Coastal freshwater wetlands: the forgotten (wet)lands

By PhD candidate Rebekah Grieger

Read Time: 468 words about 4 minutes.

Wetlands are important features in the coastal landscape, providing many important ecosystem services. Much of the research into coastal wetlands focuses on the salty ones – mangroves, saltmarsh, seagrass – but there are equally important wetlands just up-stream that are generally overlooked, coastal freshwater wetlands. 

Our recent review synthesises the current knowledge regarding impacts of climate change on coastal freshwater wetlands globally, highlighting key knowledge gaps and future research and management opportunities.  

Melaleuca swamp in southeast Queensland. Photo: R. Grieger 

Coastal freshwater wetlands (CFW) are freshwater wetlands that exist in coastal lowlands and have the potential to be impacted by coastal forces through saline intrusion and tidal inundation. In Australia, these are generally paperbark (Melaleuca) or she-oak (Casuarina) swamps which occur landward of saline wetlands. 

Due to their position, in non-tidal areas of favourable land for agriculture or urban developments, approximately 50 % of CFWs have been lost in Queensland since European development.  

Climate change – particularly sea level rise – poses a significant threat to coastal wetlands. The general academic consensus is that saline wetlands will expand inland into available areas, however this is likely to be at the cost of adjacent freshwater wetlands. 

CFW research is currently America-centric and mainly focuses on wetland responses to sea level rise, where freshwater species are negatively affected by saltwater and flooding. The impacts of rising seas are apparent in many regions of the US coastline, forming ghost forests where trees have died, and the understorey is transformed by salt tolerant species. 

The impacts of rising seas are apparent in many regions of the US coastline, forming ghost forests where trees have died, and the understorey is transformed by salt tolerant species. 

Ghost forest in the Nags Head Woods ecological preserve, North Carolina, USA. Photo: Raleigh, NC.

But, climate change impacts on CFWs extend well beyond the response of vegetation to saltwater. Many researchers suggest that accretion (accumulation of sediments and organic material in the soil) will allow saline wetlands to gain elevation, keeping pace with sea level rise. Of the little research in CFWs, accretion rates are variable and in most cases are not sufficient to keep pace with sea level rise. As a result, CFWs will have to migrate inland to survive, just like the saline wetlands. However, little evidence suggests that CFW species can migrate inland and, in many areas, CFWs border on development, leaving no space for migration even if it was possible. 

Unfortunately, this suggests a rather bleak outlook for CFWs – perhaps even worse than the expected changes to salty wetlands. We do, however, suggest further research to better inform our understanding of impacts and change, specifically into the impacts of temperature changes on CFWs. Further, climate change is inherently multiplicative and multiple stressors tend to be more damaging in combination than in isolation, where this has received little research attention. We also suggest that consideration be given to expansion of current wetland protection areas and incentives for wetland reclamation of agricultural land as options to facilitate CFW survival in a changing climate.  

Notes:

You can find Rebekah’s paper in Climatic Change here

Follow Rebekah Grieger on Twitter here: @Bek_Grieger 

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