Episodic Acidification of Small Streams in the Northeastern United States: Ionic Controls of Episodes

Abstract

As part of the Episodic Response Project (ERP), we intensively monitored discharge and stream chemistry of 13 streams located in the Northern Appalachian region of Pennsylvania and in the Catskill and Adirondack Mountains of New York from fall 1988 to spring 1990. The ERP clearly documented the occurrence of acidic episodes with minimum episodic pH ≤ 5 and inorganic monomeric Al (Alim) concentrations > 150 μg/L in at least two study streams in each region. Several streams consistently experienced episodes with maximum Alim concentrations >350 μg/L. Acid neutralizing capacity (ANC) depressions resulted from complex interactions of multiple ions. Base cation decreases often made the most important contributions to ANC depressions during episodes. Organic acid pulses were also important contributors to ANC depressions in the Adirondack streams, and to a lesser extent, in the Catskill and Pennsylvania streams. Nitrate concentrations were low in the Pennsylvania streams, whereas the Catskill and Adirondack study streams had high NO3‐ concentrations and large episodic pulses (≤ 54 μ eq/L). Most of the Pennsylvania study streams also frequently experienced episodic pulses of SO42‐ (≤ 78 μ eq/L), whereas the Adirondack and Catskill streams did not. High baseline concentrations of SO42‐ (all three study areas) and NO3‐ (Adirondacks and Catskills) reduced episodic minimum ANC, even when these ions did not change during episodes. The ion changes that controlled the most severe episodes (lowest minimum episodic ANC) differed from the ion changes most important to smaller, more frequent episodes. Pulses of NO3‐ (Catskills and Adirondacks), SO42‐ (Pennsylvania), or organic acids became more important during major episodes. Overall, the behavior of streamwater SO42‐ and NO3‐ is an indicator that acidic deposition has contributed to the severity of episodes in the study streams.

Effects of decreasing acid deposition and climate change on acid extremes in an upland stream

“…As in some other areas where similar methods have been applied (e.g. Evans et al, 1995;Wigington et al, 1996), this analysis suggests that, while long-term elevated mean SO 4 concentrations are the dominant cause of chronic acidification at the stream, short-term variability in SO 4 (between high-and low-pH conditions) is typically quite small. Therefore, variations in ions other than SO 4 must account for most of the short-term variation in ANC.…”

Nitrogen Excess in North American Ecosystems: Predisposing Factors, Ecosystem Responses, and Management Strategies

“…Trout abundance was reduced and acidsensitive fish were absent from streams with median pH Ͻ5. (Wigington et al 1996). Baker et al (1996) concluded that atmospheric deposition contributed to the severity of episodes in the streams, and that episodic acidification can have long-term effects on fish communities in small streams.…”

The decreasing importance of acidification episodes with recovery from acidification: an analysis of the 30-year record from Birkenes, Norway

“…High discharge can also cause acid episodes (Mulder et al, 1995). In the late 1980s the United States Environmental Protection Agency (US EPA) conducted a comprehensive project (Episodic Response Project) on acid episodes in 13 streams in the northeastern United States (Wigington et al, 1996).…”