New research shows that rising salinity in coastal lagoons is reshaping ecosystems, but restoring freshwater flows can quickly reverse the damage.University of AdelaideSalinity in coastal lagoons is increasing due to a combination of climate change and human activity, a new study shows. Rising salinity is reshaping microbial communities in these waters and threatening the critical role they play in ecosystems.
Salinity in coastal lagoons is rising, disrupting delicate microbial balances and threatening biodiversity. But targeted repairs can reverse this damage surprisingly quickly. (Aerial view of Magrath Plains in Coorong National Park, South Australia.)
Coastal lagoons are more than just scenic spots by the sea. They are important ecosystems that support fish and bird habitats, help capture carbon, cycle nutrients, and sustain local fisheries. As the salinity of these environments increases, the balance of life within them is being disrupted, putting biodiversity and ecosystem health at risk.
"Under normal circumstances, lagoons are nurseries for fish and crustaceans, are internationally important feeding grounds for migratory birds, and protect the coast from storm surges," said the university's Dr Chris Kennelly.
"Their microbial makeup allows this to happen, recycling nutrients and promoting high productivity so that a variety of plants and animals can thrive. However, a hot, dry summer like the one we recently experienced can completely turn this important habitat into a salty green soup, causing microbial diversity to decrease and salt-tolerant microorganisms becoming more dominant. Key processes such as nitrification, denitrification and carbon cycling are disrupted, altering nutrient retention, organic matter decomposition and greenhouse gas emissions."
Birds gather beneath the sand dunes of Lake Coorong in South Australia. Photo credit: Darcy Whitaker
Trends in hypersalinity in coastal lagoons are global and occur most frequently in arid and semi-arid coastal lagoons, such as those in Australia, the Mediterranean, and the Persian Gulf. This phenomenon has accelerated in Australia over the past 40 years.
"The rise in salinity can be attributed to rising temperatures, increased evaporation, reduced rainfall and freshwater input, and rising sea levels," said Dr. Kennelly, whose recent research was published in Earth Science Reviews.
"Anthropogenic factors such as upstream water diversion, urbanization and development, and groundwater depletion have also reduced the amount of freshwater flowing into coastal lagoons. We can mitigate the impacts of these activities by restoring environmental flows. Allocating water to the environment can sustain lagoon flushing, while upgrading sewage treatment plants, rebuilding wetlands and And increasing efforts to retain nutrients in agricultural lands in catchments around the world can reduce nutrient runoff. To mitigate the effects of drought or sea level rise, we can also reopen closed tidal inlets to improve mixing, or improve salt-tolerant vegetation cover to trap sediment and slow evaporation."
Lagoons can recover incredibly quickly when properly flushed. Following the record-breaking Murray-Darling River floods in 2022, the microbial community in South Australia's Coorong Lagoon returned to a healthier, more diverse state in just a few months, demonstrating that timely freshwater input can quickly reverse "salty soup" conditions.
Addressing the lagoon's high salinity and nutrient pollution issues benefits the ecosystems it serves while mitigating impacts on human health.
"Fish kills can damage local fisheries, algae blooms can produce toxins or air irritants, and the loss of seagrass can weaken coastal flood defences," Dr Keneally said. Emerging research also suggests that the degradation of ecosystems could make these ecosystems powerful sources of greenhouse gas emissions, exacerbating climate impacts beyond coastlines. "
Compiled from /ScitechDaily