World’s largest lakes reveal trends for climate change

Sixteen years of remote sensing data show that climate change in the earth’s largest freshwater lakes is affecting carbon sequestration trends.

NASA-funded research on the 11 largest freshwater lakes in the world, linked to field and satellite observations to provide a new understanding of how large bodies of water bind carbon, as well as how a changing climate and lakes interact.

Scientists at the Michigan Tech Research Institute (MTRI) studied the five Laurentian Great Lakes bordering the US 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 freshwater water that millions of humans and many other creatures rely on, and it emphasizes the importance of understanding how it is changed by climate change and other factors.

The two Canadian lakes and Lake Tanganyika have seen the biggest changes in primary productivity – the growth of algae in a body of water. Productivity fluctuations indicate major changes in the ecosystems of the lake.

“The basis of the food chain in these lakes is algae productivity. These lakes are ocean-sized and work with phytoplankton – small algae,” says co-author Gary Fahnenstiel, a fellow at MTRI and recently retired senior research scientist for NOAAs. Great Lakes Environmental Research Laboratory. “We measured the rate of carbon sequestration, that’s the rate at which the algae photosynthesize in these lakes. If the rate changes, whether it increases or decreases, it means that the whole lake changes, which results in the food chain. From the zooplankton to with the fish. ‘

Many factors affect these lakes. Climate change, increasing nutrients (eutrophication) and invasive species are causing joint changes, making it difficult to determine specific causes, especially from the ground with limited observations on site.

Count phytoplankton with color

But satellite imagery facilitated sorting by noise and provided insights into time and space. Michael Sayers, MTRI researcher and lead author of the study, uses ocean color remote sensing – draws inferences about the type and amount of phytoplankton based on water color – to detect freshwater phytoplankton dynamics.

“We have relied on NASA assets – the MODIS satellite, which has been flying since 2002, to which we apply the algorithm and model we have been developing at MTRI for a decade,” Sayers said. “If we start measuring the number of pixels for 11 years for 11 years worldwide, it’s really remarkable.” The pixels observed per plural ‘in the millions’, he added.

One of the most remarkable aspects of the results is how fast changes have taken place in these freshwater lakes – a noticeable amount in less than 20 years. The research contributes to the purpose of NASA’s carbon monitoring system to determine how much freshwater lakes contribute to the global carbon cycle.

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

More than algae

In the 16 years of data, Great Bear and Great Slave lakes in northern Canada have seen the largest increases in productivity, while Lake Tanganyika has declined in southeastern Africa. The trends are linked to increases in water temperatures, as well as solar radiation and a decrease in wind speed.

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

“Temperature and solar radiation are factors of climate change,” Sayers said. “The change in transparency in chlorophyll and water is not necessarily caused by climate change, but can be caused by eutrophication or invasive species, such as quail mussels.”

The researchers used measurements taken by the Great Lakes Research Center Navy for research vessels to place the satellite observations on the ground and to provide input for model estimates.

The article “Carbon Fixation Trends in Eleven of the World’s Largest Lakes: 2003–2018” is published in the journal Water. The researchers plan to continue their research and apply what they have learned so far to the role that harmful algae blossoms have on the carbon flow in the atmosphere.

As the saying goes, water is life. Gaining a better understanding of how the productivity changes of the lake affect the water masses on which many people rely is important for the communities living on the farms. It is also important for the global community as we delve deeper into the role that freshwater lakes play in the global carbon cycle and climate change.