Going underground to investigate carbon locked in soils 

Mineral-associated organic matter (MAOM) at the bottom of a test tube in a salt solution.

The activities are as follows:

Soil is an important part of the carbon cycle because it traps carbon, keeping it out of the atmosphere and locked underground. At a global level, the amount of carbon stored by soil is more than is found in all of the plants and the atmosphere combined. Carbon trapped underground does not contribute to the rising carbon dioxide concentration in our atmosphere that leads to climate change. For decades, scientists have been researching how much carbon our soils can store to understand its role in slowing the pace of climate change.

Carbon enters the soil when plants and animals die, and their organic matter is decomposed by soil bacteria and fungi. Sometimes it is broken down into very small molecules. These molecules become attached to minerals in the soil, like clay particles. We call this mineral-associated organic matter (MAOM). The carbon is connected to minerals with very strong chemical bonds. Because these bonds are hard to break, the carbon stays in the soil for long periods of time and accumulates on clay minerals. 

Some studies have shown that the carbon in MAOM can be trapped in soils for thousands of years! When more of the carbon in the soil is attached to minerals and locked in the soil for longer time periods, the ecosystem is serving an important role in keeping carbon out of the atmosphere. 

Ashley in the lab, using a saltwater solution to isolate mineral-associated organic matter (MAOM) from soil samples.

Ashley is working to understand how much stable carbon there is in soils, and the role of climate. Microbes work faster in warmer and wetter conditions, which results in quicker decomposition. Ashley thought this rapid decomposition would cause organic matter to be broken down into smaller particles sooner. Therefore, she thought that in warmer or wetter environments, more soil carbon would attach to minerals and become stable MAOM. In colder or drier environments, she expected this process to happen more slowly, leading to a smaller amount of MAOM in the soil.

To test these ideas, Ashley used soil samples from forests with different climates throughout the Eastern United States. Soil samples were collected from New Hampshire to Alabama by teams of researchers using the same sampling protocol. The samples were mailed to Ashley’s lab at Indiana University for analysis. Ashley measured the amount of MAOM in each soil sample by taking advantage of a key feature: MOAM is heavy! Ashley submerged each soil sample in a saltwater solution, and the parts that floated were discarded, while the parts that sunk to the bottom were classified as MAOM. She then rinsed the salt off and measured the amount of carbon in the MAOM with an instrument called an elemental analyzer. She compared this number to the amount of carbon in the whole soil sample to calculate what percentage of the total soil carbon was attached to minerals.

Featured scientist: Ashley Lang from Indiana University

Flesch–Kincaid Reading Grade Level = 10.8

Additional teacher resources related to this Data Nugget:

To reflect, or not to reflect, that is the question

Jen stops to take a photo while conducting fieldwork in the Arctic.

The activities are as follows:

Since 1978, satellites have measured changes in Arctic sea ice extent, or the area by the North Pole covered by ice. Observations show that Arctic sea ice extent change throughout the year. Arctic sea ice reaches its smallest size at the end of summer in September. Scientists who look at these data over time have noticed the sea ice extent in September has been getting smaller and smaller since 1978. This shocking trend means that the Arctic sea ice is declining, and fast! 

Why does this matter? Well, it turns out that Arctic sea ice plays a major role in the world’s climate system. When energy from the Sun reaches Earth, part of the energy is absorbed by the surface, while the rest is reflected back into space. The energy that is absorbed becomes heat, and warms the planet. The amount of energy reflected back is called albedo.

The higher the albedo, the more energy is reflected off a surface. Complete reflection is assigned a value of 1 (100%) and complete absorption is 0 (0%). Lighter colored surfaces (e.g., white) have a higher albedo than darker colored surfaces (e.g., black). Sea ice is white and reflects about 60% of solar energy striking its surface, so its albedo measurement is 0.60. This means that 40% of the Sun’s energy that reaches the sea ice is absorbed. In contrast, the ocean is much darker and reflects only about 6% of the Sun’s energy striking its surface, so its albedo measurement 0.06. This means that 94% of the Sun’s energy that reaches the ocean is absorbed.

Jen (second from left) preparing to teach her students at the University of Colorado Boulder while working in the Arctic. Photo by Polar Bears International.

Jen first became interested in sea ice in the summer of 2007, when a record low level of sea ice caught scientists off guard. They worried that if the albedo of the Arctic declines, energy that used to be reflected by the white ice will be absorbed by the dark oceans and lead to increased warming. At the time, Jen was working with new satellite observations and found it fascinating to understand what led to the record low sea ice year. To continue her passion, Jen joined a team of scientists studying the Arctic’s energy budget. 

Jen and her team predicted that the decline in the light-colored sea ice will cause Arctic albedo to decrease as well. Jen used incoming and reflected solar energy data to determine the changes in the Arctic’s albedo. These data were collected from satellites as part of the Clouds and Earth’s Radiant Energy System (CERES) project. Then, Jen compared the albedo data to changes in the extent of sea ice from satellite images to look for a pattern. 

Featured scientist: Jen Kay from the Cooperative Institute for Research in Environmental Sciences and the Department of Atmospheric and Oceanic Sciences at the University of Colorado Boulder. Written by Jon Griffith with support from AGS 1554659 and OPP 1839104.

Flesch–Kincaid Reading Grade Level = 9.6

Mangroves on the move

mangrove in marsh
A black mangrove growing in the saltmarshes of northern Florida.

The activities are as follows:

All plants need nutrients to grow. Sometimes one nutrient is less abundant than others in a particular environment. This is called a limiting nutrient. If the limiting nutrient is given to the plant, the plant will grow in response. For example, if there is plenty of phosphorus, but very little nitrogen, then adding more phosphorus won’t help plants grow, but adding more nitrogen will. 

Saltmarshes are a common habitat along marine coastlines in North America. Saltmarsh plants get nutrients from both the soil and the seawater that comes in with the tides. In these areas, fertilizers from farms and lawns often end up in the water, adding lots of nutrients that become available to coastal plants. These fertilizers may contain the limiting nutrients that plants need, helping them grow faster and more densely.

One day while Candy, a scientist, was out in a saltmarsh in northern Florida, she noticed something that shouldn’t be there. There was a plant out of place. Normally, saltmarshes in that area are full of grasses and other small plants—there are no trees or woody shrubs. But the plant that Candy noticed was a mangrove. Mangroves are woody plants that can live in saltwater, but are usually only found in tropical places that are very warm. Candy thought the closest mangrove was miles away in the warmer southern parts of Florida. What was this little shrub doing so far from home? The more that Candy and her colleague Emily looked, the more mangroves they found in places they had not been before.

Candy and Emily wondered why mangroves were starting to pop up in northern Florida. Previous research has shown nitrogen and phosphorus are often the limiting nutrients in saltmarshes. They thought that fertilizers being washed into the ocean have made nitrogen or phosphorus available for mangroves, allowing them to grow in that area for the first time. So, Candy and Emily designed an experiment to figure out which nutrient was limiting for saltmarsh plants. 

mangrove saltmarsh researchers
Candy (right) and Emily (left) measure the height of a black mangrove growing in the saltmarsh.

For their study, Candy and Emily chose to focus on black mangroves and saltwort plants. These two species are often found growing together, and mangroves have to compete with saltwort. Candy and Emily found a saltmarsh near St. Augustine, Florida, in which they could set up an experiment. They set up 12 plots that contained both black mangrove and saltwort. Each plot had one mangrove plant and multiple smaller saltwort plants. That way, when they added nutrients to the plots they could compare the responses of mangroves with the responses of saltwort. 

To each of the 12 plots they applied one of three conditions: control (no extra nutrients), nitrogen added, and phosphorus added. They dug two holes in each plot and added the nutrients using fertilizers, which slowly released into the nearby soil. In the case of control plots, they dug the holes but put the soil back without adding fertilizer.

Candy and Emily repeated this process every winter for four years. At the end of four years, they measured plant height and percent cover for the two species. Percent (%) cover is a way of measuring how densely a plant grows, and is the percentage of a given area that a plant takes up when viewed from above. Candy and Emily measured percent cover in 1×1 meter plots. The cover for each species could vary from 0 to 100%.

Featured scientists: Candy Feller from the Smithsonian Environmental Research Center and Emily Dangremond from Roosevelt University

Flesch–Kincaid Reading Grade Level = 8.3

The end of winter as we’ve known it?

Forrest standing in front of the ice road that forms between Bayfield and LaPointe each winter, preventing ferry traffic but allowing cars to travel between the mainland and island.

The activities are as follows:

As a boy growing up in Bayfield, Wisconsin, Forrest was familiar with the seasonal rhythms of Lake Superior and the nearby Apostle Islands. Forrest watched each year as ice formed in the Bayfield Harbor, stopping the boat traffic each winter. Eventually, as the ice thickened even more, an ice road would open between Bayfield and LaPointe. The small town of LaPointe is located on Madeline Island just over two miles from the shore of Bayfield. When the ice road opens, it frees the island residents from working around the ferry schedule and they can drive on the ice to get to the mainland.

As a senior at Bayfield High School, Forrest became interested in conducting a scientific study related to the ice season on Lake Superior. He knew that Lake Superior plays a vital role in the lives of people who live and work on its shores and therefore all sorts of data are recorded to help understand and take care of it. Based on his own observations and comments of other area residents, Forrest thought that winters were getting shorter. He wanted to know whether the length of the ice season was changing over time. Forrest turned to historical data to answer his question. 

Forrest’s first stop on his quest to find data was the Madeline Island Ferry Line, a company that operates the ferries between Bayfield and LaPointe. Since 1970, the ferry line has kept yearly records of the date on which the last ferry traveled between Bayfield and LaPointe before the water was too frozen for travel. They also recorded the date on which the first ferry traveled the channel when ice melted in the spring. That gave Forrest a start, but he wanted data that would date farther back than 1970. 

Luckily, Forrest’s father, Neil, was an interpretive ranger for the Apostle Islands National Lakeshore. Neil showed Forrest local newspaper archives that were stored in the basement of their headquarters building. News about shipping and fishing have been important to the people in the community throughout history, so it was common to find articles referencing the first and last boat of each year. Looking back through newspaper records, Forrest and Neil were able to collect data for almost every year dating back to 1857!

Armed with these data, Forrest began his analyses. He chose to define the length of the ice season as the time between the last boat each winter and the first boat each spring. This also represents the time during which there was no boat navigation due to ice cover. Forrest’s next step was to choose how to quantify the dates. He decided to use Julian dates, which start with January 1 as Day 1 and continue to count up by 1 for each day. This means that January 31 would be Day 31, February 1 would be Day 32, and March 1 would be Day 61. After assigning Julian dates to each historical data point, Forrest subtracted the day of the last boat from the day of the first boat to find the number of days without boat traffic each year. This number serves as a consistent way to estimate the length of the ice season each year. Winter begins in one calendar year but ends in the next, so Forrest identified the year based on the calendar year that the winter began.

Featured scientist: Forrest Howk, Bayfield High School. Written by: Richard Erickson, Bayfield High School and Hannah Erickson, Boston Public Schools

Flesch–Kincaid Reading Grade Level = 10.1

Additional teacher resources related to this Data Nugget include:

  • If you would like your students to interact with the raw data, we have attached the original data here.
  • Forrest’s study was published in the Journal of Great Lakes Research. 
  • Dr. Jay Austin of the Large Lakes Observatory in Duluth, MN has conducted studies related to Lake Superior’s water temperatures. His website includes real-time data collection from buoys in Lake Superior that would likely yield usable data for student investigations.
  • Dr. John Magnuson of the University of Wisconsin has conducted studies of ice cover for lakes at latitudes across the globe. He wrote an article about projected changes in ice cover due to climate change at various latitudes around the world. In addition, his website has links to publications and further information.


A window into a tree’s world

Neil taking a tree core from a pine tree.

The activities are as follows:

According to National Aeronautics and Space Administration (NASA) and the National Oceanic Atmospheric Administration (NOAA), the years 2015-2018 were the warmest recorded on Earth in modern times! And it is only expected to get warmer. Temperatures in the Northeastern U.S. are projected to increase 3.6°F by 2035. Every year the weather is a bit different, and some years there are more extremes with very hot or cold temperatures. Climate gives us a long-term perspective and is the average weather, including temperature and precipitation, over at least 30 years. 

Over thousands of years, tree species living in each part of the world have adapted to their local climate. Trees play an important role in climate change by helping cool the planet – through photosynthesis, they absorb carbon dioxide from the atmosphere and evaporate water into the air. 

Scientists are very interested in learning how trees respond to rapidly warming temperatures. Luckily, trees offer us a window into their lives through their growth rings. Growth rings are found within the trunk, beneath the bark. Each year of growth has two parts that can be seen: a light ring of large cells with thin walls, which grows in the spring; and a dark layer of smaller cells with thick walls that forms later in the summer and fall. Ring thickness is used to study how much the tree has grown over the years. Dendrochronology is the use of these rings to study trees and their environments.

Different tree species have different ranges of temperatures and rainfall in which they grow best. When there are big changes in the environment, tree growth slows down or speeds up in response. Scientists can use these clues in tree’s rings to decipher what climate was like in the past. There is slight variation in how each individual tree responds to temperature and rainfall. Because of this, scientists need to measure growth rings of multiple individuals to observe year-to-year changes in past climate.

Jessie taking a tree core in the winter.

Jessie and Neil are two scientists who use tree rings for climate research. Jessie entered the field of science because she was passionate about climate change. As a research assistant, Neil saw that warming temperatures in Mongolia accelerated growth in very old Siberian pine trees. When he later studied to become a scientist, he wanted to know if trees in the eastern U.S. responded to changes in climate in the same way as the old pine trees in Mongolia. As a result, there were two purposes for Jessie’s and Neil’s work. They wanted to determine if there was a species that could be used to figure out what the climate looked like in the past, and understand how it has changed over time.

Jessie and Neil decided to focus on one particular species of tree – the Atlantic white cedar. Atlantic white cedar grow in swamps and wetlands along the Atlantic and Gulf coasts from southern Maine to northern Florida. Atlantic white cedar trees are useful in dendrochronology studies because they can live for up to 500 years and are naturally resistant to decay, so their well-preserved rings provide a long historical record. Past studies of this species led them to predict that in years when the temperature is warmer, Atlantic white cedar rings will be wider. If this pattern holds, the thickness of Atlantic white cedar rings can be used to look backwards into the past climate of the area. 

To test this prediction, Jessie and Neil needed to look at tree rings from many Atlantic white cedar trees. Jessie used an increment borer, a specialized tool that drills into the center of the tree. This drill removes a wood core with a diameter about equal to that of a straw. She sampled 112 different trees from 8 sites, and counted the rings to find the age of each tree. She then crossdated the wood core samples. Crossdating is the process of comparing the ring patterns from many trees in the same area to see if they tell the same story. Jessie used a microscope linked to a computer to measure the thickness of both the early and late growth to the nearest micrometer (1 micrometer = 0.001 millimeter) for all rings in all 112 trees. From those data she then calculated the average growth of Atlantic white cedar for each year to create an Atlantic white cedargrowth index for the Northeastern U.S. She combined her tree ring data with temperature data from the past 100 years.

Featured scientists: Jessie K Pearl, University of Arizona and Neil Pederson, Harvard University. Written by Elicia Andrews.

Flesch–Kincaid Reading Grade Level = 9.9

Suggestions for inquiry surrounding this Data Nugget:

These videos, demonstrating the science of dendrochronology, could be a great way to spark class discussions:

Streams as sensors: Arctic watersheds as indicators of change

Jay taking field notes next to a rocky Tundra stream.

The activities are as follows:

The Arctic, Earth’s region above 66° 33’N latitude, is home to a unique biome, known as tundra. A defining trait of tundra ecosystems is the frozen land. Permafrost is the underground layer of organic matter, soil, rock, and ice that has been frozen for at least 2 full years. Plant material decays slowly in the Arctic because of the cold temperatures. Building up over thousands of years, the plants become frozen into the permafrost. Permafrost represents a very large “sink” of dead plant material, nutrients, and soil that is locked away in a deep freeze. 

Though the Alaskan Arctic may seem far away from where you live, tundra permafrost is important for the entire globe. During the past few thousand years, Earth’s climate has naturally changed a little over time, but because humans are adding greenhouse gases to the atmosphere, the average global temperature may increase by as much as 2 to 4oC over the next century. As a result of global climate change, permafrost has become less stable. By causing warmer and wetter conditions in the Arctic, thawing permafrost soils release ancient material that was previously frozen and locked away. Two important materials are dissolved nitrogen (N), which is a nutrient critical for plant growth, and carbon (C), which is stored in plant matter during photosynthesis. These released materials can be used again by plants, but some is carried away as melted water flows from the land into rivers and streams. You can imagine N and C in permafrost like a bank account where the landscape is the savings account. The land slowly deposits or withdraws N and C from the savings account, while the water receives any excess N and C that the land does not save.

Arial downloads data from a water quality monitoring station at the Kuparuk River. The station is connected a sensor that stays in the river and takes a reading for both carbon and nitrogen concentrations every 15 minutes.

The water that melts as permafrost thaws flows into a stream, ultimately ending up in an ocean. Watersheds are the network of streams and rivers that flow to a single point as they empty out into the ocean. The water at the end of the watershed therefore reflects all the changes that happened across a large area. Scientists use Arctic watersheds as large “sensors” to understand how and when landscapes may be releasing material from thawing permafrost. 

Because the Alaskan Arctic is a vast, sparsely populated area, scientists often rely on established field stations to conduct experiments, collect observational data, and develop new understanding of Arctic ecosystems. One of these field sites is Toolik Field Station. Scientists working at Toolik have been monitoring terrestrial and aquatic Arctic ecosystems since the late 1970s. 

Arial and Jay are aquatic scientists who work at Toolik. They are interested in how Arctic watersheds respond to climate change. Together, Arial and Jay act like ecosystem accountants: they use the chemistry within the water to monitor changes in ecosystem budgets of C and N. Arial and Jay used both historic data and water quality sensors deployed in 2017 and 2018 to monitor the N and C budget in the Kuparuk River. They use this data to calculate how much N and C the river is spending. They measure this as the total export in units of mass per year. This mass per year is determined by multiplying concentration (mass/volume) by flow (volume/day) and adding these values across the whole season (mass/year). These budgets at the watershed outlet help reveal signals of how this tundra landscape may be changing. In this way, they can assess if the landscape savings account for N and C is being depleted due to climate change. 

Featured scientists: Arial Shogren and Jay Zarnetske from Michigan State University

Flesch–Kincaid Reading Grade Level = 10.8

The carbon stored in mangrove soils

Tall mangroves growing close to the coast.

The activities are as follows:

In the tropics and subtropics, mangroves dominate the coast. There are many different species of mangroves, but they are all share a unique characteristic compared to other trees – they can tolerate having their roots submerged in salt water.

Mangroves are globally important for many reasons. They form dense forested wetlands that protect the coast from erosion and provide critical habitat for many animals. Mangrove forests also help in the fight against climate change. Carbon dioxide is a greenhouse gas that is a main driver of climate change. During photosynthesis, carbon dioxide is absorbed from the atmosphere by the plants in a mangrove forest. When plants die in mangrove forests, decomposition is very slow. The soils are saturated with saltwater and have very little oxygen, which decomposers need to break down plants. Because of this, carbon is stored in the soils for a long time, keeping it out of the atmosphere.

Sean is a scientist studying coastal mangroves in the Florida Everglades. Doing research in the Everglades was a dream opportunity for Sean. He had long been fascinated by the unique plant and animal life in the largest subtropical wetland ecosystem in North America. Mangroves are especially exciting to Sean because they combine marine biology and trees, two of his favorite things! Sean had previously studied freshwater forested wetlands in Virginia, but had always wanted to spend time studying the salty mangrove forests that exist in the Everglades. 

Sean Charles taking soil samples amongst inland short mangroves.

Sean arrived in the Everglades with the goal to learn more about the factors important for mangrove forests’ ability to hold carbon in their soils. Upon his arrival, he noticed a very interesting pattern – the trees were much taller along the coast compared to inland. This is because mangroves that grow close to the coast have access to important nutrients found in ocean waters, like phosphorus. These nutrients allow the trees to grow large and fast. However, living closer to the coast also puts trees at a higher risk of damage from storms, and can lead to soils and dead plants being swept out to sea. 

Sean thought that the combination of these two conditions would influence how much carbon is stored in mangrove soils along the coast and inland. Larger trees are generally more productive than smaller ones, meaning they might contribute more plant material to soils. This led Sean to two possible predictions. The first was that there might be more carbon in soils along the coast because taller mangroves would add more carbon to the soil compared to shorter inland mangroves. However, Sean thought he might also find the opposite pattern because the mangroves along the coast have more disturbance from storms that could release carbon from the soils. 

To test these competing hypothesis, the team of scientists set out into the Everglades in the Biscayne National Park in Homestead, Florida. Their mission was to collect surface soils and measure mangrove tree height. To collect soils, they used soil cores, which are modified cylinders that can be hammered into the soil and then removed with the soil stuck in the tube. Tree height was measured using a clinometer, which is a tool that uses geometry to estimate tree height. They took these measurements along three transects. The first transect was along the coast where trees had an average height of 20 meters. The second transect between the coast and inland wetlands where trees were 10 meters tall, on average. The final transect was inland, with average tree height of only 1 meter tall.  With this experimental design Sean could compare transects at three distances from the coast to look for trends. 

Once Sean was back in the lab, he quantified how much carbon was in the soil samples from each transect by heating the soil in a furnace at 500 degrees Celsius. Heating soils to this temperature causes all organic matter, which has carbon, to combust. Sean measured the weight of the samples before and after the combustion. The difference in weight can be used to calculate how much organic material combusted during the process, which can be used as an estimate of the carbon that was stored in the soil. 

Featured scientist: Sean Charles from Florida International University

Flesch–Kincaid Reading Grade Level = 9.6

Additional teacher resources related to this Data Nugget:

Beetle, it’s cold outside!

Frozen lady beetles.

The activities are as follows:

Éste Data Nugget también está disponible en Español:

Walking across a snowy field or mountain, you might not notice many living things. But if you dig into the snow, you’ll find a lot of life!

Until recently, climate change scientists thought warming in winter would be good for most species. Warmer winters would mean that species could avoid the cold and would not need to deal with freezing temperatures as often or for as long. Caroline is a scientist who is thinking about winter climate change in a whole new way. Snow covers the soil, acting like an insulating blanket. Many species rely on the snow for protection from the winter’s cold. When temperatures climb in the winter, snow melts and leaves the soil uncovered for longer periods of time. This leads to the shocking pattern that warmer temperatures actually means the soil gets colder!

Caroline is interested in how species that rely on the snow will respond to climate change. She studies a species of insect called lady beetles. Lady beetles are ectotherms, meaning their body temperature matches that of their environment. Because climate change is reducing the amount of snow in the lady beetle habitat, Caroline wanted to know how they would respond to these changes.

Caroline and her team, Andre and Nikki, decided to investigate what happens to lady beetles when they are exposed to longer periods of time in cold temperatures. When soil temperatures drop below freezing (0℃), lady beetles go into a chill coma, or a temporary, reversible paralysis. When temperatures are below freezing, it is so cold that they are unable to move. When temperatures rise back above freezing, they wake from their chill comas. When lady beetles are in chill comas, they are easier for predators to catch because they can’t escape. They are also unable to find food or mates. Scientists can measure how fast it takes lady beetles to recover from chill coma, called chill coma recovery time, and use this as a measure of their performance.

Beetles in their pre-testing habitat are on the right; tubes with beetles about to be immersed in a cooler filled with crushed ice are on the left.

They designed an experiment to test whether the amount of time lady beetles spend in freezing temperatures affects how long it takes them to wake up from a chill coma. Caroline thought that lady beetles exposed to lengthy freezing temperatures would be harmed because freezing causes tissue damage and the insect must use more energy to survive. She predicted that the longer the lady beetles had been exposed to the cold, the longer it would take them to wake up from their chill comas.

To begin the experiment, Andre and Nikki placed groups of lady beetles in tubes. They then placed the tubes in an ice bath, bringing the temperature down to 0℃, the point when lady beetles enter chill coma. They varied the amount of time each tube was in the ice baths and tested chill coma recovery times after 3, 24, 48, 72, or 96 hours. After removing the tubes from the ice baths, they put the lady beetles on their backs with their legs in the air and left them at room temperature, 20℃. Andre and Nikki timed how long it took each beetle to wake up and turn itself over.

In the experiment, they used two different populations of lady beetles. Population 1 had been living in the lab for several weeks before the experiment began. They were not in great health and some had started to die. In order to make sure they had enough beetles for the experiment, Caroline purchased more lady beetles, which she called Population 2. Population 2 only spent a few days living in the lab before testing and were in much better health. Caroline noted the differences in these populations and thought their age, health, and background might affect how they respond to the experiment. She decided to track which population the lady beetles were from so she could analyze the data separately and see if the health differences between Population 1 and 2 changed the results.

Featured scientists: Caroline Williams & Andre Szejner Sigal, University of California, Berkeley, & Nikki Chambers, Biology Teacher, West High School, Torrance, CA

Flesch–Kincaid Reading Grade Level = 9.8

Are forests helping in the fight against climate change?

Bill setting up a large metal tower in Harvard Forest in 1989, used to measure long-term CO2 exchange.

The activities are as follows:

As humans drive cars and use electricity, we release carbon in the form of carbon dioxide (CO2) into the air. Because COhelps to trap heat near the surface of the earth, it is known as a greenhouse gas and contributes to climate change. However, carbon is also an important piece of natural ecosystems, because all living organisms contain carbon. For example, when plants photosynthesize, they take COfrom the air and turn it into other forms of carbon: sugars for food and structural compounds to build their stems, roots, and leaves. When the carbon in a living tree’s trunk, roots, leaves, and branches stays there for a long time, the carbon is kept out of the air. This carbon storage helps reduce the amount of COin the atmosphere. However, not all of the COthat trees take from the air during photosynthesis remains as part of the tree. Some of that carbon returns to the air during a process called respiration.

Another important part of the forest carbon cycle happens when trees drop their leaves and branches or die. The carbon that the tree has stored breaks down in a process called decomposition. Some of the stored carbon returns to the air as CO2, but the rest of the carbon in those dead leaves and branches builds up on the forest floor, slowly becoming soil. Once carbon is stored in soil, it stays there for a long time. We can think of forests as a balancing act between carbon building up in trees and soil, and carbon released to the air by decomposition and respiration. When a forest is building up more carbon than it is releasing, we call that area a carbon sink, because overall more COis “sinking” into the forest and staying there. On the other hand, when more carbon is being released by the forest through decomposition and respiration, that area is a carbon source, because the forest is adding more carbon back into the atmosphere than it is taking in through photosynthesis.

In the 1990s, scientists began to wonder what role forests were having in this exchange of carbon in and out of the atmosphere. Were forests overall storing carbon (carbon sink), or releasing it (carbon source)? Bill is one of the scientists who decided to explore this question. Bill works at the Harvard Forest in central Massachusetts, a Long-Term Ecological Research site that specializes in setting up big experiments to learn how the environment works. Bill and his team of scientists realized they could measure the COcoming into and out of an entire forest. They built large metal towers that stand taller than the forest trees around them and use sensors to measure the speed, direction, and COconcentration of each puff of air that passes by. Bill compares the COin the air coming from the forest to the ones moving down into the forest from the atmosphere. With the COdata from both directions, Bill calculates the Net Ecosystem Exchange (or NEE for short). When more carbon is moving into the forest than out, NEE is a negative number because COis being taken out of the air. This often happens during the summer when trees are getting a lot of light and are therefore photosynthesizing. When more COis leaving the forest, it means that decomposition and respiration are greater than photosynthesis and the NEE is a positive number. This typically happens at night and in the winter, when trees aren’t photosynthesizing but respiration and decomposition still occur. By adding up the NEE of each hour over a whole year, Bill finds the total amount of COthe forest is adding or removing from the atmosphere that year.

Bill and his team were very interested in understanding NEE because of how important it is to the global carbon cycle, and therefore to climate change. They wanted to know which factors might cause the NEE of a forest to vary. Bill and other scientists collected data on carbon entering and leaving Harvard Forest for many years to see if they could find any patterns in NEE over time. By looking at how the NEE changes over time, predictions can be made about the future: are forests taking up more COthan they release? Will they continue to do so under future climate change?

Featured scientist: Bill Munger from Harvard University. Written by: Fiona Jevon.

Flesch–Kincaid Reading Grade Level = 10.5

Additional teacher resource related to this Data Nugget:

  • There are several publications based on the data from the Harvard Forest LTER. PDFs for all papers can be found online here. Citations below:
    • Wofsy, S.C., Goulden, M.L., Munger, J.W., Fan, S.M., Bakwin, P.S., Daube, B.C., Bassow, S.L. and Bazzaz, F.A., 1993. Net exchange of CO2 in a mid-latitude forest. Science260(5112), pp.1314-1317.
    • Goulden, M.L., Munger, J.W., Fan, S.M., Daube, B.C. and Wofsy, S.C., 1996. Exchange of carbon dioxide by a deciduous forest: response to interannual climate variability. Science271(5255), pp.1576-1578.
    • Barford, C.C., Wofsy, S.C., Goulden, M.L., Munger, J.W., Pyle, E.H., Urbanski, S.P., Hutyra, L., Saleska, S.R., Fitzjarrald, D. and Moore, K., 2001. Factors controlling long-and short-term sequestration of atmospheric CO2 in a mid-latitude forest. Science294(5547), pp.1688-1691.
    • Urbanski, S., Barford, C., Wofsy, S., Kucharik, C., Pyle, E., Budney, J., McKain, K., Fitzjarrald, D., Czikowsky, M. and Munger, J.W., 2007. Factors controlling CO2 exchange on timescales from hourly to decadal at Harvard Forest. Journal of Geophysical Research: Biogeosciences112(G2).
    • Wehr, R., Munger, J.W., McManus, J.B., Nelson, D.D., Zahniser, M.S., Davidson, E.A., Wofsy, S.C. and Saleska, S.R., 2016. Seasonality of temperate forest photosynthesis and daytime respiration. Nature534(7609), p.680.
  • Our Changing Forests Schoolyard Ecology project – Do your students want to get involved with research monitoring carbon cycles in forests? Check out this hands-on field investigation, led by a team of Ecologists at Harvard Forest. Students can contribute to this study by monitoring a 20 meter by 20 meter plot in a wooded area near their schools.
  • Video showcasing 30 years of research at the Harvard Forest LTER
  • A cool article about the diversity of research being done at Harvard Forest – Researchers blown away by hurricane simulation
  • Additional images from Harvard Forest, diagrams of NEE, and a vocabulary list can be found in this PowerPoint.

The case of the collapsing soil

An area in the Florida Everglades where strange soil collapse has been observed.

The activities are as follows:

As winds blow through the large expanses of grass in the Florida Everglades, it looks like flowing water. This “river of grass” is home to a wide diversity of plants and animals, including both the American Alligator and the American Crocodile. The Everglades ecosystem is the largest sub-tropical wetland in North America. One third of Floridians rely on the Everglades for water. Unfortunately, this iconic wetland is threatened by rising sea levels caused by climate change. Sea level rise is caused by higher global temperatures leading to thermal expansion of water, land-ice melt, and changes in ocean currents.

With rising seas, one important feature of the Florida Everglades may change. There are currently large amounts of carbon stored in the wetland’s muddy soils. By holding carbon in the mud, coastal wetlands are able to help in the fight against climate change. However, under stressful conditions like being submersed in sea water, soil microbes increase respiration. During respiration, carbon stored in the soil is released as carbon dioxide (CO2), a greenhouse gas. As sea level rises, soil microbes are predicted to release stored carbon and contribute to the greenhouse effect, making climate change worse.

Shelby collecting soil samples from areas where the soil has collapsed in the Everglades.

Shelby and John are ecologists who work in southern Florida. John became fascinated with the Everglades during his first visit 10 years ago and has been studying this unique ecosystem ever since. Shelby is interested in learning how climate change will affect the environment, and the Everglades is a great place to start! They are both very concerned with protecting the Everglades and other wetlands. Recently when John, Shelby, and their fellow scientists were out working in the Everglades they noticed something very strange. It looked like areas of the wetland were collapsing! What could be the cause of this strange event?

John and Shelby thought it might have something to do loss of carbon due to sea level rise. They wanted to test whether the collapsing soils were the result of increased microbial respiration, leading to loss of carbon from the soil, due to stressful conditions from sea level rise. They set out to test two particular aspects of sea water that might be stressful to microbes – salt and phosphorus.

Phosphorus is found in sea water and is a nutrient essential for life. However, too much phosphorus can lead to over enriched soils and change the way that microbes use carbon. Sea water also contains salt, which can stress soil microbes and kill plants when there is too much. Previous research has shown that both salt and phosphorus exposure on their own increase respiration rates of soil microbes.

A photo of the experimental setup. Each container has a different level of salt and phosphorus concentration.

To test their hypotheses, a team of ecologists in John’s lab developed an experiment using soils from the Everglades. They collected soil from areas where the soil had collapsed and brought it into the lab. These soils had the microbes from the Everglades in them. Once in the lab, they put their soil and microbes into small vials and exposed them to 5 different concentrations of salt, and 5 different concentrations of phosphorus. The experiment crossed each level of the two treatments. This means they had soil in every possible combination of treatments – some with high salt and low phosphorus, some in low salt and high phosphorus, and so on. Their experiment ran for 5 weeks. At the end of the 5 weeks they measured the amount of COreleased from the soils.

Featured scientists: John Kominoski and Shelby Servais from Florida International University. Written by Shelby, John, and Teresa Casal.

Flesch–Kincaid Reading Grade Level = 9.2

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