Instrumented Field Sites Research Articles

Research priorities for sound and vibration effects on fishes and aquatic invertebrates from offshore wind energy development

There are substantial knowledge gaps regarding both the bioacoustics and the responses of animals to sounds associated with pre-construction, construction, and operations of offshore wind (OSW) energy development. A workgroup of the 2020 State of the Science Workshop on Wildlife and Offshore Wind Energy recommended priority studies for the next five years to help stakeholders better understand potential cumulative biological impacts of sound and vibration to fishes and aquatic invertebrates as the OSW industry develops. The workgroup identified seven short-term priorities that include a mix of primary research and coordination efforts. Key research needs include the examination of animal displacement and other behavioral responses to sound, as well as hearing sensitivity studies related to particle motion, substrate vibration, and sound pressure. Other needs include: identification of priority taxa on which to focus research; standardization of methods; development of a long-term highly instrumented field site; and examination of sound mitigation options for fishes and aquatic invertebrates. Effective assessment of potential cumulative impacts of sound and vibration on fishes and aquatic invertebrates is currently precluded by these and other knowledge gaps. Filling critical gaps in knowledge will improve our understanding of possible sound-related impacts of OSW energy development to populations and ecosystems.

Offshore wind energy development: Research priorities for sound and vibration effects on fishes and aquatic invertebrates.

There are substantial knowledge gaps regarding both the bioacoustics and the responses of animals to sounds associated with pre-construction, construction, and operations of offshore wind (OSW) energy development. A workgroup of the 2020 State of the Science Workshop on Wildlife and Offshore Wind Energy identified studies for the next five years to help stakeholders better understand potential cumulative biological impacts of sound and vibration to fishes and aquatic invertebrates as the OSW industry develops. The workgroup identified seven short-term priorities that include a mix of primary research and coordination efforts. Key research needs include the examination of animal displacement and other behavioral responses to sound, as well as hearing sensitivity studies related to particle motion, substrate vibration, and sound pressure. Other needs include: identification of priority taxa on which to focus research; standardization of methods; development of a long-term highly instrumented field site; and examination of sound mitigation options for fishes and aquatic invertebrates. Effective assessment of potential cumulative impacts of sound and vibration on fishes and aquatic invertebrates is currently precluded by these and other knowledge gaps. However, filling critical gaps in knowledge will improve our understanding of possible sound-related impacts of OSW energy development to populations and ecosystems.

Hydrologic modeling of reach scale fluxes from flood irrigated fields

Agricultural water is of considerable interest to water managers and policymakers as irrigation—particularly flood irrigation—accounts for the largest portion of freshwater use. However, characterization of how and when flood applied water contributes to storage and adjacent surface water bodies via return flow remains limited, particularly relative to the volume of studies addressing surface processes. This study focuses on improving our understanding of return flow paths and explicitly quantifying subsurface return flow contributions using hydro-geophysical observations coupled with a vadose zone transport flow model. Our approach, which simulates return flow in agricultural fields in a small, heavily instrumented field site in northern Wyoming, leverages daily measured values of evapotranspiration obtained from a large aperture scintillometer and atmospheric conditions, and uses seismic data to characterize heterogeneous structure of the soil profiles at field scale. We use these high-resolution, site specific datasets to parameterize a process-based vadose zone flow model that quantifies hydrologic response to flood irrigation along the stream reach, allowing us to identify return flow fluxes out of the fields. Using our approach, we found that the majority of applied irrigation water (60%) left the fields through subsurface flow paths, while only 13% was consumed by vegetation. Subsurface runoff over less-permeable soil layers, governed by the subsurface structural characteristics, was identified as the dominant subsurface flow process contributing to fluxes out of the fields. Importantly, our findings about the importance of subsurface return flow paths nuance previous research which has emphasized surface flow paths. By improving our understanding of return flow processes through a high- resolution vadose zone model that leverages climatological, geophysical, and hydrological observations, this study advances our understanding of return flow processes. Understanding how subsurface characteristics influence return flow generation in semi-arid agriculturally productive regions will help managers and policy makers balance desires for improved irrigation efficiency against concerns about irrigation-dependent ecosystem services.

Development and validation of algorithms for LST measurement from NOAA-11/AVHRR satellite data

The purpose of this project was to develop the algorithms and characterise measurement errors of land surface temperature (LST). An initial investigation of the accuracy of retrieval of LST has employed synthetic radiances, produced using Lowtran7, for a series of land and atmospheric situations representative of the Australian continental climate. The synthetic data have been modelled to incorporate variation of surfaces emissivity, atmospheric temperature, water vapour profile, and the surface or boundary temperature. The study indicated that the success of the scheme depended on the validity of the modelled radiances, particularly with respect to the formulation of the radiative role of the water vapour constituent of the atmosphere. Whirls, the use of regression in deriving the coefficients for LST equation minimised the bias errors in the radiative transfer calculation that may arise from air mass dependence. However, our algorithms derived using statistical regression and synthetic atmospheres indicated good accuracy for LST measurement with and rms error of order 1°C when validated using data for an instrumented field site.

Advances in understanding river‐groundwater interactions

AbstractRiver‐groundwater interactions are at the core of a wide range of major contemporary challenges, including the provision of high‐quality drinking water in sufficient quantities, the loss of biodiversity in river ecosystems, or the management of environmental flow regimes. This paper reviews state of the art approaches in characterizing and modeling river and groundwater interactions. Our review covers a wide range of approaches, including remote sensing to characterize the streambed, emerging methods to measure exchange fluxes between rivers and groundwater, and developments in several disciplines relevant to the river‐groundwater interface. We discuss approaches for automated calibration, and real‐time modeling, which improve the simulation and understanding of river‐groundwater interactions. Although the integration of these various approaches and disciplines is advancing, major research gaps remain to be filled to allow more complete and quantitative integration across disciplines. New possibilities for generating realistic distributions of streambed properties, in combination with more data and novel data types, have great potential to improve our understanding and predictive capabilities for river‐groundwater systems, especially in combination with the integrated simulation of the river and groundwater flow as well as calibration methods. Understanding the implications of different data types and resolution, the development of highly instrumented field sites, ongoing model development, and the ultimate integration of models and data are important future research areas. These developments are required to expand our current understanding to do justice to the complexity of natural systems.

Delta‐Flux: An Eddy Covariance Network for a Climate‐Smart Lower Mississippi Basin

Core Ideas The Lower Mississippi River Basin (LMRB) is agriculturally important and ecologically unique. The Delta‐Flux network will coordinate the activities of 17 eddy covariance towers. The network addresses the need for scaled C and water cycle observations. The network aims to promote sustainable, climate‐smart land management. Delta‐Flux is open to collaborators from strategic sites and relevant disciplines. Networks of remotely monitored research sites are increasingly the tool used to study regional agricultural impacts on carbon and water fluxes. However, key national networks such as the National Ecological Observatory Network and AmeriFlux lack contributions from the Lower Mississippi River Basin (LMRB), a highly productive agricultural area with opportunities for soil carbon sequestration through conservation practices. The authors describe the rationale to create the new Delta‐Flux network, which will coordinate efforts to quantify carbon and water budgets at seventeen eddy covariance flux tower sites in the LMRB. The network structure will facilitate climate‐smart management strategies based on production‐scale and continuous measurements of carbon and water fluxes from the landscape to the atmosphere under different soil and water management conditions. The seventeen instrumented field sites are expected to monitor fluxes within the most characteristic landscapes of the target area: row‐crop fields, pasture, grasslands, forests, and marshes. The network participants are committed to open collaboration and efficient regionalization of site‐level findings to support sustainable agricultural and forestry management and conservation of natural resources.

Bacterial contamination of tile drainage water and shallow groundwater under different application methods of liquid swine manure

A 2 year field experiment evaluated liquid manure application methods on the movement of manure-borne pathogens (Salmonella sp.) and indicator bacteria (Escherichia coli and Clostridium perfringens) to subsurface water. A combination of application methods including surface application, pre-application tillage, and post-application incorporation were applied in a randomized complete block design on an instrumented field site in spring 2007 and 2008. Tile and shallow groundwater were sampled immediately after manure application and after rainfall events. Bacterial enumeration from water samples showed that the surface-applied manure resulted in the highest concentration of E. coli in tile drainage water. Pre-tillage significantly (p < 0.05) reduced the movement of manure-based E. coli and C. perfringens to tile water and to shallow groundwater within 3 days after manure application (DAM) in 2008 and within 10 DAM in 2007. Pre-tillage also decreased the occurrence of Salmonella sp. in tile water samples. Indicator bacteria and pathogens reached nondetectable levels within 50 DAM. The results suggest that tillage before application of liquid swine manure can minimize the movement of bacteria to tile and groundwater, but is effective only for the drainage events immediately after manure application or initial rainfall-associated drainage flows. Furthermore, the study highlights the strong association between bacterial concentrations in subsurface waters and rainfall timing and volume after manure application.

Field Verification of Stable Perched Groundwater in Layered Bedrock Uplands

Data substantiating perched conditions in layered bedrock uplands are rare and have not been widely reported. Field observations in layered sedimentary bedrock in southwestern Wisconsin, USA, provide evidence of a stable, laterally extensive perched aquifer. Data from a densely instrumented field site show a perched aquifer in shallow dolomite, underlain by a shale-and-dolomite aquitard approximately 25 m thick, which is in turn underlain by sandstone containing a 30-m-thick unsaturated zone above a regional aquifer. Heads in water supply wells indicate that perched conditions extend at least several kilometers into hillsides, which is consistent with published modeling studies. Observations of unsaturated conditions in the sandstone over a 4-year period, historical development of the perched aquifer, and perennial flow from upland springs emanating from the shallow dolomite suggest that perched groundwater is a stable hydrogeologic feature under current climate conditions. Water-table hydrographs exhibit apparent differences in the amount and timing of recharge to the perched and regional flow systems; steep hydraulic gradients and tritium and chloride concentrations suggest there is limited hydraulic connection between the two. Recognition and characterization of perched flow systems have practical importance because their groundwater flow and transport pathways may differ significantly from those in underlying flow systems. Construction of multi-aquifer wells and groundwater withdrawal in perched systems can further alter such pathways.

Radiative impact of boreal smoke in the Arctic: Observed and modeled

The Arctic climate is modulated, in part, by the presence of aerosols that affect the horizontal and vertical distribution of radiant energy passing through the atmosphere. Aerosols affect the surface‐atmosphere radiation balance directly through interactions with solar and terrestrial radiation and indirectly through interactions with cloud particles. During summer 2004 forest fires destroyed vast areas of boreal forest in Alaska and western Canada, releasing smoke into the atmosphere. Smoke aerosol passing over instrumented field sites near Barrow, Alaska, was monitored to determine its physical and optical properties and its impact on the surface radiation budget. Empirical determinations of the direct aerosol radiative forcing (DARF) by the smoke were used to corroborate simulations made using the Moderate Resolution Transmittance radiative transfer model, MODTRAN™5. DARF is defined as the change in net shortwave irradiance per unit of aerosol optical depth (AOD). DARF, varying with solar angle and surface type, was evaluated at the surface, at the top of the atmosphere (TOA), and within the intervening layers of the atmosphere. The TOA results are compared with fluxes derived from coincident satellite retrievals made using the Clouds and the Earth's Radiant Energy System (CERES) radiance data. Smoke tends to reduce the net shortwave irradiance at the surface while increasing it within layers in which it resides. Over the Arctic tundra during summer, a layer of smoke having AOD = 0.5 at 500 nm produces a diurnally averaged DARF of about −40 W m−2 at the surface and −20 W m−2 at TOA, while the layer itself tends to warm at a rate of ≈1 K d−1. The tendency of smoke to cool the surface while heating the layer above may lead to increased atmospheric stability and suppress cloud formation. Radiative forcing at the top of the atmosphere is especially sensitive to small changes in surface albedo, evidenced in both the model results and satellite retrievals. TOA net shortwave flux decreases when smoke is present over dark surfaces and tends to increase if the underlying surface is bright. For example, at solar noon during midsummer at Barrow, a layer of smoke having AOD(500) = 0.5 will reduce the net shortwave flux at TOA by ≈30 W m−2 over the ocean while at the same time increasing it by 20 W m−2 over an adjacent area of melting sea ice. For smoke aerosol, the sensitivity of DARF to changing surface albedo (assuming a solar zenith angle of 50°) is about +15 W m−2 AOD−1 for every increase in surface albedo of 0.10. Throughout the Arctic summer, surface and TOA cooling and a tendency toward warming in the intervening atmospheric layers are the dominant radiative impacts of boreal smoke over the ocean and tundra areas, but the radiative forcing at TOA is positive over regions covered by ice or snow. Enhanced differential cooling/heating of ocean, ice, and snow due to the presence of smoke in the atmosphere may affect regional circulation patterns by perturbing diabatic processes. Should the frequency and intensity of boreal fires increase in the future because of global warming, the more persistent presence of smoke in the atmosphere may be manifest as a negative feedback at the surface. In addition, there will likely be indirect radiative impacts of the smoke as it influences cloudiness, which in turn further modulates the Arctic radiation budget.

Incursions and radiative impact of Asian dust in northern Alaska

The Arctic region is sensitive to incursions of aerosols that affect its radiation balance, directly through interactions with solar and terrestrial radiation and indirectly as cloud condensation nuclei. During spring 2002 dust was transported from the Gobi desert passing over instrumented field sites near Barrow, Alaska, providing the opportunity to measure the dust properties. Empirical determinations of the direct radiative forcing by dust were used to corroborate simulations made using the Moderate Resolution Transmittance radiative transfer code, MODTRAN™5. During sunlit periods, dust cools the surface while warming those layers in which it resides, increasing atmospheric stability. At night, dust layers tend to cool while the surface warms slightly due to infrared emissions from the dust layer.

PM 10 emission from agricultural soils on the Columbia Plateau: comparison of dynamic and time-integrated field-scale measurements and entrainment mechanisms

Emission of particles less than 10 μm mean diameter (PM 10) from agricultural sources is an environmental issue due to health concerns and potential effects on local and global climate. The Columbia Plateau region of Washington and Oregon contains vast deposits of fine loess soils and is an active PM 10 emission source. An instrumented field site was established to continuously monitor meteorological conditions and PM 10 concentrations at 10 min intervals during periods of high winds (defined as sustained wind speeds >5 m s −1 at 2 m height) during the 2001 and 2002 field seasons. Time-integrated measurements of PM 10 and total soil movement were made using high volume air samplers (HiVols) and BSNE sediment traps, respectively. Particle impact sensors (Sensits ®) monitored particle movement (i.e. saltation) close to the surface. Tapered element oscillating microbalances (TEOMs) and wind velocity profiles were utilized to examine short-time-interval dust emission dynamics of fallow, dryland fields. TEOM data clearly identified periods of active PM 10 emission. TEOM and HiVol PM 10 concentrations integrated during high wind events (HWE) showed excellent agreement. Time-integrated PM 10 concentrations were well-correlated with horizontal soil mass transport. However, few saltator impacts were recorded during high wind events. Analysis of wind velocity profiles and friction velocities indicated little saltation was occurring. In general, for continuous emission of PM 10 from fallow fields with dust mulch conditions, threshold friction velocity was approximately 0.4 m s −1 and threshold velocity was approximately 8 m s −1. Several wind events showed evidence where PM 10 concentration gradients were extremely small, the PM 10 being well-mixed between 1 and 3 m heights.

Three-dimensional effects of hydraulic conductivity enhancement and desaturation around mined panels

Changes in the three-dimensional hydraulic conductivity field that accompany undermining by a longwall panel are evaluated to define the potential for changes in flow patterns and desaturation. Relations linking changes in conductivity with the mining-induced strain field that develops around the advancing face are defined through the assumption of an equivalent porous medium with the strain partition between fractures and matrix apportioned relative to respective deformation constants. Model results are validated against behavior recorded at a well instrumented field site, replicating the complex steady flow pattern that develops around an advancing longwall face. Significant hydraulic conductivity increases are restricted to strata at shallow depth, ahead of the advancing face, and to deep zones behind the face, particularly in the caving zone and abutment shear zones. These very large increases in conductivity at depth, that include the out-of-section conductivity enhancement that develops along the panel rib, exercise primary control on induced water level changes and the potential for saturation. Zones of desaturation are readily defined, with these enabling locations of well vulnerability (to water loss) to be identified. These zones of vulnerability are directly above the panel, with their extent potentially modulated by the presence and the location of flatlying layers of low conductivity. The complex response recorded in the near-face region mandates use of three-dimensional models to adequately represent observed behavior.

WIND EROSION: FIELD LENGTH

As the wind passes over eroding soil surfaces, the quantity of soil transported by wind between the soil surface and 2 m above the surface increases until the wind stream becomes saturated. The relationship between field length and the mass transported was used to test a transport model that has the form of a sigmoid curve. At the upwind portion of the field, the rate of increase in mass being transported is limited by the emission rate from the soil surface. The mathematics of the sigmoid equation implies that when 63% of the maximum transport capacity of the wind has been satisfied (field length at this point is called critical field length), the rate of increase in transport mass gradually decreases and approaches zero when the wind is saturated with soil particles. From the instrumented field sites, a maximum transport rate of 1231 kg/m width and average soil losses of 7.801 kg/m 2 were measured from a single event on a 2.6-ha field at Elkhart, Kansas. Critical field length varied from 31 to 129 m, depending on wind velocity and field conditions. Field mass transport data supports that a self-balancing mechanism of momentum extraction from the surface wind by accelerating soil particles and the associated shear stress reduction will limit the quantity of material that can be transported between the soil surface and a height of 2 meters.

Measurements of methane fluxes on the landscape scale from a wetland area in North Scotland

Atmospheric profiles of methane have been measured using an aircraft over an area of natural wetland in Northern Britain, Caithness and Sutherland, in Scotland. The measurements showed a clear horizontal gradient in methane concentration as air was advected over the wetland area from the Atlantic Ocean and a strong decrease in concentration in the vertical. The data, together with those from ground-based measurements including continuous measurements at an instrumented field site, were used to estimate area averaged fluxes using a simple diffusion model. The mean flux for the region was calculated to be 0.91 ± 0.51 μg m 2s−1. Methane source strengths for the NW region of Scotland were a factor of 2–3 times larger than for the NE region. Nocturnal methane fluxes were estimated at the field site from temporal concentration changes in methane near the surface and doppler sodar measurements of the boundary layer depth. Night time fluxes were found to be 0.45 ± 0.28 μg m−2s−1 and were comparable to those measured using the flux gradient technique at the same site. The aircraft area averaged fluxes were typically a factor of 2–4 times larger than those measured by cuvette techniques at the surface. This was probably due to the dryness of the site relative to the are to the west.

Frost heave characteristics of undisturbed sensitive Champlain Sea clay

Undisturbed Champlain Sea clay samples were subjected to laboratory freezing tests with pore-pressure measurements in order to determine the freezing characteristics of a structured compressible soil. Step-freezing and ramped-freezing tests with applied back pressure were conducted on 10 cm high samples in open-system conditions. Significant pore-pressure reductions in the unfrozen soil induce important frost-induced consolidation and destructuration of the clay. It was found that the freezing characteristics of Saint-Alban clay are best defined by the segregation potential at the active ice lens, SPℓ, which includes water fluxes generated within the frozen fringe and within the unfrozen soil as excess water is expelled during consolidation, and finally water from an external source. For the Saint-Alban clay, SPℓ values of the intact clay ranged between 450 and 600 × 10−5 mm2/(s °C), whereas those of destructured clay at a lower void ratio were significantly smaller. Back-calculating the segregation potential solely from surface heave measurements in laboratory tests may underestimate considerably the frost susceptibility of compressible structured clays. Segregation potential inferred from instrumented field sites was 430 × 10−5 mm2/(s °C) and is consistent with the laboratory tests results. Key words : freezing, frost heave, structured clay, undisturbed, consolidation.

Movement and fate of atrazine and bromide in central Kansas croplands

Two flooding experiments were conducted at two sites with different soils to study the transport and fate of the commonly used herbicide atrazine and inorganic chemicals in the Great Bend Prairie croplands of south-central Kansas. The instantaneous profile method supplemented by the use of an organic (atrazine) and an inorganic (bromide) tracer chemical was used to characterize in situ the hydraulic and chemical properties of the appropriately instrumented field sites. Atrazine readily degraded to hydroxyatrazine and biodegradation by-products and was not detected deeper in the soil profile and underlying shallow aquifer. The classical processes of chemical movement based on porous media-equilibrium-diffuse flow did not fit the data well at either site. Incompletely mixed, slug flow appeared to predominate at one of the sites and preferential flow at the other. The slug movement caused ‘piston-type’ displacement of more saline solutions in the soil profile to the shallow water table. Recommendations for conducting related field studies based on our sampling experience are given.