Analysis of Trends in Episodic Acidification of Streams in Western Maryland

In this study we report on changes in the magnitude and mechanisms of episodic acidification of a small acid-sensitive stream in western Maryland (U.S.) during the 1990s, a period in which wet sulfate deposition declined by 10−25% due to implementation of the Clean Air Act Amendments (CAAA) of 1990....

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Bibliographic Details
Published in:Environmental science & technology 2007-08, Vol.41 (16), p.5601-5607
Main Authors: Kline, Kathleen M, Eshleman, Keith N, Morgan, Raymond P, Castro, Nancy M
Format: Article
Language:English
Subjects:
01 COAL, LIGNITE, AND PEAT
ACID NEUTRALIZING CAPACITY
ACIDIFICATION
Acids - analysis
Acids - chemistry
AMENDMENTS
ANNUAL VARIATIONS
Applied sciences
BIOLOGICAL RECOVERY
CLEAN AIR ACTS
Continental surface waters
DATA ANALYSIS
DEPOSITION
Earth sciences
Earth, ocean, space
ENERGY PLANNING, POLICY AND ECONOMY
Engineering and environment geology. Geothermics
ENVIRONMENTAL IMPACTS
ENVIRONMENTAL SCIENCES
Exact sciences and technology
Geography
IMPLEMENTATION
MARYLAND
MONITORING
Natural water pollution
PH VALUE
Pollution
Pollution, environment geology
Rivers - chemistry
SAMPLING
Sedimentation & deposition
STREAMS
Studies
SULFATES
Sulfates - chemistry
Surface water
SURFACE WATERS
USA
Water Movements
WATER POLLUTION
Water treatment and pollution
WATERSHEDS
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Summary:In this study we report on changes in the magnitude and mechanisms of episodic acidification of a small acid-sensitive stream in western Maryland (U.S.) during the 1990s, a period in which wet sulfate deposition declined by 10−25% due to implementation of the Clean Air Act Amendments (CAAA) of 1990. We observed a relatively minor trend in the magnitude of episodic acidification over this period, as measured by transient changes in acid neutralizing capacity (ΔANC) and minimum values of ANC (ANCmin) during 22 events sampled prior to and following CAAA implementation. Any relationship to changes in atmospheric deposition appears to be confounded by large hydroclimatological variability between the two sampling periods. Nonetheless, results obtained prior to implementation of the CAAA indicated that the mechanism of episodic acidification was mostly attributable to flushing of accumulated sulfate from the watershed, whereas results obtained post-CAAA indicated domination by base cation dilution. This shift in the mechanism of episodic acidification is qualitatively consistent with hydrochemical theory, as well as with empirical results from surface waters in other regions where dramatic declines in sulfate deposition have taken place.
ISSN:0013-936X
1520-5851
DOI:10.1021/es070424u