Geology Reports⌕ Search

SEARCH · Geology Reports

Results for “Nature”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,333 records · Page 74Linked to original sources
USGS2002

Analysis and detection of the herbicides dimethenamid and flufenacet and their sulfonic and oxanilic acid degradates in natural water

Dimethenamid [2-chloro-N-(2,4-dimethyl-3-thienyl)-N-(2-methoxy-1-methylethyl)acetamide] and flufenacet [N-(4-fluorophenyl)-N-(1-methylethyl)-2-(5-(trifluoromethyl)-1,3,4- thiadiazol-2-yl)oxy] were isolated by C-18 solid-phase extraction and separated from their ethanesulfonic acid (ESA) and oxanilic acid (OXA) degradates during their elution using ethyl acetate for the parent compound, followed by methanol for the polar degradates. The parent compounds were detected using gas chromatography-mass spectrometry in selected-ion mode. The ESA and OXA degradates were detected using high-performance liquid chromatography-electrospray mass spectrometry (HPLC-ESPMS) in negative-ion mode. The method detection limits for a 123-mL sample ranged from 0.01 to 0.07 μg/L. These methods are compatible with existing methods and thus allow for analysis of 17 commonly used herbicides and 18 of their degradation compounds with one extraction. In a study of herbicide transport near the mouth of the Mississippi River during 1999 and 2000, dimethenamid and its ESA and OXA degradates were detected in surface water samples during the annual spring flushes. For flufenacet, the only detections at the study site were for the ESA degradates in samples collected at the peak of the herbicide spring flush in 2000. The low frequency of detections in surface water likely is due to dimethenamid and flufenacet being relatively new herbicides. In addition, detectable amounts of the stable degradates have not been detected in ground water.

Journal of Agricultural and Food Chemistry↗
USGS2001

Representation of natural vegetation in protected areas: Capturing the geographic range

Current conservation strategies for plant and animal species rarely address the need to protect the species throughout its geographic range thereby capturing potential genetic and ecological variation. We examined the degree that existing protected areas in the western United States satisfied this goal for four widespread vegetation cover types. We used latitude and longitude to stratify the distribution of these types into 16 cells, each of which was further stratified by up to five elevation classes. While protection of some vegetation types was high in parts of their range, it was minimal to nonexistent in other parts. While it is yet to be shown that protecting a given species throughout its geographic range is essential for its long-term existence, in the face of often unpredictable environmental changes, it seems a prudent course to follow. Our results suggest that if full range protection is a conservation goal, the existing network of protected areas may be inadequate for the task.

Biodiversity and Conservation↗
USGS2002

Use of natural 35 S to trace sulphate cycling in small lakes, Flattops Wilderness Area, Colorado, U.S.A.

Measurements of the cosmogenically-produced 35 S, a radioisotope of sulphur (t 1/2 = 87 days), are reported for the Ned Wilson Lake watershed in Colorado. The watershed contains two small lakes and a flowing spring presumed to be representative of local ground water. The watershed is located in the Flattops Wilderness Area and the waters in the system have low alkalinity, making them sensitive to increases in acid and sulphate deposition. Time series of 35 S measurements were made during the summers of 1995 and 1996 (July–September) at all three sites. The system is dominated by melting snow and an initial concentration of 16–20 mBq L -1 was estimated for snowmelt based on a series of snow samples collected in the Rocky Mountains. The two lakes had large initial 35 S concentrations in July, indicating that a large fraction of the lake water and sulphate was introduced by meltwater from that year's snowpack. In 1995 and 1996, 35 S concentrations decreased more rapidly than could be accounted for by decay, indicating that other processes were affecting 35 S concentrations. The most likely explanation is that exchange with sediments or the biota was removing 35 S from the lake and replacing it with older sulphate devoid of 35 S. In September of 1995 and 1996, 35 S concentrations increased, suggesting that atmospheric deposition is important in the sulphate flux of these lakes in late summer. Sulphur-35 concentrations in the spring water were highly variable but never higher than 3.6 mBq L -1 and averaged 2 mBq L -1 . Using a simple mixing model, it was estimated that 75% of the spring water was derived from precipitation of previous years.

Water, Air, and Soil Pollution: Focus↗
USGS2006

Natural attenuation strategy for groundwater cleanup focuses on demonstrating cause and effect

In the 20 years since cleanup of contaminated groundwater has been a high priority in the United States, recognition of both the scope of the problem and the technical difficulties involved has grown steadily. Estimates of the number of hazardous waste sites where groundwater may be contaminated vary between 300,000 and 400,000 nationwide [NRC, 1994]. Legislation passed in the 1980s by Congress and the states generally required that groundwater in contaminated aquifers be restored to background or drinking water standards. Unfortunately, attempts to meet these goals using conventional methods, such as pump and treat systems, frequently have been unsuccessful [NRC, 1994].

Eos, Transactions, American Geophysical Union↗
USGS1999

Formation of natural gas hydrates in marine sediments 1. Conceptual model of gas hydrate growth conditioned by host sediment properties

The stability of submarine gas hydrates is largely dictated by pressure and temperature, gas composition, and pore water salinity. However, the physical properties and surface chemistry of deep marine sediments may also affect the thermodynamic state, growth kinetics, spatial distributions, and growth forms of clathrates. Our conceptual model presumes that gas hydrate behaves in a way analogous to ice in a freezing soil. Hydrate growth is inhibited within fine-grained sediments by a combination of reduced pore water activity in the vicinity of hydrophilic mineral surfaces, and the excess internal energy of small crystals confined in pores. The excess energy can be thought of as a "capillary pressure" in the hydrate crystal, related to the pore size distribution and the state of stress in the sediment framework. The base of gas hydrate stability in a sequence of fine sediments is predicted by our model to occur at a lower temperature (nearer to the seabed) than would be calculated from bulk thermodynamic equilibrium. Capillary effects or a build up of salt in the system can expand the phase boundary between hydrate and free gas into a divariant field extending over a finite depth range dictated by total methane content and pore-size distribution. Hysteresis between the temperatures of crystallization and dissociation of the clathrate is also predicted. Growth forms commonly observed in hydrate samples recovered from marine sediments (nodules, and lenses in muds; cements in sands) can largely be explained by capillary effects, but kinetics of nucleation and growth are also important. The formation of concentrated gas hydrates in a partially closed system with respect to material transport, or where gas can flush through the system, may lead to water depletion in the host sediment. This "freeze-drying" may be detectable through physical changes to the sediment (low water content and overconsolidation) and/or chemical anomalies in the pore waters and metastable presence of free gas within the normal zone of hydrate stability.

Journal of Geophysical Research B: Solid Earth↗
USGS2000

Colorado River sediment transport: 1. Natural sediment supply limitation and the influence of Glen Canyon Dam

Analyses of flow, sediment‐transport, bed‐topographic, and sedimentologic data suggest that before the closure of Glen Canyon Dam in 1963, the Colorado River in Marble and Grand Canyons was annually supply‐limited with respect to fine sediment (i.e., sand and finer material). Furthermore, these analyses suggest that the predam river in Glen Canyon was not supply‐limited to the same degree and that the degree of annual supply limitation increased near the head of Marble Canyon. The predam Colorado River in Grand Canyon displays evidence of four effects of supply limitation: (1) seasonal hysteresis in sediment concentration, (2) seasonal hysteresis in sediment grain size coupled to the seasonal hysteresis in sediment concentration, (3) production of inversely graded flood deposits, and (4∥ development or modification of a lag between the time of a flood peak and the time of either maximum or minimum (depending on reach geometry) bed elevation. Analyses of sediment budgets provide additional support for the interpretation that the predam river was annually supply‐limited with respect to fine sediment, but it was not supply‐limited with respect to fine sediment during all seasons. In the average predam year, sand would accumulate and be stored in Marble Canyon and upper Grand Canyon for 9 months of the year (from July through March) when flows were dominantly below 200–300 m 3 /s; this stored sand was then eroded during April through June when flows were typically higher. After closure of Glen Canyon Dam, because of the large magnitudes of the uncertainties in the sediment budget, no season of substantial sand accumulation is evident. Because most flows in the postdam river exceed 200–300 m 3 /s, substantial sand accumulation in the postdam river is unlikely.

Colorado River, Glen Canyon Dam↗
USGS2001

The roughness of natural terrain: A planetary and remote sensing perspective

We examine the various methods and parameters in common use for quantifying and reporting surface topographic "roughness." It is shown that scale-dependent roughness parameters are almost always required, though not widely used. We suggest a method of standardizing the parameters that are computed and reported so that topographic data gathered by different workers using different field techniques can be directly and easily intercompared. We illustrate the proposed method by analyzing topographic data from 60 different surfaces gathered by five different groups and examine the information for common features. We briefly discuss the implications of our analysis for studies of planetary surface roughness, lander safety, and radar remote sensing modeling and analysis.

Journal of Geophysical Research E: Planets↗
USGS2000

Unsaturated‐zone wedge beneath a large, natural lake

Lake Belle Taine (480 ha) in north central Minnesota receives on average 76,000 m 3 d −1 of water from Little Sand Creek but has no outlet. Water seeps out of the lake, flows through glacial outwash, and discharges into three nearby lakes with stages 13–14 m lower than Belle Taine. Seepage‐meter data indicate water is seeping out of Belle Taine at velocities up to 263 cm d −1 . Hydraulic‐head measurements made in the lake bed indicate the sediments are unsaturated beneath a portion of the lake edge, and a wedge of unsaturated sediments extends beneath the lake bed as much as 20 m from the shoreline. At the shoreline the water table is as much as 6.7 m below the lake surface. Modeling results of a similar hypothetical setting indicate that the horizontal extent of an unsaturated zone beneath a lake depends on (1) the permeability contrast between the outwash and the lake bed, (2) anisotropy, (3) lake bed slope, and (4) thickness of the lower‐permeability lake bed sediments. Although rarely documented, unsaturated sediments beneath a lake may not be extremely uncommon. Similar, much smaller unsaturated‐zone areas also have been observed beneath two other lakes in Minnesota.

Minnesota↗
USGS2006

Nature and characteristics of the flows that carved the Simud and Tiu outflow channels, Mars

Geomorphic and topographic relations of higher and lower levels of dissection within the Simud and Tiu Valles outflow channels on Mars reveal new insights into their formational histories. We find that the water floods that carved the higher channel floors were primarily sourced from Hydaspis Chaos. The floods apparently branched into distributaries downstream that promoted rapid freezing and sublimation of water and limited discharge into the lowlands. In contrast, we suggest that the lower outflow channels were carved by debris flows from Hydraotes Chaos. Surges within individual debris flows possessed variable volatile contents and led to the deposition of smooth deposits marked by low relief longitudinal ridges. Lower outflow channel discharges resulted in widespread deposition within the Simud/Tiu Valles as well as within the northern plains of Mars. Copyright 2006 by the American Geophysical Union.

Geophysical Research Letters↗
USGS2006

Nature and origin of the hematite-bearing plains of Terra Meridiani based on analyses of orbital and Mars Exploration rover data sets

The ∼5 km of traverses and observations completed by the Opportunity rover from Endurance crater to the Fruitbasket outcrop show that the Meridiani plains consist of sulfate‐rich sedimentary rocks that are largely covered by poorly‐sorted basaltic aeolian sands and a lag of granule‐sized hematitic concretions. Orbital reflectance spectra obtained by Mars Express OMEGA over this region are dominated by pyroxene, plagioclase feldspar, crystalline hematite (i.e., concretions), and nano‐phase iron oxide dust signatures, consistent with Pancam and Mini‐TES observations. Mössbauer Spectrometer observations indicate more olivine than observed with the other instruments, consistent with preferential optical obscuration of olivine features in mixtures with pyroxene and dust. Orbital data covering bright plains located several kilometers to the south of the landing site expose a smaller areal abundance of hematite, more dust, and a larger areal extent of outcrop compared to plains proximal to the landing site. Low‐albedo, low‐thermal‐inertia, windswept plains located several hundred kilometers to the south of the landing site are predicted from OMEGA data to have more hematite and fine‐grained olivine grains exposed as compared to the landing site. Low calcium pyroxene dominates spectral signatures from the cratered highlands to the south of Opportunity. A regional‐scale model is presented for the formation of the plains explored by Opportunity, based on a rising ground water table late in the Noachian Era that trapped and altered local materials and aeolian basaltic sands. Cessation of this aqueous process led to dominance of aeolian processes and formation of the current configuration of the plains.

Journal of Geophysical Research E: Planets↗
USGS2007

Global impacts of conversions from natural to agricultural ecosystems on water resources: Quantity versus quality

Past land use changes have greatly impacted global water resources, with often opposing effects on water quantity and quality. Increases in rain‐fed cropland (460%) and pastureland (560%) during the past 300 years from forest and grasslands decreased evapotranspiration and increased recharge (two orders of magnitude) and streamflow (one order of magnitude). However, increased water quantity degraded water quality by mobilization of salts, salinization caused by shallow water tables, and fertilizer leaching into underlying aquifers that discharge to streams. Since the 1950s, irrigated agriculture has expanded globally by 174%, accounting for ∼90% of global freshwater consumption. Irrigation based on surface water reduced streamflow and raised water tables resulting in waterlogging in many areas (China, India, and United States). Marked increases in groundwater‐fed irrigation in the last few decades in these areas has lowered water tables (≤1 m/yr) and reduced streamflow. Degradation of water quality in irrigated areas has resulted from processes similar to those in rain‐fed agriculture: salt mobilization, salinization in waterlogged areas, and fertilizer leaching. Strategies for remediating water resource problems related to agriculture often have opposing effects on water quantity and quality. Long time lags (decades to centuries) between land use changes and system response (e.g., recharge, streamflow, and water quality), particularly in semiarid regions, mean that the full impact of land use changes has not been realized in many areas and remediation to reverse impacts will also take a long time. Future land use changes should consider potential impacts on water resources, particularly trade‐offs between water, salt, and nutrient balances, to develop sustainable water resources to meet human and ecosystem needs.

Water Resources Research↗
USGS2009

Nature versus nurture: functional assessment of restoration effects on wetland services using Nuclear Magnetic Resonance Spectroscopy

Land-use change has altered the ability of wetlands to provide vital services such as nutrient retention. While compensatory practices attempt to restore degraded wetlands and their functions, it is difficult to evaluate the recovery of soil biogeochemical functions that are critical for restoration of ecosystem services. Using solution 31 P Nuclear Magnetic Resonance Spectroscopy, we examined the chemical forms of phosphorus (P) in soils from wetlands located across a land-use gradient. We report that soil P diversity, a functional attribute, was lowest in farmland, and greatest in native wetlands. Soil P diversity increased with age of restoration, indicating restoration of biogeochemical function. The trend in soil P diversity was similar to documented trends in soil bacterial taxonomic composition but opposite that of soil bacterial diversity at our study sites. These findings provide insights into links between ecosystem structure and function and provide a tool for evaluating the success of ecosystem restoration efforts. Copyright 2009 by the American Geophysical Union.

Geophysical Research Letters↗
USGS2009

Morphologic and transport properties of natural organic floc

The morphology, entrainment, and settling of suspended aggregates (“floc”) significantly impact fluxes of organic carbon, nutrients, and contaminants in aquatic environments. However, transport properties of highly organic floc remain poorly understood. In this study detrital floc was collected in the Florida Everglades from two sites with different abundances of periphyton for use in a settling column and in racetrack flume entrainment experiments. Although Everglades flocs are similar to other organic aggregates in terms of morphology and settling rates, they tend to be larger and more porous than typical mineral flocs because of biostabilization processes and relatively low prevailing shear stresses typical of wetlands. Flume experiments documented that Everglades floc was entrained at a low bed shear stress of 1.0 × 10 −2 Pa, which is considerably smaller than the typical entrainment threshold of mineral floc. Because of similarities between Everglades floc and other organic floc populations, floc transport characteristics in the Everglades typify the behavior of floc in other organic‐rich shallow‐water environments. Highly organic floc is more mobile than less organic floc, but because bed shear stresses in wetlands are commonly near the entrainment threshold, wetland floc dynamics are often transport‐limited rather than supply limited. Organic floc transport in these environments is therefore governed by the balance between entrainment and settling fluxes, which has implications for ecosystem metabolism, materials cycling, and even landscape evolution.

Water Resources Research↗