Oxygen is fundamental to life. The loss of oxygen in water, or aquatic deoxygenation, is a threat to life at all levels. In a newly published research paper in the journal Nature Ecology and Evolution, University of Regina Canada Research Chair in Environmental Change and Society, Dr. Peter Leavitt, and his international and Canadian collaborators, explain that ongoing deoxygenation presents a major threat to the stability of the planet.
"Oxygen is one of the main controls of many of the cycles that regulate the movement of material and energy around the planet," says Leavitt. "Oxygen loss from the world's marine and freshwaters is so pervasive that it threatens fundamental planetary functions, much the same way that climate change and biodiversity loss do."
Previous research identified a suite of global scale processes, referred to as Planetary Boundaries, that regulate the overall habitability and stability of the planet. These processes include things such as climate change, land use change, and biodiversity loss. If critical thresholds in these processes are passed, then major ecological, economic, and social challenges are likely to result. The researchers argue that aquatic deoxygenation both responds to, and regulates, other Planetary Boundary processes.
"It's important that aquatic deoxygenation be added to the list of Planetary Boundaries," says lead author Dr. Kevin Rose, from New York's Rensselaer Polytechnic Institute. "This will help support and focus global monitoring, research, and policy efforts to help our aquatic ecosystems and, in turn, society at large."
Across all aquatic ecosystems, dissolved oxygen concentrations have rapidly and substantially declined in recent decades. Lakes and reservoirs have experienced oxygen losses of 5.5 per cent and 18.6 per cent respectively since 1980. The oceans have experienced oxygen losses of around two per cent since 1960 and, although that number is smaller, the spread and volume of the world's oceans makes it significant.
In Canada, rates of oxygen loss from some prairie lakes exceed that of nearly all planetary surface waters. As oxygen declines it accelerates eutrophication - when a water body becomes overly enriched with nutrients leading to the growth of simple plant life, like algae - and water quality declines, leading fisheries to collapse.
Aquatic habitats with low oxygen levels are commonly referred to as "dead zones" because of their loss of aquatic life, which threatens ecosystem services like fishing, aquaculture, tourism, and cultural practices.
"It is essential that we avoid crossing over the oxygen threshold where normal microbes and invertebrates thrive. Without a solid base of the food web, we risk collapsing entire food webs in oceans and lakes," says Leavitt. "As we deplete oxygen, we can also cause a runaway decline in water quality, with oxygen poor sediments releasing nutrients that cause more eutrophication and deepwater oxygen loss."
Rose says we are approaching critical thresholds of aquatic deoxygenation that will ultimately affect several other Planetary Boundaries.
"Improving dissolved oxygen concentrations depends on addressing the root causes, including climate warming and runoff from developed landscapes. Failure to address aquatic deoxygenation will, ultimately, not only affect ecosystems but also economic activity, and society at a global level," says Rose.
