Freshwater salinisation: a research agenda for a saltier world
Freshwater ecosystems across the world are becoming increasingly salty, with significant consequences for their health and biodiversity, and the pressing need for more research, according to a new study.
Freshwater salinisation is caused by salts entering rivers, lakes and streams as a result of human activities such as mining and intensive agriculture. Increased dissolved salt concentrations in water can place stress on aquatic organisms and reduce habitat quality. The ongoing effects of climate change, such as drought and sea level rise, are exacerbating freshwater salinisation in some areas.
Salinisation: an emerging freshwater pressure
Despite this increasing global threat, scientists still have patchy knowledge about the causes and consequences of freshwater salinisation. In response, a new open-access study proposes a global research agenda to better understand and manage the salinisation of freshwater ecosystems.
“The global [salinisation] tendency of lakes and streams is a great challenge for freshwater biodiversity, the functioning of ecosystems and human societies that depend on them,” says Professor Miguel Cañedo-Argüelles, from the Department of Evolutionary Biology, Ecology and Environmental Sciences, University of Barcelona.
“To address this challenge, we need a joint effort of the scientific community, practitioners, local communities and policy makers,” continues ICREA researcher Professor Sandra Brucet, from the University of Vic – Central University of Catalonia.
A scientific team from ten countries led by Dr David Cunillera-Montcusí from FEHM, University of Barcelona collaborated to provide an overview of current knowledge on the topic, and to provide directions for future research.
Improving global knowledge of freshwater salinisation
They suggest that global knowledge of freshwater salinisation has an unequal geography. For example, the ecological effects of salt spread on icy roads has been well studied in North America, but not in Europe. Moreover, there are large areas of Africa and South America where salinisation has barely been studied as a pressure on freshwater ecosystems. The authors also found that the salinisation of small freshwater habitats such as ponds – which are increasingly shown to be key for biodiversity across wide landscapes – is poorly studied.
This lack of knowledge is important, because scientists are increasingly showing that salinisation can negatively impact freshwater ecosystems. The authors write, “salinity is one of the main drivers of adaptation, speciation, and community assembly in aquatic systems.” Increasingly salty water can place significant stresses on the self-regulating fluid exchanges many organisms carry out with their environment. In some cases, this can cause species loss, altering the composition of freshwater foodwebs, and the impair the benefits – such as fisheries and drinking water – they can provide to human communities.
Freshwater salinisation can also cause significant alterations to habitat quality, for example by contributing to the acidification of water bodies and the mobilisation of toxic metals, or by altering natural water mixing patterns in lakes. In some areas, saltier freshwater ecosystems can become colonised by invasive saltwater species.
Preparing for a saltier world
Despite these threats, the study authors identify a lack of knowledge on the effects of different kinds of salts in aquatic environments, as well as their impacts at wider regional and landscape scales. They highlight that most existing salinisation studies focus on aquatic insects, meaning there is a need to study the responses of both microorganisms and top predators such as fish, reptiles and amphibians.
The need to understand the effects of freshwater salinisation on aquatic ecosystems, and the humans who depend on them, is exacerbated by the impacts of climate change. Ongoing alterations to patterns of rainfall and air temperatures globally have the potential to intensify salinisation by magnifying the effects of human pressures such as mining, urban run-off and intensive agriculture.
Accordingly, Dr. Miguel Matias, researcher at MNC-CSIC, concludes, ”with the collaborative effort of the international team of scientists that published the review paper, we want to promote this global effort in order to advance towards this direction and raise interest for this global problem that will lead us to a saltier world with many salinised lakes and rivers, and for which we must prepare.”
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