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At least 253 records · Page 14Linked to original sources
USGS2017

Climatology and interannual variability of boreal spring wet season precipitation in the eastern Horn of Africa and implications for its recent decline

The 1981–2014 climatology and variability of the March–May eastern Horn of Africa boreal spring wet season are examined using precipitation, upper- and lower-level winds, low-level specific humidity, and convective available potential energy (CAPE), with the aim of better understanding the establishment of the wet season and the cause of the recent observed decline. At 850 mb, the development of the wet season is characterized by increasing specific humidity and winds that veer from northeasterly in February to southerly in June and advect moisture into the region, in agreement with an earlier study. Equally important, however, is a substantial weakening of the 200-mb climatological easterly winds in March. Likewise, the shutdown of the wet season coincides with the return of strong easterly winds in June. Similar changes are seen in the daily evolution of specific humidity and 200-mb wind when composited relative to the interannual wet season onset and end, with the easterlies decreasing (increasing) several days prior to the start (end) of the wet season. The 1981–2014 decrease in March–May precipitation has also coincided with an increase in 200-mb easterly winds, with no attendant change in specific humidity, leading to the conclusion that, while high values of specific humidity are an important ingredient of the wet season, the recent observed precipitation decline has resulted mostly from a strengthening of the 200-mb easterlies. This change in the easterly winds appears to be related to an increase in convection over the Indonesian region and in the associated outflow from that enhanced heat source.

Journal of Climate↗
USGS1994

Effects of weather and tides on feeding and flock positions of wintering redheads in the Chandeleur Sound, Louisiana

We studied the effects of weather and tides on percent feeding and flock positions of wintering redheads ( Aythya americana Eyton) in the Chandeleur Sound, Louisiana, USA. Flock scans ( n = 750) were made on 55 flocks from November through March of 1988–1989. The percent of the flock that was feeding was negatively correlated with time of day, temperature, water level, and distance of the flock from shore, and was positively correlated with wind velocity, flock size, fetch, and wave height; birds also fed more in early winter and during northerly winds. Flocks were closer to land earlier in the winter on cloudy, rainy, and windy days when waves were high, and those flocks were smaller than flocks farther from shore. Conditions associated with reduced fetch by flocks included later time of day, smaller waves, warmer air temperatures, northerly wind shifts, stronger winds, increasing cloud cover, and rain. Redheads minimized energy expenditure by foraging during low tides and in shallow water closer to shore; they increased feeding and reduced fetch during times of high thermoregulatory demands.

Louisiana↗
USGS1996

Simulation of water available for runoff in clearcut forest openings during rain-on-snow events in the western Cascade Range of Oregon and Washington

Rain-on-snow events are common on mountain slopes within the transient-snow zone of the Pacific Northwest. These events make more water available for runoff than does precipitation alone by melting the snowpack and by adding a small amount of condensate to the snowpack. In forest openings (such as those resulting from clearcut logging), the amount of snow that accumulates and the turbulent- energy input to the snowpack are greater than below forest stands. Both factors are believed to contribute to a greater amount of water available for runoff during rain-on-snow events in forest openings than forest stands. Because increased water available for runoff may lead to increased downstream flooding and erosion, knowledge of the amount of snowmelt that can occur during rain on snow and the processes that control snowmelt in forest openings is useful when making land-use decisions. Snow accumulation and melt were simulated for clearcut conditions only, using an enery- balance approach that accounts for the most important energy and mass exchanges between a snowpack and its environment. Meteorological measurements provided the input for the simulations. Snow accumulation and melt were not simulated in forest stands because interception of precipitation processes are too complex to simulate with a numerical model without making simplifying assumptions. Such a model, however, would need to be extensively tested against representative observations, which were not available for this study. Snowmelt simulated during three rain-on-snow events (measured in a previous study in a clearcut in the transient-snow zone of the H.J. Andrews Experimental Forest in Oregon) demonstrated that melt generation is most sensitive to turbulent- energy exchanges between the air and the snowpack surface. As a result, the most important climate variable that controls snowmelt is wind speed. Air temperature, however, is a significant variable also. The wind speeds were light, with a maximum of 3.3 meters per second during one event and average wind speeds for all three events ranging from 1.7 to 2.1 meters per second. For observed and estimated conditions, the average simulated snowmelt ranged from 0.2 to 0.8 millimeter liquid water per hour, and turbulent-energy exchange provided 51 percent of the energy that led to snowmelt during the largest of the three rain-on-snow events. When wind speeds were multiplied by a factor of 4, the simulated snowmelt ranged from 1.0 to 2.5 millimeters per hour. Similarly, when wind speeds were multiplied by a factor of 6, the simulated snowmelt ranged from 1.6 to 3.7 millimeters per hour. Turbulent-energy exchange provided a dominant 88 and 92 percent of the energy input to the snowpack during the largest rain-on-snow event when average wind speeds were multiplied by factors of 4 and 6, respectively. During the same event, the contribution to melt by the sum of net solar and net thermal radiation (net all-wave radiation) was roughly equal to the contribution of sensible energy carried by the precipitation itself (advective heat). Estimates of snowmelt resulting from rain on snow for climate conditions other than those observed and estimated in the simulated plot-scale data were expanded by simulating snowmelt for 24-hour presumed rain-on-snow events extracted from the reconstructed, long-term historical climate records for Cedar Lake and Snoqualmie Pass National Weather Service stations in Washington State. The selected events exceeded 75 millimeters of precipitation in 24 hours. When clearcut conditions were assumed to be identical to those at the H.J. Andrews Experimental Forest site and a ripe snowpack that never completely melted was assumed to be available, simulated 24-hour snowmelt ranged from 4.2 to 47.0 millimeters (0.2 to 2.0 millimeters per hour) for low wind speeds (1.5 meters per second) and from 10.3 to 178.8 millimeters (0.4 to 7.5 millimeters per hour) for high wind speeds (8.2 meters per second). The ranges in

Water-Resources Investigations Report↗
USGS2013

Forecasting the impact of storm waves and sea-level rise on Midway Atoll and Laysan Island within the Papahānaumokuākea Marine National Monument—a comparison of passive versus dynamic inundation models

Two inundation events in 2011 underscored the potential for elevated water levels to damage infrastructure and affect terrestrial ecosystems on the low-lying Northwestern Hawaiian Islands in the Papahānaumokuākea Marine National Monument. The goal of this study was to compare passive "bathtub" inundation models based on geographic information systems (GIS) to those that include dynamic water levels caused by wave-induced set-up and run-up for two end-member island morphologies: Midway, a classic atoll with islands on the shallow (2-8 m) atoll rim and a deep, central lagoon; and Laysan, which is characterized by a deep (20-30 m) atoll rim and an island at the center of the atoll. Vulnerability to elevated water levels was assessed using hindcast wind and wave data to drive coupled physics-based numerical wave, current, and water-level models for the atolls. The resulting model data were then used to compute run-up elevations using a parametric run-up equation under both present conditions and future sea-level-rise scenarios. In both geomorphologies, wave heights and wavelengths adjacent to the island shorelines increased more than three times and four times, respectively, with increasing values of sea-level rise, as more deep-water wave energy could propagate over the atoll rim and larger wind-driven waves could develop on the atoll. Although these increases in water depth resulted in decreased set-up along the islands’ shorelines, the larger wave heights and longer wavelengths due to sea-level rise increased the resulting wave-induced run-up. Run-up values were spatially heterogeneous and dependent on the direction of incident wave direction, bathymetry, and island configuration. Island inundation was modeled to increase substantially when wave-driven effects were included, suggesting that inundation and impacts to infrastructure and terrestrial habitats will occur at lower values of predicted sea-level rise, and thus sooner in the 21st century, than suggested by passive GIS-based "bathtub" inundation models. Lastly, observations and the modeling results suggest that classic atolls with islands on a shallow atoll rim are more susceptible to the combined effects of sea-level rise and wave-driven inundation than atolls characterized by a deep atoll rim.

Hawai'i↗
USGS2010

Evaluation of 11 equations for determining evaporation for a small lake in the North Central United States

Eleven equations for calculating evaporation were compared with evaporation determined by the energy budget method for Williams Lake, Minnesota. Data were obtained from instruments on a raft, on land near the lake, and at a weather station 60 km south of the lake. The comparisons were based on monthly values for the open-water periods of 5 years, a total of 22 months. A modified DeBruin-Keijman, Priestley-Taylor, and a modified Penman equation resulted in monthly evaporation values that agreed most closely with energy budget values. To use these equations, net radiation, air temperature, wind speed, and relative humidity need to be measured near the lake. In addition, thermal surveys need to be made to determine change in heat stored in the lake. If data from distant climate stations are the only data available, and they include solar radiation, the Jensen-Haise and Makkink equations resulted in monthly evaporation values that agreed reasonably well with energy budget values.

Minnesota↗
USGS2008

Multidecadal climate-induced variability in microseisms

Microseisms are the most ubiquitous continuous seismic signals on Earth at periods between approximately 5 and 25 s (Peterson 1993; Kedar and Webb 2005). They arise from atmospheric energy converted to (primarily) Rayleigh waves via the intermediary of wind-driven oceanic swell and occupy a period band that is uninfluenced by common anthropogenic and wind-coupled noise processes on land (Wilson et al. 2002; de la Torre et al. 2005). "Primary" microseisms (near 8-s period) are generated in shallow water by breaking waves near the shore and/or the nonlinear interaction of the ocean wave pressure signal with the sloping sea floor (Hasselmann 1963). Secondary microseisms occur at half of the primary period and are especially strongly radiated in source regions where opposing wave components interfere (Longuett-Higgins 1950; Tanimoto 2007), which principally occurs due to the interaction of incident swell and reflected/scattered wave energy from coasts (Bromirski and Duennebier 2002; Bromirski, Duennebier, and Stephen 2005). Coastal regions having a narrow shelf with irregular and rocky coastlines are known to be especially efficient at radiating secondary microseisms (Bromirski, Duennebier, and Stephen 2005; Shulte-Pelkum et al. 2004). The secondary microseism is globally dominant, and its amplitudes proportional to the square of the standing wave height (Longuett-Higgins 1950), which amplifies its sensitivity to large swell events (Astiz and Creager 1994; Webb 2006).

Seismological Research Letters↗
USGS2015

Dim ultraviolet light as a means of deterring activity by the Hawaiian hoary bat Lasiurus cinereus semotus

Widespread bat fatalities at industrial wind turbines are a conservation issue with the potential to inhibit efficient use of an abundant source of energy. Bat fatalities can be reduced by altering turbine operations, but such curtailment decreases turbine efficiency. If additional ways of reducing bat fatalities at wind turbines were available such tradeoffs might not be needed. Based on the facts that bats perceive distant objects primarily through vision and can see in very dim lighting conditions, and the possibility that bats might interact with turbines after approaching them as they would trees, we propose a novel method of reducing bat activity at wind turbines: illumination of the structure with dim light. As a first step toward assessing this approach, we illuminated trees with dim flickering ultraviolet (UV) light in areas frequented by Hawaiian hoary bats Lasiurus cinereus semotus , an endangered subspecies affected by wind turbines. We used a repeated-measures design to quantify bat activity near trees with acoustic detectors and thermal video cameras in the presence and absence of UV illumination, while concurrently monitoring insect numbers. Results indicate that dim UV reduces bat activity despite an increase in insect numbers. Experimental treatment did not completely inhibit bat activity near trees, nor did all measures of bat activity show statistically significant differences due to high variance in bat activity among sites. However, the observed decreases in bat activity with dim UV illumination justify further testing of this method as a means to reduce bat fatalities at wind turbines.

Hawaii↗
USGS2023

Interaction of a legacy groundwater contaminant plume with the Little Wind River from 2015 through 2017, Riverton Processing site, Wyoming

The Riverton Processing site was a uranium mill 4 kilometers southwest of Riverton, Wyoming, that prepared uranium ore for nuclear reactors and weapons from 1958 to 1963. The U.S. Department of Energy completed surface remediation of the uranium tailings in 1989; however, groundwater below and downgradient from the tailings site and nearby Little Wind River was not remediated. Beginning in 2010, a series of floods along the Little Wind River began to mobilize contaminants in the unsaturated zone, resulting in substantial increases of uranium and other contaminants of concern in monitoring wells completed inside the contaminant plume. In 2011, the U.S. Department of Energy started a series of university and Government agency retrospective and field investigations to understand the processes controlling contaminant increases in the groundwater plume. The goals of the field investigations described in this report were to (1) identify and quantify the contaminant flux and potential associated biological effects from groundwater associated with the legacy plume as it enters a perennial stream reach, and (2) assess chemical exposure and potential effects to biological receptors from the interaction of the contaminant plume and the river. Field investigations along the Little Wind River were completed by the U.S. Geological Survey during 2015–17 in cooperation with the U.S. Department of Energy Office of Legacy Management to characterize: (1) seepage areas and seepage rates; (2) pore-water and bed sediment chemistry and hyporheic exchange and reactive loss; and (3) exposure pathways and biological receptors. All data collected during the study are contained in two U.S. Geological Survey data releases, available at https://doi.org/10.5066/F7BR8QX4 and https://doi.org/10.5066/P9J9VJBR . A variety of tools and methods were used during the field characterizations. Streambed temperature mapping, electrical resistivity tomography, electromagnetic induction, fiber-optic distributed temperature sensing, tube seepage meters, vertical thermal sensor arrays, and an environmental tracer (radon) were used to identify areas of groundwater seepage and associated seepage rates along specific sections of the study reach of the river. Drive points, minipiezometers, diffusive equilibrium in thin-film/diffusive gradients in thin-film probes, bed-sediment samples, and equal discharge increment sampling methods were used to characterize pore-water chemistry, estimate hyporheic exchange and reactive loss of selected chemical constituents, and quantify contaminant loadings entering the study reach. Sampling and analysis of surface sediments, filamentous algae, periphytic algae, and macroinvertebrates were used to characterize biological exposure pathways, metal uptake, and receptors. Areas of focused groundwater discharge identified by the fiber-optic distributed temperature sensing surveys corresponded closely with areas of elevated electrical conductivity identified by the electromagnetic induction survey results in the top 5 meters of sediment. During three monitoring periods in 2016, the mean vertical seepage rate measured with tube seepage meters was 0.45 meter per day, ranging from −0.02 to 1.55 meters per day. Five of the 11 locations where vertical thermal profile data were collected along the study reach during August 2017 indicated mean upwelling values ranging from 0.11 to 0.23 meter per day. Radon data collected from the Little Wind River during June, July, and August 2016 indicated a consistent inflow of groundwater to the central part of the study reach, in the area congruous with the center of the previously mapped groundwater plume discharge zone. During August 2017, the greatest attenuation of uranium from reactive loss in pore-water samples was observed at three locations along the study reach, at depths between 6 and 15 centimeters, and similar trends in molybdenum attenuation were also observed. Bed-sediment concentration profiles collected during 2017 also indicated attenuation of uranium and molybdenum from groundwater during hyporheic mixing of surface water with the legacy plume during groundwater upwelling into the river. Streamflow measurements combined with equal discharge increment water sampling along the study reach indicated an increase in dissolved uranium concentrations in the downstream direction during 2016 and 2017. Net uranium load entering the Little Wind River study reach was about 290 and 435 grams per day during 2016 and 2017, respectively. Biological samples indicated that low levels of uranium and molybdenum exposure were confined to the benthos in the Little Wind River within and immediately downstream from the perimeter of the groundwater plume. Concentrations of molybdenum and uranium in filamentous algae were consistently low at all sites in the study reach with no indication of increased exposure of dissolved bioavailable molybdenum or uranium at sites next to or downstream from the groundwater plume. Comparison of the August 2017 results from electromagnetic induction, tube seepage meters, vertical thermal profiling, and pore-water chemistry surveys were in general agreement in identifying areas with upwelling groundwater conditions along the study reach. However, the electroconductivity values measured with electromagnetic induction in the top 100 centimeters of sediment did not agree with sodium concentrations measured in pore-water samples collected at similar streambed depths. Differences and similarities between multiple methods can result in additional insights into hydrologic and biogeochemical processes that may be occurring along a reach of a river system interacting with shallow groundwater inputs. It may be advantageous to apply a variety of geophysical, geochemical, hydrologic, and biological tools at other Uranium Mill Tailings Remedial Action ( https://www.energy.gov/sites/prod/files/2014/10/f19/UMTRCA.pdf ) sites during the investigation of legacy contaminant plume interactions with surface-water systems.

Wyoming↗
USGS2025

Modeling diverse environmental responses of reservoirs to floating photovoltaic systems

Floating photovoltaic (FPV) systems are emerging as a promising strategy for large-scale clean energy production worldwide. However, by altering key physical drivers such as solar radiation and wind mixing, FPV installations may have also unintended consequences for lakes and reservoirs. Given the wide diversity of freshwater systems globally, understanding the consistency in direction and magnitude of environmental responses to FPV deployment is critical for informed regulatory oversight and sustainable energy development. Here, we used process-based models to simulate the effects of FPV coverage on 11 reservoirs across the United States. This is the first multi-reservoir analysis using a laterally averaged 2D process-based modeling framework to systematically evaluate FPV impacts across diverse climatic and morphometric contexts, enabling direct comparison of magnitude and direction of responses among systems. Specifically, we evaluated changes in (1) surface and outflow temperature, (2) thermocline depth, (3) water column stability, (4) dissolved oxygen concentrations, and (5) potential suitable habitat availability for warm- and cold-water fishes. We quantified changes in these response variables by an iterative approach that simulates increases in FPV coverage and compares them with reference conditions. We summarized responses for winter (January–February) and summer (July–August). As expected, our simulations show that increasing FPV coverage consistently cooled surface waters and altered thermal stratification patterns, but the magnitude and environmental implications of these changes varied among reservoirs. Notably, greater FPV coverage led to increased variability in habitat suitability for aquatic species, with some reservoirs exhibiting distinct and sometimes divergent responses. These findings underscore the importance of considering local environmental contexts when assessing FPV impacts. While large-scale FPV systems offer potential benefits for climate mitigation, their ecological effects, particularly on thermally sensitive biota, require careful site-specific evaluation to avoid unintended consequences to local freshwater biodiversity.

Arkansas, Idaho, Ohio, Oregon, Tennessee, Washingt↗
USGS2024

Tracking data highlight the importance of human-induced mortality for large migratory birds at a flyway scale

Human-induced direct mortality affects huge numbers of birds each year, threatening hundreds of species worldwide. Tracking technologies can be an important tool to investigate temporal and spatial patterns of bird mortality as well as their drivers. We compiled 1704 mortality records from tracking studies across the African-Eurasian flyway for 45 species, including raptors, storks, and cranes, covering the period from 2003 to 2021. Our results show a higher frequency of human-induced causes of mortality than natural causes across taxonomic groups, geographical areas, and age classes. Moreover, we found that the frequency of human-induced mortality remained stable over the study period. From the human-induced mortality events with a known cause ( n = 637), three main causes were identified: electrocution (40.5 %), illegal killing (21.7 %), and poisoning (16.3 %). Additionally, combined energy infrastructure-related mortality (i.e., electrocution, power line collision, and wind-farm collision) represented 49 % of all human-induced mortality events. Using a random forest model, the main predictors of human-induced mortality were found to be taxonomic group, geographic location (latitude and longitude), and human footprint index value at the location of mortality. Despite conservation efforts, human drivers of bird mortality in the African-Eurasian flyway do not appear to have declined over the last 15 years for the studied group of species. Results suggest that stronger conservation actions to address these threats across the flyway can reduce their impacts on species. In particular, projected future development of energy infrastructure is a representative example where application of planning, operation, and mitigation measures can enhance bird conservation.

Biological Conservation↗
USGS2026

The Sand AbrasioN Device for Aeolian Research (SANDAR): A new experimental device for investigating how wind transport affects sand on Earth and Mars

On Earth and Mars, aeolian transport causes sand grains to become abraded, resulting in mineralogic and textural changes. Understanding how sands evolve, or mature, with transport via experimental studies is important for understanding the origins, geologic history, and cycling of sediments, as well as dust production. Previous experimental works have used a variety of methods to simulate aeolian transport in the laboratory, but practical limitations and similitude concerns have limited such research. Here, we present and validate the Sand AbrasioN Device for Aeolian Research (SANDAR), a modified air mill that uses pressurized air to circulate sand around a small abrasion chamber, simulating the effects of aeolian transport. This device is re-circulating to simulate long-distance transport, and it allows for repeated analyses of well-constrained sediment samples, revealing their evolution over time. It is compatible with the grain sizes (74–500 μm) and grain impact velocities (∼0.6–3.7 m/s) typically expected for natural aeolian environments, and is also adaptable for diverse applications simulating different wind conditions. We show that the SANDAR achieves similitude of kinetic energy with respect to saltating sand on both Earth and Mars. SEM and optical microscope imaging reveal that the SANDAR produces microtextures on the surfaces of sand grains similar to those found with natural aeolian transport, demonstrating that it effectively simulates the mechanical effects of aeolian processes. Thus, the SANDAR is a valid tool for use in experimental research to improve our understanding of sedimentary processes across the Solar System.

Aeolian Research↗
USGS2003

Estimation of Monthly Evaporation from Lake Ashtabula in North Dakota, Orwell Lake in Minnesota, and Lake Traverse in Minnesota and South Dakota, 1931-2001

Reservoirs on tributaries of the Red River of the North provide water for Fargo and Grand Forks, N. Dak., and other cities along the river. Adequate estimates of evaporative losses from the reservoirs are needed to determine the total water supply in the Basin. Many equations could be used to estimate lake or reservoir evaporation. However, in addition to measurements of air temperature, the equations require measurements of net radiation, wind speed, and relative humidity. Evaporation and air temperature data from energy budget evaporation sites at Wetland P1 in North Dakota and at Williams Lake in Minnesota are available. Air temperature data collected from climate stations near Lake Ashtabula in North Dakota, from Orwell Lake in Minnesota, and from Lake Traverse in Minnesota and South Dakota also are available. Therefore, the combined data sets were used to estimate monthly evaporation from Lake Ashtabula, Orwell Lake, and Lake Traverse. Averaged monthly mean air temperatures determined for each reservoir study site were used to calculate monthly evaporation data sets for 1931-2001. Results from the procedure that estimates reservoir evaporation indicate that slight downward trends in annual evaporation occurred from 1931-2001. The trends may have been caused by the selected time period of the study, which began with the drought conditions in the mid 1930's and ended with the more wet conditions in the late 1990's. Average annual evaporation values for each reservoir for 1931-2001 correspond well with published average annual lake evaporation values for 1946-55.

Water-Resources Investigations Report↗
USGS1978

Reaeration capacity of the Rock River between Lake Koshkonong, Wisconsin and Rockton, Illinois

The reaeration capacity of the Rock River from Lake Koshkonong, Wisconsin, to Rockton, Illinois, was determined using the energy-dissipation model. The model was calibrated using data from radioactive-tracer measurements in the study reach. Reaeration coefficients (K2) were computed for the annual minimum 7-day mean discharge that occurs on the average of once in 10 years (Q7,10). A time-of-travel model was developed using river discharge, slope, and velocity data from three dye studies. The model was used to estimate traveltime for the Q7,10 for use in the energy-dissipation model. During one radiotracer study, 17 mile per hour winds apparently increased the reaeration coefficient about 40 times. (Woodard-USGS)

Wisconsin↗
USGS2023

Monitoring of wave, current, and sediment dynamics along the Chincoteague living shoreline, Virginia

Nature-based features, also called living shorelines, are increasingly applied in coastal protection and restoration. However, the processes and mechanisms (feedbacks and interactions) of wave attenuation, current velocity change, and sediment deposition and erosion along the living shoreline remain unclear, thus limiting the adaptive management of living shoreline restoration projects for coastal shoreline resilience under future storm conditions. In this study, wave, current, and sediment dynamics along the Little Toms Cove living shoreline, Chincoteague National Wildlife Refuge, Virginia, a low wave energy environment, were investigated during a 2-month winter period in 2019 to examine the effects of living shoreline structures on shoreline protection and oyster habitat enhancement. It was found that wave attenuation by the living shoreline structures (oyster castles or constructed oyster reefs) is dependent on water depth, wind speed, wind direction, and local bathymetry. Analysis of observed data indicate that the oyster castles along the Little Toms Cove living shoreline play a limited role in wave attenuation in this low wave energy environment. During the 2-month winter period, wave energy was attenuated by 39.7 percent when oyster castles were emergent or slightly submerged with southwest winds. In contrast, when the oyster castles were fully submerged, wave energy behind the oyster castles increased by 38.6 percent. The construction of oyster castles affected circulation patterns with increase or decrease in velocity at nearshore waters protected by the castles depending on locations of measurements in relation to the oyster castles. Bottom shear stress analysis indicates that tidal currents play a larger role than waves on shoreline and marsh edge erosion along the Little Toms Cove shoreline during the 2 months of field monitoring. The oyster castles protecting the marsh edge and tidal flat from erosion resulted in higher fine sediment concentration in the water column landward of the castles because more sediment was retained in the lee side of the castles. It is important to maximize sediment within the wetlands and adjacent mudflats behind the oyster castles. Erosion from the marsh edge and interior serves as the major source of sediment for this wetland system due to the limited sediment supply in Assateague Channel. Furthermore, it was found that the oyster castles along the Little Toms Cove living shoreline were inundated more than 60 percent of the time, leading to the enhanced oyster habitat as evidenced by suitable velocity (less than 10 centimeters per second) and mean grain size (less than 0.08 millimeters) for oyster feeding and the increased oyster shell density and growth in the intertidal zone protected by the castles than in the control area. More field data (for example, concurrent monitoring of sediment concentration and salinity) over other seasons (for example, summer) could help examine the long term and combined engineering and ecological benefits of living shoreline restoration projects under seasonal and enhanced future storm conditions.

Virginia↗
USGS2013

Does centennial morphodynamic evolution lead to higher channel efficiency in San Pablo Bay, California?

Measured bathymetries on 30 year interval over the past 150 years show that San Pablo Bay experienced periods of considerable deposition followed by periods of net erosion. However, the main channel in San Pablo Bay has continuously narrowed. The underlying mechanisms and consequences of this tidal channel evolution are not well understood. The central question of this study is whether tidal channels evolve towards a geometry that leads to more efficient hydraulic conveyance and sediment throughput. We applied a hydrodynamic process-based, numerical model (Delft3D), which was run on 5 San Pablo Bay bathymetries measured between 1856 and 1983. Model results shows increasing energy dissipation levels for lower water flows leading to an approximately 15% lower efficiency in 1983 compared to 1856. During the same period the relative seaward sediment throughput through the San Pablo Bay main channel increased by 10%. A probable explanation is that San Pablo Bay is still affected by the excessive historic sediment supply. Sea level rise and Delta surface water area variations over 150 years have limited effect on the model results. With expected lower sediment concentrations in the watershed and less impact of wind waves due to erosion of the shallow flats, it is possible that energy dissipations levels will decrease again in future decades. Our study suggests that the morphodynamic adaptation time scale to excessive variations in sediment supply to estuaries may be on the order of centuries.

California↗
USGS2002

The dynamics of subtidal poleward flows over a narrow continental shelf, Palos Verdes, CA

The Palos Verdes peninsula is a short, very narrow (< 3 km) shelf in southern California that is bracketed by two large embayments. In May 1992, arrays of up to 4 moorings and 2 benthic tripods were deployed in a yearlong study of the circulation processes over this shelf and the adjacent slope. Wind stress, coastal sea level, atmospheric pressure and wave records were obtained from offshore sites and from coastal stations surrounding Palos Verdes. Bottom stress calculated for the mid-shelf sites using a boundary-layer model and data from the above instruments indicated the bottom drag coefficient over this shelf is about 0.003 Currents flow toward the northwest along the shelf and upper slope. Speeds are generally around 20-30 cm/s. There was no obvious seasonal structure in the flow. The first EOF for subtidal alongshelf current accounted for nearly 70% of the variance at sites on the shelf and upper slope. The dominant fluctuations had periods between 5 and 20 days, periods longer than seen in the regional wind stress field. Coastal sea level and the alongshore gradient in sea level had a similar concentration of energy in the 5-20 day frequency band. About 30% of the alongshelf flow was coherent with the alongshelf pressure gradient; currents flowed down the pressure gradient with minimal phase lag. Winds accounted for only 15-20% of the variance in subtidal currents, but the measured effect of wind stress was large. A 1 dyne/cm2 wind stress was associated with a 20-30 cm/s alongshore current. Both the regional wind stress and the alongshelf pressure gradients had spatial scales much larger than found on this small shelf. Subtidal flows forced by these regional fields were set up in the adjacent, much broader basins. The currents amplified as they moved onto the narrow shelf between the basins. Hence, local wind-driven currents had anomalously large amplitudes. The momentum equations for alongshelf wind or pressure gradients did not balance because some of the measured terms were associated with regional fields, others with local process. Our observations suggest that it is more difficult to determine which measured fields reflect the local processes in regions with rapidly changing topography. ?? 2002 Elsevier Science Ltd. All rights reserved.

Continental Shelf Research↗
USGS2013

Insect prey eaten by Hoary Bats ( Lasiurus cinereus ) prior to fatal collisions with wind turbines

Wind turbines are being deployed all across the world to meet the growing demand for energy, and in many areas, these turbines are causing the deaths of insectivorous migratory bats. One of the hypothesized causes of bat susceptibility is that bats are attracted to insects on or near the turbines. We examined insect remains in the stomachs and intestines of hoary bats ( Lasiurus cinereus ) found dead beneath wind turbines in New York and Texas to evaluate the hypothesis that bats die while feeding at turbines. Most of the bats we examined had full stomachs, indicating that they fed in the minutes to hours leading up to their deaths. However, we did not find prey in the mouths or throats of any bats that would indicate the bats died while capturing prey. Hoary bats fed mostly on moths, but we also detected the regular presence of beetles, true bugs, and crickets. Presence of terrestrial insects in stomachs indicates that bats may have gleaned them from the ground or the turbine surfaces, yet aerial capture of winged insect stages cannot be ruled out. Our findings confirm earlier studies that indicate hoary bats feed during migration and eat mostly moths. Future studies on bat behaviors and insect presence at wind turbines could help determine whether feeding at turbines is a major fatality risk for bats.

Western North American Naturalist↗
USGS2019

Wind sheltering impacts on land-atmosphere fluxes over fens

Wetlands and their ability to mitigate climate change motivates restorative and protective action; however, scientific understanding of land-atmosphere interactions is restricted by our limited continuous observations of gaseous fluxes. Many wetlands are small in spatial scale and embedded in forested landscapes. Yet, little is known about how the relative sheltering of forests affects net carbon (C) and energy balance. Here, we analyze coterminous USGS and Ameriflux eddy covariance flux tower observations over three years in two shrub fens in Northern Wisconsin, one more sheltered (US-ALQ) than the other (US-Los). Unsurprisingly, the open site showed higher overall wind speeds. This should have implications for atmospheric fluxes in wetlands as wind-forced processes are essential in promoting gas exchange over water. While both sites had similar half-hourly net ecosystem exchange of CO2 (NEE) during daytime, there were significant differences in nighttime NEE, as well as in net radiation partitioning in early spring and late summer. Sensible heat (H) fluxes were smaller at the sheltered fen except for the months of July-September. In contrast, latent heat (LE) fluxes were higher in every month except July. Additionally, sheltered fen ecosystem respiration had a weaker linear correlation with air temperature (R: 0.08 versus 0.57 for the open fen). Our work suggests that canopy sheltering does not cause significant differences in half-hourly NEE during the day, but rather the largest differences such as lower CO2 emissions occur at nighttime due to higher variance at very low wind speeds. Sheltering also influenced direction of air flow, mean wind speeds in day versus night, energy balance, and sensible and latent heat fluxes. We discuss implications of these findings for wetland restoration.

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