Colorado Rocky Mountains Research Articles

Ps mantle transition zone imaging beneath the Colorado Rocky Mountains: Evidence for an upwelling hydrous mantle

We analyze teleseismic P-to-S conversions for high-resolution imaging of the mantle transition zone beneath the Colorado Rocky Mountains using data from a dense PASSCAL seismic broadband deployment. A total of 6,021 P-to-S converted receiver functions are constructed using a multi-channel minimum-phase deconvolution method and migrated using the common converted point technique with the 3-D teleseismic P- and S-wave tomography models of Schmandt and Humphreys (2010). The image finds that the average depths of the 410-km discontinuity (the 410) and 660-km discontinuity (the 660) at 408±1.9 km and 649±1.6 km respectively. The peak-to-peak topography of both discontinuities is 33 km and 27 km respectively. Additionally, prominent negative polarity phases are imaged both above and below the 410. To quantify the mean properties of the low-velocity layers about 410 km, we utilize double gradient layer models parameterization to fit the mean receiver function waveform. This waveform fitting is accomplished as a grid-search using anelastic synthetic seismograms. The best-fitting model reveals that the olivine–wadsleyite phase transformation width is 21 km, which is significantly larger than anhydrous mineral physics prediction (4–10 km) (Smyth and Frost, 2002). The findings of a wide olivine–wadsleyite phase transformation and the negative polarity phases above and below the 410, suggest that the mantle, at least in the 350–450 km depth range, is significantly hydrated. Furthermore, a conspicuous negative polarity phase below the 660 is imaged in high velocity region, we speculate the low velocity layer is due to dehydration flux melting in an area of convective downwelling. Our interpretation of these results, in tandem with the tomographic image of a Farallon slab segment at 800 km beneath the region (Schmandt and Humphreys, 2010), is that hydrous and upwelling mantle contributes to the high-standing Colorado Rocky Mountains.

The Simulated Impact of the Snow Albedo Feedback on the Large-Scale Mountain–Plain Circulation East of the Colorado Rocky Mountains

Abstract The Front Range mountain–plain circulation (FRMC) is a large-scale diurnally driven wind system that occurs east of the Colorado Rocky Mountains in the United States and affects the weather both in the Rocky Mountains and Great Plains. As the climate warms, the snow albedo feedback will amplify the warming response in the Rocky Mountains during the spring, increasing the thermal contrast that drives the FRMC. In this study, the authors perform a 7-yr pseudo–global warming (PGW) regional climate change experiment along with an idealized PGW “fixed albedo” experiment to test the sensitivity of the FRMC to the snow albedo feedback (SAF). The authors find a mean increase in the springtime FRMC strength in the PGW experiment that is primarily driven by the snow albedo feedback. Furthermore, interannual variability of changes in FRMC strength is strongly influenced by interannual variability in the SAF. An additional case study experiment configured with a much higher resolution is performed to examine the finescale details of how the SAF and the FRMC interact. This experiment includes a passive tracer to investigate subsequent impacts on pollution transport. The case study reveals that loss of snow cover causes an increase in the strength of the FRMC. Advection by the strengthened FRMC increases the concentration of tracers emitted over the Great Plains in the boundary layer over the Front Range mountains.

Snow Sublimation in Mountain Environments and Its Sensitivity to Forest Disturbance and Climate Warming

AbstractSnow sublimation is an important component of the snow mass balance, but the spatial and temporal variability of this process is not well understood in mountain environments. This study combines a process‐based snow model (SnowModel) with eddy covariance (EC) measurements to investigate (1) the spatio‐temporal variability of simulated snow sublimation with respect to station observations, (2) the contribution of snow sublimation to the ablation of the snowpack, and (3) the sensitivity and response of snow sublimation to bark beetle‐induced forest mortality and climate warming across the north‐central Colorado Rocky Mountains. EC‐based observations of snow sublimation compared well with simulated snow sublimation at stations dominated by surface and canopy sublimation, but blowing snow sublimation in alpine areas was not well captured by the EC instrumentation. Water balance calculations provided an important validation of simulated sublimation at the watershed scale. Simulated snow sublimation across the study area was equivalent to 28% of winter precipitation on average, and the highest relative snow sublimation fluxes occurred during the lowest snow years. Snow sublimation from forested areas accounted for the majority of sublimation fluxes, highlighting the importance of canopy and sub‐canopy surface sublimation in this region. Simulations incorporating the effects of tree mortality due to bark‐beetle disturbance resulted in a 4% reduction in snow sublimation from forested areas. Snow sublimation rates corresponding to climate warming simulations remained unchanged or slightly increased, but total sublimation losses decreased by up to 6% because of a reduction in snow covered area and duration.

Measuring Mountain River Discharge Using Seismographs Emplaced Within the Hyporheic Zone

AbstractFlow and sediment transport dynamics in fluvial systems play critical roles in shaping river morphology, in the design and use of riverine infrastructure, and in the broader management of watersheds. However, these properties are often difficult to measure comprehensively. Previous work has suggested the use of proximal seismic signals resulting from flow and bed load transport to construct more complete records of these fluvial processes. We investigate a small (184 km2; < 20 m3/s), snowmelt‐fed mountain river in the Northern Colorado Rocky Mountains during May–August 2015 to capture peak runoff with colocated measurements of discharge and seismic noise. Three‐component seismometers were placed in close proximity to the channel bank (~1 m) within the hyporheic zone (at times submerged beneath the water table). We recorded a broad spectrum of seismic signals excited by discharge, including novel, low‐frequency (0.1–2 Hz) signals observed predominantly on the horizontal components. The characteristics of these low‐frequency signals are not consistent with an elastically propagating seismic wave. We instead infer that they likely arise from the sensor tilting in response to viscoelastic deformation occurring near the channel and propose large‐scale turbulent eddies as a forcing mechanism. Calibrating horizontal seismic power with hydrograph flow rates over the course of a rainstorm for individual sensors, we demonstrate that these unique signals can be used to accurately estimate river discharge with simple regressions. This technique shows promise for augmenting seismic monitoring of rivers by enabling discharge rates to be estimated from outside the channel using easily deployed and noninvasive seismic instrumentation.

A Scheme to Assimilate “No Rain” Observations from Doppler Radar

Abstract Radar reflectivity observations contain valuable information on precipitation and have been assimilated into numerical weather prediction models for improved microphysics initialization. However, low-reflectivity (or so-called no rain) echoes have often been ignored or not effectively used in radar data assimilation schemes. In this paper, a scheme to assimilate no-rain radar observations is described within the framework of the Weather Research and Forecasting Model’s three-dimensional variational data assimilation (3DVar) system, and its impact on precipitation forecasts is demonstrated. The key feature of the scheme is a neighborhood-based approach to adjusting water vapor when a grid point is deemed as no rain. The performance of the scheme is first examined using a severe convective case in the Front Range of the Colorado Rocky Mountains and then verified by running the 3DVar system in the same region, with and without the no-rain assimilation scheme for 68 days and 3-hourly rapid update cycles. It is shown that the no-rain data assimilation method reduces the bias and false alarm ratio of precipitation over its counterpart without that assimilation. The no-rain assimilation also improved humidity, temperature, and wind fields, with the largest error reduction in the water vapor field, both near the surface and at upper levels. It is also shown that the advantage of the scheme is in its ability to conserve total water content in cycled radar data assimilation, which cannot be achieved by assimilating only precipitation echoes.

A Field Guild to Murder & Fly Fishing by Tim Weed

Reviewed by: A Field Guild to Murder & Fly Fishing by Tim Weed Susan Sugai Tim Weed. A Field Guild to Murder & Fly Fishing. Green Writers Press, 2017. In A Field Guild to Murder & Fly Fishing, Tim Weed masterfully leads the reader on a journey through urban and natural landscapes where boys and men face challenges involving death and deception. Although the information overload of social media and smart phone apps seems to render a “field guide” as an anachronism, Weed’s place-based stories, laced with an occasional dash of magical realism, allow time travel back to the past. Most stories take place in the late 1970s to mid-1980s, where Generation X boys and men struggling with their self-identity and societal role are lulled by drugs and peer pressures. Fly fishing plays a key role in this collection where “catch and release” rituals demonstrate the respect that hunters have for their prey, providing insight into the narrator’s distinction between empathy and murder when a teenager shoots a jay as target practice in “The Camp at Cutthroat Lake” or when an arrogant charter fisher is accidently lost at sea in “The Afternoon Client.” Indeed, Weed’s field guide provides the reader with a key to identifying characters so estranged from their natural environment (like James in “The Foreigner”) they cannot distinguish reality from conjured images. Earth is a water planet and many of the stories in A Field Guide to Murder and Fly Fishing involve liquid or solid state water. In “Tower Eight,” bullied Gen X misfits dive from granite ledges into a New Hampshire quarry while high on LSD in the summer of 1982 and in winter, downhill ski while tripping out. In “Diamondback Mountain,” the pre-World War II skiers at an alpine resort in the Colorado Rocky Mountains are intoxicated with their female companions and trigger an avalanche trying to impress them. “Keepers,” the final story, has the most contemporary backdrop, where Elliott is fly [End Page 67] fishing in Nantucket while racing an incoming tide and a departing ferry schedule. His lost “four-hundred-dollar rod,” like the lost “four-hundred-dollar spinning rig” of “The Afternoon Client,” portends the failure of the hunter’s instincts. Earth’s atmosphere is a unique feature of the planet and plays a key role in Weed’s Field Guide, too. In “Mouth of the Tropics,” when leaving the Amazon basin of Venezuela, Meech experiences turbulence in a seven-passenger Cessna, as does Kevin in his white-knuckled flights between New Bedford and Martha’s Vineyard in “Scrimshaw.” In both cases, the same model small plane yields a rough ride that mirrors the disruption to forged relationships with coworkers Juan and Phil, who were deeply entwined within their communities. In “The Dragon of Conchagua,” a wreck of a vintage Cessna that John stumbles upon in the approach to his climb of an Andean volcano with his brother Gabe, foreshadows the harrowing bus ride on the narrow highway “hugging the sides of Andean foothills that cradled the chaotic ugliness of the outer barrios of Quito.” The loss of relatively intact natural environments witnessed through the construction of vacation mansions on Martha’s Vineyard in “Scrimshaw” and the conversion of the Highlands Ranch in the Colorado Front Range into subdivisions in “Six Feet under the Prairie” result in collateral damages that in the minds of Weed’s characters approach murder of the land and the livelihoods it supported. Unlike fake news and misinformation found in Twitter feeds and Facebook posts, Weed’s short stories draw us away from the blue light of device screens. Under the blue skies and dark waters of A Field Guide to Murder & Fly Fishing, readers can feel pain, empathy, and purpose bubbling out from the sharp-detailed mental images. Although James’s photographs of Granada in “The Foreigner” required the tactile experience of removing unex-posed silver halide salts from photographic films or papers, pixilated digital images can now appear on our electronic devices without effort or lag time. The conflicts facing Tim Weed’s characters and places seem more urgent today than in the times in which the stories are based. The reader cannot...

Dark side of climate change: species‐specific responses and first indications of disruption in spring altitudinal migration in myotis bats

AbstractIn the Rocky Mountain region of North America, climate change is occurring at an accelerated rate and its effects are already changing population and community organization. Although some data have been gathered on changes in latitudinal migration patterns of animals, almost nothing is known about altitudinal migrations and climate change. Myotis bats of the Rocky Mountains provide a good model for understanding these patterns because they undergo significant seasonal altitudinal movements between high‐ and low‐elevation. In order to test if climate change is affecting spring down‐slope migrations of myotis species, I compared May and June capture data gathered over the last 21 years from 31 survey sites located between 1650 m a.s.l. and 2250 m a.s.l. on the eastern slopes of the Rocky Mountains, Colorado. Although three of the Myotis species maintained stable or slightly increasing capture numbers, indicating typical down‐slope spring migrations, two species showed significant declines in spring captures at lower elevations. When climate data for May and June were tested against capture data, the apparent causative factors for these declines differed between species. Declines in the capture of fringed myotis did not closely track annual patterns of mean June temperatures across years. Instead a steady decline occurred regardless of yearly variation in temperatures. However, declining captures of long‐legged myotis showed clear synchrony with variations in mean June temperatures wherein more captures occurred in years having cooler temperatures, and notably fewer captures in years having warmer June temperatures. In addition, zero captures of long‐legged myotis occurred in five of the last six years when mean June temperatures have shown an average increase in 1.8°C over previous years. These data indicate species‐specific responses to climate warming for bats in the Colorado Rocky Mountains and that loss of spring down‐slope migrations from hibernacula may be how some species mitigate climate warming effects.

Lab and Field Warming Similarly Advance Germination Date and Limit Germination Rate for High and Low Elevation Provenances of Two Widespread Subalpine Conifers

Accurately predicting upslope shifts in subalpine tree ranges with warming requires understanding how future forest populations will be affected by climate change, as these are the seed sources for new tree line and alpine populations. Early life history stages are particularly sensitive to climate and are also influenced by genetic variation among populations. We tested the climate sensitivity of germination and initial development for two widely distributed subalpine conifers, using controlled-environment growth chambers with one temperature regime from subalpine forest in the Colorado Rocky Mountains and one 5 °C warmer, and two soil moisture levels. We tracked germination rate and timing, rate of seedling development, and seedling morphology for two seed provenances separated by ~300 m elevation. Warming advanced germination timing and initial seedling development by a total of ~2 weeks, advances comparable to mean differences between provenances. Advances were similar for both provenances and species; however, warming reduced the overall germination rate, as did low soil moisture, only for Picea engelmannii. A three-year field warming and watering experiment planted with the same species and provenances yielded responses qualitatively consistent with the lab trials. Together these experiments indicate that in a warmer, drier climate, P. engelmannii germination, and thus regeneration, could decline, which could lead to declining subalpine forest populations, while Pinus flexilis forest populations could remain robust as a seed source for upslope range shifts.

The 17th Rocky Mountain Virology Association Meeting.

Since 2000, scientists and students from the greater Rocky Mountain region, along with invited speakers, both national and international, have gathered at the Mountain Campus of Colorado State University to discuss their area of study, present recent findings, establish or strengthen collaborations, and mentor the next generation of virologists and prionologists through formal presentations and informal discussions concerning science, grantsmanship and network development. This year, approximately 100 people attended the 17th annual Rocky Mountain Virology Association meeting, that began with a keynote presentation, and featured 29 oral and 35 poster presentations covering RNA and DNA viruses, prions, virus-host interactions and guides to successful mentorship. Since the keynote address focused on the structure and function of Zika and related flaviviruses, a special session was held to discuss RNA control. The secluded meeting at the foot of the Colorado Rocky Mountains gave ample time for in-depth discussions amid the peak of fall colors in the aspen groves while the random bear provided excitement. On behalf of the Rocky Mountain Virology Association, this report summarizes the >50 reports.

Seasonal Patterns of Dry Deposition at a High‐Elevation Site in the Colorado Rocky Mountains

AbstractIn the Colorado Rocky Mountains, high‐elevation barren soils are deficient in carbon (C) and phosphorus (P) and enriched in nitrogen (N). The seasonal variability of dry deposition and its contributions to alpine elemental budgets is critical to understanding how dry deposition influences biogeochemical cycling in high‐elevation environments. In this 2 year study, we evaluated dry and wet deposition inputs to the Niwot Ridge Long Term Ecological Research (NWT LTER) site in the Colorado Rocky Mountains. The total organic C flux in wet + dry (including soluble and particulate C) deposition was >30 kg C ha−1 yr−1 and represents a substantial input for this C‐limited environment. Our side‐by‐side comparison of dry deposition collectors with and without marble insert indicated that the insert improved retention of dry deposition by ~28%. Annual average dry deposition fluxes of water‐soluble organic carbon (4.25 kg C ha−1 yr−1) and other water‐soluble constituents, including ammonium (0.16 kg NH4+ha−1 yr−1), nitrate (1.99 kg NO3− ha−1 yr−1), phosphate (0.08 kg PO43− ha−1 yr−1), and sulfate (1.20 kg SO42− ha−1 yr−1), were comparable to those in wet deposition, with highest values measured in the summer. Backward trajectory analyses implicate air masses passing through the arid west and Four Corners, USA, as dominant source areas for dry deposition, especially in spring months. Synchronous temporal patterns of deposition observed at the NWT LTER site and a distant Rocky Mountain National Park Clean Air Status and Trends Network site indicate that seasonal dry deposition patterns are regional phenomena with important implications for the larger Rocky Mountain region.

Deglaciation of the Colorado Rocky Mountains following the Last Glacial Maximum

The availability of almost 180 cosmogenic-radionuclide (CRN) surface-exposure ages from moraine boulders and glacially polished bedrock surfaces makes possible an assessment of the timing and character of the local Last Glacial Maximum (LLGM) and subsequent deglaciation in the Colorado Rocky Mountains. A review of glacial chronologies and numerical modeling results indicates that although glaciers across Colorado responded broadly synchronously, apparent differences in the timing and magnitude of glacier retreat following the LLGM suggest that spatially variable regional forcing, possibly precipitation related, played a role in glacier behavior along with more spatially uniform hemispheric or global forcing. Glaciers in the five ranges examined reached their greatest LLGM extents before ~19.5 ka and abandoned their outermost LLGM moraines between ~23.5 and 19.5 ka. Detailed deglaciation chronologies are available for glaciers in four of the ranges. In the Sawatch Range and Sangre de Cristo Mountains, glaciers were near their LLGM extents at 17-16 ka, before retreating rapidly. In the San Juan Mountains and the Front Range, glaciers may have begun their post-LLGM recession earlier, although early deglaciation is indicated by only a few ages on polished bedrock that potentially contains pre-LLGM CRN inheritance, and thus may be too old. Regardless of the timing of the onset of deglaciation, the equilibrium-line rise associated with deglaciation was earlier and significantly larger in the San Juan Mountains than elsewhere in Colorado. This suggests that the San Juan Mountains, located well to the southwest of the other ranges, may have experienced enhanced precipitation during the LLGM, as did areas farther to the south and west, while LLGM conditions may have been drier in the northern and eastern Colorado ranges. A breakdown in this pattern after the LLGM, with precipitation decreasing in the south and west and increasing in the north and east, may have led to the range-to-range differences evident across Colorado. Deglaciation was nearly complete in all four ranges by 15-13 ka. While some proxy records indicate a later Younger Dryas-age cooling in the Colorado mountains, there is not clear moraine evidence of glacier readvance at that time.

Biostratigraphic evidence of human modification of high elevation aquatic ecosystems in the Intermountain West of the United States

Abstract High resolution analysis of subfossil chironomid remains preserved in well-dated lacustrine sediment cores was undertaken to identify whether marked shifts in chironomid assemblages have occurred in recent decades in the Colorado Rocky Mountains. This study will improve our understanding of site-specific aquatic ecosystem variability in the central Colorado Rockies during the 20th and early 21st centuries. An observed increase in chironomid taxa associated with warmer, more productive lakes, e.g. Dicrotendipes, is consistent with the movement of these lakes towards more productive aquatic systems in recent decades. The application of a chironomid-based inference model for mean July air temperature (MJAT) to the midge stratigraphies from these sites provide centennial length reconstructions of MJAT. The chironomid-inferred reconstructions of MJAT closely track gridded MJAT estimates for much of the 20th century; however, the response of the chironomid community is muted relative to the elevated temperatures that characterize this region during the last decade. Complementary analyses of sub-fossil chironomid records, previously developed from additional high elevation lakes located throughout the Intermountain West of the United States, indicate that the rate and magnitude of faunal turnover during the late 20th and early 21st centuries surpass the rate and magnitude of faunal turnover during any preceding interval in the last century. Direct gradient analyses reveal that the chironomid assemblages in the majority of sites became increasingly similar in composition to the assemblages associated with warmer, lower elevation sites between the early 20th and early 21st century.

Post-disturbance sediment recovery: Implications for watershed resilience

Sediment recovery following disturbances is a measure of the time required to attain pre-disturbance sediment fluxes. Insight into the controls on recovery processes and pathways builds understanding of geomorphic resilience. We assess post-disturbance sediment recovery in three small (1.5–100km2), largely unaltered watersheds within the northern Colorado Rocky Mountains affected by wildfires, floods, and debris flows. Disturbance regimes span 102 (floods, debris flows) to 103years (wildfires). For all case studies, event sediment recovery followed a nonlinear pattern: initial high sediment flux during single precipitation events or high annual snowmelt runoff followed by decreasing sediment fluxes over time. Disturbance interactions were evaluated after a high-severity fire within the South Fork Cache la Poudre basin was followed by an extreme flood one year post-fire. This compound disturbance hastened suspended sediment recovery to pre-fire concentrations 3years after the fire. Wildfires over the last 1900YBP in the South Fork basin indicate fire recurrence intervals of ~600years. Debris flows within the upper Colorado River basin over the last two centuries have shifted the baseline of sediment recovery caused by anthropogenic activities that increased debris flow frequency. An extreme flood on North St. Vrain Creek with an impounding reservoir resulted in extreme sedimentation that led to a physical state change. We introduce an index of resilience as sediment recovery/disturbance recurrence interval, providing a relative comparison between sites. Sediment recovery and channel form resilience may be inversely related because of high or low physical complexity in streams. We propose management guidelines to enhance geomorphic resilience by promoting natural processes that maintain physical complexity. Finally, sediment connectivity within watersheds is an additional factor to consider when establishing restoration treatment priorities.

Extent of localized tree mortality influences soil biogeochemical response in a beetle-infested coniferous forest

Recent increases in the magnitude and occurrence of insect-induced tree mortality are disrupting evergreen forests globally. To resolve potentially conflicting ecosystem responses, we investigated whether surrounding trees exert compensatory effects on biogeochemical signatures following beetle infestation. To this end, plots were surveyed within a Colorado Rocky Mountain watershed that experienced beetle infestation almost a decade prior and contained a range of surrounding tree mortality (from 9 to 91% of standing trees). Near-surface soil horizons under plot-centered live (green) and beetle-killed (grey) lodgepole pines were sampled over two consecutive summers with variable moisture conditions. Results revealed that soil respiration was 18–28% lower beneath beetle-infested trees and correlated to elevated dissolved organic carbon aromaticity. While certain edaphic parameters including pH and water content were elevated below grey compared to green trees regardless of the mortality extent within plots, other biogeochemical responses required a higher severity of surrounding mortality to overcome compensatory effects of neighboring live trees. For instance, C:N ratios under grey trees declined with increased severity of surrounding tree mortality, and the proportion of ammonium displayed a threshold effect with pronounced increases after surrounding tree mortality exceeded ∼40%. Overall, the biogeochemical response to tree death was most prominent in the mineral soil horizon where tree mortality had the largest affect on carbon recalcitrance and the enrichment of nitrogen species. These results can aid in determining when and where nutrient cycles and biogeochemical feedbacks to the atmosphere and hydrosphere will be observed in association with this type of ecological disturbance.

Substantial soil organic carbon retention along floodplains of mountain streams

AbstractSmall, snowmelt‐dominated mountain streams have the potential to store substantial organic carbon in floodplain sediment because of high inputs of particulate organic matter, relatively lower temperatures compared with lowland regions, and potential for increased moisture conditions. This work (i) quantifies mean soil organic carbon (OC) content along 24 study reaches in the Colorado Rocky Mountains using 660 soil samples, (ii) identifies potential controls of OC content based on soil properties and spatial position with respect to the channel, and (iii) and examines soil properties and OC across various floodplain geomorphic features in the study area. Stepwise multiple linear regression (adjusted r2 = 0.48, p < 0.001) indicates that percentage of silt and clay, sample depth, percent sand, distance from the channel, and relative elevation from the channel are significant predictors of OC content in the study area. Principle component analysis indicates limited separation between geomorphic floodplain features based on predictors of OC content. A lack of significant differences among floodplain features suggests that the systematic random sampling employed in this study can capture the variability of OC across floodplains in the study area. Mean floodplain OC (6.3 ± 0.3%) is more variable but on average greater than values in uplands (1.5 ± 0.08% to 2.2 ± 0.14%) of the Colorado Front Range and higher than published values from floodplains in other regions, particularly those of larger rivers.

Effects of mountain pine beetle-killed forests on source water contributions to streamflow in headwater streams of the Colorado Rocky Mountains

Natural or human-influenced disturbances are important to the health and diversity of forests, which in turn, are important to the water quantity and quality exported from a catchment. However, human-induced disturbances (prescribed fire and harvesting) have been decreasing, and natural disturbances (fires and insects) have been increasing in frequency and severity. One such natural disturbance is the mountain pine beetle (MPB), (Dendroctonus ponderosae) an endemic species. A recent epidemic resulted in the mortality of millions of hectares of lodgepole pine (Pinus contorta) forests in Colorado, USA. Beetle-induced tree mortality brings about changes to the hydrologic cycle, including decreased transpiration and interception with the loss of canopy cover. This study examined the effect of the mountain pine beetle kill on source water contributions to streamflow in snowmeltdominated headwater catchments using stable isotopes (2H and 18O) as tracers. Study catchments with varying level of beetle-killed forest area (6% to 97%) were sampled for groundwater, surface water, and precipitation. Streams were sampled to assess whether beetle-killed forests have altered source water contributions to streamflow. Groundwater contributions increased with increasing beetle-killed forest area (p = 0.008). Both rain and snow contributions were negatively correlated with beetle-killed forest area (p = 0.035 and p = 0.011, respectively). As the beetle-killed forest area increases, so does fractional groundwater contribution to streamflow.

Tusk pairs in the Ziegler Reservoir mastodon (Mammut americanum) assemblage: Implications for site taphonomy and stratigraphy

The Ziegler Reservoir (ZR) mastodon assemblage consists of remains from dozens of individuals that represent one or more populations living in a high-elevation region of the Colorado Rocky Mountains during Marine Isotope Stage (MIS) 5. Several left-right pairs of mastodon mandibular tusks were discovered in different stratigraphic units, challenging previous assumptions that depositional units preserving mastodon remains sample a comparable succession of regional populations through time. It is now recognized as likely that at least some of the specimens contained in these layers were transported from original deposits located on the lake margin, and that successive slumps transported parts of the same skeleton on different occasions, depositing them in different stratigraphic units. Assigning both tusks of a pair to the lowest depositional unit in which either occurs alters the temporal pattern in season of death for ZR mastodons and somewhat modifies a census of individuals, but does not significantly affect the secular trend previously detected in average oxygen isotope values. Two tusks with matching isotope profiles were previously treated as potential evidence of a catastrophic death event that had been proposed to explain the assemblage of remains, but these are now considered to be from the same individual. Newly paired records highlight the importance of careful taphonomic studies for any synthetic analysis of paleoecological history.

Seismicity of the rocky mountains and Rio Grande Rift from the EarthScope Transportable Array and CREST temporary seismic networks, 2008–2010

AbstractWe developed a catalog of small magnitude (ML −0.1 to 4.7) seismicity across Colorado and New Mexico from the EarthScope USArray Transportable Array and CREST (Colorado Rocky Mountains Experiment and Seismic Transects) seismic networks from 2008 to 2010 to characterize active deformation in the Rio Grande Rift. We recorded over 900 earthquakes in the Rio Grande Rift region, not including induced earthquakes and mine blasts, and find that the rift is actively deforming both broadly and in distinct regions. Seismic events that are likely induced, mostly in the Raton Basin, make up 66% of the catalog (1837 earthquakes). Neogene faults in the northern rift in north central Colorado are seismically active in the North Park Basin and northwestern Colorado. The central rift from the San Luis Basin (southern Colorado) to south of the Socorro Magma Body is the most seismically active rift region, and seismicity delineates the deformation in the Colorado Plateau transition zone, which is spatially correlated with volcanic vents, dikes, and faults within the western Jemez Lineament. The eastern Jemez Lineament is nearly aseismic and surrounded by a halo of seismicity culminating in boundaries defined by recent moderate (Mw 3.9 and Mw 3.3) earthquakes. The southern rift is characterized by diffuse seismicity in Texas and Mexico. This study provides an updated seismic catalog built with uniformity in seismometer coverage and low epicentral uncertainties (~2 km) that allows for regional evaluation of seismicity. During this time period, clusters of seismicity and moderate magnitude earthquakes characterize deformation in a low‐strain rate extensional environment.

A quantitative study on the mass elevation effect of the Rocky Mountains and its significance for treeline distribution

The Rocky Mountains are the highest and most extensive in North America. Their mass-elevation effect (MEE) should be strong and responsible for the high elevations of treelines in the interior of the mountain range. However, the MEE has been little known. We calculated the temperature difference (ΔT) between the inner and outer Rocky Mountains at the same elevation and defined it as the magnitude of MEE. Results show a mean ΔT of 1.8°C, with the highest ΔT occurring in Colorado and the basins of southern Wyoming. The MEE can be modelled with three factors: mountain base elevation (MBE), latitude, and hygric continentality. The model has a high explanatory power of 68.90%, and the three factors contribute 45.65, 36.05, and 18.03%, respectively. MBE contributed most to MEE, both in the whole range (45.65%) and in the Colorado Rocky Mountains (55.21%). Treeline is higher in the interior than the outside of the mountain range, by 700–1400 m. This difference coincides well with air temperature differences. This study developed a quantitative model for the MEE of the Rocky Mountains and improves our understanding of the intra-mountain ecology and high treelines of the Rocky Mountains.

Mountain wetland restoration: The role of hydrologic regime and plant introductions after 15 years in the Colorado Rocky Mountains, U.S.A.

Twelve wetland complexes were buried and/or drained by golf course and ski area development in the Colorado Rocky Mountains in the 1980s and early 1990s. We restored all or portions of each wetland, including fens, wet meadows and riparian areas, during 1997–2002. Intensive pre- and post-construction monitoring was used to develop restoration plans and evaluate their success. We revisited the sites to analyze long-term restoration processes in 2013–2016. Prior to construction the depth to the water table was measured weekly in monitoring wells installed through the fill, and into the wetland surfaces during and following restoration. Reference sites for each wetland type were used to characterize water table depth and vegetation for each wetland type. Restoration included removal of fill material and drains to create land surfaces with water table depth and dynamics similar to the reference areas for each wetland type. We planted each site with nursery grown sedges, willows and herbaceous dicots. Post restoration monitoring of water table depth, vegetation composition, sedge shoot density and willow growth was analyzed.The water table depth and dynamics of each restored wetland was similar to suitable reference sites on short and long time scales, indicating a stable hydrologic regime. Carex utriculata reached its maximum shoot density 4–5 years after planting indicating rapid growth and high production. Willow stems were still increasing in height 15 years after planting and basal stem density was also increasing. Most planted herbaceous dicots disappeared, indicating the difficulty of establishing them from plantings. Exotic (non-native) plants have invaded all three wetland types, with their highest cover in riparian areas. Critical factors that led to success were careful hydrological analysis of reference and restoration sites prior to earthwork, creating appropriate land/ground water interactions, and establishing clonal rhizomatous sedges and native willows.