Melting snow provides clues for acidification

Scientists investigate accumulated sulfate and nitrate in New England snow and follow it after the snow melts as clues to acidification

MADISON, WI, February 11, 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.