This book is included in the Natural Disasters section.
ACID RAIN REVISITED
Summary
Acid rain is still a problem and has had a
greater environmental impact than previously projected.
Many people believe that the problem of acid rain was solved with the
passage of the 1990 Clean Air Act Amendments (CAAA). However, research
from the Hubbard Brook Experimental Forest (HBEF) in New Hampshire and
other study sites in the northeastern United States (hereafter the
Northeast) demonstrates that acid rain (hereafter acid deposition) is
still a significant problem. Although sulfur emissions that contribute
to acid deposition have declined, nitrogen emissions have not changed
substantially region-wide and have actually increased in
some areas of the eastern United States.
Acid deposition delivers acids and acidifying compounds to the Earth’s
surface, which then move through soil, vegetation, and surface waters
and, in turn, set off a cascade of adverse ecological effects. Recent
research shows that the ability of some ecosystems to neutralize acid
deposition has diminished over time, delaying the recovery of forests,
lakes, and streams. Moreover, while the Clean Air Acts of 1970 and 1990
have improved air quality somewhat, the emissions reductions mandated in
1990 are not likely to bring about full ecosystem recovery in sensitive
areas of the Northeast.
Acid deposition has altered soils in areas
of the Northeast.
Until recently, limited understanding existed of the effects of acid
deposition on soil. However, current research shows that acid deposition
has altered, and continues to alter, soil in a number of ways:
-- Acid deposition has accelerated the leaching of base cations — elements
such as calcium and magnesium that help counteract acid deposition —
from the soil in acid-sensitive areas of the Northeast. For example, the
amount of available calcium in the soil at the HBEF appears to have
declined more than 50 percent over the past several decades.
-- A strong positive relationship exists between inputs of sulfur and
nitrogen and the concentrations of these elements in forest soils. As a
consequence, sulfur and nitrogen have accumulated in forest soils across
the region.
-- Acid deposition has increased the concentration of dissolved inorganic
aluminum in soil waters. Dissolved inorganic aluminum (hereafter simply
aluminum) is an ecologically harmful form of aluminum. At high
concentrations, aluminum can hinder the uptake of water and essential
nutrients by tree roots.
The alteration of soils by acid deposition has serious consequences for
acid-sensitive ecosystems. Soils that are compromised by acid deposition
are less able to neutralize additional amounts of acid deposition,
provide poorer growing conditions for plants, and delay ecosystem
recovery.
Acid deposition has stressed trees in
areas of the Northeast.
The 1990 National Acid Precipitation Assessment Program (NAPAP) report
to Congress concluded there was insubstantial evidence that acid
deposition had caused the decline of trees other than red spruce growing
at high-elevations. More recent research shows that acid deposition has
contributed to the decline of red spruce trees throughout the eastern
U.S. and sugar maple trees in central and western Pennsylvania. Symptoms
of tree decline include poor crown condition, reduced tree growth, and
unusually high levels of tree mortality. Red spruce and sugar maple are
the species that have been the most intensively studied and research to
date has shown that:
-- Acid deposition leaches essential calcium from needles (i.e.,
foliage) of red spruce, rendering them more susceptible to freezing
injury. Increased freezing injury has lead to the mortality of more than
half of large canopy red spruce trees in some forests in the Northeast.
-- Extensive mortality among sugar maples in Pennsylvania appears to
result from deficiencies of base cations, coupled with other stresses
such as insect defoliation or drought. The data show that sugar maples
are most prone to die on sites where base cation concentrations in soil
or foliage are lowest.
Acid deposition has impaired lakes and
streams in the Northeast.
Acid deposition has impaired, and continues to impair, the water quality
of lakes and streams in three important ways: lowering pH levels (i.e.,
increasing the acidity); decreasing acid-neutralizing capacity (ANC);
and increasing aluminum concentrations. High concentrations of aluminum
and increased acidity have reduced the species diversity and abundance
of aquatic life in many lakes and streams in the Northeast. Fish have
received the most attention to date, but entire food webs are often
negatively affected. Recent water quality data show that:
-- 41 percent of lakes in the Adirondack Mountain region of New York and
15 percent of lakes in New England exhibit signs of chronic and/or
episodic acidification.
-- Only modest improvements in ANC, an important measure of water quality,
have occurred in New England. No significant improvement in ANC has been
measured in the Adirondack or Catskill Mountains of New York.
-- Elevated concentrations of aluminum have been measured in acid-impacted
surface waters throughout the Northeast.
The Clean Air Act has had positive
effects, but emissions and deposition remain high compared to background
conditions.
Regulatory controls initiated in the 1970s and 1990s decreased sulfur
dioxide emissions, yet these emissions remain high compared to
background conditions. Controls on nitrogen oxides and ammonia have not
been fully addressed; consequently, emissions of these compounds are
high and have remained largely unchanged in recent years. In the period
1995-1997, wet deposition of sulfate in the Northeast was approximately
20 percent lower than levels in the preceding three years with
implementation of the 1990 CAAA. However, wet deposition of nitrogen has
not changed significantly since the 1980s. Importantly, the emission and
atmospheric deposition of base cations that help counteract acid
deposition have declined significantly since the early 1960s with the
enactment of pollution controls on particulate matter.
The rate and extent of ecosystem recovery
from acid deposition are directly related to the timing and degree of
emissions reductions.
Given the loss of acid-neutralizing base cations and the accumulation of
sulfur and nitrogen in the soil, many ecosystems are now more sensitive
to the input of additional acids and recovery from acid deposition will
likely be delayed. Research shows that emissions reductions mandated by
the 1990 CAAA are not sufficient to achieve full
ecosystem recovery in watersheds in the Northeast that are similar to
the HBEF within the next 25-50 years. Analyses of policy proposals
calling for an additional 40-80 percent reduction in electric utility
emissions of sulfur beyond the levels set by the 1990 CAAA show that
such proposals would result in measurable improvements in chemical
conditions. Specifically, with an additional 80 percent reduction in
sulfur emissions from electric utilities, streams such as those at the
HBEF would change from acidic to non-acidic in approximately 20-25
years. In sum, long-term research suggests that deeper emissions cuts
will lead to greater and faster recovery from acid deposition in the
Northeast.
End of Preview.
RETURN to
Main Titles Index or
Natural Disasters
Please Read The Website Disclaimer!
Copyright 1986-2012, The Survival & Self-Reliance Studies Institute (SSRsi), All
Rights Reserved
Site conceptualized, designed, created & maintained by MEG Raven
Snail Mail: SSRsi, PO Box 2572 Dillon, CO. 80435-2572