Oak Ridge Reservation Research Articles

Effects of agricultural soil loss on forest succession rates and tree diversity in east Tennessee

All land on what is today the Oak Ridge Reservation, Tennessee, was abandoned in 1942 when the United States government acquired the land for atomic weapons development. Most of the land now serves as a buffer around the government facilities and has not been managed, providing an opportunity to study forest succession on simultaneously abandoned fields. We sampled forest vegetation and soils on former pastures that had sustained varying levels of pre‐abandonment soil loss. The most eroded sites are still covered with forests of an early‐successional composition, with shortleaf pine (Pinus echinata) and Virginia pine (P. virginiana) dominating. Hardwoods, particularly oaks (Quercus) and hickories (Carya), dominate the least degraded former pastures. Canopy tree species diversity is highest at the least degraded sites, which also have the highest levels of soil nitrogen. These results suggest that soil degradation reduces the rate of secondary succession and thereby slows the increase in species diversity typical of early forest succession, while increasing the spatial complexity of the landscape.

EXTERNAL EXPOSURE TO RADIONUCLIDES ACCUMULATED IN SHORELINE SEDIMENTS WITH AN APPLICATION TO THE LOWER CLINCH RIVER

A simple analytical method was developed to estimate external doses from exposure to contaminated riverine shorelines. The method consists of deriving an adjustment factor that accounts for the geometry of the riverine shoreline; the adjustment factor is applied to the dose-rate coefficients already available for infinite contaminated surfaces. Such a geometry factor circumvents very complex radiation transport calculations which would otherwise be necessary to model exposures to a finite contaminated surface. For instance, for radionuclides emitting gamma rays of energies above 600 keV (e.g., 137Cs), the published dose-rate coefficients must be reduced by 75%, 60%, 50%, and 33% for shoreline widths of 4, 10, 20, and 50 m, respectively. The geometry factor changes only mildly with the energy of the gamma radiation. This property allows for the geometry factor to be used for radionuclides emitting multiple gamma rays of various energies. If a quick analysis is desired, the geometry factors derived for 137Cs can be used for all radionuclides. More refined analysis can be performed by deriving geometry factors for each radionuclide according to its gamma spectrum. Also, the mild variation with energy allows the geometry factors to be applied to the case when radionuclides are accumulated in layers under the soil surface, and not only to the case when radionuclides are deposited onto the soil surface. Empirical relationships between the geometry factor and the dimension of the shoreline were provided so that one can obtain values of the geometry factor for any shoreline width. These relationships can be easily used to account for the uncertainty in the dimension of the shoreline. The method was applied to derive similar adjustment factors for contaminated surfaces of other simple geometries (e.g., circular surfaces). An example of how this method can be applied to its full extent is presented for the case of external exposure to the shores of the lower Clinch River. This river received large amounts of 137Cs, 60Co, 106Ru, 95Zr, 95Nb, 144Ce, and 90Sr released during 1944-1991 from the Oak Ridge Reservation in Oak Ridge, Tennessee.

Thermal-Treated Soil for Mercury Removal: Soil and Phytotoxicity Tests

Mercury (Hg) contamination of soils and sediments is one of many environmental problems at the Oak Ridge Reservation, Oak Ridge, TN. Mercury-contaminated soil from the Lower East Fork Poplar Creek (LEFPC) at the Oak Ridge Reservation was treated thermally to reduce Hg concentration to a below target level (20 mg kg{sup {minus}1}) as a pilot scale thermal treatment demonstration. As a part of performance evaluation, the soil characteristics and plant growth response of the untreated and treated soil were examined. The soil treated at 350 C retained most of its original soil properties, but the soil treated at 600 C exhibited considerable changes in mineralogical composition and physicochemical characteristics. Growth and physiological response of the three plant species radish (Raphanus sativus L.), fescue (Festuca arundinacea Schreb.), and oat (Avena sativa L.) indicated adverse effects of the thermal treatment. The addition of N fertilizer had beneficial effects in the 350 C treated soil, but had little beneficial effect in the 600 C treated soil. Some changes of soil characteristics induced by thermal treatment cannot be avoided. Soil characteristics and phytotoxicity test results strongly suggest that changes occurring following the 350 C treatment do not limit the use of the treated soilmore » to refill the excavated site for full-scale remediation. The only problem with the 350 C treatment is that small amounts of Hg compounds (<15 mg kg{sup {minus}1}) remain in the soil and a processing cost of $45/Mg.« less

The Role of Soil Classification in Geographic Information System Modeling of Habitat Pattern: Threatened Calcareous Ecosystems

Maps of potential habitat distribution are needed for regional population models of rare species, but reliable information from ground surveys is not always available. Existing data sources from disciplines other than ecological research often are underused. In this article, we discuss the development of a geographic information system (GIS) model that predicts potential habitats from ecosystem information contained in the US soil classification and soil survey. Soil classification and survey were used in the GIS model in an earlier study on the US Department of Energy's Oak Ridge Reservation, Tennessee, to predict threatened calcareous habitats. The model predicts potential habitats from the combination of (a) soil taxon as an indication of long-term ecosystem processes; (b) geologic parent material; and (c) slope class. Satellite imagery was added to indicate current successional state. In this study, we tested the model's predictive ability by using data from the Cedar Creek Slope Glades Preserve at the 44,000-ha US Department of Defense Fort Knox Military Reservation, Kentucky. We then used the model to predict occurrences of potential suitable habitat on the remainder of the Fort Knox reservation, including heavily impacted ordnance and tank training areas that are unsafe for public access. The soil component of the model also was applied to a 1.2 × 106–km2 region of the US, by using the US Department of Agriculture–National Resources Conservation Service (USDA-NRCS) State Soil Geographic Database (STATSGO) combined with official soil series descriptions. Soil taxa from the USDA-NRCS Soil Taxonomy were demonstrated to be associated with threatened calcareous habitats of rare plant species. These soil taxa were lithic mollisols (rendolls and udolls; Food and Agriculture Organization of the United Nations (FAO) rendzinas and chernozems) and alfisols (udalfs; FAO luvisols). The combined soil/geology/slope GIS approach has potential for prediction of rare ecosystems with narrow edaphic constraints. The approach would be useful in long-term planning for conservation management and restoration, especially where intensive ground surveys are expensive and/or impractical and where disturbance history obscures patterns of historical distribution.

Modeling alternative paths of chemical evolution of Na-HCO3-type groundwater near Oak Ridge, Tennessee, USA

This paper demonstrates that both cation exchange, a commonly invoked mechanism, and silicate hydrolysis, which is less commonly considered, can produce Na-HCO3-type water in sedimentary rocks. Evolution of Na-HCO3 groundwater beneath the Oak Ridge Reservation, Tennessee, USA, was studied by comparing observed end-member groundwater composition from multiport samplers to compositions generated by reaction-path geochemical models. Observed groundwater compositions could be reproduced by either the silicate-hydrolysis model or the cation-exchange model. Secondary minerals precipitated in the silicate-hydrolysis model are similar to those present along fractures in the shale and carbonate host rocks, and observed molar Sr2+/Ca2+ ratios more closely resemble evolution from shale weathering. Both mechanisms should be considered to understand the evolution of Na-HCO3 groundwater.

Ecological risk assessment in a large river‐reservoir: 7. Environmental contaminant accumulation and effects in great blue heron

AbstractPast plant operations and waste disposal on the Oak Ridge Reservation (ORR) have introduced an assortment of potentially harmful contaminants into the surrounding environment. Elevated concentrations of mercury (Hg) and PCBs have been found in fish collected from aquatic systems on the ORR, and a screening level risk assessment has identified piscivorous wildlife downstream from the ORR as being at risk. As a component of an ecological risk assessment of a large river‐reservoir system, the great blue heron (Ardea herodias) was chosen as an endpoint species to evaluate potential adverse effects of contaminants on piscivorous wildlife using aquatic systems on or downstream of the ORR. Eggs and chick liver, muscle, and fat samples were collected from two heron colonies located on and two colonies located off the ORR. Samples were analyzed for PCBs, mercury, chromium, and arsenic to determine if differences existed among colonies. Mean mercury and PCB concentrations were greater in eggs and chick tissues collected from colonies located on the ORR. However, no biologically significant differences were observed in fecundity or in egg physical measurements or chick physiological measurements between study locations. The results of this study do not indicate that the contaminant burdens in great blue heron chicks and eggs have a detrimental effect on heron populations utilizing aquatic habitats on the ORR.

Ecological risk assessment in a large river-reservoir: 4. Piscivorous wildlife

Over 50 years of operations of facilities on the Oak Ridge Reservation (ORR), Tennessee, has resulted in the release of contaminants into the water, sediment, and biota of the Clinch River and Poplar Creek, downstream of the ORR. An iterative, weight-of-evidence approach was employed to assess risks these contaminants present to four piscivorous wildlife species (osprey [Pandion haliaetus], great blue heron [Ardea herodias], mink [Mustela vison], and river otter [Lutra canadensis]) in the Clinch River/Poplar Creek (CR/PC) watershed. Available data consisted of literature-derived NOAELs and LOAELs, field surveys, and toxicity tests. Contaminants of potential ecological concern (COPECs) were identified by comparing point estimates of exposure to NOAELs and included mercury and PCBs. Exposure to COPECs was reestimated using Monte Carlo methods, first at individual locations, then over ecologically relevant spatial scales. These exposure distributions were compared to LOAELs. Estimated exposure for mink was not sufficient to present a risk from any COPEC. Mercury and PCBs presented a significant risk to river otter at one location each. Exposure of osprey and great blue herons to mercury represented a significant risk at one and two locations, respectively. Field surveys of heron rookeries and osprey nests indicated no adverse effects on reproduction. Mink fed fish from the Clinch River displayed reduced reproduction only in the most contaminated of five toxicity test diets; this reduction was not statistically significant, however. The maximum mercury and PCB exposures estimated for mink along the Clinch River were significantly lower than the toxicity test exposures associated with adverse effects The weight of evidence indicates that contaminants from the ORR do not present a risk to mink, great blue heron, or osprey along the Clinch River; river otter, however, may be at risk from mercury and PCBs.

Ecological risk assessment in a large river‐reservoir: 6. Bioindicators of fish population health

AbstractSpatial distribution of contaminants in the sediments and biota of a large reservoir ecosystem were related to a variety of biological responses in fish populations and communities to determine possible relationships between contaminant loading in the environment and fish health. Much of the contaminant inventory in the Clinch River/Watts Bar Reservoir (CR/WBR) system has originated from three U.S. Department of Energy facilities on the Oak Ridge Reservation, which borders this system in its upper reaches. Fish sampled from areas of the CR/WBR system with the highest levels of contaminants in the sediments and biota, primarily mercury and PCBs, had the most dramatic bioindicator responses. The major changes observed were induction of detoxification enzymes, organ dysfunction, increased frequency of histopathological lesions, impaired reproduction, and reduced fish community integrity. Mercury, the dominant contaminant, displayed a decreasing concentration gradient from the upper reaches of Poplar Creek to the lower Clinch River, which was consistent with a downstream gradient in several of the biological responses. A multivariate analysis using all of the individual fish health responses at each site in a discriminant analysis procedure also revealed a downstream gradient in integrated fish health. In Poplar Creek where contaminant concentrations were the highest, statistical correlations were observed between individual bioindicator responses such as contaminant exposure indicators, organ dysfunction, histopathological damage, and reproductive impairment. Relationships between contaminant loading and fish community indices such as species richness and relative abundance, however, were more difficult to establish in Poplar Creek because of the possible dominating influence of food and habitat availability on fish community dynamics. Using a suite of bioindicators that encompass a range of levels of biological organization and response‐sensitivity scales improves the probability of identifying cause (contaminant) and effect (biological response) and helps in distinguishing between natural and anthropogenic sources of stress in aquatic ecosystems.

Ecological risk assessment in a large river-reservoir: 3. Benthic invertebrates

The sediments of Poplar Creek and the Clinch River are contaminated with a wide variety of chemicals, including heavy metals, polycyclic aromatic hydrocarbons, and PCBs. Sources include the U.S. Department of Energy's Oak Ridge Reservation as well as both known and unidentified upstream activities. We investigated the risks to benthic invertebrates posed by chemicals in these sediments as part of a comprehensive ecological risk assessment performed to support Superfund clean-up decisions. Poplar Creek was the only river reach for which significant risks were determined. This conclusion was based on several lines of reasoning: sediment-associated organisms at most sites were exposed to levels of several contaminants that have been observed to be toxic; the biosurvey results show a greater than 20% reduction relative to reference sites in taxa richness and abundance; the statistical analysis of the physical, contaminant, and biosurvey data did not exclude contaminants as possible causal factors; and the sediment toxicity tests were too ambiguous to definitively exclude impacts in this reach. This assessment demonstrates the importance of collecting biological data, including sediment toxicity tests and biological surveys; statistically analyzing the relationships of chemicals, physical variables, and measured effects (e.g., toxicity or benthic invertebrate densities); and using sediment chemical and effects distributions in addition to point estimates of exposure and screening benchmarks.

Ecological risk assessment in a large river-reservoir: 2. Fish community

This paper summarizes the assessment of risks to fishes in the Clinch River Operable Unit due to contaminants released by the U.S. Department of Energy's activities on its Oak Ridge Reservation in Tennessee. This paper focuses on the most contaminated area, the Poplar Creek (PC) embayment. The assessment is of interest because of its use of five distinct lines of evidence: fish community surveys, fish body burdens, toxicity tests of ambient waters, suborganismal bioindicators, and single chemical toxicity tests. None of these lines of evidence provided unambiguous evidence of a significant risk, but the surveys indicated that the fish community in PC was depauperate, polychlorinated biphenyl body burdens may have been at toxic levels in catfish, one of the three tests of ambient water showed clear toxicity, some of the indicators were indicative of toxic effects, and concentrations that have been toxic in the laboratory were detected periodically. Interpretation was further complicated by upstream contamination of both the Clinch River and PC. The risk characterization was performed by evaluating each line of evidence separately and then weighing the evidence using an ecoepidemiological approach.

Ecological risk assessment in a large river-reservoir: 8. Experimental study of the effects of polychlorinated biphenyls on reproductive success in mink

As a component of an ecological risk assessment of Poplar Creek (located on the Oak Ridge Reservation [ORR]) and the Clinch River (a large river–reservoir system), fish from Poplar Creek, the Clinch River, and Atlantic Ocean were fed to ranch mink to evaluate reproductive success. Five diets, each composed of 75% fish and 25% normal ranch mink chow, were prepared. Two diets served as reference diets and contained 75% Atlantic Ocean fish or 75% Clinch River fish collected above the ORR. The fish portion of the remaining three diets contained 25, 50, and 75% fish collected from Poplar Creek and 50, 25, and 0% ocean fish, respectively. Five mink groups (eight females and two males each) were each fed one of the prepared diets for 196 days. Polychlorinated biphenyl concentrations were determined in diets and various mink tissues, ethoxyresorufin-O-deethylase (EROD) activity was determined in liver tissue, and reproductive success was evaluated. Concentrations of PCB were greatest in the diet composed of 75% Poplar Creek fish and in tissues from mink fed this diet and their offspring. There was a trend toward decreased adult female and kit weights and reduced mean litter size in mink fed diets containing 75% Poplar Creek fish; however, at 6 weeks of age, kit survival was similar among diet groups. Liver EROD activity significantly increased in adult female mink fed 50 and 75% Poplar Creek fish diets. Estimated dietary concentrations of PCBs were similar to or slightly lower than concentrations associated with adverse effects in experimentally dosed mink. Mercury (Hg) concentrations previously reported in these same mink were below that associated with adverse effects, and there was no indication of additive or synergistic effects from exposure to PCBs plus Hg. It is unlikely that population-level reproductive effects would be observed in mink consuming fish from Poplar Creek on the ORR.

Containment of a genetically engineered microorganism during a field bioremediation application.

A field release of a genetically engineered microorganism was performed at the Field Lysimeter Site on the Oak Ridge Reservation. Six large lysimeters were filled with soil that had been contaminated with a mixture of naphthalene, phenanthrene, and anthracene. A genetically engineered bacterial strain, Pseudomonas fluorescens HK44, was sprayed onto the surface of the soil during soil loading. This strain contains a fusion between the lux genes of Vibrio fischeri and the promoter for the lower pathway of naphthalene degradation, enabling the strain to become bioluminescent when it is degrading naphthalene. Release of the bacteria outside the lysimeters was monitored, using selective agar plates and one-stage Anderson air samplers. Although approximately 10(14) bacteria were sprayed during the loading process, escape was only detected sporadically; the highest incidence of bacterial escape was found when the relative humidity and wind speed were low.

Using Hydrochemical Fades to Delineate Ground Water Flowpaths in Fractured Shale

AbstractLarge differences in chemistry between sampling points separated In short vertical intervals are often observed in contaminant plumes in both granular and fractured aquifers. However, most regional models assume that such differences will be reduced by dispersive mixing during transport. At a field site located in a discharge area on the Oak Ridge Reservation, Tennessee, ground water flows along discrete flowpaths, as evidenced by the presence of four distinct water types—Ca‐HCO3, Ca‐Na‐HCO3, and Na‐Ca‐HCO3, and Na‐Ca‐HCO3‐S04—in samples collected from shallow (&lt; 3D in) multilevel wells. The preservation of distinct chemical signatures suggests that ground water must he contained in discrete flow zones during much of its transport time. The chemical composition of the water types can be explained primarily by strata‐bound flow over varying flowpath lengths and secondarily by mixing of waters during cross‐formational flow in a discharge zone. The hydrochemical facies identified by correlation of water types between the boreholes indicate the general orientation of ground water How paths. These inferred flowpaths are oblique to the orientation of the measured hydraulic gradient and are more closely aligned with bedding and the calculated flow direction. Results of this study indicate that discrete multilevel sampling for analysis of major ions, in addition to information gathered from tracer tests, borehole flow tests. and visual core observations, can provide valuable information on flow directions and preferential flowpaths for contaminant transport.

Porosity characteristics of Cambrian mudrocks (Oak Ridge, East Tennessee, USA) and their implications for contaminant transport

Abstract Thirty-eight mudrock samples from the Cambrian Conasauga Group were analysed by immersion, helium and mercury porosimetry. The data generated from these techniques include effective porosities, pore throat size distributions and sample densities. The purpose of these analyses was to obtain information required to evaluate the capacity of the Conasauga Group mudrock to retard transport of and to store contaminants on the Oak Ridge Reservation (East Tennessee, USA). Results indicate that the three porosities were 9.90±2.61%, 3.8±0.7% and 8.1±4.3% for immersion (φ I ), mercury (φ Hg ) and helium porosity (φ he ), respectively. These values are considerably higher than those previously reported for these rocks (0.1–3.4%). The φ Hg values are commonly the smallest of the three. Although the three porosities generally show little change with depth, an expected trend as a result of the maximum burial depth of the Conasauga Group of &gt;4 km, a decrease with depth is seen in some of the coreholes for only φ I . Furthermore, inconsistencies between the different porosity types provide an insight into the mudrock pore structure and related geochemical characteristics. For example, they indicate the existence of considerable pore space accessed only through &lt;3 nm pore throats and the possibility of meteoric cement having replaced original diagenetic cement for some mudrock samples, which would lead to a possible instability to immersion with contaminated water. These characteristics have significant implications for the evaluation of the mudrock retardation and storage capacity for contaminants, and the design of remediation measures.

Physicochemical and Biogeochemical Stabilization of Uranium in a Low Level Radioactive Waste Disposal Cell

An on-site disposal cell is being evaluated for the long-term disposition of materials generated by CERCLA (Comprehensive Environmental Response Compensation and Liability Act of 1980) remediation activities on the U.S. Department of Energy Oak Ridge Reservation (ORR), Oak Ridge, Tennessee. The leaching characteristics of the expected waste materials indicates that uranium concentrations in the leachate could exceed 30 mg/L. Addition of a geochemical barrier to the disposal cell design, or the application of chemical amendments to the waste materials, have been suggested as methods to reduce uranium levels in leachate leaving the disposal cell. Three promising approaches were identified: a) stabilization of mobile uranium by sulfate-reducing bacteria; b) stabilization of uranium as low solubility oxides by hydrated lime addition; and c) sorption of mobile uranium by a peat moss-based geochemical barrier in the disposal cell. Bench scale tests were conducted to evaluate the relative effectiveness of these three approaches. The results suggest that: a) a peat moss-based barrier would be effective in removing uranium initially, but long-term exposure to an alkaline leachate would result in the resolubilization and transport of uranium previously sorbed onto the peat moss; b) even large applications of hydrated lime to uranium-contaminated soils would not stabilize uranium in a high alkalinity, high pH environment; and c) mixed cultures of sulfate-reducing bacteria will greatly attenuate uranium levels (even in alkaline solutions) by precipitating it in the reduced form as UO 2 . Consequently, a geochemical barrier containing sulfate-reducing bacteria should be more effective than one using peat moss or hydrated lime.

Geophysical Character of Buried Sinkholes on the Oak Ridge Reservation, Tennessee (Presented at SAGEEP95 in Orlando, FL)

Sinkholes are important near‐surface indicators of active karst features at depth, such as cavities, conduits and solutionally‐enlarged fractures. This study tests the hypothesis that ground‐penetrating radar (GPR) and other geophysical methods may be used to identify filled sinkholes as a means of inferring the existence of these deeper hydraulically‐active karst features. Geophysical surveys were made at two sites in Bear Creek Valley on the Oak Ridge Reservation in eastern Tennessee. GPR profiles (25 and 50 MHz) made along the northeast edge of Bear Creek Valley showed a troughlike pattern of radar reflections outlining a possible filled sinkhole. This feature is at least 45 m wide, 3.5 to 5 m deep, and appears on GPR profiles acquired at a variety of antenna separations and along profiles made in different directions. Its dimensions are consistent with dimensions of other mapped sinkholes in the area. GPR, electromagnetic conductivity surveys, resistivity soundings and gravity models suggest this feat...

“Evidence for Ground Water Circulation in the Brine‐Filled Aquitard, Oak Ridge, Tennessee” by Ronit Nativ, Amy Halleran, and Arnold Hunley

The question addressed by Nativ et al. (1997), whether or not circulation exists between the deep ground water system and the shallow contaminated ground water underlying the waste disposal areas of the Oak Ridge Reservation (ORR), is indeed important. The answer to this question impacts not only the potential for transport of contaminants offsite via deep ground water pathways, but also the extent and associated cost of ground water monitoring. While Nativ et al. conclude that the saline water contained at depth is not isolated and that confined water (and dissolved solutes) move along open conduits at relatively high velocity into adjacent, more permeable units, the authors of this discussion would argue that when the entire body of evidence is examined, the results are inconclusive and the interpretation proposed is but one of several that could account for the apparently conflicting observations. Further, those data that suggest possible communication between the deep and shallow ground water systems also support the conclusion that the flux of ground water exchanged between systems is likely to be very small and transport times very large, thus mitigating the effects of any contamination introduced into the deep system by either natural or anthropogenic causes.

A noninvasive shallow seismic source comparison on the Oak Ridge Reservation, Tennessee

Nine seismic sources were compared in preparation for production seismic reflection profiling to about 500 m depth at a hazardous waste site on the Oak Ridge Reservation, Tennessee. Test data provided a 125-shotpoint common midpoint profile and a walkaway vertical seismic profile for each source. Sources tested included five swept sources and four impulsive sources. Eight of the sources were “noninvasive,” in that they would not penetrate the ground surface. When spectral whitening methods were applied to the data, the IVI Minivib provided the best image of the subsurface on the basis of continuity and clarity of reflections. Without prewhitening, the performance of the IVI Minivib and the Bison elastic wave generator were similar.

Influence of fracture truncation on dispersion: A dual permeability model

Simulations with a dual permeability model show that a few discrete fractures can have a major influence on plume geometry. A limited number of truncated fractures (1–4) within a permeable matrix can create nearly circular plumes, with about the same degree of spreading in the direction transverse to the average hydraulic gradient as in the longitudinal direction. By comparison, continuous fractures in the direction of flow tend to produce elongated plumes, similar to those typically seen in granular materials. Both types of plumes have been observed in tracer experiments in fractured porous media on the Oak Ridge Reservation. Understanding the influence of fracture geometry is important in planning field characterization and subsequent remediation in fractured porous media.

Assessing Land-Use Impacts on Natural Resources

/ Much information is available on changes that occur in natural resources from both spatially-explicit data on environmental conditions and models of the interactions of these conditions and resources with human activities. The strategy for assessing land-use impacts on natural resources developed in this paper provides a framework for using relevant data and models to address questions of how management practices can promote both use and protection of resources. This assessment strategy integrates spatially explicit environmental data using geographic information systems (GIS) with computer models that simulate changes in land cover in response to land-use impacts. The computer models also simulate susceptibility of species to changes in habitat suitability and landscape patterns. The approach is applied to management of limestone barrens on the Oak Ridge Reservation in East Tennessee. Potential limestone barrens habitats are identified by overlaying appropriate soils, geology, slope, and land-use/land-cover conditions. Their validity is tested against known sites containing rare species that occur in these habitats. The location of habitats at risk in the aftermath of human activities is determined by using an available area model that identifies the size and proximity of sites that particular types of species can no longer use as habitat. The resulting risk map can be used in land management planning. The approach uses readily available in situ and remotely sensed data and is applicable to a wide range of locations and land-use scenarios. This approach can be refined based on needs identified by land managers and on the sensitivity of the results to the resolution of available resource information.KEY WORDS: Land management; Assessment; Habitat characterization; Limestone barrens; Ecological modeling; Geographic information systems