Melting snow provides clues for acidification

Feb 15, 2008

In forests of the northeastern United States, sulfate and nitrate are the dominant dissolved forms of sulfur and nitrogen in precipitation. In winter, these acidic agents accumulate in the snowpack and are released to groundwater and streams over a short period of time during spring snowmelt. This pulsed release of sulfate and nitrate in snowmelt can cause episodic acidification in poorly buffered soils, ultimately threatening the health of acid-sensitive biota.

There have been recent studies showing that biological cycling of sulfur and nitrogen persists in cold weather, despite below freezing air temperatures. Much of this activity occurs in soils, where an insulating snow layer keeps soil temperatures warm enough for a range of biological processes. Despite the growing awareness of winter’s role in sulfur and nitrogen cycling, many questions remain unanswered. In particular, there is much uncertainty about how sulfate and nitrate are retained or transformed in forest soils during cold weather.

In the November-December 2007 issue of the Soil Science Society of America Journal (SSSAJ), scientists from the U.S. Forest Service, SUNY-ESF, University of Calgary, and Cary Institute of Ecosystem Studies tracked the movement of sulfate and nitrate deposited in snow. A solution containing isotopically enriched sulfate and nitrate was sprayed on the surface of the snowpack during mid winter. The isotopic values of the labeled sulfate and nitrate were well above background levels and served as a tracer to follow the movement and transformation of these compounds in the ecosystem.

The researchers found that almost all of the labeled sulfate and nitrate deposited on the surface of the snow was recovered in snowmelt water, indicating that there were no significant transformations of sulfate and nitrate in the snowpack.

In contrast, about half of the sulfate and nitrate was retained or transformed in the forest floor, suggesting that organic soils are a sink for these compounds during winter. For sulfate, the amount retained or transformed in the forest floor was nearly equal to the amount released, resulting in no significant net gains or losses. A significant amount of ammonium was produced in the forest floor indicating that N mineralization can be important, even when soil temperatures are near freezing. By contrast, net nitrification rates were very low during winter.

Tracer results indicated that microbes did not immobilize snowpack nitrate and that other processes such as plant uptake, denitrification, and abiotic nitrate retention were probably more important factors affecting nitrate during snowmelt. More information on controls on nitrogen and sulfur cycling during winter is critical to our understanding of long-term trends and will help us predict how forest ecosystems will respond to future disturbances and global change processes.

Source: Soil Science Society of America

Explore further: Researchers question emergency water treatment guidelines

add to favorites email to friend print save as pdf

Related Stories

US clean-air efforts stay on target, analysis shows

Mar 27, 2014

National efforts in the last decade to clear the air of dangerous particulate matter have been so successful that most urban areas have already attained the next benchmark, according to new research by Rice ...

Brown carbon works both sides of the climate equation

Feb 04, 2014

There is an atmospheric particle not satisfied with only a single role in the climate. The ambitious culprit? Brown carbon aerosol steps outside the box and acts to both warm and cool the climate. A brown ...

Aerosol particles at global view

Nov 10, 2010

Of all the pollution that fills our lungs on any given day, the most dangerous is the small stuff. Aerosol particle pollution—airborne solid particles and liquid droplets--comes in a range of sizes. Particles ...

Recommended for you

Researchers question emergency water treatment guidelines

15 hours ago

The Environmental Protection Agency's (EPA's) recommendations for treating water after a natural disaster or other emergencies call for more chlorine bleach than is necessary to kill disease-causing pathogens ...

European climate at the +2 C global warming threshold

17 hours ago

A global warming of 2 C relative to pre-industrial climate has been considered as a threshold which society should endeavor to remain below, in order to limit the dangerous effects of anthropogenic climate change.

User comments : 0

More news stories

Melting during cooling period

(Phys.org) —A University of Maine research team says stratification of the North Atlantic Ocean contributed to summer warming and glacial melting in Scotland during the period recognized for abrupt cooling ...

Warm US West, cold East: A 4,000-year pattern

Last winter's curvy jet stream pattern brought mild temperatures to western North America and harsh cold to the East. A University of Utah-led study shows that pattern became more pronounced 4,000 years ago, ...