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At least 343 records · Page 19Linked to original sources
USGS2012

Remote sensing of evapotranspiration for operational drought monitoring using principles of water and energy balance

Evapotranspiration (ET) is an important component of the hydrologic budget because it režects the exchange of mass and energy between the soil-water-vegetation system and the atmosphere. Prevailing weather conditions inžuence potential or reference ET through variables such as radiation, temperature, wind, and relativity humidity. In addition to these weather variables, actual ET (ETa) is also affected by land cover type and condition, as well as soil moisture. The dependence of ETa on land cover and soil moisture, and its direct relationship with carbon dioxide assimilation in plants, makes it an important variable for monitoring drought, crop yield, and biomass-a critical capability for decision makers interested in food security, grain markets, water allocation, and carbon sequestration (Bastiaanssen et al., 2005).

Book chapter↗
USGS2000

Distribution of surficial sediment in Long Island Sound and adjacent waters: Texture and total organic carbon

The surficial sediment distribution within Long Island Sound has been mapped and described using bottom samples, photography, and sidescan sonar, combined with information from the geologic literature. The distributions of sediment type and total organic carbon (TOC) reveal several broad trends that are largely related to the sea-floor geology, the bathymetry, and the effects of modern tidal- and wind-driven currents. Sediment types are most heterogeneous in bathymetrically complex and shallow nearshore areas; the heterogeneity diminishes and the texture fines with decreasing bottom-current energy. Lag deposits of gravel and gravelly sand dominate the surficial sediment texture in areas where bottom currents are the strongest (such as where tidal flow is constricted) and where glacial till crops out at the sea floor. Sand is the dominant sediment type in areas characterized by active sediment transport and in shallow areas affected by fine-grained winnowing. Silty sand and sand-silt-clay mark transitions within the basin from higher- to lower-energy environments, suggesting a diminished hydraulic ability to sort and transport sediment. Clayey silt and silty clay are the dominant sediment types accumulating in the central and western basins and in other areas characterized by long-term depositional environments. The amount of TOC in the sediments of Long Island Sound varies inversely with sediment grain size. Concentrations average more than 1.9% (dry weight) in clayey silt, but are less than 0.4% in sand. Generally, values for TOC increase both toward the west in the Sound and from the shallow margins to the deeper parts of the basin floor. Our data also suggest that TOC concentrations can vary seasonally.

Long Island Sound↗
USGS2023

Towards a unified drag coefficient formula for quantifying wave energy reduction by salt marshes

Coastal regions are susceptible to increasing flood risks amid climate change. Coastal wetlands play an important role in mitigating coastal hazards. Vegetation exerts a drag force to the flow and dampens storm surges and wind waves. The prediction of wave attenuation by vegetation typically relies on a pre-determined drag coefficient C D "> C D . Existing C D "> C D formulas are subject to vegetation biomechanical properties, especially the flexibility. Accounting for vegetation flexibility through the effective plant height (EPH), we propose and validate a species-independent relationship between C D "> C D and the Reynolds number R e "> Re based on three independent datasets that cover a wide range of hydrodynamic conditions and vegetation traits. The proposed C D − R e "> C D − Re relationship, used together with EPH, allows for predicting wave attenuation in salt marshes with high accuracy. Furthermore, a total of 308,000 numerical experiments with diverse wave conditions are conducted using the proposed C D − R e "> C D − Re relationship and EPH to quantify the wave attenuation capacity of two typical salt mash species: Elymus athericus (highly flexible) and Spartina alterniflora (relatively rigid). It is found that wave attenuation is controlled by wave height to water depth ratio and EPH to water depth ratio. When swaying in large waves in shallow to intermediate water depth, a 50-m-long Elymus athericus field may lose up to 30% capacity for wave attenuation. As wave height increases, highly flexible vegetation causes reduced wave attenuation, whereas relatively rigid vegetation induces increased wave attenuation. The leaf contribution to wave attenuation is highly dependent on the leaf rigidity. It is recommended that leaf properties, especially its Young’s modulus be collected in future field experiments.

Coastal Engineering↗
USGS2009

Investigating the impact of surface wave breaking on modeling the trajectories of drifters in the northern Adriatic Sea during a wind-storm event

An accurate numerical prediction of the oceanic upper layer velocity is a demanding requirement for many applications at sea and is a function of several near-surface processes that need to be incorporated in a numerical model. Among them, we assess the effects of vertical resolution, different vertical mixing parameterization (the so-called Generic Length Scale -GLS- set of k-??, k-??, gen, and the Mellor-Yamada), and surface roughness values on turbulent kinetic energy (k) injection from breaking waves. First, we modified the GLS turbulence closure formulation in the Regional Ocean Modeling System (ROMS) to incorporate the surface flux of turbulent kinetic energy due to wave breaking. Then, we applied the model to idealized test cases, exploring the sensitivity to the above mentioned factors. Last, the model was applied to a realistic situation in the Adriatic Sea driven by numerical meteorological forcings and river discharges. In this case, numerical drifters were released during an intense episode of Bora winds that occurred in mid-February 2003, and their trajectories compared to the displacement of satellite-tracked drifters deployed during the ADRIA02-03 sea-truth campaign. Results indicted that the inclusion of the wave breaking process helps improve the accuracy of the numerical simulations, subject to an increase in the typical value of the surface roughness z 0 . Specifically, the best performance was obtained using ?? CH = 56,000 in the Charnok formula, the wave breaking parameterization activated, k-?? as the turbulence closure model. With these options, the relative error with respect to the average distance of the drifter was about 25% (5.5 km/day). The most sensitive factors in the model were found to be the value of ?? CH enhanced with respect to a standard value, followed by the adoption of wave breaking parameterization and the particular turbulence closure model selected. ?? 2009 Elsevier Ltd.

Ocean Modelling↗
USGS2012

Hurricane disturbance and recovery of energy balance, CO 2 fluxes and canopy structure in a mangrove forest of the Florida Everglades

Eddy covariance (EC) estimates of carbon dioxide (CO 2 ) fluxes and energy balance are examined to investigate the functional responses of a mature mangrove forest to a disturbance generated by Hurricane Wilma on October 24, 2005 in the Florida Everglades. At the EC site, high winds from the hurricane caused nearly 100% defoliation in the upper canopy and widespread tree mortality. Soil temperatures down to -50 cm increased, and air temperature lapse rates within the forest canopy switched from statically stable to statically unstable conditions following the disturbance. Unstable conditions allowed more efficient transport of water vapor and CO 2 from the surface up to the upper canopy layer. Significant increases in latent heat fluxes (LE) and nighttime net ecosystem exchange (NEE) were also observed and sensible heat fluxes (H) as a proportion of net radiation decreased significantly in response to the disturbance. Many of these impacts persisted through much of the study period through 2009. However, local albedo and MODIS (Moderate Resolution Imaging Spectro-radiometer) data (the Enhanced Vegetation Index) indicated a substantial proportion of active leaf area recovered before the EC measurements began 1 year after the storm. Observed changes in the vertical distribution and the degree of clumping in newly emerged leaves may have affected the energy balance. Direct comparisons of daytime NEE values from before the storm and after our measurements resumed did not show substantial or consistent differences that could be attributed to the disturbance. Regression analyses on seasonal time scales were required to differentiate the storm's impact on monthly average daytime NEE from the changes caused by interannual variability in other environmental drivers. The effects of the storm were apparent on annual time scales, and CO 2 uptake remained approximately 250 g C m -2 yr -1 lower in 2009 compared to the average annual values measured in 2004–2005. Dry season CO 2 uptake was relatively more affected by the disturbance than wet season values. Complex leaf regeneration dynamics on damaged trees during ecosystem recovery are hypothesized to lead to the variable dry versus wet season impacts on daytime NEE. In contrast, nighttime CO 2 release (i.e., nighttime respiration) was consistently and significantly greater, possibly as a result of the enhanced decomposition of litter and coarse woody debris generated by the storm, and this effect was most apparent in the wet seasons compared to the dry seasons. The largest pre- and post-storm differences in NEE coincided roughly with the delayed peak in cumulative mortality of stems in 2007–2008. Across the hurricane-impacted region, cumulative tree mortality rates were also closely correlated with declines in peat surface elevation. Mangrove forest–atmosphere interactions are interpreted with respect to the damage and recovery of stand dynamics and soil accretion processes following the hurricane.

Florida↗
USGS2025

Evaluation of polymer-based dust palliatives in soil and stormwater runoff in an arid environment

Dust palliatives are used to reduce fugitive dust in areas susceptible to erosion by wind and rain. In 2015, the Bureau of Land Management (BLM) temporarily approved the use of polymer-based dust palliatives during the construction and operation of a solar energy facility and, in 2019, on a mining access road in Clark County, Nevada. The areas treated with palliative are habitat to the desert tortoise. The desert tortoise consumes water opportunistically from puddles, saturated soils, or by the collection of precipitation on their carapaces. Since little is known about the toxicity of polymeric substances to the desert tortoise, the BLM is concerned with the exposure of the desert tortoise to palliative in stormwater runoff. The BLM collaborated with the US Geological Survey (USGS) to evaluate the transport of butyl acrylate vinyl acetate (BA-VA), the copolymer ingredient in the dust palliatives applied in the study, away from areas of application. BA-VA concentrations were measured in soils treated with palliative up to 90 days post-treatment, after which the copolymer became undetectable (< 0.55 mg/g). BA-VA concentrations in all stormwater samples within and outside treated areas were consistently below detection (< 0.20 mg/mL). Although stormwater and treated soils eroded from the solar facility application area were found to have BA-VA concentrations below detection (< 0.55 mg/g), it is likely that some BA-VA (parent or degradation product) was transported with suspended material. It is also likely that the amount of BA-VA transported away from areas of application was a small fraction of that applied.

Nevada↗
USGS2022

Assessing wave attenuation with rising sea levels for sustainable oyster reef-based living shorelines

In densely populated coastal areas with sea-level rise (SLR), protecting the shorelines against erosion due to the wave impact is crucial. Along with many engineered structures like seawalls and breakwaters, there are also green structures like constructed oyster reefs (CORs) that can not only attenuate the incident waves but also grow and maintain pace with SLR. However, there is a lack of data and understanding of the long-term wave attenuation capacity of the living shoreline structures under SLR. In this study, we used the phase-resolving Boussinesq model, FUNWAVE-TVD, to examine the hydrodynamics including wave height and wave-induced currents around the CORs in the Gandys Beach living shoreline project area in the upper Delaware Bay, United States. Waves were measured at six locations (offshore to onshore, with and without CORs) in the Gandys Beach living shoreline project area for two winter months, during which four nor’easters occurred. We selected three cases that represent prevailing wind, wave, and tide conditions to examine the fine spatial and temporal changes in wave height and current velocity by the construction of the reefs. Wave heights and wave energy spectra generated from FUNWAVE-TVD were then validated with field observations. It is found that FUNWAVE-TVD is capable of simulating waves and associated hydrodynamic processes that interact with CORs. The model results show that wave attenuation rates vary with the incident wave properties and water depth, and wave-induced circulation patterns are affected by the CORs. The wave attenuation capacity of CORs over the next 100 years was simulated with the incorporation of the oyster reef optimal growth zone. Our study found that sustainable wave attenuation capacity can only be achieved when suitable habitat for COR is provided, thus it can vertically grow with SLR. Suitable habitat includes optimal intertidal inundation duration, current velocity for larval transport and settlement, on-reef oyster survival and growth, and other environmental conditions including salinity, temperature, and nutrient availability. Furthermore, the model results suggest that it would take CORs approximately 9 years after construction to reach and maintain the maximum wave attenuation capacity in sustainable living shorelines.

Delaware, New Jersey↗
USGS2000

Bottom currents and sediment transport in Long Island Sound: A modeling study

A high resolution (300-400 m grid spacing), process oriented modeling study was undertaken to elucidate the physical processes affecting the characteristics and distribution of sea-floor sedimentary environments in Long Island Sound. Simulations using idealized forcing and high-resolution bathymetry were performed using a three-dimensional circulation model ECOM (Blumberg and Mellor, 1987) and a stationary shallow water wave model HISWA (Holthuijsen et al., 1989). The relative contributions of tide-, density-, wind- and wave-driven bottom currents are assessed and related to observed characteristics of the sea-floor environments, and simple bedload sediment transport simulations are performed. The fine grid spacing allows features with scales of several kilometers to be resolved. The simulations clearly show physical processes that affect the observed sea-floor characteristics at both regional and local scales. Simulations of near-bottom tidal currents reveal a strong gradient in the funnel-shaped eastern part of the Sound, which parallels an observed gradient in sedimentary environments from erosion or nondeposition, through bedload transport and sediment sorting, to fine-grained deposition. A simulation of estuarine flow driven by the along-axis gradient in salinity shows generally westward bottom currents of 2-4 cm/s that are locally enhanced to 6-8 cm/s along the axial depression of the Sound. Bottom wind-driven currents flow downwind along the shallow margins of the basin, but flow against the wind in the deeper regions. These bottom flows (in opposition to the wind) are strongest in the axial depression and add to the estuarine flow when winds are from the west. The combination of enhanced bottom currents due to both estuarine circulation and the prevailing westerly winds provide an explanation for the relatively coarse sediments found along parts of the axial depression. Climatological simulations of wave-driven bottom currents show that frequent high-energy events occur along the shallow margins of the Sound, explaining the occurrence of relatively coarse sediments in these regions. Bedload sediment transport calculations show that the estuarine circulation coupled with the oscillatory tidal currents result in a net westward transport of sand in much of the eastern Sound. Local departures from this regional westward trend occur around topographic and shoreline irregularities, and there is strong predicted convergence of bedload transport over most of the large, linear sand ridges in the eastern Sound, providing a mechanism which prevents their decay. The strong correlation between the near-bottom current intensity based on the model results and the sediment response, as indicated by the distribution of sedimentary environments, provides a framework for predicting the long-term effects of anthropogenic activities.

New York↗
USGS2006

Transport of horseshoe crab eggs by waves and swash on an estuarine beach: Implications for foraging shorebirds

The abundance of horseshoe crab eggs in the swash zone and remaining on the beach after tide levels fall was evaluated to identify how numbers of eggs available to shorebirds differ with fluctuations in spawning numbers of horseshoe crabs, wave energies and beach elevation changes. Field data were gathered 1-6 June 2004 at Slaughter Beach on the west side of Delaware Bay, USA. Counts of spawning crabs and process data from a pressure transducer and an anemometer and wind vane were related to number of eggs, embryos and larvae taken at depth and on the surface of the foreshore and in the active swash zone using a streamer trap. Beach elevation changes and depths of sediment activation were used to determine the potential for buried eggs to be exhumed by waves and swash. Mean significant wave heights during high water levels ranged from 0.08 to 0.40 m. Spawning counts were low (50-140 females km-1) when wave heights were low; no spawning occurred when wave heights were high. Vegetative litter (wrack) on the beach provides local traps for eggs, making more eggs available for shorebirds. Accumulation of litter on days when wave energy is low increases the probability that eggs will remain on the surface. High wave energies transport more eggs in the swash, but these eggs are dispersed or buried, and fewer eggs remain on the beach. Peaks in the number of eggs in the swash uprush occur during tidal rise and around time of high tide. The number of eggs in transport decreases during falling tide. Many more eggs move in the active swash zone than are found on the beach after water level falls, increasing the efficiency of bird foraging in the swash. Greater numbers of eggs in the swash during rising tide than falling tide and fewer eggs at lower elevations on the beach, imply that foraging becomes less productive as the tide falls and may help account for the tendency of shorebirds to feed on rising tides rather than on falling or low tides on days when no spawning occurs. ?? 2006 Elsevier Ltd. All rights reserved.

Estuarine, Coastal and Shelf Science↗
USGS1997

Nest morphology and body size of Ross' Geese and Lesser Snow Geese

Arctic-nesting geese build large, insulated nests to protect developing embryos from cold ambient temperatures. Ross' Geese ( Chen rossii ) are about two-thirds the mass of Lesser Snow Geese ( C. caerulescens caerulescens ), have higher mass-specific metabolic rate, and maintain lower nest attentiveness, yet they hatch goslings with more functionally mature gizzards and more protein for their size than do Lesser Snow Geese. We compared nest size (a reflection of nest insulation) in four distinct habitats in a mixed breeding colony of Ross' Geese and Lesser Snow Geese at Karrak Lake, Northwest Territories, Canada. After adjusting measurements for nest-specific egg size and clutch size, we found that overall nest morphology differed between species and among habitats. Nest size increased progressively among heath, rock, mixed, and moss habitats. When nesting materials were not limiting, nests were smaller in habitats that provided cover from wind and precipitation than in habitats that did not provide cover. Ross' Geese constructed relatively larger, more insulated nests than did Lesser Snow Geese, which may hasten embryonic development, minimize energy expenditure during incubation, and minimize embryonic cooling during recesses. We suggest that relative differences in nest morphology reflect greater selection for Ross' Geese to improve nest insulation because of their smaller size (adults and embryos), higher mass-specific metabolic rate, and lower incubation constancy.

The Auk↗
USGS1972

Comparison of evaporation computation methods, Pretty Lake, Lagrange County, northeastern Indiana

Evaporation from Pretty Lake has been computed for a 2%- year period between 1963 and 1965 by the use of an energy budget, mass-transfer parameters, a water budget, a class-A pan, and a computed pan evaporation technique. The seasonal totals for the different methods are within 8 percent of their mean and are within 11 percent of the rate of 79 centimeters (31 inches) per year determined from published maps that are based on evaporation-pan data. Period-by-period differences among the methods are larger than the annual differences, but there is a general agreement among the evaporation hydrographs produced by the different computation methods. The energy budget was an excellent means of computing unbiased evaporation data for periods of a month or longer from June through September. It is not reliable in the springtime, when Bowen ratios are large and when the large changes in stored energy may be hard to measure accurately owing to errors in the capacity table. The need for sophisticated equipment, frequent temperature surveys, and complex computations makes the energy budget the most expensive of the several methods used. Effective use was made of the Koberg method in estimating long-wave radiation when accurate instrument records were not available. Effects of sediment heating and cooling were computed to have influenced evaporation as much as 0.03 cm day" 1 (centimeters per day) just after the autumnal overturn. The change is significant during the fall, when the evaporation for Pretty Lake is low, and would be more significant in a shallow lake, where the heat storage by the sediment would be large in proportion to the storage by the water. The corrected fall in stage computed by the water-budget method agreed well with the evaporation rates computed by other methods during the dryer seasons. Decreased rates of fall in stage during the wet seasons indicated net inflow seepage that was estimated to be equivalent to a stage change of more than 0.2 cm day" 1 at some times. Evaporation data based upon class-A pan records and computed pan evaporation were too large early in the season and too small late in the season. The differences were caused by energy storage, which affected the lake evaporation as energy was stored in the spring and released late in the season. Energy-storage effects can be corrected, but the corrections require some of the same expensive data that were used in the energy budget. The mass-transfer system proved to be an effective low-cost means of computing evaporation, a means that is well suited to low evaporation rates. The mass-transfer coefficient was determined to be 0.00560 cm hr day- 1 mile" 1 mb" 1 (centimeter per day per millibar per mile/hour), the relative standard error of the energy-budget calibration being about 6 percent. Springtime and autumn evaporation rates computed by the mass-transfer method were slightly higher than rates computed by other methods, and summer rates from mass-transfer computations were slightly lower than rates computed by other methods. Anemometer stalling is believed to have caused unreliable mass-transfer evaporation data during two periods having very low wind velocities. Assuming that Pretty Lake is typical of the many small natural lakes in its region, it is concluded that in most cases the evaporation information needed for hydrologic studies can be provided with satisfactory accuracy by a combination of the mass-transfer method and one or two other methods, without the expense of a complex energy-budget study. The different methods, although poor, agree that evaporation when there is ice cover is generally small (less than 0.1 cm day" 1 ), but the evaporation rates during the few days just before freezeup or just after ice breakup are significant

Indiana↗
USGS2000

Regional evaluation of evapotranspiration in the Everglades

Nine sites in the Florida Everglades were selected and instrumented for collection of data necessary for evapotranspiration-determination using the Bowen-ratio energy-budget method. The sites were selected to represent the sawgrass or cattail marshes, wet prairie, and open-water areas that constitute most of the natural Everglades system. At each site, measurements necessary for evapotranspiration (ET) calculation and modeling were automatically made and stored on-site at 15- or 30-minute intervals. Data collected included air temperature and humidity at two heights, wind speed and direction, incoming solar radiation, net solar radiation, water level and temperature, soil moisture content, soil temperature, soil heat flux, and rainfall. Data summarized in this report were collected from January 1996 through December 1997, and the development of site-specific and regional models of ET for this period is described. Latent heat flux is the energy flux density equivalent of the ET rate. Modified Priestley-Taylor models of latent heat flux as a function of selected independent variables were developed at each site. These models were used to fill in periods of missing latent heat flux measurement, and to develop regional models of the entire Everglades region. The regional models may be used to estimate ET in wet prairie, sawgrass or cattail marsh, and open-water portions of the natural Everglades system. The models are not applicable to forested areas or to the brackish areas adjacent to Florida Bay. Two types of regional models were developed. One type of model uses measurements of available energy at a site, together with incoming solar energy and water depth, to estimate hourly ET. This available-energy model requires site data for net radiation, water heat storage, and soil heat flux, as well as data for incoming solar radiation and water depth. The other type of model requires only incoming solar energy, air temperature, and water depth data to provide estimates of hourly ET. The second model thus uses data that are more readily available than the data required for the available-energy model. Computed ET mean annual totals for all nine sites for the 1996-97 period ranged from 42.4 inches per year at a site where the water level is below land surface for several months each year to 57.4 inches per year at an open-water site with no emergent vegetation. Although the density of photosynthetically-active plant leaves has been shown to relate directly to ET in some studies, it does not appear to relate directly to ET in the Everglades, based on comparison of annual ET data with leaf-area index, defined as the Normalized Difference Vegetation Index (NDVI), data from satellite imagery. NDVI and ET appear to be inversely related in the Everglades. The greatest ET rates occurred at open-water sites where the NDVI data indicated the lowest leaf-area index. Among the remaining vegetated sites, there is no clear relation between ET and NDVI, though the highest ET rate corresponded to the lowest NDVI and one of the lowest ET rates corresponded to the highest NDVI value. The variation in ET follows a seasonal pattern, with lowest monthly ET totals occurring in December through February, and highest ET occurring in May through August. The greatest range in monthly ET among all nine sites for the 2-year period occurred at site 3: from 1.81 inches in December 1997 to 6.84 inches in July 1996. A study to compare the Bowen-ratio/energy balance method of ET measurement with the eddy-correlation method was done at one site from June 22, 1998, through September 28, 1998. This comparison indicated that both methods gave comparable values of the Bowen ratio, but there was a considerable difference in available energy measured by the two methods. The mean of all 30-minute measured turbulent heat fluxes from the eddy-correlation apparatus for June 22 through September 29, 1998, was 137.4 watts per square meter, and the mean of the corresponding measured energy was 163.6 watts per square meter, or about 20 percent greater. The disagreement in mean energy fluxes measured by the two methods is problematical and is not fully understood. Although the difference seems to be related to friction velocity, and is practically non-existent at values of friction velocity greater than 0.3 meter per second, the "correctness" of either method cannot be determined with the data available.

Florida↗
USGS2013

Characterizing wave- and current- induced bottom shear stress: U.S. middle Atlantic continental shelf

Waves and currents create bottom shear stress, a force at the seabed that influences sediment texture distribution, micro-topography, habitat, and anthropogenic use. This paper presents a methodology for assessing the magnitude, variability, and driving mechanisms of bottom stress and resultant sediment mobility on regional scales using numerical model output. The analysis was applied to the Middle Atlantic Bight (MAB), off the U.S. East Coast, and identified a tidally-dominated shallow region with relatively high stress southeast of Massachusetts over Nantucket Shoals, where sediment mobility thresholds are exceeded over 50% of the time; a coastal band extending offshore to about 30 m water depth dominated by waves, where mobility occurs more than 20% of the time; and a quiescent low stress region southeast of Long Island, approximately coincident with an area of fine-grained sediments called the “Mud Patch”. The regional high in stress and mobility over Nantucket Shoals supports the hypothesis that fine grain sediment winnowed away in this region maintains the Mud Patch to the southwest. The analysis identified waves as the driving mechanism for stress throughout most of the MAB, excluding Nantucket Shoals and sheltered coastal bays where tides dominate; however, the relative dominance of low-frequency events varied regionally, and increased southward toward Cape Hatteras. The correlation between wave stress and local wind stress was lowest in the central MAB, indicating a relatively high contribution of swell to bottom stress in this area, rather than locally generated waves. Accurate prediction of the wave energy spectrum was critical to produce good estimates of bottom shear stress, which was sensitive to energy in the long period waves.

Continental Shelf Research↗
USGS2000

Geochemical evidence for a magmatic CO 2 degassing event at Mammoth Mountain, California, September-December 1997

Recent time series soil CO 2 concentration data from monitoring stations in the vicinity of Mammoth Mountain, California, reveal strong evidence for a magmatic degassing event during the fall of 1997 lasting more than 2 months. Two sensors at Horseshoe Lake first recorded the episode on September 23, 1997, followed 10 days later by a sensor on the north flank of Mammoth Mountain. Direct degassing from shallow intruding magma seems an implausible cause of the degassing event, since the gas released at Horseshoe Lake continued to be cold and barren of other magmatic gases, except for He. We suggest that an increase in compressional strain on the area south of Mammoth Mountain driven by movement of major fault blocks in Long Valley caldera may have triggered an episode of increased degassing by squeezing additional accumulated CO 2 from a shallow gas reservoir to the surface along faults and other structures where it could be detected by the CO 2 monitoring network. Recharge of the gas reservoir by CO 2 emanating from the deep intrusions that probably triggered deep long-period earthquakes may also have contributed to the degassing event. The nature of CO 2 discharge at the soil-air interface is influenced by the porous character of High Sierra soils and by meteorological processes. Solar insolation is the primary source of energy for the Earth atmosphere and plays a significant role in most diurnal processes at the Earth surface. Data from this study suggest that external forcing due largely to local orographic winds influences the fine structure of the recorded CO 2 signals.

California↗
USGS1996

Late Quaternary transgressive large dunes on the sediment-starved Adriatic shelf

The Adriatic epicontinental basin is a low-gradient shelf where the late-Quaternary transgressive systems tract (TST) is composed of thin parasequences of backbarrier, shoreface and offshore deposits. The facies and internal architecture of the late-Quaternary TST in the Adriatic epicontinental basin changed consistently from early transgression to late transgression reflecting: (1) fluctuations in the balance between sediment supply and accommodation increase, and (2) a progressive intensification of the oceanographic regime, driven by the transgressive widening of the basin to as much as seven times its lowstand extent. One of the consequences of this trend is that high-energy marine bedforms such as sand ridges and sand waves characterize only areas that were flooded close to the end of the late-Quaternary sea-level rise, when the wind fetch was maximum and bigger waves and stronger storm currents could form. We studied the morphology, sediment composition and sequence-stratigraphical setting of a field of asymmetric bedforms (typically 3 m high and 600 m in wavelength) in 20-24 m water depth offshore the Venice Lagoon in the sediment-starved North Adriatic shelf. The sand that forms these large dunes derived from a drowned transgressive coastal deposit reworked by marine processes. Early cementation took place over most of the dune crests limiting their activity and preventing their destruction. Both the formation and deactivation of this field of sand dunes occurred over a short time interval close to the turn-around point that separates the late-Quaternary sea-level rise and the following highstand and reflect rapid changes in the oceanographic regime of the basin.

Geological Society Special Publication↗
USGS1988

Climatic data for Mirror Lake, West Thornton, New Hampshire: 1985

Research on the hydrology of Mirror Lake, West Thornton, New Hampshire, includes a study of evaporation. Those climatic data needed for energy-budget and mass-transfer evaporation studies are presented, including: water surface temperature, dry-bulb and wet-bulb air temperatures, vapor pressure at and above the water surface, wind speed, and short- and long-wave radiation. Data are collected at raft and land stations. (USGS)

New Hampshire↗
USGS1998

Frequency of effective wave activity and the recession of coastal bluffs: Calvert Cliffs, Maryland

The Calvert Cliffs, Chesapeake Bay, Maryland, USA, erode by direct wave undercutting or by freeze/thaw erosion accompanied by wave removal of slope debris. Directly undercut slopes recede more rapidly, with long-term rates exceeding 1.0 m/yr; freeze/thaw slopes recede at rates approaching 0.5 m/yr. The frequency of wave height and water level at the shoreline is estimated for eleven sites based on a 37-year wind record, estimates of storm surge, offshore wave geometry, nearshore wave transformation, and breaking wave type. Locations experiencing the largest slope recession are not uniformly those with the largest cumulative wave energy; the resistance to erosion of the slope toe must also be accounted for. An index of relative wave strength is defined as the ratio of wave pressure T and the cohesive strength S of the slope material. For the Calvert Cliffs, a minimum relative wave strength for initiating erosion of intact material is 0.05 < T/S < 0.1. A cumulative duration of ???50 hours per year for T/S ??? 0.1 distinguishes undercut and nonundercut slopes and recession rates greater or lesser than 0.5 m/yr. The relative wave strength index may be used to identify sites at risk of increased erosion. At one site with a small historical erosion rate, the loss of a protective beach and associated decrease in toe elevation caused a positive shift in the frequency of large T/S. Direct wave undercutting and increased slope recession may be anticipated at this site, as indicated by the development of an undercut notch during the course of the study.

Journal of Coastal Research↗
USGS1986

Climatic data for the Cottonwood Lake area, Stutsman County, North Dakota 1982

Research on the hydrology of the Cottonwood Lake area, Stutsman County, North Dakota, includes study of evaporation. Presented here are those climatic data needed for energy-budget and mass-transfer evaporation studies, including: water-surface temperature, sediment temperature dry-bulb and wet-bulb air temperatures, vapor pressure at and above the water surface, wind speed, and short- and long-wave radiation. Data were collected at raft and land stations.

Open-File Report↗