SoE 2006 > Water > 5.3 Surface water quality

5.3 Surface water quality

Generally, water quality is improving due to better treatment of wastewater, measures to address stormwater, and reduced salinity in rivers. However, many NSW waterways have water quality that at times does not meet guidelines for maintaining aquatic ecosystem health.

There have been reductions in the loads of nutrients from point sources of pollution discharging to waterways. Diffuse sources of pollution, such as contaminated urban and rural runoff, have a relatively greater impact and require ongoing improvements to meet guidelines on aquatic ecosystem health more often.

Salinity levels in some waterways are occasionally high, but the drought has restricted inputs of salty groundwater and so some waterways are less saline. Some inland and coastal rivers have concentrations of phosphorus that could support excessive growth of algae and other nuisance aquatic plants, and problem blooms are still frequently reported. Cold-water releases from dams are a further impact on regulated rivers.

NSW indicators

Introduction

Water quality is affected both by discharges from premises (point-source pollution) and runoff from activities such as agriculture, mining and urban areas (diffuse-source pollution).

Point sources of pollutants include sewage treatment plants (STPs) and industrial activities. STPs are often the major point-source discharges to fresh waters, particularly inland rivers. Although this wastewater is generally treated to remove pathogens and other pollutants before discharge, it usually contains phosphorus and nitrogen (depending on the level of treatment available) leading to elevated levels of these nutrients downstream of the discharge point. These can contribute to excessive growth of aquatic macrophytes and algal blooms (eutrophication), which can affect water quality and waterway users. Some forms of blue-green algae also generate toxins that can affect stock and humans when ingested.

Other water quality impacts are caused by overflows of untreated effluent when sewerage pipe capacity is exceeded, typically during wet weather. Point sources such as STP discharges affect river flow patterns as well as water quality by contributing significant volumes of water, especially during relatively dry periods.

In rural areas, diffuse-source water pollution is most significant where agricultural practices involve tilling and cropping, fertiliser and pesticide use. The relative contributions from different sources are listed in the National Pollutant Inventory.

Diffuse-source pollution is also common in urban areas where stormwater runoff containing pollutants washes from roads and other surfaces.

Common pollutants from both point and diffuse sources include nitrogen and phosphorus compounds, suspended solids, oil and grease, salts, metals, pathogens (disease-causing organisms) and toxic organic compounds. Some water pollutants contain endocrine disruptors that affect the sexual development and growth of fish and other aquatic animals. There is also developing concern about the presence of other compounds, such as pharmaceuticals (Kolpin et al. 2002; Khan & Ongerth 2005), in wastewater discharges although there is limited knowledge and understanding of the possible impacts of these on the health of aquatic ecosystems.

Current status and trends

Point-source discharges

Data from licensed point sources of pollution for the purpose of monitoring load-based licensing (LBL) shows that nitrogen, phosphorus and suspended solids dominate loads. Statewide, the levels of discharge are relatively stable within licence conditions set to protect waterways, and in some cases decreasing. Management of wastewater aims to reduce discharges to inland and estuarine receiving waters because of a higher risk of adverse environmental impact than for discharges to marine waters.

Figure 5.4 shows the relative contributions to inland waters of total suspended solids (TSS), total nitrogen (TN) and total phosphorus (TP) for the years 2001 to 2004. There has been an increase in TSS discharged, but no increase in TP and TN.

Figure 5.4: Licensed discharges of total suspended solids (TSS) and nutrients – total phosphorus (TP) and total nitrogen (TN) – to inland waters, and number of DEC licences

Source: DEC data 2005

Macroinvertebrate and water-quality sampling by Sydney Water indicates the impact of treated effluent on the health of the receiving waters (see Water 5.1). In smaller streams in the Blue Mountains, effluent discharge has reduced stream condition significantly at three of the four operational STPs, assessed by comparing macroinvertebrate indicators upstream and downstream of the STP discharges (see Water 5.1). Nutrient levels were higher downstream of the STPs. By contrast, there was no change in condition between upstream and downstream indicators at four decommissioned STPs.

Further downstream in the larger rivers of the Hawkesbury–Nepean system, however, the impact of discharges was less obvious, with generally no change in the high levels of nutrients, and with the macroinvertebrate scores deteriorating slightly, if at all. This is because the effects of STP inputs were masked by diffuse-source runoff and other unidentified impacts on river health with increasing distance downstream.

Salinity

Geology, climate and land-use practices affect the level of salinity in NSW streams. High salt concentrations can degrade water quality and freshwater aquatic ecosystems, and water with high salt loads can increase soil salinity when used for irrigation (see Land 4.3). Instream salinity (that is, the concentration of salts in the water) is decreased by the release of fresher water from storages.

Land-use practices and land clearing have led to dryland salinity and, with certain irrigation practices, have increased instream salinity levels in some areas of the State (see Land 4.3). Irrigation of highly permeable soils can exacerbate salinity, while discharges of saline wastewater from mines, power stations, paper mills and STPs are other potential sources of salt loads in waterways.

The World Health Organization (WHO) recommends a desirable upper salinity limit for drinking water of 800 EC (electrical conductivity, a measure of salinity). At a salt concentration of 1500 EC, WHO recommends against irrigation of leguminous pastures, forage crops, rice, maize and grain sorghum. In addition, adverse biological impacts are likely to occur in river, stream and wetland ecosystems at these concentrations (MDBMC 1999).

Predicted river salinities in sub-catchments of the Murray–Darling Basin are being updated in 2005–06 from an earlier audit (MDBMC 1999). Preliminary results suggest that 10 sub-catchments in the southern valleys (Murray, Murrumbidgee and Lachlan valleys) show a rising trend in salinity, eight sub-catchments show a falling trend and eight sub-catchments are stable or show no trend. In the northern valleys (Gwydir, Namoi and Border valleys), 12 sub-catchments show a rising trend, eight are falling and 16 are stable or show no trend.

Continuous monitoring of electrical conductivity has been established at 10 end-of-valley sites and 41 mid-valley sites in the inland catchments of NSW. Table 5.4 provides the mean daily salinity levels for the previous and current SoE reporting periods, and maximum salinity levels for the period of record. This shows that salinity levels at more than half the sites had improved compared to the previous report. The drought has reduced the mobilisation of salinity into streams, and this has affected salinity levels for both periods.

Table 5.4: Recorded NSW river salinity for SoE reporting periods

Source: DNR data 2006

Notes: ^(a) End-of-valley site
^(b) Incomplete period of record
^(c) Data only available to March 2006
^(d) Maximum spot readings (not means)

When daily average results are considered, none of the rivers exceed 800 EC; however, maximum spot readings in Table 5.4 show that limits for drinking water are exceeded in most systems, at least for short periods.

Cold water

Cold-water pollution is caused by low-temperature water being released into rivers from large dams during warmer months. Between spring and autumn, the water stored behind large dams can stratify thermally into a warm surface layer overlying a cold bottom layer. Since many older dams are only equipped to draw water from the bottom of the dam, water that is much colder than the natural river temperature is released downstream, causing cold-water or 'thermal' impacts (see EPA 2000a).

Cold-water releases can prevent the natural seasonal changes in river temperature and reduce the range of temperature variation, both seasonally and diurnally, sometimes for hundreds of kilometres downstream. These variations to natural temperature regimes may have severe consequences for ecosystem health including:

• native warm-water fish may fail to breed, or they may breed late in the season
• fish eggs may fail to hatch or the young may die or develop more slowly (Astles et al. 2003)
• ecosystem productivity may be reduced.

Discharges of cold water from dams is believed to be one of the main factors behind the severe decline in native warm-water fish species in the Murray–Darling Basin (Phillips 2001).

At least 140 dams in NSW have a water depth of 15 metres or more that could stratify seasonally, forming a cold bottom layer of water. However, not all of these cause cold-water pollution, because their outlets are configured to allow variable offtakes, or the quantity of water released may be relatively small. However, nine dams are likely to cause severe cold-water impacts (see Map 5.3).

Map 5.3: Potential impacts of NSW large dams releasing cold water

Source: DIPNR 2004b

Nutrients

Although a number of substances can affect water quality, nutrients (especially phosphorus and nitrogen) are a significant source of water quality problems when present in excess of natural ecosystem needs. Natural geology, discharges and land uses can affect instream nutrient levels. Phosphorus levels are considered a more significant risk for causing eutrophication in fresh water, although other nutrients, such as various forms of nitrogen, and flow and light conditions are also important in determining the abundance and types of plants, some of which themselves cause water quality problems, such as toxic algae (Davis & Koop 2006).

The current guidelines for water quality (NSW Water Quality and River Flow Objectives; ANZECC & ARMCANZ 2000) provide trigger values for water quality parameters that protect potential uses (environmental values) of water. The trigger values are used in the absence of site-specific knowledge and, as such, are designed to be conservative. The ANZECC trigger levels for phosphorus were modified for inland rivers, based on geomorphic and biological stream characteristics, such that upland streams were defined as those at altitudes higher than 250 metres (rather than 150 metres), while lowland streams were those below 250 metres. Exceedences of these trigger levels indicate the need to investigate possible causes, but do not necessarily indicate poor river health. Remedial actions may be implemented to improve water quality if environmental values, defined for NSW waterways in 1999, are found to be affected.

Map 5.4: Percentage exceedences of total phosphorus levels compared to guideline levels at NSW sites

Source: DNR data 2003–05; SCA data 2005; Sydney Water Corporation data 2005

Map 5.4 shows the levels of phosphorus in streams and rivers across NSW compared to ANZECC trigger levels. Only 48 of 220 sites (22%) exceed trigger levels (from the ANZECC & ARMCANZ 2000 guidelines) in 25% of samples or less (green dots), indicating that phosphorus levels exceed trigger levels most of the time at most of the sites, and have not changed greatly from 2003. Phosphorus levels were generally lower in South Coast streams, along the mainstream of the Murrumbidgee River and River Murray, and in some Central Coast streams, meaning these were at lower risk of nuisance plant growth or algal blooms. The northern inland catchments, the Darling River and sites in the Hawkesbury–Nepean catchment affected by urbanisation show the highest level of exceedence of trigger levels (red dots). Some sites, particularly in the north-west of NSW, exceeded the trigger levels by an order of magnitude with median total phosphorus levels of 0.4 milligrams per litre (mg/L) compared to a trigger level of 0.05 mg/L, and in these areas nearly all samples can exceed the guidelines.

Fewer than ten samples were taken at any site on the northern coastal rivers and at most sites in the Lachlan and Macquarie rivers, and none after 2003, so there is no recent information regarding nutrient levels in these river systems.

Freshwater algal blooms

Most of the problematic algal blooms that occur in fresh water in NSW are caused by blue-green algae (also called cyanobacteria), some of which can produce potent toxins harmful to humans, livestock, domestic animals and aquatic fauna. Non-toxic blooms can also have significant impacts on the health of aquatic ecosystems, but the hazards they pose are usually not as great as from toxic blooms. Problems associated with both toxic and non-toxic algal blooms include the depletion of dissolved oxygen, which can kill fish and other aquatic species; changes in pH; reduced light penetration; and the smothering of habitat.

A number of environmental factors may interact to increase the risk of blue-green algal blooms developing in fresh waters. These include warm water temperatures, elevated nutrient concentrations and, in rivers, low river flow. Drought exacerbates the problems of algal blooms by providing ideal growth conditions in still, warm waters.

Water storages are particularly prone to algal bloom outbreaks. Although algal blooms occur naturally in Australia, changes in land and water management since European arrival have favoured the conditions that suit their rapid development (Mitrovic et al. 2005). These changes include:

• reduced flows and flow variability in rivers, and more ponding of water behind dams and weirs, because of river regulation
• removal of riparian vegetation, which increases the availability of light for algal photosynthesis and raises water temperatures
• increased nutrient loads from such sources as erosion, STPs and the application of fertiliser.

For more information on algal blooms, nutrients and eutrophication, see EPA 2000a.

Algae levels in dams are routinely monitored. Monitoring networks have been established on most NSW rivers, to monitor for a range of algal concentrations. Mechanisms are in place to inform the public of outbreaks. Public warnings are only issued for NSW rivers at times of high blue-green algal presence. These are known as 'red' alerts and are based on national guidelines published in 2005.

All major inland dams and the Lake Cargelligo storage supported blooms of blue-green algae in the warmer months of 2003, 2004 and 2005. Low flows, in addition to high nutrient concentrations, also caused blooms in the lower Darling River in 2003, 2004 and 2005, and in the Namoi River in 2003 and 2004. In North Coast catchments, a number of dams and some lakes (Lake Ainsworth and the Blue Pools) supported blooms in 2002–03; rivers such as the Richmond and Tweed also had blooms that summer (DNR data 2005).

Response to the issue

The main response to poor surface water quality is the development of programs to reduce the amount of pollution entering waterways and to improve river flow regimes. Responses to river extraction and flows are discussed in Water 5.2, while major responses aimed specifically at improving surface water quality and reducing pollution are outlined below.

Point-source discharges are regulated through licences under the Protection of the Environment Operations Act 1997 (administered by DEC), and can include conditions to reduce the impacts of the discharges (through pollution reduction programs). Sewerage systems are now licensed for all possible emissions (including overflows, leakage and end-of-system discharges). Specific pollutants, such as nutrients and heavy metals, are subject to load-based licensing, where the greater the quantity of pollutant emitted, the greater the fee charged (the polluter-pays principle). Load-based licensing is already a driver for some operations to reuse effluent for irrigation rather than discharge it to waterways, and the system is now being extended to include additional pollutants. Licensing has been effective in reducing the impact of discharges on water quality. However, there are still some sub-systems affected by poor water quality caused, at least in part, by discharges, such as South Creek in the Hawkesbury–Nepean system.

Sydney Water Corporation has an ongoing program to improve sewerage systems by reducing the leakages and blockages that cause overflows; improving monitoring at overflow points to determine the frequency and volume of overflows; improving system modelling to improve performance; upgrading STPs and improving the level of treatment of wastewater, such as at South Creek, Berowra, Richmond and Penrith; and installing sewerage systems in previously unsewered areas in the outer Sydney and Illawarra regions, such as at Illawarra northern towns and Jamberoo, Mulgoa, Wallacia and Silverdale. Hunter Water Corporation is also upgrading STPs, for example at Cessnock. Both corporations are fostering reuse and recycling of wastewater, where cost-effective opportunities arise.

CMAs and local government have a role in investing in and promoting measures to control diffuse sources of pollution. While on-farm and urban practices are improving, some areas require more attention, including the prevention of runoff of sediments, fertilisers and chemicals from crops and cropped areas, and better management of stock access to waterways. Diffuse-source pollution, except from public forestry and some irrigation corporations, is not generally regulated through licensing.

The Sydney Drinking Water Catchments Regional Environmental Plan No. 1 has been prepared by the Department of Planning. This provides a streamlined planning process for ensuring that all new land uses in the drinking water catchment (the Hawkesbury–Nepean, Shoalhaven and Woronora catchments above the dams) have a neutral or beneficial impact on drinking water quality. This is complemented by the development and funding of rectification action plans by the Sydney Catchment Authority (SCA) for these sub-catchments.

The SCA's Healthy Catchments Program operates within the Hawkesbury–Nepean, Shoalhaven and Woronora catchments. The Accelerated Sewerage Program aims to upgrade sewerage systems in these catchments. Together, these are conservatively expected to reduce annual loads of suspended solids by 90 tonnes, total nitrogen by 70 tonnes and total phosphorus by 30 tonnes. The SCA also conducts monitoring and modelling to identify and prioritise sources of sediment, nutrients and pathogens, and supports incentive programs for action. The SCA Riparian Strategy focuses on stock management, revegetation, gully and instream erosion control, and weed management to reduce the risk of pathogens, sediment and nutrients entering streams, rivers and Sydney's water supply reservoirs.

DEC's Urban Stormwater Program and Beachwatch Program have both reduced diffuse-point and point-source pollution by raising awareness of the potential for stormwater to cause pollution. The Urban Stormwater Program has also provided funds for plans, works and guidelines (see Water 5.6).

Offset programs have been introduced whereby pollutants generated by one activity can be offset by reducing the amounts of the same pollutants through other means. South Creek, part of the Hawkesbury–Nepean system, has high levels of nutrients that cause particular problems downstream. To help reduce nutrient levels in South Creek, the South Creek Nutrient Offset Pilot was launched in 2003 as a voluntary trial program. It is being reviewed and, if successful, the scheme may become permanent.

Salinity management measures include the Hunter River Salinity Trading Scheme and a pilot of green offsets/market-based instruments at three sites – Ulan Coal Mine near Mudgee (Macquarie and Hunter catchments); the Norske Skog Paper Mill near Albury (Murray catchment); and the Moree Spa Baths (Gwydir catchment). At Ulan, salty mine water is used to irrigate fodder crops, and native vegetation has been planted or enhanced, which helps lower groundwater levels and reduce the added salt load. The Ulan offset program has cost the company an estimated $1.3 million, with annual operating costs of about $94,000, but has avoided a range of waste management issues and associated greater costs (such as desalinising water before discharge). The other two pilots have not progressed beyond the design stage (DEC 2005a).

Salinity management strategies have been developed at the State level (DLWC 2000) and within the Murray–Darling Basin (MDBMC 2001). At the national level, the National Action Plan for Salinity and Water Quality funds projects for reducing salinity and improving water quality.

The Premier's Annual Report on the NSW Salinity Strategy for 2003–04 (DIPNR 2004c) describes a number of resources the Government has made available for addressing the issue of salinity. These include numerical models (the Catchment Scale Salt Balance Model – CATSALT), $21 million over four years to develop and implement market-based schemes to manage salinity, booklets such as Groundwater Basics for Understanding Urban Salinity (DIPNR 2005), and numerous statewide mapping products (for example the Landuse, Salinity Outbreak and Salinity Hazard Index). The Government has also developed decision-support systems such as the Land-use Options Simulator to help translate these resources and information into practical activities for mitigating the causes and effects of salinity at both property and catchment scales.

The NSW Government has agreed to a strategic approach for mitigating cold-water releases from large dams and made an amendment to the Water Management Act 2000 in 2005. In this staged program, selected dams are investigated to develop the most cost-effective solution for allowing warmer water to be released, and protocols have been developed to allow dam operations to minimise downstream impacts on aquatic ecosystems. Works for mitigating the impacts of cold water at a number of storages include Jindabyne Dam (to be operational in 2006), Avon Dam (works underway to facilitate operation), Keepit Dam (works being planned) and Burrendong Dam (under investigation). In addition, Tallowa Dam is destratified each summer to improve the quality of its releases. Structures with existing cold-water pollution mitigation devices (Tantangara, Pindari, Windamere, Split Rock, Chaffey, Glenbawn and Glennies Creek dams) have, or will soon have, protocols for operating more effectively.

Other important responses to surface water quality issues include the management of algal blooms through the activities of Regional Algal Coordinating Committees and the State Algal Advisory Group, and the improvement of environmental flows in rivers throughout NSW (see Water 5.2).

Future directions

Diffuse water pollution remains an area requiring further attention, both for on-farm practices (such as reducing runoff from cropped lands and controlling stock access to waterways) and urban catchments. A continued focus will be on controlling water quality at source (that is, preventing water pollution). Stormwater harvesting projects which are being introduced in urban areas will assist in preventing diffuse water pollution.

Existing market-based economic instruments will continue to be applied, where they are demonstrated to be effective, and new instruments may be developed to improve surface water quality in NSW.

The decrease in the extent of water quality monitoring is not necessarily a problem, provided it is replaced with programs to directly measure ecological health (see Water 5.1). There does need to be provision made for monitoring certain physico-chemical parameters that are a demonstrated problem, such as acid in coastal waterways and salinity in affected streams. However, more information is needed on:

• the impacts of diffuse-source water pollution, including how variations in its magnitude and characteristics affect receiving waters
• the effectiveness and costs of various management actions to reduce pollution from diffuse sources.