Parker J. Wigington

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

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.

Transient storage and hyporheic flow along the Willamette River, Oregon: Field measurements and model estimates

Transient storage is a measure of the exchange of main channel flow with subsurface hyporheic flow and surface water dead zones. Hyporheic flow, in which river water enters the channel bed and banks to reemerge downstream, promotes biochemical processes that are important for water quality and aquatic habitat. Previous studies have quantified transient storage and hyporheic flow on small streams but were not specifically developed to identify both of these processes over long reaches of large rivers. We studied transient storage on the eighth-order upper Willamette River, which flows through high- porosity gravel deposits conducive to hyporheic flow. We used main channel dye tracer studies and solute transport modeling to estimate transient storage on nine study reaches in a 26-km-long study area. We also took dye measurements within the transient storage zone to identify transient storage flow paths. We obtained estimates of transient storage exchange coefficient, αs (mean equals 1.6×10−4 s−1), and transient storage to main channel cross-sectional area, As/A (mean equal to 0.28), that show that significant amounts of water follow flow paths with 0.2–30 hour transient storage zone residence times. Our dye measurements from the transient storage zone itself showed the occurrence of both subsurface and surface flow paths, confirming that hyporheic flow is an important component of estimated transient storage. We found that the two highest As/Aestimates were for reaches that spanned the only length of active main channel in our study area that is unconstrained and where the river can rework large gravel deposits. Much of the natural channel complexity that historically promoted hyporheic flow no longer exists on the upper Willamette River. River management targeting the ecological functions provided by hyporheic flow might best focus on restoring historic hydrogeomorphic processes for creating sites conducive to hyporheic flow.

Non‐navigable streams and adjacent wetlands: addressing science needs following the Supreme Court's Rapanos decision

In June of 2006, the US Supreme Court ruled in two cases concerning jurisdiction under the Clean Water Act (CWA). The decisions suggest that hydrological permanence of non-navigable streams and adjacent wetlands (NNSAWs) and their effects on the chemical, physical, and biological integrity of navigable waters (“significant nexus”) are relevant in determining CWA jurisdiction. This has increased the need for scientific information to support regulatory determinations and to inform future policies, rule making, and legislation. Here, we propose an approach for addressing these science needs. We define a metric – maximum duration of continuous flow – to assess hydrological permanence. We also define two metrics to evaluate significant nexus: proportion of total benefit to the navigable water contributed by an NNSAW class, and proportion of time that a navigable water receives benefit from an NNSAW. These metrics could be useful in implementing the Courts new legal standards.

Episodic Acidification of Small Streams in the Northeastern United States: Episodic Response Project

The Episodic Response Project (ERP) was an interdisciplinary study de- signed to address uncertainties about the occurrence, nature, and biological effects of ep- isodic acidification of streams in the northeastern United States. The ERP research consisted of intensive studies of the chemistry and biological effects of episodes in 13 streams draining forested watersheds in the three study regions: the Northern Appalachian region of Penn- sylvania and the Catskill and Adirondack Mountains of New York. Wet deposition was measured in each of the three study regions. Using automated instruments and samplers, discharge and chemistry of each stream was monitored intensively from fall 1988 through spring 1990. Biological studies focused on brook trout and native forage fish. Experimental approaches included in situ bioassays, radio transmitter studies of fish movement, and fish population studies. This paper provides an overview of the ERP, describes the methodology used in hydrologic and water chemistry components of the study, and summarizes the characteristics of the study sites, including the climatic and deposition conditions during the ERP and the general chemical characteristics of the study streams.

Acidic episodes in surface waters in Europe

Abstract Pronounced and short-term changes in freshwater chemistry (‘acidic episodes’) can have a significant biological impact. More attention has been paid to chronic acidification, and there has been no previous attempt to produce a regional summary of occurrence of episodes in Europe, to describe their chemical characteristics, or to synthesise what is known of their controlling processes. These are the objectives of this review. The basic characteristics of episodes are explained, along with the problems of establishing an adequate description. Because of the relative paucity of other information on water composition, the review is based largely on measurements of short-term pH depressions, although other data are considered where available. Most of the studies reported here were conducted in Norway, Sweden, Scotland and Wales. The differing physical characteristics of the various study catchments are assessed; these influence the hydrochemical responses to hydrological events (snowmelt or rainfall). Antecedent conditions are also important. Nevertheless, it is possible to arrive at some generalising conclusions about episodes. Snowmelt appears to instigate the most pronounced episodes, particularly in lakes. However, rainfall-induced episodes are generally much more frequent. Direct links between the chemistry of the snowmelt or rainfall which induced the episode and surface water chemistry are relatively rare, except in the case of a large input of sea-salt. Sulphate is the strong acid anion most strongly related to pH depression during episodes, although nitrate is important in some locations at snowmelt. Organic acids can play an important role in some peaty catchments. Dilution of base cations during episodes was also observed in most of the studies reviewed. Some depression of pH in surface waters seems ubiquitous during hydrological events, but in areas which have experienced large depositions of pollution, long-term acidification has conditioned catchments for the episodic release of acid. Changing flowpaths through hydrological events are of overwhelming importance in controlling the chemical character of episodes.

Use of factor analysis to investigate processes controlling the chemical composition of four streams in the Adirondack Mountains, New York

Abstract Four streams were monitored intensively over a 2 year period. Factor analysis was used to identify interrelationships between dissolved species during this period, and to determine physical processes controlling their behaviour. Analysis of the full dataset identified species which varied predominantly on an episodic timescale, and species which were subject to seasonal cycles. Two-month subsets of data were defined to remove the influence of seasonal cycles, and factor analysis of individual subsets then allowed episodic behaviour to be examined for each 2 month period. Results showed that base cation dilution was a consistent cause of changes in acid neutralising capacity (ANC) in all four streams. NO 3 − exhibited strong seasonality in concentration and also in episode behaviour, increasing during winter-snowmelt episodes, but diluting during some summer episodes. DOC concentrations also varied seasonally, but 2 month analysis indicated episodic increases during all periods. SO 4 2− did not exhibit consistent episodic behaviour, as it was strongly influenced by antecedent conditions. Behaviour of Ca 2+ and Mg 2+ was apparently influenced by a significant soil source in three of the streams.

Coho salmon dependence on intermittent streams

In February 2006, the US Supreme Court heard cases that may affect whether intermittent streams are jurisdictional waters under the Clean Water Act. In June 2006, however, the cases were remanded to the circuit court, leaving the status of intermittent streams uncertain once again. The presence of commercial species, such as coho salmon (Oncorhynchus kisutch), can be an important consideration when determining jurisdiction. These salmon spawn in the upper portions of Oregon coastal stream networks, where intermittent streams are common. In our study of a coastal Oregon watershed, we found that intermittent streams were an important source of coho salmon smolts. Residual pools in intermittent streams provided a means by which juvenile coho could survive during dry periods; smolts that overwintered in intermittent streams were larger than those from perennial streams. Movement of juvenile coho into intermittent tributaries from the mainstem was another way in which the fish exploited the habitat and illustrates the importance of maintaining accessibility for entire stream networks. Loss of intermittent stream habitat would have a negative effect on coho salmon populations in coastal drainages, including downstream navigable waters.

Comparison of episodic acidification in Canada, Europe and the United States

Episodic acidification is practically a ubiquitous process in streams and drainage lakes in Canada, Europe and the United States. Depressions of pH are often smaller in systems with low pre-episode pH levels. Studies on European surface waters have reported episodes most frequently with minimum pH levels below 4.5. In Canada and the United States, studies have also reported a number of systems that have had minimum pH levels below 4.5. In all areas, change in water flowpath during hydrological events is a major determinant of episode characteristics. Episodic acidification is also controlled by a combination of other natural and anthropogenic factors. Base cation decreases are an important contributor to episodes in circumneutral streams and lakes. Sulphate pulses are generally important contributors to episodic acidification in Europe and Canada. Nitrate pulses are generally more important to episodic acidification in the Northeast United States. Increases in organic acids contribute to episodes in some streams in all areas. The sea-salt effect is important in near-coastal streams and lakes. In Canada, Europe and the United States, acidic deposition has increased the severity (minimum pH reached) of episodes in some streams and lakes.

The Bear Brook Watershed, Maine (BBWM), USA

The Bear Brook Watershed Manipulation project in Maine is a paired calibrated watershed study funded by the U. S. EPA. The research program is evaluating whole ecosystem response to elevated inputs of acidifying chemicals. The project consists of a 2.5 year calibration period (1987-1989), nine years of chemical additions of (NH4)2SO4 (15N- and 34S-enriched for several years) to West Bear watershed (1989-1998), followed by a recovery period. The other watershed, East Bear, serves as a reference. Dosing is in six equal treatments/yr of 1800 eq SO4 and NH4/ha/yr, a 200% increase over 1988 loading (wet plus dry) for SO4 and 300% for N (wet NO3 + NH4). The experimental and reference watersheds are forested with mixed hard- and softwoods, and have thin acidic soils, areas of 10.2 and 10.7 ha, and relief of 210 m. Thin till of variable composition is underlain by metasedimentary pelitic rocks and calc-silicate gneiss intruded by granite dikes and sills. For the period 1987-1995, precipitation averaged 1.4 m/yr, had a mean pH of 4.5, with SO4, NO3, and NH4 concentrations of 26, 14, and 7 μeq/L, respectively. The nearly perrenial streams draining each watershed have discharges ranging from 0 (East Bear stops flowing for one to two months per year) to 150 L/sec. Prior to manipulation, East Bear and West Bear had a volume weighted annual mean pH of approximately 5.4, alkalinity = 0 to 4 μeq/L, total base cations = 184 μeq/L (sea-salt corrected = 118 μeq/L), and SO4 = 100 to 111 μeq/L. Nitrate ranged from 0 to 30 μeq/L with an annual mean of 6 to 25 μeq/L; dissolved organic carbon (DOC) ranged from 1 to 7 mg/L but was typically less than 3. Episodic acidification occurred at high discharge and was caused by dilution of cations, slightly increased DOC, significantly higher NO3, and the sea-salt effect. Depressions in pH were accompanied by increases in inorganic Al. The West Bear catchment responded to the chemical additions with increased export of base cations, Al, SO4, NO3, and decreased pH, ANC, and DOC. Silica remained relatively constant. Neutralization of the acidifying chemicals occurred dominantly by cation desorption and mobilization of Al.

A Two‐Component Mixing Model for Predicting Regional Episodic Acidification of Surface Waters During Spring Snowmelt Periods

A two-component mixing model of acid neutralizing capacity (ANC) is proposed for explaining two observed features related to the episodic acidification of surface waters during snowmelt periods: (1) maximum episodic declines in ANC are largest in high ANC systems and increase linearly with antecedent ANC and (2) relative depressions in ANC attributable to increases in nitric acid concentrations are larger in low ANC systems, while relative depressions in ANC attributable to dilution of base cations are larger in high ANC systems. Conceptually, the model represents the physical mixing of two hydrochemical end-members within a surface water environment, although the physical sources of water in the model are undefined. The model is shown to explain 55–72% of the total variation of these characteristics among various surface water systems within the Catskill and Adirondack mountain regions of New York. In addition, the model also explains 11–47% of the relative depression in ANC attributable to natural organic acidity in surface waters in these regions. The model is subsequently linked to an empirical equilibrium acidification model for predicting the long-term episodic acidification response of Adirondack lakes during snowmelt periods. Model predictions suggest that percentage decreases in sulfuric acid concentrations of the magnitude mandated by the 1990 Clean Air Act Amendments (40%) will not restore to positive values the ANC of all Adirondack lakes which are currently acidic (ANC < 0) during spring snowmelt periods. Long-term increases in nitric acid concentrations may counterbalance the expected increases in ANC attributable to reductions in sulfur deposition.