Coastal Wetlands are under pressure. They face rising seas from climate change, but their biggest obstacle to migrate naturally inland is human development with roads, houses and other infrastructure blocking their way. And our urban planners are largely unaware of this tricky situation.
We all love to live beside the sea, but coastal urban development and rising seas will increasingly threaten sensitive coastal wetlands with no room to move and imperilling the survival of their unique plants, birds and fish.
Our urban planners have taken a stable sea level for granted with development to date, often destroying wetland environments for coastal development, agriculture and aquaculture.
More recent urban planning incorporating sea level rise predictions places an emphasis on the threat to peoples houses, roads, railway embankments and other human infrastructure. But planning also needs to encompass the coastal wetland environments that share our coastlines. These ecosystems will also need to migrate inland as the ocean rises.
You can see in this November 2009 report from ABC News posted on youtube that all the emphasis on the impact of rising seas on Australian coasts is on the damage to human infrastructure. Adaptation by coastal ecosystems is not mentioned at all
Researchers at the Australian Research Council (ARC) Centre of Excellence for Environmental Decisions (CEED) say Australia's planners and coastal communities need to think up to 100 years ahead to ensure the survival of mangroves, salt marshes, sedge lands and melaleuca swamps and their wildlife.
"Sea levels are currently predicted to rise by up to 1 metre during this century - and there are indications they may be rising even faster than this," says Dr Jonathan Rhodes of CEED and The University of Queensland. A recent study published in November 2012 found that Sea Level rising 60% faster than IPCC projections.
"In past periods of rising sea levels, coastal wetlands have coped by migrating inland as the salt waters rose - but today, especially along the east coast of Australia, they are likely to run into urban development on and behind the coast.
"Unless we can make room for them to move, there is a risk they may go locally extinct - along with the bird, fish and other wildlife they support, and the services they provide to humans."
Coastal wetlands, mangroves and salt marshes are important hotspots for biodiversity providing nursery facilities for many fish species, and important wetland environments for endemic and migratory bird species, the more important ones listed as RAMSAR wetlands. Australia's extensive areas of mangroves (100,000 hectares) and seagrass (>500,000 hectares) are a significant proportion of the global carbon-intensive vegetated coastal ecosystems.
They are high efficiency carbon sinks sequestering carbon in the sediment layers that build up over time. Along with seagrass meadows, they are known as 'blue carbon' sinks. They can sequester carbon far more effectively (up to 100 times faster) and more permanently than terrestrial forests.
In an email comment Dr Jonathon Rhodes said "Coastal wetland are important carbon sinks and is another reason why don’t want to lose them."
Dr Rhodes and his colleagues Ms Rebecca Runting and Dr Morena Mills have been using a computer model called SLAMM (Sea Level Affecting Marshes Model) to identify areas where coastal wetlands would naturally retreat to as the ocean comes up - and where existing or future urban development may clash with this.
"It isn't just about looking at the land contours - you also have to factor in changes in erosion and sediment deposition, in salinity levels and the effects of man-made structures, if you want to work out where mangroves and salt marshes could move to in the future," Ms Runting says.
"These models give you a much better idea of what is going to happen than the so-called 'bath-tub' models that only account for water level. Importantly too, if you're a coastal planner or conservation manager, it makes planning decisions much more cost-effective."
Dr Rhodes says that while many Australian coastal cities and towns now take steps to conserve their existing mangroves and salt marshes, these may prove in vain if they don't look and plan a century or more ahead to account for rising sea levels, which will bring dramatic change to coastal landscapes.
Another important ecological service of coastal wetlands is the natural shield they provide from coastal flooding, the impact of storms and storm surge. "they are really important as coastal defences. We can put up sea walls as defences, but there is no guarantee that they will work, and we will also lose the wetlands in the process. The services provided by coastal wetland in terms of coastal defence provide solutions that provide much more resilience to coastal communities than sea walls." said Dr Rhodes.
"It's true you can build a one kilometre long sea wall at a cost of about $7-8 million per metre in height and put urban development in behind it - but the reality is that we're not going to be able to defend the entire Australian coastline with such measures, as sea levels will keep on rising as long as the climate is warming and the polar ice melting."
The Australian Marine Climate Report Card for 2012 section on Tidal wetlands describes the major problem facing coastal wetlands caught between the rising ocean and human development: (pp159)
"The largest threat to the resilience of intertidal wetlands with climate change is the presence of barriers that will prevent the landward migration of intertidal wetland communities. Barriers to landward migration of intertidal communities can be imposed by natural features e.g. steep slopes, but urban, agricultural and other human developments that build berms, bunds, seawalls and roads on coastal plains impose significant threats to resilience of mangroves, salt marsh and salt flats with sea level rise. Barriers also reduce connectivity between ecosystems and overall productivity (Skilleter et al. 2005). Landward barriers to wetland migration will have particularly negative consequences for salt marsh and salt flat communities that are compressed between human imposed landward barriers and encroaching mangroves (Saintilan and Williams 1999, Adam 2002, Saintilan et al. 2009). Landward retreat is currently inhibited in NSW by in excess of 4000 impediments to tidal flow (Williams and Watford 1997). One third of these impediments, if removed or regulated, would provide opportunities for wetland restoration (Williams and Watford 1997).
"It means that low-lying communities and their native ecosystems are going to have to move - and we should begin planning right now for where they might move to."
The team's research indicates that under sea level rise, mangroves may be initial winners and salt marshes losers in the struggle for new places to survive - but if the rise accelerates, even mangroves may fail to keep up, and require human assistance to translocate and protect them. The same applies to threatened native animals such as the false water rat, which suffers from cat predation as its mangrove habitat becomes increasingly impacted by urbanisation.
Tidal marshes and mudflats near Queenscliff on Port Philip - Image by Takver
Dr Mills says that many cities and towns are proud of the way they are managing to incorporate native Australian landscapes, vegetation and wildlife into their plans for the future. Now, for sea-side communities, these plans need to take account of the area of land needed to accommodate coastal wetlands displaced by the rising tides.
Dr Rhodes added "Potentially, low lying suburbs that become increasingly flood-prone under climate change may need to be abandoned as the cost of defending them becomes too high - but if these were highly urbanised, it may be very difficult to return some of these areas to natural wetlands".
"Sea level rise means that anyone and anything that lives along the coast has to be ready and willing to move - and our research is helping provide the answers about where they might move to, in plenty of time to do something about it."
According to the Australian Marine Report Card for 2012, mangroves have been able to hold their own with current sea level rise of 1 to 3 mm per year. "Whether mangroves and saltmarshes will persist in their current distribution and abundance will depend on the rate of sea-level rise. Preliminary results from the SE Australian surface elevation table (SET) network indicate that mangroves have been able to increase elevation primarily as a result of sediment accretion, at a rate comparable to the rate of sea-level rise over the past decade, of 1-3 mm per year. Saltmarshes have not been able to maintain this rate of vertical accretion and have been colonised by mangroves."
Under the IPCC projections of the rate of sea level rise by the end of the century of 10mm per year, "It is unlikely that mangroves will persist in their current position in the landscape given these rates of sea-level rise." says the report (pp158)
I asked Dr Rhodes what would be the impact if sea levels rose much faster than the 1 metre rise they currently use in their models. Some sea level projections give a maximum rise this century of 1.9 metres, and if sea level rise adopts an exponential rate as argued as a possibility by NASA climatologist James Hansen, then it may be 5 metres or more.
Dr Rhodes responded to my question, "Yes, you’re right seal levels could rise much more than 1 m. In this case, wetlands have more difficulty “keeping up” and we tend to see reductions in coastal wetland extent. This makes it even more important that we plan for these possibilities and not prevent any potential migration of wetlands."
I have been aware of the importance of coastal wetlands only relatively recently through my reading of scientific studies of their ecological biodiversity, the environmental services and benefits they provide, and climate importance as carbon sinks. At the Climate Commission Melbourne Public Forum in July 2012 I asked Professor Lesley Hughes, an ecologist in the Department of Biological Sciences at Macquarie University and an expert on the impacts of climate change on species and ecosystems, about what long term planning had been done so far to encourage the migration of coastal wetlands inland as sea level rises. Her brief answer to me? None.
This is a major failing in climate adaptation planning for coastal areas and needs to be urgently addressed at all levels of Government to take into account the importance of wetland ecosystems and the valuable services they provide to human communities.
When I asked Dr Rhodes how do you convince planners of the importance of long term planning for wetlands and to make significant allowance in planning schemes for wetlands migration inland he responded:
"I don’t think the migration of wetlands inland has really been considered yet by planners. So, one of the first things we need to do is make planners aware that this is likely to happen and to provide predictions of where wetlands may move to. Also, emphasising what the consequences are if sea level rise is not considered in their environmental planning is also important. This is what we are trying to do at the moment." explained Dr Rhodes.
Sea level rise for coastal wetlands is a global problem. This timelapse video on youtube from the US Geological Service of a high tide in 2010 shows how sea-level rise will affect the China Camp marsh in the San Francisco Bay. Only 12 percent of salt marshes in San Francisco Bay will still be around by 2100 due to sea-level rise, according to a USGS report. "Seven of the marsh sites we surveyed had adjacent open space, but five marshes were surrounded by urban infrastructure prohibiting upslope movement."
The importance of coastal wetlands for blue carbon has been recognised by the United Nations Environment Program who launched a new web portal in December 2012 - bluecarbonportal.org - to provide news and initiatives for people actively working in or interested in blue carbon and the role of our coasts and oceans as carbon sinks. The UNEP media release describes the global problem of degradation and destruction of coastal wetland and marine environments:
"More than half of the world's original mangrove forest has disappeared, often due to the conversion of habitat for shrimp and fish aquaculture. Over-exploitation of wood products, urbanization, and diversion of fresh water flow are other major drivers or degradation. The annual global rate of mangrove loss is presently between 1 and 2 per cent."
"Seagrass meadows are found on every continent except Antarctica, with a global area estimated to exceed 177,000 km2. This is a reduction of 30 per cent in the last 100 years, and the rate of loss is thought to have accelerated considerably in the past 40 years."
There is an active Australian program of protection of wetlands and restoration of degraded coastal ecosystems from pollution and siltration. WetlandCare Australia have been protecting, promoting and restoring Wetlands in Australia since 1991.
But we also need to start long range planning, by all levels of Government, to allow coastal wetland ecosystems to migrate inland as sea level rises. The work of Dr Rhodes and his colleagues is an important start in providing the necessary tools and ecosystem information for planners to use effectively. It would be an environmental disaster to see these ecosystems, and the valuable economic and environmental services they provide, decline due to poor planning as we ramp up adaptation plans for sea level rise due to climate change.
- Australian Research Council Centre of Excellence for Environmental Decisions. (CEED') media release, 14 January 2013 - Australia's Coastal Wetlands 'need room to move' (PDF)
- Interview by email with Dr Jonathon Rhodes, 18 January 2013
- Lovelock CE et al. (2012) Tidal wetlands. In Marine Climate Change Impacts and Adaptation Report Card for Australia 2012 (Eds. E.S. Poloczanska, A.J. Hobday and A.J. Richardson). Retrieved from www.oceanclimatechange.org.au 17 January 2013
- United Nations Environment Programme (UNEP) media release, 19 December 2012 - New Website Puts Spotlight on Blue Carbon
- Australian Online Coastal Information - Changes in coastal wetland coverage
- Images of coastal wetlands on the Eyre peninsula and near Queenslcliff by Takver