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Soil microbial respiration is a critical component of the global carbon cycle, but it is uncertain how properties of microbes affect this process. Previous studies have noted a thermodynamic trade-off between the rate and efficiency of growth in heterotrophic organisms. Growth rate and yield determine the biomass-specific respiration rate of growing microbial populations, but these traits have not previously been used to scale from microbial communities to ecosystems. Here we report seasonal variation in microbial growth kinetics and temperature responses (Q10) in a coniferous forest soil, relate these properties to cultured and uncultured soil microbes, and model the effects of shifting growth kinetics on soil...
Frequent and persistent droughts exacerbate the problems caused by the inherent scarcity of water in the semiarid to arid parts of the southwestern United States. The occurrence of drought is driven by climatic variability, which for years before about the beginning of the 20th century in the Southwest must be inferred from proxy records. As part of a multidisciplinary study of the potential hydrologic impact of severe sustained drought on the Colorado River, the physical basis and limitations of tree rings as indicators of severe sustained drought are reviewed, and tree-ring data are analyzed to delineate a “worst-case� drought scenario for the Upper Colorado River Basin (UCRB). Runs analysis of a 121-site...
We describe a new method for the calculation of river flow that uses the oxygen isotope composition of bivalve mollusk shells that grew in the river-water/seawater mixing zone of the Colorado River estuary. Sclerochronological techniques are used to identify tidally-induced, fortnight-scale bundles of daily growth increments within shell cross-sections. These fortnightly markers are used to establish a chronology for samples taken for δ18O analysis. A composite seasonal δ18O profile derived from five shells that grew in the absence of river-water flow is used as a baseline against which profiles of river-influenced shells are compared. Because this comparison is between matched fortnights within a year, the temperature...
Human activities have caused the decline of numerous species and ecosystems. To promote ecosystem resilience, recent management efforts aim to maintain ecosystem patterns and processes within their historical range of variability. There has been substantial concern that quaking aspen, the most widely distributed tree in North America and the most important deciduous tree in the subalpine forests of the Rocky Mountains, has declined significantly in the western landscape during the 20th century. This reported decline has been attributed to conifer encroachment associated with fire exclusion, as well as other causes. To assess long-term changes in the extent of quaking aspen in a 175000-ha study area in western Colorado,...
The determination of plant and soil temperatures using remote sensing technology is examined in a shrub-steppe ecosystem. The emissivities of Artemisia tridentata L. shrubs and the soil surface were examined in such an ecosystem. The emissivity of A. tridentata plants was calculated to be 0.97, which is in the range of reported values for other green plants. The soil emissivity was 0.93. Temperature readings from an infrared thermometer (IRT) must be corrected for the emissivity value of the target and the reflected sky radiation. Although these two factors produce errors which are opposite in sign, they will not offset one another. An analysis is presented which quantifies the temperature error resulting from ignoring...
There is now a fairly substantial literature that addresses transboundary water allocation both at the international and interstate level. However, most of this literature deals almost exclusively with the question of allocation and ignores quality considerations. At the same time, there is a growing literature on transboundary pollution control and upstream/downstream externalities. What is missing is an attempt to integrate quality consideration into allocation agreements. This paper examines several allocation agreements and disputes in the southwestern United States and Mexico and looks at the ramifications of omitting pollution control and quality considerations in these negotiations. Published in Agricultural...
The exchange of nutrients, nitrogen in particular, between closely associated plants has attracted considerable interest due to its importance in agroecosystems under low external nutrient-input management. The intuitive observation of farmers that grasses benefit from near associations with clovers has not been easy to quantify, mainly because (i) the net effect is measured against large background fluxes, and (ii) excluding one species from one agroecosystem change the system fundamentally. The study of Moyer-Henry et al. (pp. 7–20 in this issue) approaches this problem elegantly by choosing a soil with a relatively low background mineralisation of nitrogen, while maintaining the same species in the system,...
Galloway plans to sell surface water, which was appropriated to Colorado under interstate compacts and acquired pursuant to state law, to users in a different stat and in a different river basin. Galloway poses a new question for the Colorado River compacts: Do compacts limit water use to specific geographic territory? This paper finds express or implied territorial use limitations in the compacts. The compact language would preclude out-of-basin use of Colorado River water which Galloway proposes. Because the compacts are federal law, they are immune from commerce clause attack and preempt inconsistent state law. This paper explores these propositions in depth. Published in Natural Resources Journal, volume 25,...
Downy brome (Bromus tectorum L. #3 BROTE) has developed into a severe weed in several agricultural production systems throughout North America, particularly on rangeland and in winter wheat (Triticum aestivum L.). Several million hectares of winter wheat, pastureland, alfalfa (Medicago sativa L.), grass seed fields, and overgrazed rangeland, as well as other crops, have been invaded by this annual grass since its introduction into this hemisphere. Downy brome is most abundant in the Great Basin and Columbia Basin areas of the western United States, but is found throughout the continental United States and parts of Canada and Mexico. In some cases, the vegetation on overgrazed rangeland consists totally of downy...
Categories: Publication; Types: Citation, Journal Citation; Tags: Weed Science
Cheatgrass (Bromus tectorum) is a recognized, invasive annual weed of the western United States that reduces fire return times from decades to less than 5 years. To determine the interaction between rising carbon dioxide concentration ([CO2]) and fuel load, we characterized potential changes in biomass accumulation, C : N ratio and digestibility of three cheatgrass populations from different elevations to recent and near-term projections in atmospheric [CO2]. The experimental CO2 values (270, 320, 370, 420 μmol mol−1) corresponded roughly to the CO2 concentrations that existed at the beginning of the 19th century, that during the 1960s, the current [CO2], and the near-term [CO2] projection for 2020, respectively....
Runoff generated directly on Mancos Shale hillslopes initially picks up solutes by surface flushing. The major mechanism of subsequent solute pickup involves transport of soluble minerals as particulate matter with sediment. Solute release increases contemporaneously with increase in sediment concentration during rilling and rill entrenchment. Moreover, solute release increases as the power per unit width of surface area increases, thereby causally explaining the high correlation between runoff salinity and slope inclination. The regression between these two variables may be used as a tool to assess salinity hazard. Published in Journal of Hydrology, volume 59, issue 1-2, on pages 189 - 207, in 1982.
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Abstract The potential effects of climate change on the hydrology and water resources of the Colorado River basin are assessed by comparing simulated hydrologic and water resources scenarios derived from downscaled climate simulations of the U.S. Department of Energy/National Center for Atmospheric Research Parallel Climate Model (PCM) to scenarios driven by observed historical (1950–1999) climate. PCM climate scenarios include an ensemble of three 105-year future climate simulations based on projected `business-as-usual'(BAU) greenhouse gas emissions and a control climate simulation based on static 1995 greenhouse gas concentrations. Downscaled transient temperature and precipitation sequences were extracted...
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Understanding the passive microwave emissions of a snowpack, as observed by satellite sensors, requires knowledge of the snowpack properties: water equivalent, grain size, density, and stratigraphy. For the snowpack in the Upper Colorado River Basin, measurements of snow depth and water equivalent are routinely available from the U.S. Department of Agriculture, but extremely limited information is available for the other properties. To provide this information, a field program from 1984 to 1995 obtained profiles of snowpack grain size, density, and temperature near the time of maximum snow accumulation, at sites distributed across the basin. A synoptic basin�wide sampling program in 1985 showed that the snowpack...
We assessed the effectiveness of the western pearl mussel (Margaritifera falcata, Gould, 1850) as a bioindicator of aquatic system health. Fifty-years ago a large dredge mining operation for columbite-tantalite ores [(Fe,Mn)(Nb,Ta)2O6] disturbed a substantial portion of the Middle Fork of the Salmon River headwaters in Idaho. The disturbance likely increased concentrations of dissolved metals at the time. To evaluate the potential long-term impacts, if any, concentrations of Fe, Mg, Mn, and Zn in shell and soft tissues of western pearl mussels, collected from five reaches in Bear Valley Creek, were analyzed. We quantified the partitioning and bioaccumulation with respect to age of the four metals in the shell, gills...
This paper delineates bioclimatic zones of the Colorado Front Range. It develops a methodology which might be useful for making inventories of mountain bioclimates in other parts of the world. Following a description of the vegetation and the climate of the Front Range some insight is gained into the bioclimatic systems of the area by examining the applicability of established climatic classifications. The main part of the paper explains procedures for distinguishing the bioclimatic zones. The variables employed in determining the zones are the ratio of growing season thawing degree days to growing season precipitation, summer mean temperature, and growing season soil moisture deficit. Aspect is examined as a possible...
Desert iguanas (Dipsosaurus dorsalis) were maintained at 10, 20, 30 or 40°C for one week. Animals were autopsied at zero time, and 30 and 90 minutes after a single injection of ACTH. Basal plasma corticosterone (B) level was similar in all lizards regardless of environmental temperature. Both blood glucose and liver glycogen levels showed highly significant correlations with environmental temperature. Injection of ACTH increased plasma B level in all temperature groups but the rate and magnitude of the response were temperature dependent. Liver glycogen was increased after ACTH injection at 20°C and plasma glucose response to ACTH was significantly correlated with temperature. Published in Journal of Comparative...
The Colorado River Extensional Corridor (CREC) of southeastern California, southern Nevada, and western Arizona experienced up to 100% extension between ~23 and 12 Ma. Extension was accommodated by low-angle normal faulting in the upper and middle crust, subvertical brittle failure of the lower crust, emplacement of mantle-derived magma in a crustal-scale fracture, and, later, crustal flow. Evidence for brittle, whole-crustal failure includes geophysical observations, structural analysis, geochronology, thermochronology, geobarometry, and paleomagnetic studies of surface exposures of syntectonic, mantle-derived mafic plutonic sheets emplaced as subvertical, crustal-scale intrusions tracking the zone of maximum extension....
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Summers on the Colorado Plateau (USA) are typified by harsh conditions such as high temperatures, brief soil hydration periods, and high UV and visible radiation. We investigated whether community composition, physiological status, and pigmentation might vary in biological soil crusts as a result of such conditions. Representative surface cores were sampled at the ENE, WSW, and top microaspects of 20 individual soil crust pedicels at a single site in Canyonlands National Park, Utah, in spring and fall of 1999. Frequency of cyanobacterial taxa, pigment concentrations, and dark adapted quantum yield [F(v)/F(m)] were measured for each core. The frequency of major cyanobacterial taxa was lower in the fall compared to...
We capitalized on a regional-scale, anthropogenic experiment?the reduction of black-tailed prairie dog (Cynomys ludovicianus) towns across the Great Plains of North America?to test the hypothesis that decline of this species has led to declines in diversity of native grassland vertebrates of this region. We compared species richness and species composition of non-volant mammals, reptiles and amphibians at 36 prairie dog towns and 36 paired sites in the Panhandle Region of Oklahoma during the summers and falls of 1997, 1998 and 1999. We detected 30 species of mammals, 18 species of reptiles and seven species of amphibians. Comparisons between communities at prairie dog towns and paired sites in the adjacent landscape...
Continental successions of the North American Western Interior retroarc foreland basin provide an excellent opportunity to evaluate the tectonic controls on nonmarine sequence stratigraphy. The transition between the Upper Jurassic Brushy Basin Member anastomosed fluvial system of the Morrison Formation and the gravelly braided-river deposits of the Buckhorn Conglomerate has been studied to assess the dispersal of coarse clastics and the development of associated basin-wide unconformities in a sequence stratigraphic framework. The sharp contact between the two members is interpreted to be conformable based on stratigraphic, sedimentologic, and petrologic data collected at and near Cedar Mountain in central Utah,...
map background search result map search result map The Effects of Climate Change on the Hydrology and Water Resources of the Colorado River Basin The effects of snowpack grain size on satellite passive microwave observations from the Upper Colorado River Basin Temporal variation in community composition, pigmentation, and F(v)/F(m) of desert cyanobacterial soil crusts. Temporal variation in community composition, pigmentation, and F(v)/F(m) of desert cyanobacterial soil crusts. The effects of snowpack grain size on satellite passive microwave observations from the Upper Colorado River Basin The Effects of Climate Change on the Hydrology and Water Resources of the Colorado River Basin