Mountain Lake, Virginia is a small, unique, oligotrophic, subalpine ecosystem in the southern Appalachians. Previous studies have disclosed that this lake has manifested periodic prolonged low water levels during the several thousand years of its existence. The most recent low water level occurred during the drought years of 1999-2002. Measurements of lake level, precipitation, and other meteorological data including calculated evapotranspiration in the lake basin from 2/19/02 to 8/31/03 have enabled estimation of net subterranean water losses presumably through cracks between Clinch sandstone boulders and/or the recently discovered deep hole at the northwest end of Mountain Lake. These net losses reflect the balance between total losses and any gains from springs and boulder cracks not quantified in this study. Scuba divers have documented the existence of these cracks and the deep hole. Subterranean net water losses of about 0.04-0.05 m3/s (634-792 gpm) apparently occur year-round

Jansons, Martin

Parker, Bruce C.

Waller, Jacob E.

English

Old Dominion University

Virginia Journal of Science Volume 55 Number 3 Fall 2004 Subterranean Loss and Gain of Water in Mountain Lake, Virginia: A Hydrologic Model Martin Jansons, P.E., Peed & Bortz, L.L.C. Civil/Environmental Engineers, 20 Midway Plaza Drive Suite 100, Christiansburf, VA 24073, U.S.A. Bruce C. Parker , Department of Biology, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, U.S.A. and Jacob E. Waller, Department of Biology, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, U.S.A. ABSTRACT Mountain Lake, Virginia is a small, unique, oligotrophic, subalpine ecosys-tem in the southern Appalachians. Previous studies have disclosed that this lake has manifested periodic prolonged low water levels during the several thousand years of its existence. The most recent low water level occurred during the drought years of 1999-2002. Measurements of lake level, precipi-tation, and other meteorological data including calculated evapotranspiration in the lake basin from 2/19/02 to 8/31/03 have enabled estimation of net subterranean water losses presumably through cracks between Clinch sand-stone boulders and/or the recently discovered deep hole at the northwest end of Mountain Lake. These net losses reflect the balance between total losses and any gains from springs and boulder cracks not quantified in this study. Scuba divers have documented the existence of these cracks and the deep hole. Subterranean net water losses of about 0.04-0.05 m3 /s (634-792 gpm) appar-ently occur year-round. INTRODUCTION Mountain Lake, Giles County, Virginia (37°27'56"N, 80°3 l '39"W) is the only natural lake in the unglaciated highlands of the southern Appalachians. This oligotro-phic montane lake located at 1181 m (3875 ft) elevation occupies a watershed only 7.4 times the surface area of the full lake (188,000 m\ In a review of the literature, Parker (2003) showed that this lake has manifested numerous fluctuations in water level from 100-20% full since its discovery and first description by Gist in 1751 (Johnston, 1898). Past intervals of lower lake levels also have been inferred by the occurrence of numerous in place stumps of trees that colonized and grew in the temporary meadow surrounding the less than full lake-e.g., a white pine (Pinus strobus )( ca. 1885-1904) and a southern yellow pine (Pinus sp., possibly P.pungens)(ca. 1645-65) at 7m and IOm below full pond respectively (Parker, 2003). Marland (1967) and Cawley et al. Corresponding Author (Phone) 540-552-5932, (E-mail) genera@vtedu Virginia Journal of Science, Vol. 55, No. 3, 2004 https://digitalcommons.odu.edu/vjs/vol55/iss3108 VIRGINIA JOURNAL OF SCIENCE 'tr N FIGURE 1. Sketch of Mountain Lake showing locations of Ordovician Martinsburg Shale [Om], Ordovician Juniata Sandstone [Oj], Silurian Clinch Sandstone [Sc], Quaternary Colluvium [Qc] which forms the natural dam, Springs [SP], Pond Drain [PD], Newport House [NJ, and the deep crevice and hole [ t-]. (2001 b) used biological indicators from sediment cores showing that prolonged reduc-tions of Mountain Lake water levels also occurred before 1751 going back several thousand years. These prolonged low water intervals in the lake have been attributed to large volumes of water lost through cracks in the incompletely sealed natural dam of Clinch sandstone colluvium at the northwestern end of the lake (Figure l)(Parker et al., 197 5; Parker, 2003 ). Mountain Lake's origin by formation of a natural dam across a mountain stream has been addressed by numerous investigators (Hutchinson and Pickford, 1932; Sharp, 1933; Eckroade, 1962; Marland, 1967; Parker et al., 1975; and Parker, 2003). Cawley et al. (200 la) further proposed that in addition to cracks between colluvial boulders at shallower water depths, sediment escape or entry may occur through a southeast-to-northwest fracture trace or fault located by sonar at the lake's maximum depth (Figure 1). This crevice-like feature has not been observed to fill with sediment since its first discovery by Williams (1930). Parker (2003) elaborated upon this aspect of the lake's hydrology, suggesting that the subterranean water loss should occur during drought and cause a lowering of the water table, whereas net gain should occur during wet (non-drought) conditions and cause a rising of the water table. A prolonged drought during 1999-2002 accompanied the total cessation of surface outflow in Pond Drain (Figure 1) and a gradual drop in lake level, providing an opportunity to collect more information on Mountain Lake's hydrology. The purpose of this study was to measure lake water level in conjunction with precipitation and estimates of evapotranspiration, enabling a more complete hydrologic model for the Virginia Journal of Science, Vol. 55, No. 3, 2004 https://digitalcommons.odu.edu/vjs/vol55/iss3MOUNTAINLAKE,VA SUBSURFACE WATER LOSS/GAIN 109 lake. We also conducted several SCUBA reconnaissances at the north end of the lake to obtain more information on possible holes between Clinch sandstone boulders and to examine the deep crevice feature. METHODS Documented monitoring of the lake level began in February 2002 with resort employee water line observations on the large ( 4m) Clinch boulders at the north end. Survey leveling undertaken by Jansons in May 2002 established local benchmarks and tied previous data. During June-August 2002 employees working at the floating boat dock recorded many daily readings at a partially submerged level rod. Beginning in September 2002 and continuing through August 2003 when the lake level reached the 0.46 m notch below the top of the dam (1180.64 m, 3873.5 ft), periodic lake level readings were recorded by Jansons and Parker near the Newport House by combination string-level and rod method. A digital model of the lake bottom was developed using the Autodesk AutoCAD 2002 software package and the sonar-generated morphometric map of the lake in Cawley et al.(2002), from which lake volumes for each level reading were derived. Daily precipitation data was obtained for the period January 2002 through August 2003 from the National Weather Service Automated Flood Warning System (AFWS) rain gauge at Mountain Lake Biological Station (MLBS). Additional weather data was obtained from the MLBS web site and used to predict evaporation and transpiration (ET). Mean monthly temperature, wind speed, relative humidity, and photosyntheti-cally available radiation (PAR) for the study period was utilized with the Penman-Mon-teith method for calculating ET (http://www.ierm.ed.ac.uk/cw2h/lec8/pm10.htm, W/m2 = 0.22 x µmol/s!m\ The hydro logic model used was: L = (Pb x Ab)- Li V L - ET = whereL =average net subterranean water loss for the period = Pb =precipitation for the period = Ab=basin area =1,398,748 m2 (346 acres) = Li V L=lake volume change for the period = ET =calculated basin evapotranspiration for the period RESULTS AND DISCUSSION Figure 2 summarizes the precipitation and lake level data from February 2002 to September 2003. The lake reached its lowest level of about 6.6 m below full in November 2002, at which time the drought began to subside with the onset of increased precipitation. From November 2002 to September 2003, Mountain Lake levels con-tinuously rose to reach a nearly full capacity. Table I shows the monthly hydro logic model output for the period February 2002 to August 2003, during which no surface outflow occurred in Pond Drain. Time lag introduces a wide variability in outflow when the model is configured monthly (0.003-0.106 m3 Is). Over the 18-month study period the model indicates an average subterranean net water loss of0.043 in3/s (676 gpm). While data from the model shows that water continuously leaves Mountain Lake via subterranean channels, equal or greater amounts of water must pe entering during times when lake levels are steady or rising. Much of this entering water not indicated Virginia Journal of Science, Vol. 55, No. 3, 2004 https://digitalcommons.odu.edu/vjs/vol55/iss3110 VIRGINIA JOURNAL OF SCIENCE LAKE ELEVATION (In) OJO 1180.64 1179_50 1178.00 117B.50 1175.00 117l.50 FIGURE 2. Mountain Lake precipitation and lake water level from February 2002 to September 2003. TABLE 1. Mountain Lake hydrologi:: model data Calculated Net Subterranean Basin Volume Outflow Precipitation Change Basin MONTH L(m3) Pb(m3) ~VL(m3) ET{m3) MAR02 141,864 163,074 -20,000 41,210 APR02 68,031 170,535 40,000 62,504 MAY02 9,372 121,862 50,000 62,490 JUN02 149,456 135,718 -60,000 46,262 JUL02 243,948 240,881 -20,000 16,934 AUG02 31,122 46,897 -10,000 25,775 SEP02 259,456 217,433 -50,000 7,976 OCT02 283,013 243,013 -40,000 0 NOV02 179,131 234,131 55,000 0 DEC02 94,114 169,114 75,000 0 JAN03 8,756 81,004 70,000 2,248 FEB03 237,120 277,120 40,000 0 MAR03 24,580 142,113 100,000 17,533 APR03 84,266 243,013 80,000 78,747 MAY03 70,789 282,449 170,000 41,660 JUN03 84,995 313,003 170,000 58,009 JUL03 46,802 265,396 160,000 58,594 AUG03 6,919 154,192 120,000 27,274 TOTAL 2,023,735 3,500,949 930,000 547,215 PERIOD NET OUTFLOW= 3,686 m3/d 0.043 m3/s 676 gpm -., I I Virginia Journal of Science, Vol. 55, No. 3, 2004 https://digitalcommons.odu.edu/vjs/vol55/iss3MOUNTAINLAKE,VA SUBSURFACE WATER LOSS/GAIN 111 FIGURE 3. Hole (0. 76m high, 0.46m wide) located at 32m depth at the northwe.5tem end of the deep crevice in Mountain Lake (Photograph by J.E. Waller) in the model probably comes from springs. Gist in 1751 (Johnston, 1898) reported five springs at the south end of the not full lake, and Cawley et al (1999) used SCUBA divers to locate these springs in the full lake at the Martinsburg shale-Juniata sandstone interface (Figure 1). Also, during a SCUBA reconnaissance of the north end of the lake, turbidity was noted at ca. 22 m below full pond moving from southeast to northwest approximately in line with the 1-4 subterranean input stream that never dried up during the summer droughts of 1997 and 1998 (Cawley et al., 1999, 2001a). SCUBA reconnaissance at the north end of the lake visually confirmed the probable existence of numerous potential cracks between Clinch sandstone boulders through which water might escape or enter. A dive into the deep crevice or fault, located earlier by Cawley et al. (2001a) using sonar, revealed both the sediment-free nature of this crevice and at the deepest (32 m or 108 ft) point to the northwest end a 0.76 m (2.5 ft) high and 0.46 m (1.5 ft) wide hole (Figure 1,3). During that brief visit, no detectable . currents or movement of suspended sediments toward or away from the hole were noted. However, Cawley (pers. comm.,2003) documented the occurrence of abundant Virginia Journal of Science, Vol. 55, No. 3, 2004 https://digitalcommons.odu.edu/vjs/vol55/iss3112 VIRGINIA JOURNAL OF SCIENCE deep-water Mountain Lake diatom species in sediments from Pond Drain (the only outflow stream for the lake) ca. 1.0 km to the northwest at 40-45 m lower elevation than the lake surface. These species do not occur in the shallower depths of the lake and therefore would not be carried by Pond Drain surface outflow. This observation suggested that subterranean sediments and water were reaching Pond Drain via the deep hole and/or cracks between Clinch colluvial boulders (Parker 2003). CONCLUSIONS This paper represents the first in which a hydrologic model has been used for Mountain Lake. The results obtained using this model support previous qualitative observations and assumptions that much of the water leaving the lake does so below the lake's surface. The results also show that subterranean water losses occur continu-ously regardless of whether the lake level is dropping or rising. The deep hole within the crevice feature or fault has not been previously viewed. ACKNOWLEDGMENTS We thank the Wilderness Conservancy at Mountain Lake and the Mountain Lake Hotel and Resort for their contribution of funds to support publication of the color plate and for assistance in collecting some of the data. Jansons collected or obtained much of the data used in his calculations for the model; Parker helped interpret the model output and prepared much of the text; Waller used SCUBA to confirm probable cracks between boulders, discover and photograph the deep hole. LITERATURE CITED Cawley, J.C., B. C. Parker and M. H. Beaty. 1999. A Re-evaluation of the trophic state of Mountain Lake, Virginia, USA. J. Freshw. Ecol. 14: 535-544. Cawley, J. C., B. C. Parker and L. J. Perren. 2001a. New observations on the geomorphology and origins of Mountain Lake. Earth Surf. Process. Land Forms. 26: 429-440. Cawley, J. C., B. C. Parker and T. L. Hufford. 2001b. An examination of the first sediment cores from Mountain Lake, Giles County, Virginia. Va. J. Sci. 52: 241-258. Cawley, LC., B. C. Parker and T. L. Hufford. 2002. Sediment diatoms assemblages of Mountain Lake, a subalpine ecosystem, Giles County, Virginia. Castanea 67: 120-133. Eckroade, W. M. 1962. Geology of the Butt Mountain area, Giles County, Virginia. M.S. Thesis. Virginia Polytechnic Institute, Blacksburg, VA. 64 pp. Hutchinson, G. E. and G. E. Pickford. 1932. Limnological observations of Mountain Lake, Virginia. Intemat. Rev. Gesamt. Hydrobiol. Hydrograph. 27: 252-264. Johnston, J. S. 1898. First Explorations of Kentucky: Dr. Thomas Walter's Journal of an Exploration of Kentucky in 1750, Being the First Record of a White Man to the Interior of that Territory Now First Published Entire, With Notes of a Biographical Sketch: Also Colonel Christopher Gist's Journal of a Tour Through Ohio and Kentucky in 1751, with Notes and Sketch. J.P. Morton & Co., Louisville, KY [Filson Historical Society Publication 13]. 222 pp. Marland, F. C. 1967. The history of Mountain Lake, Giles County, Virginia: An interpretation based on paleolimnology. Ph.D. Dissertation. Virginia Polytechnic Institute, Blacksburg, V A.129 pp. Virginia Journal of Science, Vol. 55, No. 3, 2004 https://digitalcommons.odu.edu/vjs/vol55/iss3MOUNTAINLAKE,VA SUBSURFACE WATER LOSS/GAIN 113 Parker, B. C. 2003. A review of research studies at Mountain Lake, Virginia. Banisteria 22: 3-21 . Parker, B. C., H. E. Wolfe and R. V. Howard. 1975. On the origin and history of Mountain Lake, Virginia. Southeast. Geol. 16: 213-226. Sharp, H. S. 1933. The origin of Mountain Lake, Virginia. J.Geol. 41: 636-641. Williams, M.G. 1930. The net plankton of Mountain Lake. M.A. Thesis (no. 461), University of Virginia, Charlottesville, VA. 25 pp. Virginia Journal of Science, Vol. 55, No. 3, 2004 https://digitalcommons.odu.edu/vjs/vol55/iss3

Subterranean Loss and Gain of Water in Mountain Lake, Virginia: A Hydrologic Model

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Subterranean Loss and Gain of Water in Mountain Lake, Virginia: A Hydrologic Model

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