Sarah E. Kruse

Not All Salmon Are Created Equal: Life Cycle Assessment (LCA) of Global Salmon Farming Systems

We present a global-scale life cycle assessment of a major food commodity, farmed salmon. Specifically, we report the cumulative energy use, biotic resource use, and greenhouse gas, acidifying, and eutrophying emissions associated with producing farmed salmon in Norway, the UK, British Columbia (Canada), and Chile, as well as a production-weighted global average. We found marked differences in the nature and quantity of material/energy resource use and associated emissions per unit production across regions. This suggests significant scope for improved environmental performance in the industry as a whole. We identify key leverage points for improving performance, most notably the critical importance of least-environmental cost feed sourcing patterns and continued improvements in feed conversion efficiency. Overall, impacts were lowest for Norwegian production in most impact categories, and highest for UK farmed salmon. Our results are of direct relevance to industry, policy makers, eco-labeling programs, and consumers seeking to further sustainability objectives in salmon aquaculture.

Annual Layers Revealed by GPR in the Subsurface of a Prograding Coastal Barrier, Southwest Washington, U.S.A.

ABSTRACT The southwest Washington coastline has experienced extremely high rates of progradation during the late Holocene. Subsurface stratigraphy, preserved because of progradation and interpreted using ground-penetrating radar (GPR), has previously been used successfully to document coastal response to prehistoric storm and earthquake events. New GPR data collected at Ocean Shores, Washington, suggest that the historic stratigraphy of the coastal barrier in this area represents a higher resolution record of coastal behavior than previously thought. GPR records for this location at 200 MHz reveal a series of gently sloping, seaward-dipping reflections with slopes similar to the modern beach and spacings on the order of 20-45 cm. Field evidence and model results suggest that thin (1-10 cm), possibly magnetite-rich, heavy-mineral lags or low-porosity layers left by winter storms and separated by thick (20-40 cm) summer progradational sequences are responsible for generating the GPR reflections. These results indicate that a record of annual progradation is preserved in the subsurface of the prograding barrier and can be quantified using GPR. Such records of annual coastal behavior, where available, will be invaluable in understanding past coastal response to climatic and tectonic forcing.

Ground penetrating radar imaging of cap rock, caliche and carbonate strata

Abstract Field experiments show ground penetrating radar (GPR) can be used to image shallow carbonate stratigraphy effectively in a variety of settings. In south Florida, the position and structure of cap rock cover on limestone can be an important control on surface water flow and vegetation, but larger scale outcrops (tens of meters) of cap rock are sparse. GPR mapping through south Florida prairie, cypress swamp and hardwood hammock resolves variations in thickness and structure of cap rock to ∼3 m and holds the potential to test theories for cap rock–vegetation relationships. In other settings, carbonate strata are mapped to test models for the formation of local structural anomalies. A test of GPR imaging capabilities on an arid caliche (calcrete) horizon in southeastern Nevada shows depth penetration to ∼2 m with resolution of the base of caliche. GPR profiling also succeeds in resolving more deeply buried (∼5 m) limestone discontinuity surfaces that record subaerial exposure in south Florida.

Evidence of small-volume igneous diapirism in the shallow crust of the Colorado Plateau, San Rafael Desert, Utah

Magma is transported through Earth9s solid crust by two different processes, diking and diapirism, although other mechanisms, such as porous and channeled flow, can transport melt through partially molten crustal areas. Dikes are ubiquitous indicators of the transport of magma in the shallow crust by brittle fracture, and there is ample geological and geophysical evidence supporting diking as a magma-ascent mechanism through the crust. On the other hand, igneous diapirism, involving magma ascent by gravitational instability and requiring viscous or plastic flow of country rock (“hot Stokes” diapirs), is often invoked as a magma-transport mechanism restricted to the ductile upper mantle or lower crust. However, unequivocal geological field evidence for igneous diapirism has proven elusive and has been a matter of considerable debate. We report geological and geophysical evidence showing that Pliocene sills emplaced in the upper levels of brittle continental crust of the Colorado Plateau in the San Rafael subvolcanic field (Utah) became gravitationally unstable by mechanically altering the overlying sedimentary rocks. These sills grew into structures that we recognize as domes and plugs at the current level of exposure. Some of these plugs continued to transport magma to shallower levels of the continental crust and eventually acted as conduits feeding volcanic eruptions. Our geological and geophysical findings indicate that gravitational instability is a viable mechanism for the initiation of magma ascent in the upper continental crust for small volumes of basaltic magma under specific conditions.

Neotectonic faulting and forearc sliver motion along the Atirro–Río Sucio fault system, Costa Rica, Central America

The Atirro–Rio Sucio fault system forms a major northwest-trending strike-slip fault zone in east-central Costa Rica. We examined the kinematics and temporal evolution of this fault system through geomorphic, structural, and seismologic analysis. This 150-km-long strike-slip fault zone traverses the northern flank of the paleovolcanic Cordillera de Talamanca and extends northwestward into the active Cordillera Volcanica Central. Historical seismicity includes frequent minor swarms and occasional moderate-magnitude (M 5.0–6.5) damaging earthquakes. Field geomorphic evidence, fault kinematic data, and earthquake focal mechanisms are consistent in showing dextral slip along the mapped traces of northwest-striking faults. Continuity with other transcurrent faults in northwest Costa Rica indicates that the Atirro–Rio Sucio fault system may form the southeastern end of a regional network of northwest-trending dextral faults that accommodate margin-parallel displacement of the Central American forearc sliver. The Atirro–Rio Sucio fault system originates within the Central Costa Rica Deformed Belt inboard of the indenting Cocos Ridge. We infer that ridge collision drives lateral escape of crustal fragments northwestward along an array of dextral Central Costa Rica Deformed Belt faults including the major structures of the Atirro–Rio Sucio fault system. This zone of arc-parallel extrusion thus represents the root of the Central American forearc sliver. Consistent with recent geodynamic models, we propose that northwestward sliver escape along the Atirro–Rio Sucio faults is driven by rigid indentation of the aseismic Cocos Ridge into southern Costa Rica.

Joint Time-Frequency Analysis of GPR Data Over Layered Sequences

Ground-penetrating radar (GPR) is widely used for interpretation of sedimentary deposits, where beds often occur in layered sequences and are often too thin to be individually resolved. Guha et al. (2005) showed that GPR traces over laminated sequences shift toward higher frequencies, and spectral analysis can be used to detect thin beds. In that study, very finely laminated sequences (well below the tuning thickness, 1/250 of dominant wavelength) were considered, and the radar frequency response was obtained using the Fourier transform. Estimating frequency response through the Fourier transform, however, does not provide information regarding the variation of frequency with time. On the other hand, joint time-frequency analysis, or JTFA, is a processing method that captures energy localization of a signal with time and allows representation of variations in spectral content of a signal in both the time and frequency domains.

Amplitude analysis of repetitive GPR reflections on a Lake Bonneville delta, Utah

Abstract Several recent theoretical studies have documented the sensitivities of the amplitude and waveform of a ground penetrating radar (GPR) reflection to the contrast in electromagnetic properties across the reflecting contact. Here we show that, in a setting with repetitive layering, it is possible to place constraints on conductivity and variations in permittivity within layers and across layer boundaries. The data set consists of 50 MHz, 100 MHz and 200 MHz profiles that image subparallel dipping bedding planes in a gravelly deltaic forest facies on a Lake Bonneville delta, Utah, USA. Strongly reflecting horizons with 1–2 m spacings bound packages with finer internal layering. From finite-difference time-domain (FDTD) simulations of radarwave propagation through such strata, constraints are placed on the variations in permittivity across larger-scale and finer-scale layering. Modelling the relative amplitudes of reflections demonstrates that the finer-scale permittivity contrasts are ∼0.4–0.8 times that of the 1–2 m layering. Amplitude v. offset (AVO) analysis yields an upper bound of ∼3.5 for the contrast in permittivity at the larger-scale layer boundaries. Overall signal attenuation requires the average conductivity to be in the range of 0.7–0.8 mS/m.

Predicting Water Table Response to Rainfall Events, Central Florida

A rise in water table in response to a rainfall event is a complex function of permeability, specific yield, antecedent soil-water conditions, water table level, evapotranspiration, vegetation, lateral groundwater flow, and rainfall volume and intensity. Predictions of water table response, however, commonly assume a linear relationship between response and rainfall based on cumulative analysis of water level and rainfall logs. By identifying individual rainfall events and responses, we examine how the response/rainfall ratio varies as a function of antecedent water table level (stage) and rainfall event size. For wells in wetlands and uplands in central Florida, incorporating stage and event size improves forecasting of water table rise by more than 30%, based on 10 years of data. At the 11 sites studied, the water table is generally least responsive to rainfall at smallest and largest rainfall event sizes and at lower stages. At most sites the minimum amount of rainfall required to induce a rise in water table is fairly uniform when the water table is within 50 to 100 cm of land surface. Below this depth, the minimum typically gradually increases with depth. These observations can be qualitatively explained by unsaturated zone flow processes. Overall, response/rainfall ratios are higher in wetlands and lower in uplands, presumably reflecting lower specific yields and greater lateral influx in wetland sites. Pronounced depth variations in rainfall/response ratios appear to correlate with soil layer boundaries, where corroborating data are available.

Postimpact Deformation Associated with the Late Eocene Chesapeake Bay Impact Structure in Southeastern Virginia

Upper Cenozoic strata covering the Chesapeake Bay impact structure in southeastern Virginia record intermittent differential movement around its buried rim. Miocene strata in a graben detected by seismic surveys on the York River exhibit variable thickness and are deformed above the crater rim. Fan-like interformational and intraformational angular unconformities within Pliocene–Pleistocene strata, which strike parallel to the crater rim and dip 2°–3° away from the crater center, indicate that deformation and deposition were synchronous. Concentric, large-scale crossbedded, bioclastic sand bodies of Pliocene age within ∼20 km of the buried crater rim formed on offshore shoals, presumably as subsiding listric slump blocks rotated near the crater rim.

3.5 Near-Surface Geophysics in Geomorphology

Near-surface geophysical methods can provide information on subsurface structure and stratigraphy that is critical to understanding surficial processes. Gravity, magnetics, resistivity, electromagnetics, ground-penetrating radar, and various seismic methods are applied across a range of process domains, including faulting, volcanism, topography and weathering, hillslope processes, coastal and sea-level change, aeolian and fluvial processes, and glacial and periglacial processes. Gravity and magnetic methods have long been used to image faults and other tectonic and volcanic features, and they have also been used to document weathering patterns. With the development of multi-electrode resistivity systems, resistivity profiling has become a staple tool to map the structure and water content of slope deposits and volcanic features. Ground-penetrating radar studies have been crucial to understanding of geologic features as varied as the internal structure of aeolian dunes, coastal and fluvial deposits, the structure and volume of glaciers, the spatial distribution of sinkholes, and the geometry of tephra and lahar deposits. Key to successful studies are calibrations against direct observations and/or uses of multiple complementary methods. Increased efficiencies in geophysical data acquisition and positioning in recent years have made possible very-high-resolution three-dimensional (3-D) or quasi-3-D imaging of subsurface structures. However, there is still a mismatch in the typical spatial scales of large remote-sensing-based studies and smaller geophysical surveys. Bridging this disconnect with new geophysical acquisition techniques and new instrumentation such as terrestrial laser scanning should improve our understanding of the role that subsurface structure plays in the evolution of topography.