Discovery: Acid Rain.- Scourge of the Past or Trend of the Present?

Hi My Friends: A VUELO DE UN QUINDE EL BLOG., Acid rain. It was a problem that largely affected U.S. eastern states. It began in the 1950s when Midwest coal plants spewed sulfur dioxide and nitrogen oxides into the air, turning clouds--and rainfall--acidic.

Has acid rain washed out of forests and streams? Or is a new threat on the way?
Credit: NSF Hubbard Brook LTER Site
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Northeastern lakes were once a witches' brew of acidifying waters that killed fish and birds.
Credit: NSF Hubbard Brook LTER Site
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Will sugar maples turn red in fall? Climate change and acidification of soils may tell the tale.
Credit: NSF Hubbard Brook LTER Site
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Meteorological and precipitation chemistry monitoring at NSF's Hubbard Brook LTER Site.
Credit: NSF Hubbard Brook LTER Site
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Scientist collecting a stream sample at the Hubbard Brook LTER Site.
Credit: NSF Hubbard Brook LTER Site
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A gauging station at Hubbard Brook provides new data on acidification of streams.
Credit: NSF Hubbard Brook LTER Site
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Discovery
Acid Rain: Scourge of the Past or Trend of the Present?
 

The following is part nine in a series on the National Science Foundation's Long Term Ecological Research (LTER) Network. Visit parts one, two, three, four, five, six , seven and eight in this series.

Acid rain. It was a problem that largely affected U.S. eastern states. It began in the 1950s when Midwest coal plants spewed sulfur dioxide and nitrogen oxides into the air, turning clouds--and rainfall--acidic.

As acid rain fell, it affected everything it touched, leaching calcium from soils and robbing plants of important nutrients. New England's sugar maples were among the trees left high and dry.

Acid rain also poisoned lakes in places like New York's Adirondack Mountains, turning them into a witches' brew of low pH waters that killed fish and brought numbers of fish-eating birds like loons to the brink.

Then in 1970 the U.S. Congress imposed acid emission regulations through the Clean Air Act, strengthened two decades later in 1990. By the 2000s, sulfate and nitrate in precipitation had decreased by some 40 percent.

Has acid rain now blown over? Or is there a new dark cloud on the horizon?

In findings recently published in the journal Water Resources Research, Charles Driscoll of Syracuse University and the National Science Foundation's (NSF) Hubbard Brook Long Term Ecological Research (LTER) site in New Hampshire reports that the reign of acid rain is far from over.

It's simply "shape-shifted" into a different form.

Hubbard Brook is one of 26 NSF LTER sites across the nation and around the world in ecosystems from deserts to coral reefs to coastal estuaries.

Co-authors of the paper are Afshin Pourmokhtarian of Syracuse University, John Campbell of the U.S. Forest Service in Durham, N.H., and Katharine Hayhoe of Texas Tech University. Pourmokhtarian is the lead author.

Acid rain was first identified in North America at Hubbard Brook in the mid-1960s, and later shown to result from long-range transport of sulfur dioxide and nitrogen oxides from power plants.

Hubbard Brook research influenced national and international acid rain policies, including the 1990 Clean Air Act amendments.

Researchers at Hubbard Brook have continued to study the effects of acid rain on forest growth and on soil and stream chemistry.

Long-term biogeochemical measurements, for example, have documented a decline in calcium levels in soils and plants over the past 40 years. Calcium is leaching from soils that nourish trees such as maples. The loss is primarily related to the effects of acid rain (and acid snow).

Now Hubbard Brook LTER scientists have discovered that a combination of today's higher atmospheric carbon dioxide level and its atmospheric fallout is altering the hydrology and water quality of forested watersheds--in much the same way as acid rain.

"It's taken years for New England forests, lakes and streams to recover from the acidification caused by atmospheric pollution," says Saran Twombly, NSF program director for long-term ecological research.

"It appears that these forests and streams are under threat again. Climate change will likely return them to an acidified state. The implications for these environments, and for humans depending on them, are severe."

Climate projections indicate that over the 21st century, average air temperature will increase at the Hubbard Brook site by 1.7 to 6.5 degrees C, with increases in annual precipitation ranging from 4 to 32 centimeters above the average from 1970-2000.

Hubbard Brook scientists turned to a biogeochemical model known as PnET-BGC to look at the effects of changes in temperature, precipitation, solar radiation and atmospheric carbon dioxide on major elements such as nitrogen in forests.

The model is used to evaluate the effects of climate change, atmospheric deposition, and land disturbance on soil and surface waters in northern forest ecosystems.

It was created by linking the forest-soil-water model PnET-CN with a biogeochemical sub-model, enabling the incorporation of major elements like calcium, nitrogen, potassium and others.

The results show that under a scenario of future climate change, snowfall at Hubbard Brook will begin later in winter, snowmelt will happen earlier in spring, and soil and stream waters will become acidified, altering the quality of water draining from forested watersheds.

"The combination of all these factors makes it difficult to assess the effects of climate change on forest ecosystems," says Driscoll.

"The issue is especially challenging in small mountain watersheds because they're strongly influenced by local weather patterns."

The Hubbard Brook LTER site has short, cool summers and long, cold winters. Its forests are made up of northern hardwood trees like sugar maples, American beeches and yellow birches. Conifers--mostly balsam firs and red spruces--are more abundant at higher elevations.

The model was run for Watershed 6 at Hubbard Brook. "This area has one of the longest continuous records of meteorology, hydrology and biogeochemistry research in the U.S.," says Pourmokhtarian.

The watershed was logged extensively from 1910 to 1917; it survived a hurricane in 1938 and an ice storm in 1998.

It may have more to weather in the decades ahead.

The model showed that in forest watersheds, the legacy of an accumulation of nitrogen, a result of acid rain, could have long-term effects on soil and on surface waters like streams.

Changes in climate may also alter the composition of forests, says Driscoll. "That might be very pronounced in places like Hubbard Brook. They're in a transition forest zone between northern hardwoods and coniferous red spruces and balsam firs."

The model is sensitive to climate that is changing now--and climate changes expected to occur in the future. 

In scenarios that result in water stress, such as decreases in summer soil moisture due to shifts in hydrology, the end result is further acidification of soil and water.

--	Cheryl Dybas, NSF (703) 292-7734 cdybas@nsf.gov

Related Websites
NSF LTER Network: http://www.lternet.edu/
NSF Hubbard Brook LTER Site: http://www.hubbardbrook.org/
Science, Engineering and Education for Sustainability NSF-Wide Investment (SEES): http://www.nsf.gov/funding/pgm_summ.jsp?pims_id=504707

Guillermo Gonzalo Sánchez Achutegui

ayabaca@gmail.com

ayabaca@hotmail.com

ayabaca@yahoo.com 

SCIENCE: Seeing the Forest Under the Trees

Hi my Friends: A VUELO DE UN QUINDE EL BLOG., New Effect of Acid Rain on Forests: Too Many Dead Leaves a Bad Sign for Sugar Maples.

Ecologists found a new effect of acid rain: too many dead leaves on the forest floor.
Credit: NPS
A long-term experiment continues on sugar maple forests in the northern U.S.

Credit: Sierra Patterson and Alan TalhelmAcid rain affects vast maple areas; it slows the process of leaf decomposition.Credit: Sierra Patterson and Alan Talhelm
Heavy leaf litter: not a good sign for sugar maples; new seedlings can't get through.Credit: NPS
Scientists study atmospheric nitrogen deposition from acid rain and its effects on forests.Credit: Sierra Patterson and Alan Talhelm
A lovely stand of sugar maples, but for how long? The next generation is threatened.Credit: Sierra Patterson and Alan Talhelm

December 7, 2011
Scientists have discovered that nitrogen that falls from the atmosphere in acid rain can influence large tracts of sugar maples in North America.
The atmospheric nitrogen in acid rain can affect forest ecosystems by acidifying soils and causing nutrient imbalances.
Sugar maples in northeastern North America are especially vulnerable. Vast maple areas have been affected by this acidification process, which depletes soil calcium in already calcium-poor soils such as those of the Eastern United States.
In the calcium-rich soils of the upper Great Lakes, however, acid rain also wreaks havoc, ecologists have found. It slows leaf decomposition, leading to a pile-up of leaves and hindering new young maples from sprouting up.
The researchers published their results on-line in the current issue of the Journal of Applied Ecology.
"The process has the potential to affect sugar maple-dominated forests throughout the Great Lakes region," says Donald Zak, an ecologist at the University of Michigan, "especially as nitrogen deposition continues in the future."
He and colleagues Sierra Patterson of the University of Michigan, Andrew Burton of Michigan Technological University and Alan Talhelm and Kurt Pregitzer of the University of Idaho conducted seventeen years of nitrogen deposition experiments at rates that will likely happen by the end of this century.
"The effects have slowed the natural processes of decomposition, such as the decay of dead leaves, causing the leaves to build up and the forest floor to thicken," says Zak.
The leaf-littered ground has become a barrier to the small seeds of sugar maples, hence numbers of young sugar maples--the forest's next generation--are dropping.
"There were significantly fewer seedlings in the nitrogen treatment area," says Patterson, the paper's lead author.
"Increasing the amount of fallen leaves on the forest floor caused a significant reduction in successful sugar maple seedlings," she says. "On the other hand, decreasing the thickened forest floor increased seedling survival."
"The surprising results reported in this study are an example of the value of long-term research," says Saran Twombly, program director in the National Science Foundation (NSF)'s Division of Environmental Biology, which funded the work.
"Uncovering an unexpected link between nitrogen deposition and sugar maple seedling success depended on the ability to simulate increased nitrogen deposition year after year," Twombly says.
"The manipulations used to reveal the details of this link could not have worked in other than a long-term study."
Scientists need to re-think the myriad ways in which acid rain may affect forests, Zak believes, especially those made up largely of sugar maples.
"We need to learn to see the forest," he says, "that's under the trees."
Information By: the National Science Foundation (NSF).
Guillermo Gonzalo Sánchez Achutegui
ayabaca@gmail.com
ayabaca@hotmail.com
ayabaca@yahoo.com
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