������Ƶ

Researchers at the Royal Ontario Museum and University of Toronto estimate that 4.1 million tonnes of carbon dioxide and other greenhouse gases were released in 2020 by the drying lake bed of Great Salt Lake in Utah.

The finding, , suggest that drying lake beds are an overlooked, but potentially significant, source of greenhouse gases, which may further increase due to climate change.

“Human-caused desiccation of Great Salt Lake is exposing huge areas of lake bed and releasing massive quantities of greenhouse gases into the atmosphere,” says lead author Soren Brothers, who is an assistant professor in the department of ecology and evolutionary biology in the Faculty of Arts & Science and Allan and Helaine Shiff Curator of Climate Change at the Royal Ontario Museum.

“The significance of lake desiccation as a driver of climate change needs to be addressed in greater detail and considered in climate change mitigation and watershed planning.”

The Great Salt Lake’s water level varies depending on the volume of meltwater that flows into the lake from the surrounding mountains – from record highs in the 1980s to a record low in 2022. However, growing freshwater consumption by agriculture, industry and municipalities has depleted the lake over time.

Similar trends are observed worldwide as competing uses for water have a significant impact on lake levels. As iconic saline lakes such as the Aral Sea, Lake Urmia, the Caspian Sea and Great Salt Lake dry up, they not only destroy critical habitat for biodiversity and create air quality conditions that deteriorate human health, but they accelerate climate change as newly exposed sediments emit carbon dioxide and methane.

The research team measured carbon dioxide and methane emissions from the exposed sediments of Great Salt Lake from April to November 2020 and compared them with aquatic emissions estimates to determine the anthropogenic greenhouse gas emissions associated with desiccation. Calculations based on this sampling indicate the lake bed emitted 4.1 million tonnes of greenhouse gases to the atmosphere – primarily carbon dioxide (94 per cent), constituting an approximately seven per cent increase to Utah’s human-caused greenhouse gas emissions.

Fieldwork was conducted while Brothers was assistant professor of limnology at Utah State University (USU). Lead author Melissa Cobo, meanwhile, was a master’s student at USU and co-author Tobias Goldhammer is a collaborating researcher at the Leibniz Institute for Freshwater Research (IGB Institute) in Berlin, Germany.

Measurements of carbon dioxide and methane gases were made every two weeks from the dried-up lake bed using a portable greenhouse gas analyzer attached to a closed chamber. Seven sites at one location at the south end of the lake were visited repeatedly over the course of the year, and another three locations were sampled during an intensive three-day campaign to determine spatial variability across the 4,400-square-kilometre  lake, which is the largest saline lake in the western hemisphere. As methane is 28 times more powerful a greenhouse gas than carbon dioxide, the global warming impact of these emissions was calculated as “carbon dioxide equivalents.” 

Ultimately, the research indicated that greenhouse gas emissions from the dried lake bed were strongly and positively related to warm temperatures – even at sites exposed for more than two decades. To determine whether the lake would have historically been a significant source of greenhouse gases, the team carried out measurements of near-shore greenhouse gas emissions, as well as analyzing water chemistry collected by the team and government data sets. Together, these analyses showed that the original lake was not likely a significant source of greenhouse gases to the atmosphere, making the dried-up lake bed a novel driver of atmospheric warming.

As climate change exacerbates drought in arid regions, researchers say desiccation of rivers and lakes may be contributing to climate change feedback loops and should be considered in assessments of global greenhouse gas output as well as reduction policies and efforts.

With files from the Royal Ontario Museum