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The effects of acidic deposition in the northeastern US include the acidification of soil and water, which stresses terrestrial and aquatic biota. Driscoll et al examine the ecological effects of acidic deposition in New England and New York and explore the relationship between emissions reductions and ecosystem recovery.

Principal Component Analysis (PCA) was used to derive estuarine salinity zones based on field data on the salinity ranges of 316 species/life stages in the mid-Atlantic region (chiefly Chesapeake Bay and Delaware Bay species). Application of PCA to the data matrix showed that the structure underlying a diversity of salinity distributions could be represented by only five Principal Components corresponding to five overlapping salinity zones: freshwater to 4‰, 2-14‰, 11-18‰, 16-27‰, and 24‰ to marine. The derived salinity zonation showed both differences and similarities to the Venice System of estuarine zonation. However, unlike the static and essentially descriptive Venice System, the new method will allow researchers to establish biologically-relevant local salinity zones, and then develop hypotheses about the processes that give rise to the resulting patterns. Examples of this procedure are given for the mid-Atlantic region. The method used here may also be useful for studying distributions across other environmental gradients, such as temperature, pH, substrate, turbidity, vegetation, or latitude.

Shenandoah National Park (SNP) receives more acid deposition than any other national park in the United States of America. As part of an effort to assess the impact of acidification upon fish in the park, in situ sub-lethal stress bioassays (measured by monitoring hematocrit) were conducted with acid sensitive blacknose dace Rhinichthys atratulus. Study streams experienced moderate acidification events that resulted in reduced pH (the largest reductionbeing 6.18 to 5.37) and increased total monomeric aluminum (TMA) concentration (the largest being 15 to 39 μg L^sup -1^). Although some of these acidification events were within the pH and TMA range expected to result in blacknose dace stress, none was detected by monitoring hematocrit. In an acid-sensitive stream, mean baseflow (pre-event) hematocrit ± SD, was 33.5±4.5%, and hematocrit during the largest event was 31.5±4.9%, A moderate acidification event also occurred in a less acid sensitive stream; pH dropped from 7.18 to 6.38 but TMA remained below 10 μg L^sup -1^. Mean hematocrit during baseflowin this stream was 32.3±2.8%, and hematocrit during event flow was 34.1±5.0%. At the time of this bioassay, acidificationevents that would result in acute toxicity for most species of fish did not occur, however the conditions documented in this investigation do not represent the most acute acidification events that have been observed in SNP. It should be noted that a chronic sub-lethal stress, measured by condition indices, has been observed among blacknose dace in SNP streams.[PUBLICATION ABSTRACT]

Between July and December 1994, three acidification episodes occurred in Shenandoah National Park, VA, and stream water samples and blacknose dace Rhinichthys atratulus samples were collected and analyzed. The fish samples were collected from Paine Run and Piney River, and hematocrit values were examined against water chemical composition. Results indicated that the hematocrit values did not reflect the changes in pH and total monomeric aluminum detected during the events.

Southern Appalachian streams host a rich diversity of fishes, but the Southern Appalachian Assessment concluded that 70% of stream locations showed significant fish community degradation, partly due to acid deposition. About 40% of total Southern Appalachian trout stream length occurs in Virginia. Our research in Shenandoah National Park, Virginia, has documented both chronic and episodic acidification in streams and brook trout (Salvelinus fontinalis) mortality during acid episodes. Here, we analyze a representative sample of 60 Virginia brook trout streams on noncarbonate bedrock with minimal human disturbance in their watersheds. Of more than 300 such streams in Virginia, only about 50% are currently suitable for brook trout, based on their acidification status. For the population of brook trout streams to which this analysis applies, model-based projections indicate that continued sulfate deposition at 1991 levels will result in about 70 additional streams becoming chronically acidic and unsuitable for brook trout. A 40% reduction will result in about 48 additional chronically acidic streams. Even a 70% reduction will likely result in about 15 additional streams becoming acidified. We conclude that reductions in sulfate deposition greater than 70% (relative to 1991 levels) are needed to prevent more brook trout stream losses in Virginia.

Hybridization in nature between Poeciliopsis monacha and P. lucida has resulted in diploid and triploid all-female populations which are self-replicating, and extremely successful, outnumbering their parental species at some localities by as much as 20:1 (Schultz, 1977). Their habitats in the streams of northwestern Mexico are characterized by thermal fluctuations sufficiently extreme to affect the local success of fish populations. Two unusual reproductive mechanisms (gynogenesis or hybridogenesis) in hybrids perpetuate their highly heterozygous F1genotypes generation after generation. Tests of thermal tolerance in the two bisexual species and their unisexual hybrids demonstrated both heterosis and presumably adaptive interclonal variation in thermal characteristics among the clones and hemiclones which make up populations of these hybrids. Heterosis and interclonal variation may contribute to hybrid success by increasing niche width, heterosis by increasing the range of conditions invidivuals can tolerate, and interclonal variation by diversifying the population's thermal adaptations.

Hemiclones of the unisexual fish Poeciliopsis monacha-occidentalis are not better adapted to cold temperatures in the northern part of their range than in the southern part of their range, nor is there conclusive evidence that they are coadapted to local populations of the sexual host species, P occidentalis. Response of the introgressed monacha genome to thermal stress is not clinal, whether the maternal genome is combined with a paternal genome of P. occidentalis or of P lucida; in fact, the differences in response among populations from the five river systems tested were of the same magnitude as from among hemiclones within the Rio Mayo, the southernmost river and the apparent site of origin of P monacha-occidentalis. Although the resistance to cold stress exhibited by P. monacha-occidentalis may play a role in its survival in the north, and heterosis for resistance to heat stress may contribute to its success in the south, these traits more likely derive from the original hybrid genotypes than from adaptive changes subsequent to their hybrid origin. Thus, it remains to be demonstrated that unisexual Poeciliopsis in the absence of a mechanism for recombination, have the capacity to evolve.