Pitt Water - Orielton Lagoon Ramsar Site Ecological Character Description

Dr Helen Dunn, 2012

for
Department of Sustainability, Environment, Water, Population and Communities

About the document

An Ecological Character Description describes the ecological character of a wetland at the time of its listing as a Wetland of International Importance. The Ecological Character Description is a fundamental management tool for site managers, forming the basis of management planning and action as well as including guidance on site monitoring requirements to detect changes in the ecological character of the site.

The Pitt Water - Orielton Lagoon Ramsar site is located in the south east of Tasmania, close to the state capital, Hobart, and surrounded by agricultural land and small towns. The surrounding lands were cleared for agriculture from the time of early settlement in the 1800s. Pitt Water lies in the path of major transportation routes used since colonial times. These factors have had an effect on Pitt Water 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.

The ecological character of a wetland is the sum of all the components, processes and services of that wetland. Ecosystem components are physical, chemical and biological parts of a wetland, from large-scale to very small-scale (e.g. habitat, species and genes). Ecosystem processes are the dynamic forces within an ecosystem. They include all those processes that occur between organisms and within and between populations and communities, including interactions with the non-living environment that result in existing ecosystems and bring about changes in ecosystems over time. Ecosystem services are the benefits that people receive from ecosystems.

This document describes the critical components, processes and services for the Pitt Water - Orielton Lagoon Ramsar site. Critical components and processes within the site are climate, hydrology, water quality, geomorphology, wetland vegetation, fish and birds. Critical ecosystem services have been identified as pollution control and detoxification, potential moderation of the effects of sea level rise in some areas, nutrient and sediment cycling, and the maintenance of biodiversity. The description also identifies limits of acceptable change which describe the range of variation which key aspects of the ecology of the site can vary without representing a change in the ecological character. Limits of acceptable change for Pitt Water-Orielton Lagoon have been proposed for all critical components, processes and benefits and services based on existing data.

The ecological character description also describes the current Ramsar listing criteria met by the site, the key threats and knowledge gaps for Pitt Water - Orielton Lagoon. Recommended monitoring needs and communication messages are also provided.

Further information on what Ecological Character Descriptions are and how critical components, processes and services are identified is available in the National Framework and Guidance for Describing the Ecological Character of Australian Ramsar Wetlands – Module 2 of the National Guidelines for Ramsar Wetlands – Implementing the Ramsar Convention in Australia.