Microbes in soggy soil remove nitrogen, a critical nutrient -- and pollutant
Even during summer dry spells, some isolated patches of soil in forested watersheds remain waterlogged.
These patches act as hot spots of microbial activity that remove nitrogen from groundwater and return it to the atmosphere, researchers from several institutions, including Virginia Tech, report in a leading scientific journal.
The discovery provides insight into the health of a forest. Nitrogen is an important nutrient for plant growth and productivity, but in streams, it can be a pollutant.
"The importance of these fragmented patches of saturated soil and their role in the fate of nitrogen in forested watersheds has been underappreciated until recently," said Kevin McGuire, an associate director of the Virginia Water Resources Research Center based in Virginia Tech's College of Natural Resources and Environment, co-author of the article to be published in the Proceedings of the National Academy of Sciences.
"We were able to determine the importance of denitrification in patches of shallow groundwater, which have largely been overlooked control points for nitrogen loss from temperate forested watersheds," McGuire said.
Most nitrogen is deposited by rain. Temperate forests receive much larger inputs of nitrogen from the atmosphere than they export to streams. Once nitrogen leaves the forest in streams, it can become a water pollutant.
"In some ecosystems, there have been long-term declines in stream water export of nitrogen when inputs have remained elevated," said co-author Christine Goodale, an associate professor of ecology and evolutionary biology at Cornell University.
"Understanding the fate of this nitrogen has been a challenge because denitrification — a gaseous loss of nitrogen to the atmosphere — is notoriously difficult to measure," said co-author Peter Groffman, an expert on denitrification at the Cary Institute of Ecosystem Studies.
Denitrification removes nitrogen from water and can therefore improve water quality in downstream lakes and estuaries.
However, nitrogen is also an important nutrient for plant growth in the forest so removals of nitrogen by natural processes can reduce the productivity of the forest.
The research, led by Sarah Wexler while she was a postdoctoral associate in hydrology and stable isotope geochemistry at Cornell University, took place in the Hubbard Brook Experimental Forest in the White Mountains of New Hampshire, where the atmosphere annually deposits five to seven pounds of nitrogen per acre.
The Hubbard Brook Experimental Forest is part of the National Science Foundation's Long Term Ecological Research Network.
McGuire, also an associate professor of hydrology in the Department of Forest Resources and Environmental Conservation, led another National Science Foundation-funded project at the site, which developed an organizing framework to describe and map variations of soil in the watershed that explain shallow groundwater occurrence and frequency.
Groundwater wells from this earlier study were used in the new research to monitor soils that may have had the right conditions to function as hot spots for denitrification.
At sites throughout the forest, the research team measured the presence of nitrate, a form of nitrogen that is highly mobile and reactive in the environment, determined whether the nitrate is a result of atmospheric deposition or microbial conversion, and discovered the nitrogen loss to the atmosphere.
"We were able to differentiate sources of nitrate and show that some of the nitrate was lost to the atmosphere by looking at nitrate at the atomic level, that is, at the isotopic composition of the nitrogen and oxygen in nitrate," said Wexler, who is now at the School of Environmental Sciences at the University of East Anglia in the United Kingdom. "The isotopic composition of nitrate provides a natural way to directly track the details of nitrogen cycling."
McGurie said, "Some work remains to be done, but the aim is to be able to develop a better sense of where and how nitrogen is processed in the environment and be in a position to predict how changes in climate, for example warmer and wetter conditions, affect nitrogen cycling and water quality in forested ecosystems."
Lynn Davis | EurekAlert!
Gran Chaco: Biodiversity at High Risk
17.01.2018 | Humboldt-Universität zu Berlin
Dead trees are alive with fungi
10.01.2018 | Helmholtz Centre for Environmental Research (UFZ)
What enables electrons to be transferred swiftly, for example during photosynthesis? An interdisciplinary team of researchers has worked out the details of how...
For the first time, scientists have precisely measured the effective electrical charge of a single molecule in solution. This fundamental insight of an SNSF Professor could also pave the way for future medical diagnostics.
Electrical charge is one of the key properties that allows molecules to interact. Life itself depends on this phenomenon: many biological processes involve...
At the JEC World Composite Show in Paris in March 2018, the Fraunhofer Institute for Laser Technology ILT will be focusing on the latest trends and innovations in laser machining of composites. Among other things, researchers at the booth shared with the Aachen Center for Integrative Lightweight Production (AZL) will demonstrate how lasers can be used for joining, structuring, cutting and drilling composite materials.
No other industry has attracted as much public attention to composite materials as the automotive industry, which along with the aerospace industry is a driver...
Scientists at Tokyo Institute of Technology (Tokyo Tech) and Tohoku University have developed high-quality GFO epitaxial films and systematically investigated their ferroelectric and ferromagnetic properties. They also demonstrated the room-temperature magnetocapacitance effects of these GFO thin films.
Multiferroic materials show magnetically driven ferroelectricity. They are attracting increasing attention because of their fascinating properties such as...
The oceans are the largest global heat reservoir. As a result of man-made global warming, the temperature in the global climate system increases; around 90% of...
08.01.2018 | Event News
11.12.2017 | Event News
08.12.2017 | Event News
17.01.2018 | Ecology, The Environment and Conservation
17.01.2018 | Physics and Astronomy
17.01.2018 | Awards Funding