Rocky Mountain National Park Research Articles

Historic range of variability in geomorphic processes as a context for restoration: Rocky Mountain National Park, Colorado, USA

ABSTRACTEvaluation of historic range of variability (HRV) is an effective tool for determining baseline conditions and providing context to researchers and land managers seeking to understand and enhance ecological function. Incorporating HRV into restoration planning acknowledges the dynamic quality of landscapes by allowing variability and disturbance at reasonable levels and permitting riverine landscapes to adapt to the physical processes of their watersheds. HRV analysis therefore represents a practical (though under‐utilized) method for quantifying process‐based restoration goals. We investigated HRV of aggradational processes in the subalpine Lulu City wetland in Rocky Mountain National Park to understand the impacts of two centuries of altered land use and to guide restoration planning following a human‐caused debris flow in 2003 that deposited up to 1 m of sand and gravel in the wetland. Historic aerial photograph interpretation, ground penetrating radar surveys, and trenching, coring, and radiocarbon dating of valley‐bottom sediments were used to map sediment deposits, quantify aggradation rates, and identify processes (in‐channel and overbank fluvial deposition, direct hillslope input, beaver pond filling, peat accumulation) creating alluvial fill within the wetland. Results indicate (i) the Lulu City wetland has been aggrading for several millennia, (ii) the aggradation rate of the past one to two centuries is approximately six times higher than long‐term pre‐settlement averages, (iii) during geomorphically active periods, short‐term aggradation rates during the pre‐settlement period were probably much higher than the long‐term average rate, and (iv) the processes of aggradation during the last two centuries are the same as historic processes of aggradation. Understanding the HRV of aggradation rates and processes can constrain management and restoration scenarios by quantifying the range of disturbance from which a landscape can recover without active restoration. Copyright © 2011 John Wiley & Sons, Ltd.

The Impact of Local Source Sediments on Bed Texture in the Fall River, Rocky Mountain National Park, USA

The bed texture of a gravel-bed river is related to the size distribution and quantity of source sediments, the routing of sediment through the reach, and the distribution of flow velocity. A reach morphology that is consistent in depth with little lateral topographic variation will typically have a bed texture that is characterized by a fairly uniform grain size distribution. However, spatial variations in source sediments within a given watershed may impact the distribution of gravel-bed river sediments, even at the reach scale, such that two proximal reaches of the same river having the same general morphology can exhibit contrasting distributions of surface sediments. We collected extensive topographic and sedimentological data from two reaches of the Fall River in Rocky Mountain National Park, Colorado. These were chosen for their simple morphology (both are straight reaches with fairly uniform depths) and contrasting location relative to alluvial fan deposits that were introduced into the valley in a dam-break event in 1982; the upstream reach was unaffected by the introduced sediments. Despite the long duration since this event, surveying in 2008 revealed that the fan sediment continues to coarsen the left and upstream portions of the affected reach relative to other regions of the channel. The persistent nonuniformity in bed texture in the downstream reach may eventually result in morphological adjustment by promoting differential routing of fine versus coarse bed load size fractions, which may induce meandering.

Scale and Pattern of Cheatgrass (Bromus tectorum) Invasion in Rocky Mountain National Park

ABSTRACT: Cheatgrass (Promus tectorum L.), a winter-annual grass native to Eurasia, is one of the most widely distributed and damaging invasive annual grasses in North America. We studied the scale and pattern of cheatgrass in Rocky Mountain National Park, Colorado, examining possible dispersal and disturbance mechanisms and inherently susceptible environmental characteristics that may facilitate the spread of cheatgrass in the park. We distinguished facilitating factors related to land uses and natural processes. We mapped (with GPS) cheatgrass patches along randomly selected transects along roads, trails, in natural vegetation, and around developments. For each patch, we recorded: (1) patch size, (2) percentage cover of cheatgrass, (3) characteristics of microenvironments, and (4) amount of cheatgrass within microenvironments. Using MANOVA, we found that, at a broad scale, cheatgrass is concentrated on the east side of the park, at lower elevations, and in grassland and shrubland vegetation, with roads ...

A comparison of permafrost prediction models along a section of Trail Ridge Road, Rocky Mountain National Park, Colorado, USA

The distribution of mountain permafrost along Trail Ridge Road (TRR) in Rocky Mountain National Park, Colorado, was modeled using ‘frost numbers’ and a ‘temperature of permafrost model’ (TTOP) in order to assess the accuracy of prediction models. The TTOP model is based on regional observations of air temperature and heat transfer functions involving vegetation, soil, and snow; whereas the frost number model is based on site-specific ratios of ground temperature measurements of frozen and thawed degree-days. Thirty HOBO© temperature data loggers were installed near the surface as well as at depth (30 to 85 cm). From mid-July 2008 to 2010, the mean annual soil temperature (MAST) for all surface sites was − 1.5 °C. Frost numbers averaged 0.56; TTOP averaged − 1.8 °C. The MAST was colder on western-facing slopes at high elevations. Surface and deeper probes had similar MASTs; however, deeper probes had less daily and seasonal variation. Another model developed at the regional scale based on proxy indicators of permafrost (rock glaciers and land cover) classified 5.1 km 2 of permafrost within the study area, whereas co-kriging interpolations of frost numbers and TTOP data indicated 2.0 km 2 and 4.6 km 2 of permafrost, respectively. Only 0.8 km 2 were common among all three models. Three boreholes drilled within 2 m of TRR indicate that permafrost does not exist at these locations despite each borehole being classified as containing permafrost by at least one model. Addressing model uncertainty is important because nutrients stored within frozen or frost-affected soils can be released and impact alpine water bodies. The uncertainty also exposes two fundamental problems: empirical models designed for high latitudes are not necessarily applicable to mountain permafrost, and the presence of mountain permafrost in the alpine tundra of the Colorado Front Range has not been validated.

Estimating visitors’ travel mode choices along the Bear Lake Road in Rocky Mountain National Park

The National Park Service (NPS) in the United States of America (USA) is looking to alternative transportation systems to provide visitors access to the national parks in a manner that potentially reduces traffic congestion, enhances visitors’ experiences, and more effectively protects park resources. However, shuttle bus systems without adequate planning and management may lead to unintended consequences such as eliminating the constraint to visitor use levels associated with parking lot capacities. As a consequence, the demand for recreation use in the area increases the potential impacts to the visitor experience and park resources. This study examined the trade-offs Rocky Mountain National Park visitors were willing to make about transportation mode choice using a stated choice survey to inform park managers about visitor acceptance of potential transportation related management actions. Results indicate that visitors prefer to use their private vehicles over the parks transit system but are willing to make trade-offs to ride the shuttle bus in order to avoid crowding along the trail at Bear Lake and vehicle traffic along the Bear Lake Road. In addition, there were statistically significant differences among choices of transportation mode trade-offs among different age groups (i.e., less than 40years of age, 40–60years of age, and more than 60years of age) Specifically, results suggest that visitors less than 40years are more willing than the older age groups to make trade-offs among transportation options to enhance their chances of being on the trail system at Bear Lake with fewer other people. The significant and interacted relationships with shuttle bus use, visitor use, and vehicle traffic levels found in this study provide RMNP managers opportunities to influence visitors’ transportation mode choices.

Spatial variation of natural ambient sound pressure levels in Rocky Mountain National Park.

The soundscape is a critical component of an ecological community, and knowledge of natural ambient sound pressure levels is crucial to assessing impacts of noise. However, the spatial correlation of natural ambient sound pressure levels is largely unknown and a given measurement may not be representative of the locale. Much anthropogenic noise can be considered point or line sources; the spatial correlation of the resulting sound pressure levels can be completely described by directivity and the inverse square law in an isotropic medium. However, most natural sources (wind, birdsong, rain, insects, etc.) may be better described in aggregate as an irregular source with stochastic characteristics. Recently, a 9-day long study collected continuous audio data at 18 locations over a roughly 3.5 s km1 area in Rocky Mountain National Park. Analysis seeks to investigate the spatial variation of natural ambient sound pressure level measurements and the degree to which they are correlated across space. Results will suggest how sparsely an area can be measured as well as placement of a finite number of microphones to best observe the acoustical environment.

Forest developmental trajectories in mountain pine beetle disturbed forests of Rocky Mountain National Park, Colorado

A mountain pine beetle (Dendroctonus ponderosae Hopkins) epidemic has caused widespread mortality of lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) trees across western North America,. We characterized the initial effects of beetle-induced mortality on forest structure and composition in Rocky Mountain National Park, Colorado. In 2008, we surveyed stand structure and tree species composition across lodgepole pine dominated forests in the western portion of the Park. We defined five lodgepole pine forest types to describe variability in pre-epidemic forest conditions. This forested landscape appears to be resilient to the effects of the beetle. Surviving trees, including both canopy trees and saplings, were plentiful in most of the post-epidemic forests, even after accounting for anticipated future mortality. Subalpine fir (Abies lasiocarpa (Hook.) Nutt.), Engelmann spruce (Picea engelmannii Parry ex Engelm.), and aspen (Populus tremuloides Michx.) had modestly higher relative abundances after the epidemic. Lodgepole pine remained the dominant species on approximately 85% of the landscape. The impact of the outbreak on forest structure and composition varied considerably among the five forest types, suggesting that post-epidemic forest developmental trajectories will vary according to pre-outbreak stand characteristics. Active management efforts to regenerate lodgepole pine forests, e.g., tree planting, will likely not be necessary on this landscape.

Distributional Changes and Range Predictions of Downy Brome (Bromus tectorum) in Rocky Mountain National Park

AbstractDowny brome (Bromus tectorumL.), an invasive winter annual grass, may be increasing in extent and abundance at high elevations in the western United States. This would pose a great threat to high-elevation plant communities and resources. However, data to track this species in high-elevation environments are limited. To address changes in the distribution and abundance of downy brome and the factors most associated with its occurrence, we used field sampling and statistical methods, and niche modeling. In 2007, we resampled plots from two vegetation surveys in Rocky Mountain National Park for presence and cover of downy brome. One survey was established in 1993 and had been resampled in 1999. The other survey was established in 1996 and had not been resampled until our study. Although not all comparisons between years demonstrated significant changes in downy brome abundance, its mean cover increased nearly fivefold from 1993 (0.7%) to 2007 (3.6%) in one of the two vegetation surveys (P = 0.06). Although the average cover of downy brome within the second survey appeared to be increasing from 1996 to 2007, this slight change from 0.5% to 1.2% was not statistically significant (P = 0.24). Downy brome was present in 50% more plots in 1999 than in 1993 (P = 0.02) in the first survey. In the second survey, downy brome was present in 30% more plots in 2007 than in 1996 (P = 0.08). Maxent, a species–environmental matching model, was generally able to predict occurrences of downy brome, as new locations were in the ranges predicted by earlier generated models. The model found that distance to roads, elevation, and vegetation community influenced the predictions most. The strong response of downy brome to interannual environmental variability makes detecting change challenging, especially with small sample sizes. However, our results suggest that the area in which downy brome occurs is likely increasing in Rocky Mountain National Park through increased frequency and cover. Field surveys along with predictive modeling will be vital in directing efforts to manage this highly invasive species.

The Relationships Among Plant Cover, Density, Seed Rain, and Dispersal ofBromus tectorumin High-Elevation Populations

The invasive species Bromus tectorum L. is recognized as one of the most ecologically and economically devastating weeds in the western United States. Although B. tectorum has been studied extensively, few studies have examined its dispersal and spread. We collected data from sites with B. tectorum in and around Rocky Mountain National Park to quantify the relationships between plant cover/density and seed rain and dispersal distance. Results suggest that there is a positive relationship between density within a patch and local seed rain and that B, tectorum exhibits relatively limited short-distance dispersal (where seeds fell in close proximity to plants and no seeds were found to have dispersed more than 0.1 m from the edge of a patch). These data can inform modelers and managers who are attempting to better understand population dynamics and options for controlling this species.

Sclerotia as indicators of mid-Holocene tree-limit altitude, Colorado Front Range, USA

Studies in the Front Range of north-central Colorado have shown that sclerotia of Cenococcum geophilum, a common ectomycorrhizal fungus, are larger beneath spruce-fir-forest and tree-island vegetation than beneath tundra grasses and herbs. The presence, in alpine-tundra soils, of C. geophilum sclerotia with median diameters that approach or exceed 1.0 mm is evidence that tree limit formerly stood higher than it does today. A sediment sample collected 116 m above tree limit on Rowe Mountain, in Rocky Mountain National Park, contained charred sclerotia with a median diameter of 1.1 mm. Wood-charcoal particles too large to have been transported by wind were associated. Radiocarbon dates of 4770 ± 25 yr BP (charred sclerotia) and 4900 ± 15 yr BP (charred spruce twig) apply to the wildfire that destroyed forest or tree-island vegetation at this locality. Lack of evidence for post-fire regeneration suggests that growing-season temperatures had already begun to decline from elevated middle Holocene levels.

Characterization of ten microsatellite loci in the Broad-tailed Hummingbird (Selasphorus platycercus)

The Broad-tailed Hummingbird (Selaphorus platycercus) breeds at higher elevations in the central and southern Rockies, eastern California, and Mexico and has been studied for 8 years in Rocky Mountain National Park, Colorado. Questions regarding the relatedness of Broad-tailed Hummingbirds banded together and then recaptured in close time proximity in later years led us to isolate and develop primers for 10 polymorphic microsatellite loci. In a screen of 25 individuals from a population in Rocky Mountain National Park, the 10 loci were found to have levels of variability ranging from two to 16 alleles. No loci were found to depart from linkage disequilibrium, although two loci revealed significant departures from Hardy–Weinberg equilibrium. These 10 microsatellite loci will be applicable for population genetic analyses, investigation of mating systems and relatedness, and may help gain insight into the migration timing and routes for this species.

Determining contributions of biomass burning and other sources to fine particle contemporary carbon in the western United States

Six-day integrated fine particle samples were collected at urban and rural sampling sites using Hi-Volume samplers during winter and summer 2004–2005 as part of the IMPROVE (Interagency Monitoring of PROtected Visual Environments) Radiocarbon Study. Filter samples from six sites (Grand Canyon, Mount Rainier, Phoenix, Puget Sound, Rocky Mountain National Park, and Tonto National Monument) were analyzed for levoglucosan, a tracer for biomass combustion, and other species by High-Performance Anion-Exchange Chromatography with Pulsed Amperometric Detection (HPAEC-PAD). Contemporary carbon concentrations were available from previous carbon isotope measurements at Lawrence Livermore National Laboratory. Primary contributions of biomass burning to measured fine particle contemporary carbon were estimated for residential wood burning (winter) and wild/prescribed fires (summer). Calculated contributions ranged from below detection limit to more than 100% and were typically higher at rural sites and during winter. Mannitol, a sugar alcohol emitted by fungal spores, was analyzed and used to determine contributions of fungal spores to fine particle contemporary carbon. Contributions reached up to 13% in summer samples, with higher contributions at rural sites. Concentrations of methyltetrols, oxidation products of isoprene, were also measured by HPAEC-PAD. Secondary organic aerosol (SOA) from isoprene oxidation was estimated to contribute up to 22% of measured contemporary carbon. For each sampling site, a substantial portion of the contemporary carbon was unexplained by primary biomass combustion, fungal spores, or SOA from isoprene oxidation. This unexplained fraction likely contains contributions from other SOA sources, including oxidation products of primary smoke emissions and plant emissions other than isoprene, as well as other primary particle emissions from meat cooking, plant debris, other biological aerosol particles, bio-diesel combustion, and other sources. Loss of levoglucosan during atmospheric aging of biomass burning emissions likely also results in an underestimate of apportioned primary smoke contributions.

Modeling the Effects of Shuttle Service on Transportation System Performance and Quality of Visitor Experience in Rocky Mountain National Park

Rocky Mountain National Park (RMNP) was one of the first national parks to adopt an alternative transportation system: a shuttle bus system initiated in 1978. To address parking lot shortages while accommodating growing numbers of park visitors, RMNP expanded its shuttle bus service in 2001. Although the expanded shuttle service has helped to alleviate parking congestion at popular trailheads, expansion may also be enabling levels of visitation that cause or exacerbate visitor crowding. Thus, there is a need to evaluate and potentially refine RMNP's shuttle service according to the amount of visitor use that can be accommodated at popular destinations in the park without unacceptable effects on the quality of visitors’ experiences. This study evaluated and quantified transportation system performance and visitor crowding at popular recreation sites in the Bear Lake Road corridor resulting from RMNP's shuttle service operations. The study used integrated transportation and visitor use modeling to provide quantitative estimates of the extent of parking congestion, transportation-related greenhouse gas emissions, transit operating costs per passenger, and visitor crowding associated with existing and alternative transit service operations scenarios. The National Park Service will use information from the study to refine the operation of shuttle service in RMNP in a manner that both optimizes transportation system performance and protects the quality of visitors’ experiences. Further, the study framework can be generalized to other public lands units to design and operate transit service in accordance with transportation, resource, and visitor experience objectives.

Assessing Public Acceptance of Wildlife Management Trade-Offs: A Case Study of Elk and Vegetation Management in Rocky Mountain National Park, Colorado

Balancing wildlife management trade-offs is likely to result in differential impacts and varying levels of support among stakeholders. Science should guide discourse regarding these trade-offs, and science can, in turn, quantify the discourse to inform management. This study developed a unique visual-based instrument to explain complex trade-offs to the public and quantify preferences for elk and vegetation management in Rocky Mountain National Park (RMNP), Colorado, USA. Results (n = 1,324) showed a preference for future conditions that are expected to result from elk (Cervus elaphus nelsoni) reductions and active vegetation protection on the elk's winter range, but revealed less agreement on appropriate actions to achieve these conditions. Management actions that actively restore wildlife habitat were evaluated favorably, and hazing techniques were consistently evaluated as unacceptable. Respondents were divided on the acceptability of elk reduction measures and various other actions to keep elk from browsing on vegetation.

Back-trajectory-based source apportionment of airborne sulfur and nitrogen concentrations at Rocky Mountain National Park, Colorado, USA

The Rocky Mountain Atmospheric Nitrogen and Sulfur Study (RoMANS), conducted during the spring and summer of 2006, was designed to assess the sources of nitrogen and sulfur species that contribute to wet and dry deposition and visibility impairment at Rocky Mountain National Park (RMNP), Colorado. Several source apportionment methods were utilized for RoMANS, including the Trajectory Mass Balance (TrMB) Model, a receptor-based method in which the hourly measured concentrations are the dependent variables and the residence times of back trajectories in several source regions are the independent variables. The regression coefficients are estimates of the mean emissions, dispersion, chemical transformation, and deposition between the source areas and the receptors. For RoMANS, a new ensemble technique was employed in which input parameters were varied to explore the range, variability, and model sensitivity of source attribution results and statistical measures of model fit over thousands of trials for each set of concentration measurements. Results showed that carefully chosen source regions dramatically improved the ability of TrMB to reproduce temporal patterns in the measured concentrations, and source attribution results were also very sensitive to source region choices. Conversely, attributions were relatively insensitive to trajectory start height, trajectory length, minimum endpoints per source area, and maximum endpoint height, as long as the trajectories were long enough to reach contributing source areas and were not overly restricted in height or horizontal location. Source attribution results estimated that more than half the ammonia and 30–45% of sulfur dioxide and other nitrogen-containing species at the RoMANS core site were from sources within the state of Colorado. Approximately a quarter to a third of the sulfate was from within Colorado. ► New ensemble method for air quality source apportionment receptor model discussed. ► Trajectory Mass Balance used to attribute nitrogen and sulfur concentrations. ► Half ammonia at Rocky Mountain National Park, CO, USA estimated from within state. ► Third of sulfate at Rocky Mountain National Park, Colorado, USA from within state. ► Trajectory Mass Balance insensitive to many parameters if all sources included.

Modeling the fate of atmospheric reduced nitrogen during the Rocky Mountain Atmospheric Nitrogen and Sulfur Study (RoMANS): Performance evaluation and diagnosis using integrated processes rate analysis

Excess wet and dry deposition of nitrogen-containing compounds is a concern at a number of national parks. The Rocky Mountain Atmospheric Nitrogen and Sulfur Study (RoMANS) was conducted during the spring and summer of 2006 to identify the overall mix of ambient and deposited sulfur and nitrogen at Rocky Mountain National Park (RMNP), in north-central Colorado. The Comprehensive Air Quality Model with extensions (CAMx) was used to simulate the fate of gaseous and particulate species subjected to multiple chemical and physical processes during RoMANS. This study presents an operational evaluation with a special emphasis on the model performance of reduced nitrogen species. The evaluation showed large negative biases and errors at RMNP and the entire domain for ammonia; therefore the model was considered inadequate for future source apportionment applications. The CAMx Integrated Processes Rate (IPR) analysis tool was used to elucidate the potential causes behind the poor model performance. IPR served as a tool to diagnose the relative contributions of individual physical and chemical processes to the final concentrations of reduced nitrogen species. The IPR analysis revealed that dry deposition is the largest sink of ammonia in the model, with some cells losing almost 100% of the available mass. Closer examination of the ammonia dry deposition velocities in CAMx found that they were up to a factor of 10 larger than those reported in the literature. A series of sensitivity simulations were then performed by changing the original deposition velocities with a simple multiplicative scaling factor. These simulations showed that even when the dry deposition values were altered to reduce their influence, the model was still unable to replicate the observed time series; i.e., it fixed the average bias, but it did not improve the precision.

Presence of antibiotic-resistant commensal bacteria in samples from agricultural, city, and national park environments evaluated by standard culture and real-time PCR methods

This study examined the presence of antibiotic-resistant commensal bacteria among cattle operations representing areas heavily affected by agriculture, city locations representing areas affected by urban activities and indirectly affected by agriculture, and a national park representing an area not affected by agriculture. A total of 288 soil, fecal floor, and water samples were collected from cattle operations, from the city of Fort Collins, and from Rocky Mountain National Park (RMNP) in Colorado. In addition, a total of 42 new and unused feed, unused bedding, compost, and manure samples were obtained from the cattle operations. Total, tetracycline-resistant, and ceftiofur-resistant bacterial populations were enumerated by both standard culture plating and real-time PCR methods. Only wastewater samples from the cattle operations demonstrated both higher tetracycline-resistant bacterial counts (enumerated by the culture plating method) and tetracycline resistance gene copies (quantified by real-time PCR) compared to water samples collected from non-farm environments. The ceftiofur resistance gene, blaCMY-2, was not detectable in any of the samples, while the tetracycline resistance genes examined in this study, tet(B), tet(C), tet(W), and tet(O), were detected in all types of tested samples, except soil samples from RMNP. Tetracycline resistance gene pools quantified from the tet(O) and tet(W) genes were bigger than those from the tet(B) and tet(C) genes in fecal and water samples. Although only limited resistance genes, instead of a full set, were selected for real-time PCR quantification in this study, our results point to the need for further studies to determine natural and urban impacts on antibiotic resistance.

Development of Equations Predictive of Size and Condition for Black Bears in Rocky Mountain National Park, Colorado

Abstract Knowledge of body condition is important in predicting health and performance of large mammal populations. Therefore, we assessed body condition in black bears (Ursus americanus) in Rocky Mountain National Park (RMNP), Colorado, using body mass (BM), percent body fat (BF) and a body condition index (BCI) to: (1) develop a model predictive of BM for bears in RMNP using morphometric measures, (2) compare three models predictive of BM to provide further information on the influence of elevation and more complex models on model accuracy, and (3) assess the relationship between BF and BCI to determine if BF could be estimated from BCI. Our best BM model included only girth (r2 = 0.923) and indicated that mass-morphology relationships were more consistent within specified elevation zones; complexity of models had little influence on model efficiency. We also observed a strong relationship between BF and BCI (r2 = 0.962) indicating that BCI scores can be accurately converted to estimates of BF. This...

Historical deposition of mercury and selected trace elements to high-elevation National Parks in the Western U.S. inferred from lake-sediment cores

Atmospheric deposition of Hg and selected trace elements was reconstructed over the past 150 years using sediment cores collected from nine remote, high-elevation lakes in Rocky Mountain National Park in Colorado and Glacier National Park in Montana. Cores were age dated by 210Pb, and sedimentation rates were determined using the constant rate of supply model. Hg concentrations in most of the cores began to increase around 1900, reaching a peak sometime after 1980. Other trace elements, particularly Pb and Cd, showed similar post-industrial increases in lake sediments, confirming that anthropogenic contaminants are reaching remote areas of the Rocky Mountains via atmospheric transport and deposition. Preindustrial (pre-1875) Hg fluxes in the sediment ranged from 5.7 to 42 μg m −2 yr −1 and modern (post-1985) fluxes ranged from 17.7 to 141 μg m −2 yr −1. The average ratio of modern to preindustrial fluxes was 3.2, which is similar to remote lakes elsewhere in North America. Estimates of net atmospheric deposition based on the cores were 3.1 μg m −2 yr −1 for preindustrial and 11.7 μg m −2 yr −1 for modern times. Current-day measurements of wet deposition range from 5.0 to 8.6 μg m −2 yr −1, which are lower than the modern sediment-based estimate of 11.7 μg m −2 yr −1, perhaps owing to inputs of dry-deposited Hg to the lakes.

Denning Chronology of Black Bears in Eastern Rocky Mountain National Park, Colorado

ABSTRACT. Understanding factors influencing the timing of den entrance and emergence of black bears (Ursus americanus) provides insight for bear management. We determined den entrance and emergence dates for bears in Rocky Mountain National Park (RMNP) and related these dates to vegetative productivity, weather, habitat, and demographic factors to assess the influence of these factors on denning chronology. Date of den entrance was most strongly influenced by age class, precipitation, and proportion of human-use areas in annual home ranges. Den entrance was typically later for adult bears during wetter years and when annual home ranges contained a greater proportion of human-use areas. Sex and presence of human-use areas were most strongly related to den emergence. Male bears typically emerged from dens before females, and bears emerged from dens earlier when human-use areas composed a greater proportion of annual home ranges. Collectively, our results suggest that denning behavior of black bears in RMNP ...