Leschenault Peninsula

Posted on Jan 23, 2015


Leschenault PeninsulaCoastAndMarine

Leschenault Peninsula (DP)

Looking across the Leschenault Estuary to the Peninsula (D Postma).

 

The Leschenault Peninsula is located about 150 km south of Perth and 22 km north of Bunbury. It forms a north-south, finger-like projection that separates the Indian Ocean from the Leschenault Estuary. The Leschenault Peninsula Conservation Park is about 11 km long, varies in width from 600 m to 1600 m, and covers an area of 1071 ha.

Biological and Physical Values

Leschenault Peninsula’s geomorphological and biological importance are well documented, for example:

  • the Quindalup Dunes form a unique extensive linear barrier (Semeniuk and Semeniuk 1990);
  • the Peninsula supports 201 species of native plant (G. Keighery, pers. comm.);
  • plant species of special interest include Carex pumila, the only record in Western Australia, and a previously unrecorded species of the family Brassicaceae (Rorippa sp.) (G. Keighery, pers. comm.);
  • well developed stands of Peppermint and Tuart  exist on the Peninsula and are inadequately reserved elsewhere on the Swan Coastal Plain;
  • the Peninsula contains one of the largest and healthiest populations of the annual Native Pellitory (Parietaria debilis) in south-western Australia, and thus one of the most significant breeding areas in the region for the Yellow Admiral Butterfly (Vanessa itea) (R. Powell, pers. comm.);
  • the Peninsula also contains extensive samphire marshes and Quindalup Dune vegetation in excellent condition(G.Keighery, pers. comm.)
  • the occurrence of the White Mangrove, Avicennia marina, coupled with the stands in Leschenault Inlet, Bunbury, represent the southernmost occurrence of this species on the west coast; and
  • the Peninsula/Estuary interface provides significant waterbird breeding areas (Ninox Wildlife Consulting 1989).

Social Values

The Peninsula is historically significant. Its history encompasses early settlement by the Prinsep family, grazing, a tie with Irishman John Boyle O’Reilly, alternative lifestyles and, more recently, a link with industry.

The Peninsula provides the opportunity for a diverse range of recreational activities including ocean and estuary-based water activities. The Park has developed a clientele of visitors from the local, regional and Perth metropolitan area (Rosier and de Tores 1992). The Peninsula is also a prominent visual resource and displays a spectacular silhouette when viewed at sunset from the estuary’s eastern shore.

Threats

Winter storms have, and will continue to cause erosion. In several instances winter storms have initiated the erosion stage of the cyclic erosion/stabilisation sequence. Although such storms and the damage created are natural phenomena, they may necessitate major labour intensive and costly rehabilitation work and sever beach access to the southern end of the Park. Potential impacts of climate change are unclear; however, a rise in water levels has the potential to affect dramatically the Peninsula’s vegetation communities.

Although summer temperatures are moderated by sea breezes, extreme fire-hazard conditions occur.

Past Effluent Disposal

From 1963 until 1990 Leschenault Peninsula was used as a disposal site for acid effluent produced as waste from the production of titanium dioxide. The hydrological effects of industrial effluent disposal have been predominantly confined to the surficial aquifer. Effluent disposal has led to:

  • Waterlogging of surface soils. This has occurred where effluent has displaced natural groundwater and caused a raising or mounding of the surface watertable. In some cases, where the adjacent land is low lying, this displacement has led to waterlogging of the surface soils (Semeniuk and Semeniuk 1990). This effect was localised and has not been observed since effluent disposal ceased.
  • Staining of the ocean and less frequently the Estuary. As acid effluent percolates through the surficial aquifer, iron as ferrous sulphate reacts rapidly and precipitates as a range of chemical compounds, including iron sulphates, oxides, hydroxides and carbonates, and acid in the solutions would liberate carbon dioxide from the calcareous sands. The result is an aquifer contaminated with varying quantities of neutralised and unneutralised acidic effluent and chemically altered sediments. As the natural groundwater is progressively displaced by effluent, seepage of water high in iron content occurs. This seepage is predominantly towards the ocean where any unneutralised effluent causes discolouration due to precipitation of red ferrous sulphate on contact with salt water.

Industrial effluent disposal on the Peninsula has also resulted in:

  • vegetation dissected by numerous access tracks;
  • contaminated groundwater and altered or killed vegetation adjacent to disposal lagoons.;
  • damaged foliage; and
  • waterlogged roots (Seminuik and Seminuik 1990).

With the effluent disposal now ceased and rehabilitation programs continuing, the impacts of effluent disposal will progressively diminish.

Landscape Qualities

Potential detrimental effects on the Peninsula’s landscape qualities include:

  • developments and operations, particularly roads and buildings that are visible from the Estuary or Australind;
  • redundant infrastructure, discarded materials and disused buildings from past land uses; and
  • Marram Grass and its ability to create a beach berm or frontal dune shapes that are different from those created by naturally occurring species.

Vegetation

Only a small portion of the Swan Coastal Plain is reserved for conservation. With increasing land clearing and urbanisation, many species of the Plain have the potential to become rare, threatened or geographically restricted. This places greater conservation significance on those remaining species and communities in the conservation estate.

Increasing public use of the Park may degrade sensitive vegetation communities of the Peninsula / Estuary interface.

Weeds

Several introduced species occur in the Park, some of which have the potential to spread rapidly, displace native species and alter vegetation structure. This can have a significant adverse effect on conservation values. However, not all introduced species are detrimental. Some introduced species previously used to rehabilitate or stabilise dunes may continue to be of value, provided they do not pose any threat to native plant communities.

Pests

Relatively high densities of cats and rabbits have been observed within the Park.

Fire

With increasing recreational use of the Park it is anticipated there will be an increase the risk of wildfires  occurring.

Disease

The risk of introducing and spreading Phytophthora dieback is greatly increased when soil is moved. Implementing strict dieback hygiene conditions greatly reduces the risk of its introduction and spread. Similarly, using brushing material free of Armillaria reduces the risk of introducing and spreading Armillaria.

Conservation Status

The Leschenault Peninsula Conservation Park is a gazetted A Class Reserve.

Leschenault Peninsula and Climate Change

 

 

 

SWCC Strategic Priority

The Leschenault Peninsula is identified within SWCC’s NRM Strategy as a first order priority asset under the Coasts and Marine Environment themes.

Projects

 

Source:

 

Header and thumbnail images supplied by Joanna Hugues-Dit-Ciles

Submit a Comment

Your email address will not be published. Required fields are marked *