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Natural gas accumulations with high CO2 concentrations may be useful natural analogs for the study of long-term CO2 storage in geologic strata if viewed in the context of ?CO2 systems?. Comprehensive evaluation of a CO2 system involves the identification of the following parameters: (1) the source and timing of CO2 generation, (2) the CO2 migration pathways, (3) the timing of CO2 migration, and (4) the locations and nature of CO2 traps and seals. The following three examples are described in terms of CO2 systems: (1) the Ellenburger Fields of West Texas, (2) the Leadville Fields of the Paradox Basin, and (3) the Big Escambia Creek and Flomaton Fields of Mississippi. The USGS is applying this concept to the Indian...
Categories: Publication; Types: Citation, Conference Citation; Tags: Elsevier
We hypothesize that drought-avoidance in Gutierrezia sarothrae populations is characterized by well-developed lateral roots. Root growth and hydraulic conductance were studied in four populations of Gutierrezia sarothrae. Seedlings from a Malta, Idaho (ID) seed source had four times higher root/shoot ratio (P<0.05), but only 17% hydraulic conductance of those from Tahoka, Texas (TA) seed source. Consequently, transpiration surface area of the ID seedlings was 17% that of the TA seedlings. There was no difference in total root length between the seedlings, but hydraulic conductance per unit root length was 3.8 fold greater (P<0.05) in the TA seedlings, which was accompanied by a lower specific lateral root length...
Most models of resource competition assume that coexistence of consumers depends on tradeoffs in their abilities to exploit shared resources along dimensions of environmental heterogeneity generated by factors external to the consumers. However, consumers may create heterogeneity themselves by modifying resources that they do not immediately consume; such ?resource processing? is predicted to allow coexistence if consumers vary in use of resources in primary vs. modified form. To explore whether external food storage (caching) represents a form of resource processing that contributes to observed patterns of species coexistence, we developed a biologically explicit simulation model of competition for a well-studied...
Semiarid forests across the western USA and elsewhere are being thinned to reduce risk from fire, restore previous ecological conditions, and/or salvage trees from recently burned areas. Prescriptions and monitoring for thinning generally focus on biotic characteristics of vegetation, like tree density, rather than abiotic characteristics of soils and their loss, which are usually only considered in association with water erosion. Recent studies indicate that sediment transport by wind in forests is substantial and can exceed water transport, yet forest wind erosion responses to tree thinning and/or burning are unknown. We measured wind-driven horizontal dust flux, a metric related to wind erosion, with respect...
Experiments suggest that plants and soil microorganisms are both limited by inorganic nitrogen, even on relatively fertile sites. Consequently, plants and soil microorganisms may compete for nitrogen. While past research has focused on competition for inorganic nitrogen, recent studies have found that plants/mycorrhizae in a wide range of ecosystems can use organic nitrogen. A new view of competitive interactions between plants and soil microorganisms is necessary in ecosystems where plant uptake of organic nitrogen is observed. Published in Trends in Ecology & Evolution, volume 12, issue 4, on pages 139 - 143, in 1997.
Deep, high-pressure fluid injections induce earthquakes. Most are microearthquakes, detectable only by instrumentation (i.e., seismometers) in neighboring wells at or near the injection depth. In deep injections, we estimate that nearly 0.1% of the events can be recorded by standard earthquake seismometers at the surface, and less than 15 km from the injection well. A small percentage of the surface-recorded events can be felt by humans if the injection exceeds injection volume, injection pressure, and duration thresholds (e.g., Baisch et al., 2002). In the early 1960s, deep high-pressure injection near Denver, Colorado, induced over 1300 surface-recorded earthquakes. The largest was a magnitude M5.6 in a region...
Maintaining healthy ecosystems is a prerequisite for conserving biodiversity. The complex nature of ecosystems often necessitates the use of indicator taxa to monitor ecosystem health. However, ambiguous selection criteria and the use of inappropriate taxa have brought the utility of indicator taxa under question. This review compiles existing selection criteria from the literature, evaluates inconsistencies among these criteria, and proposes a step-wise selection process. In addition, 100 vertebrate and 32 invertebrate taxa documented in the conservation science literature as indicators of ecosystem health are examined to assess how well they adhere to the referenced criteria. Few vertebrate taxa fulfill multiple...
Deep, high-pressure fluid injections induce earthquakes. Most are microearthquakes, detectable only by instrumentation (i.e., seismometers) in neighboring wells at or near the injection depth. In deep injections, we estimate that nearly 0.1% of the events can be recorded by standard earthquake seismometers at the surface, and less than 15 km from the injection well. A small percentage of the surface-recorded events can be felt by humans if the injection exceeds injection volume, injection pressure, and duration thresholds (e.g., Baisch et al., 2002). In the early 1960s, deep high-pressure injection near Denver, Colorado, induced over 1300 surface-recorded earthquakes. The largest was a magnitude M5.6 in a region...
The leaves, litter, and soil from within a community of Artemisia tridentata ssp. vaseyana were analyzed for secondary metabolic products. Methacrolein, five monterpenes, three sesquiterpene lactones, six coumarins, and one flavonoid were identified in the leaves; the contents of the litter were nearly identical. Soils collected directly beneath the shrubs contained the three sesquiterpene lactones, two coumarins and an unknown flavonoid. The litter and water extracts of the litter inhibited the germination of sagebrush seeds. Soils charged with monoterpenes from sagebrush leaves also inhibited seed germination. In addition, the monoterpene contents from eight sagebrush taxa collected from Western Montana are reported....
Differences in rhizosphere microbial community function in response to Gutierrezia sarothrae plants grown in elevated CO2 (750 ?l 1?1) and fertilized with nitrogen were studied using the Biolog microplate analysis of sole C substrate utilization. Compared to ambient CO2, under elevated CO2, polymers were more slowly oxidized by the microbial community, amides showed no change in usage, and all other substrate groups were more rapidly utilized, although there was no significant change in the number of viable bacteria. No microbial community responses to N fertilization were detected. The results indicate that potential functional changes in the soil microbial community in response to elevated CO2 have to be taken...
Argillic horizons with reddish hues were studied in Haplargids and Argiborolls across an elevation transect. The eolian parent materials were deposited in two, or more episodes. The younger deposit, late Wisconsinan, was 14C dated from a buried musk ox (Symbos cavifrons) at Grass Mesa as beginning about 16,000 ybp. The late Wisconsinan soil at this site and those at lower elevations have illuviation argillans coating and bridging sand grains. Maximum clay content of the late Wisconsinan soil at Grass Mesa is 22% vs. 13% in the eolian parent material. In the bisequal Monticello pedon above Grass Mesa, the late Wisconsinan argillic horizon has common illuviation argillans in channels and voids. In higher upper parts...
Over the last century and a half, groundwaters have become contaminated by a growing number of organic and inorganic substances ranging from petroleum-derived hydrocarbons to radioactive compounds, to cancer-causing hexavalent chromium. The importance of uncontaminated groundwater for agriculture, human consumption, and the environmental health of ecosystems is paramount to the health and productivity of industrial society. Water scientists and managers are focused on developing cost-effective methods to reverse this trend. Several methodologies have been developed, however few are as cost-effective as the use of readily available materials, such as iron and organic compost, for absorbing and isolating contaminants...
Categories: Publication; Types: Book Citation, Citation; Tags: Elsevier
We hypothesise that genotypic differences in transpiration and root growth in the southern and northern populations of Gutierrezia sarothrae are driven by growing season vapour pressure deficit (VPD) and that ecotypic differentiations are linked to corresponding variations in tissue and leaf water relations. Seedlings from an Idaho (ID) and a Texas (TX) seed source were grown either in an open nursery (full sunlight) or under shade. There were no population differences in transpiration, root growth and tissue water relation parameters when the plants were grown under the shade. However, significant population differences were observed in the plants grown in the open where VPD was substantially higher. Transpiration...
Pressure-volume analyses were done on a half-shrub broom snakeweed (Gutierrezia sarothrae) subjected to different soil water regimes under pot- and field-grown conditions. Under pot and field conditions, water deficit decreased water and osmotic potentials. In the severely droughted pot-grown, osmotic potential at full turgor (?100) decreased by 0.44 MPa due to reduced symplastic volume, the result of a decreased leaf turgid to dry weight (TW/DW) ratio. A reduction of 0.86 MPa in ?100 was observed in the field-grown plants subjected to the first drought cycle, but increased cell wall elasticity occurred in the second drought cycle. The lowered ?100 was attributed to osmotic adjustment and reduced symplastic volume....
Rivers of North America is an important reference for scientists, ecologists, and students studying rivers and their ecosystems. It brings together information from several regional specialists on the major river basins of North America, presented in a large-format, full-color book. The introduction covers general aspects of geology, hydrology, ecology and human impacts on rivers. This is followed by 22 chapters on the major river basins. Each chapter begins with a full-page color photograph and includes several additional photographs within the text. These chapters feature three to five rivers of the basin/region, and cover several other rivers with one-page summaries. Rivers selected for coverage include the largest,...
The hydrography of the shallow (<30 m) Upper Gulf of California was mapped during a rare Colorado River fresh water discharge, which occurred during March and April, 1993. This provided (a) an opportunity to observe what may have been the hydrographic conditions before the damming of the river, and (b) a data base that can be used to calibrate numerical models with a view to simulating those conditions for ecological applications. In opposition to the now normal inverse estuarine situation, salinity and density decreased toward the head. Dilution was detectable in a coastal band flowing to the right-hand side of the river discharge, up to some 70 km from the river mouth. Tidal mixing maintained vertical homogeneity...
Argillic horizons with reddish hues were studied in Haplargids and Argiborolls across an elevation transect. The eolian parent materials were deposited in two, or more episodes. The younger deposit, late Wisconsinan, was 14C dated from a buried musk ox (Symbos cavifrons) at Grass Mesa as beginning about 16,000 ybp. The late Wisconsinan soil at this site and those at lower elevations have illuviation argillans coating and bridging sand grains. Maximum clay content of the late Wisconsinan soil at Grass Mesa is 22% vs. 13% in the eolian parent material. In the bisequal Monticello pedon above Grass Mesa, the late Wisconsinan argillic horizon has common illuviation argillans in channels and voids. In higher upper parts...
Elevated selenium concentrations documented in water, sediment, and biota in irrigation drain water studies by U.S. Department of the Interior agencies and academia have raised concerns that selenium may be adversely affecting endangered fish in the upper Colorado River basin. The objective of the study was to determine the effects on endangered razorback sucker (Xyrauchen texanus) larvae from exposure to selenium and other trace elements in water and zooplankton collected from sites adjacent to the Colorado River near Grand Junction, CO. A 30-day study was initiated with 5-day-old larvae exposed in a 4�4 factor experiment with four food and four water treatments, and the biological endpoints measured were survival,...
Black-tailed prairie dogs (Cynomys ludovicianus) increasingly compete for available habitat with human development in the Colorado Front Range. Because the effects of increased urbanization on prairie dog colonies are unknown, we studied how landscape context affects prairie dog density in Boulder County, Colorado, USA. We used burrow density as a proxy for prairie dog density because these variables were correlated at our study sites (r=0.60). Using remotely sensed data and a GIS, we quantified percent urbanization, road density, and the percentage of other prairie dog colonies in the surrounding landscape at 200, 1000, and 2000 m from the perimeter of 22 prairie dog colonies, and compared burrow density with each...
In this study we present a technique to discriminate between climate or human-induced dryland degradation, based on evaluations of AVHRR NDVI data and rainfall data. Since dryland areas typically have high inter-annual rainfall variations and rainfall has a dominant role in determining vegetation growth, minor biomass trends imposed by human influences are difficult to verify. By performing many linear regression calculations between different periods of accumulated precipitation and the annual NDVImax, we identify the rainfall period that is best related to the NDVImax and by this the proportion of biomass triggered by rainfall. Positive or negative deviations in biomass from this relationship, expressed in the...
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