Vasse-Wonnerup Wetlands

Posted on Dec 23, 2014


Vasse-Wonnerup WetlandsWaterResourcesCoastAndMarineAquaticBiodiversity

Vasse Wonnerup wetlands (M Durcan)

Vasse Wonnerup wetlands (M Durcan)

The Ramsar-listed Vasse-Wonnerup wetland system, is a very large wetland, estuarine marshland and tidal floodplain area located within the Geographe Bay catchment and at the northern-most extent of the City of Busselton boundary.

Biological and Physical Values

Hydrology

The Vasse Wonnerup Wetlands are comprised of the Vasse and Wonnerup estuaries and their exit channels; the Wonnerup Inlet; and the seasonal connection between the two estuaries known as Malbup Creek. The Dead Water and Swan Lake are also associated wetlands. Today only the Lower Vasse, Lower Sabina and Abba rivers flow into the Vasse Estuary, while the Ludlow River flows into the Wonnerup Estuary. Floodgates were installed near the mouths of the Vasse and Wonnerup estuaries during the early 1900s to prevent flooding of the surrounding agricultural land with saltwater. These floodgates have since enabled the Busselton town site to expand into land that was previously inundated during winter. The floodgates have also served to maintain fresh–brackish water within the system for a longer period than would have occurred under ‘natural’ conditions. Large areas of the wetland system dry out during summer, though some water is retained in both estuaries that provides important summer refuge habitat for thousands of waterbirds.

Waterbirds and the Ramsar Convention

The Vasse-Wonnerup Wetlands are recognised as one of the most important waterbird habitats in Western Australia. More than 30 000 waterbirds comprising 90 different species make use of the habitat provided by the wetlands each year. These include a range of migratory and resident species in addition to the largest breeding colony of black swan in Western Australia (WAPC 2005). The only waterway in the state to support larger numbers of waterbirds is the Peel Harvey Estuary, though this is close to 13 times the size of the Vasse-Wonnerup Wetlands (WRM 2007). Many of the species recorded in surveys of the Vasse-Wonnerup Wetlands have special conservation value (WRM 2007).

These include:

  • 40 species with priority conservation status at a state, national or global level,including 22 migratory waterbird species
  • 61 resident Australian species, including large numbers of Australian pelican, great egret, yellow-billed spoonbill, Eurasian coot, black-winged stilt and red-necked avocet
  • species that regularly occur in numbers greater than or equal to one per cent of the estimated Ramsar populations (back-winged stilt, red-necked avocet, Australian shelduck and Australasian shoveler)
  • species that in some years occur in numbers greater than one percent of the East Asian–Australasian Flyway population (wood sandpiper, sharp-tailed sandpiper, long-toed stint, curlew sandpiper and greenshank).

Owing to these significant waterbird values, since 1990 the Vasse-Wonnerup Wetlands have been included in a list of wetlands of international importance under the Ramsar Convention. Australia is one of 158 countries that are contracting parties to this international convention, which was ratified in Ramsar, Iran, in 1971. Among other responsibilities, contracting parties are required to implement measures to promote wetlands conservation, ensure wise use of the listed wetlands, and to protect migratory waterbirds and their habitats.

Macrophytes such as the estuarine seagrass species Ruppia megacarpa grow throughout both estuaries and provide an important food source for waterbirds. The black swan, which breeds in large numbers on the wetlands, feeds directly on this species. Maintenance of macrophyte populations within the wetlands is important to ensure the long-term availability of feeding habitats for waterbirds.

The Vasse-Wonnerup Wetlands Ramsar site currently covers approximately 1115 ha and includes the non-freehold and seasonally inundated floodplains and marshes of the Vasse and Wonnerup estuaries and Wonnerup Inlet. Recent extensions encompass the lower reaches of the Sabina River, Abba River and sections of the Tuart Forest (Government of Western Australia 2000). An Ecological Character Description for the wetlands (WRM 2007)– prepared as part of the Coastal Catchments Initiative project – provides a summary of the wetlands’ ecological values relevant to the Ramsar listing. Threatening processes affecting the wetlands and potential thresholds for change are also identified in this document here.

Other values

Aside from providing waterbird habitat, the Vasse-Wonnerup Wetlands are also used by a wide variety of other fauna that play an important part in the wetland ecosystem. Twelve marine and estuarine fish species have been recorded in the wetlands, and of these, seven species use the system as a nursery area. Black bream and mullet are also fished commercially on a seasonal basis (WRM 2007). The western school prawn and blue swimmer crab appear occasionally, while a wide variety of frogs and snakes make use of the wetlands – as do long-neck tortoises and water rats.

The values of the Vasse-Wonnerup Wetlandsare not limited to ecological functions. They play an important flood-protection role for the surrounding low-lying coastal properties by providing water storage to buffer storm surges and peak river flows (WAPC 2005). The fringing vegetation and open water areas of the wetlands also hold important aesthetic landscape values for the town of Busselton. These values, together with the huge number of waterbirds that visit each year, provide the site with enormous potential for ecotourism that is unrealised as yet.

Vasse-Wonnerup wetlands in summer (m Durcan)

Vasse-Wonnerup wetlands in summer (M Durcan).

Current Condition and Trends

The Vasse-Wonnerup Wetlands have been experiencing symptoms of nutrient enrichment for many years. Instances of sudden mass fish kills have been recorded since the early 1900s and became more regular during the 1980s and 1990s (Lane et al. 1997). The majority of fish kills occurred immediately upstream of the Vasse and Wonnerup floodgates and have been attributed to low oxygen conditions in the water column (Lane et al. 1997). Blooms of macroalgae and phytoplankton have also regularly occurred, though some of these have been isolated to the immediate area of the floodgates. The Lower Vasse River, which flows to the Vasse Estuary, is also suffering from elevated nutrients and experiences toxic blooms of phytoplankton every summer for most of the season.

Extensive meadows of macrophytes within the wetlands, such as the estuarine seagrass Ruppia sp., are an important food source for waterbirds – especially for the black swan that feeds directly on this species. Surveys of the macrophytes, macroalgae, phytoplankton and water quality in the wetland system have highlighted that Ruppia meadows may be at risk should blooms of macroalgae and phytoplankton become more dominant in the estuary (Wilson et al. 2007; Wilson et al. 2008).

The Vasse-Wonnerup and Geographe Bay Water Quality Improvement Plan discusses, in detail, the water quality issues impacting these systems and the management measures required to address nutrient loads causing poor water quality and the flow on environmental impacts.

Conservation Status

The Vasse-Wonnerup wetland system is Ramsar-listed.

Threats

The Ecological Character Description of the Vasse-Wonnerup Wetlands Ramsar Site documents the actual and likely threats to the system in Table 28. Click on images below to enlarge. The full report is accessible here.

Table 28: Summary table of actual and likely threats to the Vasse-Wonnerup Ramsar Site, together with the risk to the ecological integrity of the Site as a whole (WRM 2007).

Vasse Wonnerup Table 28 page 1 ECD vimage

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Vasse-Wonnerup Wetlands and Climate Change

 

 

SWCC Strategic Priority

The Vasse-Wonnerup Wetlands are identified within SWCC’s NRM Strategy as a first order priority asset under the Aquatic Biodiversity, Water Resources and Coasts and Marine Environment themes.

ProjectsVasse wonnerup case study

Over the years, the Vasse-Wonnerup Wetlands have been the subject of many studies and projects.

One recent SWCC project being:

 

Source:

 

Header and thumbnail images supplied by Monica Durcan.

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