|SALTWATER WETLANDS – A GUIDE TO REHABILITATION
Department of Environment and Climate Change
Along parts of the NSW coast up to 70% of wetlands have been destroyed over the last 200 years (for example, the Illawarra region, Merrin and Chafer 2000). In heavily populated areas, such as the Sydney region, even greater losses of wetland types such as saltmarsh have occurred (Stricker, 1995). In many cases remaining wetlands have been severely degraded. Degradation of coastal wetlands has resulted from poor catchment management practices, land reclamation, pollution of surface and groundwater, agricultural drainage works and construction of navigation channels, ports and canals.
In some locations wetlands continue to be degraded through urban encroachment and vandalism. Impending climate change is likely to further threaten these fragile environments. Action undertaken by communities now to recognise vulnerable areas and implement rehabilitation measures will provide the best chance to help these remaining wetland systems to adapt into the future.
The NSW Department of Environment and Climate Change and NSW Department of Commerce have prepared the Saltwater Wetlands Rehabilitation Manual to assist coastal communities to rehabilitate and manage degraded saltwater wetlands.
What is the Saltwater Wetlands Rehabilitation Manual?
The Saltwater Wetlands Rehabilitation Manual has recently been completed by the Department of Environment and Climate Change (Estuary Management Program) and Department of Commerce (Manly Hydraulics Laboratory). The manual provides not just an understanding of saltwater wetlands, including their hydraulic, physical, chemical, biological and ecological processes, but also guidance in undertaking the rehabilitation process from planning to implementation to maintenance and monitoring.
What are saltwater wetlands?
Saltwater wetlands are those wetlands whose inundation regime and vegetation characteristics are influenced by brackish or saline waters. These wetland types include swamp forest, saltmarsh, mangrove forest and seagrass beds.
Why are saltwater wetlands important?
The range of services derived from saltwater wetlands are substantial and varied, they include habitat value, food production, waterway and riparian protection, nutrient cycling, flood control, water quality improvement and recreational amenity. The importance of individual wetland types are briefly summarised below.
Swamp forests are generally associated with clay-loams and sandy loam soils, where the groundwater is saline or sub-saline, on waterlogged or periodically inundated flats, drainage lines and estuarine fringes associated with coastal floodplains. As a buffer between dry land communities and the estuary the community is important in terms of habitat value, riparian protection, flood control and water quality improvement. The structure and species composition can vary considerably based on physical factors, however in NSW, many will consist principally of swamp oak (Casuarina glauca), paperbark (Melaleuca spp.) or swamp mahogany (Eucalyptus robusta), the understorey is characterised by vines, shrubs, and a groundcover of forbs, sedges, grasses and leaf litter.
Saltmarshes occur at the upper levels of the intertidal zone. They are not subject to daily tidal inundation but are flooded by larger tides. Saltmarshes have a number of important structural functions including flood and erosion control, buffering storm surges, and improving water quality by filtering pollutants and excess nutrients. They support a rich and diverse community of invertebrates, provide roosting sites for many species of birds, and also provide habitat for juvenile fish when inundated. In NSW, saltmarshes are characterised by herbaceous species such as samphire (Sarcocornia quinqueflora), saltwater couch (Sporobolus virginicus) and rushes (for example, Juncus kraussii).
Mangroves grow along the shorelines of many NSW estuaries in areas subject to regular tidal inundation. In addition to structural functions such as erosion control and buffering of storm surges, mangrove forests are important habitats for fish, molluscs, crabs, bats and birds, and the trees provide large amounts of organic matter as a food source for the estuarine system. The two most common species in NSW are grey mangrove (Avicennia marina) and river mangrove (Aegiceras corniculatum).
Seagrasses occur in the subtidal zones of estuaries. Seagrass meadows are important in sustaining recreational and commercial fisheries, maintaining sediment stability and water quality in estuaries and providing food and shelter for fish and invertebrates. The most common species in NSW are eelgrass (Zostera spp.), paddleweed (Halophila spp.), strapweed (Posidonia australis) and sea tassel (Ruppia spp.).
Why rehabilitate saltwater wetlands?
It is estimated that over 60 percent of the coastal wetlands of NSW have been lost or severely degraded over the last 200 years (Bowen et al., 1995).
Increased community awareness of the ecological significance of wetlands has created greater interest in the preservation of existing wetlands, rehabilitation of degraded wetlands and the construction of wetlands. The destruction or degradation of wetlands, the resultant loss in ecosystem services and the desire to reinstate some or all of those values are common issues that have been raised in many natural resource management plans developed in NSW.
A number of saltwater wetland vegetation types (eg. coastal saltmarsh, swamp oak floodplain forest) have been declared as endangered ecological communities as it is considered that they are likely to become extinct in nature in NSW unless the circumstances and factors threatening their survival cease to operate (NSW Scientific Committee, 2004a and 2004b)
Rehabilitation projects usually aim to protect or restore some of a wetland’s values. A key goal of wetland rehabilitation is to maintain an ecologically healthy system that is functioning to a feasible condition, maintains its structure over time and is able to recover from some level of stress.
Why prepare the Saltwater Wetlands Rehabilitation Manual?
In conjunction with the growing awareness of the ecological significance of wetlands in recent years there has been an increase in the amount of information available in Australia regarding the design, use and management of constructed and rehabilitated wetlands. As such techniques used in all aspects of wetland rehabilitation including construction, propagation and planting, and monitoring are increasingly being used and reported on. The NSW Estuary Management Program (now part of the Department of Environment and Climate Change) with Manly Hydraulics Laboratory (Department of Commerce) has brought together information relevant to saltwater wetland rehabilitation into the form of an easy to use manual to guide the wetland rehabilitation process.
The aim of the Saltwater Wetland Rehabilitation Manual is to provide technical information and guidance to assist with the rehabilitation of degraded saltwater wetlands, that is, restoration to a feasible functional condition. A wetland’s functional capacity relates to its ability to perform natural functions, such as providing habitat or performing biogeochemical transformations.
How does this manual differ from The Constructed Wetlands Manual?
Given the aim of the Saltwater Wetland Rehabilitation Manual is to provide technical information and guidance to assist with the rehabilitation of saltwater wetlands, the manual was prepared as a complementary volume to The Constructed Wetlands Manual (Department of Land and Water Conservation, 1998). The Constructed Wetlands Manual provides readers with guidance to plan, design, construct and operate a freshwater constructed wetland. Whilst The Constructed Wetlands Manual is useful in providing guidelines and general information on wetland rehabilitation, it does not specifically address the rehabilitation of saltwater wetlands.
Why should the manual be used?
If you require general information on saltwater wetlands or are embarking upon a rehabilitation project the Saltwater Wetland Rehabilitation Manual has been prepared in order to provide not just an understanding of the functioning of saltwater wetlands, but also guidance throughout the rehabilitation process from planning to implementation to maintenance and monitoring.
Saltwater wetlands have complex hydraulic, physical, chemical, biological and ecological interactions which are quite different from freshwater wetlands and which need to be understood and addressed before undertaking rehabilitation projects. Furthermore, there are significantly different issues for excavation and construction works in saltwater wetlands, due to the physical (low strength, saturated conditions) and chemical (potentially low pH, highly saline and high organic content) nature of soils in these areas.
Although the science of rehabilitating estuarine wetlands is still in its relative infancy in Australia, quite a number of restoration projects of various scales have been undertaken. A comprehensive literature review has informed the preparation of the manual. A bibliography is included to ensure an authoritative document, and allow the reader to follow up more detailed information if required.
The manual should be used where:
sufficiently detailed information is required to design, implement, manage and monitor a saltwater wetland rehabilitation project;
a logical and robust process for wetland rehabilitation, capable of accommodating developing technologies, information, concepts and ideas should be applied; and
detailed information is required to convey the complexity of saltwater wetlands ecosystems to assist with planning and management of wetland rehabilitation projects.
Guidance on the rehabilitation process from planning to data collection and design, plan preparation and implementation through to operation and maintenance is provided. Where possible, the manual includes simple guidelines to address some of the tasks involved in wetland rehabilitation.
Who should use the manual?
The manual has been prepared for an audience that includes:
technical staff in Local government (engineers, planners and landscape architects);
technical staff in government agencies;
consulting firms and construction companies;
potential operators, managers and owners of rehabilitated saltwater wetlands (private landholders, agencies, Local councils, community groups and schools); and
How should the manual be used?
The ‘Saltwater Wetland Rehabilitation Manual’ is structured into three sections:
Overview of saltwater wetlands;
Planning and implementation for rehabilitation projects, including:
Data collection and plan preparation;
Operation and maintenance;
Monitoring and reporting;
Characteristics and processes of saltwater wetlands, specifically:
Legislation and Policy.
Section 2 of the manual provides a process for the effective rehabilitation of saltwater wetlands which encourages rehabilitation based on accurate assessments of the problems, in a manner which is adaptive, and therefore able to be changed in response to changing conditions or additional information.
The scale and location of the project being undertaken will determine the effort required in the various stages of the process, however all stages are important to consider and will assist with effective outcomes. Many saltwater wetland species require specific environmental elements for successful establishment and growth. Tidal influence, elevation and topography are essential components to get right in the overall plan and design.
The selection of a suitable site for rehabilitation will depend on local conditions, works required and the species to be encouraged or planted. Some aspects of rehabilitation will be more important in some locations than others, for example, designing saltmarsh rehabilitation so as to minimise mosquito numbers will be more important in wetlands adjacent to urban areas. A flowchart of the suggested process for undertaking rehabilitation projects is presented in Figure 1.
Section 3 provides an overview of characteristics and processes important to the understanding of saltwater wetlands through the inclusion of detailed background information on saltwater wetland flora and fauna, physical processes (including surface water and groundwater characteristics and processes) and soils. A chapter on Commonwealth and NSW legislation and policy relevant to saltwater wetland rehabilitation is also included.
Technical appendices provide detailed information relevant to Section 2 such as information on carrying out topographic/bathymetric surveys and tidal gaugings, planting information and construction materials in the saline environment.
Figure 1: Management process to achieve effective rehabilitation of saltwater wetlands.
Who prepared the manual?
The production of the Saltwater Wetlands Rehabilitation Manual has involved contributions from numerous people with skills in various saltwater wetland related disciplines, including: Kerryn Stephens (Department of Environment and Climate Change), Dayle Green, Dr Pia Laegdsgaard, Dr David Rissik, Andrew Rawson, Susan Fox (Department of Natural Resources), Dr Ian Turner (University of New South Wales, Water Research Laboratory), Peter Nelson and Ann Finnigan (Shortland Wetlands Centre), Dr Julie Phillips (EcoAlgae Research Pty Ltd) and Phil Anderson, Dr Brian Wallace, Michael Barratt (Manly Hydraulics Laboratory).
The production of the manual was managed by David Miller (Department of Environment and Climate Change) and David Van Senden (Manly Hydraulics Laboratory).
The manual benefited from review by a number of government and non-government wetland practitioners.
Bowen, R., Stephens, N. and Donnelly, P. (1995). SEPP 14 - wetland protection and the role of mitigation. Wetlands (Australia), 14: 6 - 12.
Department of Land and Water Conservation (1998) The Constructed Wetlands Manual Volumes 1 and 2. Department of Land and Water Conservation, New South Wales.
Merrin J. and Chafer C. (2000) Illawarra Wetlands Action Plan, Illawarra Catchment Management Committee, Wollongong.
NSW Scientific Committee (2004a) Coastal saltmarsh in the NSW North Coast, Sydney Basin and South East Corner bioregions - endangered ecological community listing - final determination. NSW National Parks and Wildlife Service.
NSW Scientific Committee (2004b) Swamp oak floodplain forest of the NSW North Coast, Sydney Basin and South East Corner bioregions - endangered ecological community listing - final determination. NSW National Parks and Wildlife Service.
Stricker, J. (1995). Reviving Wetlands. Wetlands (Australia), 14: 20 - 25.