Years' worth of remote sensing data reveals that climate change influences carbon fixation trends in the earth's largest freshwater lakes.
A study published in MDPI details the NASA-funded research of the 11 largest freshwater lakes. A combination of satellite observations and field data provided a new understanding of how water fix carbon in large bodies of water and how climate change influences these interactions.
Lake-Wide Carbon Fixation Trends
Large freshwater lakes are known to provide to their surrounding populations. However, there is limited understanding of how these bodies of water respond to climate change and external factors.
Calculating annual, lake-wide primary production from 2003-2008. These lakes included the
Researchers from the Michigan Tech Research Institute utilized satellite remote sensing to three African Great Lakes, the five Laurentian Great Lakes, Lake Baikal, Great Slave Lakes, and the Great Bear.
The great lakes hold roughly more than 50% of surface freshwater that millions of creatures and people rely on, underscoring the need to understand how climate change and other factors altered the lakes.
The study shows the annual production in these lakes ranges from 200 mg of Carbon/m2 per day to over 1100 mg of Carbon/m2 per day. The lakes were then categorized into three groups: eutrophic, mesotrophic, and oligotrophic, depending on their levels of production.
Two Canadian lakes and Lake Tanganyika had the greatest changes in primary production and algae growth. Fluctuations in productivity boast of big changes in the underlying ecosystem.
"The base of the food chain in these lakes is algal productivity. These lakes are oceanic in size and are teaming with phytoplankton," says Gary Fahnestiel, co-author and retired senior researcher from NOAA's Great Lakes Environmental Research Laboratory.
"We measured the carbon fixation rate, which is the rate at which algae photosynthesize in these lakes. As that rate changes, the whole lake changes, which has ramifications on the food chain," explains Fahnestiel.
There are several factors that influence changes in the lake's production. Climate change, invasive species, increasing nutrients, and more combine to cause lake-wide changes making it difficult for researchers to pinpoint specific causes.
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Satellite Imaging in Counting Phytoplankton
Satellite imagery has made it possible to sort through the noise and provide insights over time and space, says Michael Sayers, MTRI researcher and lead author of the study.
"We relied on NASA's assets--the MODIS satellite which has been flying since 2002 to which algorithms and models have been applied," says Sayers.
The research results show how drastic changes in the lakes have occurred, especially over the past 20 years. The research contributes to the Carbon Monitoring Systems of NASA, whose goal is to determine how much water bodies contribute to the global carbon cycle.
According to findings, three of the largest lakes showed major changes due to climate change, with a 20-25% overall biological productivity in the past 16 years.
Sayers explains that looking at algal abundance, productivity, water temperature, water clarity, solar radiation, and wind speeds shows how rich the ecosystem of freshwater lakes has changed over time.
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