NSW State of the Environment 2012

SoE 2012 > Water > 4.6 Estuaries and coastal lakes

Water chapter 4

4.6 Estuaries and coastal lakes

New South Wales estuaries and coastal lakes continue to come under increasing pressure from coastal development. While many estuaries are resilient to some level of change and remain in reasonably good condition, the condition of more vulnerable estuaries or those subject to greater pressures is poorer.

The condition of NSW estuaries is highly variable. Many remain in good condition but a small number are considered to be in poor condition. The overall condition of individual estuaries generally reflects their level of resilience to change caused by disturbances to their waterways and catchments.

The pressures facing NSW estuaries are also highly variable. Most have been modified to some extent, but around 20% have experienced little or no clearing of their immediate catchments, especially those along the south coast. However a significant proportion are considered to be under high pressure due to a range of intensive catchment and waterway activities, particularly in more settled areas.

Catchment and waterway disturbance results in habitat modification, including changes in runoff characteristics which increase the loads of sediments and nutrients that affect estuarine water quality and ecosystem health.

Continuing population growth and urban development along the NSW coast are expected to intensify pressures on estuaries and coastal lakes.

NSW indicators

Notes: Terms and symbols used above are defined in About SoE 2012 at the front of the report.

Introduction

Estuaries are semi-enclosed bodies of water with an open or intermittently open connection with the ocean, where water levels vary in a predictable and periodic way in response to the ocean tide at the entrance. Coastal lakes are a relatively common estuary type in NSW; many have only intermittent connections to the ocean often referred to as 'intermittently closed and open lakes and lagoons'.

Estuaries occupy the transition zone between the freshwater and marine environments. They are highly productive natural systems that form the basis of complex food webs and underpin life in near-shore waters and marine environments.

The desirability of coastal lifestyles and increasing settlement along the coast are placing estuaries and coastal lakes under ever greater levels of stress. The attendant pressures of development and urbanisation, and disturbance of the natural values of surrounding catchments need to be carefully managed in order to protect the health and preserve the condition of estuarine environments.

Systematic data has generally been lacking on the overall condition and long-term health of estuaries and the important ecosystems they support. However in implementing the NSW Natural Resources Monitoring, Evaluation and Reporting Strategy (DECCW 2010d), relevant data from a range of stakeholders was collected, consolidated and analysed for the State of the Catchments Reports series (DECCW 2010e). Data is still not available on the condition of all NSW estuaries but data collection and analysis is ongoing and reporting coverage is improving over time.

Status and trends

Estuary types

The types of estuaries found along the NSW coast vary according to their geophysical setting. The north coast is generally characterised by broad coastal floodplains that have been extensively cleared and settled. The Sydney Basin is highly urbanised with drowned river valleys that cut through a sandstone plateau. Much of the south coast is less developed and characterised by many coastal lakes and lagoons with relatively small catchments and often intermittent connections to the ocean.

Water quality

The health of estuarine ecosystems and the food webs they support is heavily influenced by water quality. While water quality is naturally variable across different estuaries, pressures on it over time can lead to a reduction in ecosystem health, including changes in the distribution and abundance of species, the loss of biodiversity, and reduced recreational value and amenity.

Turbidity and chlorophyll-a are monitored in NSW to assess estuary condition as part of the NSW Natural Resources Monitoring, Evaluation and Reporting Strategy (MER Strategy) (DECCW 2010d). Two datasets are available for comparison: the first a baseline dataset compiled from a variety of sources for the period July 2005–June 2008, the second containing monitoring data from July 2008 to June 2011. Both datasets include estuaries from the three regions (north, central and south) and the range of estuary types, but the specific estuaries monitored vary. However, the same estuaries were used to monitor both turbidity and chlorophyll-a in the second dataset.

Trigger values and compliance intervals for turbidity and chlorophyll-a have been derived for the MER Strategy program using an approach consistent with the Australian and New Zealand Guidelines for Fresh and Marine Water Quality (ANZECC & ARMCANZ 2000). Exceeding the guidelines' trigger levels does not automatically indicate that estuarine conditions are poor, but any pattern of exceedences is regarded as a cue for further investigation to determine whether water quality issues exist. Further details on site selection, monitoring procedures and data analysis are available in the MER Strategy technical report for estuaries (Roper et al. 2011).

Turbidity

Water clarity is an indication of the amount of particulate matter in the water, which may consist of clay and silt particles, phytoplankton or natural tannins. Measuring turbidity provides an indication of the amount of light available for aquatic plants and other benthic organisms that inhabit the water column and substrate of estuaries.

Turbidity data is available for 92 estuaries for the period July 2008–June 2011 and 31 estuaries between July 2005 and June 2008. Results were generally similar for the two periods of monitoring (Figure 4.13). During 2008–11, compliance with trigger values was very good (over 90% of sampling occasions) in 29 estuaries (32% of those monitored) and good (50–90% compliance) in 34 (37%); for 2005–08, compliance was very good in seven estuaries (23% of those monitored) and good in 11 estuaries (35%) (Figure 4.13).

Figure 4.13: Water quality sampling from selected NSW estuaries, 2005–08 and 2008–11

Source: Department of Environment, Climate Change and Water data 2010 and NSW Office of Environment and Heritage (OEH) data 2012

Notes: The values shown above the bars in the graphs are the number of estuaries in each compliance category.

These estuaries are generally under relatively little pressure with low to moderate sediment inputs (Roper et al. 2011). However, it appears that some estuaries may receive larger sediment inputs from catchment disturbance than are reflected in this turbidity data possibly because the sediment is delivered by rainfall outside the summer sampling period.

Fifteen estuaries (16%) had very poor compliance with trigger levels, complying on less than 10% of sampling occasions during 2008–11 and three estuaries (10%) in 2005–08. Many of these estuaries receive relatively large sediment inputs because of the scale and nature of disturbance in their catchments (Roper et al. 2011).

Chlorophyll-a

Abnormally high levels of chlorophyll-a indicate high phytoplankton levels or algal blooms and are a symptom of eutrophication, the over-enrichment of a water body with nutrients. High levels of algae may lead to reduced levels of dissolved oxygen in the water column and some algal species may produce toxins which have serious implications for fish, shellfish and humans coming into contact with the water.

Increased levels of chlorophyll-a are generally recorded in the warmer months when higher temperatures and more light provide better growing conditions. The generally higher rainfall over the warmer months is also when nutrient inflows to an estuary are greatest. This combination of conditions gives a better indication of the potential for eutrophication to occur.

Chlorophyll-a data is available from 92 estuaries for the period 2008–11 and 31 estuaries during the period 2005–08. For 2008–11, compliance with trigger values was very good (more than 90% of sampling occasions) in five estuaries (5% of those monitored) and good in 35 (38%); for 2005–08, it was very good in three estuaries (10% of those monitored) and good in 16 estuaries (52%) (Figure 4.13). These estuaries are generally under low to moderate pressure (Roper et al. 2011).

While there are generally similarities in monitoring results for chlorophyll-a across the compliance categories, the largest difference between 2005–08 and 2008–11 was the increase in the proportion of estuaries with very poor ratings (<10% compliance with the trigger values) in the second sampling period. The majority of these estuaries receive relatively high loads of nutrients from catchment disturbance which probably explains the findings (Roper et al. 2011), although two exceptions on the south coast – Baragoot Lake and Tuross River – receive relatively low nutrient loads and require further investigation.

Recreational water quality

Beachwatch programs monitor recreational water quality at swimming beaches in NSW. While not an assessment of overall water quality, the results provide an indication of sewage and stormwater pollution which affects the fitness of water bodies for human recreational use as well as the effectiveness of stormwater management.

In the Sydney region, 55 estuarine beaches are monitored for the bacterial indicator enterococci, in accordance with the Guidelines for Managing Risks in Recreational Water issued by the National Health and Medical Research Council (NHMRC 2008). Sites are located in Pittwater, Sydney Harbour, Botany Bay, Lower Georges River and Port Hacking. Map 4.8 shows the outcomes of this monitoring.

Map 4.8: Beach suitability grades at estuary swimming sites in the Sydney area, 2010–11

Rainfall during 2010–11 was extremely high and only 38 of the 55 swimming locations (69%) received a beach suitability grading of 'very good' or 'good' (Map 4.8). The poorest performing swimming sites were generally those located in the upper reaches of tributaries. These sites have less capacity to dilute pollution sources and lower levels of tidal flushing.

While the results for 2010–11 indicate that there is still a need to improve the management of stormwater inflows to estuaries in urban catchments, they are a significant improvement compared with a similarly wet period in 1998–99 (assessed under an older measurement system). When the data for 1998–99 is converted to the assessment system currently used, only 2% of estuarine swimming sites in that year recorded low levels of enterococci (Microbial Assessment Category A or B) compared with 85% of sites in 2010–11.

Water 4.5 has further information on Beachwatch monitoring programs.

Estuarine macrophytes

Estuarine macrophytes include seagrass, mangroves and saltmarsh communities. The distribution of macrophytes in NSW estuaries has been systematically mapped several times, firstly in the 1980s (West et al. 1985), then as part of the Comprehensive Coastal Assessment (CCA) (Williams et al. 2006) and the Seabed Mapping Project which filled in some gaps not mapped in the CCA. This data was compiled in Creese et al. 2009.

Estuarine macrophyte mapping is continuing as part of the NSW Natural Resources Monitoring, Evaluation and Reporting Strategy (DECCW 2010d).and 26 estuaries have now been remapped. These represent a range of estuary types from large river systems, such as the Clarence and Shoalhaven, to small coastal lake systems, such as Dalhousie Creek and Dee Why Lagoon.

Distribution of seagrass

Seagrasses occur in the subtidal zones of estuaries. They are particularly important because of their role in maintaining sediment stability and water quality, and providing shelter and food to a wide variety of aquatic biota. Causes of seagrass decline include:

• impaired water quality due to increased sediment and nutrient levels, which reduces the light that enables their growth
• physical disturbance through such activities as dredging and reclamation
• changes to hydrologic flows
• natural phenomena such as storms.

Four estuaries account for more than 60% of the total area of seagrass in NSW. However the distribution and area of seagrass and of the species represented is highly variable. Three of the four main species of seagrass found in NSW often display substantial variations in distribution over time with cyclical patterns of loss followed by slower periods of regeneration and regrowth. The fourth, Posidonia australis, is the exception.

The natural variability of seagrass communities and lack of consistent mapping prior to the 1970s makes it difficult to assess their overall status or trends in distribution over the longer term. It is believed that there has been an overall decline in the extent of seagrasses since European settlement, but this is difficult to quantify. Based on the historic evidence available, the total loss has been estimated at less than 30% (Keith 2004). However, many major estuaries in NSW lost as much as 85% of their seagrass beds in the 30–40 years prior to the commencement of systematic mapping in the 1970s (DPI 1997).

Reference to the most recent seagrass mapping indicates a slight overall decline (<4%) in the total area of seagrass since 2009 (Figure 4.14), with significant to total loss of seagrass in several of the smaller estuaries in the northern part of NSW. The distribution of seagrass increased in four estuaries, where the dominant species is Zostera capricorni, which has highly dynamic distribution patterns that may relate to localised climatic events, such as high rainfall and flooding, rather than direct human impacts. The cause of specific declines requires further investigation.

Figure 4.14: Change in macrophyte distribution

Source: Department of Primary Industries data 2012

Distribution of mangroves

Mangroves grow along the intertidal shores of many NSW estuaries, in some places forming extensive forests. They are absent from many intermittently closed and open lakes and lagoons, particularly those where entrances are frequently closed.

Although five mangrove species occur in NSW, only the grey mangrove and river mangrove are found extensively. The diversity of mangroves decreases southwards along the coast with only grey mangroves found beyond Merimbula Lake on the far south coast. Three major estuaries – Port Stephens and the Hunter and Hawkesbury rivers – account for approximately 50% of the total distribution of mangroves in NSW.

Mangroves are quite resilient and are able to rapidly colonise favourable areas. Expansion may be due to a range of factors, including:

• regrowth in areas of past clearing
• expansion into areas of saltmarsh
• colonisation of areas where sedimentation has occurred and altered hydrology and tidal regimes favour them, such as coastal lakes where artificial entrance regimes have increased tidal inundation.

A lack of consistent mapping over the longer term has made it difficult to assess overall trends in the status and extent of mangroves. It is believed that there has been an overall decline in their extent since European settlement, but this is difficult to quantify. Based on the historic evidence available, Keith 2004 has estimated the loss of mangroves at between 30 and 70%.

The most recent surveys indicate that the total area of mangroves across 26 estuaries has increased by about 8% since 2009 (Figure 4.14). The distribution of mangroves in the majority of estuaries expanded or remained similar. The largest expansion was recorded in the Clarence River, while two estuaries – Darkum Creek and Lake Macquarie – registered a slight decline. Given the relatively small area of mangroves around Darkum Creek, these changes may relate to the resolution of mapping, whereas the losses around Lake Macquarie occur in a number of areas and require further investigation.

The overall distribution of mangroves, however, is still greater than that mapped in the 1980s (West et al. 1985).

Distribution of saltmarsh

Saltmarsh communities grow to the highest tide levels, meaning that they are only inundated by larger tides or extremes in water levels. Where saltmarsh occurs in conjunction with mangroves, it occupies the landward area. Saltmarsh can also occur around coastal lakes where conditions do not favour mangroves. Typically vegetated by low shrubs, herbs and grasses, they can range from narrow fringes on steep shorelines to nearly flat expanses.

There has been a substantial decline in the extent of saltmarsh since European settlement, but this is difficult to quantify. However, based on the historic evidence available, the loss has been estimated at 30–70% (Keith 2004). Losses of saltmarsh have been particularly severe in the Sydney region and on the central coast (Wilton 2002; Williams & Meehan 2004; Kelleway et al. 2007). Saltmarsh has been listed as an endangered ecological community in NSW due to the nature of ongoing losses. The processes threatening saltmarsh include infilling, modified tidal flows, weed invasion, human disturbance and climate change (Adam 2002).

An overall loss of saltmarsh of around 9% was found across the 26 estuaries recently remapped (Figure 4.14). An increase in saltmarsh distribution was mapped in 13 estuaries: 10 had distributions similar to the previous mapping and three had reduced saltmarsh distributions.

The largest area of change was in Cathie Creek where saltmarsh species have been replaced by freshwater wetland species (a reduction of 412 hectares or 22% of the saltmarsh distribution mapped by Williams et al. 2006). This change is likely to be in response to varying hydrologic conditions as the entrance to the creek has become constricted over recent years and water levels have increased, submerging saltmarshes and favouring freshwater species.

Excluding Cathie Creek from the analysis, the overall trend for NSW is an increase in saltmarsh distribution of about 230 ha or 16%.

Pressures

Pressures influencing the condition of NSW estuaries originate in the surrounding catchment, in the area immediately adjacent to the estuary known as the foreshore or riparian zone, and within the estuarine waterway itself.

Many of the pressures on estuaries are associated with the growth in population along the coast and the land clearing and development this entails. These activities increase the volume and change the nature of rainfall runoff and stormwater which carries sediment and other pollutants to coastal environments with impacts on water quality. Areas of mangroves, saltmarsh and coastal wetland have been cleared or reclaimed for port infrastructure, recreation, housing and rubbish disposal. Aquatic communities, such as seagrasses, have been disturbed by waterway activities and infrastructure, including boat ramps, jetties and moorings, and affected by changes in water quality.

Catchment disturbance

Changes in land use and the removal of vegetation in coastal catchments are good indicators of the pressures affecting water bodies from increased loads of diffuse source nutrients and sediments. Where vegetation has been cleared, the nature of the subsequent land use will determine the extent of the increase in runoff transporting nutrients and sediment from the catchment to estuaries. For example, increasing urbanisation leads to greater runoff from the hard non-porous surfaces found in built-up areas.

The level of disturbance affecting the catchments of NSW estuaries has been mapped as part of the NSW Natural Resources Monitoring, Evaluation and Reporting Strategy (DECCW 2010d). The area of the catchment can be divided into the 'estuary catchment' where runoff drains directly to the estuary below the tidal limit and the 'fluvial catchment' where drainage is to areas above the tidal limit, including freshwater tributaries. The largest fluvial catchments tend to be associated with larger estuaries which have significant tributaries. The catchments of 30 NSW estuaries have no mapped fluvial component due to their small size and absence of major freshwater tributaries draining to the estuary.

The average rate of vegetation clearance in the catchments of NSW estuaries is approximately 38%. For that part of the catchment that drains directly to the estuary, the average rate of disturbance increases to 44%. It is possible that pressures originating nearer to waterways have a greater influence on condition.

Thirty-seven estuaries (about 20%) have experienced little or no clearing of their direct catchments (less than 10% of vegetation cover), while for the total catchment the figure is 40 estuaries (22%) (Figure 4.15). The majority of these are within the public reserve system of national parks or other public lands.

Thirty-four estuaries (around 18%) have experienced extensive clearing of 80% or more of their immediate catchment areas, while 20 estuaries (11%) have experienced this level of disturbance throughout the whole catchment (Figure 4.15). Many of these estuaries are considered to be in a fair to poor state, particularly the smaller systems with intermittent connections to the ocean. The smaller number of larger, well-flushed estuaries that have been extensively cleared are generally considered to be in better condition.

Figure 4.15: Level of catchment disturbance (vegetation clearing) in NSW estuaries

Source: OEH data 2012

Notes: The data covers 184 estuaries and the values shown above the bars in the graphs are the number of estuaries in each disturbance category.

Population and demographic change

The majority of the NSW population lives close to the coast and this places considerable pressure on coastal and estuarine ecosystems through increased development and disturbance of the catchments.

Population density data has been calculated from data collected by the Australian Bureau of Statistics in the 1996, 2001and 2006 Censuses. The population density of estuary catchments ranges from nil for estuaries with catchments located wholly within national parks to very high densities for estuaries in metropolitan Sydney, where Port Jackson and Dee Why catchments support over 5000 people per square kilometre (km²). The average population density for NSW estuary catchments is 211 people/km².

An ongoing shift of population to the coast occurred across the three Censuses. The proportion of the NSW population living in estuary and coastal catchments increased from 80.6% of the total NSW population in 1996 to 82.1% in 2006. Population density across all coastal catchments has increased from 38.3 to 42.2 people/km² or an increase of 9.2% for the period (Roper et al. 2011). A continuation of this trend is likely to increase the pressures on NSW estuaries and coastlines that are adjacent to population centres.

Nutrient and sediment loads

Many NSW estuaries face the threats of eutrophication (excessive nutrient enrichment) and sedimentation.

Increases in nutrient loads to estuaries are associated with a range of land uses and activities, such as urban development, agricultural land-use practices and effluent discharges. Increases in nutrient loads may lead to excessive production of algae and aquatic plants, with flow-on effects up the food chain. System productivity may increase temporarily but, because excessive levels of nutrients tend to favour a smaller number of species, overall biodiversity and ecosystem health is reduced.

Sediment loads entering estuaries can increase as a result of disturbance to soils, erosion in catchments, and riverbank, shoreline and in-stream erosion. Following its transport by rainfall, coarse sediment settles out, smothering sensitive species, while finer sediment may remain suspended and limit primary production by reducing water clarity.

Direct measurement of the sediment and nutrient loadings to coastal lakes and estuaries from a range of diffuse sources in a catchment is difficult and costly. Therefore sediment and nutrient loads are estimated using models of the surface flows across catchments associated with a range of land uses.

Point source discharges from sewage treatment plants (STPs) directly into estuaries or their tributaries are another source of sediment and nutrient inputs. Discharges from STPs and sewage overflow points are licensed by the NSW Environment Protection Authority. Combining the annual discharge loads with the diffuse source loads from modelling provides an estimate of the annual loads for total suspended solids (TSS), total nitrogen (TN) and total phosphorus (TP).

The percentage increase above natural levels of TSS, TN and TP in NSW estuaries has been estimated using this approach. Figure 4.16 shows the combined results for TSS and demonstrates that while some estuaries still have nearly natural loads, in many others the loads are well above natural, undisturbed levels. An estimated 54% of NSW estuaries have undergone a doubling (or greater) of loads of TSS.

The modelled results for nutrients are similar with an estimated 48% of NSW estuaries experiencing a doubling (or greater) of TN levels, while TP levels in 73% of estuaries have at least doubled (Figure 4.16). With a small number of exceptions, estuaries determined to be in a fair to very poor condition (DECCW 2010e) are generally within this group of estuaries.

Figure 4.16: Modelled loads of total suspended solids and nutrients to NSW estuaries

Source: Roper et al. 2011

Notes: The data covers 184 estuaries and the values shown above the bars in the graphs are the number of estuaries in each increase category.

Riparian disturbance

Riparian zones are the areas directly adjacent to a waterway, often referred to as 'foreshores' in estuaries. Disturbance within this zone is of particular interest as riparian vegetation acts as a barrier or filter to protect the water body and minimise erosion. Pressures originating in this area are likely to have a more direct impact on estuary condition than the same pressure acting further away.

The riparian zones around each of the 184 estuaries in NSW have been mapped. These cover the area that is within 100 metres of the waterway and less than 0.6 m above mean sea level, an area that generally defines the outer edge of seagrass, mangrove or saltmarsh communities. Within this zone, land-use mapping identifies the areas of disturbance based on the same land-use classes used to determine catchment disturbance and diffuse nutrient and sediment loads (Roper et al. 2011).

Similar to the patterns of disturbance within the estuary catchments, 11% of estuaries have riparian zones with little or no disturbance and a further 9% have disturbance levels of less than 10% (Figure 4.17). Around 11% of estuaries have experienced disturbance to 80% or more of their riparian zone, a similar proportion to estuaries with the same level of disturbance throughout the whole catchment.

Figure 4.17: Levels of disturbance to riparian vegetation and waterways in NSW estuaries

Source: OEH data 2012

Notes: The data covers 184 estuaries and the values shown above the bars in the graphs are the number of estuaries in each disturbance category.

Waterway disturbance

Change in estuarine habitats, water quality and estuarine processes can also occur as the result of disturbance directly to the waterway itself, including:

• the removal of vegetation
• competition from introduced species
• the building of structures, such as marinas, boat ramps, foreshore reclamation, hard erosion control structures, weirs, training walls and artificial entrance openings
• activities such as fishing, trawling and aquaculture.

One measure of direct waterway disturbance is the percentage of the estuary perimeter that is occupied by foreshore structures on Crown land above or below the mean high water mark. Structures include buildings, jetties and wharves, boat ramps, foreshore reclamation and seawalls. Another measure is the percentage of estuary area leased for waterway-based aquaculture, such as oyster and mussel farming. The levels of these disturbances in NSW estuaries are shown in Figure 4.17.

Just over 50% of estuaries have few, if any, foreshore structures and 75% of estuaries contain no aquaculture leases. Estuaries in the metropolitan area with higher percentages of their perimeters occupied by foreshore leases tend to be waterways with a proliferation of boating infrastructure associated with urban development. As such, these estuaries are generally subject to catchment, riparian and waterway pressures and determining the dominant pressures influencing their condition can be difficult.

Estuaries with over 10% of their waterway area occupied by aquaculture leases are all located on the south coast of NSW in waterways that are generally in good condition, have moderate to low levels of catchment development and consistent patterns of tidal variation, all conditions that favour a productive aquaculture industry.

Climate change

Variations in climate and sea level are inextricably linked (BoM 2011b). Warming temperatures lead to sea level rise for two main reasons: water expands as it warms and, as average temperatures rise, the polar ice sheets begin to melt (IPCC 2007). Sea level rise is not uniform around the world or in Australia as climatic cycles such as El Niño–Southern Oscillation and the Indian Ocean Dipole create further variations that can mask or enhance changes due to global warming.

Such variations will only become evident over the longer term and it is not possible to identify changes over a relatively short time frame such as the three-year cycle of SoE reporting. Since 1993, sea levels around Australia have risen 7–10 millimetres per year in the north and west and about 4 mm per year in the south and east. Off the east coast of NSW, warm water currents have elevated sea levels by about 6 mm per year as demonstrated by tidal gauge readings from Port Kembla shown in Map 4.9 (CSIRO & BoM 2012).

Sea level rise is virtually certain to increase tidal levels, enlarging the areas of low-lying land near coastal waterways that are exposed to more frequent tidal inundation (DECCW 2010b). Due to the combined influence of sea level rise and higher rainfall events, the frequency, height and extent of floods are expected to increase in the lower parts of coastal floodplains (DECCW 2010b). With 63% of the NSW population living in Sydney – a coastal city – and a further 20% living in the non-metropolitan coastal strip (ABS 2012), rising sea levels are likely to have a significant effect on human settlements in coastal NSW.

Most coastal dunes and some beach-barrier systems and estuaries are expected to be affected by an increased threat of erosion from a combination of sea level rise, changes in wave direction, and greater storm intensity. A number of sites along the NSW coast have already experienced heightened coastal erosion (DECCW 2010b).

The effect of rising sea levels on natural systems is demonstrated by mangrove swamps encroaching on areas previously occupied by saltmarsh. In 70% of estuaries surveyed in Queensland, NSW, Victoria and South Australia, the area of saltmarsh taken over by mangroves has been greater than 30% and in some cases mangroves have completely replaced saltmarsh. This change has largely been attributed to subsidence and sea level rise (Saintilan & Williams 1999; Saintilan & Williams 2000; Rogers et al. 2006). As water levels rise, the ability of some communities, such as saltmarsh, to colonise new areas at more suitable elevations may be impeded by the presence of coastal development (Goudkamp & Chin 2006).

Map 4.9: Sea level rise between 1993 and 2011 at Port Kembla, NSW

Source: CSIRO & BoM 2012

Other pressures

A range of other pressures also affect waterway health, but their cumulative impact is more difficult to measure or assess. Tidal flows may be affected by rock training walls designed to keep estuary entrances open, the artificial opening of lagoon entrances to alleviate flooding, and other flood mitigation structures. Changes to hydrology and flows can have a significant impact on water and salinity levels and the distribution and composition of estuarine ecosystems.

Changes in the volume of freshwater flows entering estuaries can arise from upstream water storages, extraction of water for agriculture, and barriers such as weirs. A reduction in freshwater flows to estuaries can influence the location of the tidal limit and the salinity profile, as well as affect the distribution and composition of ecosystems.

Commercial and recreational fishing place pressures on the fisheries they target as well as the broader estuarine environment. Impacts from fishing and trawling can include damage to habitat, bycatch, waste and infrastructure pressures.

Responses

Established responses

Management of the NSW coastal zone is the responsibility of all levels of government. The expected growth in population in coastal areas is likely to increase the importance of integrated coastal zone management and strategies that enable communities to adapt to changing environmental conditions.

Local government plays a key role in protecting the health of estuarine ecosystems through a variety of mechanisms including land-use and strategic planning, development controls and a range of policies affecting water utilities and water quality management, including sewage and stormwater management strategies and estuary management plans.

NSW 2021

NSW 2021: A plan to make NSW number one (NSW Government 2011) is the Government's 10-year plan for NSW. Under Goal 22 – 'Protect our natural environment', the plan contains the following target: 'Protect rivers, wetlands and coastal environments'. Further details on Goal 22 are provided in Water 4.1.

Legislation

The NSW Environmental Planning and Assessment Act 1979 sets the framework for land-use planning decisions. The Coastal Protection Act 1979 and NSW Coastal Policy 1997 (NSW Government 1997) provide the strategic direction and legislative framework for managing the NSW coastal zone, including the requirement for coastal zone management plans and the matters these plans should consider. Mangroves and seagrass habitats are protected under the Fisheries Management Act 1994.

State environmental planning policies

State environmental planning policies (SEPPs) address specific planning issues in NSW.

State Environmental Planning Policy No. 71 – Coastal Protection ensures that:

• development in the NSW coastal zone is appropriate and suitably located
• there is a consistent and strategic approach to coastal planning and management
• there is a clear framework for assessing development in the coastal zone.

State Environmental Planning Policy No. 14 – Coastal Wetlands ensures that coastal wetlands are preserved and protected for environmental and economic reasons. The policy applies to coastal local government areas outside the Sydney metropolitan area and identifies over 1300 wetlands of high natural value from Tweed Heads to Broken Bay and Wollongong to Cape Howe. All land clearing, construction of levees, and drainage work or filling within wetland boundaries requires consent and the preparation of an environmental impact statement.

Other SEPPs relevant to coastal development include:

• State Environmental Planning Policy No. 26 – Littoral Rainforests
• State Environmental Planning Policy No. 50 – Canal Estate Development
• State Environmental Planning Policy No. 62 – Sustainable Aquaculture.

Review of coastal protection and NSW Sea Level Rise Policy

A Coastal Ministerial Taskforce has been established to review coastal protection arrangements. Stage 1 coastal reforms were announced in October 2012. These included the removal of sea level rise benchmarks, which will no longer apply to coastal zone planning in NSW. Further developments will be announced in stage 2 of the reforms.

Coastal zone and estuary management plans

The Guidelines for Preparing Coastal Zone Management Plans (DECCW 2010f) provide advice to local councils, their consultants and coastal communities on the preparation of Coastal Zone Management Plans. The primary purpose of these plans is to address priority management issues in the coastal zone including:

• managing risks to public safety and built assets
• pressures on coastal ecosystems
• community uses of the coastal zone.

Plans for estuaries should include:

• a description of the condition of estuaries within the plan's area
• details of the pressures affecting estuary condition and their relative magnitude
• proposed actions to respond to pressures on estuary condition
• an entrance management strategy for intermittently closed and open lakes and lagoons
• an estuarine monitoring program consistent with the NSW Natural Resources Monitoring, Evaluation and Reporting Strategy (DECCW 2010d).

Coastal zone and estuary management plans are being prepared and implemented by local councils for over 90 estuaries in order to achieve integrated, balanced and ecologically sustainable management.

Regional strategies

Regional strategies are in place for six coastal areas of regional NSW: Central Coast, Lower Hunter, Far North Coast, Mid North Coast, Illawarra and South Coast.

The strategies set a strategic direction for these rapidly growing coastal regions on issues including management of the high rates of population growth in a sustainable manner, while protecting valuable natural and cultural assets. The strategies require local environmental plans to protect and zone lands with aquatic, riparian and wetland conservation values.

Catchment action plans

Catchment action plans are developed by catchment management authorities and represent the key process that coordinates and drives natural resource management at the regional level. The plans describe the approaches to be adopted for addressing statewide targets at the regional scale and also specify the regional targets and the programs of investments and works that are needed to deliver outcomes at the regional and local levels.

Management of water quality

The main responses aimed specifically at improving estuarine water quality by reducing pollution include:

• planning strategies covering land use and catchment management, which set water quality objectives
• licensing or management of pollution from major point sources
• works to manage stormwater and diffuse runoff
• programs to prevent and manage pollution incidents
• tools to assist in managing estuaries.

The Coastal Catchments Initiative is the Australian Government's primary vehicle to deliver significant reductions in the discharge of pollutants to 'hot spots' identified through agreement with relevant state jurisdictions. The Great Lakes (Wallis, Smiths and Myall Lakes) and Botany Bay have been identified as hot spots in NSW. Implementation of the initiative included the preparation of water quality improvement plans for hot spots to guide investment in water quality projects.

NSW Water Quality Objectives set out the agreed environmental values and long-term goals for NSW surface waters. The objectives are consistent with the agreed national framework for assessing water quality described in the Australian and New Zealand Guidelines for Fresh and Marine Water Quality (ANZECC & ARMCANZ 2000). They set out a range of water quality indicators and criteria to determine whether water quality in estuaries and coastal lakes is able to support healthy ecosystems and a range of beneficial uses, including recreational activities. Consistent with the Water Quality Objectives and the process recommended in the ANZECC Water Quality Guidelines, the NSW Natural Resources Monitoring, Evaluation and Reporting Strategy (DECCW 2010d) provides further advice on estuarine water quality indicators and monitoring and has derived a number of water quality trigger values that can be used in lieu of the default values provided.

The NSW Diffuse Source Water Pollution Strategy (DECC 2009) recognises that diffuse source pollution accounts for the majority of the pollution load in NSW waterways. The strategy aims to coordinate the NSW Government's approach to the management of diffuse water pollution and identifies a list of actions to be implemented.

Future opportunities

The strong preference of many Australians to live near the coast means that it is likely that pressures on the NSW coastal zone will continue to grow, due to expanding population and development.

The poor condition of water quality in some highly urbanised estuaries suggests that stormwater runoff and new urban development can be managed better in order to maintain the health of estuaries and coastal lakes and the desirability of coastal lifestyles.

Due to a lack of consistent and reliable data, there are still many uncertainties in assessing the status of estuaries and coastal lakes and any related trends.

Susceptibility to inundation and coastal erosion should be a significant consideration in the location and planning of all future settlements in catering for an expanding population and development needs.