NSW State of the Environment 2012

SoE 2012 > Water > 4.3 Wetlands

Water chapter 4

4.3 Wetlands

The condition of wetlands in inland New South Wales has improved markedly since 2009, mainly due to increased rainfall and river flows following a prolonged drought. Despite their resilience, wetland systems require careful management of water inflows to maintain or improve their condition.

The majority of inland floodplain wetlands are presently undergoing a cycle of enhanced productivity with increases in extent and vegetation, and more waterbird breeding than has been experienced in over 10 years. The highest level of breeding activity and the second largest area of wetlands in 30 years of monitoring were recorded in 2010, followed by the second highest number of waterbirds in 2011.

Long-term surveys demonstrate a general pattern of decline in the extent and productivity of inland wetlands over the longer term due to the effects of water extraction and altered flow regimes.

Reduced water availability and changed patterns of river flows remain the principal causes of wetland decline. Habitat degradation as the result of changes in catchment land use, clearing and modified drainage patterns are other significant pressures.

Many important wetlands occur within regulated catchments and are dependent on careful management of environmental water and river flows to maintain ecosystem health. Around 7% of inland wetlands and 19% of coastal wetlands are now protected within the terrestrial reserve system of NSW.

NSW indicators

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

Introduction

Wetlands are dynamic by nature and an important part of the natural environment. They are 'hot spots' for plant and animal biodiversity and integral to landscape processes at regional and larger scales. Wetlands moderate the impacts of floods and contribute to regional economies by providing nurseries for estuarine commercial fisheries and also supporting grazing, apiary and tourism. They provide a regional focus for many communities, including ones based on Aboriginal culture.

NSW has 12 'Ramsar' wetlands recognised as internationally important for their biodiversity and ecosystem values under the Ramsar Convention. Wetlands provide vital habitat for the migratory bird species protected under various bilateral international agreements, such as the Japan–Australia Migratory Bird Agreement (JAMBA), China–Australia Migratory Bird Agreement (CAMBA) and the Republic of Korea–Australia Migratory Bird Agreement (ROKAMBA).

Status and trends

Wetland extent and condition

Little new statewide or systematic mapping of the extent and condition of wetlands in NSW has become available recently. However, catchment-specific studies clearly demonstrate that, despite significant declines in extent over the long term (Table 4.9), wetlands are resilient to climatic variability and have responded to recent drought-breaking rains.

Table 4.9: Declines in significant NSW wetlands

The first statewide map of wetland extent in NSW was published in 2004 (Kingsford et al. 2004). It found that wetlands then covered 4.3 million hectares or 5.6% of the state. The map used satellite imagery from 1984 to 1993 to delineate inland wetlands and satellite imagery from 1994 to 1995 to delineate coastal wetlands.

While no update of the statewide extent of wetlands is available, inundation frequency and extent have recently been mapped for the Macquarie Marshes, Gwydir wetlands and Lowbidgee floodplain using satellite imagery (Landsat MSS and TM data). This mapping shows that the frequency of inundation of these key wetlands has declined over the past 30 years and the areas that are frequently inundated have also declined over this time (Thomas et al. 2012)

The condition of wetland vegetation has also been assessed in the Macquarie Marshes, Gwydir wetlands and Lowbidgee, in relation to the frequency, duration and extent of inundation. SoE 2009 (DECCW 2009) noted that between 2001 and 2009 reduced flooding in the Macquarie Marshes resulted in a decline in condition and extent of characteristic wetland vegetation communities there (Bowen & Simpson 2010b). The condition of river red gum forests and woodlands and semi-permanent wetland vegetation in the marshes improved in response to floods in 2010–11, which inundated more than 80% of all wetland vegetation communities (Spencer et al. 2011). A substantial waterbird breeding event was also stimulated by the floods.

In 2010, it was estimated that only 25% of the original extent of the Gwydir wetlands still remained (Bowen & Simpson 2010a), with much of the wetland area converted to cropping. In 2008, the remaining area of wetland was mostly in poor condition (Bowen & Simpson 2010a). However, in response to prolonged natural flows of about 117,000 megalitres (ML) and environmental releases of 20,000 ML into the Gwydir wetlands from mid-2010 to March 2011, the health of wetland vegetation in areas receiving this inundation improved markedly and an increase in waterbird abundance, species diversity and breeding occurred (GECAOAC 2011).

Extensive flooding in the Lowbidgee wetlands in 2010–11 significantly increased the extent of wetland habitat and created breeding opportunities for waterbird species when compared with 2008 and 2009 (Spencer et al. 2011). Scientific studies found that, during the flood, wetlands that had previously been intermittently flooded (in at least 5–6 years of the last 10) supported the greatest abundance and diversity of waterbirds. This large-scale flood event also facilitated the re-colonisation of wetlands formerly occupied by threatened frog species, including the vulnerable southern bell frog (Litoria raniformis) (Spencer et al. 2011).

Mapping of the extent and condition of river red gum communities in the Millewa Forest in June 2010 found that 78% of those reserved were in intermediate condition and 17% in good condition. This provides a benchmark for adaptive management within the new Murray Valley National Park and State Conservation Area (Bowen et al. 2011).

Waterbird surveys

The best long-term data on changes in wetland extent in NSW is provided by the annual aerial waterbird surveys conducted since 1983 (Porter & Kingsford 2011). These estimate the area of available wetland habitat and also the abundance and diversity of waterbirds, which are useful indicators of wetland condition because waterbirds are sensitive to environmental changes (Kingsford 1999; Baldwin et al. 2005).

Following a prolonged drought over the past decade, widespread and extensive rains occurred across most areas of inland NSW during 2010 and 2011. The long-term aerial monitoring program found that the area of wetlands rose sharply in response to the inundation, exceeding the long-term average for the first time in 10 years. Wetland habitat was widely available with many large areas in the Murray–Darling Basin, including the Paroo overflow lakes, Cuttaburra channels, Macquarie Marshes, Lowbidgee wetlands and Menindee Lakes all holding water.

Total breeding for all waterbird species, based on the number of nest sites, was the highest on record in 2010, but then declined in 2011 to below the long-term average (Figure 4.5). However, following the successful breeding season in 2010, total waterbird numbers in eastern Australia during 2011 were the second-highest on record and the highest recorded since 1984 (Figure 4.5).

Breeding in 2011 was concentrated in the Lowbidgee and Murray River wetlands. Three species of ibis (glossy, straw-necked and white) accounted for more than 80% of total breeding abundance in the Lowbidgee wetlands during the 2011 survey.

Although total waterbird abundance and wetland area were above the long-term average in 2011, these increases have not reversed long-term declines. Trend analyses indicate long-term declines in waterbird abundance, wetland area and breeding species richness remain significant (Porter & Kingsford 2011).

Figure 4.5: Estimated number of waterbirds, wetland area and breeding in eastern Australia, 1983–2011

Source: Porter & Kingsford 2011

Notes: Aerial survey along 10 aerial survey bands, 1983–2011

Reservation of wetlands

Protection of wetlands under the National Parks and Wildlife Act 1974 or through Ramsar listing or other means is desirable to achieve effective conservation of these areas over the longer term. Studies suggest that the size of the protected area and the management of the surrounding catchment are critical for effectively protecting aquatic biodiversity (Nevill 2004; Kingsford et al. 2005). However, the sustainability of wetlands within the reserve system still depends heavily on the provision of adequate environmental flows, as well as sympathetic management of land and water resources by government agencies and surrounding landowners (see Water 4.1).

Table 4.10 shows that, at December 2011, 7% of the area of inland wetlands in NSW was managed within the national parks estate, an increase in area of 4% over the preceding three years. Coastal wetlands are better represented, with nearly 19% of their area in the formal reserve system, a 1% increase since 2008. This analysis is based on a wetlands compilation map drawn from satellite imagery for the period 1986–95 which is presently the best available statewide representation of wetland distribution in NSW (Kingsford et al. 2004).

Table 4.10: Extent of wetland types and their inclusion in the NSW national parks estate, 2011

Source: NSW Office of Environment and Heritage data 2012

Significant wetlands have been added to the NSW parks estate with the creation in July 2010 of the Murray Valley and Murrumbidgee Valley national parks by combining a number of former state forests. The Murray Valley National Park protects most of the largest remaining river red gum forest in Australia (with the section located in Victoria also being protected). The reserve also includes freshwater wetlands in the former Millewa State Forest that are Ramsar-listed. In July 2010, responsibility for the Ramsar-listed Werai Forests wetlands was vested in the Minister for the Environment and will be transferred to traditional owners for conservation purposes.

In 2010, the Gwydir Wetlands State Conservation Area became the first wetland reserve to be created in the Gwydir Valley. Part of this reserve is also Ramsar-listed.

Pressures

Flow modification (and drought)

Water availability is the most significant pressure on the health of wetland ecosystems. In NSW, the stresses caused by altered flow regimes due to water resource development over the longer term were most prevalent during the drought of 2000–10. Current conditions have improved as a result of flooding rains in 2010 and 2011.

Scientific studies of the response of water-dependent ecosystems to changes in the flow regime show that variability in stream flow and flooding is critical for maintaining and improving ecological health (Roberts & Marston 2000; Rogers & Ralph 2010). Essentially, different characteristics of a river's flow regime support specific flora, fauna, ecological functions and processes in the river channel and across its floodplains. Major dams modify flow patterns by storing inflows then releasing stored water when downstream water needs exceed downstream flows or on the few occasions when they overflow during flood periods. The overall effect of this is to smooth out flow variability and remove the 'boom and bust' patterns that many wetland plants and animals require to reproduce.

The impacts of water extraction, altered flow regimes and drought on water availability are discussed in greater detail in Water 4.1, while Water 4.2 outlines the implications of flow modification and drought for aquatic ecosystems.

Habitat degradation

A number of processes are responsible for habitat degradation. Clearing of wetlands for development and/or cropping may result in irreparable damage to wetland ecosystems and the loss of biodiversity. Modifications to natural patterns of drainage are often difficult to detect or monitor, particularly during dry spells when the changes are less visible. Over-draining of coastal landscapes is a particular threat to freshwater wetlands that may create acid discharges to rivers.

More diffuse impacts to wetland habitats can be caused by surrounding land uses, pests and weeds. Increased nutrient and sediment loads and turbidity are particular threats to submerged aquatic vegetation in wetlands. Subsidence and cracking of watercourses and upland swamps resulting from long-wall mining can also pose problems for water quality and aquatic ecosystems.

In rural and semi-rural areas, grazing of wetland plants by livestock and pest species, such as rabbits and goats, can have a serious impact on the diversity, distribution and health of wetland plants. Grazing of stock may also lead to the compaction of soils, increased nutrient levels, the introduction of weed species, trampling of native plants, and the ringbarking of mature trees.

Invasive species

Introduced plants, which can change wetland structure and function, are favoured by disturbances such as altered flow regimes, clearing or draining of wetlands, and increased nutrient loads. Significant weed species in NSW wetlands include lippia, salvinia, alligator weed and water hyacinth, which can all rapidly clog waterways when conditions are favourable for recruitment and spread (see Biodiversity 5.4).

Lippia has taken over thousands of hectares of the state's inland watercourse country and has had a major impact on the condition of the Gwydir wetlands. Lippia can out-compete all native vegetation, including tree seedlings, and it poses a severe threat to watercourses and adjacent grazing lands.

Introduced aquatic species, such as European carp and gambusia (commonly known as mosquito fish or plague minnow), can decimate native fish populations in wetlands and affect water quality. Introduced herbivores, such as pigs and goats, have caused extensive damage to the condition of wetland vegetation and soils through grazing, trampling and digging and are also capable of altering the channel and bank structure of watercourses (see Biodiversity 5.4).

Water quality

Water quality plays an important role in wetland health. Runoff from towns, cities and farms may contain toxic substances or high levels of nutrients and sediments. Where excessive levels of nutrients enter wetlands, they can cause problems, such as eutrophication (the severe depletion of dissolved oxygen levels), fish kills or excessive plant growth. Increased turbidity affects the productivity of submerged vegetation and leads to siltation, which may have an impact on the composition and habitat of many dependent species. Increased salinity can affect other characteristics of water quality, contribute to the development of acid sulfate sediments, and adversely affect biodiversity.

Acid sulfate soils

Acid sulfate soils are generally regarded as an issue for coastal waterways. If left undisturbed and covered with water, sulfidic material poses little or no threat of acidification. However, when it is exposed to oxygen in the air, the sulfides react to form sulfuric acid which can contaminate waterways. See Land 3.1 for more detail.

River regulation has seen some wetlands used as water storages, causing the loss of their dry phase. Where these wetlands are associated with saline groundwater that is high in sulfur, sulfidic sediments may accumulate in the inundated wetland. The drought conditions (2000–10) led to the drying of many otherwise permanently inundated wetlands in the Murray–Darling Basin, exposing sulfidic material with the potential to cause the acidification of some inland wetlands, as occurred at Bottle Bend on the Murray River. While some investigations have been conducted (Hall et al. 2006), the full extent of the threat posed by acid sulfate soils to inland wetlands is still unclear. The Murray–Darling Basin Commission has done a rapid assessment of the acid sulfate soil risk across the basin and identified key areas along the Murray and Murrumbidgee in NSW for detailed assessment.

Climate change

Climate change is likely to affect wetlands through changes in water availability and higher temperatures and rates of evaporation. These are expected to affect wetland condition and productivity and potentially lead to shifts in wetland distribution or ecosystem types (CSIRO 2008c). For further consideration of this issue, see Water 4.1 and Water 4.2.

Responses

Established responses

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: 'Improve the environmental health of wetlands and catchments through actively managing water for the environment by 2021'. This includes the strategic recovery and management of water for the environment to improve the health of the most stressed rivers and wetlands. Further details on Goal 22 are provided in Water 4.1.

NSW Wetlands Policy

The NSW Wetlands Policy (DECCW 2010c) updates the 1996 NSW Wetlands Management Policy to reflect developments in natural resource management and planning that affect wetlands. It promotes the sustainable conservation, management and wise use of wetlands in NSW and the need for all stakeholders to work together to protect wetland ecosystems and their catchments.

Water sharing plans

Water sharing plans provide for flows of environmental water to inland and coastal wetlands to improve wetland health. The amount of water received by the environment depends on the share specified in the water sharing plan and water availability. For example, with the end of the drought, the 2010–11 water year was the first time that the Macquarie Marshes received 100% of its environmental water allowance since the introduction of the water sharing plan in 2004–05. Water sharing plans are discussed in Water 4.1.

For inland water sources, the proposed Murray–Darling Basin Plan requires the development of long-term environmental watering plans that identify assets within each valley, their water requirements and targets for their management. Once developed, these long-term plans will be taken into account when water sharing plans are reviewed.

Purchase of water licences

The purchase of water licences has increased the share of water available for the environment and its active management under programs such as NSW RiverBank has enhanced the levels and patterns of flows to wetlands. Water 4.1 describes water purchases for the environment.

Adaptive environmental water plans

These plans facilitate the delivery of available environmental water to key wetlands. Adaptive environmental water plans have been approved for the Lachlan, Macquarie and Gwydir valleys and a draft plan prepared for the Murrumbidgee.

NSW Wetland Recovery Program

The NSW Wetland Recovery Program was completed in 2010. Management plans were developed for environmental watering of the Gwydir wetlands and Macquarie Marshes. In addition, infrastructure projects were delivered, including the Gingham pipeline project, providing water savings of 958 megalitres (ML) to water ecological assets in the Gwydir wetlands, and the upgrade of Gradgery Lane, upstream of the Macquarie Marshes, to remove a system choke and allow the passage of increased volumes of environmental water.

NSW Rivers Environmental Restoration Program

The NSW Rivers Environmental Restoration Program was completed in 2011. This program to arrest the decline in iconic rivers and wetlands in NSW delivered the following outcomes:

• the purchase of 108,000 ML of water entitlement across the Lowbidgee floodplain, Lachlan wetlands, Macquarie Marshes, Gwydir wetlands and Narran Lakes
• preparation of decision support systems and hydrologic and hydrodynamic models for the Gwydir Valley, Macquarie Marshes, Lowbidgee floodplain and Narran Lakes to assist in managing environmental flows
• completion of major infrastructure works, including 10 regulating structures, 10 floodways and the breaching of 40 pre-existing embankments in Yanga National Park to improve environmental flows
• engagement of Aboriginal communities to reconnect to culturally significant wetlands on private land and the identification of over 1200 new sites of cultural significance
• negotiation of 15 land management agreements with landholders to improve management of over 3200 hectares of wetlands of high conservation value
• acquisition of 14,000 hectares of significant wetlands for inclusion in the National Reserve System, including Booligal Station (Lachlan), Old Dromana (Gwydir), and parts of Pillicawarrina (Macquarie) and Geramy (Lachlan).

Change in ecological character: Macquarie Marshes

The notification of a 'likely change in ecological character' under the Ramsar Convention was made in August 2009 for the Macquarie Marshes Ramsar site. The key driver of change was identified as water management. The NSW Office of Environment and Heritage is currently taking action and preparing a response strategy consistent with the Adaptive Environmental Management Plan for the Macquarie Marshes (DECCW 2010a).

Coastal wetland rehabilitation

In 2012, four major coastal wetland areas were restored at Darawakh Swamp (929 hectares – Great Lakes region), Yarrahapinni (600 ha – Macleay River), Ash Island (500 ha – Hunter River) and Hexham Swamp (2000 ha – Hunter River). These large-scale rehabilitation projects will benefit fish and other species that were lost due to drainage changes associated with flood mitigation schemes, improving the breeding of fish targeted by commercial and recreational fishers.

Future opportunities

Assets such as priority wetlands will be identified for each Water Resource Plan area within the Murray–Darling Basin so that environmental water can be directed to them.

The monitoring of environmental flows will facilitate adaptive management so that these flows better replicate natural conditions and optimise the benefits to the health of wetland ecosystems.

Inland rivers and wetlands are not well represented within the national parks estate. The NSW National Parks Establishment Plan 2008 (DECC 2008) identified wetlands as a key priority for building the reserve system over the 10 years to 2018.

Better scientific information on the location and types of wetlands found in NSW is desirable, particularly the conservation values of the smaller and less well-studied wetland types that may have unique values and inadequate protection.

A better understanding of the processes and factors affecting the health and resilience of floodplain wetlands will enhance their management, given the intermittent and unpredictable nature of inundation patterns which vary substantially over longer time frames.