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Effects of Acidic Deposition on Fish and Water Quality


NRPC Leads:

Funding Source: USEPA

Project Description
Native brook trout (Salvelinus fontinalis) have been extirpated in six headwater streams of the GRSM including some streams that were populated as recently as fifteen years ago. To be sure, all fish in these streams were extirpated but brook trout receive the most attention because their range is confined to higher elevations where streams are most threatened. This extirpation has been well quantified by fish surveys conducted by the RSM staff. Acidic deposition is believed to be the main contributing cause of these losses. The reasons for this belief are:

  • the GRSM receives the highest acid deposition of any national park,
  • baseline water quality monitoring shows worrisome long-term declining pH trends at elevations lower than 3500 ft as well as already low pH at higher elevations (pH 5.6-6.0),
  • limited storm event data shows pH dropping one to two units during storm events and rising concentrations of aluminum and other metals (Cu and Zn) known to be toxic to fish and aquatic insects, and
  • limited storm event data in one stream shows similar concentrations between stream water and precipitation of the acidic anions sulfate and nitrate.

Water quality monitoring in the GRSM and elsewhere provides considerable circumstantial but not conclusive evidence that acid deposition is harming trout. Baseline water quality data from elevations above 3500 ft have low but stable pH (5.6-6.0). At elevations below 3500 ft, the baseline pH (6.0-6.5) shows worrisome long-term slowly declining trends such that the pH will be less than 6.0 within about 25 years if current trends continue. However, base line data are from grab samples that by their nature are hydrologically biased against storm events. The worst water quality occurs during storm events when the volume of acidic runoff overwhelms the stream’s acid neutralizing capacity. Limited data from sites less than 4000 ft show pH depressions of one to two units in storm events from a baseline of roughly 6.0-6.5 to levels at times below 4.5 (Robinson et al., 2004). Additionally, the concentrations of aluminum and other metals (Cu and Zn) toxic to fish and aquatic insects rise during storm events and have exceeded EPA water quality criteria. The reason that the GRSM is very sensitive to acid deposition is the lack of carbonate geology. Only a small fraction of the GRSM has carbonate bedrock with the rest being sandstones, slates, phylites, and other non-carbonate geologies.

The objectives of this research are to:

  • determine the impact of acidic storm events on fish health and survival in the GRSM;
  • determine the impact of acidic storm events on stream water quality;
  • evaluate whether acidic storm events and/or base flow water quality may be responsible for fish extirpation in headwater streams;
  • develop predictive models for stream water quality during storm events and fish health that can be used to assess the potential for impairment of streams in the GRSM; and
  • perform exploratory work to begin to understand the importance of ground water – surface water interactions.

To accomplish the above objectives, this research will monitor three watersheds in the GRSM. At least one of the watersheds will serve as a control watershed in that it has not seen fish extirpation. Other watersheds will be chosen because they have shown historical fish extirpation for unknown reasons. Each watershed will be monitored with two stream sites, two precipitation gauges, and two acid deposition collectors. Stream monitoring at each site will consist of 1) continuous water measurements with a multi-parameter monitor (sonde), 2) collection of storm event stream samples with an automated sampler, 3) measurement of fish population metrics with standard electrofishing gear, 4) in situ fish survival experiments and 5) collection of individual fish for further physiology testing. Additionally, this research will perform exploratory research in at least two watersheds on ground water – surface water interaction.

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