World’s Largest Lakes Reveal Climate Change Trends

Sixteen years of remote sensing data show that in the largest freshwater lakes on earth, climate change is influencing carbon sequestration trends.

NASA-funded research on the world’s 11 largest freshwater lakes has coupled field and satellite observations to provide a new understanding of how large bodies of water fix carbon, as well as the way a changing climate and lakes interact.

Scientists from the Michigan Tech Research Institute (MTRI) studied the five Laurentian Great Lakes bordering the United States and Canada; the three African Great Lakes, Tanganyika, Victoria and Malawi; Lake Baikal in Russia; and Great Bear and Great Slave Lakes in Canada.

These 11 lakes contain more than 50% of the surface freshwater that millions of people and countless other creatures rely on, underscoring the importance of understanding how they are being altered by climate change and other factors. .

The two Canadian lakes and Lake Tanganyika experienced the most significant changes in primary productivity – the growth of algae in a body of water. Fluctuations in productivity indicate large changes in lake ecosystems.

“The basis of the food chain in these lakes is the productivity of algae. These lakes are ocean-sized and team up with phytoplankton – small algae,” said co-author Gary Fahnenstiel, MTRI member and recently retired scientist. senior for NOAA. Great Lakes Environmental Research Laboratory. “We measured the carbon sequestration rate, which is the rate at which algae photosynthesize in these lakes. As that rate changes, whether it is increasing or decreasing, it means the whole lake is changing, which has ramifications throughout the food chain, from zooplankton to fish. “

Many factors affect these lakes. Climate change, increased nutrients (eutrophication), and invasive species combine to cause system-wide changes, making it difficult to identify specific causes, especially from the ground with limited observations on square.

Counting phytoplankton with color

But satellite imagery has made it easier to sort out the noise and provide information on time and space. Michael Sayers, MTRI researcher and lead author of the study, uses remote sensing of ocean color – making inferences about the type and amount of phytoplankton based on the color of the water – to track the dynamics freshwater phytoplankton.

“We have relied on the resources of NASA – the MODIS satellite, which has been flying since 2002, to which we apply the algorithm and model that we have been developing at MTRI for a decade,” Sayers said. “When we start counting the number of pixels as observations globally for 11 lakes for 16 years, it’s really quite remarkable. The pixels observed by lake are “in the millions”, he added.

One of the most remarkable aspects of the results is how quickly the changes in these freshwater lakes occurred – a notable amount in less than 20 years. The research contributes to the goal of NASA’s carbon monitoring system to determine the extent to which freshwater lakes contribute to the global carbon cycle.

“Three of the largest lakes in the world are showing major changes linked to climate change, with a 20-25% change in overall biological productivity in the past 16 years alone,” Fahnenstiel said.

More than algae

Over the 16 years of data, Great Bear and Great Slave Lakes in northern Canada experienced the largest increases in productivity, while Lake Tanganyika in Southeast Africa experienced decreases. The trends are related to the increase in water temperature, as well as solar radiation and a reduction in wind speed.

Sayers said examining productivity, algae abundance, water clarity, water temperature, solar radiation, and wind speed in freshwater lakes provides a richer picture of the overall ecosystem.

“Temperature and solar radiation are drivers of climate change,” Sayers said. “Changes in chlorophyll and water transparency are not necessarily caused by climate change, but could be caused by eutrophication or invasive species, such as quagga mussels.”

The researchers used measurements of the lakes taken by the Great Lakes Research Centre’s fleet of research vessels to ground-verify satellite observations and provide data for the model estimates.

The article “Carbon sequestration trends in eleven of the world’s largest lakes: 2003–2018” is published in the journal The water. The researchers plan to continue their research, applying what they have learned so far to the role of harmful algal blooms on carbon flux in the atmosphere.

As the saying goes, water is life. It is important for the communities that live on the lake shores to better understand how changes in lake productivity affect the bodies of water on which many people depend. It is also important for the global community as we delve deeper into the role of freshwater lakes in the global carbon cycle and climate change.