Geology topics

P.J. Wigington

Publications and source records attributed to P.J. Wigington.

3 recordsLinked to original sources

USGS1999

Prediction of episodic acidification in North-eastern USA: An empirical/mechanistic approach

Observations from the US Environmental Protection Agency's Episodic Response Project (ERP) in the North-eastern United States are used to develop an empirical/mechanistic scheme for prediction of the minimum values of acid neutralizing capacity (ANC) during episodes. An acidification episode is defined as a hydrological event during which ANC decreases. The pre-episode ANC is used to index the antecedent condition, and the stream flow increase reflects how much the relative contributions of sources of waters change during the episode. As much as 92% of the total variation in the minimum ANC in individual catchments can be explained (with levels of explanation >70% for nine of the 13 streams) by a multiple linear regression model that includes pre-episode ANC and change in discharge as independent variable. The predictive scheme is demonstrated to be regionally robust, with the regional variance explained ranging from 77 to 83%. The scheme is not successful for each ERP stream, and reasons are suggested for the individual failures. The potential for applying the predictive scheme to other watersheds is demonstrated by testing the model with data from the Panola Mountain Research Watershed in the South-eastern United States, where the variance explained by the model was 74%. The model can also be utilized to assess 'chemically new' and 'chemically old' water sources during acidification episodes.Observations from the US Environmental Protection Agency's Episodic Response Project (ERP) in the Northeastern United States are used to develop an empirical/mechanistic scheme for prediction of the minimum values of acid neutralizing capacity (ANC) during episodes. An acidification episode is defined as a hydrological event during which ANC decreases. The pre-episode ANC is used to index the antecedent condition, and the stream flow increase reflects how much the relative contributions of sources of waters change during the episode. As much as 92% of the total variation in the minimum ANC in individual catchments can be explained (with levels of explanation >70% for nine of the 13 streams) by a multiple linear regression model that includes pre-episode ANC and change in discharge as independent variables. The predictive scheme is demonstrated to be regionally robust, with the regional variance explained ranging from 77 to 83%. The scheme is not successful for each ERP stream, and reasons are suggested for the individual failures. The potential for applying the predictive scheme to other watersheds is demonstrated by testing the model with data from the Panola Mountain Research Watershed in the South-eastern United States, where the variance explained by the model was 74%. The model can also be utilized to assess `chemically new' and `chemically old' water sources during acidification episodes.

Hydrological Processes↗

USGS1996

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 (Al im ) concentrations > 150 μg/L in at least two study streams in each region. Several streams consistently experienced episodes with maximum Al im 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 NO 3 - concentrations and large episodic pulses (≤ 54 μ eq/L). Most of the Pennsylvania study streams also frequently experienced episodic pulses of SO 4 2- (≤ 78 μ eq/L), whereas the Adirondack and Catskill streams did not. High baseline concentrations of SO 4 2- (all three study areas) and NO 3 - (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 NO 3 - (Catskills and Adirondacks), SO 4 2- (Pennsylvania), or organic acids became more important during major episodes. Overall, the behavior of streamwater SO 4 2- and NO 3 - is an indicator that acidic deposition has contributed to the severity of episodes in the study streams.

Ecological Applications↗

USGS1996

Episodic acidification of small streams in the northeastern United states: Effects on fish populations

As part of the Episodic Response Project (ERP), we studied the effects of episodic acidification on fish in 13 small streams in the northeastern United States: four streams in the Adirondack region of New York, four streams in the Catskills, New York, and five streams in the northern Appalachian Plateau, Pennsylvania. In situ bioassays with brook trout (Salvelinus fontinalis) and a forage fish species (blacknose dace (Rhinichthys atratulus), mottled sculpin (Cottus bairdi), or slimy sculpin (Cottus cognatus), depending on the region) measured direct toxicity. Movements of individual brook trout, in relation to stream chemistry, were monitored using radiotelemetry. Electrofishing surveys assessed fish community status and the density and biomass of brook trout in each stream. During low flow, all streams except one had chemical conditions considered suitable for the survival and reproduction of most fish species (median pH 6.0-7.2 during low flow; inorganic Al < 60 μg/L). ERP streams with suitable conditions during low flow, but moderate-to-severe episodic acidification during high flow, had higher fish mortality in bioassays, net down-stream movement of brook trout during events, and lower brook trout density and biomass compared to nonacidic streams, and lacked acid-sensitive fish species (blacknose dace and sculpin). Movement of trout into refugia (areas with higher pH and lower Al) during episodes partially mitigated the adverse effects of episodes. Recolonization from alkaline tributaries or microhabitats can maintain low densities of fish in streams that experience severe acidic episodes, but it is not sufficient to sustain fish densities and community composition at levels expected in the absence of these episodes. Fish responses to acid-base chemistry were fairly consistent across regions. In general, trout abundance was reduced and acid-sensitive fish species were absent from ERP streams with median pH < 5.0-5.2 during high flow and inorganic Al > 100-200 μg/L. We conclude that episodic acidification can have long-term effects on fish communities in small streams.

Ecological Applications↗