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Causes of episodic acidification in five Pennsylvania streams on the Northern Appalachian Plateau
Author(s) -
DeWalle David R.,
Swistock Bryan R.
Publication year - 1994
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/94wr00758
Subject(s) - streams , plateau (mathematics) , acid neutralizing capacity , hydrology (agriculture) , geology , base flow , dilution , drainage basin , bedrock , structural basin , environmental science , geomorphology , soil water , soil science , geography , physics , cartography , acid deposition , thermodynamics , mathematical analysis , computer network , mathematics , geotechnical engineering , computer science
Causes of episodic stream acidification and acid‐neutralizing capacity (ANC) declines were investigated in five streams on forested, unglaciated catchments on the northern Appalachian Plateau of Pennsylvania, during October 1988 to April 1990. Increased SO 4 concentrations during episodes were the primary cause of ANC declines on three of the streams. Episodes on the remaining two streams were dominated by base cation dilution and/or SO 4 increases. Base cation dilution was most important in a stream with initially high preepisode ANC caused by seeps from limestone outcrops. Bedrock layers on this basin were dipping toward the channel, which promoted more rapid movement of low‐ANC subsurface storm flow water to the channel. A stream with even higher preepisode ANC, but on a basin with geologic structure that shunted low‐ANC subsurface storm flow away from the channel, exhibited only minor base cation dilution. Organic acidity contributed to ANC decreases on all five streams, although it was a minor source compared with SO 4 and dilution. NO 3 and Cl did not contribute to ANC decreases on any of the study streams. Aluminum increases acted to reduce episodic ANC declines especially in the more acidic streams. Episodic acidification on the northern Appalachian Plateau in Pennsylvania was similar to that found in mid‐Atlantic streams where SO 4 increases play a dominant role, but unlike glaciated regions in the Northeast where NO 3 can be important.