograms of municipal waste per person, of which 58 per cent ended up in landfill (OECD 2015). This amount of waste per person is a reduction from previous years. Information on landfill is collected by local governments, but there is no national dataset that consolidates the volume of landfill or the area affected. Microplastics are an increasing source of contamination in soils to which ground solid waste is added, sometimes with the intention of improving nutrient content and reducing water loss (Browne et al. 2011).

Chemical pollutants can be divided into historical and contemporary sources. Most contaminated sites are the result of historical sources, particularly areas that have been used for heavy industry or chemically intensive agriculture. State government databases hold information of known contaminated sites (e.g. Western Australian Contaminated Sites Database), but many contaminated sites are undocumented until developers are required to investigate levels of soil contamination. Contaminants can break down over time into substances called residues, which can infiltrate ecosystems and, in some cases, affect human health. Methods of remediating contaminated sites are being researched, including use of new materials such as biochar (Zhang et al. 2013).

Contemporary sources of pollutants have been documented by the National Pollutant Inventory (NPI) since 1998, although data are contributed by companies producing the emissions, and some industries are excluded. Ammonia is the most abundant agricultural pollutant recorded by the NPI; and the total amount of ammonia reported entering land in 201415 was 73 million tonnes, which is less than in previous years.

Nutrients, herbicides and pesticides are particularly problematic for the Great Barrier Reef catchment because of intensive agriculture (King et al. 2013). These pollutants are released in large quantities from farming in the catchment, and are transported to the coast, where they create diffuse pollution on the Reef (see Nutrient pollution). Initiatives are now under way to reduce inputs of land-based pollutants to the Reef, although it will be many years before the effectiveness of management can be determined.

Invasive species (terrestrial)

A large number of non-native plants and animals have invaded coastal land since European colonisation. Many invaders were introduced intentionally for food, agriculture or aesthetics, before their populations expanded and became difficult or impossible to eradicate (see Box COA2). Invaders tend to benefit from disturbance and assisted dispersal (e.g. seed adherence to vehicles, species transport in ballast water), and such conditions are often created in urban and agricultural areas. Some native species can also expand in range and explode in population in response to a human activity.

Significant terrestrial animal invaders include cane toads (Rhinella marina), European red foxes (Vulpes vulpes), feral European rabbits (Oryctolagus cuniculus) and feral cats (Felis catus). Cane toads have mostly invaded the tropical north, but are now spreading from Queensland to the west and increasingly south. Cane toads are toxic to many native Australian predators and have severe impacts on coastal native fauna (Shine 2010). Black rats (Rattus rattus) are also a significant invader; however, see Box COA3 for an example of competitive interactions between invasive and native species of rat.

Invasive coastal weeds are a major concern in dune systems (see Beaches and sand dunes). They compete with native vegetation and affect coastal morphology by changing the stabilisation of sand and soil. The top 5 species being actively controlled by local governments are African boxthorn (Lycium ferocissimum), sea spurge (Euphorbia paralias), bitou bush/boneseed (Chrysanthemoides monilifera), Geraldton carnation weed (Euphorbia terracina) and bridal creeper (Asparagus asparagoides). A national threat abatement plan was released in 2012 to reduce the impacts of 5 listed grasses on northern Australian biota.

A recent review found that there is scant knowledge about the impacts of coastal weeds, because most studies focus on a small number of high-profile species or are not scientifically rigorous (Cousens et al. 2013). Most weeds invade native habitats easily, with minimal resistance besides removal by community action groups. The bulk of management and control is done by volunteers or community groups (e.g. Coastcare Victoria), but efforts are rarely coordinated regionally. There is little research about impacts on native species or postcontrol recovery, and weed control activities are usually only assessed for herbicide efficacy.

In Victoria, foredunes are now composed of a mixture of exotic and native species, with exotics replacing natives at most sites. The dominant invasive species are marram grass (Ammophila arenaria), sea spurge and sea wheatgrass (Thinopyrum junceiforme), and, as these invade, they change dune morphology. Marram grass tends to produce higher and narrower dunes, whereas sea wheatgrass lowers foredunes and moves them seawards. Marram grass also affects nesting habitat for beach-nesting birds, such as hooded plovers (see Shorebirds and Nursing, roosting and nesting).

Solutions to weeds in Australia require a long-term, integrated, multistakeholder and multidisciplinary approach. Where control is implemented, assessment of the impacts of management decisions would support more adaptive and effective management. Additionally, the response of dunes dominated by weeds to storm events needs to be quantified to enable managers to respond appropriately to potentially increasing rates of coastal erosion.

Box COA2 Macquarie Island: a history of invasion and recent eradication

Invasive species cause havoc when they encounter a productive environment with few or no predators. Such has been the case at Macquarie Island, an Australian subantarctic island that teems with marine mammal and bird life. Macquarie Island is a biological oasis in the Southern Ocean, with beaches often covered by pupping seals and densely packed penguin breeding colonies (DoE 2014). The extraordinary natural values of Macquarie Island have been recognised, with World Heritage listing since 1997.

Timeline

1810—Rats and mice were accidentally introduced by early fur sealers. Cats were introduced to control the rodents, but these had devastating effects on seabirds (DoE 2014)

1870—Rabbits were left on the island by sealers to breed for food

1970—Rabbit numbers had grown (to around 130,000) and caused tremendous damage to vegetation

1983—Myxomatosis was introduced, and rabbit numbers declined to around 10,000

1985—Efforts began to remove cats, which were causing an estimated 60,000 seabird deaths per year

2000—The last of the nearly 2500 cats were culled to save the seabirds (Robinson & Copson 2014). Seabird populations responded rapidly, but rats and rabbits continued to cause widespread environmental damage

2006—Rabbit numbers had grown to more than 100,000, likely in response to the eradication of cats and reduction in the use of myxoma virus. Rabbits removed grass and led to soil erosion and cliff collapses; large portions of the Macquarie Island bluffs are eroding as a result. Erosion and cliff collapses destroyed seabird nests, and rats fed on young chicks. In September 2006, a large landslip at Lusitania Bay was attributed to heavy spring rains and severe erosion caused by rabbits, and partially destroyed an important penguin breeding colony

2011—A mass baiting program began to eradicate rabbits, rats and mice. Species unintentionally affected by baiting included kelp gulls, giant petrels, black ducks and skuas

2012—Hunting teams culled the last remaining rabbits

2014—Macquarie Island was officially declared vertebrate pest–free after 7 years of eradication efforts. This is hailed as the largest successful island pest-eradication program ever attempted

Box COA3 Native water rats keep invasive black rats at bay

Black rats (Rattus rattus) have invaded bushland areas around most of Australia’s major coastal cities, often replacing native mammals which have become locally extinct. Their numbers are kept high by the food and habitat resources that are available in urban areas (Banks & Smith 2015). Black rats are a problem in these systems because, unlike many native rodents, they climb trees to prey on eggs and chicks in bird nests. They also carry novel pathogens such as rat lungworm which can be lethal to humans and wildlife (Banks & Hughes 2012).

It is possible that some of the remaining native species play a role in keeping black rat numbers down. Research into the nature of competitive interactions between Australia’s largest rodent—the native water rat (Hydromys chrysogaster)—and the black rat has shown that water rats can potentially exclude black rats from a preferred habitat through aggressive interactions.

Analysis of spatial patterns of abundance and distribution of black rats and water rats in bushland around Sydney has found that both species prefer similar environments (areas of dense vegetation and fresh water), which indicates the potential for interspecies competition for space. Wildlife cameras also showed that, where there were high levels of water rat activity, there was very little black rat activity.

A behavioural study examining the responses of black rats and water rats to each other’s odours showed that black rats did not avoid the odour of water rats, nor did they display any recognition or anxiety and vigilance behaviour when in the presence of water rat odour. However, camera footage showed evidence of direct aggressive attacks on black rats by water rats, which suggests that water rats might defend resources or areas from the invasion of black rats. Among animals that differ in size, the larger species is usually competitively dominant.

The findings suggest that there is the potential for the water rat to play a positive role in biotic resistance against the spread of invasive black rats, and a greater understanding of these complex competitive interactions may be able to inform the management of invaded mammal communities in Australia.

Source: Peter Banks and Margarita Goumas, University of Sydney

Clark GF, Johnston EL (2016). Coasts: Coastal land. In: Australia state of the environment 2016, Australian Government Department of the Environment and Energy, Canberra, https://soe.environment.gov.au/theme/coasts/topic/2016/coastal-land, DOI 10.4226/94/58b659bdc758b