Pitt Water – Orielton Lagoon Tasmania Ecological Character

Pitt WaterWater – Orielton Lagoon Tasmania Ecological Character Description AugustDraft 1 2012August 2009 Pitt Water – Orielton Lagoon Tasmania Ecological Character Description August 2012 Introductory Notes The Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) prohibits actions that are likely to have a significant impact on the ecological character of a Ramsar wetland unless the Commonwealth Environment Minister has approved the taking of the action, or some other provision in the EPBC Act allows the action to be taken. The information in this ECD Publication does not indicate any commitment to a particular course of action, policy position or decision. Further, it does not provide assessment of any particular action within the meaning of the Environment Protection and Biodiversity Conservation Act 1999 (Cth), nor replace the role of the Minister or his delegate in making an informed decision to approve an action. The Water Act 2007 requires that in preparing the [Murray-Darling] Basin Plan, the Murray Darling Basin Authority (MDBA) must take into account Ecological Character Descriptions of declared Ramsar wetlands prepared in accordance with the National Framework. This ECD publication is provided without prejudice to any final decision by the Administrative Authority for Ramsar in Australia on change in ecological character in accordance with the requirements of Article 3.2 of the Ramsar Convention. Disclaimer While reasonable efforts have been made to ensure the contents of this ECD are correct, the Commonwealth of Australia as represented by the Department of Sustainability, Environment, Water, Population and Communities does not guarantee and accepts no legal liability whatsoever arising from or connected to the currency, accuracy, completeness, reliability or suitability of the information in this ECD. Note: There may be differences in the type of information contained in this ECD publication, to those of other Ramsar wetlands. ii Executive Summary This Ecological Character Description (ECD) has been prepared in accordance with the National Framework and Guidance for Describing the Ecological Character of Australia’s Ramsar wetlands (DEWHA 2008). The purpose of the ECD is to provide an integrated description of the critical components, processes and ecosystem services for this Ramsar site. It also outlines threats to the ecological character of the site, information gaps and limits of acceptable change. A recommended monitoring program identifies key measurable indicators of change. The ECD draws on available information and knowledge of estuarine ecosystem function, including evidence of some trends at the site since the time of listing in 1982 to 2009. The Pitt Water - Orielton Lagoon Ramsar site (PWOL) is located in the south east of Tasmania, close to Tasmania’s state capital, Hobart, and surrounded by agricultural land and small towns, now within the commuter belt of the capital. The surrounding lands were cleared for agriculture from the time of early settlement in the 1800s and PWOL lies in the path of major transportation routes used since colonial times. These factors have had an effect on PWOL, thereby altering the natural processes of the system for decades. In addition to changes to river flows and sediment transport, two causeways were constructed in 1874 across the upper parts of the estuary. Thus at the time of listing, the site was already a modified system. PWOL lies in the driest area of Tasmania and has variable annual rainfall: therefore it is especially prone to the effects of loss of river flows. The site boundary crosses the main central basin of the estuary, thereby excluding some estuary features and habitats. The upper areas of the estuary are defined by the presence of the two causeways. The large area, known as Upper Pitt Water, reaches upstream as far as the town of Richmond at the mouth of the Coal River. It marks the upper tidal limit, now barred with a weir. Tides move freely through an extensive bridge in the western causeway. The second distinctive area of PWOL is Orielton Lagoon, formed by iii the second (eastern) causeway. Once a wide, open bay of a secondary estuary feature, at the time of listing Orielton Lagoon (as it became known) was virtually cut off with only two narrow culverts with sills set at high tide level linking it to the main body of water. As a consequence, the lagoon was almost certainly eutrophic and the extensive saltmarsh at the head of the lagoon was in very poor condition. Nevertheless, Orielton Lagoon was important for bird life. Some other locations within the PWOL boundary but below the causeways also provided small alternative feeding and roosting for birds. These are at Iron Creek and the mouth of the Sorell Rivulet. When PWOL was Ramsar listed in 1982, it was considered to meet four criteria: 2 a, 2b, 2d, and 3. Since 1982 the Ramsar criteria have been modified and extended, and the standards applied by DSEWPaC (or its former equivalent agencies) have been clarified. Biodiversity criteria for which the site was originally listed are still supported at the site, albeit with some loss in species diversity and abundance. The condition of the site may be considered to be generally poorer, with the exception of the waters of Orielton Lagoon which has benefited from improved tidal exchange and removal of sewage outfalls. The status of key environmental components and processes within PWOL and the wider estuarine functions that support the system is now considered modified, so the site no longer justifies inclusion under Criterion 1 as a rare or representative wetland in ‘natural or near-natural condition’. PWOL meets five criteria for Ramsar listing as follows: Group B of the Criteria. Sites of international importance for conserving biological diversity Criteria based on species and ecological communities Criterion 2: A wetland should be considered internationally important if it supports vulnerable, endangered, or critically endangered species or threatened ecological communities. Criterion 3: A wetland should be considered internationally important if it supports populations of plant and/or animal species important for maintaining the biological diversity of a particular biogeographic region. Criterion 4: A wetland should be considered internationally important if it supports plant and/or animal species at a critical stage in their life cycles, or provides refuge during adverse conditions. Specific criteria based on fish Criterion 8: A wetland should be considered internationally important if it is an important source of food for fishes, spawning ground, nursery and/or migration path on which fish stocks, either within the wetland or elsewhere, depend. Specific criteria based on other taxa iv Criterion 9: A wetland should be considered internationally important if it regularly supports 1% of the individuals in a population of one species or subspecies of wetland-dependent non-avian animal species. The PWOL system supports important biodiversity values, including saltmarshes hosting different facies of vegetation communities and species with several saltmarsh, wetland and coastal plant and invertebrate species considered rare in Tasmania. The birdlife of PWOL includes migratory and resident waterbirds, including shorebirds, and seabirds. Orielton Lagoon is the most important site for migratory shorebirds in the Bruny Marine Bioregion. It is the most southerly area used by waders of the East Asian - Australasian Flyway. PWOL supports the biodiversity of the South-East Bioregion and Bruny Marine Bioregion. It is also important as the most significant shark breeding area in southern Tasmania and the habitat it provides for a rare endemic seastar and rare bird species. Details of how PWOL meets the five criteria are provided in Section 2. Figure ES1. summarises the components, processes and services of the site. Physical components and Supporting biological processes components •Climate •Phytoplankton •Landscape context, geomorphology •Zooplankton •Water quality /salinity •Invertebrates •Sediments •Tidal regime •River flows Communities and Habitats species •Estuarine water •Saltmarsh communities and species •Intertidal flats •Waterbirds •Saltmarsh •Seastar •Seagrass beds •Fish •Rocky shorelines Ecosystem benefits and services •Provisioning: Contributes and supports wetland products •Regulating: Maintains a complex and diverse estuarine ecosystem important for a range of biotic communities and species, including supporting critical biological processes and interactions •Cultural: Offers a range of community benefits for recreation, tourism, inspiration, education and community identity and affiliation •Supporting: Provides benefits through regulating and processing sediments, nutrients and waste, and maintaining water quality through tidal exchange v Figure ES1: Summary framework of components, processes and ecosystem services at PWOL. Section 3 provides details of critical components and processes for the site, summarised in Table ES1. The critical components and processes were selected using the criteria set out in the guidelines. Table ES1: Critical components and processes in PWOL showing commonalities and differences between the two main areas within the site. Component Sub-component Features and Features and processes processes Upper Pitt Water Orielton Lagoon Climate Rainfall Low and variable Cool temperate climate Exposed to NW and SW winds Wave-dominated estuary Hydrology Estuary type Shallow estuary with Shallow water body

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