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 2014–15 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.