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Research about Colorado Plateau

Source-linked reports with geographic coverage including Colorado Plateau.

At least 55 records · Page 3Linked to original sources
USGS2012

Seismic constraints on the nature of lower crustal reflectors beneath the extending Southern Transition Zone of the Colorado Plateau, Arizona

We determine the reflection polarity and exploit variations in P and S wave reflectivity and P wave amplitude versus offset (AVO) to constrain the origin of lower crustal reflectivity observed on new three-component seismic data recorded across the structural transition of the Colorado Plateau. The near vertical incidence reflection data were collected by Stanford University in 1989 as part of the U.S. Geological Survey Pacific to Arizona Crustal Experiment that traversed the Arizona Transition Zone of the Colorado Plateau. The results of independent waveform modeling methods are consistent with much of the lower crustal reflectivity resulting from thin, high-impedance layers. The reflection polarity of the cleanest lower crustal events is positive, which implies that these reflections result from high-velocity contrasts, and the waveform character indicates that the reflectors are probably layers less than or approximately equal to 200 m thick. The lower crustal events are generally less reflective to incident S waves than to P waves, which agrees with the predicted behavior of high-velocity mafic layering. Analysis of the P wave AVO character of lower crustal reflections demonstrates that the events maintain a constant amplitude with offset, which is most consistent with a mafic-layering model. One exception is a high-amplitude (10 dB above background) event near the base of lower crustal reflectivity which abruptly decreases in amplitude at increasing offsets. The event has a pronounced S wave response, which along with its negative AVO trend is a possible indication of the presence of fluids in the lower crust. The Arizona Transition Zone is an active but weakly extended province, which causes us to discard models of lower crustal layering resulting from shearing because of the high degree of strain required to create such layers. Instead, we favor horizontal basaltic intrusions as the primary origin of high-impedance reflectors based on (1) The fact that most xenoliths in eruptive basalts of the Transition Zone are of mafic igneous composition, (2) indications that a pulse of magmatic activity crossed the Transition Zone in the late Tertiary period, and (3) the high regional heat flow observed in the Transition Zone. The apparent presence of fluids near the base of the reflective zone may indicate a partially molten intrusion. We present a mechanism by which magma can be trapped and be induced to intrude horizontally at rheologic contrasts in extending crust.

Arizona↗
USGS2012

Changes to dryland rainfall result in rapid moss mortality and altered soil fertility

Arid and semi-arid ecosystems cover ~40% of Earth’s terrestrial surface, but we know little about how climate change will affect these widespread landscapes. Like many drylands, the Colorado Plateau in southwestern United States is predicted to experience elevated temperatures and alterations to the timing and amount of annual precipitation. We used a factorial warming and supplemental rainfall experiment on the Colorado Plateau to show that altered precipitation resulted in pronounced mortality of the widespread moss Syntrichia caninervis. Increased frequency of 1.2 mm summer rainfall events reduced moss cover from ~25% of total surface cover to <2% after only one growing season, whereas increased temperature had no effect. Laboratory measurements identified a physiological mechanism behind the mortality: small precipitation events caused a negative moss carbon balance, whereas larger events maintained net carbon uptake. Multiple metrics of nitrogen cycling were notably different with moss mortality and had significant implications for soil fertility. Mosses are important members in many dryland ecosystems and the community changes observed here reveal how subtle modifications to climate can affect ecosystem structure and function on unexpectedly short timescales. Moreover, mortality resulted from increased precipitation through smaller, more frequent events, underscoring the importance of precipitation event size and timing, and highlighting our inadequate understanding of relationships between climate and ecosystem function in drylands.

Colorado Plateau↗
USGS2012

Avian community responses to vegetation structure within chained and hand-cut pinyon-juniper woodlands on the Colorado Plateau

We investigated relationships between breeding birds and vegetation characteristics in fuels-reduction treatment areas within pinyon-juniper woodlands at locations over the Colorado Plateau. The goal of this study was to document differences in avian community responses to two types of pinyon-juniper fuels-reduction treatments (chained vs. hand-cut), relative to control sites. We selected 73 vegetation plots in southern Utah and northern Arizona, of which 33 had been previously thinned by handcutting or chaining, and 40 control plots in untreated pinyon-juniper woodlands. At the 73 locations we documented vegetation structure and counted birds within 3.1 ha circular plots during the 2005 and 2006 breeding seasons. We focused in particular on the effects of fuels-reduction treatments to 16 bird species that are considered pinyon-juniper obligates. We found that density of pinyon pines was the most important variable in predicting bird species richness in all treatments and at control sites. Abundance of Brewer&rsquo;s Sparrow (<i>Spizella breweri</i>) was negatively related to chained, but positively related to hand cut areas. Vesper Sparrow (<i>Poocetes graminius</i>) abundance was negatively related to both chaining and handcutting. Within 16 pinyon-juniper obligate bird species, abundance of five was positively related to pinyon-pine density, while two were positively related to juniper density. These responses, along with other bird-vegetation relationships influenced by treatment type, need to be considered by land managers when planning fuels reduction treatments in pinyon-juniper woodland habitat in the Colorado Plateau.

Arizona, Colorado, New Mexico, Utah↗
USGS2011

Responses of wind erosion to climate-induced vegetation changes on the Colorado Plateau

Projected increases in aridity throughout the southwestern United States due to anthropogenic climate change will likely cause reductions in perennial vegetation cover, which leaves soil surfaces exposed to erosion. Accelerated rates of dust emission from wind erosion have large implications for ecosystems and human well-being, yet there is poor understanding of the sources and magnitude of dust emission in a hotter and drier climate. Here we use a two-stage approach to compare the susceptibility of grasslands and three different shrublands to wind erosion on the Colorado Plateau and demonstrate how climate can indirectly moderate the magnitude of aeolian sediment flux through different responses of dominant plants in these communities. First, using results from 20 y of vegetation monitoring, we found perennial grass cover in grasslands declined with increasing mean annual temperature in the previous year, whereas shrub cover in shrublands either showed no change or declined as temperature increased, depending on the species. Second, we used these vegetation monitoring results and measurements of soil stability as inputs into a field-validated wind erosion model and found that declines in perennial vegetation cover coupled with disturbance to biological soil crust resulted in an exponential increase in modeled aeolian sediment flux. Thus the effects of increased temperature on perennial plant cover and the correlation of declining plant cover with increased aeolian flux strongly suggest that sustained drought conditions across the southwest will accelerate the likelihood of dust production in the future on disturbed soil surfaces.

Utah↗
USGS2011

Differences in macroinvertebrate community structure in streams and rivers with different hydrologic regimes in the semi-arid Colorado Plateau

Aquatic macroinvertebrates are sensitive to changes in their chemical and physical environment, and as such, serve as excellent indicators of overall ecosystem health. Moreover, temporal and spatial differences in macroinvertebrate community structure can be used to investigate broad issues in aquatic science, such as the hypothesis that changes in climate are likely to have disproportionately large effects on small, intermittent stream ecosystems. We quantified macroinvertebrate community structure and abiotic conditions at ten stream sites with different dominant hydrologic regimes in the Colorado Plateau, ranging from small, intermittent desert streams to large perennial mountain rivers. Considerable differences were observed in community structure between sites with differing hydrologic regimes. Quantitative results of non-metric multidimensional scaling (NMDS) ordination and Spearman rank correlations between physical habitat and macroinvertebrate resemblance matrices indicate that discharge, geomorphic channel unit type (% pools vs. % riffles), percent of substrate composed of sand, and velocity were the subset of measured habitat variables that best explained the differences in macroinvertebrate community structure among sites. Of the 134 taxa identified, nine taxa explained 95 % of the variability in community structure between sites. These results add to a growing base of knowledge regarding the functioning of lotic ecosystems in the Colorado Plateau, and provide timely information on anticipated changes in the structure and function of aquatic ecosystems in response to predicted future environmental conditions.

Colorado Plateau↗
USGS2011

Monitoring and analysis of sand dune movement and growth on the Navajo Nation, southwestern United States

Recurring drought and rising temperatures have caused reactivation and renewed growth of sand dunes on the lands of the Navajo Nation on the Colorado Plateau. Migrating dunes threaten health, housing, and transportation pathways. U.S. Geological Survey (USGS) scientists are conducting research to better understand the processes of dune growth and movement. This research will provide critical data to the Native peoples of the region in their response to the changing environment.

Colorado Plateau↗
USGS2010

Carbon, water, and energy fluxes in a semiarid cold desert grassland during and following multiyear drought

The net exchanges of carbon dioxide, water vapor, and energy were examined in a perennial Colorado Plateau grassland for 5 years. The study began within a multiyear drought and continued as the drought ended. The grassland is located near the northern boundary of the influence of the North American monsoon, a major climatic feature bringing summer rain. Following rain, evapotranspiration peaked above 8 mm d -1 but was usually much smaller (2-4 mm d -1 ). Net productivity of the grassland was low compared to other ecosystems, with peak hourly net CO 2 uptake in the spring of 4 (mu or u)mol m -2 s -1 and springtime carbon gain in the range of 42 + or - 11 g C m -2 (based on fluxes) to 72 + or - 55 g C m -2 (based on carbon stocks; annual carbon gain was not quantified). Drought decreased gross ecosystem productivity (GEP) and total ecosystem respiration, with a much larger GEP decrease. Monsoon rains led to respiratory pulses, lasting a few days at most, and only rarely resulted in net CO 2 gain, despite the fact that C 4 grasses dominated plant cover. Minor CO 2 uptake was observed in fall following rain. Spring CO 2 uptake was regulated by deep soil moisture, which depended on precipitation in the prior fall and winter. The lack of CO 2 uptake during the monsoon and the dependence of GEP on deep soil moisture are in contrast with arid grasslands of the warm deserts. Cold desert grasslands are most likely to be impacted by future changes in winter and not summer precipitation.

Colorado Plateau↗
USGS2010

High-resolution receiver function imaging reveals Colorado Plateau lithospheric architecture and mantle-supported topography

After maintaining elevations near sea level for over 500 million years, the Colorado Plateau (CP) has a present average elevation of 2 km. We compute new receiver function images from the first dense seismic transect to cross the plateau that reveal a central CP crustal thickness of 42–50 km thinning to 30–35 km at the CP margins. Isostatic calculations show that only approximately 20% of central CP elevations can be explained by thickened crust alone, with the CP edges requiring nearly total mantle compensation. We calculate an uplift budget showing that CP buoyancy arises from a combination of crustal thickening, heating and alteration of the lithospheric root, dynamic support from mantle upwelling, and significant buoyant edge effects produced by small-scale convecting asthenosphere at its margins.

Arizona, Colorado, New Mexico, Texas, Utah↗
USGS2010

The Colorado Plateau IV: shaping conservation through science and management

Roughly centered on the Four Corners region of the southwestern United States, the Colorado Plateau covers some 130,000 square miles of sparsely vegetated plateaus, mesas, canyons, arches, and cliffs in Arizona, Utah, Colorado, and New Mexico. With elevations ranging from 3,000 to 14,000 feet, the natural systems found within the plateau are dramatically varied, from desert to alpine conditions. This book focuses on the integration of science and resource management issues in this unique and highly varied environment. Broken into three subsections, this volume addresses conservation biology, biophysical resources, and inventory and monitoring concerns. The chapters range in content, addressing conservation issues&ndash;past, present, and future&ndash;on the Colorado Plateau, measurement of human impacts on resources, grazing and wildland-urban interfaces, and tools and methods for monitoring habitats and species. An informative read for people interested in the conservation and natural history of the region, the book will also serve as a valuable reference for those people engaged in the management of cultural and biological resources of the Colorado Plateau, as well as scientists interested in methods and tools for land and resource management throughout the West.

Utah;Colorado;Arizona;New Mexico↗
USGS2008

Holocene debris flows on the Colorado Plateau: The influence of clay mineralogy and chemistry

Holocene debris flows do not occur uniformly on the Colorado Plateau province of North America. Debris flows occur in specific areas of the plateau, resulting in general from the combination of steep topography, intense convective precipitation, abundant poorly sorted material not stabilized by vegetation, and the exposure of certain fine-grained bedrock units in cliffs or in colluvium beneath those cliffs. In Grand and Cataract Canyons, fine-grained bedrock that produces debris flows contains primarily single-layer clays—notably illite and kaolinite—and has low multilayer clay content. This clay-mineral suite also occurs in the colluvium that produces debris flows as well as in debris-flow deposits, although unconsolidated deposits have less illite than the source bedrock. We investigate the relation between the clay mineralogy and major-cation chemistry of fine-grained bedrock units and the occurrence of debris flows on the entire Colorado Plateau. We determined that 85 mapped fine-grained bedrock units potentially could produce debris flows, and we analyzed clay mineralogy and major-cation concentration of 52 of the most widely distributed units, particularly those exposed in steep topography. Fine-grained bedrock units that produce debris flows contained an average of 71% kaolinite and illite and 5% montmorillonite and have a higher concentration of potassium and magnesium than nonproducing units, which have an average of 51% montmorillonite and a higher concentration of sodium. We used multivariate statistics to discriminate fine-grained bedrock units with the potential to produce debris flows, and we used digital-elevation models and mapped distribution of debris-flow producing units to derive a map that predicts potential occurrence of Holocene debris flows on the Colorado Plateau.

Arizona, Colorado, New Mexico, Utah↗
USGS2008

The Colorado Plateau III: integrating research and resources management for effective conservation

Roughly centered on the Four Corners region of the southwestern United States, the Colorado Plateau covers an area of 130,000 square miles. The relatively high semi-arid province boasts nine national parks, sixteen national monuments, many state parks, and dozens of wilderness areas. With the highest concentration of parklands in North America and unique geological and ecological features, the area is of particular interest to researchers. Derived from the Eighth Biennial Conference of Research on the Colorado Plateau, this third volume in a series of research on the Colorado Plateau expands upon the previous two books. This volume focuses on the integration of science into resource management issues, summarizes what criteria make a successful collaborative effort, outlines land management concerns about drought, provides summaries of current biological, sociological, and archaeological research, and highlights current environmental issues in the Four Corner States of Arizona, New Mexico, Colorado, and Utah. With broad coverage that touches on topics as diverse as historical aspects of pronghorn antelope movement patterns through calculating watershed prescriptions to the role of wind-blown sand in preserving archaeological sites on the Colorado River, this volume stands as a compendium of cuttingedge management-oriented research on the Colorado Plateau. The book also introduces, for the first time, tools that can be used to assist with collaboration efforts among landowners and managers who wish to work together toward preserving resources on the Colorado Plateau and offers a wealth of insights into land management questions for many readers, especially people interested in the natural history, biology, anthropology, wildlife, and cultural management issues of the region.

Utah;Arizona;Colorado;New Mexico↗
USGS2007

Field-based evaluations of sampling techniques to support long-term monitoring of riparian ecosystems along wadeable streams on the Colorado Plateau

To better plan for and implement long-term ecological monitoring, we measured riparian vegetation and fluvial geomorphic features at pilot study sites on four wadeable perennial stream reaches, representative of drainages across the Colorado Plateau. Our primary objectives were to (1) collect field data, (2) evaluate the efficiency and effectiveness of various ecological measures and measurement techniques for riparian ecosystems, and (3) use field-based sampling to inform and refine the development of standard operating procedures for use in implementing integrated, long-term monitoring of riparian ecosystems. Ultimately, this work was aimed at providing NPS staff with some of the information and methods needed to design and implement long-term monitoring of NPS riparian resources, which is both relevant to management, and fully operational within institutional resource constraints. Our results suggest that selecting sampling reaches and establishing a sampling frame of 11 transects, across a range of stream types, is feasible given a limited set of decision rules. A distinctive feature of richness across all sites was the high percentage of rare species, defined here as species having a single occurrence at a site. Rare species represented from 33 percent to 47 percent of the species total across the four pilot sites. Our data show that the two smallest quadrat sizes, 0.01 m 2 and 0.1 m 2 , rarely had any species that occurred in the desired frequency range and can be omitted from the monitoring protocol. Few species fell within the 30&ndash;70 percent range in the 1-m 2 quadrats, but this quadrat size appears to be useful at the Tsaile Creek (CACH) site. We recommend continuing to collect information at the 1-m 2 scale and reevaluating its usefulness after more data are available from different types of sites. The 10-m 2 quadrat is adequate for monitoring changes in frequencies of very common species at all sites. Based on pilot study results, we conclude that at sites with low total species numbers (< 60 species), 40&ndash;60, 10-m 2 quadrats, would be sufficient to characterize overall species diversity for relatively common species. At sites with higher total numbers of species (> 100), 60&ndash;80, 10-m 2 quadrats would be required to characterize overall species diversity. Rare species of interest should be monitored using alternative approaches, such as a site inventory and/or mapping (see Elzinga and others, 1998). A large number of the systematically placed 10-m 2 quadrats span two or more geomorphic surfaces, especially adjacent to the channel. This makes resolution of species affinities with distinct geomorphic landforms difficult. Thus, we provide an amendment to improve characterization of herbaceous and shrub species on narrow, near-channel surfaces by sampling additional 0.5-m by 1-m quadrats on those surfaces. It appears that for sites in narrow valley settings where riparian zones average less than approximately 40 m, the number of 10-m 2 quadrats systematically placed on 11 transects will not provide shrub cover estimates at 20 percent precision. In such cases, additional sample reaches should be added in order to attain a minimum of 130 to 140 10-m 2 shrub quadrats. The line-intercept technique can provide a relatively rapid, reach-scale quantification of proportional cover for woody vegetation and geomorphic surface types and that variance in these measures stabilizes by the eighth or ninth transect sampled. An overlay of the distribution of geomorphic surface data derived from line-intercept sampling on topographic survey information indicates that delineation of geomorphic surfaces could be done in conjunction with the topographic survey of each transect, obviating the need to record surface breaks using the line intercept. To include geomorphic surface identifications with the topographic survey, surface breaks and transitional surfaces should be included and identified in the survey, in addition to systematically placed survey points. Compared to 5-m by 20-m tree quadrats, belt transects were shown to provide similar estimates of stand structure (stem density and stand basal area) in less than 30 percent of the time. Further, for the streams sampled, there were no statistically significant differences in stem density and basal area estimates between 10-m and 20-m belt transects and the smaller belts took approximately half the time to sample. There was, however, high variance associated with estimates of stand structure for infrequently occurring stems, such as large, relict or legacy riparian trees. Legacy riparian trees occurred in limited numbers at all sites sampled. A reachscale population census of these trees indicated that the 10-m belt transects tended to underestimate both stem density and basal area for these riparian forest elements and that a complete reach-scale census of legacy trees averaged less than one hour per site.

Colorado Plateau↗
USGS2004

The Colorado Plateau: cultural, biological, and physical research

Stretching from the four corners of Arizona, New Mexico, Colorado, and Utah, the Colorado Plateau is a natural laboratory for a wide range of studies. This volume presents 23 original articles drawn from more than 100 research projects presented at the Sixth Biennial Conference of Research on the Colorado Plateau. This scientific gathering revolved around research, inventory, and monitoring of lands in the region. The book's contents cover management techniques for cultural, biological, and physical resources, representing collaborative efforts among federal, university, and private sector scientists and land managers. Chapters on cultural concerns cover benchmarks of modern southwestern anthropological knowledge, models of past human activity and impact of modern visitation at newly established national monuments, challenges in implementing the 1964 Wilderness Act, and opportunities for increased federal research on Native American lands. The section on biological resources comprises sixteen chapters, with coverage that ranges from mammalian biogeography to responses of elk at the urban-wildland interface. Additional biological studies include the effects of fire and grazing on vegetation; research on bald eagles at Grand Canyon and tracking wild turkeys using radio collars; and management of palentological resources. Two final chapters on physical resources consider a proposed rerouting of the Rio de Flag River in urban Flagstaff, Arizona, and an examination of past climate patterns over the Plateau, using stream flow records and tree ring data. In light of similarities in habitat and climate across the Colorado Plateau, techniques useful to particular management units have been found to be applicable in many locations. This volume highlights an abundance of research that will prove useful for all of those working in the region, as well as for others seeking comparative studies that integrate research into land management actions.

Utah;Colorado;Arizona;New Mexico↗
USGS2002

Treatment effects on performance of N-fixing lichens in disturbed crusts of the Colorado Plateau

Biological soil crusts arrest soil erosion and supply nitrogen to arid ecosystems. To understand their recovery from disturbance, we studied performances of Collema spp. lichens relative to four experimental treatments plus microtopography of soil pedicels, oriented north-northwest to south-southeast in crusts. At sites in Needles (NDLS) and Island in the Sky (ISKY) districts of Canyonlands National Park, lichens were transplanted to NNW, SSE, ENE, WSW, and TOP pedicel faces and exposed to a full-factorial, randomized block experiment with four treatments: nutrient addition (P and K), soil stabilization with polyacrylamide resin (PAM), added cyanobacterial fiber, and biweekly watering. After 14.5 mo (NDLS) and 24 mo (ISKY), both visual rankings of lichen condition and measures of chlorophyll fluorescence were generally higher at ISKY than on more fertile but less stable soils at NDLS. On ENE and NNW pedicel faces, both these values and nitrogenase activity (NDLS only) exceeded corresponding values on WSW and SSE faces. Treatment effects were site specific and largely negative at NDLS; both nutrient and cyanobacterial addition led to poorer lichen condition, and added nutrients led to reduced fluorescence. Responses to nutrients may have been mediated partly by disturbance of unstable soils and by competition with cyanobacteria. In a separate experiment investigating recruitment responses to adding fungal spores or Nostoc cells, rates of Collema establishment responded significantly to the former but not the latter. Low establishment overall suggests that natural recruitment may occur mainly from iscidia or thallus fragments, not spores. Measured simultaneously on artificial soil pedicels at NDLS and ISKY, both deposition and erosion declined at NDLS across the four pedicel microaspects as: WSW > SSE > NNW > ENE (or ENE > NNW), during fall and spring trials. Patterns were similar at ISKY, but WSW ≈ SSE for spring deposition, and deposition did not differ by microaspect in fall. Greater deposition at ISKY, despite higher abundance of cyanobacteria, may be explained by stronger wind velocities. Together, microtopographic differences in erosion, microclimate, and nutrient regimes help explain variable lichen performance, but microtopography influenced lichen performance more consistently than did any treatment. Demonstrated effects of pedicel development in crust recovery concur with prior surveys showing greatest microbial biomass and/or cover on ENE and NNW exposures at various spatial scales.

Colorado Plateau↗
USGS2000

Geologic assessment of coal in the Colorado Plateau: Arizona, Colorado, New Mexico, and Utah

This CD-ROM set contains a geologic assessment of coal deposits of the Colorado Plateau region and new resource estimates for selected assessment units within the Colorado Plateau. Original resource estimates (in-place resources before production) for the 12 priority assessment units of the Colorado Plateau exceed one half trillion short tons of coal in beds greater than 1 ft thick and under less than 6,000 ft of overburden. The coal is high quality and low sulfur, and a portion of these resources will provide future energy production for the Nation. Disc 1, in Portable Document Format, contains results of the assessment in summary and (or) technical reports for 12 priority coal assessment units in the Colorado Plateau and also contains an ArcView Data Publisher project, which is an interactive geographic information system of digital data collected during the assessment. Disc 2 contains stratigraphic data bases for seven of the priority coal assessment areas within the Colorado Plateau region and an ArcView project identical to the ArcView Data Publisher project on disc 1 except that it retains some of the functionality that is disabled in the ArcView Data Publisher program.

Arizona, Colorado, New Mexico, Utah↗