Kevin Briggs | University of Southern Mississippi (original) (raw)
Papers by Kevin Briggs
We compared in situ and laboratory velocity and attenuation values measured in seafloor sediments... more We compared in situ and laboratory velocity and attenuation values measured in seafloor sediments from the shallow water delta of the Eel River, California. This region receives a substantial volume of fluvial sediment that is discharged annually onto the shelf. Additionally, a high input of fluvial sediments during storms generates flood deposits that are characterized by thin beds of variable grain-sizes between the 40-and 90-m isobaths. The main objectives of this study were (1) to investigate signatures of seafloor processes on geoacoustic and physical properties, and (2) to evaluate differences between geoacoustic parameters measured in situ at acoustic (7.5 kHz) and in the laboratory at ultrasonic (400 kHz) frequencies. The in situ acoustic measurements were conducted between 60 and 100 m of water depth. Wet-bulk density and porosity profiles were obtained to 1.15 m below seafloor (m bsf) using gravity cores of the mostly cohesive fine-grained sediments across-and along-shelf. Physical and geoacoustic properties from six selected sites obtained on the Eel margin revealed the following. (1) Sound speed and wet-bulk density strongly correlated in most cases. (2) Sediment compaction with depth generally led to increased sound speed and density, while porosity and in situ attenuation values decreased. (3) Sound speed was higher in coarser-than in finer-grained sediments, on a maximum average by 80 m s 31. (4) In coarse-grained sediments sound speed was higher in the laboratory (1560 m s 31) than in situ (1520 m s 31). In contrast, average ultrasonic and in situ sound speed in finegrained sediments showed only little differences (both approximately 1480 m s 31). (5) Greater attenuation was commonly measured in the laboratory (0.4 and 0.8 dB m 31 kHz 31) than in situ (0.02 and 0.65 dB m 31 kHz 31), and remained almost constant below 0.4 m bsf. We attributed discrepancies between laboratory ultrasonic and in situ acoustic measurements to a frequency dependence of velocity and attenuation. In addition, laboratory attenuation was most likely enhanced due to scattering of sound waves at heterogeneities that were on the scale of ultrasonic
IEEE Journal of Oceanic Engineering, Jul 1, 2002
During the 1999 sediment acoustics experiment (SAX99), porometric properties were measured and pr... more During the 1999 sediment acoustics experiment (SAX99), porometric properties were measured and predicted for a well sorted, medium sand using standard laboratory geotechnical methods and image analysis of resin-impregnated sediments. Sediment porosity measured by laboratory water-weight-loss methods (0.372 0.0073 for mean 1 standard deviation) is 0.026 lower than determined by microscopic image analysis of resin-impregnated sediments (0.398 0.029). Values of intrinsic permeability (m 2) determined from constant-head permeameter measurements (3.29 10 11 0.60 10 11) and by microscopic image analysis coupled with effective medium theory modeling (2.78 10 11 1.01 10 11) are nearly identical within measurement error. The mean value of tortuosity factor measured from images is 1.49 0.09, which is in agreement with tortuosity factor determined from electrical resistivity measurements. Slight heterogeneity and anisotropy are apparent in the top three centimeters of sediment as determined by image-based porometric property measurements. However, the overall similarity for both measured and predicted values of porosity and permeability among and within SAX99 sites indicates sediments are primarily homogeneous and isotropic and pore size distributions are fairly uniform. The results indicate that an effective medium theory technique and two-dimensional image analysis accurately predicts bulk permeability in resin-impregnated sands.
Our long term goal is to develop accurate models for high-frequency acoustic penetration into, pr... more Our long term goal is to develop accurate models for high-frequency acoustic penetration into, propagation within, and scattering from shallow water ocean sediments. This work should specifically improve the Navy's ability to detect buried mines and, in general, improve sonar performance in shallow water. Additional objectives of the NRL program are to understand and model the complex interactions among environmental processes, sediment structure, properties, and behavior. These models allow portability of high-frequency bottom interaction models to sites of naval interest. OBJECTIVES Provide statistical characterization of the environmental properties, especially the roughness and sediment volume properties, required to determine and model the dominant mechanisms controlling the penetration into and scattering from the seafloor of high-frequency acoustic energy. Determine the effects of biological, geological, biogeochemical, and hydrodynamic processes on the spatial and temporal distribution of sediment physical, geotechnical and geoacoustic properties at the experimental site. Develop predictive empirical and physical models of the relationships among those properties.
Journal of the Acoustical Society of America, May 1, 2008
Grain roughness and packing may be important sediment properties for newer acoustic models. We pr... more Grain roughness and packing may be important sediment properties for newer acoustic models. We present Scanning Electron Stereomicroscopic imagery of natural sand grains of varying shape and roughness for evaluation of potential grain interactions of individual grains. The grain shape and presence of microasperities will determine the probability of the contact with surrounding grains being a point or a broader area. Moreover, the use of a micro-roughness power spectrum in characterizing the sand grain roughness may be appropriate. Grain contact information is an essential starting point for developing and evaluating acoustic models that address acoustic losses at high frequencies. This information provides the basis to understand contact mechanics, such as grain slip and frame dilation, during insonification. Because media frame stiffness depends, at the grain scale, on the number and type of grain-to-grain contacts, ultimately we would like to characterize sand sediments with imagery identifying such grain contact information. The natural shapes of grains, their variations, and their packing density present a variety of non-ideal (point) contacts. X-ray micro-focus Computed Tomography shows great promise for documenting of the number and size (area) of grain contacts within grain aggregations, and a demonstration of these data will also be presented.
AGU Fall Meeting Abstracts, Dec 1, 2017
The interaction of high-frequency sound with the seafloor is inherently a stochastic process. Inv... more The interaction of high-frequency sound with the seafloor is inherently a stochastic process. Inversion techniques must, therefore, employ good stochastic models for bottom acous- tic scattering. An assortment of physical models for bottom backscattering strength is tested by comparison with scattering strength data obtained at 40 kHz at three shallow water sites spanning a range of sediment types from fine silt to coarse sand. These acoustic data are accompanied by sediment physical property data obtained by core sample analysis and in situ probes. In addition, stereo photography was used to measure the power spectrum of bottom relief on centimeter scales. These physical data provided the inputs needed to test the backscatter models, which treat scattering from both the rough sediment-water in- terface and the sediment volume. For the three sites considered here, the perturbation model for scattering from a slightly rough fluid seafloor performs well. Volume scattering is predicted...
Abstract—Variation in the spatial and temporal extent of hypoxia in coastal bottom waters ofthe n... more Abstract—Variation in the spatial and temporal extent of hypoxia in coastal bottom waters ofthe northern Gulf of Mexico leads to changes in benthic community structure and sediment physical properties. Past and present benthic community structure determines what types of biogenic structures are present in the sediment as well as faunal mixing rates. Therefore, hypoxia has an important effect upon biorurbation. This study focuses upon the effects of hypoxia on biorurbation specifically on the continental shelf of Louisiana, where hypoxia has become an important issue due to its seasonal reoccurrence and increasing expansion across the northern Gulf of Mexico over the past 30 years. In this project, characteristics of biogenic structures in the sediment including number, diameter, and depth are correlated with benthic communities dwelling in hypoxic, intermittently hypoxic, and normoxic conditions using non-destructive Computed Tomography (CT) imagery of sediment cores and Sediment Pr...
The public reporting burden for this collection of information is estimated to average 1 hour per... more The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection
: Our long-term goal is to improve sonar performance through interpretation of geological data an... more : Our long-term goal is to improve sonar performance through interpretation of geological data and high-frequency acoustic modeling. This work should improve understanding of the variability of the salient geoacoustic properties of the sea floor that control acoustic propagation and scattering.
Journal of Marine Research, 2017
The Pearson and Rosenberg (P-R) conceptual model of macrobenthic succession was used to assess th... more The Pearson and Rosenberg (P-R) conceptual model of macrobenthic succession was used to assess the impact of hypoxia (dissolved oxygen concentration ≤2 mg L–1) on the macrobenthic community on the continental shelf of the northern Gulf of Mexico. The stress-response relationship between bottom-water oxygen concentration and the macrobenthic community was used to determine the ecological condition of the benthic habitat. In lieu of testing the effect of decreasing influence of organic enrichment on the macrobenthic community as a function of distance from the source of organic pollution, we tested the effect of bottom-water dissolved oxygen concentration as a proxy for distance from the source. To include the seasonal response in the long-term cumulative effect of recurring hypoxia on the macrobenthic community, samples were collected during early spring (April 2009), late summer (September 2009), and midsummer (August 2010). The cumulative effect of annual hypoxia on the macrobenthos at each site was apparent from the species diversity, abundance, and biomass. High diversity values at site H7 and low diversity values at site A6 indicated the existence of a westward-diminishing hypoxic gradient on the Louisiana/Texas shelf, interrupted by the Atchafalaya River discharge. Unsurprisingly, the macrobenthos collected during midsummer were generally the most stressed community, with the exception of site E4. Assessment of successional stages of the benthic communities of the four sites with multivariate analyses of nonmetric multidimensional scaling, distance-based redundancy analysis, and principal component analysis identified the influence of bottom-water hypoxia. The study demonstrated the applicability of the P-R model in predicting successional change in the macrobenthic community on the Louisiana continental shelf. Site H7 was in the advanced phase of stage II, sites E4 and D5 were in the intermediate phase of stage II, and site A6 was in the intermediate phase of stage I in the P-R successional continuum
Physical and geoacoustic property data were collected during the Key West Campaign as a part of t... more Physical and geoacoustic property data were collected during the Key West Campaign as a part of the Coastal Benthic Boundary Layer research program.
Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std. Z39.18 Public reporting burden for this col... more Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std. Z39.18 Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 5a. CONTRACT NUMBER a. REPORT 19a. NAME OF RESPONSIBLE PERSON 19b. TELEPHONE NUMBER
Estuaries and Coasts, 2018
Continuing trends of declining bottom-water dissolved oxygen (BWDO) in coastal oceans are a threa... more Continuing trends of declining bottom-water dissolved oxygen (BWDO) in coastal oceans are a threat to marine organisms, especially the benthos, and in the northern Gulf of Mexico (nGOM), the hypoxic area is expected to expand. Within-sediment vertical functional metric responses of macrobenthos were examined in four depth strata at four sites with different histories of exposure to seasonal hypoxia. The sites H7, D5, E4, and A6 between 30 and 39-m water depth represented a historical oxygen stress gradient from 5.4 to 2.1 mg L −1 BWDO (mid-summer 11-year mean), from which macrobenthos were sampled in spring and late summer 2009 and in midsummer in 2010. High abundance together with high biomass and production potential within upper strata under low BWDO stress supports the primacy of a numerically driven response in this system. Total abundance decreased along the BWDO stress gradient, and the lowest abundance coincided at the highest stress (MaxStress) site together with the highest proportion of opportunists, the smallest mean size, and the shortest turnover time. Accordingly, the relative abundance of opportunists within the upper two strata increased while surface deposit feeders decreased with greater hypoxic stress. Notwithstanding the proportion of opportunists, functional metrics generally decreased across the BWDO stress gradient within the upper strata, and metrics generally varied inversely between upper and lower strata. The findings underscore how vertical benthos distribution patterns reflect the BWDO exposure regime and how secondary production varies as an indicator of trophic transfer potential and organic matter processing within this system.
Quarterly Journal of Engineering Geology and Hydrogeology, 2018
In situ measurements of near-saturated hydraulic conductivity in fine grained soils have been mad... more In situ measurements of near-saturated hydraulic conductivity in fine grained soils have been made at six exemplar UK transport earthwork sites: three embankment and three cutting slopes. This paper reports 143 individual measurements and considers the factors that influence the spatial and temporal variability obtained. The test methods employed produce near-saturated conditions and flow under constant head. Full saturation is probably not achieved due to preferential and bypass flow occurring in these desiccated soils. For an embankment, hydraulic conductivity was found to vary by five orders of magnitude in the slope near-surface (0 to 0.3 metres depth), decreasing by four orders of magnitude between 0.3 and 1.2 metres depth. This extremely high variability is in part due to seasonal temporal changes controlled by soil moisture content, which can account for up to 1.5 orders of magnitude of this variability. Measurements of hydraulic conductivity at a cutting also indicated a four orders of magnitude range of hydraulic conductivity for the near-surface, with strong depth dependency of a two orders of magnitude decrease from 0.2 to 0.6 metres depth. The main factor controlling the large range is found to be spatial variability in the soil macro structure generated by wetting/drying cycle driven desiccation and roots. The measurements of hydraulic conductivity reported in this paper were undertaken to inform and provide a benchmark for the hydraulic parameters used in numerical models of groundwater flow. This is an influential parameter in simulations incorporating the combined weather/vegetation/infiltration/soil interaction mechanisms that are required to assess the performance and deterioration of earthwork slopes in a changing climate.
: Long term goals are to (1) to develop/improve inversion techniques for normal incidence sedimen... more : Long term goals are to (1) to develop/improve inversion techniques for normal incidence sediment classification systems and remotely determine sediment physical and geoacoustic properties; (2) determine mechanisms responsible for scattering of high frequency energy.
Public reporting burden for this collection of information is estimated lo average 1 hour per res... more Public reporting burden for this collection of information is estimated lo average 1 hour per response, including the lime for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of
Journal of the Acoustical Society of America, 2017
Four sites on the continental shelf off Louisiana, each subjected to different historical exposur... more Four sites on the continental shelf off Louisiana, each subjected to different historical exposures to low concentrations of bottom-water dissolved oxygen, are investigated in terms of their macrobenthos species composition, sediment physical properties, and sediment geoacoustic properties (sound speed, attenuation, and impedance). From macrobenthos species composition, feeding type is identified, which allows categorization of some bioturbation activity as either dilation or compaction of sediment. Dilation and compaction should affect sediment properties of bulk density and porosity, which are significant predictor variables of geoacoustic properties. Different levels of oxygen stress correspond with statistically separable macrobenthos assemblages, abundance and diversity of biogenic structures (burrows and voids), and ratios of dilators to compactors. Sediment sound speed and attenuation values measured in subcores from box cores are compared at each of the four sites with diffe...
We compared in situ and laboratory velocity and attenuation values measured in seafloor sediments... more We compared in situ and laboratory velocity and attenuation values measured in seafloor sediments from the shallow water delta of the Eel River, California. This region receives a substantial volume of fluvial sediment that is discharged annually onto the shelf. Additionally, a high input of fluvial sediments during storms generates flood deposits that are characterized by thin beds of variable grain-sizes between the 40-and 90-m isobaths. The main objectives of this study were (1) to investigate signatures of seafloor processes on geoacoustic and physical properties, and (2) to evaluate differences between geoacoustic parameters measured in situ at acoustic (7.5 kHz) and in the laboratory at ultrasonic (400 kHz) frequencies. The in situ acoustic measurements were conducted between 60 and 100 m of water depth. Wet-bulk density and porosity profiles were obtained to 1.15 m below seafloor (m bsf) using gravity cores of the mostly cohesive fine-grained sediments across-and along-shelf. Physical and geoacoustic properties from six selected sites obtained on the Eel margin revealed the following. (1) Sound speed and wet-bulk density strongly correlated in most cases. (2) Sediment compaction with depth generally led to increased sound speed and density, while porosity and in situ attenuation values decreased. (3) Sound speed was higher in coarser-than in finer-grained sediments, on a maximum average by 80 m s 31. (4) In coarse-grained sediments sound speed was higher in the laboratory (1560 m s 31) than in situ (1520 m s 31). In contrast, average ultrasonic and in situ sound speed in finegrained sediments showed only little differences (both approximately 1480 m s 31). (5) Greater attenuation was commonly measured in the laboratory (0.4 and 0.8 dB m 31 kHz 31) than in situ (0.02 and 0.65 dB m 31 kHz 31), and remained almost constant below 0.4 m bsf. We attributed discrepancies between laboratory ultrasonic and in situ acoustic measurements to a frequency dependence of velocity and attenuation. In addition, laboratory attenuation was most likely enhanced due to scattering of sound waves at heterogeneities that were on the scale of ultrasonic
IEEE Journal of Oceanic Engineering, Jul 1, 2002
During the 1999 sediment acoustics experiment (SAX99), porometric properties were measured and pr... more During the 1999 sediment acoustics experiment (SAX99), porometric properties were measured and predicted for a well sorted, medium sand using standard laboratory geotechnical methods and image analysis of resin-impregnated sediments. Sediment porosity measured by laboratory water-weight-loss methods (0.372 0.0073 for mean 1 standard deviation) is 0.026 lower than determined by microscopic image analysis of resin-impregnated sediments (0.398 0.029). Values of intrinsic permeability (m 2) determined from constant-head permeameter measurements (3.29 10 11 0.60 10 11) and by microscopic image analysis coupled with effective medium theory modeling (2.78 10 11 1.01 10 11) are nearly identical within measurement error. The mean value of tortuosity factor measured from images is 1.49 0.09, which is in agreement with tortuosity factor determined from electrical resistivity measurements. Slight heterogeneity and anisotropy are apparent in the top three centimeters of sediment as determined by image-based porometric property measurements. However, the overall similarity for both measured and predicted values of porosity and permeability among and within SAX99 sites indicates sediments are primarily homogeneous and isotropic and pore size distributions are fairly uniform. The results indicate that an effective medium theory technique and two-dimensional image analysis accurately predicts bulk permeability in resin-impregnated sands.
Our long term goal is to develop accurate models for high-frequency acoustic penetration into, pr... more Our long term goal is to develop accurate models for high-frequency acoustic penetration into, propagation within, and scattering from shallow water ocean sediments. This work should specifically improve the Navy's ability to detect buried mines and, in general, improve sonar performance in shallow water. Additional objectives of the NRL program are to understand and model the complex interactions among environmental processes, sediment structure, properties, and behavior. These models allow portability of high-frequency bottom interaction models to sites of naval interest. OBJECTIVES Provide statistical characterization of the environmental properties, especially the roughness and sediment volume properties, required to determine and model the dominant mechanisms controlling the penetration into and scattering from the seafloor of high-frequency acoustic energy. Determine the effects of biological, geological, biogeochemical, and hydrodynamic processes on the spatial and temporal distribution of sediment physical, geotechnical and geoacoustic properties at the experimental site. Develop predictive empirical and physical models of the relationships among those properties.
Journal of the Acoustical Society of America, May 1, 2008
Grain roughness and packing may be important sediment properties for newer acoustic models. We pr... more Grain roughness and packing may be important sediment properties for newer acoustic models. We present Scanning Electron Stereomicroscopic imagery of natural sand grains of varying shape and roughness for evaluation of potential grain interactions of individual grains. The grain shape and presence of microasperities will determine the probability of the contact with surrounding grains being a point or a broader area. Moreover, the use of a micro-roughness power spectrum in characterizing the sand grain roughness may be appropriate. Grain contact information is an essential starting point for developing and evaluating acoustic models that address acoustic losses at high frequencies. This information provides the basis to understand contact mechanics, such as grain slip and frame dilation, during insonification. Because media frame stiffness depends, at the grain scale, on the number and type of grain-to-grain contacts, ultimately we would like to characterize sand sediments with imagery identifying such grain contact information. The natural shapes of grains, their variations, and their packing density present a variety of non-ideal (point) contacts. X-ray micro-focus Computed Tomography shows great promise for documenting of the number and size (area) of grain contacts within grain aggregations, and a demonstration of these data will also be presented.
AGU Fall Meeting Abstracts, Dec 1, 2017
The interaction of high-frequency sound with the seafloor is inherently a stochastic process. Inv... more The interaction of high-frequency sound with the seafloor is inherently a stochastic process. Inversion techniques must, therefore, employ good stochastic models for bottom acous- tic scattering. An assortment of physical models for bottom backscattering strength is tested by comparison with scattering strength data obtained at 40 kHz at three shallow water sites spanning a range of sediment types from fine silt to coarse sand. These acoustic data are accompanied by sediment physical property data obtained by core sample analysis and in situ probes. In addition, stereo photography was used to measure the power spectrum of bottom relief on centimeter scales. These physical data provided the inputs needed to test the backscatter models, which treat scattering from both the rough sediment-water in- terface and the sediment volume. For the three sites considered here, the perturbation model for scattering from a slightly rough fluid seafloor performs well. Volume scattering is predicted...
Abstract—Variation in the spatial and temporal extent of hypoxia in coastal bottom waters ofthe n... more Abstract—Variation in the spatial and temporal extent of hypoxia in coastal bottom waters ofthe northern Gulf of Mexico leads to changes in benthic community structure and sediment physical properties. Past and present benthic community structure determines what types of biogenic structures are present in the sediment as well as faunal mixing rates. Therefore, hypoxia has an important effect upon biorurbation. This study focuses upon the effects of hypoxia on biorurbation specifically on the continental shelf of Louisiana, where hypoxia has become an important issue due to its seasonal reoccurrence and increasing expansion across the northern Gulf of Mexico over the past 30 years. In this project, characteristics of biogenic structures in the sediment including number, diameter, and depth are correlated with benthic communities dwelling in hypoxic, intermittently hypoxic, and normoxic conditions using non-destructive Computed Tomography (CT) imagery of sediment cores and Sediment Pr...
The public reporting burden for this collection of information is estimated to average 1 hour per... more The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection
: Our long-term goal is to improve sonar performance through interpretation of geological data an... more : Our long-term goal is to improve sonar performance through interpretation of geological data and high-frequency acoustic modeling. This work should improve understanding of the variability of the salient geoacoustic properties of the sea floor that control acoustic propagation and scattering.
Journal of Marine Research, 2017
The Pearson and Rosenberg (P-R) conceptual model of macrobenthic succession was used to assess th... more The Pearson and Rosenberg (P-R) conceptual model of macrobenthic succession was used to assess the impact of hypoxia (dissolved oxygen concentration ≤2 mg L–1) on the macrobenthic community on the continental shelf of the northern Gulf of Mexico. The stress-response relationship between bottom-water oxygen concentration and the macrobenthic community was used to determine the ecological condition of the benthic habitat. In lieu of testing the effect of decreasing influence of organic enrichment on the macrobenthic community as a function of distance from the source of organic pollution, we tested the effect of bottom-water dissolved oxygen concentration as a proxy for distance from the source. To include the seasonal response in the long-term cumulative effect of recurring hypoxia on the macrobenthic community, samples were collected during early spring (April 2009), late summer (September 2009), and midsummer (August 2010). The cumulative effect of annual hypoxia on the macrobenthos at each site was apparent from the species diversity, abundance, and biomass. High diversity values at site H7 and low diversity values at site A6 indicated the existence of a westward-diminishing hypoxic gradient on the Louisiana/Texas shelf, interrupted by the Atchafalaya River discharge. Unsurprisingly, the macrobenthos collected during midsummer were generally the most stressed community, with the exception of site E4. Assessment of successional stages of the benthic communities of the four sites with multivariate analyses of nonmetric multidimensional scaling, distance-based redundancy analysis, and principal component analysis identified the influence of bottom-water hypoxia. The study demonstrated the applicability of the P-R model in predicting successional change in the macrobenthic community on the Louisiana continental shelf. Site H7 was in the advanced phase of stage II, sites E4 and D5 were in the intermediate phase of stage II, and site A6 was in the intermediate phase of stage I in the P-R successional continuum
Physical and geoacoustic property data were collected during the Key West Campaign as a part of t... more Physical and geoacoustic property data were collected during the Key West Campaign as a part of the Coastal Benthic Boundary Layer research program.
Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std. Z39.18 Public reporting burden for this col... more Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std. Z39.18 Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 5a. CONTRACT NUMBER a. REPORT 19a. NAME OF RESPONSIBLE PERSON 19b. TELEPHONE NUMBER
Estuaries and Coasts, 2018
Continuing trends of declining bottom-water dissolved oxygen (BWDO) in coastal oceans are a threa... more Continuing trends of declining bottom-water dissolved oxygen (BWDO) in coastal oceans are a threat to marine organisms, especially the benthos, and in the northern Gulf of Mexico (nGOM), the hypoxic area is expected to expand. Within-sediment vertical functional metric responses of macrobenthos were examined in four depth strata at four sites with different histories of exposure to seasonal hypoxia. The sites H7, D5, E4, and A6 between 30 and 39-m water depth represented a historical oxygen stress gradient from 5.4 to 2.1 mg L −1 BWDO (mid-summer 11-year mean), from which macrobenthos were sampled in spring and late summer 2009 and in midsummer in 2010. High abundance together with high biomass and production potential within upper strata under low BWDO stress supports the primacy of a numerically driven response in this system. Total abundance decreased along the BWDO stress gradient, and the lowest abundance coincided at the highest stress (MaxStress) site together with the highest proportion of opportunists, the smallest mean size, and the shortest turnover time. Accordingly, the relative abundance of opportunists within the upper two strata increased while surface deposit feeders decreased with greater hypoxic stress. Notwithstanding the proportion of opportunists, functional metrics generally decreased across the BWDO stress gradient within the upper strata, and metrics generally varied inversely between upper and lower strata. The findings underscore how vertical benthos distribution patterns reflect the BWDO exposure regime and how secondary production varies as an indicator of trophic transfer potential and organic matter processing within this system.
Quarterly Journal of Engineering Geology and Hydrogeology, 2018
In situ measurements of near-saturated hydraulic conductivity in fine grained soils have been mad... more In situ measurements of near-saturated hydraulic conductivity in fine grained soils have been made at six exemplar UK transport earthwork sites: three embankment and three cutting slopes. This paper reports 143 individual measurements and considers the factors that influence the spatial and temporal variability obtained. The test methods employed produce near-saturated conditions and flow under constant head. Full saturation is probably not achieved due to preferential and bypass flow occurring in these desiccated soils. For an embankment, hydraulic conductivity was found to vary by five orders of magnitude in the slope near-surface (0 to 0.3 metres depth), decreasing by four orders of magnitude between 0.3 and 1.2 metres depth. This extremely high variability is in part due to seasonal temporal changes controlled by soil moisture content, which can account for up to 1.5 orders of magnitude of this variability. Measurements of hydraulic conductivity at a cutting also indicated a four orders of magnitude range of hydraulic conductivity for the near-surface, with strong depth dependency of a two orders of magnitude decrease from 0.2 to 0.6 metres depth. The main factor controlling the large range is found to be spatial variability in the soil macro structure generated by wetting/drying cycle driven desiccation and roots. The measurements of hydraulic conductivity reported in this paper were undertaken to inform and provide a benchmark for the hydraulic parameters used in numerical models of groundwater flow. This is an influential parameter in simulations incorporating the combined weather/vegetation/infiltration/soil interaction mechanisms that are required to assess the performance and deterioration of earthwork slopes in a changing climate.
: Long term goals are to (1) to develop/improve inversion techniques for normal incidence sedimen... more : Long term goals are to (1) to develop/improve inversion techniques for normal incidence sediment classification systems and remotely determine sediment physical and geoacoustic properties; (2) determine mechanisms responsible for scattering of high frequency energy.
Public reporting burden for this collection of information is estimated lo average 1 hour per res... more Public reporting burden for this collection of information is estimated lo average 1 hour per response, including the lime for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of
Journal of the Acoustical Society of America, 2017
Four sites on the continental shelf off Louisiana, each subjected to different historical exposur... more Four sites on the continental shelf off Louisiana, each subjected to different historical exposures to low concentrations of bottom-water dissolved oxygen, are investigated in terms of their macrobenthos species composition, sediment physical properties, and sediment geoacoustic properties (sound speed, attenuation, and impedance). From macrobenthos species composition, feeding type is identified, which allows categorization of some bioturbation activity as either dilation or compaction of sediment. Dilation and compaction should affect sediment properties of bulk density and porosity, which are significant predictor variables of geoacoustic properties. Different levels of oxygen stress correspond with statistically separable macrobenthos assemblages, abundance and diversity of biogenic structures (burrows and voids), and ratios of dilators to compactors. Sediment sound speed and attenuation values measured in subcores from box cores are compared at each of the four sites with diffe...