Methods

In 1994, nine streamwater sampling sites were established throughout the wilderness areaby determining the major site dynamics ofinterest, such as geology, wetlands andelevation (Figure 1 ). Samples were collected from these sites once every two weeks until1996. In 1996, the number of sampling sites was reduced to four (sites 2,3,8 and 9) andthe sampling interval was changed to three weeks. These four sites were chosen becausethey had the lowest pH and acid neutralizing capacity values of the nine sites.Streamwater grab samples were collected at these locations from May 1996 throughOctober 1996.

Detennination of pH was made using a portable pH meter on the day the samples werecollected. Cation values were obtained using direct current plasma spectroscopy. Anions,~ + and SiO2 were measured on a continuous flow system (Autoanalyzer ll). Speciated

At was also determined with an Autoanalyzer using pyrochatechol violet colorimetry(McAvoyet al. 1992). Total At concentrations were calculated in ~eq/L using a charge of3 if the pH :54.5,2.5 if the pH was 4.6 to 5.5 and 2 if the pH ;?: 5.5. A Schimadzu 5000organic carbon analyzer was used to measure TOC. The value ofTOC in ~eq/L wascalculated using a constant charge density approach similar to the one developed by Oliveret al. (1983).

Results and Discussion

Measurements of pH were used to determine the acidity of streams and to assess whetherthe streams in this region are susceptible to the affects of acid deposition. Sites 2, 3, 8 and9 were sampled in 1996 because these sites were the most acidic of the nine original sites.Table 1 lists the streamwater chemistry for these four sites in mg/L and table 2 lists thestreamwater chemistry in ~eq/L. Streamwater ion values were converted from mg/L to~eq/L for the p\lrpose of making comparisons of ionic strength.

Based on the values in table 2, 8O42- was the dominant strong acid anion at all sitesfollowed by CI- and NO3-. In addition, weak organic acids associated with TOCcontributed substantially to the acidity of streamwater and was greater than cr and NO3-acidity. The concentrations ofbase cations followed a general trend of Ca2+ > Na+>Mg2+ > K+ with the exception of site 2 which had slightly higher Mg2+ than Na+.

There are several factors that may affect the concentration of cations and anions andwhich consequently affect the acid-base status of streams. In the Lye Brook Wildernesswatershed geology may influence the concentration of some ions in streamwater .The geologic substrates underlying the sampled streams consist of rock that is resistant tochemical weathering. Therefore weathering rates are generally not fast enough tocompletely buffer incoming acids. These rocks contain low concentrations of Ca2+, Mg2+

49

and K+ and higher concentrations of Fe and AI resulting in leachates that are low in basecations and high in metals.

In addition, the soils in this area generally have a low cation exchange capacity. Thiscauses a subsequent reduction ofbase cations in soilleachates and ultimately results in lowconcentrations ofbase cations in streamwater. Soils that are highly affected by aciddeposition are characterized by the movement ofNO3- and SO42- in soil water. As thesemobile anions are exported to streams they are balanced by mobile cations. Unless thesecations are replaced by atmospheric deposition or weathering inputs, the base saturation ofthe soil will decrease and the soil will become acidified. In areas where base saturation isseverely reduced, Al concentrations in soil water and streamwater increase.

In addition to factors associated with geology and soils, biological reactions can alsoincrease or decrease acidity in surface waters. For example, factors such as uptake byvegetation and microbial decomposition can have a strong impact on inorganic elements,particularly NO3- which is biologically important. In Lye Brook streams NO3-concentrations were highest during May and early June. Concentrations ofNO3- generallypeak during spring because soil temperatures increase and mineralization and subsequentnitrification of N begins before vegetation initiates nutrient uptake (Likens et al. 1970;Galloway et al. 1987, Rascher et al. 1987). In the study streams, concentrations ofNO3-were highest during spring which caused a subsequent reduction in pH. Despite thisincrease, SO42- remained the dominant strong acid, unlike some other areas where NO3-acidity exceeds SO42- ( Stoddard and Murdoch 1991).

The presence of wetlands at the source of streams sampled resulted in high concentrationsof TOC and organic acids. These naturally occurring, organic acids may partially explainthe low pH ofstreamwater draining wetlands (McKnight et al. 1985). Site 8 is anexception because it does not have headwater wetlands and it had relatively high TOCconcentrations compared to the nine original sample sites. The most likely reason for highTOC at this site is related to soil depth. Site 8 is located on an exposed ridge at a highelevation where soils are thin. Mineral soils absorb organic C; therefore streams drainingthick soils generally have lower organic C concentrations (Lawrence et al. 1988; Cronan1985). Factors regulating organic C concentrations are important because organic C mayinfluence mineral weathering, cation leaching and trace metal speciation. Streams withhigh concentrations ofTOC typically exhibit low pH values because of the contribution oforganic acids associated with TOC.

In addition to contributing to stream acidity, organic acids can also increase weatheringrates through chelation (Huang 1988). In this process, organic acids form complexes withFe and Al, which subsequently affects the form and concentration of these elements insolution. When chelation occurs it causes a reduction in the concentration of inorganic Feand Al because these metals are bound in non-labile, organic forms. In general, watersdominated by naturally occurring acids are less likely to cause damage to acid-sensitivebiota because of the tendency of these waters to form Al complexes (Driscoll et al. 1980).

~o

Therefore, the four sites that were sampled in 1996 had low inorganic At concentrationsdespite low pH values.

Conclusion

This research indicates that the streams sampled in the Lye Brook Wilderness are acidicand have a low buffering capacity. Sulfate was the most abundant ion contributing to theacidity of streams, however NO3- was seasonally important, particularly during the spring.Increases in air pollution may increase streamwater concentrations of SO42- and NO3-causing further reductions in pH. Although organic acidity contributed greatly to the lowpH of sampled streams, it reduced concentrations of inorganic Al which is the form of Althat is most toxic to aquatic biota. Therefore although the pH of streams sampled waslow enough to cause damage to acid-sensitive species, Al toxicity does not appear to be amajor threat because of the complexation of inorganic Al with organic C compounds.

Literature Cited

Adarns, M. B., D. S. Nichols, C. A. Federer, K. F. Jensen and H. Parrott. 1991.Screening procedure to evaluate effects of air pollution on eastern regionwildernesses cited as class I air quality areas. General Technical Report NE-151United States Department of Agriculture, Forest Service. 33 pp.

Cronan, C. S. 1985. Biogeochemical influence of vegetation and soils in the ll- W ASwatersheds. Water, Air and Soil Pollution 26: 354-371.

Driscoll, C. T., I. P. Baker, I. I. Bisogni, c. L. Schofield. 1980. Effect of aluminumspeciation on fish in dilute acidified waters. Nature 284: 161-164.

Galloway, J. N. G. R. Hendrey, C. L. Schofield, N. E. Peters and A. H. Johannes. 1987Processes and causes oflake acidification during spring snowmelt in the west-central Adirondack Mountains, New York. Canadian Journal of Fisheries andAquatic Science 44: 1595-1602.

Huang, P. M. 1988. Ionic factors affecting aluminum transformations and the impact onsoil and environment sciences. Advances in Soil Science 8: 1- 78.

Lawrence, G. B., C. T. Driscoll and R. D. Fuller. 1988. Hydrologic control ofaluminum chemistry in an acidic headwater stream. Water Resources Research24: 659-669.

Likens, G. E., F. H. Borrnann, N. M. Johnson, D. W. Fisher, and R. S. Pierce. 1970. Theeffect of forest cutting and herbicide treatment on nutrient budgets in the HubbardBrook watershed-ecosystem. Ecological Monographs 40:23-47.

51

McAvoy, D. C., R. C. Santore, J. D. Shosa, and C. T. Driscoll. 1992. Comparisonbetween pyrocatechol violet and 8-hydroxyquinoline procedures for determiningaluminum fractions. Journal of the American Society of Soil Science 56: 449-455.

McKnight, D. M., E. M. Thurrnan, R. L. Wershaw and H. F. Hemond. 1985.Biogeochemistry of aquatic and humic substances in Thoreau's Bog, ConcordMassachusetts. Ecology 66: 1339-1352.

Oliver, B. G. and E. M. Thurman and R. L. Malcolm. 1983. The contribution of humicsubstances to the acidity of colored natural waters. Geochemica et CosmochimicaActa 47: 2031-2035.

Rascher, C. M., C. T. Driscoll, and N. E. Peters. 1987. Concentration and flux of solutesfrom snow and forest floor during snowmelt in the West-Central Adirondackregion of New York. Biogeochemistry 3: 209-224.

Stoddard, I. L. and P. S. Murdoch. 1991. Catskill Mountains. In: Charles, D. F. ed.,Acidic Deposition and Aquatic Ecosystems: Regional Case Studies. Springer-Verlag, New York.

52

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