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At least 271 records · Page 15Linked to original sources
USGS2001

Moss and lichen cover mapping at local and regional scales in the boreal forest ecosystem of central Canada

Mosses and lichens are important components of boreal landscapes [Vitt et al., 1994; Bubier et al., 1997]. They affect plant productivity and belowground carbon sequestration and alter the surface runoff and energy balance. We report the use of multiresolution satellite data to map moss and lichens over the BOREAS region at a 10 m, 30 m, and 1 km scales. Our moss and lichen classification at the 10 m scale is based on ground observations of associations among soil drainage classes, overstory composition, and cover type among four broad classes of ground cover (feather, sphagnum, and brown mosses and lichens). For our 30 m map, we used field observations of ground cover-overstory associations to map mosses and lichens in the BOREAS southern study area (SSA). To scale up to a 1 km (AVHRR) moss map of the BOREAS region, we used the TM SSA mosaics plus regional field data to identify AVHRR overstory-ground cover associations. We found that: 1) ground cover, overstory composition and density are highly correlated, permitting inference of moss and lichen cover from satellite-based land cover classifications; 2) our 1 km moss map reveals that mosses dominate the boreal landscape of central Canada, thereby a significant factor for water, energy, and carbon modeling; 3) TM and AVHRR moss cover maps are comparable; 4) satellite data resolution is important; particularly in detecting the smaller wetland features, lakes, and upland jack pine sites; and 5) distinct regional patterns of moss and lichen cover correspond to latitudinal and elevational gradients. Copyright 2001 by the American Geophysical Union.

Journal of Geophysical Research D: Atmospheres↗
USGS2013

Roost selection by western long-eared myotis (Myotis evotis) in burned and unburned piñon–juniper woodlands of southwestern Colorado

All 16 species of bats known to occur in western Colorado are found at Mesa Verde National Park (MVNP) in the southwestern United States. Since 1996, wildfires have burned more than 70% of MVNP (> 15,000 ha), potentially altering food and roosting resources for bats. During the summers of 2006–2007, we investigated roost use by reproductive female western long-eared myotis ( Myotis evotis ). We located 33 bat roosts in rock crevices and 1 in a juniper snag. All but 2 of the roosts were in unburned habitat. Bats roosted alone or in small groups (≤3 individuals) and switched roosts frequently (1–7 roosts per bat, median = 1.5 roosts per bat, SE = 0.5 roosts per bat). We compared occupied roosts with randomly selected unoccupied crevices and used an information theoretic approach to determine which variables were most important in determining roost use at microhabitat and landscape scales. At the microhabitat scale, maternity roosts were higher above the ground and deeper than random, unoccupied rock crevices. At the landscape scale, roosts were closer to water and farther from burned habitat than random crevices, providing reproductive female M. evotis with the best opportunities to drink and forage for insects. Tree roosts are apparently not a vital resource for reproductive female M. evotis during the summer months at our study site, presumably because of the extensive availability of rock crevices. Understanding site-specific roosting behavior is important for proper management of bat populations because differences can exist between geographic regions, even among areas with similar plant communities.

Colorado↗
USGS2003

Effects of water level, shade and time on germination and growth of freshwater marsh plants along a simulated successional gradient

1. We examined the effect of soil organic content (1.4, 3.6, 7.2% soil C), water level (+2, -1, -4 cm from soil surface) and duration (13 or 33 days) on 10 species that varied in abundance during succession in freshwater marshes. We also determined the effect of shade (0, 40, 80% shade) and soil organic content (1.4 and 7.2% soil C) on germination of six species over 62 days with water 0.5 cm below the soil surface. 2. Water level consistently affected species germination on both dates. Above-ground biomass was generally higher with increasing organic content of soil, but shade had little effect on germination or height. 3 The hydrologic zone in which species were found in the field was a good indicator of the response of germination to hydrology. Both early successional species and species wide-spread across the successional gradient show similar germination on all organic contents, while later successional species appear to germinate best at higher organic contents. 4. Successional changes in soils are capable of affecting plant community development, independent of disturbance.

Journal of Ecology↗
USGS1975

The distribution of seepage within lakebeds

The mutual exchange of water between lakes and contiguous permeable ground-water bodies, which are thin relative to the diameter of the lakes, was modeled digitally. A significant rate of seepage was found to extend only a relatively short distance from shore, thus forming a narrow band around the lake's perimeter. This near-shore concentration of seepage is an effect only of the geometry of the ground-water flow system, which is governed by the geometry of the body of permeable material, the spatial distribution of permeability within it, and the form of the water table. Near-shore seepage occurs independently of the presence of fine-grained, lowpermeability sedimentary bottom materials in the central part of the lake. Digital modeling indicates that the velocity of seepage generally decreases at an exponential rate as a function of distance from shore. Field measurements of seepage rates through the bottom of Lake Sallie, west-central Minnesota, confirm the model results by demonstrating that both the near-shore seepage band and the exponential decrease in seepage velocity actually exist.

Minnesota, Wisconsin↗
USGS1976

Use of thermal-infrared imagery in ground-water investigations, northwestern Montana

Thermal-infrared imagery was used to locate ground-water inflow along a 50-mile (80-kilometre) reach of the Kootenai River and Lake Koocanusa and a 55-mi (88-km) reach of the Clark Fork of the Columbia River in northwestern Montana and northeastern Idaho. The imagery confirmed that measured streamflow gains below Noxon Rapids Dam, ranging from 1,000 to 2,500 cubic feet per second (28 to 71 cubic metres per second), resulted from inflow of ground water, which was about 2.5° Celsius warmer than surface water. The thermal scanner (8.5-11 micrometres) used in May 1972 and March 1973 was mounted in a twin-engined aircraft. On the March 1973 flight, the data were recorded in an analog format on magnetic tape in flight, later were converted to digital format, and then were computer processed using an assignment of patterns to indicate differences in water temperature. Thus, subtle temperature differences are much easier to identify than they are oh conventional film-negative displays. The output data from the image-processing program can be converted to temperature maps having an isotherm spacing of 0.5°C.

Montana↗
USGS1994

The travel-time ellipse: An approximate zone of transport

A zone of transport for a well is defined as the area in the horizontal plane bounded by a contour of equal ground-water travel time to the well. For short distances and ground-water travel times near a well, the potentiometric surface may be simulated analytically as that for a fully penetrating well in a uniform flow field. The zone of transport for this configuration is nearly elliptical. A simple method is derived to calculate a travel-time ellipse that approximates the zone of transport for a well in a uniform flow field. The travel-time ellipse was nearly congruent with the exact solution for the theoretical zone of transport for ground-water travel times of at least 10 years and for aquifer property values appropriate for southeastern Minnesota. For distances and travel times approaching infinity, however, the ellipse becomes slightly wider at its midpoint and narrower near its upgradient boundary than the theoretical zone of transport. The travel-time ellipse also may be used to simulate the plume area surrounding an injection well. However, the travel-time ellipse is an approximation that does not account for the effect of dispersion in enlarging the true area of an injection plume or zone of transport; hence, caution is advised in the use and interpretation of this simple construction.

Journal of Hydrology↗
USGS1972

Lake Erie: Effects of exploitation, environmental changes and new species on the fishery resources

In no other lake as large as Lake Erie (surface area, 25,690 km 2 ) have such extensive changes taken place in the drainage basin, the lake environment, and the fish populations over the last 100 years. Deforestation and prairie burning led to erosion and siltation of valuable spawning grounds. Marsh spawning areas were drained. Lake-to-river spawning migrations were blocked by mill dams. Accelerated cultural nutrient loading increased total dissolved solids by nearly 50% (1920-70). Average summer water temperatures increased 1.1 C. Phytoplankton and zooplankton abundance increased severalfold. Severe oxygen depletion developed in the bottom waters of all three basins of the lake. Lake sturgeon were fished out as nuisance fish in the late 1800s. The commercial fisheries for lake trout, lake whitefish, and lake herring collapsed by 1940 and those for blue pike and walleye by 1960. Yellow perch production became unstable in the 1960s. The effects of exploitation, environmental changes, and new species on these fish populations are discussed.

Lake Erie↗
USGS1996

Chloride mass-balance method for estimating ground water recharge in arid areas: Examples from western Saudi Arabia

The chloride mass-balance method, which integrates time and aerial distribution of ground water recharge, was applied to small alluvial aquifers in the wadi systems of the Asir and Hijaz mountains in western Saudi Arabia. This application is an extension of the method shown to be suitable for estimating recharge in regional aquifers in semi-arid areas. Because the method integrates recharge in time and space it appears to be, with certain assumptions, particularly well suited for and areas with large temporal and spatial variation in recharge. In general, recharge was found to be between 3 to 4% of precipitation - a range consistent with recharge rates found in other arid and semi-arid areas of the earth.

Asir mountains, Hijaz mountains↗
USGS1973

An accurate Invar-wire extensometer

Stevens Type F water-level recorders have been modified to measure changes in the distance between two points, with amplification of up to 10 times. Such recorders are capable of measuring strains of 10 -5 and possibly 10 -6 over 10-m distances when corrections are made for frictional effects and temperature. In two field experiments, one on Kilauea Volcano in Hawaii, and the other on the San Andreas fault in central California, measurements by the recorders agree well with those by several different methods for the same episodes of ground deformation. Equipment for the entire system costs about $300 and requires 1 to 2 man-days for installation.

Journal of Research of the U.S. Geological Survey↗
USGS1973

Hydraulic sand-model studies of miscible-fluid flow

Hydraulic sand models are useful physical tools in the investigation of the transition zone that occurs between salt and fresh ground water in coastal aquifers. Such models are used to demonstrate the effects of transport mechanisms that influence the dynamic behavior and the shape of the transition zone. The techniques employed in obtaining in-place measurements of solute concentrations are generally the stumbling block in generating data for two-dimensional dispersion systems. Two in-place measurement techniques were used in the studies described: (1) conductivity probes when salt was used as a tracer; and (2) photoelectric cells when organic dye was used as a tracer. Results indicate that conductivity methods are more reliable; however, care must be exercised inasmuch as the probes tend to disturb the fluid flow.

Journal of Research of the U.S. Geological Survey↗
USGS2013

The transboundary non-renewable Nubian Aquifer System of Chad, Egypt, Libya and Sudan: Classical groundwater questions and parsimonious hydrogeologic analysis and modeling

Parsimonious groundwater modeling provides insight into hydrogeologic functioning of the Nubian Aquifer System (NAS), the world’s largest non-renewable groundwater system (belonging to Chad, Egypt, Libya, and Sudan). Classical groundwater-resource issues exist (magnitude and lateral extent of drawdown near pumping centers) with joint international management questions regarding transboundary drawdown. Much of NAS is thick, containing a large volume of high-quality groundwater, but receives insignificant recharge, so water-resource availability is time-limited. Informative aquifer data are lacking regarding large-scale response, providing only local-scale information near pumps. Proxy data provide primary underpinning for understanding regional response: Holocene water-table decline from the previous pluvial period, after thousands of years, results in current oasis/sabkha locations where the water table still intersects the ground. Depletion is found to be controlled by two regional parameters, hydraulic diffusivity and vertical anisotropy of permeability. Secondary data that provide insight are drawdowns near pumps and isotope-groundwater ages (million-year-old groundwaters in Egypt). The resultant strong simply structured three-dimensional model representation captures the essence of NAS regional groundwater-flow behavior. Model forecasts inform resource management that transboundary drawdown will likely be minimal—a nonissue—whereas drawdown within pumping centers may become excessive, requiring alternative extraction schemes; correspondingly, significant water-table drawdown may occur in pumping centers co-located with oases, causing oasis loss and environmental impacts.

Hydrogeology Journal↗
USGS1982

Uraniferous opal, Virgin Valley, Nevada: Conditions of formation and implications for uranium exploration

Uraniferous, fluorescent opal, which occurs in tuffaceous sedimentary rocks at Virgin Valley, Nevada, records the temperature and composition of uranium-rich solutions as well as the time of uranium-silica coprecipitation. Results are integrated with previous geologic and geochronologic data for the area to produce a model for uranium mobility that may be used to explore for uranium deposits in similar geologic settings. Uraniferous opal occurs as replacements of diatomite, or silicic air-fall ash layers in tuffaceous lakebeds of the Virgin Valley Formation (Miocene) of Merriam (1907). Fission-track radiography shows uranium to be homogeneously dispersed throughout the opal structure, suggesting coprecipitation of dissolved uranium and silica gel. Fluid inclusions preserved within opal replacements of diatomite have homogenization temperatures in the epithermal range and are of low salinity. Four samples of opal from one locality all have U-Pb apparent ages which suggest uraniferous opal precipitation in late Pliocene time. These ages correspond to a period of local, normal faulting, and highangle faults may have served as vertical conduits for transport of deep, thermalized ground water to shallower levels. Lateral migration of rising solutions occurred at intersections of faults with permeable strata. Silica and some uranium were dissolved from silica-rich host strata of 5–20 ppm original uranium content and reprecipitated as the solutions cooled. The model predicts that in similar geologic settings, ore-grade concentrations of uranium will occur in permeable strata that intersect high-angle faults and that contain uranium source rocks as well as efficient reductant traps for uranium. In the absence of sufficient quantities of reductant materials, uranium will be flushed from the system or will accumulate in low-grade disseminated hosts such as uraniferous opal.

Nevada↗
USGS2009

Flood effects on an Alaskan stream restoration project: the value of long-term monitoring

On a nationwide basis, few stream restoration projects have long-term programs in place to monitor the effects of floods on channel and floodplain configuration and floodplain vegetation, but long-term and event-based monitoring is required to measure the effects of these stochastic events and to use the knowledge for adaptive management and the design of future projects. This paper describes a long-term monitoring effort (15 years) on a stream restoration project in Glen Creek in Denali National Park and Preserve in Alaska. The stream channel and floodplain of Glen Creek had been severely degraded over a period of 80 years by placer mining for gold, which left many reaches with unstable and incised streambeds without functioning vegetated floodplains. The objectives of the original project, initiated in 1991, were to develop and test methods for the hydraulic design of channel and floodplain morphology and for floodplain stabilization and riparian habitat recovery, and to conduct research and monitoring to provide information for future projects in similar degraded watersheds. Monitoring methods included surveyed stream cross-sections, vegetation plots, and aerial, ground, and satellite photos. In this paper we address the immediate and outlying effects of a 25-year flood on the stream and floodplain geometry and riparian vegetation. The long-term monitoring revealed that significant channel widening occurred following the flood, likely caused by excessive upstream sediment loading and the fairly slow development of floodplain vegetation in this climate. Our results illustrated design flaws, particularly in regard to identification and analysis of sediment sources and the dominant processes of channel adjustment.

Alaska↗
USGS2005

Effects of iron on arsenic speciation and redox chemistry in acid mine water

Concern about arsenic is increasing throughout the world, including areas of the United States. Elevated levels of arsenic above current drinking-water regulations in ground and surface water can be the result of purely natural phenomena, but often are due to anthropogenic activities, such as mining and agriculture. The current study correlates arsenic speciation in acid mine drainage and mining-influenced water with the important water-chemistry properties Eh, pH, and iron(III) concentration. The results show that arsenic speciation is generally in equilibrium with iron chemistry in low pH AMD, which is often not the case in other natural-water matrices. High pH mine waters and groundwater do not always hold to the redox predictions as well as low pH AMD samples. The oxidation and precipitation of oxyhydroxides deplete iron from some systems, and also affect arsenite and arsenate concentrations through sorption processes. ?? 2004 Elsevier B.V. All rights reserved.

Journal of Geochemical Exploration↗
USGS1995

Anomalous gold, antimony, arsenic, and tungsten in ground water and alluvium around disseminated gold deposits along the Getchell Trend, Humboldt County, Nevada

Ground-water, alluvium, and bedrock samples were collected from drill holes near the Chimney Creek, Preble, Summer Camp, and Rabbit Creek disseminated gold deposits in northern Nevada to determine if Au and ore-related metals, such as As, Sb, and W, are being hydromorphically mobilized from buried mineralized rock, and, if they are, to determine whether the metal-enriched ground water is reacting with the alluvial material to produce a geochemical anomaly within the overburden. Results of chemical analyses of drill-hole water samples show the presence of hydromorphic dispersion anomalies of Au, As, Sb, and W in the local ground-water systems associated with these deposits. Background concentrations for Au in the ground water up-gradient from the buried deposits was less than 1 nanogram per liter (ng/L), near the deposits the Au values ranged from 1 to 140 ng/ L, and in drill holes penetrating mineralized rock, concentrations of Au in the ground water were as high as 4700 ng/L. Highest concentrations of Au were found in ground-water samples where the measured E h and the distribution of arsenic species, arsenite [As(III)] and arsenate [As(V)], indicated oxidizing redox potentials. Similarly, As, Sb, and W concentrations in the ground water near the deposits were significantly enriched relative to concentrations in the ground water up-gradient from the deposits. In general, however, the highest concentrations of As, Sb, and W occurred in ground-water samples where the measured E h and the distribution of arsenic species indicated reducing conditions. Arsenic concentrations ranged from 9 to 710 micrograms per liter (μg/L); Sb, from less than 0.1 to 250 μg/L; and W, from 1 to 260 μg/L. In addition, analysis of sequential dissolution and extraction solutions of drill cuttings of alluvium and bedrock indicate geochemical anomalies of gold and ore-related metals in the overburden at depths corresponding to the location of the present-day water table. This relationship suggests that water-rock reactions around these buried deposits are active and that this information could be very useful in exploration programs for concealed disseminated gold deposits.

Journal of Geochemical Exploration↗
USGS2005

Successional trends in Sonoran Desert abandoned agricultural fields in northern Mexico

Excessive ground-water use and saline intrusion to the aquifer led, in less than three decades, to an increase in abandoned agricultural fields at La Costa de Hermosillo, within the Sonoran Desert. Using a chronosequence from years since abandonment, patterns of field succession were developed. Contrary to most desert literature, species replacement was found, both in fields with and without saline intrusion. Seasonal photosynthetic capacity as well as water and nitrogen use efficiencies were different in dominant early and late successional plant species. These ecological findings provided a framework for a general explanation of species dominance and replacement within abandoned agricultural fields in the Sonoran Desert. ?? 2004 Elsevier Ltd. All rights reserved.

Journal of Arid Environments↗
USGS2006

A rainfall loading response recorded at 300 meters depth: Implications for geological weighing lysimeters

Static pore water pressures in confined aquifers vary in response to ground surface loading changes, including precipitation and evaporation. Under certain hydrogeological conditions such aquifers can function as giant natural weighing lysimeters, referenced here as 'geological weighing lysimeters'. The extent of the land area 'weighed' increases with aquifer depth and it is of interest to establish at what depth it is still possible to monitor surface water budgets. An 86 mm rainfall event produced a clear loading signal in a well in western Kansas at 300 m depth. The loading effect is quantitatively consistent with elastic deformation induced by the rainfall mass and suggests that geological weighing lysimeters could operate at considerably greater depths, thereby monitoring water budgets over a significant land area. ?? 2005 Elsevier Ltd All rights reserved.

Journal of Hydrology↗
USGS1996

Hydrologic impact of Great Flood of 1993 in south-central Kansas

The writers analyze the hydrologic budget and quantify the ground-water recharge impact of the Great Flood of 1993 on the Great Bend Prairie aquifer of south-central Kansas. During the summer of 1993, rainfall totals exceeded normal levels by 200% in the northern portion of the study area, while air temperature and evapotranspiration were below normal levels. This extreme event provided the opportunity to revisit previously developed recharge-estimation algorithms. Average ground-water recharge for 1993 at four index sites was estimated at 178 mm using the hybrid water-fluctuation method of Sophocleous. Employing the recharge-estimation multiple-regression methodology of Sophocleous for the area, the writers estimated the 1993 recharge to be 145 mm. Both estimates are higher than the maximum annual recharge observed at the index sites during the 1985–1992 period. A January–July 1993 hydrologic balance analysis resulted in 130 mm of recharge. The recharge caused by the flood was three to more than four times the average annual recharge of the previous eight years. The regression-based recharge-estimation methodology proved to be generally reliable, even under extreme conditions.

Journal of Irrigation and Drainage Engineering↗