Climate change and human activity are transforming vital coastal lagoons into hypersaline hotspots—threatening biodiversity, fisheries, and even the planet’s carbon balance.
Key Points at a Glance
- New research finds rising salinity is damaging coastal lagoons across arid regions worldwide.
- Heat, drought, sea-level rise, and human water use disrupt microbial life and nutrient cycles.
- Vital processes like carbon cycling and denitrification are breaking down under salt stress.
- The Coorong Lagoon in South Australia exemplifies both the threat and potential for recovery.
- Targeted interventions like restoring freshwater flow and wetlands can help reverse damage.
Beneath the dunes of South Australia’s windswept coastline, birds circle above the Coorong Lagoon—a once-thriving ecosystem now showing signs of distress. Across the globe, similar coastal lagoons are slipping into ecological crisis, as climate change and human intervention create an accelerating trend of hypersalinity. A new study from the University of Adelaide warns that these changes are transforming critical coastal waters into stagnant, salty “soups”—with profound consequences for biodiversity, water quality, and global climate feedbacks.
Coastal lagoons aren’t just pretty postcard scenes. They’re dynamic nurseries for fish and crustaceans, essential rest stops for migratory birds, and powerful carbon sinks that trap nutrients and protect coastlines from storm surges. Their hidden engines are microbial communities, microscopic powerhouses that drive nutrient recycling, organic matter decomposition, and climate regulation.
But according to Dr. Chris Keneally, lead author of the study published in Earth-Science Reviews, even a single extreme summer can unravel this balance. “Just one hot, dry season can shift a lagoon into a hypersaline, green-stained body of water dominated by salt-loving microbes,” he explains. “When that happens, key ecological processes start to collapse.”
Processes like nitrification, de-nitrification, and carbon cycling are severely disrupted in these “salty soup” conditions, changing how nutrients move, how carbon is stored, and how greenhouse gases are released. The result isn’t just a local loss of biodiversity—but potentially increased emissions of climate-warming gases from degraded waters.
This trend is not isolated. Across Australia, the Mediterranean, and the Persian Gulf, hypersalinity has risen over the last four decades. The primary culprits: elevated temperatures, reduced rainfall, increased evaporation, rising sea levels—and human impacts such as upstream water diversions, urban development, and groundwater depletion.
The Coorong, one of Australia’s most iconic coastal lagoons, illustrates the peril—and the potential for renewal. During the 2022 Murray–Darling floods, a surge of freshwater transformed the lagoon’s microbiome within months, bringing back diversity and restoring ecological functions. “It shows that these ecosystems are resilient if we act fast and give them what they need,” says Keneally.
What they need, according to the study, is strategic freshwater input. This can be achieved by restoring environmental flows—allocating water not for irrigation or industry, but for ecosystems. Reopening tidal inlets, planting salt-tolerant vegetation to trap sediment, and re-establishing wetlands can also help buffer against the effects of climate-driven salinization.
On the human side, the stakes are high. Algae blooms triggered by nutrient pollution can release toxins or airborne irritants, impacting health and local economies. Fish kills devastate fisheries, and the loss of seagrass weakens natural flood defenses. And beyond the shoreline, degraded lagoons may begin emitting more greenhouse gases, creating a feedback loop that worsens global climate change.
Still, there’s reason for hope. “A lagoon can bounce back surprisingly fast when it’s flushed and supported with the right measures,” says Keneally. With the right blend of ecological restoration, policy reform, and catchment-wide water management, we can pull these vital ecosystems back from the brink.
As sea levels rise and droughts intensify, coastal lagoons are more than just casualties of climate change—they’re frontline indicators of how Earth’s systems are shifting. Whether they remain biodiversity havens or devolve into lifeless salty basins may depend on what we do next.
Source: University of Adelaide
