It takes hundreds of years for some environmental effects to become fully realized. It’s a domino effect, meaning that what we do in this day and age will affect generations hundreds of years from now.
Hence, what University of Delaware scientists are witnessing from their research in the Alaskan tundra today near Toolik Field Station (TFS), about 150 miles north of the Arctic Circle, is the result of a succession of environmental changes that began taking place hundreds of years ago.
UD’s Tom Hanson, associate professor of marine biosciences and biological sciences, and Barbara Campbell, assistant professor of marine biosciences, have been studying the effects of global warming on this “arctic prairie.” The TFS, which is part of the U.S. Long-Term Ecological Research network, is operated by the University of Alaska Fairbanks for scientists around the world.
Hanson and Campbell are working in collaboration with scientists Michelle Mack and Ted Schuur at the University of Florida. Their project, funded by the National Science Foundation, seeks to understand how changes in temperature and nitrogen deposition in different soil layers of the tundra have affected this fragile ecosystem.
In their study, nitrogen was added to plots on a yearly basis for 20 years, mimicking what is happening naturally over a longer period. Their work will enable them to determine if other tundra ecosystems will be similarly affected by global warming.
“Understanding how changes in climate affect microbial populations will refine predictions of how stored carbon will behave relative to existing trends in global change,” says Campbell. “Changes found in this study may also reflect past climate change events, helping scientists to understand the geological record.”
Tundra soil, like that at TFS, is a large reserve of carbon derived from plants. In fact, this soil is not granular, but rather an amalgamation of dead plant leaves, Campbell says. Because it is so cold much of the year, these dead plant leaves and detritus are not broken down, but instead accumulate.
However, climate change in the form of increased temperature or increased nitrogen input to the soil appears to increase the breakdown of plant material and the loss of soil carbon. This breakdown is carried out primarily by soil microbes, leading to the release of carbon dioxide and methane that has been observed in many tundra sites. Both are greenhouse gases.
“The soil freezes seasonally to become rock solid,” says Hanson. “It thaws in the late spring to early summer. But what’s relatively new is that increased nitrogen seems to be increasing microbial
activity and soil carbon loss. We are studying the DNA of the organisms
responsible for breaking down plant detritus and soil carbon to see if the same
microbes are just more active now, or if different types of microbes occur in
these more active soils.”
Hanson and Campbell have used a high-throughput sequencing technique called pyrosequencing to analyze the DNA extracted from the soil samples.
“We used a novel method to identify between 5,000 to 10,000 microbes per sample
by sequencing a short fragment of DNA present in all organisms,” says Campbell. “This allowed us to get a snapshot of the microbial community in the soil
These snapshots were compared between plots exposed to nitrogen and control plots with no added nitrogen. Microbial community function — what types of carbon the microbes degraded — also was measured.
The results, published in the journal Environmental Microbiology, indicate that nitrogen additions changed both microbial community structure and function in the soils exposed to nitrogen. This profiling of samples will allow scientists to identify microbial DNA and functional markers that can then be identified in other tundra microbial communities to signal that this same process — the loss of tundra soil carbon — may be occurring there as well.
“The goal of this research is to understand the role of microbes in this process,
so we can better document where and how fast carbon is being leaked from the
tundra,” says Hanson. “This will help us predict the future of other tundras around the world.”
Through their work, Hanson and Campbell have already seen indications that change has occurred in the soil samples from Alaska. The next step is to study the mechanism of the microbes and how it contributes to the soil carbon loss — and to recognize what functions are being lost as well. Hanson will be working on this during a visit to the DSMZ, the German Collection of Microorganisms and Cell Cultures, in Braunschweig, Germany, where he will be trying to culture relevant microbes from the Toolik tundra.
“We have seen major changes in how the microbes are behaving,” he says. “The functions seem to be different as well, leading us to believe there is a
correlation between the change in the microbial community’s structure and the change in function.”
It’s clear from this research, as well as other reports, Hanson says, that nature’s carbon footprint has increased because the human carbon footprint has increased. The world is changing, as some of our most beautiful natural phenomena degenerate — and this is one more great reason we should continue down the path of becoming more Earth friendly.
“A lot of studies indicate that if we made some changes today, and reduced our carbon footprint by 50 percent, we might see some significant, positive, changes in the environment in 50 to 100 years at the earliest. It’s going to take that long,” says Hanson.
It’s a domino effect.
Frederick (Fritz) Nelson, professor of geography, learned early on that a firearm is handy for dealing with inquisitive bears while doing field research on Alaska’s remote North Slope. The “Slope,” as Alaskans call it, is the region extending from the northern foothills of the Brooks Range to the Arctic Ocean. The North Slope is a vast inclined plain festooned with striking geometric patterns such as ice-wedge polygons, frost boils and thaw lakes.
This tundra ecosystem is home to caribou, bears, arctic foxes and muskoxen. It is also home to the oil fields of Prudhoe Bay and the town of Barrow, the northernmost community in the United States, on the shores of the Arctic Ocean. Inhabited mostly by Iñupiat people, Barrow is on the front lines of a changing climate.
Permafrost is any part of the ground (soil, rock, ice, humus) that remains at or below 0°C (32°F) continuously for two or more years. Nelson and his team are studying the dynamics of the“active layer,” the layer of ground between the surface and the permafrost, which freezes and thaws each year.
An authority on permafrost, Nelson has made the trip to northern Alaska nearly every year since the late 1970s. He has been a driving force behind the development of the Circumpolar Active Layer Monitoring (CALM) network, established in the early 1990s and now consisting of nearly 200 sites in 15 countries. The network is producing a long-term record of permafrost behavior that is used to document the response of permafrost to climatic “drivers” and to evaluate the performance of climate models.
The CALM network’s observatories are distributed throughout the Arctic, parts of Antarctica, and several mountain ranges in the mid-latitudes. Nelson has received funding continuously for both Alaskan fieldwork and administration of the international CALM network since the mid-1990s primarily from the U.S. National Science Foundation’s Office of Polar Programs.
On the North Slope, permafrost extends from a few inches below the surface to depths of up to 2,000 feet. During their fieldwork, Nelson and his team collect data on soil and air temperature, conduct field experiments, monitor active layer depth and processes, and obtain soil cores to examine ice content. They have been at the forefront of applying new technologies, including three-dimensional ground-penetrating radar, differential GPS, and LIDAR, to examine the structure and dynamics of near-surface permafrost.
Warming temperatures in the polar regions could lead to thicker active layers, which could change the moisture and plant communities on the surface and destabilize the ice-rich permafrost through the process of “thaw settlement,” causing damage to roads, houses and other structures.
“While permafrost isn’t necessarily an impediment to human occupation of the world’s cold regions, all bets are off when ice is involved,” Nelson notes. “Changes of temperature at the ground surface — whether induced by human activity or a warming climate — may trigger melting of the subsurface ice, which in turn leads to decreased volume and uneven subsidence of the ground surface.
“If permafrost degrades over large regions, as climate simulations indicate will be the case,” Nelson says, “liberation of organic carbon stored in the shallow permafrost in the form of methane and carbon dioxide could make a very significant contribution to further warming of the climate.”