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18 December 2023 4 min read

Key points

  • An estuary, where river meets sea, is a biodiversity hotspot essential for marine life and natural coastal protection.
  • The effects of climate change on estuaries are significant, given their trillion-dollar value in services and critical role in food security and infrastructure.
  • Blue carbon, captured by coastal ecosystems like mangroves, acts as an organic carbon 'sink' and helps mitigate climate change.

Climate change is impacting our environment from the land to the sea.  As the link between rivers and the ocean, estuaries are buffeted by climate impacts from both sides. 

As much as 90 per cent of the Australian population lives within 50 kilometres of the coast. So, the effects of climate change on estuaries could have big impacts on our everyday lives. This includes everything from food security to infrastructure. 

The importance of understanding estuaries and the increasing pressure they’re facing are highlighted in a new book, Climate Change and Estuaries, co-edited by CSIRO’s Dr Joey Crosswell along with Dr Michael Kennish from Rutgers University in New Jersey, USA and Dr Hans Paerl from the University of North Carolina

The book brings together 75 authors from ten countries to cover local and global perspectives on estuarine ecosystems.

So here are three facts about climate change and estuaries. 

Estuaries are ecological, cultural, and economic powerhouses

More intense storms are among many threats to estuary services such as biodiversity and blue carbon hotspots. For example, mangrove loss near the Starcke River, Junjuwarra country, has shown only minor recovery in the ten years since Cyclone Ita in 2014. ©  Joey Croswell, CSIRO

Estuaries play an important part in our lives. Globally, about 40 per cent of the population lives within 100 km of the coast. Experts estimate the global value of estuarine and wetland services to be in the trillions of dollars. This includes the ecological, economic, and societal benefits estuaries bring to countries all around the world.

Senior research scientist Dr Joey Crosswell highlighted many services we value in our daily lives are tied to estuaries. Estuaries are key to numerous industries, from recreational and commercial fisheries to aquaculture, tourism, electric power generation. Oil and gas operations, transportation, shipping and leisure activities also rely on them. 

"The world economy depends heavily on estuaries and the rich resources and services they provide,” Joey said. 

Beyond their immediate economic value, these dynamic environments have been cradles of civilisation. They have fostered human settlements and cultures for millennia. Historically, estuaries have served as natural harbours and gateways for exploration, trade, and cultural exchange, helping shape the course of human history.

“I like to think that estuaries hold deep cultural history that is invaluable to both our individual and shared identities."  

Joey, who has visited coastlines around the world, says a personal highlight of his own research is continually learning about the relationships between people and estuaries. 

Climate change threatens the vital role estuaries play

About 90 per cent of the Australian population lives within 50 km of the coast. ©  CSIRO

Joey said the consequences for water and food security are among the most fundamental risks posed by climate change. Beginning with access to clean water being threatened by saltwater intrusion due to sea level rise and altered hydrology. 

Meanwhile, surface waters are under siege from a cascade of environmental threats. Rapid and often toxic algal blooms are on the rise, posing risks to both wildlife and humans. Oxygen-starved waters, a state known as hypoxia, endanger marine life. Unprecedented marine heatwaves disrupt the balance of aquatic ecosystems. And the ongoing acidification of these waters, a result of absorbing excess carbon dioxide, is changing marine habitats.

Together, these challenges, fuelled by climate change and human impact, weave a complex web of stress on our aquatic environments.

“These risks are also inextricably linked to food security due to the reliance of fisheries and aquaculture on healthy coastal waters,” Joey said.

Infrastructure is also directly threatened by climate change. Intense storms, sea level rise, floods and other extreme events could impact coastal communities.

“The consequences include loss of land and intertidal wetlands, with adverse implications for biodiversity, ecosystem services and associated human livelihoods, particularly economies dependent on fisheries and tourism,” he said. 

The risks faced by estuaries vary compared to open coasts and even among different types of estuaries. For instance, lagoon-style estuaries and those formed at river deltas have different challenges. Similarly, estuaries in tropical regions face different issues than those located in higher latitudes.

“We structured Climate Change and Estuaries to help understand these processes. There are chapters focussing on specific drivers of change and specific habitats, while other chapters examine the interactive effects of multiple stressors on the structure and function of estuarine systems,” he said.

Estuaries could store away ‘blue carbon’ to mitigate climate change 

Blue carbon ecosystems like mangroves, seagrasses and tidal marshes lock away large quantities of organic carbon and support food security and livelihoods. ©  Lauren Hardiman, CSIRO

Blue carbon is a relatively young and rapidly evolving concept in carbon-cycle science. 

So, what is blue carbon exactly?

“It has often been simplified as carbon stored in coastal and marine systems. Most research over the past decade has focussed on stocks of organic carbon in mangroves, seagrass and saltmarshes,” Joey said. 

These vegetated coastal ecosystems can act as ‘sinks’ for organic carbon, in turn reducing the amount of CO2 in the atmosphere. They accomplish this mostly by storing it as soil carbon.

“Management actions aimed at preserving and enhancing these blue carbon stocks are therefore an important tool for climate mitigation. However, there is growing recognition that we need to ‘see the forest through the mangroves’ when it comes to blue carbon," he said. 

“That is, the deeper value lies in many cumulative benefits of vegetated coastal ecosystems. They support resilient and healthy coasts, including providing shoreline protection while sustaining fisheries and biodiversity."

The broad benefits of blue carbon have led to a recent focus on blue carbon habitats as ‘nature-based solutions’ for coastal adaptation, sparking major research initiatives within CSIRO and globally. 

The global value of estuarine and wetland services is estimated to be in the trillions of dollars and includes ecological, economic, and societal benefits. ©  Joey Croswell, CSIRO

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