Acid deposition sensitivity map of the Southern Appalachian Assessment Area: Virginia, North Carolina, South Carolina, Tennessee, Georgia, and Alabama By John D. Peper, Andrew E. Grosz, Thomas H. Kress U.S. Geological Survey Reston, VA Thomas K. Collins, Gary B. Kappesser, Cindy M. Huber U.S. Forest Service Roanoke, VA and James R. Webb University of Virginia Charlottesville, VA U.S. Geological Survey On-line Digital Data Series Open-File Report CONTENTS ABSTRACT ................................................................. ......................................................3 INTRODUCTION ................................................................. .............................................3 PHYSIOGRAPHIC AND GEOLOGIC SETTING ...............................................................6 The Appalachian Plateau Province ................................................................. .......6 The Valley and Ridge Province ................................................................. .............6 The Blue Ridge Province ................................................................. ......................7 The Piedmont Province ................................................................. .........................8 ACID DEPOSITION SENSITIVITY ................................................................. ...................9 REFERENCES ................................................................. ..............................................12 APPENDIX A--Digital data structure ................................................................. ...............17 ABSTRACT Areas having various susceptibilities to acid deposition from air pollution are designated on a three tier ranking in the region of the Southern Appalachian Assessment (SAA). The assessment is being conducted by Federal agencies that are members of the Southern Appalachian Man and Biosphere (SAMAB) Cooperative. Sensitivities to acid deposition, ranked high, medium, and low are assigned on the basis of bedrock compositions and their associated soils, and their capacities to neutralize acid precipitation. Fifty four percent of the approximately 37 million acres comprising the area of the SAA region is highly sensitive to acid deposition (having negligible or no capacity to neutralize), twenty percent as medium, and twenty six percent is rated as having low sensitivity. INTRODUCTION Acid-base status is a critical ecosystem parameter in forested upland watersheds of the mid-Appalachian mountain region. The term, acid-base status, refers to the effective balance between acids and bases in soils and surface waters. Concern about watershed acid-base status in the mid-Appalachian mountain region is based on a number of factors, including: 1) observation of low acid-neutralization capacity (ANC) in many of the upland streams in the region (Cosby and others, 1991; Herlihy and others, 1993), 2) identification of the region as having one of the highest rates of acidic deposition in the United States (NADP, 1990; Herlihy and others, 1993), 3) identification of the region as one of the two areas (the other being the Adirondacks) of the United States most affected by surface-water acidification due to acidic deposition (Baker and others, 1991a, b), and 4) the potential for further acidification of regional streams as a consequence of continuing acidic deposition associated with atmospherically transported sulfur compounds (Webb and others, 1989 a, b; Church and others, 1992). Scientific evidence indicates that in some areas, acid deposition from air pollution is causing the water in streams and lakes to become more acidic over time, with resulting adverse effects on fish and other aquatic organisms. This effect has been most pronounced in areas that are downwind from certain sources of air pollution, and also where bedrock and associated soils lack the buffering capacity to neutralize acid precipitation. Bedrock geology and surficial geologic deposits have been shown to exert an important influence on the chemical composition of stream water and on the sensitivity of aquatic ecosystems to acid deposition (Norton and others, 1982). The accompanying map, based on bedrock geology, depicts the regional sensitivity of areas in the Southern Appalachians to acidification as a result of acid deposition (air pollution). This map was prepared at the request of, and in cooperation with, the U.S. Forest Service's Southern Appalachian Assessment (SAA) Atmospheric and Aquatic Team. The Assessment is being prepared by the U.S. Forest Service in cooperation with other Federal agencies that are members of the Southern Appalachian Man and the Biosphere (SAMAB) Cooperative. Designated by the United Nations Scientific, Educational, and Cultural Organization (UNESCO) in 1988 (Anonymous, 1994), the Southern Appalachian Biosphere Reserve is the first regional Reserve in the United States. The Reserve's Zone of Cooperation includes portions of the southern Appalachians in Virginia, North Carolina, South Carolina, Tennessee, Georgia, and Alabama. The chemical composition of stream water varies according to the bedrock geology of the watershed. Webb and others (1994) developed a watershed classification scheme that relates bedrock type to various parameters of stream chemistry as derived from the Virginia Trout Stream Sensitivity Survey (VTSS). The range, median, and interquartile distribution of stream-water chemical concentrations for spring-quarter samples from about 70 sites were used to differentiate between the various rock types, and group them by response classes. The differences among these classes as related to acid neutralization capacity (ANC) were used to assign sensitivity ratings of high, medium, or low to each group. A generalized bedrock geologic setting map for the crystalline and sedimentary rocks of the southern Appalachian Mountains compiled by J.D. Peper and others (in preparation) at a scale of 1:1,000,000, provides the basis for assignment of lithology-based acid deposition sensitivity ratings in this study. The generalized geologic map groups rocks by dominant lithology using mineralogic, petrographic, and other characteristics that influence the composition and texture of the rocks without regard to specific age or stratigraphic name. Broad areas were generalized as to dominant rock type in terms of areal significance at 1:1,000,000 scale, so that the map units are useful for regional considerations, but are not detailed enough for site-specific or large-scale work. Thus, for example, all quartz sandstones are mapped as a single rock type. For portions of the SAA region west of the highlands of the Appalachian Mountains that were not covered by Peper's compilation, geologic information was appended from a digital version of the King and Beikman geologic map of the conterminous United States (Schruben and others, 1994). PHYSIOGRAPHIC AND GEOLOGIC SETTING The SAA region, which includes the SAMAB Reserve, spans four physiographic provinces (Figure 1). Each physiographic province has a framework of geologic structure and rock types that yield a distinctive set of landforms, and associated sets of soils, hydrologic and climatic regimes, and natural resources. From northwest to southeast these physiographic provinces are: 1) the Appalachian Plateau, 2) the Valley and Ridge, 3) the Blue Ridge, and 4) the Piedmont Provinces. The Appalachian Plateau Province The SAA region includes a segment of the Appalachian Plateau Province extending from westernmost Virginia to northeastern Alabama. This Province is comprised of a dissected plateau of openly folded sedimentary rocks including sandstone, shale, and limestone. Plateau soils over sedimentary rocks are mostly brown podzols of temperate climate under mixed forest cover. Soils are thin and stoney or lacking on steep slopes. The Valley and Ridge Province Southeast of the Appalachian Plateau Province, more tightly folded, and progressively to the southwest increasingly thrust- faulted, sedimentary rocks are exposed in a series of plunging anticlines and synclines of the Valley and Ridge Province, frequently referred to as the Folded Appalachians. In this Province sinuous or long linear ridges of steeply dipping sandstones parallel valleys underlain by shale and limestone through western Virginia and northwestern Georgia, although northwestern Georgia is mostly a broad lowland and valley area of limestone and shale. This province extends throughout the SAA region from northeastern Alabama to northern Virginia. Valley and Ridge soils are thicker clayey and silty over limestone and shales in the valleys, thin and sandy on sandstone ridges, and stoney on slopes. The Blue Ridge Province To the east of the Valley and Ridge Province, the Blue Ridge Province occupies the topographic highlands of west-central Virginia, western North Carolina, eastern Tennessee, and northern Georgia. This province includes the Blue Ridge and Catoctin Mountains (both over 2,500 feet in elevation) in a narrow northern Virginia portion, a plateau in the upper reaches of the New River in southwestern Virginia, and the Mt. Rodgers area in southwestern Virginia (about 6,000 feet above sea level). This province includes rugged high peaks in the Great Smoky Mountains in western North Carolina and east Tennessee as well as Mt. Mitchell in North Carolina (over 6,500 feet above sea level), and numerous other peaks in North Georgia near or over 5,000 feet above sea level. This Province includes high-grade metamorphic gneisses and schists and metaigneous rocks in massifs and domes that are termed crystalline basement. This Province also includes low- to high-grade metamorphic rocks in fault-imbricated and fault-bounded sheets that extend over a thick section of sedimentary rocks at depth along the western margin of the province constituting an" eastern overthrust belt". Granitoid and high-grade metamorphic rocks, designated as crystalline basement are exposed along the axis of the Blue Ridge Mountains in western Virginia, North Carolina and in northwest Georgia. These basement rocks are dominantly granitic gneiss with much lesser schist and gneiss in western Virginia, and in western North Carolina. Crystalline basement rocks are also exposed in in western North Carolina and in northwestern Georgia. Blue Ridge soils are temperate-humid brown podzols (in the north) to warm-temperate red and yellow podzols (to the south) over metamorphic rocks. Soils are thin to absent on craggy peaks, and thin to thick, transported, and stoney on steep slopes. The Piedmont Province Southeast from the mountains of the Blue Ridge Province and extending due east is an area of low-lying foothills and uplands of low relief underlain predominantly by deformed metamorphic rocks that constitute the Piedmont Province. Residual soils are thick and bedrock outcrops are relatively sparse, except along major rivers. Elevations typically range from about 300 - 400 feet near the Province's eastern boundary with the Atlantic Coastal Plain, to about 800 to 1,000 feet at the base of the mountains. A broad in southern Virginia, the Carolinas, and Georgia area of high-grade metamorphic rocks, largely gneiss and schist, with characteristic shallow dips of foliation and compositional layering, is referred to as the Inner Piedmont. A series of fault block basins, for the most part trending northeast, are filled with sandstones, shales, conglomerates, and basalt flows of Late Triassic to Early Jurassic age. These sequences were deposited on rocks of the Piedmont and locally overlap rocks of the Blue Ridge Province in northern Virginia. Piedmont residual soils are thick red-yellow podzols of warm- temperate humid climate. They are silty and clayey over metamorphic rocks, and sandy over granites. Bedrock outcrops are generally sparse except along major rivers. Mesozoic basin soils are mostly iron- and manganese-rich sandy and silty soils over sandstones and shales; they are thin and clayey over basalt trap sheets. ACID DEPOSITION SENSITIVITY The SAA is a regional assessment encompassing about 37 million acres spanning portion of six States. In such a broad assessment, the data used must be generalized to some extent. The sensitivity ratings are based on a generalized map of bedrock geology. As a result there can be significant local variations from the rating shown on the acid deposition sensitivity map. For example, in some parts of the Valley and Ridge Province in Virginia, some of the narrow limestone valleys can not be displayed on the generalized bedrock geology map at this scale. Consequently, these low acid deposition sensitivity areas are not indicated on the acid deposition sensitivity map. The map emphasizes the natural regional capacity of the bedrock and derived soils to neutralize acid precipitation but does not consider the effects of biomass alteration by gypsy moth denudation or other natural agents. Nor are the areal effects of extensive anthropogenic alteration assessed: paving of built-up areas, farming of soils with attendant use of limestone and fertilizers, mining with accompanying tailings piles, landscape alterations, and the like. The map showing relative acid deposition sensitivities in the SAA region (Plate 1) is derived from a map compilation showing the generalized geologic setting of the southern U.S. Appalachians (Peper and others, in preparation). The geologic setting map shows general ages and broadly generalized lithologies of the rocks, their regional structural setting, and geologic features that are considered significant for the formation and occurrence of metallic mineral deposits (Gair and others, 1987). The principal feature is lithology, grouped according to volcanic or sedimentary, corresponding metamorphic, or igneous plutonic origin and as mafic-ultramafic bodies. Examples of some of these lithologies are: 1) dominantly felsic volcanic, 2) dominantly coarse clastic sedimentary, 3) dominantly carbonate sedimentary, 4) igneous plutonic (for example, granite, tonalite, gabbro) and, 5) felsic or mafic paragneiss. Each rock unit on the generalized geologic map was assigned a sensitivity rating based on the VTSS classification. It should be noted, however, that the VTSS data are restricted to streams associated with forested ridges. The VTSS data will thus tend to represent the dominant rock type of the generalized map units, but may not provide information concerning the less extensive areas of other rock types and alluvial deposits within the map units (e.g., the narrow limestone and shale valleys). The VTSS data may be further biased toward more extreme (low ANC) conditions in that the VTSS sites were selected from the least disturbed wild-land watersheds in the region. These tend to be base-poor lands that have been unsuitable for direct human use. For rock units not included in the VTSS classification, sensitivities were assigned by collaboration among the authors (Table 1). A key mineralogic-compositional factor is the expected ability of the rock type to release acid-neutralizing calcium upon weathering and thus produce an acid neutralizing soil in the catchment basin of the stream. Rocks composed of mostly calcium- or calcium-magnesium carbonate (limestones, dolomites, marbles, and calcareous rocks) are rated as having low susceptibilities, as are most mafic rocks (gabbros, mafic paragneisses and schists, amphibolites), predominantly mafic volcanic rocks, diabase, and ultramafic rocks and mafic-ultramafic complexes. These latter groups of rocks generally contain sufficient calcium-rich feldspar or other calcium-magnesium silicate minerals to generate acid-neutralizing soils upon weathering. In addition, many of these mafic rocks have undergone deuteric alteration or greenschist facies metamorphism, and have dispersed carbonate minerals within their altered matrices. Dominantly siliceous clastic rocks (sandstones, shales) were shown by Webb and others (1994) to be associated with areas of high acid-precipitation susceptibility. These rocks release little or no acid-neutralizing components; indeed sulfidic shales and sulfidic schists may be acid generators. These and their metamorphic equivalents, as well as siliceous mylonites, were rated as high susceptibility areas. Areas of felsic volcanic rocks , granitic rocks (granite, granodiorite, quartz diorite), volcanic and volcaniclastic rocks, felsic paragneiss and schist, alkalic rocks and anorthosite are characterized by the presence of alkali (potassium and sodium) feldspars and slightly calcareous plagioclase feldspar. Based on rock composition alone, most geologists would consider large areas of inclusion-free potassium-feldspar-rich granite to have little ANC and resultant high acid-deposition sensitivity rating. However, most granites in the map area are granodioritic, and contain inclusions. Areas dominated by these rocks, as expected, and as evidenced by Webb and others (1994) were designated to be of medium susceptibility. REFERENCES Anonymous, 1994, Action Plan 1994-1996, Southern Appalachian Man the Biosphere Foundation, SAMAB, Gatlinburg, TN, 17 p. Baker, L.A., Kaufman, A.T., Herlihy, J.M., and Eilers, J.M., 1991a, Acid lakes and streams in the United States: the role of acidic deposition: Science, v. 252, p. 1151-1154. Baker, L.A., Eilers, J.M., Cook, R.B., Kaufmann, P.R., and Herlihy, A.T., 1991b, Interregional comparisons of surface water chemistry and biogeochemical processes, in, Acidic deposition and aquatic ecosystems, regional case studies, Charles, D.F., ed., Springer-Verlag, New York, p. 567-614. Church, M.R., Shaffer, P.W., Thornton, P.L., Cassell, D.L., Liff, C.I., Johnson, M.G., Lammers, D.A., Lee, J.J., Holdren, G.R., Kern, J.S., Liegel, L.H., Pierson, S.M., Stevens, D.L., and Rochelle, B.P., 1992, Direct/Delayed response project: Future effects of long-term sulfur deposition on surface water chemistry in the mid-Appalachian region of the Eastern United States: U.S. Environmental Protection Agency, EPA/600/R-92/186, 384 p. Cosby, B.J., Ryan, P.F., Webb, J.R., Hornberger, G.M., and Galloway, J.N., 1991, Mountains of western Virginia, in, Acidic deposition and aquatic ecosystems, regional studies, Charles, D.F., ed., Springer-Verlag, New York. P. 297-318. Gair, J.F., Cannon, W.C., Peper, J.D., Cannon, S., and Martin, B., 1987, Metallogenic map of the U.S. Appalachians: U.S. Geological Survey Circular 995, p. 22-23. Herlihy, A.T., Kaufmann, P.R., Church, M.R., Wigington, P.J., Webb, J.R., and Sale, M.J., 1993, The effects of acidic deposition on streams in the Appalachian mountain and Piedmont region of the mid-Atlantic region of the United States: Water Resources Research, v. 29, p. 2687-2703. National Atmospheric Deposition Program (NADP), 1990, NADP/NTN annual data summary of precipitation chemistry in the United States: Natural Resources Ecology Laboratory, Colorado State University, Fort Collins. Norton, S.A., Akielaszek, J.J., Haines, T.A., Stromberg, K.L., and Longcore, J.R., 1982, Bedrock geologic control of sensitivity of aquatic ecosystems in the United States to acid deposition, p. 1-13. National Atmospheric Deposition Program. Peper, J.D., Kress, T.H., and Turner, R.M., in preparation, Map showing the generalized geologic setting of the southern Appalachians: U.S. Geological Survey On Line Digital Data Series Open-File Report. Schruben, P.G., Arndt, R.E., and Bawiec, W.J., 1994, Geology of the conterminous United States at 1:2,500,000 -- A digital representation of the 1974 P.B. King and H.M. Beikman map: U.S. Geological Survey Digital Data Series DDS- 11. Webb, J.R., Deviney, F.A., and Galloway, J.N., 1994, The acid- base status of native brook trout streams in the mountains of Virginia; Report to the Virginia Department of Game and Inland Fisheries, 91 p. Webb, J.R., Cosby, B.J., Galloway, J.N., Hornberger, G.M., and Ryan, P.F., 1989a, Acidification of native brook trout streams in Virginia, January 1987 - December 1988, Report to Virgina Department of Game and Inland Fisheries, 67 p. Webb, J.R., Cosby, B.J., Galloway, J.N., and Hornberger, G.M., 1989b, Acidification of native brook trout streams in Virginia: Water Resources Research, v. 25, p. 1367-1377. Table 1. -- Acid deposition sensitivities of bedrock units in the Southern Appalachian Assessment region. Acid Deposition Rock type Sensitivity SEDIMENTARY ROCKS High Predominantly coarse-grained rocks, includes mixed coarse-and fine-grained sequences of Mississippian - Pennsylvanian age High Predominantly fine-grained clastic rocks METAMORPHIC ROCKS High Coarse-grained metaclastics, metaconglomerate, and quartzite. High Fine-grained metaclastics, slate and schist High Mylonite METAMORPHIC ROCKS Medium Felsic gneiss and schist VOLCANIC ROCKS Medium Volcanic and volcaniclastic rocks undivided Medium Predominantly felsic volcanic rocks INTRUSIVE ROCKS Medium Granitic rocks, undivided Medium Granite Medium Tonalite (quartz diorite) Medium Granodiorite Medium Quartz monzonite Medium Alkalic rocks Medium Anorthosite SEDIMENTARY ROCKS Low Predominantly carbonate rocks METAMORPHIC ROCKS Low Mafic paragneiss and schist, amphibolite Low Marble VOLCANIC ROCKS Low Predominantly mafic volcanic rocks INTRUSIVE ROCKS Low Diorite Low Gabbro Low Diabase, includes trap sheets in Mesozoic basins Low Ultramafic rocks and mafic-ultramafic complexes APPENDIX A DIGITAL DATA DESCRIPTION This digital data product represents the Acid Deposition Sensitivity of the Southern Appalachian Assessment Area. The following text is documentation for the digital covers/files associated with the digital product. The data was compiled in ARC/INFO, a commercial Geographic Information System (Environmental Systems Research Institute, Redlands, California), and is stored in ARC/INFO Export format (ARC/INFO version 7.0.3) in a UNIX tar file. A UNIX computer system is therefore required to extract the database from the tar file, and ARC/INFO is required for its use or conversion to other formats. The tar file contains the following files: 1) saa- acid.e00: ARC export file for the acid deposition sensitivity polygon coverage, 2) saa-acid_base.e00: ARC export file for the map base information, 3) plot_saa-acid.aml: Arc Macro Language program used to create graphic plot file, and 4) saa-acid.gra: ARC/INFO graphics file of Acid Deposition Sensitivity Map. The ARC/INFO version of the Acid Deposition Sensitivity Map of the Southern Appalachian Assessment Area consists of two coverages: 1) SAA-ACID: Acid Deposition Sensitivity, and 2) SAA- ACID_BASE: Southern Appalachian Assessment geographic base information. Data sources SAA-ACID: Compiled from a digital map of the generalized geologic setting of the southern U.S. Appalachians (Peper and others, in preparation). This data source was compiled by J.D. Peper from a draft map at a scale of 1:1,000,000 from various federal, state, and academic geologic maps. SAA-ACID_BASE: (1) State boundary data was extracted from the Digital Chart of the World on CD-ROM (1994) in Vector Product Format (VPF) and converted to ARC/INFO using VPFIMPORT on a Sun workstation. This digital data product was produced by the Defense Mapping Agency to produce small scale mapping of global coverage (except Antarctica) based on the 1:1,000,000-scale Operational Navigation Charts (ONC series). (2) Southern Appalachian Assessment Area boundary was obtained from K.A. Hermann of the National Biological Service, Norris, TN (karl@utkux1.utk.edu). Coverage attribute information SAA-ACID_BASE Polygon attribute table: COLUMN ITEM NAME 1 AREA 5 PERIMETER 9 SAA-ACID_BASE# 13 SAA-ACID_BASE-ID 17 CODE Attribute Label: CODE Attribute Definition: Physiographic Province CODE 1 Appalachian Plateau Province 2 Valley and Ridge Province 3 Blue Ridge Province 4 Piedmont Province SAA-ACID_BASE Arc attribute table: COLUMN ITEM NAME 1 FNODE# 5 TNODE# 9 LPOLY# 13 RPOLY# 17 LENGTH 21 SAA-ACID_BASE# 25 SAA-ACID_BASE-ID 29 BNDTYPE Attribute Label: BNDTYPE Attribute Definition: Boundary Type BNDTYPE 1 2 3 4 5 SAA-ACID Polygon attribute table: COLUMN ITEM NAME 1 AREA 5 PERIMETER 9 SAA-ACID# 13 SAA-ACID-ID 17 LITHOLOGY 20 SENSITIVITY Attribute Label: LITHOLOGY Attribute Definition: Geologic Lithology LITHOLOGY DESCRIPTION an Anorthosite cc Coarse-grained clastics: sandstones, conglomerates ccm Metamorphosed coarse clastics d Diorite di Diabase fc Fine-grained clastics: shales and mudstones fcm Metamorphosed fine-grained clastics: slates, schists,phyllites fp Felsic paragneiss and schist fv Felsic volcanics gb Gabbro gd Granodiorite gr Granite ls Limestone mb Marble mpg Mafic paragneiss and schist; amphibolite mv Mafic volcanics my Mylonite um Ultramafic rocks vu Volcanic and volcaniclastic rocks; undifferentiated Attribute Label: SENSITIVITY Attribute Definition: Acid Deposition Sensitivity SENSITIVITY HIGH MEDIUM LOW Coordinate system description: Projection LAMBERT Units METERS Spheroid CLARKE1866 Parameters: 1st standard parallel: 33 0 0.000 2nd standard parallel: 45 0 0.000 central meridian: -81 0 0.000 latitude of projection's origin: 0 0 0.000 false easting (meters): 0.00000 false northing (meters): 0.00000 Graphic plot file: An aml written to generate the ARC/INFO graphics file is included. It may help to address questions concerning the coverages. Also included is an ARC/INFO graphics file: saa- acid.gra. plot_saa-acid.aml: draws up acid deposition sensitivity map. Cautions relating to use of the map The users of the Acid Deposition Sensitivity Map should respect the intentions of the compilers of the map and some of its limitations. The Map is intended to be used at a scale of 1:1,000,000: it is not intended to be used at a more detailed scale. Users should also be aware that small areas of other rock types are included in the generalized map units. This digital product, identified as open-file report 95-810, has been approved for release and publication by the Director of the USGS. Although this digital product has been subjected to rigorous review and is substantially complete, the USGS reserves the right to revise the product pursuant to further analysis and review. Furthermore, it is released on condition that neither the USGS nor the United States Government may be held liable for any damages resulting from its authorized or unauthorized use.