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AGCSA Water Management

Water Quality

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2.    WATER QUALITY

 2.1 INTRODUCTION

Water is essential for sustaining and maintaining the quality of life that we are used to in Australia. For most Australians in urban environments, water arrives at the turn of a tap, clean and free of disease. Water is often taken for granted and very little concern is shown for the economic, environmental and social costs associated with its supply.

Under the Protection of the Environment Operations Act 1997 (POEO) it is an offence to pollute waters (Section 120). It is also an offence to cause or permit water pollution. 'Waters' means the whole or any part of:

  • any river, stream, lake, lagoon, swamp, wetlands, unconfined surface water, natural or artificial watercourse, dam or tidal waters (including the sea); or
  • any water stored in artificial works, any water in water mains, water pipes or water channels, or any underground or artesian water.

 Under POEO it is an offence to willfully or negligently cause a substance to leak, spill or otherwise escape in a manner that harms or is likely to harm the environment. Heavy penalties apply, including up to $1 million for a corporation and $250 000 and 7 years gaol for an individual.

Australia is a dry continent and our water resources are essentially finite. It is fortunate that we are able to supplement our surface catchment areas with millions of litres of subterranean water that has been stored over millions of years.

The major pressures on our waterways have been described as:

  • excessive surface and groundwater abstractions;
  • loss of riparian vegetation;
  • loss of wetlands;
  • altered flow regimes resulting from dam and barrage construction and water abstraction;
  • increased sediment, nutrient, salt and contaminant (e.g. pesticide) inputs from agricultural and urban developments;
  • introduced, translocated and nuisance species;
  • hazardous industrial and mining waste discharge; and
  • river modification.

Australia is a country that is often subjected to severe drought, which places increasing pressure on the available water. It is necessary to carefully prioritise where water is to be used, whether in households, agriculture, irrigating turf or industry. Acknowledging that the available water is finite, there is a need to utilise alternative sources.

The maintenance of a high-quality turf relies on having access to a constant water source that is of moderate to good uality. The time is approaching where high quality potable (drinking) water will not be available for turf areas and lower-quality water higher in salts and other contaminants will have to be used. As a consequence of droughts, the cost of potable water and the lack of potable water available for irrigating turf, many golf courses have been forced to use alternative water sources such as reclaimed wastewater and saline bore water. This has increased the emphasis on research toward environmental stress-resistant and water-efficient turfgrasses (Kenna and Horts 1993). In the long term, to be ecologically and economically sustainable golf courses will have to: 

  • make do with lower-quality water sources;
  • alter management practices;
  • treat the water and soils to offset the detrimental effects of salts, bicarbonates and nutrients;
  • introduce more water-efficient and salt-tolerant turfgrass species;
  • have a greater knowledge of water quality and its impact on soils and plants;
  • undergo increased soil, water and plant monitoring; and
  • use improved irrigation practices.

 2.2. WATER QUALITY CRITERIA

The quality of a water supply is judged by the amount of dissolved and suspended materials present (VIRASC 1980). High quality is generally associated with low amounts of these materials; however, in practice quality must always be considered in relation to the intended use.

Key source water indicators for turf (Harivandi 1997) include the following:

  • Salinity - measures the presence of soluble salts in or on soils or in waters. High salinity levels in soils can result in reduced plant productivity.
  • Sodium (Na) - contributes to soil salinity and sodicity, and has the potential to result in foliar injury when present in spray irrigation.
  • Sodicity or sodium adsorption ratio (Na, Ca, Mg) - to assess potential soil structural or permeability problems.
  • Chloride (Cl) - risks relate to foliar injury from spray irrigation, and increased chloride and cadmium uptake by plants.
  • Bicarbonate (HCO3) and carbonate (CO3) - elevated levels can adversely affect soil structure, crop foliage or irrigation equipment.
  • Boron - essential for turf growth but high levels can be toxic.
  • pH - indicates potential impacts of acidity or alkalinity of irrigation water (very high or low soil pH affects the availability of nutrients and other elements to plants; is used to assess the potential affects of other parameters at various pH levels; is one surrogate measure of effluent treatment efficiency; and is used to assess potential for corrosion and fouling of irrigation systems).
 Additional key reclaimed water indicators include the following
  • Nutrients (phosphorus, nitrogen and potassium) for plant requirements and surface and groundwater protection against nutrient enrichment.
  • Human pathogens (indicated by thermotolerant coliforms) for public health protection.

Monitoring a sub-set of the above indicators and any additional risk factors may be required for assessing potential impacts on surface and ground waters (e.g. BOD, thermotolerant coliforms, plant-available nutrients) and additional indicators in soils or plants for sound agronomic practice (e.g. turf grass nutrient status) or potential groundwater pollution (e.g. phosphorus sorption capacity, nitrates).

Key indicators from above are addressed in relation to turf management in the following sections.

2.2.1 Salinity

The soluble salt level is a key indicator of the quality of bore, dam, recycled, or runoff water used for irrigation. High-salinity water causes an increase in soil salts and as soil salinity increases it becomes more difficult for plants to extract water from the soil. This is due to an increase in the osmotic pressure of the soil water, that is the salts 'hold' the water so strongly that plants cannot remove it and therefore appear to be under drought stress even when adequate moisture is present.

Table 2.1 outlines the different classes for irrigation water based on the soluble salt content. As a general rule, salts exceeding 1000 mg/L (about 1.5 dS/m) severely limit water use on turf; however, this is dependent on grass species and variety, soil type, thatch level and irrigation and soil management.

Salt-tolerant grasses growing on well-drained soils that are readily leached of salts can be irrigated with saline water with up to 2000 mg/L (about 3 dS/m) total salts. Excessive and frequent applications of water are required so that leaching occurs and the soil is prevented from drying out excessively.

ANZECC and ARMCANZ (2000) provides useful guidance on managing saline water used for irrigation.  See: http://www.ea.gov.au/water/quality/nwqms/index.html#quality

2.2.2 Sodium

High concentrations of sodium, relative to calcium and magnesium, in irrigation water can adversely affect plant growth and soil structure and can lead to reduced permeability, aeration, infiltration, leaching and soil workability. The degree to which soil dispersion occurs is also dependent on the soil's clay content and mineralogy, pH, Ca/Mg ratio, EC, organic matter content and the presence of iron and aluminium oxides (ANZECC and ARMCANZ 2000). The most commonly used method to evaluate the potential for saline irrigation water to cause soil problems is to calculate the sodium adsorption ratio. Soil sodicity refers to the amount of exchangeable sodium cations relative to other cations in the soil and is expressed in terms of exchangeable sodium percentage (ESP).

Australian soil scientists have concluded that soils with an ESP of greater than 5 are at risk of showing the adverse structural impacts associated with sodicity.  Effluent with an SAR of greater than 6 is likely to raise ESP in non sodic soils, whereas effluent with a SAR of less than 3 may lower ESP in sodic soils. Prior to irrigating with saline water it may be beneficial to determine the existing ESP in the soil and conduct ongoing soil monitoring of ESP where SAR of irrigation water is elevated.

The sodium adsorption ratio (SAR) is defined by the equation:

SAR = Na+ /  [(Ca++ + Mg++) / 2]

where Na, Ca and Mg represent the concentrations in milli-equivalents per litre of the respective ions. Tables 2.2 and 2.3 show the sodium hazard based on SAR and related to clay type.

On some clay soils or soils with a low Cation Exchange Capacity (CEC), an SAR greater than 6-8 gives cause for concern and efforts have to be made to minimise the breakdown in soil structure. On sandy soils where permeability is less of a problem, the cation exchange sites become saturated with Na at the expense of Ca, K and Mg and sodium is taken up by the plant in preference to these other cations. Sodium accumulation in the plant can then reach toxic concentrations, resulting in a loss of turf vigour, low recovery potential, lower tolerance to heat stress, reduced tolerance to pests and diseases, and potential death of sodium-sensitive plant species. Fortunately, most turfgrass species have moderate to good tolerance to sodium and while there may be a reduction in vigour, death of the plant is unlikely.

Calcium must be applied to counteract the effects of high-sodium waters, most often in the form of gypsum (CaSO4). Gypsum can be applied directly to the turf, or it can be applied through the irrigation system. In situations where the sodium content of the water is very high and there is a need to apply large amounts of gypsum, regular small applications applied through the irrigation system are more convenient and effective than large, irregular applications to the turf.

2.2.3 Bicarbonate and carbonate

Permeability problems are also related to the carbonate (CO3) and bicarbonate (HCO3) content in the irrigation water and this is not considered in the SAR calculation. When drying of the soil occurs, part of the CO3 and HCO3 precipitates as Ca-MgCO3, therefore removing Ca and Mg from the soil water and increasing the relative proportion of sodium. The presence of high concentrations of CO3 and HCO3 can cause nutritional disturbances, such as reducing the availability of calcium and the uptake of iron. The effect of CO3-HCO3 on soil permeability can be calculated by the Residual Sodium Carbonate (RSC) method or by using a modified SAR equation (adjusted SAR) (Carrow and Duncan 1998). The adjusted SAR includes the influence of carbonate and bicarbonate ions and their effects on calcium and magnesium. Calculating the RSC is the most convenient method of determining the bicarbonate/carbonate hazard, which is as follows:

RSC = (CO3) + (HCO3) - (Ca + Mg)

where CO3, HCO3, Ca and Mg are in milli-equivalents per litre (meq/L).

Table 2.4 lists the potential problems associated with bicarbonate and carbonate.

High-bicarbonate waters can be treated by acidification of the irrigation water to remove the excess bicarbonate (Carrow et al. 2000). Acid treatment systems available in Australia inject acid into the irrigation mainline, the quantity of acid being determined by the volume of water applied and the pH. 

CASE STUDY: ACID INJECTION

At one Australian golf course an acid injection system was installed four years ago. The acid injection system provided several advantages:

  • no mains water was required
  • fungicide usage was reduced
  • greens retained complete turf cover
  • golfer satisfaction increased.

 The costs and benefits are as follows:

  • acid injection unit$35,000
  • acid (annual cost)$20,000
  • savings in mains water$40,000
  • savings in fungicides$5,000 (approx.)
  • payback period  1.4-2 years  

  2.2.4 Chloride

Sodium and chloride are the most damaging ions, chloride being particularly toxic (see table 2.5). Plants accumulate chloride to the exclusion of calcium, magnesium and potassium, causing nutritional disturbances. In addition to being taken up by the plant, chloride will cause direct injury to the plant as water dries on the leaf, particularly if irrigation is undertaken during the heat of the day. However, there is significant variation in plant tolerance to chloride, enabling the selection of more tolerant plants to be used under saline conditions. Table 2.10 shows the levels of various ions that can be associated with soluble salts and their acceptable levels.



                                   

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