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At least 253 records · Page 14Linked to original sources
USGS2008

A linear geospatial streamflow modeling system for data sparse environments

In many river basins around the world, inaccessibility of flow data is a major obstacle to water resource studies and operational monitoring. This paper describes a geospatial streamflow modeling system which is parameterized with global terrain, soils and land cover data and run operationally with satellite‐derived precipitation and evapotranspiration datasets. Simple linear methods transfer water through the subsurface, overland and river flow phases, and the resulting flows are expressed in terms of standard deviations from mean annual flow. In sample applications, the modeling system was used to simulate flow variations in the Congo, Niger, Nile, Zambezi, Orange and Lake Chad basins between 1998 and 2005, and the resulting flows were compared with mean monthly values from the open‐access Global River Discharge Database. While the uncalibrated model cannot predict the absolute magnitude of flow, it can quantify flow anomalies in terms of relative departures from mean flow. Most of the severe flood events identified in the flow anomalies were independently verified by the Dartmouth Flood Observatory (DFO) and the Emergency Disaster Database (EM‐DAT). Despite its limitations, the modeling system is valuable for rapid characterization of the relative magnitude of flood hazards and seasonal flow changes in data sparse settings.

International Journal of River Basin Management↗
USGS1999

Does Europa have a subsurface ocean? Evaluation of the geological evidence

It has been proposed that Jupiter's satellite Europa currently possesses a global subsurface ocean of liquid water. Galileo gravity data verify that the satellite is differentiated into an outer H 2 O layer about 100 km thick but cannot determine the current physical state of this layer (liquid or solid). Here we summarize the geological evidence regarding an extant subsurface ocean, concentrating on Galileo imaging data. We describe and assess nine pertinent lines of geological evidence: impact morphologies, lenticulae, cryovolcanic features, pull‐apart bands, chaos, ridges, surface frosts, topography, and global tectonics. An internal ocean would be a simple and comprehensive explanation for a broad range of observations; however, we cannot rule out the possibility that all of the surface morphologies could be due to processes in warm, soft ice with only localized or partial melting. Two different models of impact flux imply very different surface ages for Europa; the model favored here indicates an average age of ∼50 Myr. Searches for evidence of current geological activity on Europa, such as plumes or surface changes, have yielded negative results to date. The current existence of a global subsurface ocean, while attractive in explaining the observations, remains inconclusive. Future geophysical measurements are essential to determine conclusively whether or not there is a liquid water ocean within Europa today.

Journal of Geophysical Research: Planets↗
USGS2007

Structure and composition of a watershed-scale sediment information network

A 'Watershed-Scale Sediment Information Network' (WaSSIN), designed to complement UNESCO's International Sedimentation Initiative, was endorsed as an initial project by the World Association for Sedimentation and Erosion Research. WaSSIN is to address global fluvial-sediment information needs through a network approach based on consistent protocols for the collection, analysis, and storage of fluvial-sediment and ancillary information at smaller spatial scales than those of the International Sedimentation Initiative. As a second step of implementation, it is proposed herein that the WaSSIN have a general structure of two components, (1) monitoring and data acquisition and (2) research. Monitoring is to be conducted in small watersheds, each of which has an established database for discharge of water and suspended sediment and possibly for bed load, bed material, and bed topography. Ideally, documented protocols have been used for collecting, analyzing, storing, and sharing the derivative data. The research component is to continue the collection and interpretation of data, to compare those data among candidate watersheds, and to determine gradients of fluxes and processes among the selected watersheds. To define gradients and evaluate processes, the initial watersheds will have several common attributes. Watersheds of the first group will be: (1) six to ten in number, (2) less than 1000 km2 in area, (3) generally in mid-latitudes of continents, and (4) of semiarid climate. Potential candidate watersheds presently include the Weany Creek Basin, northeastern Australia, the Zhi Fanggou catchment, northern China, the Eshtemoa Watershed, southern Israel, the Metsemotlhaba River Basin, Botswana, the Aiuaba Experimental Basin, Brazil, and the Walnut Gulch Experimental Watershed, southwestern United States.

International Journal of Sediment Research↗
USGS2016

Internal loading of phosphorus in western Lake Erie

This study applied eight techniques to obtain estimates of the diffusive flux of phosphorus (P) from bottom sediments throughout the western basin of Lake Erie. The flux was quantified from both aerobic and anaerobic incubations of whole cores; by monitoring the water encapsulated in bottom chambers; from pore water concentration profiles measured with a phosphate microelectrode, a diffusive equilibrium in thin films (DET) hydrogel, and expressed pore waters; and from mass balance and biogeochemical diagenetic models. Fluxes under aerobic conditions at summertime temperatures averaged 1.35 mg P/m 2 /day and displayed spatial variability on scales as small as a centimeter. Using two different temperature correction factors, the flux was adjusted to mean annual temperature yielding average annual fluxes of 0.43–0.91 mg P/m 2 /day and a western basin-wide total of 378–808 Mg P/year as the diffusive flux from sediments. This is 3–7% of the 11,000 Mg P/year International Joint Commission (IJC) target load for phosphorus delivery to Lake Erie from external sources. Using these average aerobic fluxes, the sediment contributes 3.0–6.3 μg P/L as a background internal contribution that represents 20–42% of the IJC Target Concentration of 15 μg P/L for the western basin. The implication is that this internal diffusive recycling of P is unlikely to trigger cyanobacterial blooms by itself but is sufficiently large to cause blooms when combined with external loads. This background flux may be also responsible for delayed response of the lake to any decrease in the external loading.

Lake Erie↗
USGS2024

Automated Cropland Fallow Algorithm (ACFA) for the Northern Great Plains of USA

Cropland fallowing is choosing not to plant a crop during a season when a crop is normally planted. It is an important component of many crop rotations and can improve soil moisture and health. Knowing which fields are fallow is critical to assess crop productivity and crop water productivity, needed for food security assessments. The annual spatial extent of cropland fallows is poorly understood within the United States (U.S.). The U.S. Department of Agriculture Cropland Data Layer does provide cropland fallow areas; however, at a significantly lower confidence than their cropland classes. This study developed a methodology to map cropland fallows within the Northern Great Plains region of the U.S. using an easily implementable decision tree algorithm leveraging training and validation data from wet (2019), normal (2015), and dry (2017) precipitation years to account for climatic variability. The decision trees automated cropland fallow algorithm (ACFA) was coded on a cloud platform utilizing remotely sensed, time-series data from the years 2010–2019 to separate cropland fallows from other land cover/land use classes. Overall accuracies varied between 96%-98%. Producer’s and user’s accuracies of cropland fallow class varied between 70-87%.

International Journal of Digital Earth↗
USGS2018

Computational fluid dynamics simulations of the Late Pleistocene Lake Bonneville flood

At approximately 18.0 ka, pluvial Lake Bonneville reached its maximum level. At its northeastern extent it was impounded by alluvium of the Marsh Creek Fan, which breached at some point north of Red Rock Pass (Idaho), leading to one of the largest floods on Earth. About 5320 km 3 of water was discharged into the Snake River drainage and ultimately into the Columbia River. We use a 0D model and a 2D non-linear depth-averaged hydrodynamic model to aid understanding of outflow dynamics, specifically evaluating controls on the amount of water exiting the Lake Bonneville basin exerted by the Red Rock Pass outlet lithology and geometry as well as those imposed by the internal lake geometry of the Bonneville basin. These models are based on field evidence of prominent lake levels, hypsometry and terrain elevations corrected for post-flood isostatic deformation of the lake basin, as well as reconstructions of the topography at the outlet for both the initial and final stages of the flood. Internal flow dynamics in the northern Lake Bonneville basin during the flood were affected by the narrow passages separating the Cache Valley from the main body of Lake Bonneville. This constriction imposed a water-level drop of up to 2.7 m at the time of peak-flow conditions and likely reduced the peak discharge at the lake outlet by about 6%. The modeled peak outlet flow is 0.85·10 6 m 3 s −1 . Energy balance calculations give an estimate for the erodibility coefficient for the alluvial Marsh Creek divide of ∼0.005 m y −1 Pa −1.5 , at least two orders of magnitude greater than for the underlying bedrock at the outlet. Computing quasi steady-state water flows, water elevations, water currents and shear stresses as a function of the water-level drop in the lake and for the sequential stages of erosion in the outlet gives estimates of the incision rates and an estimate of the outflow hydrograph during the Bonneville Flood: About 18 days would have been required for the outflow to grow from 10% to 100% of its peak value. At the time of peak flow, about 10% of the lake volume would have already exited; eroding about 1 km 3 of alluvium from the outlet, and the lake level would have dropped by about 10.6 m.

Lake Bonneville↗
USGS2002

Trace element abundances in major minerals of Late Permian coals from southwestern Guizhou province, China

Fourteen samples of minerals were separated by handpicking from Late Permian coals in southwestern Guizhou province, China. These 14 minerals were nodular pyrite, massive recrystallized pyrite, pyrite deposited from low-temperature hydrothermal fluid and from ground water; clay minerals; and calcite deposited from low-temperature hydrothermal fluid and from ground water. The mineralogy, elemental composition, and distribution of 33 elements in these samples were studied by optical microscopy, scanning electron microscope equipped with energy-dispersive X-ray spectrometer (SEM-EDX), X-ray diffraction (XRD), cold-vapor atomic absorption spectrometry (CV-AAS), atomic fluorescence spectrometry (AFS), inductively coupled-plasma mass spectrometry (ICP-MS), and ion-selective electrode (ISE). The results show that various minerals in coal contain variable amounts of trace elements. Clay minerals have high concentrations of Ba, Be, Cs, F, Ga, Nb, Rb, Th, U, and Zr. Quartz has little contribution to the concentration of trace elements in bulk coal. Arsenic, Mn, and Sr are in high concentrations in calcite. Pyrite has high concentrations of As, Cd, Hg, Mo, Sb, Se, Tl, and Zn. Different genetic types of calcite in coal can accumulate different trace elements; for example Ba, Co, Cr, Hg, Ni, Rb, Sn, Sr, and Zn are in higher concentrations in calcite deposited from low-temperature hydrothermal fluid than in that deposited from ground water. Furthermore, the concentrations of some trace elements are quite variable in pyrite; different genetic types of pyrites (Py-A, B, C, D) have different concentrations of trace elements, and the concentrations of trace elements are also different in pyrite of low-temperature hydrothermal origin collected from different locations. The study shows that elemental concentration is rather uniform in a pyrite vein. There are many micron and submicron mosaic pyrites in a pyrite vein, which is enriched in some trace elements, such as As and Mo. The content of trace element in pyrite vein depends upon the content of mosaic pyrite and of trace elements in it. Many environmentally sensitive trace elements are mainly contained in the minerals in coal, and hence the physical coal cleaning techniques can remove minerals from coal and decrease the emissions of potentially hazardous trace elements. ?? 2002 Elsevier Science B.V. All rights reserved.

International Journal of Coal Geology↗
USGS2003

The strength and rheology of methane clathrate hydrate

Methane clathrate hydrate (structure I) is found to be very strong, based on laboratory triaxial deformation experiments we have carried out on samples of synthetic, high-purity, polycrystalline material. Samples were deformed in compressional creep tests (i.e., constant applied stress, ??), at conditions of confining pressure P = 50 and 100 MPa, strain rate 4.5 ?? 10-8 ??? ?? ??? 4.3 ?? 10-4 s-1, temperature 260 ??? T ??? 287 K, and internal methane pressure 10 ??? PCH4 ??? 15 MPa. At steady state, typically reached in a few percent strain, methane hydrate exhibited strength that was far higher than expected on the basis of published work. In terms of the standard high-temperature creep law, ?? = A??ne-(E*+PV*)/RT the rheology is described by the constants A = 108.55 MPa-n s-1, n = 2.2, E* = 90,000 J mol-1, and V* = 19 cm3 mol-1. For comparison at temperatures just below the ice point, methane hydrate at a given strain rate is over 20 times stronger than ice, and the contrast increases at lower temperatures. The possible occurrence of syntectonic dissociation of methane hydrate to methane plus free water in these experiments suggests that the high strength measured here may be only a lower bound. On Earth, high strength in hydrate-bearing formations implies higher energy release upon decomposition and subsequent failure. In the outer solar system, if Titan has a 100-km-thick near-surface layer of high-strength, low-thermal conductivity methane hydrate as has been suggested, its interior is likely to be considerably warmer than previously expected.

Journal of Geophysical Research B: Solid Earth↗
USGS2012

Frictional properties of saponite-rich gouge from a serpentinite-bearing fault zone along the Gokasho-Arashima Tectonic Line, central Japan

We studied a serpentinite-bearing fault zone in Gokasho-Arashima Tectonic Line, Mie Prefecture, central Japan, characterizing its internal structures, mineral assemblage, permeability, and frictional properties. The fault core situated between the serpentinite breccia and the adjacent sedimentary rocks is characterized by a zone locally altered to saponite. The clayey gouge layer separates fault rocks of serpentinite origin containing talc and tremolite from fault rocks of sedimentary origin containing chlorite but no quartz. The minerals that formed within the fault are the products of metasomatic reaction between the serpentinite and the siliceous rocks. Permeability measurements show that serpentinite breccia and fault gouge have permeability of 10 −14 –10 −17 m 2 and 10 −15 –10 −18 m 2 , respectively, at 5–120 MPa confining pressure. Frictional coefficient of the saponite-rich clayey fault gouge ranged between 0.20 and 0.35 under room-dry condition, but was reduced to 0.06–0.12 when saturated with water. The velocity dependence of friction was strongly positive, mostly ranging between 0.005 and 0.006 in terms of a–b values. The governing friction law is not constrained yet, but we find that the saponite-rich gouge possesses an evolutional behavior in the opposite direction to that suggested by the rate and state friction law, in addition to its direct velocity dependence.

Journal of Structural Geology↗
USGS1996

Paleoslumps in coal-bearing strata of the Breathitt Group (Pennsylvanian), Eastern Kentucky Coal Field, U.S.A

The benefits of geologic analysis for roof-control studies and hazard prediction in coal mines are well documented. Numerous case studies have illustrated the importance of recognizing geologic features such as paleochannels, coal riders, and kettlebottoms in mine roofs. Relatively understudied features, in terms of mining, are paleoslumps .Paleoslumps represent ancient movement and rotation of semi-consolidated sediment. Because bedding in paleoslumps is deformed or inclined, these features cause instability in mine roofs, haul roads, surface highwalls, and other excavations. Various types of paleoslumps above coals in the Eastern Kentucky Coal Field were studied in order to aid in their recognition and prediction in mines. The paleoslumps studied all showed characteristic slump-deformation features, although some differences in magnitude of deformation and overall slump size were noted. Coals beneath slumps often exhibited folding, reverse displacements, truncation, clastic dikes, and locally increased thickness. Slumps are inferred to have been triggered by a wide range of mechanisms, such as loading of water-saturated sediment on rigid substrates, synsedimentary faulting, and over-pressurization of channel margin and bar slopes. Analysis of paleoslumps in underground mines, where paleoslumps are viewed from beneath rather than in profile is difficult, since characteristic bed rotation may not be conspicuous. Sudden increases in bed-dip angle inferred from changes in rock type or bedding contacts in the roof; occurrence of bounding, polished rotation surfaces; or roof irregularity and occurrence of loading features may indicate the presence of paleoslumps. Another key to recognition may be the sudden appearance of over-thickened coal, which can occur because of slump-created paleotopography, synsedimentary faults, and slump-generated overthrusting. In addition, steeply inclined, folded, or transported coal marginal to paleoslumps can create apparent increases in coal thickness in cores. Although thick coals are obviously a target of exploration, anomalously thick coals may actually indicate adjacent paleoslumps accompanied by hazardous roof conditions and loss of seam thickness.

International Journal of Coal Geology↗
USGS2023

Time-lapse seafloor surveys reveal how turbidity currents and internal tides in Monterey Canyon interact with the seabed at centimeter-scale

Here we show how ultra-high resolution seabed mapping using new technology can help to understand processes that sculpt submarine canyons. Time-lapse seafloor surveys were conducted in the axis of Monterey Canyon, ∼50 km from the canyon head (∼1,840 m water depth) over an 18-month period. These surveys comprised 5-cm resolution multibeam bathymetry, 1-cm resolution lidar bathymetry, and 2-mm resolution stereophotographic imagery. Bathymetry data reveal centimeter-scale textures that would be undetectable by more traditional survey methods. Upward-looking Acoustic Doppler Current Profilers at the site recorded the flow character of internal tides and the passage of three turbidity currents, while sediment cores collected from the site record flow deposits. Combined with flow and core data, the bathymetry shows how turbidity currents and internal tides modify the seabed. The turbidity currents drape sediment across the site, infilling bedform troughs and smoothing erosional features carved by the internal tides (e.g., rippled scours). Turbidity currents with speeds of 0.9–3.3 m/s failed to cause notable bedform movement, which is surprising given that flows with similar speeds produced rapid bedform migration elsewhere, including the upper Monterey Canyon. The lack of migration may be related to the character of the underlying substrate or indicate that turbidity currents at the site lack dense, near-bed layers. The scale of scours produced by the internal tides (≤0.7 m/s) approaches the scale of features recorded in the ancient rock record. Thus, these results illustrate how the scale gap between seabed mapping technology and the rock record may eventually be bridged.

California↗
USGS2014

Application of near-surface geophysics as part of a hydrologic study of a subsurface drip irrigation system along the Powder River floodplain near Arvada, Wyoming

Rapid development of coalbed natural gas (CBNG) production in the Powder River Basin (PRB) of Wyoming has occurred since 1997. National attention related to CBNG development has focused on produced water management, which is the single largest cost for on-shore domestic producers. Low-cost treatment technologies allow operators to reduce their disposal costs, provide treated water for beneficial use, and stimulate oil and gas production by small operators. Subsurface drip irrigation (SDI) systems are one potential treatment option that allows for increased CBNG production by providing a beneficial use for the produced water in farmland irrigation. Water management practices in the development of CBNG in Wyoming have been aided by integrated geophysical, geochemical, and hydrologic studies of both the disposal and utilization of water. The U.S. Department of Energy (DOE) National Energy Technology Laboratory (NETL) and the U.S. Geological Survey (USGS) have utilized multi-frequency airborne, ground, and borehole electromagnetic (EM) and ground resistivity methods to characterize the near-surface hydrogeology in areas of produced water disposal. These surveys provide near-surface EM data that can be compared with results of previous surveys to monitor changes in soils and local hydrology over time as the produced water is discharged through SDI. The focus of this investigation is the Headgate Draw SDI site, situated adjacent to the Powder River near the confluence of a major tributary, Crazy Woman Creek, in Johnson County, Wyoming. The SDI system was installed during the summer of 2008 and began operation in October of 2008. Ground, borehole, and helicopter electromagnetic (HEM) conductivity surveys were conducted at the site prior to the installation of the SDI system. After the installation of the subsurface drip irrigation system, ground EM surveys have been performed quarterly (weather permitting). The geophysical surveys map the heterogeneity of the near-surface geology and hydrology of the study area. The geophysical data are consistent between surveys using different techniques and between surveys carried out at different times from 2007 through 2011. This paper summarizes geophysical results from the 4-year monitoring study of the SDI system.

Wyoming↗
USGS1998

A policy model to initiate environmental negotiations: Three hydropower workshops

How do I get started in natural resource negotiations? Natural resource managers often face difficult negotiations when they implement laws and policies regulating such resources as water, wildlife, wetlands, endangered species, and recreation. As a result of these negotiations, managers must establish rules, grant permits, or create management plans. The Legal‐Institutional Analysis Model (LIAM) was designed to assist managers in systematically analyzing the parties in natural resource negotiations and using that analysis to prepare for bargaining. The LIAM relies on the theory that organizations consistently employ behavioral roles. The model uses those roles to predict likely negotiation behavior. One practical use of the LIAM is when all parties to a negotiation conduct a workshop as a way to open the bargaining on a note of trust and mutual understanding. The process and results of three LIAM workshops designed to guide hydroelectric power licensing negotiations are presented. Our experience with these workshops led us to conclude that the LIAM can be an effective tool to begin a negotiation and that trust built through the workshops can help create a successful result.

Human Dimensions of Wildlife: An International Jou↗
USGS2008

Developing conceptual hydrogeological model for Potsdam sandstones in southwestern Quebec, Canada

A hydrogeological study was conducted in Potsdam sandstones on the international border between Canada (Quebec) and the USA (New York). Two sandstone formations, arkose and conglomerate (base) and well-cemented quartz arenite (upper), underlie the study area and form the major regional aquifer unit. Glacial till, littoral sand and gravel, and marine silt and clay discontinuously overlie the aquifer. In both sandstone formations, sub-horizontal bedding planes are ubiquitous and display significant hydraulic conductivities that are orders of magnitude more permeable than the intact rock matrix. Aquifer tests demonstrate that the two formations have similar bulk hydrologic properties, with average hydraulic conductivities ranging from 2 ?? 10-5 to 4 ?? 10-5 m/s. However, due to their different lithologic and structural characteristics, these two sandstones impose rather different controls on groundwater flow patterns in the study area. Flow is sustained through two types of fracture networks: sub-horizontal, laterally extensive fractures in the basal sandstone, where hydraulic connectivity is very good horizontally but very poor vertically and each of the water-bearing bedding planes can be considered as a separate planar two-dimensional aquifer unit; and the more fractured and vertically jointed system found in the upper sandstone that promotes a more dispersed, three-dimensional movement of groundwater. ?? Springer-Verlag 2007.

Hydrogeology Journal↗
USGS2021

Perfluoroalkyl substances in plasma of smallmouth bass from the Chesapeake Bay Watershed

Smallmouth bass Micropterus dolomieu is an economically important sportfish and within the Chesapeake Bay watershed has experienced a high prevalence of external lesions, infectious disease, mortality events, reproductive endocrine disruption and population declines. To date, no clear or consistent associations with contaminants measured in fish tissue or surface water have been found. Therefore, plasma samples from two sites in the Potomac River and two in the Susquehanna River drainage basins, differing in land-use characteristics, were utilized to determine if perfluoroalkyl substances were present. Four compounds, perfluorooctane sulphonic acid (PFOS), perfluoroundecanoic acid (PFUnA), perfluorodecanoic acid (PFDA) and perfluorododecanoic acid (PFDoA), were detected in every fish. Two additional compounds, perfluorooctane sulphonamide (PFOSA) and perfluorononanoic acid (PFNA), were less commonly detected at lower concentrations, depending on the site. Concentrations of PFOS (up to 574 ng/mL) were the highest detected and varied significantly among sites. No seasonal differences (spring versus fall) in plasma concentrations were observed. Concentrations of PFOS were not significantly different between the sexes. However, PFUnA and PFDoA concentrations were higher in males than females. Both agricultural and developed land-use appeared to be associated with exposure. Further research is needed to determine if these compounds could be affecting the health of smallmouth bass and identify sources.

New York, Pennsylvania, Maryland, Virginia↗
USGS2025

Visioning and conceptual framework for coordinating Great Lakes connecting waters research and monitoring

The Laurentian Great Lakes are connected via naturally occurring straits and rivers: St. Marys River, Straits of Mackinac, St. Clair-Detroit River System, Niagara River, and the St. Lawrence River. Despite the historical ecological and economic importance of these waters, international agreements (e.g., Great Lakes Water Quality Agreement) only recently explicitly named the Great Lakes Connecting Waters (GLCWs), requiring governments to address the challenges of adequate restoration and protection from historical use and degradation. Standardized research and monitoring activities are needed; however, there is no established mechanism for coordination across the GLCWs. A three-day summit in 2023 convened experts to form the initial framework for a GLCWs Collaborative to increase standardizations and knowledge transfer. Participants drafted a governance structure and priorities following the principles of collective impact but allowed for place-based specificity for local connecting water organizations. Priorities and suggestions for success included: 1) co-development of the collaborative with all rights holders, stakeholders, and surrounding communities; 2) investment in research and technology specific to GLCWs; 3) investment in information transfer and training; 4) increased communication; and 5) better integration into existing Great Lakes research, monitoring, and funding programs. Expanding participation in all local GLCWs organizations with principles of inclusivity was identified as a larger collaborative goal. Next steps in the development of a GLCWs Collaborative include increased communication and formation of working groups and obtaining funding for a dedicated organization to begin supporting activities (communication, facilitation, logistics). By using a deliberate process for establishment, the potentially slower time frame for establishment may result in increased participation and success.

Laurentian Great Lakes↗
USGS2013

Leaf gas exchange and nutrient use efficiency help explain the distribution of two Neotropical mangroves under contrasting flooding and salinity

Rhizophora mangle and Laguncularia racemosa co-occur along many intertidal floodplains in the Neotropics. Their patterns of dominance shift along various gradients, coincident with salinity, soil fertility, and tidal flooding. We used leaf gas exchange metrics to investigate the strategies of these two species in mixed culture to simulate competition under different salinity concentrations and hydroperiods. Semidiurnal tidal and permanent flooding hydroperiods at two constant salinity regimes (10 g L −1 and 40 g L −1 ) were simulated over 10 months. Assimilation (A), stomatal conductance (g w ), intercellular CO 2 concentration (C i ), instantaneous photosynthetic water use efficiency (PWUE), and photosynthetic nitrogen use efficiency (PNUE) were determined at the leaf level for both species over two time periods. Rhizophora mangle had significantly higher PWUE than did L. racemosa seedlings at low salinities; however, L. racemosa had higher PNUE and stomatal conductance and g w , accordingly, had greater intercellular CO 2 (calculated) during measurements. Both species maintained similar capacities for assimilation at 10 and 40 g L−1 salinity and during both permanent and tidal hydroperiod treatments. Hydroperiod alone had no detectable effect on leaf gas exchange. However, PWUE increased and PNUE decreased for both species at 40 g L −1 salinity compared to 10 g L −1 . At 40 g L −1 salinity, PNUE was higher for L. racemosa than R. mangle with tidal flooding. These treatments indicated that salinity influences gas exchange efficiency, might affect how gases are apportioned intercellularly, and accentuates different strategies for distributing leaf nitrogen to photosynthesis for these two species while growing competitively.

Florida;Louisiana↗
USGS1995

Mudflow generated by retrogressive slope failure, Santa Barbara Basin, California continental borderland

The morphology and internal geometry of a mudflow deposit on the mainland slope of the Santa Barbara Basin are defined using high-resolution seismic-reflection data in combination with core samples. Sediment failure occurred on a 4 degrees slope in the uppermost part of late Quaternary well-bedded slope deposits. The failure zone extends from water depths of 374-510 m near the base of slope, occupies an area of 4 km 2 , and involved the translation of 0.01-0.02 km 3 of sediment. Major geomorphic features of the mudflow deposit include a headscarp 6-8 m high, a scar 50-700 m wide, and a main body 1 km long and 12 m thick. The hummocky surface of the mudflow deposits, their chaotic internal structure, and the bulbous toe tapering upslope to a thin tail are consistent with mass flow involving extensive internal deformation. Sediment failed in stages, ending with upslope retrogressive retreat of the headwall along the east side of the failure zone. Known sedimentation rates of 0.8-1.4 m/k.y., as well as the presence of a thin (0.15-0.5 m thick) sediment cap resting atop the scar surface, indicate that the failure probably occurred within the past few centuries. A geotechnical analysis incorporating the results of both static and dynamic triaxial strength tests shows that the failure was probably caused by a strong (M nearly equal 7.5) nearby earthquake. The weakened sediment that remained after earthquake shaking continued to flow down the gentle basin slope under the stresses generated by gravity alone. The analysis also shows that much of the slope sediment is marginally stable and that additional mudflows will probably occur during future strong seismic shaking.

California↗