By Mia Dalby-Ball
Key words: Wetland, Saltmarsh, Intertidal, Urban Ecology, Construction
Introduction: Coastal Saltmarsh is an intertidal ecosystem under threat and currently listed on both the state (New South Wales (NSW)) and Australia’s national list as an Endangered Ecological Community. Saltmarsh provides a variety of ecosystem services, including providing habitat for crabs which then release larvae during some high-tides. Crab larvae from saltmarshes have been found to be key food for small fish.
Over 80% of urban saltmarshes in NSW have been filled for a range of uses including playing fields, often after their use as rubbish dumps. With an increase in awareness of the value of these ecosystems, the restoration of saltmarsh in urban areas is occurring globally and locally. Here we describe two saltmarsh reconstruction projects at Kooroowall Reserve and Gough Whitlam Park, Sydney.
Aim of the works. In each example the aim was to create a functioning saltmarsh – that is a saltmarsh with appropriate tidal inundation, appropriate plant species and cover and invertebrate species (e.g. crabs, molluscs).
Works undertaken. In both cases works commenced with soil testing (soil type, pollutants, acid sulfate soils and depth to ground water) followed by the development of a detailed design. Hydrology was observed from surrounding areas to identify location-specific elevations connected to nearby existing intertidal areas. Substrate was then excavated to the desired level, top-soil was put in place to provide appropriate nutrients, then planting carried out and/or natural regeneration encouraged.
Results to date. Around 80% cover of saltmarsh plant species has established and persists at both sites to date. (Figs 1 and 2.) Non-saltmarsh plants dominate the upper 5m of the Gough Whitlam Park as this was not excavated low enough, with a similar area occurring at the Kooroowall Reserve saltmarsh (Fig 3). Saltmarsh crabs and gastropods are present at both sites. Density of saltmarsh plants at both sites is greatest where the tidal inundation is most frequent. The before and after images show the dramatic change from a weed dominated, neglected area of fill (Kooroowall reserve) to Saltmarsh and from Turf (GWP) to Saltmarsh.
Natural regeneration and establishment of saltmarsh plants was highest where there was “wrack” covering the exposed sandy substrate. (Wrack is organic material such as washed up sea-grass or a mix of leaves fine twigs.) That is, saltmarsh seedlings that germinated in areas without wrack were found to die during consecutive hot dry days while those in wrack generally survived.
Lessons learned. Lessons include the importance of achieving the required tidal inundation. In both examples the level of some sections of the sites could have been lowered at the time of construction. In the case of Kooroowall an area of heavy clay was encountered and additional resources would have been required to implement the planned works. As the resources were not available, this was not done. The higher area now has Coastal Wattle growing on it, shading out the saltmarsh. There is now either a reoccurring cost to remove this plant, or if nothing is done, that area becomes terrestrial vegetation.
Fencing was found to be essential at the Kooroowall Saltmarsh as its proximity to a children’s play area resulted in it becoming a de facto bike jump area. No fencing was required at Gough Whitlam Park; however there is a high level of community engagement and interpretive signage.
It is likely that the wrack was beneficial in retaining moisture to assist survival of species.
Acknowledgements: Both Saltmarsh creation projects were facilitated and managed through local government. Kooroowall by Pittwater Council and Gough Whitlam Park by Canterbury Council. Both projects had grant funding (over 50%) from federal government sources distributed through the then Catchment Management Authorities. These agencies have now changed name to Local Land Services. Dragonfly Environmental designed the Saltmarsh re-creation and Gough Whitlam Park.
Contact: Mia Dalby-Ball, Director, Ecological Consultants Australia, 30 Palmgrove Road Avalon Beach Sydney NSW, 2107, Tel: +61 488 481 929, Email: firstname.lastname@example.org