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At least 1,009 records · Page 56Linked to original sources

USGS1992

Mid-Mesozoic (Mid-Jurassic to Early Cretaceous) evolution of the Georges Bank Basin, U.S. North Atlantic outer continental shelf: Sedimentology of the Conoco 145-1 well

The Conoco 145-1 exploratory well, located in the southeastern portion of the Georges Bank Basin, was drilled to a total depth of 4303 m below the sea floor. The oldest sedimentary rocks sampled are of Middle Jurassic age (Late Bathonian-Callovian). A dolomite-limestone-evaporite sequence dominates the section below 3917 m; limestone is the predominant lithology in the intervals of 3271-3774 m, 2274-3158 m, and 1548-1981 m. Siliciclastics dominate the remainder of the drilled section. Calcite tightly cements most of the rocks below 1548 m; dolomite, silica, siderite, and diagenetic clay cements are locally important. Restricted inner marine environments, representing lagoonal and tidal flat conditions, prevailed at the wellsite during much of the deposition recorded by the Callovian-Bathonian age Iroquois Formation. These environments gave way to a carbonate platform, which formed part of the > 5,000 km long Bahama-Grand Banks gigaplatform that lasted through the end of the Late Jurassic (encompassing the uppermost portion of the Iroquois Formation and the Scatarie Limestone and Bacarro Limestone Members of the Abenaki Formation). The absence of a skeletal-reef association and the dominance of muddy limestone fabrics are evidence that the 145-1 wellsite was located on the platform interior. Major periods of siticiclastic deposition interrupted carbonate deposition, and they are recorded by stratigraphic equivalents of the Mohican Formation, Misaine Shale Member of the Abenaki Formation, and the Mohawk and Mic Mac Formations. A series of sustained prograding delta systems, the earliest of which is preserved as the Missisauga Formation, buried the carbonate platform following its drowning in the Early Cretaceous (Berriasian-Valanginian). The sparser, primarily allochthonous lignite content and better-sorted, glauconite-bearing sands of the Missisauga strata at the 145-1 wellsite suggest that shallow marine or barrier-bar environments were more prevalent than the low delta-plain facies recorded farther shoreward at the COST G-1 wellsite.

Sedimentary Geology↗

USGS1975

Vertical crustal movements preceding and accompanying the San Fernando earthquake of February 9, 1971: A summary

Comparative elevations referred chiefly to a tidal bench mark with a history of relatively positive movement show that much of the Transverse Ranges of southern California sustained major changes in elevation both before and in association with the M L 6.4 San Fernando earthquake of February 9, 1971. Preseismic changes in elevation in the southern Transverse Ranges were almost uniformly positive and generally episodic. Maximum uplift measured between 1960/61 and 1968/69 was 0.205 m (observed) or 0.200 m (adjusted); it occurred about 30 km northeast of the 1971 epicenter. As much as 0.129 m (observed) of preseismic uplift was also measured about 30 km northwest of the epicenter between 1964 and 1968. A comparison between 1968 and 1969 elevation data revealed 0.078 m (observed) of differential uplift centered about 10 km west of the epicenter; earlier leveling indicates that this uplift began between February 1967 and May 1968. Changes in elevation measured during the interval 1968/69-71 (postearthquake) are interpreted as chiefly coseismic and were concentrated along a 15-km ruptured segment of the east-trending, north-dipping San Fernando fault. These changes were characterized by subsidence of as much as 0.111 m (observed) or 0.092 m (adjusted) south of the fault and a ridge of uplift of up to at least 2.195 m (observed) or 2.196 m (adjusted) immediately north of the fault. The more episodic preseismic movements are interpretable as deep-seated creep events on the San Fernando fault. Alternatively, these episodic movements may be due partly to the operation of dilatancy; the onset of the 196849 epicentral uplift accords closely with the initiation of a V p / V s anomaly recognized in this same area. The 1968/69-71 elevation changes can be attributed almost entirely to slip on the San Fernando fault.

California↗

USGS1985

Rock mechanics observations pertinent to the rheology of the continental lithosphere and the localization of strain along shear zones

Emphasized in this paper are the deformation processes and rheologies of rocks at high temperatures and high effective pressures, conditions that are presumably appropriate to the lower crust and upper mantle in continental collision zones. Much recent progress has been made in understanding the flexure of the oceanic lithosphere using rock-mechanics-based yield criteria for the inelastic deformations at the top and base. At mid-plate depths, stresses are likely to be supported elastically because bending strains and elastic stresses are low. The collisional tectonic regime, however, is far more complex because very large permanent strains are sustained at mid-plate depths and this requires us to include the broad transition between brittle and ductile flow. Moreover, important changes in the ductile flow mechanisms occur at the intermediate temperatures found at mid-plate depths. Two specific contributions of laboratory rock rheology research are considered in this paper. First, the high-temperature steady-state flow mechanisms and rheology of mafic and ultramafic rocks are reviewed with special emphasis on olivine and crystalline rocks. Rock strength decreases very markedly with increases in temperature and it is the onset of flow by high temperature ductile mechanisms that defines the base of the lithosphere. The thickness of the continental lithosphere can therefore be defined by the depth to a particular isotherm Tc above which (at geologic strain rates) the high-temperature ductile strength falls below some arbitrary strength isobar (e.g., 100 MPa). For olivine Tc is about 700??-800??C but for other crustal silicates, Tc may be as low as 400??-600??C, suggesting that substantial decoupling may take place within thick continental crust and that strength may increase with depth at the Moho, as suggested by a number of workers on independent grounds. Put another way, the Moho is a rheological discontinuity. A second class of laboratory observations pertains to the general phenomenon of ductile faulting in which ductile strains are localized into shear zones. Ductile faults have been produced in experiments of five different rock types and is generally expressed as strain softening in constant-strain-rate tests or as an accelerating-creep-rate stage at constant differential stress. A number of physical mechanisms have been identified that may be responsible for ductile faulting, including the onset of dynamic recrystallization, phase changes, hydrothermal alteration and hydrolytic weakening. Microscopic evidence for these processes as well as larger-scale geological and geophysical observations suggest that ductile faulting in the middle to lower crust and upper mantle may greatly influence the distribution and magnitudes of differential stresses and the style of deformation in the overlying upper continental lithosphere.

Tectonophysics↗

USGS1985

Stratigraphic and interregional changes in Pennsylvanian coal-swamp vegetation: Environmental inferences

Quantitative analysis of Pennsylvanian coal-swamp vegetation provides a means of inferring organization and structure of communities. Distribution of these communities further provides inferences about environmental factors, including paleoclimate. Our observations are based on in situ, structurally preserved peat deposits in coal-ball concretions from 32 coal seams in the eastern one-half of the United States and from several seams in western Europe and on spore assemblages from more than 150 seams. There were three times of particularly significant and nearly synchronous vegetational changes in the Midcontinent and Appalachian coal regions during the Pennsylvanian Period. Each was different in kind and magnitude. The first marked changes occurred during the early part of the Middle Pennsylvanian with the fluctuating decline in the high level of lycopod dominance. The abundance of cordaites increased. There was a rise in the occurrences of the lycopod herbs to form intercalated marshlands and an overall increase in floral diversity. Changes ensuing from this time also include shifts in dominant species of lycopod trees and a sustained rise in abundance and diversity of tree-fern spores. The next significant time of change was during the middle part of the Middle Pennsylvanian, representing both a culmination of earlier trends and expansions of cordaites in the Midcontinent where there was a maximum change in species without net loss of diversity. Tree ferns and medullosan pteridosperms attained subdominant levels of abundance and diverse lycopod species dominated except in the Atokan-Desmoinesian transition of the Midcontinent. The third and sharpest break occurred near the Middle—Late Pennsylvanian boundary when extinctionsof the dominant, coal-swamp lycopods allowed development of tree-fern dominance. The Late Pennsylvanian coal swamps apparently were colonized or recolonized mainly by species from outside coal swamps rather than by the survivor populations of the Middle Pennsylvanian swamps. Paralleling the changes in floras through the Pennsylvanian are changes in preservational aspects of the peat. These include a decline in shoot/root ratios from approximately 1 to < 1 during the first time of vegetational changes and a rise in this ratio during the second; there was a parallel rise and fall in fusain abundance and a rise in wood/periderm ratios. The stratigraphic distribution of identified coal resources in the United States is interpreted as largely dependent on net changes in relative wetness of Pennsylvanian coal swamps, a pattern of drying during the first period of vegetational change, followed by a concomitant increase in continuous wet climate with brackish influence in the Midcontinent during the second; this was followed by a time of extreme moisture stress bringing on the third, and most severe, vegetational change.

International Journal of Coal Geology↗

USGS1993

Modeling steady-state methanogenic degradation of phenols in groundwater

Field and microcosm observations of methanogenic phenolic compound degradation indicate that Monod kinetics governs the substrate disappearance but overestimates the observed biomass. In this paper we present modeling results from an ongoing multidisciplinary study of methanogenic biodegradation of phenolic compounds in a sand and gravel aquifer contaminated by chemicals and wastes used in wood treatment. Field disappearance rates of four phenols match those determined in batch microcosm studies previously performed by E.M. Godsy and coworkers. The degradation process appears to be at steady-state because even after a sustained influx over several decades, the contaminants still are disappearing in transport downgradient. The existence of a steady-state degradation profile of each substrate together with a low biomass density in the aquifer indicate that the bacteria population is exhibiting no net growth. This may be due to the oligotrophic nature of the biomass population in which utilization and growth are approximately independent of concentration for most of the concentration range. Thus a constant growth rate should exist over much of the contaminated area which may in turn be balanced by an unusually high decay or maintenance rate due to hostile conditions or predation.

Journal of Contaminant Hydrology↗

USGS1991

Pliocene-climate history of the western United States derived from lacustrine ostracodes

Pliocene sediments from several sites in western North America contain ostracodes indicating deposition in lacustrine and wetland settings. The ostracodes offer a means of reconstructing the aquatic paleoenvironment. Because water temperature, chemistry, and lake volume are coupled to climate, reconstruction of these parameters provides a direct insight into Pliocene climate. The site ages were determined from tephrochronology, paleomagnetics, and associated mammals. The morphology of many ostracode species also provides direct information about the paleoenvironment in which they lived. During the Pliocene (about 3.5-2.5 Ma) some species have unusually ornate carapace morphology indicative of large geologically stable lakes, which must have required a stable climate to sustain them. North American Pliocene climate changed from a modern-like state 4.5-3.5 Ma to a period with greater precipitation and less evaporation than today, 3.5-2.5 Ma. This wetter period, inferred from the large geologically long-lived lakes, implies a stable atmospheric circulation pattern. The stable circulation pattern collapsed around 2.5 Ma and climate returned to a modern-like situation.

western United States↗

USGS1991

Steady- and non-steady-state carbonate-silicate controls on atmospheric CO2

Two contrasting hypotheses have recently been proposed for the past long-term relation between atmospheric CO 2 and the carbonate-silicate geochemical cycle. One approach (Berner, 1990) suggests that CO 2 levels have varied in a manner that has maintained chemical weathering and carbonate sedimentation at a steady state with respect to tectonically controlled decarbonation reactions. A second approach (Raymo et al. , 1988), applied specificlly to the late Cenozoic, suggests a decrease in CO 2 caused by an uplift-induced increase in chemical weathering, without regard to the rate of decarbonation. According to the steady-state (first) hypothesis, increased weathering and carbonate sedimentation are generally associated with increasing atmospheric CO 2 , whereas the uplift (second) hypothesis implies decreasing CO 2 under the same conditions. An ocean-atmosphere-sediment model has been used to assess the response of atmospheric CO 2 and carbonate sedimentation to global perturbations in chemical weathering and decarbonation reactions. Although this assessment is theoretical and cannot yet be related to the geologic record, the model simulations compare steady-state and non-steady-state carbonate-silicate cycle response. The e-fold response time of the ‘CO 2 -weathering’ feedback mechanism is between 300 and 400 ka. The response of carbonate sedimentation is much more rapid. These response times provide a measure of the strength of steady-state assumptions, and imply that certain systematic relations are sustained throughout steady-state and non-steady-state scenarios for the carbonate-silicate cycle. The simulations suggest that feedbacks can maintain the system near a steady state, but that non-steady-state effects may contribute to long-term trends. The steady-state and uplift hypotheses are not necessarily incompatible over time scales of a few million years.

Quaternary Science Reviews↗

USGS1992

Effect of salinity on the critical nitrogen concentration of Spartina alterniflora Loisel

Nitrogen was withheld from the salt marsh grass Spartina alterniflora Loisel., in order to determine the effect of salinity (sea salts) on critical tissue nitrogen concentrations (defined here as the minimum tissue concentration required to sustain biomass accumulation). The critical nitrogen concentration per kilogram dry weight of above-ground tissue increased non-linearly from a mean of 8.2 g kg −1 at 5 g l −1 and 20 g l −1 salinity to 13.6 g kg −1 and 22.9 g kg −1 at salinities of 40 g l −1 and 50 g l −1 , respectively. Below-ground tissue nitrogen concentrations averaged 62% of the above-ground values irrespective of salinity treatment. These results suggest that the critical nitrogen concentration is a function of salinity and indicate that the internal nitrogen supply required in support of growth increases with salinity. Above-ground tissue nitrogen concentrations reported in the literature and the relationship between salinity and critical nitrogen concentration observed in this study were used to evaluate the nitrogen status of S. alterniflora over a wide range of geographical locations. Comparisons suggest that both short and tall forms of S. alterniflora are nitrogen limited in the majority of marshes along the Gulf and Atlantic Coasts of the US.

Aquatic Botany↗

USGS1983

The compositionally zoned eruption of 1912 in the Valley of Ten Thousand Smokes, Katmai National Park, Alaska

On June 6–8, 1912, ∼ 15 km 3 of magma erupted from the Novarupta caldera at the head of the Valley of Ten Thousand Smokes (VTTS), producing ∼ 20 km 3 of air-fall tephra and 11–15 km 3 of ash-flow tuff within ∼ 60 hours. Three discrete periods of ash-fall at Kodiak correlate, respectively, with Plinian tephra layers designated A, CD, and FG by Curtis (1968) in the VTTS. The ash-flow sequence overlapped with but outlasted pumice fall A, terminating within 20 hours of the initial outbreak and prior to pumice fall C. Layers E and H consist mostly of vitric dust that settled during lulls, and Layer B is the feather edge of the ash flow. The fall units filled and obscured the caldera, but arcuate and radial fissures outline a 6-km 2 depression. The Novarupta lava dome and its ejecta ring were emplaced later within the depression. At Mt. Katmai, 10 km east of the 1912 vent, a 600-m-deep caldera of similar area also collapsed at about this time, probably owing to hydraulic connection with the venting magma system; but all known ejecta are thought to have erupted at Novarupta. Mingling of three distinctive magmas during the eruption produced an abundance of banded pumice, and mechanical mixing of chilled ejecta resulted in deposits with a wide range of bulk composition. Pumice in the initial fall unit (A) is 100% rhyolite, but fall units atop the ash flow are > 98% dacite; black andesitic scoria is common only in the ash flows and in near-vent air-fall tephra. Pumice counts show the first half of the ash-flow deposit to be 91–98% rhyolite, but progressive increases of dacite and andesite eventually reduced the rhyolitic component to < 2%. The later, rhyolite-poor flows were hotter, less mobile, and widely produced partially welded tuff and vapor-indurated sillar. The main ash flow was too deflated and sluggish 16 km from the vent to surmount a 25-m-high moraine in its path but was diverted around it and continued 5 km down-valley, engulfing and charring trees but not toppling all of them. Thin ash-flow veneers feather 30–40 m up the enclosing valley walls but only where a constriction in the central VTTS locally raised the flow level. In the upper VTTS, the “high sand mark” is not a veneer but a marginal bench formed in thick tuff by differential compaction. Flooding from adjacent glaciers led to phreatic explosions that ejected blocks of tuff more welded than any yet exposed. A cluster of phreatic craters dammed a lake atop the tuff, the breaching of which caused a flood that scoured the ash-flow surface in the central VTTS, transported 50-cm blocks of welded tuff > 20 km to the lowermost VTTS, and deposited 1–8 m of debris there. Rhyolitic ejecta contain only 1–2% phenocrysts but andesite and dacite have 30–45%. Quartz is present and augite absent only in the rhyolite, but all ejecta contain plagioclase, orthopyroxene, titanomagnetite, ilmenite, apatite, and pyrrhotite; rare olivine occurs in the andesite. The zoning ranges of phenocrysts in the rhyolitic and intermediate ejecta do not overlap. New chemical data show the bulk SiO 2 range to be: rhyolite 77 ± 0.6, dacite 66-64.5, and andesite 61.5–58.5%. The dacitic and andesitic ejecta contrast in color and density, and it is not certain whether they form a compositional continuum. Analyses reported by Fenner within the 66–76% SiO 2 range were of banded pumice and lava and of bulk tephra that mechanically fractionated and mixed during flight. Despite the gap of 10% SiO 2 , Fe-Ti-oxide temperatures show a continuous range from rhyolite (805–850°C) through dacite (855–955°C) to andesite (955–990°C). Thermal continuity and isotopic and trace-element data suggest that all were derived from a single magmatic system, whether or not they were physically contiguous before eruption. If the rhyolitic liquid separated from dacitic magma, extraction was so efficient that no dacitic phenocrysts were retained and no bulk compositions in the range 66–76% SiO 2 were created; if it were a partial melt of roof rocks atop an intermediate magma body, then such rocks had no O- or Sr-isotopic contrast with the andesite-dacite magma and clearly did not include the Jurassic arkosic or granitic basement. The presence of Holocene domes of pre-1912 glassy dacite adjacent to the 1912 vent suggest that the 7 km 3 (or more) of high-silica rhyolitic magma (a composition rare in the Aleutian arc) was generated in less than a few thousand years. The 1912 vent is semi-encircled by several andesitic stratocones and is as close to Mageik, Trident, and Griggs volcanoes as it is to Mt. Katmai. The erupted magma probably occupied only shallow levels of an extensive system of injection and storage under a cluster of several stratovolcanoes. Although Quaternary basalt is not known to have erupted here, the intrusion of basaltic magma probably sustains the greater-VTTS magmatic system.

Alaska↗

USGS1996

Pliocene and early Pleistocene environments and climates of the western Snake River Plain, Idaho

Sedimentological, palynological, and magnetic susceptibility data provide paleoenvironmental and paleoclimatic information from a 989 ft (301 m) core of sediments from the upper Glenns Ferry and Bruneau Formations from near the town of Bruneau in Owyhee County, Idaho. Chronology is based on stratigraphic position, paleomagnetism, and biostratigraphic data, which collectively suggest a late Gauss Normal-Polarity Chron age for the Glenns Ferry sediments and a middle Matuyama Reversed-Polarity Chron age for the Bruneau sediments. A deep lake was present on the western Snake River Plain during the portions of the time represented by the Glenns Ferry Formation, and the mudstones of the lower half of the core were apparently deposited in this lake. The terminal regression of the Glenns Ferry lake may be represented in the Bruneau core by sandy mudstones and sands that overlie the deep-water mudstones. A cobble layer present in the core between the Glenns Ferry lake beds and those of the overlying Bruneau Formation may indicate through-flow by the ancestral Snake River. Palynological data from the Glenns Ferry sediments in the Bruneau core reveal a pollen flora similar to the modern regional pollen flora, with very rare occurrences of now-extirpated taxa common earlier in the Tertiary. Palynological data from the Pliocene portion of this core indicate conditions more moist than today, with cooler summers and perhaps warmer winters. Quasi-periodic fluctuations in coniferous pollen (primarily Pinus) versus arid steppe taxa (primarily Chenopodiaceae/ Amar-anthus ) indicate significant variations in moisture through the lower two-thirds of the Glenns Ferry portion of the core. Shorter wave-length fluctuations in magnetic susceptibility and (inversely) Artemisia may reflect variations in temperature or other unidentified climatic variables. The pollen spectra from the Bruneau Formation sediments in the Bruneau core are dominated by Artemisia and resemble those of the Wisconsinan glacial period on the Snake River Plain, and hence indicate cold and dry conditions during some portion of the early Pleistocene. The deep-water Glenns Ferry lacustrine episode appears to date between approximately 3.5 to 3.3 and 2.5 Ma, and thus occurred during the middle Pliocene period of warmer-than-modern global temperatures. Similar sustained wetter-than-present conditions occurred in the same age range at sites across the western U.S.A. from southern California and Arizona to northern California and Idaho. This moist period was apparently followed by an interval of regional arid conditions that persisted for several hundred thousand years.

Idaho↗

USGS1989

Late neogene history of the Pacific-Caribbean gateway

Planktic foraminiferal provinces of Caribbean DSDP Hole 502A and East Pacific DSDP Hole 503A have been analyzed and compared with benthic and planktic isotope records, carbonate, hiatus events, and sea level changes. Four major events are evident in the closure history of the Pacific-Caribbean gateway, at 6.2, 4.2, 2.4 and 1.8 Ma. The faunal change at 6.2 Ma coincides with the δ 13 C shift and is primarily caused by upwelling in the western Caribbean. This suggests restricted circulation of intermediate water and deflection northeastward, strengthening the Gulf Stream as reflected in the first major erosion on Blake Plateau. The second faunal change, at 4.2 Ma, coincides with increased surface water salinity evident in δ 18 O data and indicates increasingly restricted surface water exchange. Divergence of faunal provinces beginning at 2.4 Ma is marked by increasing abundance of high salinity tolerant species ( Globigerinoides ruber ) in the Caribbean. This suggests that initial closure of the Pacific-Caribbean gateway and cessation of sustained surface current flow between the Pacific and Caribbean occurred as late as 2.4 Ma. Maximum divergence of faunal provinces begins at 1.8 Ma and continues to the present. This implies that at least incipient littoral-neritic leakage occurred across the Pacific-Caribbean gateway between 2.4 and 1.8 Ma, with final closure by 1.8 Ma.

Journal of South American Earth Sciences↗

USGS1994

An integrated model of human-wildlife interdependence

This paper attempts to integrate wildlife-related ecologic and economic variables into an econometric model. The model reveals empirical evidence of the presumed interdependence of human-wildlife and the holistic nature of humanity's relationship to the ecosystem. Human use of biologic resources varies not only with income, education, and population, but also with sustainability of humankind's action relative to the quality and quantity of the supporting ecological base.

Ecological Economics↗

USGS2009

Application of models to conservation planning for terrestrial birds in North America

Partners in Flight (PIF), a public–private coalition for the conservation of land birds, has developed one of four international bird conservation plans recognized under the auspices of the North American Bird Conservation Initiative (NABCI). Partners in Flight prioritized species most in need of conservation attention and set range-wide population goals for 448 species of terrestrial birds. Partnerships are now tasked with developing spatially explicit estimates of the distribution, and abundance of priority species across large ecoregions and identifying habitat acreages needed to support populations at prescribed levels. The PIF Five Elements process of conservation design identifies five steps needed to implement all bird conservation at the ecoregional scale. Habitat assessment and landscape characterization describe the current amounts of different habitat types and summarize patch characteristics, and landscape configurations that define the ability of a landscape to sustain healthy bird populations and are a valuable first step to describing the planning area before pursuing more complex species-specific models. Spatially linked database models, landscape-scale habitat suitability models, and statistical models are viable alternatives for predicting habitat suitability or bird abundance across large planning areas to help assess conservation opportunities, design landscapes to meet population objectives, and monitor change in habitat suitability or bird numbers over time. Bird conservation in the United States is a good example of the use of models in large-scale wildlife conservation planning because of its geographic extent, focus on multiple species, involvement of multiple partners, and use of simple to complex models. We provide some background on the recent development of bird conservation initiatives in the United States and the approaches used for regional conservation assessment and planning. We focus on approaches being used for landscape characterization and assessment, and bird population response modeling.

Book chapter↗

USGS2016

Hydrologic exchange flows and their ecological consequences in river corridors

The actively flowing waters of streams and rivers remain in close contact with surrounding off-channel and subsurface environments. These hydrologic linkages between relatively fast flowing channel waters, with more slowly flowing waters off-channel and in the subsurface, are collectively referred to as hydrologic exchange flows (HEFs). HEFs include surface exchange with a channel’s marginal areas and subsurface flow through the streambed (hyporheic flow), as well as storm-driven bank storage and overbank flows onto floodplains. HEFs are important, not only for storing water and attenuating flood peaks, but also for their role in influencing water conservation, water quality improvement, and related outcomes for ecological values and services of aquatic ecosystems. Biogeochemical opportunities for chemical transformations are increased by HEFs as a result of the prolonged contact between flowing waters and geochemically and microbially active surfaces of sediments and vegetation. Chemical processing is intensified and water quality is often improved by removal of excess nutrients, metals, and organic contaminants from flowing waters. HEFs also are important regulators of organic matter decomposition, nutrient recycling, and stream metabolism that helps establish a balanced and resilient aquatic food web. The shallow and protected storage zones associated with HEFs support nursery and feeding areas for aquatic organisms that sustain aquatic biological diversity. Understanding of these varied roles for HEFs has been driven by the related disciplines of stream ecology, fluvial geomorphology, surface-water hydraulics, and groundwater hydrology. A current research emphasis is on the role that HEFs play in altered flow regimes, including restoration to achieve diverse goals, such as expanding aquatic habitats and managing dissolved and suspended river loads to reduce over-fertilization of coastal waters and offset wetland loss. New integrative concepts and models are emerging (eg, hydrologic connectivity) that emphasize HEF functions in river corridors over a wide range of spatial and temporal scales.

Book chapter↗

USGS2019

Lotic freshwater: Rivers

Ecosystems associated with rivers are intricately connected to their entire watershed. The river ecosystem includes the channel of active water flow, floodplain, and riparian and hyporheic zones. This ecosystem is shaped by interactions among the natural flow of water, sediments within the river and entering the river, and large wood regimes within the riparian zone. River integrity describes the ability of a river ecosystem to adjust to changes in these elements and through these adjustments maintain the habitat, disturbance regime, and connectivity necessary to sustain native biotic communities. Riverine food webs conceptualize the coupling between the physical environment and biotic communities and can be used to examine recovery from disturbance, variation in the structure of communities, and sources of energy that fuel metabolism within the ecosystem.

Book chapter↗

USGS2019

Conservation of temporary wetlands

Temporary wetlands are characterized by frequent drying resulting in a unique, highly specialized assemblage of often rare or specialized plant and animal species. They are found on all continents and in a variety of landscape settings. Although accurate estimates of the abundance of temporary wetlands are available in only a few countries, global estimations identify a decline in number and quality. The key environmental factors driving the structure of ecological communities in temporary wetlands are the duration, timing, frequency and predictability of the aquatic and dry phases, which varies greatly with region and hydrogeomorphic setting. Temporary wetlands have been historically neglected, but improved social awareness of the functions and values of, and increases in scientific interest, suggest that this is changing. They play an ecological role in both global cycles (i.e., CO 2 emissions) and biodiversity (in proportion to their size, they contribute disproportionately to regional and global biodiversity). Moreover, they provide valuable ecosystem services including wildlife habitat, nutrient flux to adjacent ecosystems, flood control, water filtration, and cultural services. Effective conservation of temporary wetlands requires addressing threats (i.e., inconsistent and inadequate regulatory protections; climate change; changes in land use) and management challenges (i.e., management at both local and landscape scales; incomplete understanding of the ecosystem services provided by them; the need to enhance inventories). The most suitable approaches for conserving temporary wetlands include (1) regulations or other forms of protection; (2) sustainable management; (3) restoration and creation; and (4) collaborative conservation.

Book chapter↗

USGS2015

Formulating the American Geophysical Union's Scientific Integrity and Professional Ethics Policy: Challenges and lessons learned

Creating an ethics policy for a large, diverse geosciences organization is a challenge, especially in the midst of the current contentious dialogue in the media related to such issues as climate change, sustaining natural resources, and responding to natural hazards. In 2011, the American Geophysical Union (AGU) took on this challenge, creating an Ethics Task Force to update their ethics policies to better support their new Strategic Plan and respond to the changing scientific research environment. Dialogue with AGU members and others during the course of creating the new policy unveiled some of the following issues to be addressed. Scientific results and individual scientists are coming under intense political and public scrutiny, with the efficacy of the science being questioned. In some cases, scientists are asked to take sides and/or provide opinions on issues beyond their research, impacting their objectivity. Pressure related to competition for funding and the need to publish high quality and quantities of papers has led to recent high-profile plagiarism, data fabrication, and conflict of interest cases. The complexities of a continuously advancing digital environment for conducting, reviewing, and publishing science has raised concerns over the ease of plagiarism, fabrication, falsification, inappropriate peer review, and the need for better accessibility of data and methods. Finally, students and scientists need consistent education and encouragement on the importance of ethics and integrity in scientific research. The new AGU Scientific Integrity and Ethics Policy tries to address these issues and provides an inspirational code of conduct to encourage a responsible, positive, open, honest scientific research environment.

Book chapter↗

USGS2019

Population dynamics of reintroduced Whooping Cranes

Because of the small size and restricted range of the Aransas-Wood Buffalo Population, reintroduction is a prominent element of the recovery effort to ensure persistence of Whooping Cranes ( Grus americana ). A fundamental objective of all Whooping Crane reintroduction efforts is the establishment of a self-sustaining population. Therefore, success of reintroduction efforts will ultimately be determined by demography: births and deaths of Whooping Cranes in the released population. We present a detailed review of the demographic modeling efforts for two reintroduced populations of Whooping Cranes: the Florida Nonmigratory Population and the Eastern Migratory Population. Both of these populations have struggled with poor demographic performance, and the Florida Nonmigratory Population is now nearly extirpated. The focus of our review is on the models used to represent Whooping Crane population dynamics and the major uncertainties that still exist about population dynamics in reintroduced Whooping Cranes. We also discuss the centrality of population models to the management of reintroduced Whooping Cranes, and the use of decision analysis to navigate multiple-objective decisions made under uncertainty. Development of demographic models, and articulation and testing of hypotheses about the causes of poor demographic performance in reintroduced populations, will continue to be research areas of importance in support of Whooping Crane reintroduction.

Book chapter↗