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Highlights

• When lakes dry up, their exposed lake beds become sources of greenhouse gases
• Many lakes, such as Great Salt Lake (United States), are drying up because of human actions
• High emissions from such lake beds should be assessed with regional carbon budgets

Science for society

Great Salt Lake (Utah, United States) illustrates the many impacts of lake drying, including regional air quality impacts and losses of migratory bird habitat. Here, we show that Great Salt Lake’s drying has exposed lake-bed sediments that are also a major source of greenhouse gas emissions. By comparing these emissions to estimates of the lake’s aquatic emissions, we show that they are likely a new source of greenhouse gases to the atmosphere. The emissions from this and likely many other saline lake beds around the world are anthropogenic, being the direct result of the human activities responsible for their drying, including agriculture, mining, and urban consumption. The emissions are high enough to be accounted for in regional carbon budgets and warrant efforts to halt and reverse the loss of saline lakes around the world.

Summary

Saline lake desiccation is widespread and typically caused by anthropogenic withdrawals for agricultural, industrial, and municipal uses, but its impact on greenhouse gas (GHG) emissions is unknown. While dry-flux studies have shown that desiccating waterbodies emit carbon dioxide (CO2) and methane (CH4) from exposed sediments, these studies are often seasonal and for freshwater systems, limiting their application to chronically desiccating saline lakes. We measured CO2 and CH4 emissions (April to November, 2020) from the exposed sediments of Great Salt Lake (Utah, United States), and compared them with aquatic emissions estimates to determine the anthropogenic emissions associated with desiccation. In 2020, the lake bed emitted 4.1 million tons of CO2eq to the atmosphere, primarily (94%) as CO2, constituting a ∼7% increase to Utah’s anthropogenic GHG emissions. As climate change exacerbates drought in arid regions, anthropogenic desiccation and associated climate feedbacks should be considered in assessments of global GHG trajectories as well as local GHG emissions reduction efforts.