Threats

Increasing salinity

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

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.

The EPA has released a series of guidelines to advise on responsible agricultural practices:

• 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
• Guidelines for the Lower Murray Reclaimed Irrigation Areas
• Guidelines for responsible pesticide use.

These bring together all the requirements contained in the several pieces of state and federal legislation that regulate the responsible use of pesticides. 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:

• Safe and effective pesticide use: A handbook for rural lifestyle landholders
• Safe and effective pesticide use: A handbook for commercial spray operators.

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.

Managing agricultural impacts on water quality depends on the strategies put in place by several organisations:

• EPA
• Primary Industries SA
• Department for Environment and Water
• Natural Resources Management (NRM) Boards
• WaterConnect
• Industry groups

EPA strategies include:

• development of codes of practice and guidelines linked to the Environment Protection (Water Quality) Policy 2015
• 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 on ground actions to reduce pollutants and the development of industry codes of practice.

Water is pumped from rivers and underground water supplies for use by rural towns, farms, industries and cities. Many rivers also feed dams and reservoirs for public water supplies and hydro-power, and are used as transport routes for boats.

While these activities provide economic and social benefits, there are many adverse environmental effects caused by altering the natural flow of rivers (river regulation). These include the decline and loss of native species of plants and animals, encouragement of habitats favourable to pest species (carp, gambusia and redfin), declining water quality and loss of amenity.

Major efforts are now underway to understand the impact of river regulation, and to develop strategies to restore and/or protect the natural flow regime of rivers and creeks to improve the environmental condition of our waterways.

Native vegetation clearance has wide-ranging effects on water quality, habitats and biodiversity. Clearing the landscape of trees and shrubs changes the direction and rate of runoff and increases erosion. This means more sediment, nutrients, salt, pesticides and other toxicants are transported into rivers and streams.

Towns and cities increase the volume of stormwater due to their large area of impervious surfaces (roads, roofs, footpaths, carparks) compared with well-vegetated catchments.

The National Land and Water Resources Audit found that, of the river length assessed in South Australia, 95% had water with elevated loads of suspended solids, total phosphorus and total nitrogen.

Habitats are where organisms live. Loss of habitat can range from the removal of whole wetland ecosystems, to the loss of a small stand of reeds in a swamp or creek.

The effect of habitat loss is invariably a reduction in biological diversity. This can limit the ability of the environment to tolerate climatic variation and the effects of human activities. It can also affect the ability of the environment to recover from a major event such as a drought, or a significant pollutant discharge.

Pests or invasive species are usually introduced by humans. They threaten the survival of native plants and animals, and can also damage valuable agricultural and personal resources.

Terrestrial and aquatic pests affect the health of our waterways as well as native animals and plants. For example, the mosquito fish (Gambusia holbrooki) was introduced from the USA to control mosquitoes. However, it now outnumbers native fish in many parts of south eastern Australia, as they out compete indigenous species for food.

Exotic trees such as willows (Salix sp) are another problem. Willows produce dense shade, suppressing understorey growth, resulting in bare banks that are susceptible to erosion. The trees are a poor habitat for land animals, and the population and diversity of aquatic invertebrates and native fish is greatly reduced under their canopy.

Salinity is a measure of how much dissolved salts are in the water. It is also called total dissolved solids or total dissolved salts.

Dissolved salts are usually sodium and chloride ions, although there can also be many others such as potassium and bicarbonate ions. In South Australia, inland waters such as rivers, streams and lakes can naturally have a wide range of salinities due to evaporation and saline groundwater inflows.

Salinity can vary during the year due to rain diluting the salt in the water. Therefore, high salinity is usually recorded in the summer and low salinity in the winter. As a general rule, salinity is relatively low during periods of high flow and vice versa.

Salinity ranges from fresh to hyper-saline as indicated in the table below.

The salinity in a watercourse influences aquatic ecosystems and the water's suitability for agricultural uses such as irrigation and livestock drinking water. However, salinity is not classified (as good, moderate or poor) by reference to guideline values because there are confounding issues that can cause misinterpretation. These issues are explained briefly below.

Salt is a natural part of the Australian landscape and a number of plants and animals inhabiting rivers and wetlands are adapted to it. Salt enters aquatic systems dissolved in rain and from a number of other sources such as groundwater, or erosion of sediments (eg weathering, microbial activity). Under natural flow conditions, periods of low flow result in salts being concentrated in wetland and riverine pool habitats. The plants and animals in these ecosystems survive increasing salinity by either tolerating or avoiding it.

It is widely accepted that many of Australia's freshwater ecosystems are becoming degraded by increasing salinity; a result of rising saline groundwater and modifications to the water regime. Available data indicates that aquatic organisms are adversely affected when salinity exceeds 1,000 mg/L.

Salinities between 1,000–5,000 mg/L reduce species richness and aquatic plant abundance, zooplankton and macroinvertebrate populations. Freshwater species are generally restricted to salt levels of less than 3,000 mg/L.

It is now widely recognised that greater salinity will progressively lead to a reduction in diversity of wetlands and rivers, and see the dominance of saline tolerant animals and plants that can cope with high salt concentrations.

Salinity is not necessarily bad for biodiversity

The taste of drinking water is rated according to salinity as follows (Australian Drinking Water Guidelines):

Note also that water with extremely low salinity may taste flat and insipid.

The salinity tolerance of crops varies from as low as around 360 mg/L (for some sensitive vegetable crops) up to several thousand mg/L (eg barley). More detail on crop salinity tolerances can be obtained from .

For livestock drinking a salinity guideline of 2,000 mg/L is recommended for poultry, 2,400 mg/L for dairy cattle and 4,000 mg/L for beef cattle, sheep and horses. More detail on livestock salinity tolerance can be obtained from Primary Industries and Regions SA.