Agricultural activities have changed much of the South Australian landscape. Previously rich and abundant native vegetation has been cleared to make way for crops and grazing land needed to produce food products and textiles. An unfortunate consequence of this agricultural development is that many of our river systems have become degraded.
What problems does agriculture create for our watercourses?
Agricultural activities have affected rivers and streams through various processes.
Clearing native vegetation has raised the water table in many parts of the state and consequently the soils and watercourses in many areas have become increasingly saline.
Reduced environmental flows
The use of water for irrigation has put pressure on rivers and streams because of reduced environmental flows. This has been particularly significant for the River Murray.
Increasing nutrients and turbidity
Many crops rely on the addition of fertilisers to promote rapid growth. Fertilisers usually contain readily soluble nitrogen and phosphorus compounds. The problem is that some of these fertilisers are washed off the land or through the soil to surface water bodies where they can create too much algal growth.
Livestock access to rivers and streams can also introduce nutrients as well as cause excessive bank erosion and increase the turbidity (ie cloudiness) of the water.
Pesticides used in agricultural regions can be washed into rivers and streams after rain. Some pesticides are persistent and can be detected in water long after use. In South Australia pesticides have been found in waterways and groundwater, and historical contamination of soil is common around cattle and sheep dip sites. Pesticides have caused fish and aquatic invertebrate kills in inland and estuarine waters. Bird deaths have been attributed to pesticides, and spraying to kill locusts has been shown to affect other organisms.
What is happening to reduce the impacts of agriculture on rivers and streams?
The State Natural Resource Management (NRM) Plan 2012-2017 is the main impetus for the improving the health of rivers and streams in South Australia while maintaining economic and social development. The State NRM Plan is being administered through the Regional NRM Boards. >> More
Catchment water management boards (CWMBs) have been officially replaced by NRM Boards, although several catchment management plans (produced by the CWMBs) are still current and these provide strategies for reducing the impacts of agricultural activities on rivers and streams.
WaterConnect can provide useful advice on environmentally responsible irrigation.
The EPA has released a series of guidelines to advise on responsible agricultural practices. These include:
- Guidelines for establishment and operation of cattle feedlots in South Australia (a joint publication with Primary Industries SA)
- Reclaimed water irrigation of pasture for grazing of cattle and pigs
- EPA Guidelines for the Lower Murray Reclaimed Irrigation Areas
- EPA Guidelines for responsible pesticide use
These bring together all the requirements that regulate the responsible use of pesticides. These requirements are contained in the several pieces of state and federal legislation. They include pesticide registration and labelling, licensing of pest controllers and commercial sprayers, dangerous substances administration and occupational health and safety requirements.
Two guidelines that address the practical issues of pesticide application have also been produced:
Water quality monitoring
The EPA ambient water quality monitoring program includes many rivers and streams in agricultural regions. We monitor the concentrations of nutrients in the water to determine how much is entering our rivers and streams. We also monitor the aquatic ecological health to determine if these nutrients are impacting on ecosystems. >> More
Effects of agricultural activities on groundwater
Groundwater provides much of the state's water for human use and is the source of some of the water in many of the state's creeks, rivers, wetlands and coastal waters.
Agricultural land use generates large nutrient loads through livestock waste, fertiliser application, and wastewater storage and reuse. Pesticide application is often part of agricultural land management practice. Increased natural recharge of groundwater has occurred because of land clearance and irrigation. This has the potential to increase the leaching of nutrients (particularly nitrogen) and pesticides into the aquifers.
Many of the state's aquifers are already stressed because of high rates of water extraction and increasing salinity. Water table aquifers are particularly susceptible to these pressures, although leaky wells are also a potentially significant pathway for pollution of deeper confined aquifers.
Elevated nitrogen (mainly in the form of nitrate) concentrations have been detected in all of the EPA groundwater monitoring programs across the state. Further work is required to determine whether this pollution is localised to a well or represents broader influences. Elevated nitrate in groundwater may restrict its use for drinking. This is because nitrate can be toxic at the concentrations detected in some wells. Nitrate may also adversely affect groundwater ecosystems or surface water ecosystems that are fed by groundwater.
Heavy metal concentrations above national guidelines for ecosystem protection have been found in several of the state's key aquifers. However, it is most probably that these metals are naturally occurring because of local geology and are therefore unlikely to be a threat to ecosystem health.
A review of EPA groundwater monitoring programs in the Willunga and Northern Adelaide Plains (NAP), Barossa Valley and Eyre Peninsula aquifers indicated that water quality in all aquifers has been influenced by nutrient pollution. As yet however, no trends have been identified.
The pollution of aquifers with very high ammonia, nitrate and nitrite concentrations compromises irrigation, drinking water supply and ecosystem values. The detection of high nitrogen concentrations in the confined NAP aquifers, together with the detection of pesticides in other regions, indicates potential seepage down poorly constructed or maintained wells. Further investigations are required to assess whether the impacts are localised to the monitored wells or representative of broader pollution problems.
What is being done to improve the condition of groundwaters across the state?
Managing agricultural impacts on groundwater depends on the strategies put in place by several organisations:
- Primary Industries SA
- Department of Environment, Water & Natural Resources
- Natural Resources Management (NRM) Boards
- Industry groups
EPA strategies include:
- development of codes of practice and guidelines linked to the Environment Protection (Water Quality) Policy
- audits of industries including dairies and wineries
- input into changes of development policy
- licence management of industries such as piggeries.
Initiatives by other government agencies include implementation of catchment water management plans, incorporating policies, strategies, education programs and onground actions to reduce pollutants and the development of industry codes of practice.