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Research about Colorado

Source-linked reports with geographic coverage including Colorado.

At least 217 records · Page 12Linked to original sources
USGS2022

Urban landcover differentially drives day and nighttime air temperature across a semi-arid city

Semi-arid urban environments are undergoing an increase in both average air temperatures and in the frequency and intensity of extreme heat events. Within cities, different composition and densities of urban landcovers (ULC) influence local air temperatures, either mitigating or increasing heat. Currently, understanding how combinations of ULC influence air temperature at the block to neighborhood scale is necessary for heat mitigation plans, and yet limited due to the complexities integrating high-resolution ULC with spatial and temporally high-resolution microclimate data. We quantify how ULC influences air temperature at 60 m resolution for day and nighttime climate normals and extreme heat conditions by integrating microclimate sensor data sensor and high-resolution (1 m 2 ) ULC for Denver, Colorado's urban core. We derive ULC drivers of air temperature using a structural equation model, then use a random forest algorithm to predict air temperatures for 30-year climate normals and an extreme heat condition. We find that, in conjunction with other ULC, urban tree canopy reduces daytime air temperatures (−0.026 °C per % cover), and the combination of impervious surfaces and buildings increases daytime air temperature (0.021 °C per % cover). Compared to daytime hours, nighttime irrigated turf temperature cooling effects are increased from being non-significant to −0.022 °C per % cover, while tree canopy effects are reduced from −0.026 °C during the day to −0.016 °C at night. Overall, ULC drives ~17% and 25% of local air temperature during the day and night, respectively. ULC influence on daytime air temperatures is altered in extreme heat events, both depending on the ULC type and time of day. Our findings inform urban planners seeking to identify potential hot and cool spots within a semi-arid city and mitigate high urban air temperatures through using ULC within larger urban climate mitigation strategies.

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USGS2022

Snow depth retrieval with an autonomous UAV-mounted software-defined radar

We present results from a field campaign to measure seasonal snow depth at Cameron Pass, Colorado, using a synthetic ultrawideband software-defined radar (SDRadar) implemented in commercially available Universal Software Radio Peripheral (USRP) software-defined radio hardware and flown on a small hexacopter unmanned aerial vehicle (UAV). We coherently synthesize an ultrawideband signal from stepped frequency 50-MHz subpulses across 600-2100-MHz frequency bands using a novel nonuniform nonlinear synthetic wideband waveform reconstruction technique that minimizes sweep time and completely eliminates problematic grating lobes and other processing artifacts traditionally seen in stepped waveform synthesis. We image seasonal snow across two transects: a 400-m open Meadow Transect and a 380-m forested transect. We present a surface detection algorithm that fuses data from LiDAR, global navigation satellite system (GNSS)/global positioning system (GPS), and features in the radargram itself to obtain high precision estimates of both snow and ground surface reflections, and thus total snow depth, represented as two-way travel time. The measurements are validated against independent ground-based ground-penetrating radar measurements with correlations coefficients as high as ρ = 0.9 demonstrated. Finally, we compare backscattered radar data collected by the UAV-SDRadar while hovering proximal to a known snow pit with in situ measured snow dielectric profiles and demonstrate imaging of snow stratigraphy.

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USGS2022

Surface parameters and bedrock properties covary across a mountainous watershed: Insights from machine learning and geophysics

Bedrock property quantification is critical for predicting the hydrological response of watersheds to climate disturbances. Estimating bedrock hydraulic properties over watershed scales is inherently difficult, particularly in fracture-dominated regions. Our analysis tests the covariability of above- and belowground features on a watershed scale, by linking borehole geophysical data, near-surface geophysics, and remote sensing data. We use machine learning to quantify the relationships between bedrock geophysical/hydrological properties and geomorphological/vegetation indices and show that machine learning relationships can estimate most of their covariability. Although we can predict the electrical resistivity variation across the watershed, regions of lower variability in the input parameters are shown to provide better estimates, indicating a limitation of commonly applied geomorphological models. Our results emphasize that such an integrated approach can be used to derive detailed bedrock characteristics, allowing for identification of small-scale variations across an entire watershed that may be critical to assess the impact of disturbances on hydrological systems.

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USGS2022

Tectonic influence on axial-transverse sediment routing in the Denver Basin

Detrital zircon U-Pb and (U-Th)/He ages from latest Cretaceous–Eocene strata of the Denver Basin provide novel insights into evolving sediment sourcing, recycling, and dispersal patterns during deposition in an intracontinental foreland basin. In total, 2464 U-Pb and 78 (U-Th)/He analyses of detrital zircons from 21 sandstone samples are presented from outcrop and drill core in the proximal and distal portions of the Denver Basin. Upper Cretaceous samples that predate uplift of the southern Front Range during the Laramide orogeny (Pierre Shale, Fox Hills Sandstone, and Laramie Formation) contain prominent Late Cretaceous (84–77 Ma), Jurassic (169–163 Ma), and Proterozoic (1.69–1.68 Ga) U-Pb ages, along with less abundant Paleozoic through Archean zircon grain ages. These grain ages are consistent with sources in the western U.S. Cordillera, including the Mesozoic Cordilleran magmatic arc and Yavapai-Mazatzal basement, with lesser contributions of Grenville and Appalachian zircon recycled from older sedimentary sequences. Mesozoic zircon (U-Th)/He ages confirm Cordilleran sources and/or recycling from the Sevier orogenic hinterland. Five of the 11 samples from syn-Laramide basin fill (latest Cretaceous–Paleocene D1 Sequence) and all five samples from the overlying Eocene D2 Sequence are dominated by 1.1–1.05 Ga zircon ages that are interpreted to reflect local derivation from the ca. 1.1 Ga Pikes Peak batholith. Corresponding late Mesoproterozoic to early Neoproterozoic zircon (U-Th)/He ages are consistent with local sourcing from the southern Front Range that underwent limited Mesozoic–Cenozoic unroofing. The other six samples from the D1 Sequence yielded detrital zircon U-Pb ages similar to pre-Laramide units, with major U-Pb age peaks at ca. 1.7 and 1.4 Ga but lacking the 1.1 Ga age peak found in the other syn-Laramide samples. One of these samples yielded abundant Mesozoic and Paleozoic (U-Th)/He ages, including prominent Early and Late Cretaceous peaks. We propose that fill of the Denver Basin represents the interplay between locally derived sediment delivered by transverse drainages that emanated from the southern Front Range and a previously unrecognized, possibly extraregional, axial-fluvial system. Transverse alluvial-fluvial fans, preserved in proximal basin fill, record progressive unroofing of southern Front Range basement during D1 and D2 Sequence deposition. Deposits of the upper and lower D1 Sequence across the basin were derived from these fans that emanated from the southern Front Range. However, the finer-grained, middle portion of the D1 Sequence that spans the Cretaceous-Paleogene boundary was deposited by both transverse (proximal basin fill) and axial (distal basin fill) fluvial systems that exhibit contrasting provenance signatures. Although both tectonic and climatic controls likely influenced the stratigraphic development of the Denver Basin, the migration of locally derived fans toward and then away from the thrust front suggests that uplift of the southern Front Range may have peaked at approximately the Cretaceous-Paleogene boundary.

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USGS2022

Provenance of Devonian-Carboniferous strata of Colorado: The influence of the Cambrian and the Proterozoic

We report new LA-ICPMS U-Pb detrital zircon ages and sedimentary petrology of silty to sandy limestones and dolostones, as well as calcareous to dolomitic sandstones of the Devonian-Carboniferous (Mississippian) Chaffee Group, as well as detrital zircon ages from the Late Cambrian Sawatch Quartzite and a U-Pb zircon crystallization age on a late Mesoproterozoic (1087.9 13.5 Ma) granitoid of underlying basement from the Eagle basin of Colorado. Grain populations in the Chaffee Group are mostly bimodal, with over 84% of zircons centered around a Paleoproterozoic (ca. 1.78 Ga) mode typical of the Yavapai Province that forms much of the basement of Colorado and an early Mesoproterozoic (ca. 1.42 Ga) mode typical of A-type granites that intrude this region. A notable late Mesoproterozoic (ca. 1.08 Ga) mode exists in some Chaffee samples, giving those samples a trimodal detrital zircon age distribution. These bipartite or tripartite detrital zircon age modes exist in Cambrian, Devonian and Carboniferous strata from paleogeographically adjacent successions, but the correlation between the Chaffee zircons is highest with the regions basal Cambrian sandstones (Sawatch, Flathead, Ignacio formations) which have similar (1.08 Ga, 1.43 Ga, 1.71 Ga) zircon populations and a paucity of >1.8 Ga grains. This similarity suggests that the majority of grains in the Chaffee Group derive from recycling of these basal sandstones, and that little sediment was derived directly from then-exposed Precambrian basement highs, from the Wyoming Craton to the north, or from Paleoproterozoic arcs and orogens to the west and northeast. Minor Mesoarchean to early Paleoproterozoic (ca. 3.00 to 2.40 Ga) grains exist in the Chaffee Group, an attribute shared by the Late Ordovician Harding Sandstone of Colorados Front Range, but that is absent from the regions underlying Cambrian sandstonessuggesting some recycled mixture of Cambrian and Ordovician sedimentary rocks. No near-depositional age grains are present in the Chaffee Group; the youngest grain is Early Devonian (~417 Ma), >45 m.y. older than these strata, and Paleozoic grains are extremely uncommon (<0.1%; n=2927 grains).

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USGS2022

Living with wildfire in Grand County, Colorado: 2021 data report

Wildfire affects hundreds of wildland-urban interface communities each year, and yet most communities lack data reflecting the conditions before an event. This study was conducted before the devastating 2020 East Troublesome Fire1, which spread across 193,812 acres and resulted in two lives lost and 366 homes and 214 other structures burned. The fire’s dramatic run threatened over 7,000 structures and led to a mandatory evacuation of over 35,000 people in Grand and Larimer Counties. The data reported here serve as baseline data to aid in understanding the parcel and social conditions before the fire. This report presents results from WiRē Rapid Wildfire Risk Assessment (WiRē RA) data, collected from 1,162 private residential properties in six communities in five fire protection districts (FPDs), the majority (72%) of which were characterized as high, very high, or extreme risk. This report also presents results from household surveys sent to homeowners in the study area. Household survey respondents underestimated their risk compared to the conditions observed through the professional risk assessment. Respondents consistently overestimated the amount of defensible space and the distance from their homes to nonvegetative combustibles. Respondents also overestimated the availability of driveway clearance that would enable access for response vehicles and for safe passing of residents evacuating and responders arriving to their homes.

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USGS2022

Geologic setting and geomorphic history of La Botica and surrounding area

La Botica is located on the gently east-dipping marginal area between the high San Juan Mountains to the west and the San Luis Basin to the east in south-central Colorado. The site is positioned on a topographic bench perched about 70 to 80 m above La Jara Creek (figure 2.1), a tributary to the Rio Grande. The unique floral assemblage at La Botica has resulted in intermittent occupation over the last several thousand years. The physical environment supporting this assemblage is a result of Quaternary surface processes that have modified the underlying Tertiary bedrock. Underlying bedrock at the site consists of Oligocene to Pliocene volcanic and sedimentary deposits related to the Rio Grande rift and the San Juan volcanic locus of the Southern Rocky Mountains volcanic field. Local bedrock is mildly deformed by normal faulting and eastward tilting due to the onset of Oligocene extensional deformation and initial formation of the San Luis Basin. The geomorphic evolution and incision history of La Jara Creek are directly linked to middle to late Pleistocene evolution of the Rio Grande and to regional alpine glacial cycles over the last 500 k.y. (thousand years). Subsequent degradation of surrounding bedrock and development of mass-wasting deposits, such as landslides and talus slopes, have strongly influenced the incision history of La Jara Creek and the local environment at La Botica. In addition, local talus slopes and blockfields can host processes that actively modify the local environment, and these processes may have contributed to establishment of the floral assemblage.

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USGS2022

Gene flow and spatial population structure of Brook Trout in a large headwater stream network in Colorado

We studied gene flow of non-native Brook Trout Salvelinus fontinalis in a 60-km section of continuous stream network in the upper Cache la Poudre River basin, where a large-scale reclamation effort to restore federally threatened Greenback Cutthroat Trout Oncorhynchus clarkii stomias (GBCT) is taking place. This effort—the Poudre Headwaters Project—represents the most important recovery effort of the state fish of Colorado and could result in a fivefold increase in total occupied GBCT habitat. However, the reclamation area is currently dominated by non-native Brook Trout; key steps to ensure the success of the Poudre Headwaters Project include removing non-native Brook Trout and physically isolating the area from reinvasion. We examined existing genetic population structure in the reclamation area to provide science-based guidance for effective Brook Trout removal and subsequent GBCT reintroduction. During 2018 and 2019, tissue samples were collected from 23 sites in the Long Draw region. We genotyped 792 Brook Trout using 12 microsatellite loci to examine genetic population structure within the reclamation area. Our results show that fine-scale genetic population structure is present among sites (F ST = 0.038) and overall genetic diversity is comparable to previously published estimates throughout the native range of Brook Trout (H O = 0.610; HE = 0.618). Analysis of genetic differentiation among sites indicates that sites in the reclamation area may function as a metapopulation, with fine-scale genetic structure present among tributaries that are connected by gene flow. Understanding how the landscape influences connectivity and population persistence will provide sciencebased guidance for Brook Trout removal efforts and allow managers to release GBCT in stretches of key habitat that ensure the highest probability of reintroduction success.

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USGS2022

Geologic map of the Mount Blue Sky (formerly Mount Evans) quadrangle, Clear Creek and Park Counties, Colorado

The Mount Blue Sky (formerly Mount Evans) 7.5’ quadrangle lies in Park and Clear Creek counties, Colorado, about 60 km west of Denver. The highest elevation in the quadrangle is 14,265 ft (4,348 m) at the top of Mount Blue Sky. The lowest is at about 9,200 ft (2,804 m) on Guanella Pass Road at the southern edge of the quadrangle. Bedrock directly underlies most of the map area, with surficial deposits primarily in the valleys. The geology of the quadrangle was previously mapped at 1:100,000 scale as part of a regional compilation by Kellogg and others (2008). The oldest rocks in the Mount Blue Sky 7.5-minute quadrangle are Paleoproterozoic metasedimentary rocks, and mafic to felsic metaigneous rocks (all units starting with ‘X’ on Plate 1). These rocks were metamorphosed under upper amphibolite facies conditions and intruded by Mesoproterozoic felsic igneous rocks of the ~1442 Ma Mount Blue Sky (YgR, Yt, Ygdm, Ymgm and ~1424 Ma Silver Plume (Yg) batholiths (Spurr and others, 1908; Tweto, 1897; Aleinikoff and others, 1993; du Bray and others, 2018) and, in the southern part of the quadrangle, by rocks that may also be part of the Mount Blue Sky batholith, but may alternatively interpreted as part of the ~1115 Ma to ~1066 Ma Pikes Peak batholith (Unruh and others, 1995; Guitreau and others, 2016). Four generations of folds affected the area. The oldest, F1 folds are isoclinal of various orientations, but primarily northerly-plunging in the southern part of the quadrangle (Mahatma, 2019; Mahatma and others, 2022). In the northern part of the quadrangle (Powell, 2020), open to close F2 chevron folds exist with various orientations. F3 folds in the northern part of the quadrangle are open to close with upright axial planes and plunges to the north and south, and in the southern part of the quadrangle they are open centimeter- to meter- scale northerly-plunging folds, possibly overprinted by another generation of northerly-plunging folds based on orientations of axial planes (F2 and F3 of Mahatma and others, 2022). F4 folds throughout the quadrangle are open to gentle with upright axial planes and shallow plunges to the east and west. The Mount Blue Sky batholith displays a pervasive moderately NW-dipping biotite-hornblende foliation (Fig. 1) in addition to a flow foliation near the margins, indicating NW-directed shortening after ~1442 Ma (Powell, 2020). The relationship between this foliation and the folds is not clear. Various joint sets are present in the area. The most pervasive joint set strikes 355°-020° and is subvertical. It is best developed in the western to southwestern part of the map area, and may be related to late Cenozoic extension associated with the Rio Grande Rift. Joint orientations are generally consistent with the trends of topographical lineaments. Surficial deposits include two series of glacial till deposits (Qtb and Qtp), and outwash (Qgp) deposits. They correlate with the Bull Lake (170-120 ka) and Pinedale (30-12 ka) glacial periods (Dahms, 2004) based on original depositional morphology, geomorphic and topographic position, deposit weathering and pedogenic properties. Possible older glacial deposits (Qti) have been observed along topographically higher surfaces.

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USGS2021

Living with wildfire in Chalk Creek, Chaffee County, Colorado: 2019 data report

Wildfire affects many types of communities and is a particular concern for communities in the wildland urban interface (WUI), such as Chalk Creek in Chaffee County. The core intent of this project was to provide evidence to support Colorado State Forest Service (CSFS) Salida Field Office’s wildfire mitigation and education program. This report analyzes existing wildfire risk data collected in late 2017 through 2019 and pairs it with social data collected in the summer of 2019, in order to better understand Chalk Creek residents’ knowledge, experiences, and perceptions about wildfire risk. This greater understanding will help CSFS focus its programs and outreach and ultimately promote increased mitigation and reduced wildfire risk in Chalk Creek.

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USGS2021

Quantification of metal loading using tracer dilution and instantaneous synoptic sampling and importance of diel cycling in Leavenworth Creek, Clear Creek County, Colorado, 2012

Leavenworth Creek, a tributary of South Clear Creek and Clear Creek near Georgetown, Colorado, contains copper, lead, and zinc at concentrations close to or in excess of aquatic-life standards. In the summer of 2012, the U.S. Geological Survey, in cooperation with the U.S. Department of Agriculture Forest Service and the Colorado Division of Reclamation, Mining and Safety, conducted monitoring to (1) quantify the effects of diel cycling and perform synoptic sampling in a way to minimize those effects, (2) separate “point” or distinct single tributaries or sources of load from diffuse load sources along the study reach to aid remediation planning, and (3) quantify metal loading from transmountain diversion of water from Peru Creek through the Vidler Tunnel into Leavenworth Creek. The study included monitoring for diel cycles in June 2012 and diel and synoptic sampling in August 2012 along an approximately 2-kilometer stream reach. Synoptic samples were collected at 26 stream and 35 inflow, tributary, mine waste seep, and mine tunnel sites from August 28 to 30, 2012. In June 2012, temperature, dissolved oxygen, and pH showed strong diel signals at two sites in Leavenworth Creek, with temperature and pH having minimum values near dawn and maximum values during the afternoon and dissolved oxygen having maximum values in the early morning and minimum values in late afternoon. Concentrations of zinc, cadmium, cobalt, manganese, and yttrium showed strong diel fluctuations at both sites with minimum concentrations during daytime and maximum concentrations during nighttime. Because of these diel cycles, all stream sites were sampled during synoptic sampling at 1200 hours on August 30, 2012. During synoptic sampling from August 28 to 30, 2012, zinc showed maximum concentrations at nighttime and minimum concentrations at midday and diel variation ranged from 26 to 33 percent. Inflows from the Wilcox Tunnel and Waldorf seep area were the greatest source of zinc load to the stream (about 45 percent), and a left-bank inflow in the dispersed tailings area was the greatest source of lead (about 45 percent) and manganese (about 25 percent) loads to the stream, and a secondary source for zinc (about 40 percent). Copper load was almost equally divided (about 35 percent) between these two sources. Diffuse loading, likely from left-bank sources, was evident for copper, lead, manganese, and zinc in the stream reach from approximately 800 to 1,200 meters, and for copper, lead, and, to a lesser extent, manganese in the reach containing left-bank dispersed tailings (from approximately 1,300 to 1,800 meters). The load values reported herein are minimum estimates because the stream synoptic samples were collected at 1200 hours when positively charged elements, including copper, lead, manganese, and zinc, have minimum concentrations. Diel patterns measured for zinc during the synoptic sampling indicate maximum daily zinc loads were as much as 33 percent greater than those measured at 1200 hours on August 30, 2012. Transmountain diversion of water through Vidler Tunnel negatively affects water quality in Leavenworth Creek as indicated by much greater metal loads and concentrations and a visually evident mixing zone where Vidler Tunnel water joins Leavenworth Creek when diversion is active compared to when it is not.

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USGS2021

Using isotopic data to evaluate Esox lucius (Linnaeus, 1758) natal origins in a hydrologically complex river basin

Otolith microchemistry has emerged as a powerful technique with which to identify the natal origins of fishes, but it relies on differences in underlying geology that may occur over large spatial scales. An examination of how small a spatial scale on which this technique can be implemented, especially in water bodies that share a large proportion of their flow, would be useful for guiding aquatic invasive species control efforts. We examined trace isotopic signatures in northern pike ( Esox lucius ) otoliths to estimate their provenance between two reservoirs in the Upper Yampa River Basin, Colorado, USA. This is a challenging study area as these reservoirs are only 11-rkm apart on the same river and thus share a high proportion of their inflow. We found that three isotopes ( 86 Sr, 137 Ba, and 55 Mn) were useful in discriminating between these reservoirs, but their signatures varied annually, and the values overlapped. Strontium isotope ratios ( 87 Sr/ 86 Sr) were different between sites and relatively stable across three years, which made them an ideal marker for determining northern pike provenance. Our study demonstrates the usefulness of otolith microchemistry for natal origin determination within the same river over a relatively small spatial scale when there are geologic differences between sites, especially geologic differences underlying tributaries between sites.

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USGS2021

Effects of hydrologic variability and remedial actions on first flush and metal loading from streams draining the Silverton caldera, 1992–2014

This study examined water quality in the upper Animas River watershed, a mined watershed that gained notoriety following the 2015 Gold King mine release of acid mine drainage to downstream communities. Water-quality data were used to evaluate trends in metal concentrations and loads over a two-decade period. Selected sites included three sites on tributary streams and one main-stem site on the Animas River downstream from the tributary confluences. During the study period, metal concentrations and loads varied seasonally and annually because of hydrologic variability and remedial actions designed to ameliorate the effects of acid mine drainage. Water-quality data were divided into two periods based on the timing of remedial activities in the watershed. The first period includes active water treatment, surface reclamation and installation of bulkheads in adits; the second period includes the decade following these activities. Water-quality data were used to estimate annual and monthly zinc loads using the Adjusted Maximum Likelihood Method (using LOADEST software) and U.S. Geological Survey streamflow data. This study presents one of the first applications of LOADEST focused on metal loads. Monthly flow-weighted concentrations were analysed using a Mann-Kendall trend test to determine the direction, magnitude, and significance of temporal trends in zinc loading in any given month and using t -test comparisons between the two periods. Zinc loads estimated for the Animas River below the tributaries indicate decreased zinc loading during the rising limb of the hydrograph in the second period, perhaps reflecting a reduction of snowmelt-derived zinc load following surface reclamation activities. In contrast, base-flow zinc loading increased at the main-stem site, perhaps because of the cessation of water treatment in tributary streams. Flow weighting of monthly load estimates yielded increased statistical significance and enabled more nuanced differentiation between the effects of hydrologic variability and remedial activities on zinc loading.

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USGS2021

Evidence of glacial activity during MIS 4 in the Rocky Mountains, Colorado, USA

The Ziegler Reservoir fossil site near Snowmass Village, Colorado, provides a rare opportunity to examine environmental conditions in the Rocky Mountains during marine isotope stage (MIS) 4 (71–57 ka). Although recognized as a global-scale cold event, MIS 4 is typically absent from Rocky Mountain glacial chronologies because the geologic evidence was covered or destroyed during the subsequent, and more extensive, MIS 2 (Pinedale; 29–14 ka) glaciation. Ziegler Reservoir lies beyond the Pinedale glacial extent, which allowed for the preservation of a long-lived sequence of eolian sediments deposited in a lacustrine environment that spans from late MIS 6 (ca. 140 ka) through early MIS 3 (ca. 55 ka). Sediments dating to MIS 4 exhibit a significant increase in clay-sized particles, suggesting that the source areas, most likely nearby glacio-fluvial deposits, were enriched with fine-grained material at that time. We hypothesize that the elevated clay content was the result of rock flour production by nearby valley glaciers that were active in the Rocky Mountains during MIS 4. The results of our study illustrate how recognizing indirect evidence of glacial activity can result in a more complete record of past climate conditions than what could be achieved by the study of moraines alone.

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USGS2021

Elevation and elevation-change maps of Fountain Creek, southeastern Colorado, 2015-20

The U.S. Geological Survey, in cooperation with Colorado Springs Utilities, has collected topographic data annually since 2012 at 10 study areas along Fountain Creek, southeastern Colorado. The 10 study areas were located between Colorado Springs and the terminus of Fountain Creek at the Arkansas River in Pueblo. The purpose of this report is to present elevation maps based on topographic surveys collected in 2020 and to present maps of elevation change that occurred between 2015 and 2020 at all 10 study areas. Elevation and elevation-change maps were developed in Global Mapper, R, and ArcGIS from topographic surveys collected at each study area during the winters of 2015 and 2020. Topographic surveys in 2015 were completed using real-time kinematic Global Navigation Satellite Systems. Topographic surveys in 2020 were completed using both real-time kinematic Global Navigation Satellite Systems and light detection and ranging. Elevation-change maps were created using propagated uncertainties associated with the 95-percent confidence limit. Study areas along Fountain Creek underwent a range of geomorphic responses between 2015 and 2020 that were often related to the dominant channel planform pattern of the study area. The results of this ongoing monitoring effort can be used to assess long-term changes in land-surface elevation and to advance understanding of the geomorphic response to possible changes in flow conditions on Fountain Creek.

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USGS2021

Persistent nitrate in alpine waters with changing atmospheric deposition and warming trends

Nitrate concentrations in high-elevation lakes of the Colorado Front Range remain elevated despite declining trends in atmospherically deposited nitrate since 2000. The current source of this elevated nitrate in surface waters remains elusive, given shifts in additional nitrogen sources via glacial inputs and atmospheric ammonium deposition. We present the complete isotopic composition of nitrate (δ 15 N, δ 18 O, and Δ 17 O) from a suite of nitrate-bearing source waters collected during the summers of 2017–2018 from two alpine ecosystems to constrain the provenance of elevated nitrate in surface waters during the summer open-water season. The results indicate a consistent contribution of uncycled atmospheric nitrate throughout the summer (13–23%) to alpine lakes, despite seasonal changes in source water inputs. The balance of nitrate (as high as 87% in late summer) is likely from nitrate production within the catchment via nitrification of reduced nitrogen sources (e.g., thawed soil organic matter and ammonium deposition) and released with rock glacier meltwater. The role of microbially produced nitrate has become increasingly important over time based on historical surface water samples from the mid-90s to present, a trend coincident with increasing ammonium deposition to alpine systems.

Colorado↗
USGS2021

Integrating observations and models to determine the effect of seasonally frozen ground on hydrologic partitioning in alpine hillslopes in the Colorado Rocky Mountains, USA

This study integrated spatially distributed field observations and soil thermal models to constrain the impact of frozen ground on snowmelt partitioning and streamflow generation in an alpine catchment within the Niwot Ridge Long-Term Ecological Research site, Colorado, USA. The study area was comprised of two contrasting hillslopes with notable differences in topography, snow depth and plant community composition. Time-lapse electrical resistivity surveys and soil thermal models enabled extension of discrete soil moisture and temperature measurements to incorporate landscape variability at scales and depths not possible with point measurements alone. Specifically, heterogenous snowpack thickness (~0–4 m) and soil volumetric water content between hillslopes (~0.1–0.45) strongly influenced the depths of seasonal frost, and the antecedent soil moisture available to form pore ice prior to freezing. Variable frost depths and antecedent soil moisture conditions were expected to create a patchwork of differing snowmelt infiltration rates and flowpaths. However, spikes in soil temperature and volumetric water content, as well as decreases in subsurface electrical resistivity revealed snowmelt infiltration across both hillslopes that coincided with initial decreases in snow water equivalent and early increases in streamflow. Soil temperature, soil moisture and electrical resistivity data from both wet and dry hillslopes showed that initial increases in streamflow occurred prior to deep soil water flux. Temporal lags between snowmelt infiltration and deeper percolation suggested that the lateral movement of water through the unsaturated zone was an important driver of early streamflow generation. These findings provide the type of process-based information needed to bridge gaps in scale and populate physically based cryohydrologic models to investigate subsurface hydrology and biogeochemical transport in soils that freeze seasonally.

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