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One Lake, Two Lake; Green Lake, Blue Lake

A large lake divided by a shallow spit of land, water to the left of the spit appears green and murky, the right side clear and blue.

Paper: Shallow lakes under alternative states differ in the dominant
greenhouse gas emission pathways

Authors: Sofia Baliña, María Laura Sánchez, Irina Izaguirre, Paul A. del Giorgio (2023)

Imagine some of the most dynamic, ecologically important lakes in the world…. you are picturing a deep, wide lake, not something knee deep and murky, or so full of aquatic plants you can’t see the bottom, right? Well, perhaps you should; while they don’t always make the most inviting swimming holes, small, shallow lakes have an outsized importance in the cycling of carbon and other nutrients through the landscape. 

Shallow depths tend to lead to warmer temperatures and more concentrated growth of algae and aquatic plants, not always the most desirable features for recreation.  But what these lakes might lack aesthetically, they make up for with a massive contribution to the global carbon cycle. Combine the abundance of small lakes with a tendency for frequent mixing of the water column, and high rates of organic input from the surrounding watershed and small lakes pack a big punch in terms of cycling nutrients, including carbon, through pathways in both the water and lake bottom sediments. 

These carbon cycling power houses are tricky to pin down because they can operate in what scientists call two different ‘stable states’: a murky, turbid state, dominated by algal growth that blocks the sunlight from reaching the bottom, and a clearwater state where plants anchored in the lake bottom sediments are dominant. A number of natural events, including floods, droughts, or changes in surrounding vegetation can lead to a ‘flip’ between states. Human activity can lead to a ‘flip’ as well, for example, in the Pampean Plains of Argentina, agricultural practices have added excess nutrients to the system, which tends to push lakes toward the murky, turbid state. The two lake states not only look different from the surface, but also have important differences in rates of photosynthesis, burial of organic material, and circulation in the water.

Knowing the importance of small lakes to global carbon cycling, a team in Argentina did a detailed investigation on how the different states impact carbon cycling and green house gas emissions.  By monitoring sets of turbid and clear shallow lakes in the Pampean Plains over the course of a year, they found important seasonal differences in rates of carbon dioxide (CO2) diffusion into and out of water column, and in the flux of methane (CH4) from lake bottom sediments.

Through monitoring instrumentation suspended in the air above the lakes, as well as measurements taken in the water and sediments, researchers were able to observe weather-driven seasonal changes. The biggest differences were between winter and spring: cold, clear lakes tended to act as CO2 source. When the lakes warmed up, they started to move gas from the water into the atmosphere and became carbon sinks, while turbid lakes did the opposite. 

Figure 3 from Baliña et al. (2022) showing the different pathways and relative ratios for carbon flow in clear-water, vegetated lakes (on the left) compared to more green, or turbid, lakes with heavy algal growth on the right. In total, the total greenhouse gas emissions (or CO2 equivalents) for both lake states was similar, but came from different pathways in the lake.

Over an annual cycle, clear lakes had as much as 5 times the CO2 emissions to the atmosphere as compared to turbid lakes, mainly attributed to the vegetation. Turbid lakes, however, had a higher annual emission of CH4. On balance, the two groups of lakes had roughly the same total contribution to green house gas fluxes, but the seasonal variability and differences in carbon pathway are important to understand as we continue to learn more about these dynamic ecosystems and how they change over time.


One Lake, Two Lake; Green Lake, Blue Lake by Avery Shinneman is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

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Forests under (mega)fire in the Pacific Northwest

Accompaniment to the Third Pod from the Sun Episode

Featured Image: “Forests under fire” original artwork by Jace Steiner. Used with permission.

Paper: Cascadia Burning: The historic, but not historically unprecedented, 2020 wildfires in the Pacific Northwest, USA

Authors: Matthew Reilly, Aaron Zuspan, Joshua Halofsky, Crystal Raymond, Andy McEvoy, Alex Dye, Daniel Donato, John Kim, Brian Potter, Nathan Walker, Raymond Davis, Christopher Dunn, David Bell, Matthew Gregory, James Johnston, Brian Harvey, Jessica Halofsky, Becky Kerns

The natural legacy of fire in the Pacific Northwest (PNW) is complex.  The variable geography of the wet, westside temperate rain forests, to the dry, high elevation forests beyond the Cascade crest make it difficult to find a “catch-all” description of PNW forest fires.  For instance, drier forests of ponderosa pines in eastern Washington experience more frequent, low-severity fires while the temperate rain forests of western Oregon rarely see fires.  However, scientists can reconstruct historical fire regimes and identify centuries-long patterns of burning related to precipitation, temperature, and ignition frequency to define what are historical patterns and what is modern climate change.  In 2020, multiple megafires (a wildfire that burnt more than 100,000 acres of land) broke out in the typically wet parts of Oregon and Washington, burning more than 700,000 acres combined.  This event is called the 2020 Labor Day Fires, and Matthew Reilly and colleagues have revealed these fires were likely part of historical regimes and not a product of accelerated climate change.

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Getting to Grips With the Sixth Mass Extinction

Featured Image: It is well-understood that the Earth’s biodiversity is in severe decline. However, it is less clear if this decline can now be called a mass extinction. Public domain image via. The Wilderness Society.

Paper: The Sixth Mass Extinction: fact, fiction, or speculation?

Authors: Robert H Cowie, Philippe Bouchet & Benoît Fontaine

Human-driven emissions and land use changes have impacted Earth’s biosphere greatly, causing global extinction rates to climb fast. However, does the current undeniable biodiversity crisis meet the requirements to be called a mass extinction? 

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We’re Here Because We’re Here Because… of Chance?

A painting of many stars as in a night sky, surrounded by planets, with their orbits drawn out.

Featured image: An artist’s depiction of many, many possible planets. This image was created by the European Southern Observatory (ESO).

Paper: Tyrrell, T. Chance played a role in determining whether Earth stayed habitable. Commun Earth Environ 1, 61 (2020). https://doi.org/10.1038/s43247-020-00057-8

Have you ever stayed up at night and wondered, why am I here? Or, more broadly, why are we here, including all living things on this Earth? Don’t worry, you’re not alone, and scientists like Professor Toby Tyrrell of the University of Southampton (UK) have been trying to answer these questions using the scientific method.

His conclusion? It may have just been the luck of the draw. After all, if we weren’t here in the first place, we couldn’t wonder why we were. (Scientists call this the weak anthropic principle.)

Climate scientists often describe their models as alternate (climate) histories. Tyrrell’s 2020 paper takes this idea to its ultimate conclusion, running 100 alternate climate histories on 100,000 randomly generated planets within the habitable zone of their randomly generated stars for 3 billion years. The question he’s trying to help answer is this: how likely was it that the Earth’s climate stayed habitable for the 4 billion years between the evolution of the first prokaryotic cells and us? Was it due to some intrinsic properties of planet Earth, or of life, or was it merely chance?

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Is geothermal energy fit for megacities?

Featured image: Steam rising from Nesjavellir Geothermal Power Station in Iceland via Wikimedia commons. Public Domain.

Article: Geothermal energy as a means to decarbonize the energy mix of megacities

Authors: Carlos A. Vargas, Luca Caracciolo, Philip Ball

As the world grapples with climate change, the transition to renewable energy has become a necessity. Governments are investing heavily in solar and wind power to reduce the dependence on fossil fuels. Another non-conventional source of energy that’s still understudied is geothermal energy. But what is geothermal energy? Geo means earth, thermal means heat. The internal heat of Earth is harnessed to heat water and produce power. An advantage of using geothermal energy over solar and wind is that, it doesn’t rely on weather to produce electricity. It provides clean, constant, stable and predictable supply of power. The question is, can geothermal energy cater to the demand of megacities where a large chunk of the world’s population resides?

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How Machine Learning Helps in the Fight Against Climate Change

Featured Image: Machine Learning has proven itself to be an effective tool in interdisciplinary research, but how can it be useful in understanding climate change? CC BY-NC 4.0, via. Dean Long

Paper: Tackling Climate Change with Machine Learning (Chapter 8)

Authors: David Rolnick et al.

Machine Learning (ML) gives researchers extremely valuable ways of revealing patterns within enormous datasets, and making predictions. Climate change research is one of many fields that is beginning to explore ML approaches. There are three major areas of interest: (1) climate prediction/modeling, (2) assessing impacts, and (3) exploring solutions as we attempt to decarbonize energy production. Rolnick and his coworkers explored the merit of machine learning in climate research and where it can support scientists best. The authors also call for greater collaboration between researchers of different backgrounds to advance our understanding of such a complex issue.

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Methanotrophs: Nature’s catalytic converters

Featured image: A car exhaust pipe, by Matt Boitor on Unsplash.

Paper: Microbial methane oxidation efficiency and robustness during lake overturn

Authors: M. Zimmerman, M. Mayr, H. Bürgmann, W. Eugster, T. Steinsberger, B. Wehrli, A. Brand, D. Bouffard

If you own a car, you’re likely aware that your engine emits greenhouse gases to the atmosphere. Although we usually think of cars and other human activities as the primary source of such greenhouse gases, living ecosystems can also produce these gases through natural processes. For example, lakes are an important global source of methane, a potent greenhouse gas produced in lake sediments as organic matter decomposes. In their recent paper, Zimmerman and colleagues focus on a small but mighty team of microbes that work hard to limit the amount of methane emitted from lakes.

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Earth’s darkest hour

Featured image: This is a Trilobite fossil from Volkhov river, Russia. Trilobites were marine arthropods which went extinct at the end of Permian period. CC BY-SA 3.0 via Wikimedia commons

Paper: Bioindicators of severe ocean acidification are absent from the end-Permian mass extinction.

Authors: William J. Foster, J.A. Hirtz, C. Farrell, M. Reistrofer, R. J.Twitchett, R. C. Martindale

What if I told you that an extinction event occurred In Earth’s history that dwarfs the demise of dinosaurs? This turbulent period dawned 252 million years ago, during the Late Permian period. The largest volcanic eruptions in the history of our planet began in now what is known as Siberia. The eruptions spewed out millions of cubic kilometers of lava, enough to bury an area the size of United States under a mile thick layer of rock!

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The first mass extinction

Featuring image: Life on during the Ordovician period looked very different then today. Animals like anomalocarididaes were very common, but many species vanished at the end of the Ordovician. A new study sheds light on the first mass extinction event. Model created by Espen Horn, photo: H. Zell, Creative Commons (CC BY-SA 3.0).

Paper: Geochemical Records Reveal Protracted and Differential Marine Redox Change Associated With Late Ordovician Climate and Mass Extinctions

Authors: N. P. Kozik, B. C. Gill, J. D. Owens, T. W. Lyons and S. A. Young

As mountains rise and continents fall apart, it not only changes the face of the Earth, but also drastically affects its inhabitants.

Earth’s biosphere was disrupted by several mass extinction events, often connected to great changes in large geologic cycles. These times of great disasters were also a chance for pioneers and led to great evolutionary leaps. A new study suggests that the oldest of the known major mass extinctions during the Ordovician was caused by a change in climate and the ocean’s circulation system.

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The third pole is in peril !

Featured image: The terminus of the debris-covered Gangotri glacier. CC BY-SA 4.0, via Wikimedia commons

Article : Accelerated mass loss of Himalayan glaciers since the Little Ice Age

Authors : Ethan Lee, Jonathan L. Carrivick, Duncan J.Quincey, Simon J. Cook, William H. M. James, Lee H. Brown

The health of Himalayan glaciers is deteriorating at an alarming rate. These Himalayan ‘water towers’ are on the brink of undergoing irreversible changes due to climate change, which in turn will have an adverse effect on the water and food security of South Asia. Getting a good idea of what might happen to these glaciers is imperative, but until now, glaciologists have focused on recent fluctuation patterns of these glaciers spanning the past few decades. In a new study, Lee and colleagues tried to reconstruct the glacial surface of some 14,798 Himalayan glaciers during the Little Ice Age and found that compared to other non-polar regions, Himalayan glaciers might be even more sensitive to fluctuations in the climate.

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