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A refined mathematical model is now capable of predicting carbon inputs and outputs for freshwater lakes around the world, according to new research from INSTAAR’s Isabella Oleksy and collaborators. Their work could help scientists understand the role of freshwater lakes in the global carbon cycle.

Oleksy's most recent paper, which was published, tests and revises an equation that allows scientists to estimate the overall biological activity in a lake from limited data.

The equation  by a group of scientists, including Oleksy's co-author , in 2018. It’s a mathematical formulation of  — a longstanding theory in the field. Basically, the theory posits that you can estimate the total growth of phytoplankton in a lake from the color of the water and measurements of a few key nutrients. Phytoplankton is the basis of the marine food web, which makes it a good stand-in for lake productivity on the whole.

  Further refinements of a model like this might be used to generate estimates of how much carbon is being fixed by lakes annually

-- Isabella Oleksy

Isabella Oleksy prepares to take measurements from The Loch, a high altitude lake in Rocky Mountain National Park, Colorado.  

“This is a way to potentially be able to understand what algal biomass and water quality might look like in a bunch of different lakes, even when you can’t necessarily get out there and measure it,” Solomon said.

Oleksy's study is the first to test the model against real world data — quite a bit of it. Back in 2019, when Oleksy was a postdoctoral researcher at the , she put out a call for data at a meeting of the .

“I asked people, ‘Hey. I want to test this model, but we need observations from lakes around the world,’” she said.

Collaborators were eager to help out. With the help of 30 scientists at many different institutions, Oleksy gathered detailed measurements from 58 different freshwater lakes around the world. Then, she tested the model’s predictions against the data. The initial test was encouraging.

“The results were pretty realistic,” she said.

The next step was to make the predictions even better. Through a process called Monte Carlo analysis, Oleksy pitted the model’s predictions against the on-the-ground data. Where the model faltered, she added new parameters to improve it.

In the end, Oleksy and her collaborators created a model capable of estimating the conditions of freshwater lakes in a diverse range of locations and ecosystems.

According to Oleksy, the new model could have implications far beyond freshwater lakes. It elucidates one small element of the global carbon cycle — a cycle that has become a priority for scientists in the era of global warming.

Policy makers and researchers rely on global-scale models of the carbon sources and sinks to predict the Earth’s future climate and inform large-scale solutions for climate change. These models are vast and complex — they must take into account the inputs and outputs of diverse human activities, ecosystems and geologic phenomena. Oleksy and her collaborators hope that their new study can be used to eliminate some uncertainty from these estimates.

“There is a lot of uncertainty about the role of inland waters,” Oleksy said. “Further refinements of a model like this might be used to generate estimates of how much carbon is being fixed by lakes annually.”

Global distribution of the 58 lakes included in Oleksy et al. 2024 (Figure 2, JGR Biogeosciences).  The “calibration” lakes are shaded in yellow and all others (“validation”) are in blue.

If you have questions about this story, or would like to reach out to INSTAAR for further comment, you can contact Senior Communications Specialist Gabe Allen at gabriel.allen@colorado.edu.