Sites In Colorado Research Articles

Geophysical and Hydrochemical Identification of Flow Paths with Implications for Water Quality at an ARR Site

AbstractTwo key challenges regarding the design and operation of aquifer recharge and recovery (ARR) systems are evaluating aquifer heterogeneity and understanding hydrochemical interactions. Uncertainty in this respect can impact the volume of recoverable water and the improvement in water quality. The objective of this research is to leverage the advantages of geophysical measurements and hydrochemical sampling to reveal the properties of an ARR site to inform current ARR system operations and future design decisions. Electrical resistivity tomography was used to image the subsurface below two key infiltration/extraction areas of an ARR site in Colorado, USA. Hydrochemical measurements on transects intersecting the geophysical measurements resolved bulk parameters (i.e., total organic carbon, nitrate, and major cations and anions) and trace organic chemicals (e.g., pharmaceuticals, personal care products). Conservative tracers were also used to estimate degrees of mixing and water travel times and to better assess the performance of the ARR site regarding water quality changes and water recovery. The electrical resistivity measurements suggest that certain areas of the infiltration basins have hydraulic connections to the extraction wells through preferential flow paths, compared with other infiltration basins that are separated by fine‐grained materials from their respective extraction wells. The hydrochemical results indicate that consistent improvements in water quality can be achieved in these preferential flow paths within relatively short travel times (<5 d) at this ARR site.

A quantitative midge-based reconstruction of mean July air temperature from a high-elevation site in central Colorado, USA, for MIS 6 and 5

Sediments recovered from the Ziegler Reservoir fossil site (ZRFS) in Snowmass Village, Colorado (USA) were analyzed for subfossil chironomids (or midges). The midge stratigraphy spans ~140–77ka, which includes the end of Marine Oxygen Isotope Stage (MIS) 6 and all of MIS 5. Notable shifts in midge assemblages occurred during two discrete intervals: the transition from MIS 6 to MIS 5e and midway through MIS 5a. A regional calibration set, incorporating lakes from the Colorado Rockies, Sierra Nevada, and Uinta Mountains, was used to develop a midge-based mean July air temperature (MJAT) inference model (r2jack=0.61, RMSEP=0.97°C). Model results indicate that the transition from MIS 6 to MIS 5e at the ZRFS was characterized by an increase in MJAT from ~9.0 to 10.5°C. The results also indicate that temperatures gradually increased through MIS 5 before reaching a maximum of 13.3°C during MIS 5a. This study represents the first set of quantitative, midge-based MJAT estimates in the continental U.S. that spans the entirety of MIS 5. Overall, our results suggest that conditions in the Colorado Rockies throughout MIS 5 were cooler than today, as the upper limit of the reconstructed temperatures is ~2°C below modern July air temperatures.

Influence of large wood on channel morphology and sediment storage in headwater mountain streams, Fraser Experimental Forest, Colorado

Large fallen wood can have a significant impact on channel form and process in forested mountain streams. In this study, four small channels on the Fraser Experimental Forest near Fraser, Colorado, USA, were surveyed for channel geometries and large wood loading, including the size, source, and characteristics of individual pieces. The study is part of a larger effort to understand the impact of mountain pine beetle infestation on a suite of watershed properties. Here, we present baseline data collected at the onset of widespread tree mortality. Channels range from 1.5 to 2m in width, with slopes ranging from 3 to >10%. Median (D50) streambed particle sizes range from gravel to very coarse gravel. Channels are characterized as cascade, step-pool, and plane bed over varying scales. Large wood loads ranged from about 0.4 to 1.0 piece per meter length of channel, which is comparable to values reported for other Colorado sites. Much of the wood showed indications of being in place for long periods of time (decayed/rotten, broken into ramps, and partially buried in beds and banks). Nearly all surveyed reaches contained steps formed from small boulders and/or logs. Significant portions of the elevation drop in some of the reaches were made up by log steps, though the percentages varied (0 to 60%). Individual log steps trap a portion of the coarse sediment moved as bedload, forming wedge-shaped accumulations upstream of the logs. The particle size distributions for measured bedload and step accumulations largely overlapped, but more so for the coarse ends of the distributions, suggesting a trapping inefficiency for the finer component of bedload. Estimates of the total volume of sediment stored behind log steps were approximately an order of magnitude greater than the mean sediment volume exported on an annual basis, as determined from measured accumulations in weir ponds. The particle size distribution of sediment in the ponds – ranging from sand to medium gravel – is considerably finer than sediment stored in steps. The series of comparisons between storage volumes, particle size distributions, and sediment export suggests that log steps effectively trap coarse sediment moved in these small streams and act as a series of check dams that inhibit channel erosion, but may be less effective at trapping finer sediment (sand and small gravel).

Size-resolved aerosol composition and its link to hygroscopicity at a forested site in Colorado

Abstract. Aerosol hygroscopicity describes the ability of a particle to take up water and form a cloud droplet. Modeling studies have shown sensitivity of precipitation-producing cloud systems to the availability of aerosol particles capable of serving as cloud condensation nuclei (CCN), and hygroscopicity is a key parameter controlling the number of available CCN. Continental aerosol is typically assumed to have a representative hygroscopicity parameter, κ, of 0.3; however, in remote locations this value can be lower due to relatively large mass fractions of organic components. To further our understanding of aerosol properties in remote areas, we measured size-resolved aerosol chemical composition and hygroscopicity in a forested, mountainous site in Colorado during the six-week BEACHON-RoMBAS (Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics and Nitrogen–Rocky Mountain Biogenic Aerosol Study) campaign. This campaign followed a year-long measurement period at this site, and results from the intensive campaign shed light on the previously reported seasonal cycle in aerosol hygroscopicity. New particle formation events were observed routinely at this site and nucleation mode composition measurements indicated that the newly formed particles were predominantly organic. These events likely contribute to the dominance of organic species at smaller sizes, where aerosol organic mass fractions were between 70 and 90%. Corresponding aerosol hygroscopicity was observed to be in the range κ = 0.15–0.22, with hygroscopicity increasing with particle size. Aerosol chemical composition measured by an aerosol mass spectrometer and calculated from hygroscopicity measurements agreed very well during the intensive study, with an assumed value of κorg = 0.13 resulting in the best agreement.

English

Abstract: Difficulty in re-establishing native vegetation on surface mined lands in the semi-arid western U.S. prompted this study to determine the effectiveness of landscape fabric and supplemental irrigation on survival and growth of the woody perennials aspen (Populus tremuloides Michx.) and serviceberry (Amelanchier alnifolia (Nutt.) Nutt. ex M. Roem.) at a high elevation reclaimed surface coal mine site in Colorado. The study compared growth and survival of container-grown aspen and serviceberry planted with or without landscape fabric for control of competing vegetation, and with or without biweekly supplemental irrigation during the first growing season. Response after three years indicated that the landscape fabric was particularly crucial in survival and growth of aspen on sites with heavy competing vegetative cover. Serviceberry plants grew better with landscape fabric but the fabric did not increase survival. Supplemental irrigation provided only limited advantage compared to the landscape fabric. Photosynthesis and pre-dawn moisture stress measurements on the aspen indicated that they were more stressed without landscape fabric. Soil moisture was higher under the landscape fabric.

Relating variation of dust on snow to bare soil dynamics in the western United States

The deposition of desert dust to mountain snow directly impacts the hydrologic cycle and water resource management through the depression of snow albedo and acceleration of snowmelt. However, the key processes that control the variation of dust deposition to snow are poorly understood. Here we relate the bare soil exposure from the moderate resolution imaging spectroradiometer (MODIS) reflectance data for the period of 2002–2011, with dust loading in snow at downwind mountain sites in southern Colorado, the United States. We found that, for many pixels, remotely sensed fraction of bare soil in the dust-emitting area is significantly correlated with end-of-season dust concentrations in snow, and that the highest number of significantly correlated pixels in the dust-source area corresponds well with the period of peak dust deposition in the mountain snow (April–May). This analysis indicates that surface conditions in the dust-source area may provide first-order controls on emission of dust and deposition of that dust to the mountain snowcover. A preliminary analysis of precipitation records indicates that bare ground cover is strongly affected by prior rainfall in the months preceding the dust-emission season.

Bradley S. Keefer. Conflicting Memories on the “River of Death”: The Chickamauga Battlefield and the Spanish-American War, 1863–1933; Ari Kelman. A Misplaced Massacre: Struggling over the Memory of Sand Creek.

The stubborn idea that heritage and history are irreconcilable lingers, but most historians who work in the public sector operate in the space between them. The best scholarship on history and memory has focused attention on this space, analyzing memorials and historic sites as stages for reconciling popular and professional interpretations of the past. This body of literature has grown dramatically in the last thirty years. Spurred by the public response to the Vietnam Veterans Memorial, scholars began to examine the cultural significance of commemorative activities. Histories examining the effort to remember—or to forget—war and tragedy have been particularly influential. Two recent works in this genre raise important questions about power and agency in the space between history and memory. Both A Misplaced Massacre: Struggling over the Memory of Sand Creek and Conflicting Memories on the “River of Death”: The Chickamauga Battlefield and the Spanish-American War, 1863–1933 explore the relative place of experience, recollection, and research in the creation of cultural meaning and historical significance. In Conflicting Memories, Bradley S. Keefer reconstructs the experiences of two generations of soldiers who fought or trained on the Chickamauga Creek in northern Georgia. He explores the impact that both commemorative and practical activities have had on the site's preservation as a battlefield park. In A Misplaced Massacre, Ari Kelman analyzes the effort to establish the Sand Creek Massacre National Historic Site in Colorado. These works demonstrate that both history and heritage have the potential to challenge or to legitimize the myths that underscore American national identity.

Sensitivity of downward longwave surface radiation to moisture and cloud changes in a high‐elevation region

AbstractSeveral studies have suggested enhanced rates of warming in high‐elevation regions since the latter half of the twentieth century. One of the potential reasons why enhanced rates of warming might occur at high elevations is the nonlinear relationship between downward longwave radiation (DLR) and specific humidity (q). Using ground‐based observations at a high‐elevation site in southwestern Colorado and coincident satellite‐borne cloud retrievals, the sensitivity of DLR to changes in q and cloud properties is examined and quantified using a neural network method. It is also used to explore how the sensitivity of DLR to q (dDLR/dq) is affected by cloud properties. When binned by season, dDLR/dq is maximum in winter and minimum in summer for both clear and cloudy skies. However, the cloudy‐sky sensitivities are smaller, primarily because (1) for both clear and cloudy skies dDLR/dq is proportional to 1/q, for q > 0.5 g kg−1, and (2) the seasonal values of q are on average larger in the cloudy‐sky cases than in clear‐sky cases. For a given value of q, dDLR/dq is slightly reduced in the presence of clouds and this reduction increases as q increases. In addition, DLR is found to be more sensitive to changes in cloud fraction when cloud fraction is large. In the limit of overcast skies, DLR sensitivity to optical thickness decreases as clouds become more opaque. These results are based on only one high‐elevation site, so the conclusions here need to be tested at other high‐elevation locations.

Geographic variation in growth and phenology of two dominant central US grasses: consequences for climate change

Aims The rate of climate change may exceed many plant species' migration rates, particularly for long-lived perennial species that dominate most ecosystems. If bioclimatic envelopes shift more rapidly than dominant species can migrate, individuals located peripheral to biomes or in adjacent biomes may become a significant source of traits for future dominant populations (DPs). Thus, traits of individuals from peripheral populations (PPs) may affect future ecosystem functioning more than those of today's DPs. Methods We assessed key traits of individuals collected from populations that currently dominate two central US grasslands, the shortgrass steppe (Bouteloua gracilis) and the tallgrass prairie (Andropogon gerardii). We compared these to individuals from PPs in a reciprocal-transplant common garden experiment with gardens at the Shortgrass Steppe Long Term Ecological Research site in Colorado and the Konza Prairie Biological Station Long Term Ecological Research site in Kansas. DPs and PPs were subjected to high and reduced water availability in common gardens located in each biome. Traits measured included the following: individual plant biomass, reproductive allocation, specific leaf area (SLA) and plant-water relations. We focused on the climate-change relevant comparisons of traits from PPs versus DPs expressed under the climate of DPs. Important Findings PPs of B. gracilis differed from DPs primarily in phenological traits. Under a semiarid shortgrass steppe climate, PPs initiated flowering later in the season, produced fewer reproductive tillers and were more sensitive to water stress. Biomass differences between populations were minimal. For A. gerardii, biomass in PPs was 50% lower than in DPs under the mesic tallgrass prairie climate and reproductive tillers were considerably smaller, despite higher SLA in PPs. Biomass of PPs was less sensitive to water stress, however. From these results, we conclude that key traits of PPs differed from DPs in both grassland types, but potential effects on reproductive phenology were greater for the bioclimatic shift in which a mesic biome becomes arid, whereas aboveground productivity may be affected more when a semiarid biome becomes more mesic.

Simulation of Nitrous Oxide Emissions and Estimation of Global Warming Potential in Turfgrass Systems Using the DAYCENT Model

Nitrous oxide (NO) emissions are an important component of the greenhouse gas budget for turfgrasses. To estimate NO emissions and global warming potential, the DAYCENT ecosystem model was parameterized and applied to turfgrass ecosystems. The annual cumulative NO emissions predicted by the DAYCENT model were close to the measured emission rates of Kentucky bluegrass ( L.) sites in Colorado (within 16% of the observed values). For the perennial ryegrass ( L.) site in Kansas, the DAYCENT model initially overestimated the NO emissions for all treatments (urea and ammonium sulfate at 250 kg N ha yr and urea at 50 kg N ha yr) by about 200%. After including the effect of biological nitrification inhibition in the root exudate of perennial ryegrass, the DAYCENT model correctly simulated the NO emissions for all treatments (within 8% of the observed values). After calibration and validation, the DAYCENT model was used to simulate NO emissions and carbon sequestration of a Kentucky bluegrass lawn under a series of management regimes. The model simulation suggested that gradually reducing fertilization as the lawn ages from 0 to 50 yr would significantly reduce long-term NO emissions by approximately 40% when compared with applying N at a constant rate of 150 kg N ha yr. Our simulation indicates that a Kentucky bluegrass lawn in Colorado could change from a sink to a weak source of greenhouse gas emissions 20 to 30 yr after establishment.

Abiotic U(VI) reduction by sorbed Fe(II) on natural sediments

Laboratory experiments were performed as a function of aqueous Fe(II) concentration to determine the uptake and oxidation of Fe(II), and Fe(II)-mediated abiotic reduction of U(VI) by aquifer sediments from the DOE Rifle field research site in Colorado, USA. Mössbauer analysis of the sediments spiked with aqueous 57Fe(II) showed that 57Fe(II) was oxidized on the mineral surfaces to 57Fe(III) and most likely formed a nano-particulate Fe(III)-oxide or ferrihydrite-like phase. The extent of 57Fe oxidation decreased with increasing 57Fe(II) uptake, such that 98% was oxidized at 7.3 μmol/g Fe and 41% at 39.6 μmol/g Fe, indicating that the sediments had a limited capacity for oxidation of Fe(II). Abiotic U(VI) reduction was observed by XANES spectroscopy only when the Fe(II) uptake was greater than approximately 20 μmol/g and surface-bound Fe(II) was present, possibly as oligomeric Fe(II) surface species. The degree of U(VI) reduction increased with increasing Fe(II)-loading above this level to a maximum of 18% and 36% U(IV) at pH 7.2 (40.7 μmol/g Fe) and 8.3 (56.1 μmol/g Fe), respectively in the presence of 400 ppm CO2. Greater U(VI) reduction was observed in CO2-free systems [up to 44% and 54% at pH 7.2 (17.3 μmol/g Fe) and 8.3 (54.8 μmol/g Fe), respectively] compared to 400 ppm CO2 systems, presumably due to differences in aqueous U(VI) speciation. While pH affects the amount of Fe(II) uptake onto the solid phase, with greater Fe(II) uptake at higher pH, similar amounts of U(VI) reduction were observed at pH 7.2 and 8.3 for a similar Fe(II) uptake. Thus, it appears that abiotic U(VI) reduction is controlled primarily by sorbed Fe(II) concentration and aqueous U(VI) speciation. The range of Fe(II) loadings tested in this study are within the range observed in biostimulation experiments at the Rifle site, suggesting that Fe(II)-mediated abiotic U(VI) reduction could play a significant role in field settings.

Cluster analysis of WIBS single-particle bioaerosol data

Abstract. Hierarchical agglomerative cluster analysis was performed on single-particle multi-spatial data sets comprising optical diameter, asymmetry and three different fluorescence measurements, gathered using two dual Wideband Integrated Bioaerosol Sensors (WIBSs). The technique is demonstrated on measurements of various fluorescent and non-fluorescent polystyrene latex spheres (PSL) before being applied to two separate contemporaneous ambient WIBS data sets recorded in a forest site in Colorado, USA, as part of the BEACHON-RoMBAS project. Cluster analysis results between both data sets are consistent. Clusters are tentatively interpreted by comparison of concentration time series and cluster average measurement values to the published literature (of which there is a paucity) to represent the following: non-fluorescent accumulation mode aerosol; bacterial agglomerates; and fungal spores. To our knowledge, this is the first time cluster analysis has been applied to long-term online primary biological aerosol particle (PBAP) measurements. The novel application of this clustering technique provides a means for routinely reducing WIBS data to discrete concentration time series which are more easily interpretable, without the need for any a priori assumptions concerning the expected aerosol types. It can reduce the level of subjectivity compared to the more standard analysis approaches, which are typically performed by simple inspection of various ensemble data products. It also has the advantage of potentially resolving less populous or subtly different particle types. This technique is likely to become more robust in the future as fluorescence-based aerosol instrumentation measurement precision, dynamic range and the number of available metrics are improved.

Source Signature of Volatile Organic Compounds from Oil and Natural Gas Operations in Northeastern Colorado

An extensive set of volatile organic compounds (VOCs) was measured at the Boulder Atmospheric Observatory (BAO) in winter 2011 in order to investigate the composition and influence of VOC emissions from oil and natural gas (O&NG) operations in northeastern Colorado. BAO is 30 km north of Denver and is in the southwestern section of Wattenberg Field, one of Colorado's most productive O&NG fields. We compare VOC concentrations at BAO to those of other U.S. cities and summertime measurements at two additional sites in northeastern Colorado, as well as the composition of raw natural gas from Wattenberg Field. These comparisons show that (i) the VOC source signature associated with O&NG operations can be clearly differentiated from urban sources dominated by vehicular exhaust, and (ii) VOCs emitted from O&NG operations are evident at all three measurement sites in northeastern Colorado. At BAO, the reactivity of VOCs with the hydroxyl radical (OH) was dominated by C(2)-C(6) alkanes due to their remarkably large abundances (e.g., mean propane = 27.2 ppbv). Through statistical regression analysis, we estimate that on average 55 ± 18% of the VOC-OH reactivity was attributable to emissions from O&NG operations indicating that these emissions are a significant source of ozone precursors.

The impact of rain on ice nuclei populations at a forested site in Colorado

AbstractIt has long been known that precipitation can impact atmospheric aerosol, altering number concentrations and size‐dependent composition. Such effects result from competing mechanisms: precipitation can remove particles through wet deposition, or precipitation can lead to the emission of particles through mechanical ejection, biological processes, or re‐suspension from associated wind gusts. These particles can feed back into the hydrologic cycle by serving as cloud nuclei. In this study, we investigated how precipitation at a forested site impacted the concentration and composition of ice nuclei (IN). We show that ground level IN concentrations were enhanced during rain events, with concentrations increasing by up to a factor of 40 during rain. We also show that a fraction of these IN were biological, with some of the IN identified using DNA sequencing. As these particles get entrained into the outflow of the storm, they may ultimately reach cloud levels, impacting precipitation of subsequent storms.

Selective measurements of isoprene and 2-methyl-3-buten-2-ol based on NO<sup>+</sup> ionization mass spectrometry

Abstract. Biogenic VOC emissions are often dominated by 2-methyl-1,3-butadiene (isoprene) and 2-methyl-3-buten-2-ol (232 MBO). Here we explore the possibility to selectively distinguish these species using NO+ as a primary ion in a conventional PTR-MS equipped with an SRI unit. High purity of NO+ (>90%) as a primary ion was utilized in laboratory and field experiments using a conventional PTR-TOF-MS. Isoprene is ionized via charge transfer leading to the major product ion C5H8+ (>99%) (e.g. Spanel and Smith, 1998). 232 MBO undergoes a hydroxide ion transfer reaction resulting in the major product ion channel C5H9+ (>95%) (e.g. Amelynck et al., 2005). We show that both compounds are ionized with little fragmentation (>5%) under standard operating conditions. Typical sensitivities of 11.1 ± 0.1 (isoprene) and 12.9 ± 0.1 (232 MBO) ncps ppbv−1 were achieved, which correspond to limit of detections of 18 and 15 pptv respectively for a 10 s integration time. Sensitivities decreased at higher collisional energies. Calibration experiments showed little humidity dependence. We tested the setup at a field site in Colorado dominated by ponderosa pine, a 232 MBO emitting plant species. Our measurements confirm 232 MBO as the dominant biogenic VOC at this site, exhibiting typical average daytime concentrations between 0.2–1.4 ppbv. The method is able to detect the presence of trace levels of isoprene at this field site (90–250 ppt) without any interference from 232 MBO, which would not be feasible using H3O+ ionization chemistry, and which currently also remains a challenge for other analytical techniques (e.g. gas chromatographic methods).

Russian Olive (Elaeagnus angustifolia) Removal in the Western United States: Multi-Site Findings and Considerations for Future Research

Elaeagnus angustifolia (Russian olive) is an introduced tree that has become one of the dominant species in many watersheds in the American West. Although it is a target of restoration efforts, very little is known about vegetation response after removal of this exotic species. To address this gap we surveyed 25 sites in Colorado, Wyoming, and Montana where E. angustifolia was removed. We collected information regarding plant cover and richness, climate, soil characteristics, management history, and geography. We analyzed these data using regression tree modeling. Our results indicate that moisture and temperature are key environmental factors relating to restoration success as measured by abundance of native cover; lower temperatures and greater availability of water were generally associated with more native cover. These results have important implications for selection of restoration sites, and for understanding the consequences of removing this species.

HOBBLING AND TORTURE AS PERFORMATIVE VIOLENCE

Violent interactions have three distinct actors: aggressors, victims and witnesses. Social identities of individuals within these groups are created and enforced through performative violence such as hobbling or torture. The Sacred Ridge site is a Pueblo I (AD 700–900) habitation site in Southwestern Colorado; during excavation, an assemblage consisting of 14,882 bone fragments representing at least 33 individuals was discovered. Perimortem trauma and tool marks indicate heavy processing of all individuals; the remains were deposited completely commingled within a pit structure. Foot and ankle bones from the Sacred Ridge processed assemblage have damage suggesting hobbling by blows to the sides of the ankle and torture by beating the soles and tops of the feet. These performative acts form the basis for social control of victims and witnesses by aggressors. Taphonomic analysis of human remains can be used to examine behaviors of each group creating the assemblage.

Soil sorptivity enhancement with crop residue accumulation in semiarid dryland no-till agroecosystems

Water capture and precipitation use efficiency are of great importance in dryland cropping systems because the world's dependence on food produced in dryland areas continues to increase. Growing season evapotranspiration potential greatly exceeds growing season precipitation rates in dryland areas, creating a water deficit for crops. Management practices that positively impact soil physical properties increase the potential for soils to capture water. One way to assess the ability of soils to capture water is through the measurement of sorptivity. Sorptivity is defined as the cumulative infiltration proportionality constant and is governed by surface soil physical properties such as texture, degree of aggregation and aggregate stability. A study was conducted to determine how crop residue accumulation after 12years of no-till management affects surface soil sorptivity under semi-arid dryland conditions and how sorptivity is related to surface soil physical properties known to be related to crop residue accumulation. Surface soil sorptivity, bulk density, porosity (total and effective) and aggregation measurements were made across cropping systems and soil positions representing a wide gradient of crop residue accumulation at 3 sites in eastern Colorado. Results show that increasing crop residue accumulation will have the indirect effect of increased sorptivity via improvements in soil aggregation, bulk density, and porosity that are conducive to water infiltration. Management practices that result in greater amounts of crop residue returned to the soil system lead to beneficial soil physical properties that increase water sorptivity, greatly reducing the potential for runoff and erosion, and thereby increase the precipitation use efficiency of the system.

Implications of Representing Snowpack Stratigraphy for the Assimilation of Passive Microwave Satellite Observations

Abstract Under certain conditions, passive microwave satellite observations can be used to estimate snow water equivalent (SWE) across large areas, either through direct retrieval or data assimilation. However, the layered character of snowpacks increases the complexities of estimation algorithms. A multilayer model of snowpack stratigraphy that can serve as the forward model of a snow data assimilation system is described and evaluated. The model’s ability to replicate large-scale snowpack layer features is evaluated using observations from the Cold Land Processes Experiment (Colorado, 2002 and 2003) and a 2002 Nome–Barrow snowpit transect [Snow Science Traverse—Alaska Region (SnowSTAR2002)]. The multilayer model linked with a radiative transfer scheme improved the estimation of brightness temperatures both in terms of absolute values and frequency/polarization differences (error reductions ranging from 47% to 72%) relative to a one-layer model with similar, but depth-averaged, physics at the Colorado sites. The two models were also employed along the SnowSTAR2002 transect of snowpit measurements. The general unavailability of meteorological forcings along the transect made the use of coarse-scale reanalysis data necessary to simulate snow properties and microwave radiances. Errors in the precipitation forcings led to overestimation of SWE, and the simulated brightness temperatures from the two models showed large differences, due mostly to the inability of the single-layer model to simulate the observed larger grain sizes. These differences had implications for the estimation of snow depth; assimilation of Special Sensor Microwave Imager (SSM/I) observations into the multilayer model resulted in improved snow depth estimates (RMSEs of 18.1 cm versus 34.1 cm without assimilation), while the single-layer assimilation slightly decreased the estimation skill (RMSEs of 34.1 versus 33.6 cm).

Parasite infection and host dynamics in a naturally fluctuating rodent population

Parasites can both influence and be affected by host population dynamics, and a growing number of case studies support a role for parasites in causing or amplifying host population cycles. In this study, we examined individual and population predictors of gastrointestinal parasitism on wild cyclic montane voles ( Microtus montanus (Peale, 1848)) to determine if evidence was consistent with theory implicating parasites in population cycles. We sampled three sites in central Colorado for the duration of a multiannual cycle and recorded the prevalence and intensity of directly transmitted Eimeria Schneider, 1875 and indirectly transmitted cestodes from a total of 267 voles. We found significant associations between host infection status, individual traits (sex, age, and reproductive status) and population variables (site, trapping period, and population density), including a positive association between host density and cestode prevalence, and a negative association between host density and Eimeria prevalence. Both cestode and Eimeria intensity correlated positively with host age, reproductive status, and population density, but neither parasite was associated with poorer host condition. Our findings suggest that parasites are common in this natural host, but determining their potential to influence montane vole cycles requires future experimental studies and long-term monitoring to determine the fitness consequences of infection and the impact of parasite removal on host dynamics.