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At least 1,423 records · Page 79Linked to original sources
USGS1998

Relation of usage to the occurrence of cotton and rice herbicides in three streams of the Mississippi delta

During the 1995 growing season water samples were collected from three streams in the Mississippi delta and were analyzed for selected cotton and rice herbicides and metabolites. The purpose of the study was to relate the use of these herbicides to their occurrence in streams of the delta, to describe how the geochemistry of these herbicides affects their occurrence, and to report the occurrence of selected metabolites. The total concentration of eight herbicides and their metabolites exceeded 5 μg/L throughout most of the growing season with a median total of 15 μg/L. The order of occurrence was molinate > fluometuron > cyanazine > metolachlor > norflurazon > atrazine > prometryn > propanil. The distribution and duration of the total herbicide concentration found in this study are much different from that found in regional studies of herbicides in the U.S. Midwest. In the Midwest, the total herbicide concentration in surface water showed a sharp peak during the spring immediately after application of herbicides to crops, followed by a gradual decrease. In the Mississippi delta, the total herbicide concentration in surface water was more sustained, with multiple peaks due to different application times and postemergent applications to cotton and rice.

Environmental Science & Technology↗
USGS1998

Peat characteristics and groundwater geochemistry of calcareous fens in the Minnesota River Basin, U.S.A

Calcareous fens in Minnesota are spring-seepage peatlands with adistinctive flora of rare calciphilic species. Peat characteristics andgroundwater geochemistry were determined for six calcareous fens in theMinnesota River Basin to better understand the physical structure andchemical processes associated with stands of rare vegetation. Onset of peataccumulation in three of the fens ranged from about 4,700 to 11,000 14 C yrs BP and probably resulted from acombination of climate change and local hydrogeologic conditions. Most peatcores had a carbonate-bearing surface zone with greater than 10%carbonates (average 27%, dry wt basis), an underlyingcarbonate-depleted zone with 10% or less carbonates (average4%), and a carbonate-bearing lower zone again with greater than10% carbonates (average 42%). This carbonate zonation washypothesized to result from the effect of water-table level on carbonateequilibria: carbonate precipitation occurs when the water table is above acritical level, and carbonate dissolution occurs when the water table islower. Other processes that changed the major ion concentrations inupwelling groundwater include dilution by rain water, sulfate reduction orsulfide oxidation, and ion adsorption or exchange. Geochemical modelingindicated that average shallow water in the calcareous fens during the studyperiod was groundwater mixed with about 6 to 13% rain water.Carbonate precipitation in the surface zone of calcareous fens could bedecreased by a number of human activities, especially those that lower thewater table. Such changes in shallow water geochemistry could alter thegrowing conditions that apparently sustain rare fen vegetation.

Minnesota↗
USGS2002

Environmentalism and natural aggregate mining

Sustaining a developed economy and expanding a developing one require the use of large volumes of natural aggregate. Almost all human activity (commercial, recreational, or leisure) is transacted in or on facilities constructed from natural aggregate. In our urban and suburban worlds, we are almost totally dependent on supplies of water collected behind dams and transported through aqueducts made from concrete. Natural aggregate is essential to the facilities that produce energy—hydroelectric dams and coal-fired powerplants. Ironically, the utility created for mankind by the use of natural aggregate is rarely compared favorably with the environmental impacts of mining it. Instead, the empty quarries and pits are seen as large negative environmental consequences. At the root of this disassociation is the philosophy of environmentalism, which flavors our perceptions of the excavation, processing, and distribution of natural aggregate. The two end-member ideas in this philosophy are ecocentrism and anthropocentrism. Ecocentrism takes the position that the natural world is a organism whose arteries are the rivers—their flow must not be altered. The soil is another vital organ and must not be covered with concrete and asphalt. The motto of the ecocentrist is “man must live more lightly on the land.” The anthropocentrist wants clean water and air and an uncluttered landscape for human use. Mining is allowed and even encouraged, but dust and noise from quarry and pit operations must be minimized. The large volume of truck traffic is viewed as a real menace to human life and should be regulated and isolated. The environmental problems that the producers of natural aggregate (crushed stone and sand and gravel) face today are mostly difficult social and political concerns associated with the large holes dug in the ground and the large volume of heavy truck traffic associated with quarry and pit operations. These concerns have increased in recent years as society's demand for living space has encroached on the sites of production; in other words, the act of production has engendered condemnation. Many other environmental problems that are associated with dust and noise and blasting from quarry and pit operations have been reduced through the efficient use of technology. Recycling concrete in buildings, bridges, and roads and asphaltic pavements will ultimately reduce the demand for virgin natural aggregate. The impact created by the large holes in the ground required for the mining of natural aggregate can be greatly reduced by planning their reclamation before mining begins.

Natural Resources Research↗
USGS2002

Mexican native trouts: A review of their history and current systematic and conservation status

While biologists have been aware of the existence of native Mexican trouts for over a century, they have received little study. The few early studies that did much more than mention their existence began in the 1930s and continued into the early 1960s, focusing primarily on distributional surveys and taxonomic analyses. Starting in the 1980s the Baja California rainbow trout became the subject of more detailed studies, but very little remains known of mainland trouts of the Sierra Madre Occidental. We review earlier studies and report on our own collections and observations made between 1975 and 2000. We present newly discovered historical evidence that leads us to conclude that a "lost" cutthroat trout, a lineage not previously known from Mexico, was collected more than a century ago from headwaters of the Ri??o Conchos (a major tributary of the Rio Grande (= Ri??o Bravo)), a basin not previously considered to harbor a native trout. We review the last century of regional natural resource management and discuss our own observations of trout habitats. Impacts of logging, road building and overgrazing are widespread and expanding. Many streams suffer from heavy erosion, siltation and contamination, and though long-term hydrologic data are generally not available, there is evidence of decreased discharge in many streams. These problems appear related to region-wide land management practices as well as recent regional drought. Trout culture operations using exotic rainbow trout have rapidly proliferated throughout the region, threatening genetic introgression and/or competition with native forms and predation on them. Knowledge of distribution, abundance, relationships and taxonomy, not to mention ecology and population biology, of native trouts of the Sierra Madre Occidental remains inadequate. Vast areas of most mainland drainages are still unexplored by fish collectors, and even rudimentary information regarding basic biology, ecology and population structure of stocks remains lacking. Concentrated exploration, research and management of this long overlooked and undervalued resource are all urgently needed. The history of natural resources exploitation that placed so many native trouts of the western United States on threatened and endangered species lists is repeating itself in the Sierra Madre Occidental. Without concentrated action and development of region-wide socio-economic solutions for current, largely non-sustainable resource management practices, native Mexican trout gene pools will soon be in grave danger of extinction.

Reviews in Fish Biology and Fisheries↗
USGS2004

Urbanization impacts on the structure and function of forested wetlands

The exponential increase in population has fueled a significant demographic shift: 60% of the Earth's population will live in urban areas by 2030. While this population growth is significant in its magnitude, the ecological footprint of natural resource consumption and use required to sustain urban populations is even greater. The land use and cover changes accompanying urbanization (increasing human habitation coupled with resource consumption and extensive landscape modification) impacts natural ecosystems at multiple spatial scales. Because they generally occupy lower landscape positions and are linked to other ecosystems through hydrologic connections, the cascading effects of habitat alteration on watershed hydrology and nutrient cycling are particularly detrimental to wetland ecosystems. I reviewed literature relevant to these effects of urbanization on the structure and function of forested wetlands. Hydrologic changes caused by habitat fragmentation generally reduce species richness and abundance of plants, macroinvertebrates, amphibians, and birds with greater numbers of invasives and exotics. Reduction in soil saturation and lowered water tables result in greater nitrogen mineralization and nitrification in urban wetlands with higher probability of NO − 3 export from the watershed. Depressional forested wetlands in urban areas can function as important sinks for sediments, nutrients, and metals. As urban ecosystems become the predominant human condition, there is a critical need for data specific to urban forested wetlands in order to better understand the role of these ecosystems on the landscape.

Urban Ecosystems↗
USGS1999

Coupling groundwater and riparian vegetation models to assess effects of reservoir releases

Although riparian areas in the arid southwestern United States are critical for maintaining species diversity, their extent and health have been declining since Euro‐American settlement. The purpose of this study was to develop a methodology to evaluate the potential for riparian vegetation restoration and groundwater recharge. A numerical groundwater flow model was coupled with a conceptual riparian vegetation model to predict hydrologic conditions favorable to maintaining riparian vegetation downstream of a reservoir. A Geographic Information System (GIS) was used for this one‐way coupling. Constant and seasonally varying releases from the dam were simulated using volumes anticipated to be permitted by a regional water supplier. Simulations indicated that seasonally variable releases would produce surface flow 5.4–8.5 km below the dam in a previously dry reach. Using depth to groundwater simulations from the numerical flow model with conceptual models of depths to water necessary for maintenance of riparian vegetation, the GIS analysis predicted a 5‐ to 6.5‐fold increase in the area capable of sustaining riparian vegetation.

Water Resources Research↗
USGS2001

Rapid fluid disruption: A source for self-potential anomalies on volcanoes

Self-potential (SP) anomalies observed above suspected magma reservoirs, dikes, etc., on various volcanoes (Kilauea, Hawaii; Mount Unzen, Japan; Piton de la Fournaise, Reunion Island, Miyake Jima, Japan) result from transient surface electric fields of tens of millivolts per kilometer and generally have a positive polarity. These SP anomalies are usually attributed to electrokinetic effects where properties controlling this process are poorly constrained. We propose an alternate explanation that contributions to electric fields of correct polarity should be expected from charge generation by fluid vaporization/disruption. As liquids are vaporized or removed as droplets by gas transport away from hot dike intrusions, both charge generation and local increase in electrical resistivity by removal of fluids should occur. We report laboratory observations of electric fields in hot rock samples generated by pulses of fluid (water) through the rock at atmospheric pressure. These indicate the relative amplitudes of rapid fluid disruption (RFD) potentials and electrokinetic potentials to be dramatically different and the signals are opposite in sign. Above vaporization temperatures, RFD effects of positive sign in the direction of gas flow dominate, whereas below these temperatures, effects of negative sign dominate. This suggests that the primary contribution to observed self-potential anomalies arises from gas-related charge transport processes at temperatures high enough to produce vigorous boiling and vapor transport. At lower temperatures, the primary contribution is from electrokinetic effects modulated perhaps by changing electrical resistivity and RFD effects from high-pressure but low-temperature CO2 and SO2 gas flow ripping water molecules from saturated crustal rocks. If charge generation is continuous, as could well occur above a newly emplaced dike, positive static potentials will be set up that could be sustained for many years, and the simplest method for identifying these hot, active regions would be to identify the SP anomalies they generate.

Hawai'i↗
USGS2002

Fire dynamics and implications for nitrogen cycling in boreal forests

We used a dynamic, long-term mass balance approach to track cumulative carbon (C) and nitrogen (N) losses to fire in boreal Manitoba over the 6500 years since deglaciation. Estimated C losses to decomposition and fire, combined with measurements of N pools in mature and burned forest floors, suggest that loss of N by combustion has likely resulted in a long-term loss that exceeds the amount of N stored in soil today by 2 to 3 times. These estimates imply that biological N fixation rates could be as high as 5 to 10 times atmospheric deposition rates in boreal regions. At the site scale, the amount of N lost is due to N content of fuels, which varies by stand type and fire severity, which in turn vary with climate and fire dynamics. The interplay of fire frequency, fire severity, and N partitioning during regrowth are important for understanding rates and sustainability of nutrient and carbon cycling over millenia and over broad regions.

Manitoba↗
USGS2003

Editorial

In our 3 years serving as editors, we have learned to our delight that Water Resources Research is truly the journal of the hydrologic community. Many individuals have expressed to us their sense of ownership of the journal and their passion for the sustained excellence of the journal. This is extremely healthy as it leads to productive discussions in which varying points of view are put forward, all for the purpose of making the journal better. The community decides the future of its journal. For WRR to be strong the community must be engaged, committed, and willing to discuss matters in a way that will enhance the journal. At this time, there are a number of challenges that face Water Resources Research . These are challenges for each member of the hydrologic community to consider.

Water Resources Research↗
USGS2005

Response of seismicity to Coulomb stress triggers and shadows of the 1999 Mw=7.6 Chi-Chi, Taiwan, earthquake

The correlation between static Coulomb stress increases and aftershocks has thus far provided the strongest evidence that stress changes promote seismicity, a correlation that the Chi-Chi earthquake well exhibits. Several studies have deepened the argument by resolving stress changes on aftershock focal mechanisms, which removes the assumption that the aftershocks are optimally oriented for failure. Here one compares the percentage of planes on which failure is promoted after the main shock relative to the percentage beforehand. For Chi-Chi we find a 28% increase for thrust and an 18% increase for strike-slip mechanisms, commensurate with increases reported for other large main shocks. However, perhaps the chief criticism of static stress triggering is the difficulty in observing predicted seismicity rate decreases in the stress shadows, or sites of Coulomb stress decrease. Detection of sustained drops in seismicity rate demands a long catalog with a low magnitude of completeness and a high seismicity rate, conditions that are met at Chi-Chi. We find four lobes with statistically significant seismicity rate declines of 40-90% for 50 months, and they coincide with the stress shadows calculated for strike-slip faults, the dominant faulting mechanism. The rate drops are evident in uniform cell calculations, 100-month time series, and by visual inspection of the M ??? 3 seismicity. An additional reason why detection of such declines has proven so rare emerges from this study: there is a widespread increase in seismicity rate during the first 3 months after Chi-Chi, and perhaps many other main shocks, that might be associated with a different mechanism. Copyright 2005 by the American Geophysical Union.

Journal of Geophysical Research B: Solid Earth↗
USGS2006

Hurricanes, submarine groundwater discharge, and Florida's red tides

A Karenia brevis Harmful Algal Bloom affected coastal waters shallower than 50 m off west-central Florida from January 2005 through January 2006, showing a sustained anomaly of ???1 mg chlorophyll m-3 over an area of up to 67,500 km2. Red tides occur in the same area (approximately 26-29??N, 82-83??W) almost every year, but the intense 2005 bloom led to a widespread hypoxic zone (dissolved oxygen <2 mg L-1) that caused mortalities of benthic communities, fish, turtles, birds, and marine mammals. Runoff alone provided insufficient nitrogen to support this bloom. We pose the hypothesis that submarine groundwater discharge (SGD) provides the missing nutrients, and indeed can trigger and support the recurrent red tides off west-central Florida. SGD inputs of dissolved inorganic nitrogen (DIN) in Tampa Bay alone are ???35% of that discharged by all central Florida rivers draining west combined. We propose that the unusual number of hurricanes in 2004 resulted in high runoff, and in higher than normal SGD emerging along the west Florida coast throughout 2005, initiating and fueling the persistent HAB. This mechanism may also explain recurrent red tides in other coastal regions of the Gulf of Mexico. Copyright 2006 by the American Geophysical Union.

Geophysical Research Letters↗
USGS2007

Geochemical evidence for African dust inputs to soils of western Atlantic islands: Barbados, the Bahamas, and Florida

We studied soils on high-purity limestones of Quaternary age on the western Atlantic Ocean islands of Barbados, the Florida Keys, and the Bahamas. Potential soil parent materials in this region, external to the carbonate substrate, include volcanic ash from the island of St. Vincent (near Barbados), volcanic ash from the islands of Dominica and St. Lucia (somewhat farther from Barbados), the fine-grained component of distal loess from the lower Mississippi River Valley, and wind-transported dust from Africa. These four parent materials can be differentiated using trace elements (Sc, Cr, Th, and Zr) and rare earth elements that have minimal mobility in the soil-forming environment. Barbados soils have compositions that indicate a complex derivation. Volcanic ash from the island of St. Vincent appears to have been the most important influence, but African dust is a significant contributor, and even Mississippi River valley loess may be a very minor contributor to Barbados soils. Soils on the Florida Keys and islands in the Bahamas appear to have developed mostly from African dust, but Mississippi River valley loess may be a significant contributor. Our results indicate that inputs of African dust are more important to the genesis of soils on islands in the western Atlantic Ocean than previously supposed. We hypothesize that African dust may also be a major contributor to soils on other islands of the Caribbean and to soils in northern South America, central America, Mexico, and the southeastern United States. Dust inputs to subtropical and tropical soils in this region increase both nutrient-holding capacity and nutrient status and thus may be critical in sustaining vegetation. Copyright 2007 by the American Geophysical Union.

Journal of Geophysical Research F: Earth Surface↗
USGS2006

Local infrasound observations of large ash explosions at Augustine Volcano, Alaska, during January 11–28, 2006

We present and interpret acoustic waveforms associated with a sequence of large explosion events that occurred during the initial stages of the 2006 eruption of Augustine Volcano, Alaska. During January 11–28, 2006, 13 large explosion events created ash-rich plumes that reached up to 14 km a.s.l., and generated atmospheric pressure waves that were recorded on scale by a microphone located at a distance of 3.2 km from the active vent. The variety of recorded waveforms included sharp N-shaped waves with durations of a few seconds, impulsive signals followed by complex codas, and extended signals with emergent character and durations up to minutes. Peak amplitudes varied between 14 and 105 Pa; inferred acoustic energies ranged between 2×10 8 and 4×10 9 J. A simple N-shaped short-duration signal recorded on January 11, 2006 was associated with the vent-opening blast that marked the beginning of the explosive eruption sequence. During the following days, waveforms with impulsive onsets and extended codas accompanied the eruptive activity, which was characterized by explosion events that generated large ash clouds and pyroclastic flows along the flanks of the volcano. Continuous acoustic waveforms that lacked a clear onset were more common during this period. On January 28, 2006, the occurrence of four large explosion events marked the end of this explosive eruption phase at Augustine Volcano. After a transitional period of about two days, characterized by many small discrete bursts, the eruption changed into a stage of more sustained and less explosive activity accompanied by the renewed growth of a summit lava dome.

Alaska↗
USGS2008

Constraining fault constitutive behavior with slip and stress heterogeneity

We study how enforcing self-consistency in the statistical properties of the preshear and postshear stress on a fault can be used to constrain fault constitutive behavior beyond that required to produce a desired spatial and temporal evolution of slip in a single event. We explore features of rupture dynamics that (1) lead to slip heterogeneity in earthquake ruptures and (2) maintain these conditions following rupture, so that the stress field is compatible with the generation of aftershocks and facilitates heterogeneous slip in subsequent events. Our three-dimensional fmite element simulations of magnitude 7 events on a vertical, planar strike-slip fault show that the conditions that lead to slip heterogeneity remain in place after large events when the dynamic stress drop (initial shear stress) and breakdown work (fracture energy) are spatially heterogeneous. In these models the breakdown work is on the order of MJ/m2, which is comparable to the radiated energy. These conditions producing slip heterogeneity also tend to produce narrower slip pulses independent of a slip rate dependence in the fault constitutive model. An alternative mechanism for generating these confined slip pulses appears to be fault constitutive models that have a stronger rate dependence, which also makes them difficult to implement in numerical models. We hypothesize that self-consistent ruptures could also be produced by very narrow slip pulses propagating in a self-sustaining heterogeneous stress field with breakdown work comparable to fracture energy estimates of kJ/M2. Copyright 2008 by the American Geophysical Union.

Journal of Geophysical Research B: Solid Earth↗
USGS2007

Water use regimes: Characterizing direct human interaction with hydrologic systems

The sustainability of human water use practices is a rapidly growing concern in the United States and around the world. To better characterize direct human interaction with hydrologic systems (stream basins and aquifers), we introduce the concept of the water use regime. Unlike scalar indicators of anthropogenic hydrologic stress in the literature, the water use regime is a two‐dimensional, vector indicator that can be depicted on simple x‐y plots of normalized human withdrawals ( h out ) versus normalized human return flows ( h in ). Four end‐member regimes, natural‐flow‐dominated (undeveloped), human‐flow‐dominated (churned), withdrawal‐dominated (depleted), and return‐flow‐dominated (surcharged), are defined in relation to limiting values of h out and h in . For illustration, the water use regimes of 19 diverse hydrologic systems are plotted and interpreted. Several of these systems, including the Yellow River Basin, China, and the California Central Valley Aquifer, are shown to approach particular end‐member regimes. Spatial and temporal regime variations, both seasonal and long‐term, are depicted. Practical issues of data availability and regime uncertainty are addressed in relation to the statistical properties of the ratio estimators h out and h in . The water use regime is shown to be a useful tool for comparative water resources assessment and for describing both historic and alternative future pathways of water resource development at a range of scales.

Water Resources Research↗
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↗
USGS2007

Mount St. Helens Petrology Workshop

Following seismic activity in late September 2004, the current eruption of Mount St. Helens began with an explosive steam and ash emission on 1 October 2004, with hot dacite emerging from the crater floor on 11 October 2004. Nearly two years later, with more than 80 million cubic meters of erupted dacite, accompanied by rare explosions and predominantly shallow seismicity questions still remain about what initiated and what is sustaining the eruption. The U.S. Geological Survey's (USGS) Cascade Volcano Observatory (CVO) hosted the 2006 Mount St. Helens Petrology Workshop in Vancouver, Wash., on 27–30 August 2006. With many of the more than 40 workshop participants finalizing contributions to a USGS Professional Paper on the current Mount St. Helens eruption, the workshop was a timely opportunity to share results, reconcile interpretations, and plan future research.

Washington↗
USGS2007

Warming may create substantial water supply shortages in the Colorado River basin

The high demand for water, the recent multiyear drought (1999-2007), and projections of global warming have raised questions about the long-term sustainability of water supply in the southwestern United States. In this study, the potential effects of specific levels of atmospheric warming on water-year streamflow in the Colorado River basin are evaluated using a water-balance model, and the results are analyzed within the context of a multi-century tree-ring reconstruction (1490-1998) of streamflow for the basin. The results indicate that if future warming occurs in the basin and is not accompanied by increased precipitation, then the basin is likely to experience periods of water supply shortages more severe than those inferred from the longterm historical tree-ring reconstruction. Furthermore, the modeling results suggest that future warming would increase the likelihood of failure to meet the water allocation requirements of the Colorado River Compact.

Geophysical Research Letters↗