ESTUARY WETLANDS AND SEA-LEVEL RISE

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Over the past three decades or so much has been written on the response of wetland ecosystems bordering estuarine waterways to sea-level rise. In some ways this followed many geological studies supported by radiocarbon dating and lots of coring in marshes and swamps in the northern hemisphere where continued sea-level rise in the late Holocene has left behind a distinctive buried record of marine transgression. It is not surprising that those involved in such studies have maintained an interest in the potential impacts of sea-level rise associated with global warming. An example is the early paper by Ellison and Stoddart on “Mangrove ecosystem collapse during predicted sea-level rise: Holocene analogues and implications” (Journal of Coastal Research, 1991, 151-165).

In Australia, Colin Woodroffe has continued this tradition. Colleagues such as Neil Saintilan and Kerry-Lee Rogers and their students have undertaken outstanding field studies including experiments and modelling of the impacts of water-level changes on sediments and habitats around different estuaries. A recent 2019 paper by Saintilan et al. in Wetlands (39, 1145-1154) on “Climate change impacts on the coastal wetlands of Australia” is a good example. Their work highlights the importance of these habitats as a depository of blue carbon.

I have been very interested in a recent set of publications (2019) that have arisen out of work undertaken by another group of authors associated with the Coastal Processes and Responses Node that formed part of the NSW Adaptation Research Hub. This was established by the former NSW Office of Environment and Heritage (OEH) in 2013. The Node has produced a set of guidelines for assessing climate change risk in estuaries with a focus on NSW conditions. The project involved many partners and was led by the Sydney Institute of Marine Science (SIMS). I am indebted to Will Glamore, one of the key authors, for supplying me with hard copies of the guidelines; they represent a valuable addition to the literature on potential adaptation responses to the impacts of climate change in estuaries.

The 2019 guidelines take the form of a series of eight modules (available online: https://estuaries.wrl.unsw.edu.au/climatechange). Each module is a stand-alone document addressing aspects of assessing climate change risks in estuaries. The following are the titles of each module:

  1. Introduction: climate change in estuaries—state of the science and guidelines for assessment.
  2. Prioritizing climate changes.
  3. Physical responses to climate change.
  4. Ecological responses to climate change.
  5. Managing local stressors to enhance ecological resistance.
  6. Application of the framework.
  7. Physiological thresholds and ecological responses of NSW estuarine species.
  8. Knowledge gaps and research needs.

The comprehensive nature of these modules builds on extensive research of those noted above as well as others from OEH such as the team led by Dave Hanslow that developed tidal inundation projections in different types of estuaries (see download at NSW Estuary Tidal Inundation Assessment Report 2018) which highlights the strong commitment that the NSW Government has made to coastal science over the past decade; long may it continue.

 A recent paper by Rayner et al. on “Intertidal wetland vegetation dynamics under rising sea levels” (Science of the Total Environment, 766,2021, 144237) tested many aspects of this research at a Ramsar listed Tomago wetland. Their work highlights various challenges of managing intertidal wetlands under future sea-level rise and vertical accretion scenarios. Their results indicate that the current rate of sediment capture by wetland species, and the subsequent rate of elevation change, will need to increase significantly to adapt with projected rates of sea-level rise. Again this highlights the importance of long-term field studies in defining threshold situations in east coast estuaries. This will be a matter for further consideration this year.

One aspect of estuarine wetland resilience is the way changes in condition and location are reflected in the NSW Coastal Management Framework. The Coastal Management Act 2016 not only highlights climate change impacts as a matter for consideration in the objects of the Act (s.3 (f) (i)), but most importantly in s. 6 (2) (c) it states as an objective “to improve the resilience of coastal wetlands and littoral rain forests to the impacts of climate change, including opportunities for migration”. This point is reinforced by development controls for wetlands and their proximity areas as defined in the NSW Coastal Management SEPP 2018. The Coastal SEPP serves to promote the objects of the Act through the mapping of wetland areas. I understand that such a clause in legislation, where it is tied to mapped areas, is unique in Australia and perhaps globally. The challenge will be to ensure that it is used by coastal managers when the occasion arises.

Bruce Thom

Words by Prof Bruce Thom. Please respect the author’s thoughts and reference appropriately: (c) ACS, 2021. For correspondence about this blog post please email austcoastsoc@gmail.com

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