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At least 1,639 records · Page 91Linked to original sources

USGS2019

Status and trends of pelagic prey fish in Lake Huron, 2018

Scientists from the U.S. Geological Survey’s Great Lakes Science Center conducted integrated acoustic and mid-water trawl surveys of Lake Huron annually from 2004-2018. The 2018 survey was conducted during September and included transects in Lake Huron’s main basin, Georgian Bay, and North Channel. Mean lake-wide pelagic fish density was 1532 fish/ha and mean pelagic fish biomass was 4151 g/ha in 2018, which represents 128% and 108% of the long-term mean, respectively. Mean lake-wide biomass was 24% lower in 2018 and mean lake-wide fish density was 3.3% lower in 2018 as compared to 2017. Lake-wide density and biomass of small alewife (< 100 mm) increased significantly in 2018 and was due primarily to increased abundance in the western main basin. Lake-wide density of small rainbow smelt (< 90 mm) increased in 2018 and was a result of increased abundance in the eastern main basin, Georgian Bay, and the North Channel. Biomass of large rainbow smelt (> 90 mm) increased in 2018 and was a result of increased biomass in the main basin and Georgian Bay. Density of small bloater (< 120 mm) declined in the western main basin but increased in other regions of Lake Huron. Biomass of large bloater (> 120 mm) remained at levels similar to 2017 in most regions of Lake Huron. Emerald shiner density and biomass increased in 2018 due to increased abundance in the main basin south and main basin west regions. Density and biomass of large cisco (> 200 mm) declined marginally between 2017 and 2018, but cisco biomass and density has shown an increasing trend in the North Channel and Georgian Bay since 2011.

Lake Huron↗

USGS2019

Hawaiian hoary bat (Lasiurus cinereus semotus) activity, diet and prey availability at the Waihou Mitigation Area, Maui

Habitat use, diet, prey availability, and foraging ecology of the endangered Hawaiian hoary bat (Lasiurus cinereus semotus, Vespertilionidae), was examined in the east Maui region inclusive of the Waihou Mitigation Area, Pu‘u Makua Restoration Area and the wind energy facility operated by Auwahi Wind Energy, LLC. The study was conducted to inform the mitigation and management requirements of Auwahi Wind Energy. Acoustic monitoring over the three-year period demonstrated that bats are present and actively forage year-round at the Waihou Mitigation Area. Over an 8-month span, 11 bats were uniquely color-banded and released, 3 of which were pregnant or lactating females, and highlights the importance of the area to breeding residents. Our study included the first genetic analysis of Hawaiian hoary bat diet, and confirms the inclusion of Coleoptera, Lepidoptera, Diptera, Hemiptera, and Blattodea among the prey items of this bat identified in previous microscopy-based studies. Hawaiian hoary bats consumed both native and non-native insect species, including several invasive species damaging to crop agriculture. Moths were the primary dietary component, both in prevalence among individual bats and the proportion of gene sequence counts. Through genetic analysis, we identified 18 Lepidoptera families (dominated by Noctuidae, Geometridae, Crambidae, Oecophoridae and Tortricidae) including 24 genus- or species-level taxa. Lepidoptera collected as caterpillars directly from vegetation did not appear in the diet of the 8 bat guano samples at the genus or species level. However, the occurrence of moth larva on native plants suggests that reforestation that includes host plants for these insect families may provide food for locally foraging bats.

Hawaii↗

USGS2004

Combined use of borehole geophysics and packers to site potable wells in a contaminated area in Montville, Connecticut

A leaking underground gasoline tank contaminated a crystalline bedrock aquifer in Montville, Connecticut, USA with MTBE and benzene. At the original residential bedrock supply wells, the median MTBE concentration was 165 micrograms per liter (mg/L), and the median benzene concentration was 320 mg/L. The maximum concentrations of MTBE and benzene were 4,300 mg/l and 1,700 mg/L, respectively. Because of the unavailability of a public water supply and the long-term expense of point-of-use (on-site) treatment systems, the Connecticut Department of Environmental Protection Leaking Underground Storage Tank Program considered drilling replacement wells for water supply, if suitable drill sites could be located. Borehole geophysical methods were used as part of the investigation to find suitable drill sites. The U.S. Geological Survey performed borehole radar logging in three of the most contaminated wells. Other geophysical logs were run in two of the wells to enhance the hydrogeological characterizations. These data, combined with straddle-packer testing provided by a drilling contractor, formed the basis of a conceptual model used in the search for discrete fractures with better water quality than provided by an open-hole sample. At Property A, a single transmissive fracture was identified at the bottom of the well. This well, although having historically lower gasoline concentrations than the other two wells, had persistent high iron bacteria fouling of the filtration system. By 2002, concentrations of MTBE and benzene had decreased to 59 and 3 mg/L, respectively, and the water was treatable except for the iron. Because no water-bearing fractures were encountered above the well bottom, an alternate well site was selected based on a set of vertical fractures observed in a nearby outcrop, rather than on the geophysical data. The new well, sited along the strike of these fractures, yielded 9 gallons per minute (gpm) but was found to be more contaminated than the original well. MTBE and benzene were detected at 224 and 7 mg/L, respectively. At Property B, the isolated fractures associated with four radar reflections contained MTBE in concentrations ranging from 460 to 680 mg/L, with concentration increasing with depth. A new well site was selected based upon topography and physical limitations of the property. A target drilling depth was selected to avoid encountering the most contaminated fracture, as projected from the radar data in the contaminated well. A new well, drilled to the target depth, yielded 2 gpm, which was sufficient for domestic supply. No contaminants were detected during 7 years of annual sampling. Over the next 2 years, MTBE was detected twice at 2 and 8 mg/L. At Property C, the isolated fractures associated with 12 radar reflections and acoustic televiewer images yielded MTBE concentrations ranging from 47 to 1,200 mg/L and benzene concentrations from 6 to 1,000 mg/L, with concentrations generally increasing with depth. A new well site was selected based upon physical limitations of the site. A target drilling depth was chosen to avoid encountering the most contaminated fractures, as projected from the radar data in the contaminated well. A new well, drilled to the target depth, yielded 6 gpm. MTBE was detected at concentrations ranging from trace levels to 12 mg/L for 6 years. Benzene was not detected. These case histories suggest that the combined use of borehole geophysics and discrete-fracture sampling can, in some cases, be used to predict the locations of less contaminated or uncontaminated fractures, at distances of tens of feet from contaminated bedrock wells. This information may be used to improve the chances of successfully siting alternate potable water wells. Likewise, the same data and approach potentially could be used for targeting specific fractures for remediation.

Connecticut↗

USGS1999

Integrated use of continuous seismic-reflection profiling and ground-penetrating radar methods at John's Pond, Cape Cod, Massachusetts

Continuous seismic-reflection profiling (CSP) and ground-penetrating radar (GPR) surveys were conducted by the U.S. Geological Survey in April 1998 over the northern part of John’s Pond, a glacial kettle pond southeast of Otis Air National Guard Base, Cape Cod, Massachusetts. The surveys were conducted to delineate the types and thickness of sedimentary units that may control the infiltration of contaminated groundwater into John’s Pond. Sand-and-gravel deposits, collapse features and recent organic sediments were imaged with the CSP and GPR methods. Hummocky to chaotic reflections were interpreted as sand- and-gravel deposits. Slightly wavy, parallel reflections located in depressions in the sand-and- gravel deposits were interpreted as filled collapse features. Lower amplitude, horizontal, laminar reflections were interpreted as organic sediments. Entrapped methane gas within some of the organic sediments created a reflection zone that obscured deeper reflections in the CSP records. The CSP and GPR methods provide complementary information over most of the surveyed part of the pond. The methods detect similar interfaces, but a particular interface may produce a stronger reflection in one record than in the other. For example, regions of the pond containing organic sediments with entrapped methane gas, which prevent penetration of the acoustic signal, were penetrated and imaged by GPR. Conversely, regions of the pond containing electrically conductive sediments or deep water, which attenuate the GPR signal, were imaged using CSP. The CSP and GPR data were interpreted to generate a bathymetric map and a map of sediment type and thickness beneath John’s Pond.

Massachusetts↗

USGS2019

A physically based method of combining ADCP velocity data with point samples to compute suspended-sand discharge -- Application to the Rhone River, France

Measuring suspended-sand flux in rivers is a challenge since sand concentrations are highly variable in time and space throughout a river cross section. Most of the present methodologies rely on point or depth-integrated sampling (Nolan et al., 2005, Topping et al., 2016). The standard method estimates mean concentration and multiply it by discharge to compute the suspended-sand discharge. Here, we demonstrate methods of combining point suspended-sediment samples with ADCP (Acoustic Doppler Current Profiler) high-resolution depth and velocity measurements to improve vertical and lateral integration of concentration and flux. A preliminary version of this method is applied to data collected in the Rhône River in Lyon, France, during a 10-year flood in January 2018. Two options for vertically integrating the measured suspended-sediment concentrations were tested whereas lateral integration was based on nearest-neighbor interpolation only, as a baseline option. Sand flux results are similar, thus suggesting that vertical integration options may be less critical than lateral integration options that will be implemented and tested in future work.

Rhone River↗

USGS2019

Interpreting flux-based sediment budgets in a habitat context: Linking precise temporal-resolution measurements of sediment flux to spatially robust characterization of channel change

Continuous measurements of sediment transport at reach-bracketing gaging stations allow for the construction of continuous mass-balance sediment budgets for the intervening reach. Although these budgets identify periods of sediment surplus (net deposition) or sediment deficit (net erosion), such analyses cannot identify the locations within the reach where channel change occurs. Because channel change and associated changes in habitat are of greater interest to river managers than the precise value of reach-scale loss or accumulation of sediment, it is important to explicitly link reach-scale changes in sediment mass balance to field measurements of channel change. In this study we will evaluate the relationship between the magnitude of the sediment mass imbalance measured by acoustic-Doppler profilers and the resulting channel change on the Yampa River in Dinosaur National Monument.

Conference Paper↗

USGS2020

Design and operations of the Hydrate 01 Stratigraphic test well, Alaska North Slope

The National Energy Technology Laboratory, the Japan Oil, Gas and Metals National Corporation, and the U.S. Geological Survey are leading an effort to conduct an extended gas hydrate production test in northern Alaska. The proposed production test required the drilling of an initial stratigraphic test well (STW) to confirm the geologic conditions of the proposed test site. This well was completed in December 2018 in cooperation with the Prudhoe Bay Unit Interest Owners. With the success of the STW, the project leadership group is developing plans to drill a geologic data well and a production test well. Drilling plans for the STW were advanced in late 2018. The Prudhoe Bay Unit Hydrate-01 well was spudded on 10-December-2018. Downhole data acquisition was completed on 25-December-2018 and the rig was released on 01-January-2019. The STW was drilled in two sections. The surface hole was drilled to a depth of 2248 ft (MD, measured depth) and cased, and the “production hole section” was drilled to a depth of 3558 ft (MD) and also cased. A thermally chilled mineral-oilbased mud was used to maintain drillhole stability and quality of the borehole acquired data. The primary borehole data were acquired using a suite of Schlumberger logging-while-drilling tools. To gather grain size and other data needed to inform the design of the production test well, sidewall pressure cores were collected using Halliburton’s CoreVault tool. In addition to confirming the geologic conditions at the test site, the Hydrate-01 well was designed to serve as a monitoring well during future field operations. Therefore, two sets of fiber optic cables, each including bundled Distributed Acoustic Sensors (DAS) and Distributed Temperature Sensors (DTS), were clamped to the outside of the well casing and cemented in place. In March 2019, the project team worked with SAExploration to acquire 3D DAS Vertical Seismic Profiling (VSP) data in the Hydrate-01 well, which was the largest 3D DAS-VSP ever conducted. Additionally, since the December 2018 completion of the STW, several borehole temperature surveys have been acquired with the DTS deployed in the Hydrate-01 well.

Alaska↗

USGS2021

Status and trends of pelagic and benthic prey fish populations in Lake Michigan, 2020

Lakewide acoustic (AC) and bottom trawl (BT) surveys are conducted annually to generate indices of pelagic and benthic prey fish densities in Lake Michigan. The BT survey had been conducted each fall from 1973 through 2019 using 12-m trawls at depths ranging from 9 to 110 m and included 70 fixed locations distributed across seven transects; this survey estimates densities of seven prey fish species (i.e., alewife, bloater, rainbow smelt, deepwater sculpin, slimy sculpin, round goby, ninespine stickleback) as well as for age-0 yellow perch and large burbot. The AC survey, which serves to estimate densities of three prey fish species (i.e., alewife, bloater, and rainbow smelt), had been conducted each late summer/early fall from 2004-2019. The data generated from these surveys are used to estimate various population parameters that are, in turn, used by state and tribal agencies in managing Lake Michigan fish stocks. The 2020 COVID-19 pandemic severely limited the Lake Michigan pelagic and benthic prey fish surveys. While the AC survey was not conducted, 32 tows across three of seven standard BT transects (Saugatuck, Waukegan and Port Washington) were completed during an abbreviated survey. Total prey fish biomass density from the abbreviated BT survey was 1.91 kg/ha, continuing a recent trend of historically low estimates below the long-term (i.e., 1973-2020) average of 34.94 kg/ha. Mean biomass of yearling and older (YAO) alewives in 2020 was 0.025 ± 0.017 kg/ha, tied for the lowest ever recorded on the BT survey. No age-0 alewife were captured in the bottom trawl and of the limited number (n=16) of alewife collected, none were older than age four. Bloater (1.39 kg/ha) and deepwater sculpin (0.47 kg/ha) accounted for greatest proportion of biomass in the BT survey, while biomass density of slimy sculpin, round goby and rainbow smelt were all ≤ 0.01 kg/ha. While caution must be taken when interpreting the results of the abbreviated BT survey, the estimates suggest that prey fish densities remain well below historical values.

Lake Michigan↗

USGS2021

Ambassador wolves participate In scientific research

The International Wolf Center wolves are famous for providing unique educational opportunities to visitors to Ely and to people around the globe. Less known, are the contributions these wolves make to scientific research. Recently the Center’s Exhibit Pack were subjects of behavioral and acoustic research.

International Wolf↗

USGS2022

Status and trends of the Lake Huron prey fish community, 1976-2019

The USGS Great Lakes Science Center has assessed annual changes in the offshore prey fish community of Lake Huron since 1973. Assessments are based on a bottom trawl survey conducted in October of each year and an acoustics-midwater trawl survey, which began in 2004 and is conducted in September-October. Both surveys were completed in their entirety in 2019. Prey fish biomass in Lake Huron in 2019 was dominated by two species, Bloater ( Coregonus hoyi ) and Rainbow Smelt ( Osmerus mordax ). In the main basin, prey fish biomass remained below levels observed prior to community-wide declines that began in the early to mid 1990s. Bloater was the most abundant prey fish species in the main basin, whereas Rainbow Smelt was the most abundant prey species in the North Channel and in Georgian Bay. Both surveys suggested that Bloater biomass is increasing in the main basin. Low biomass of invasive species like Alewife ( Alosa pseudoharengus ) and Rainbow Smelt is consistent with fish community objectives focused on restoration of native fish communities. Abundance of invasive Round Goby (Neogobius melanostomus) in 2019 was low relative to 2018. Biomass of the native Cisco ( Coregonus artedi ) continued to increase in the North Channel and Georgian Bay. Biomass of slimy sculpin ( Cottus cognatus ) and Deepwater Sculpin ( Myoxocephalus thompsoni ) in 2019 was down from 2018 but within the range observed over the past decade. Reduced lake productivity, predation by a recovering piscivore community, and shifts in food web dynamics that favor fish production in nearshore environments may prevent prey fish biomass in offshore areas from returning to levels observed prior to the early 1990’s. However, increased biomass of Bloater and Cisco suggests that lake conditions may favor recovery of native coregonids.

Lake Huron↗

USGS2021

Geohydrologic and water-quality characterization of a fractured-bedrock test hole in an area of Marcellus Shale gas development, Sullivan County, Pennsylvania

The stratigraphy, water-bearing zones, and quality of groundwater were characterized in a 1,400-ft-deep test hole drilled during 2013 in fractured bedrock in Sullivan County, Pa., by collection and analysis of measurements made during drilling, geophysical logs, and depth-specific hydraulic tests and water samples. The multidisciplinary characterization of the test hole was a cooperative effort between the Pennsylvania Department of Natural Resources, Bureau of Geological Survey (BGS), and the U.S. Geological Survey (USGS). The study provided information to aid the bedrock mapping of the Laporte 7.5-minute quad-rangle by BGS to help quantify the depth and character of fresh and saline groundwater in an area of shale-gas exploration (described in this report), which could help gas operators protect groundwater resources. The Laporte test hole was drilled with air-hammer methods in an upland setting in the headwaters of Loyalsock Creek in the Glaciated High Plateau section of the Appalachian Plateaus physiographic province. Bedrock residuum and till were penetrated from land surface to 8.5 ft, the Huntley Mountain Formation of Mississippian and Devonian age was penetrated from 8.5 to 540 ft, and the Catskill Formation of Devonian age was penetrated from 540 to 1,400 ft. Fractures, determined from optical televiewer, acoustic televiewer, and video logs, were commonly encountered to 200 ft bls (below land surface), then decreased exponentially with depth, except at a highly fractured zone from 637 to 644 ft bls. Most fractures were along bedding planes and had a strike of about 243 degrees and dip about 4 degrees to the northwest, consistent with the test-hole location on the north limb of the Muncy Creek anticline. Few fractures were noted below 650 ft. The depths of fresh and saline water-bearing fracture zones were identified in the test hole by geophysical-log analysis and were verified by pumping samples from zones isolated with packers and by collecting samples in the open hole with a wire-line point sampler. Six water-bearing zones associated with single or multiple fractures were identified at depths of 130–135, 180, 267–275, 425, 637–644, and 1,003 ft bls. Under ambient conditions, fresh water entered the hole from fractures at 130-135 and 180 ft bls, flowed downward and exited at fractures from 267–275, 425, and 637–644 ft. When pumped at 16.2 gal/min, most of the water from the open test hole was contributed from the fracture at 180 ft bls. Transmissivity, estimated from analysis of the specific-capacity data and flowmeter logs, is about 850 ft 2 /d for the entire open hole, and about 60 percent of the transmissivity is contributed from the fracture zone at 180 ft bls. The hydraulic heads in the deep water-bearing zones at 425 and 637–644 ft were about 100 ft lower than hydraulic heads in shallow water-bearing zones at 180 ft bls and above, indicating a large downward vertical hydraulic gradient. Water samples pumped from fracture zones isolated by packers at and above the water-bearing zone at 450 ft bls were fresh with dissolved-solids contents of 105 mg/L or less. The sample isolated at 637–644 ft bls was probably affected by leakage around packers, but the specific-conductance samples collected during drilling that were believed to be representa-tive of the fracture zone at 637–644 ft bls indicated slightly saline water. Below the 637–644 ft zone, a flowmeter log in the open hole did not detect any vertical flow, and the temperature log approached the geothermal gradient, indicating little ambient fluid flow and minimal fracture transmissivity below this depth. A petrophysical-log analysis using estimates of formation water resistivity from Archie’s Equation indicated an apparent transition from fresh to saline water in the sandstones occurs between 450 to 900 ft bls, with saline water indicated below 900 ft. Small seeps of saline water were delineated at 958, 989, and 1,003 ft bls by a time series of specific-conductance logs, and a discrete-point water sample at 990 ft bls with total dissolved-solids concentration of 19,900 mg/L verified that highly saline water was present below 900 ft bls. Occurrence of saline water at a depth of about 900 ft bls is below altitude of streams within 3 to 5 miles of the test hole but is about 930 ft above the altitude at the mouth of Loyalsock Creek where is enters the West Branch Susquehanna River at Montours-ville, Pa. The depth to saline water in this test hole is close to depths estimated at two other deep test holes drilled by the BGS in upland settings in Bradford and Tioga Counties in north-ern Pennsylvania. The saline water from 990 ft bls had a chemical composition similar to Appalachian Basin brines that had been diluted with fresh water. Predominant ions in the saline water were sodium, chloride, and calcium. Trace constituents of strontium, bromide, barium, lithium, and molybdenum were all more than 5,000 times greater than in freshwater samples from 167 or 270 ft bls. Methane concentration in the saline water sample from 990 ft was 120 mg/L. The concentration ratios of methane to higher-chain hydrocarbon gases and isotopic ratios of 13 C/ 12 C and 2 H/ 1 H of methane indicate that the gases are likely of thermogenic origin. In the sample from 990 ft bls, the 13 C/ 12 C of methane was less negative (-34.81 per mil) than 13 C/ 12 C of ethane (-37.1 per mil). Isotopic reversals such as this are generally found in gases from rocks older than the Catskill Formation, so its recognition in a natural upland setting at relatively shallow depth could be important when interpreting isotopic results to identify the origin of stray gas in the area.

Pennsylvania↗

USGS2021

Lake Ontario April prey fish survey and Alewife assessment, 2021

The Lake Ontario April bottom trawl survey and Alewife, Alosa psuedoharengus population assessment are conducted annually to track prey fish community status and aid management decisions related to predator-prey balance. No survey was conducted in 2020 due to the Covid-19 pandemic. The 2021 survey included 248 bottom trawls in both U.S. and Canadian waters, from March 30 - May 7 in the main lake and embayment regions, at depths ranging from 5 – 221 m (16 - 729 ft). The survey captured 947,102 fish, from 30 species with a total weight of 9,191 kg (20,220 lbs). Alewife were 89.2% of the catch by number while Rainbow Smelt, Osmerus mordax , Round Goby Neogobius melanostomus , and Deepwater Sculpin Myoxocephalus thompsonii comprised 5.6, 2.3, and 1.7% of the catch, respectively. Rainbow Smelt biomass in 2021 was among the highest values observed since 1997, especially in U.S. waters. The biomass index for Cisco, Coregonus artedii also increased, primarily due to catches and greater survey effort in the Bay of Quinte. Threespine stickleback, Gasterosteus aculeatus and Emerald Shiner, Notropis atherinoides biomasses remain low. No Bloater, Coregonus hoyi were captured during the 2021 survey. In 2021, the lake-wide Alewife biomass index increased substantially from 2019 due to the presence of an exceptionally high catch of age-1 Alewife (2020 year class). The biomass index of adult Alewife (age-2 and up) declined slightly since 2019, which was expected since Alewife reproduction was generally below average from 2016 to 2019. Expanding the survey spatial extent from U.S. waters to a lake-wide survey in 2016 has improved our ability to estimate Alewife survival and has provided more accurate estimates of Lake Ontario Alewife biomass and density. Simulation modeling based on recent estimates of survival, growth, and reproduction suggests the adult Alewife biomass will likely increase in 2022 and 2023. As part of a continued effort to improve prey fish surveys, we employed hydroacoustic sampling during the 2021 April trawl survey to estimate fish densities in open-water, pelagic habitats not sampled by the bottom trawl. We found fish density, in waters above the trawl headline depth (3m off bottom to surface), were approximately ~100 times lower than pelagic prey fish densities from bottom trawls. These results support the idea that at this time of year, when the warmest water is on the lake bottom, Alewife and most other prey fish primarily inhabit deep, near bottom regions and can be effectively sampled with bottom trawls. We were not able to apportion acoustics targets to species, however the low mean target strength (-43 decibels, dB) suggested these were small fishes (e.g., 100 mm). The greatest hydroacoustics densities were found near the Niagara River confluence and future surveys may use midwater trawls to determine which species these were and continue to improve this multi-agency survey.

Lake Ontario↗

USGS2018

Genetic integrity, population status, and long-term viability of isolated populations of shoal bass in the upper Chattahoochee River basin, Georgia

This report characterizes the status of multiple isolated Shoal Bass ( Micropterus cataractae ) populations in the upper Chattahoochee River basin (UCRB), Georgia. The Shoal Bass, a sport fish endemic to the Apalachicola-Chattahoochee-Flint River (ACF) basin, is a fluvial-specialist species considered vulnerable to local extirpations and extinction due to habitat fragmentation and introgression with non-native congeners. Perhaps one of the most isolated populations of Shoal Bass exists in a 2-km reach of Big Creek, a tributary of the Chattahoochee River located near Roswell, Georgia. Big Creek is partially contained within the Chattahoochee River National Recreation Area, although the Big Creek watershed is riddled with urban land cover. Roswell Mill Dam limits the upstream extent of the Shoal Bass population at Big Creek, and the downstream extent is presumably limited to the confluence of Big Creek and the Chattahoochee River. This reach of the Chattahoochee River is thermally depressed because of coldwater releases from Lake Lanier, and is considered unsuitable for Shoal Bass. Herein, we examine the genetic integrity, population status, and long-term viability of the Shoal Bass population in Big Creek. We also examine two additional Shoal Bass populations that occur in the UCRB, specifically the Chestatee River and the upper Chattahoochee River, both of which are impounded at Lake Lanier. Together, the Shoal Bass inhabiting these three stream systems comprise a distinct genetic stock of Shoal Bass (Taylor 2017), underscoring the importance of conserving these populations towards maintaining the overall diversity and adaptive potential of the species. We assessed genetic diversity and estimated effective population sizes within these three rivers by genotyping fish with 16 microsatellite DNA markers. Results demonstrated that the Shoal Bass population in Big Creek has experienced high rates of introgression with non-native Smallmouth Bass (M. dolomieu), purportedly introduced into the Chattahoochee River in the past 10-15 years. Alarmingly, only 24% (15 of 62) of putative Shoal Bass collected from Big Creek were genetically pure Shoal Bass, whereas the majority of fish were first-filial (F1) generation hybrids and unidirectional backcrosses towards Shoal Bass. Fleeting opportunity may remain to conserve the native genome of the Shoal Bass population in Big Creek. High hybridization rates prevented genetic diversity analysis for the Big Creek population. Shoal Bass populations in the Chestatee and Chattahoochee rivers displayed levels of genetic diversity similar to populations that persist in other rivers in the ACF basin, namely the Flint and Chipola rivers. Effective population sizes of 93.8– 197.4 for the Chestatee and Chattahoochee rivers (combined) suggest that the conservation status of these populations is stable for the short-term, but may be at risk of losing genetic diversity and adaptive potential in the long-term. To estimate age and mortality of the three populations, we used fish scales and capture-markrecapture (CMR) as complementary, non-lethal methods for age estimation. Estimated ages of phenotypic Shoal Bass ranged from 1-12 years in all three populations, demonstrating increased longevity compared to populations elsewhere within the native range. Catch-curve estimates of annual mortality ranged from 18.4-23.7%, which are markedly lower than those observed in other Shoal Bass populations in the ACF basin. These differences in life-history characteristics underscore the need for the development of population-specific management and conservation strategies for Shoal Bass in the UCRB. The lowest recruitment variability (i.e., the variation in year-class strength) was observed in the Chestatee River, a forested watershed, whereas the highest variability was observed in Big Creek, an urbanized watershed. Recruitment strength in Big Creek was negatively influenced by discharge variability in the summer months, suggesting that flashy, sediment-laden flows hinder survival of recently hatched young. Other statistically significant models from Big Creek and the Chattahoochee River indicated that over-winter survival could be an important pinch-point for recruitment in UCRB populations. A multi-agency sampling effort was conducted from May 2013-May 2016 to estimate the population size of Shoal Bass occupying the 1-km of wadeable shoal habitats in Big Creek. Using CMR models, we estimated that approximately 219-348 Shoal Bass (≥ 70 mm total length) occupied the area throughout the duration of our study. These estimates largely reflect abundance of individuals aged 0-2 years, as only 9% (36 of 408) tagged fish were aged ≥ 7 years. Local abundance appeared similar to that reported for a population that inhabited Little Uchee Creek, a similar-sized tributary of the Chattahoochee River, prior to its recent functional extirpation. The low abundance of large, adult Shoal Bass further suggests the long-term viability of the Big Creek population may be in jeopardy. Perhaps most importantly, CMR estimates reflect abundance of phenotypic Shoal Bass – genetic analyses suggest the abundance of pure Shoal Bass could be an order of magnitude smaller. To evaluate the potential for adult Shoal Bass to emigrate from Big Creek into the mainstem Chattahoochee River, we tagged eight adults with acoustic telemetry tags and assessed their seasonal residency at two stationary receiver locations located in increasing proximity to the confluence with the Chattahoochee River. Fish took up residency near the confluence during the fall and winter months, during which time water temperatures in Big Creek were periodically colder than the Chattahoochee River. Although we were unable to document emigration, we conclude that the potential for emigration is highest during the winter months when the Chattahoochee River may be warmer than Big Creek. Two of the tagged fish were caught by anglers near the confluence, suggesting that angling pressure at Big Creek may be higher than previously suspected. Overall, this study observed unique life-history characteristics and characterized the population status of multiple Shoal Bass populations in the UCRB. Populations in the Chestatee and Chattahoochee rivers appear stable at present and likely represent the last remaining strongholds for pure Shoal Bass in the UCRB. Efforts to preserve forested watershed conditions, natural hydrology, and shoal habitats would contribute to the long-term persistence of Shoal Bass populations in these two rivers. Additionally, the detection of non-native Alabama Bass and their associated hybrids in both rivers is cause for concern. Diligent monitoring of hybridization dynamics between Alabama Bass and Shoal Bass is warranted, along with an assessment of Alabama Bass invasion extent upstream of Lake Lanier. The Shoal Bass population in Big Creek is threatened by elevated levels of introgression with nonnative Smallmouth Bass, recruitment variability, low abundance of adults, and isolation from other populations. Conservation intervention is urgently needed to restore and preserve this genetically distinct population, which would contribute to preservation of range wide genetic diversity and adaptability of the species. Additionally, an urban sport fishery for Shoal Bass at Big Creek has the potential to serve as a tool for increasing public awareness, engagement, and support of Shoal Bass conservation efforts in the UCRB. We suggest strategies for conservation of the remnant shoal habitats and Shoal Bass population in Big Creek, including potential development of a supplemental stocking program, selective removal of non-native congeners, and delivery of environmental education programs that could bolster awareness and appreciation.

Georgia↗

USGS1974

Tectonic transition zone in the northeastern Caribbean

Seismic reflection data indicate that the Atlantic plate has been underthrust beneath the Caribbean plate east of the Lesser Antilles. The data further reveal that the transition from underthrust to strike-slip plate motion occurs near lat 19.3° N. and long 62° W. in alinement with the Anegada Trough. Oceanic basement and reflectors above basement have not been detected beneath the landward wall of the Puerto Rico Trench west of the transition zone. Southeast of the zone, the horizontal distance over which the reflectors and basement can be traced beneath the landward wall (outer part of the Lesser Antilles rise) systematically increases from a few kilometers in the north to as much as 37 km near lat 16.5° N. If a thrust fault emerges at the landward trench wall, the data suggest that a decollement exists between reflectors above basement and an overlying acoustically transparent zone. Gravity and seismic refraction data indicate a thick accumulation of low-density, low-velocity material beneath the Lesser Antilles rise, possibly sediments scraped off the underthrusting Atlantic plate, although massive slumping might cause a similar low-density configuration. The magmatic history of the Lesser Antilles arc suggests two periods of underthrusting, one in the Mesozoic or early Cenozoic and a second in the late Cenozoic. Although the magmatic history of the Lesser Antilles apparently began in the Mesozoic, its Cenozoic history is remarkably similar to the Cenozoic histories of circum-Pacific arcs. Magmatic histories in both areas suggest that island arc evolution in the Cenozoic may have worldwide synchroneity.

Journal of Research of the U.S. Geological Survey↗

USGS2023

Assessment and guidance for using Laser In-situ Scattering and Transmissometry– Stream-Lined 2 (LISST-SL2)

The Laser In-situ Scattering and Transmissometry–Stream-Lined 2 (LISST-SL2) is a second-generation isokinetic river sediment monitoring device that uses laser diffraction to measure suspended-sediment concentration and particle size between 1 and 500 microns in 36 log-spaced bins at a point in a river every second. We compare this latest laser diffraction instrument for suspended-sediment sampling in rivers, with concurrent physical measurements of suspended sediment concentration (SSC) and particle size distribution (PSD) and velocity measurements by an acoustic Doppler current profiler (ADCP). We collected 136 LISST-SL2 samples along with 61 physical samples for SSC measurement, of which 24 physical samples included PSD measurement, during 2018-2020 from 11 sites in Washington and Virginia, USA. The required computed effective density (mass SSC/volumetric SSC) to convert volumetric SSC by the LISST-SL2 into mass SSC ranged from 0.5 to 5.4 g/mL, with a best-fit value of 2.05 g/mL, while the default value (typically assumed as 2.65 g/mL) is much higher. As the comparison also showed that the LISST-SL2 was not able to measure the finest sediment sizes in suspension, we propose some adjustments of the LISST-SL2 data with a supporting physical sample to account for these effective density and PSD issues. When doing so, we were able to reduce the RMSRE (Root Mean Square Relative Error) to 18% from 117% for SSC, and to 26% from 78% for PSD. LISST-SL2 velocities were generally higher than ADCP velocities with a 21% RMSRE. Our results and guidance will allow for more accurate sampling by the LISST-SL2, which has great potential for studying spatial and temporal variation of suspended sediment characteristics in rivers.

Conference Paper↗

USGS1992

Microcrack interaction leading to shear fracture

In this paper we draw upon recent laboratory results concerning the nucleation and growth of shear fractures in brittle rock. In homogeneous, crystalline rock such as granite, fault nucleation occurs rapidly and with only subtle changes in precursory microcrack patterns. Once nucleated, the fault grows rapidly, restricting microcrack damage to a small region near the advancing fracture front. Observations of acoustic emission locations during fault nucleation and growth combined with determinations of microcrack densities in the fractured samples have led to a conceptual model in which brittle fracture is controlled by microcrack interactions.

Conference Paper↗

USGS2023

Geophysical logging For hydrogeology

Geophysical logging is the measurement and analysis of electrical, acoustic, nuclear, and other physical properties in a borehole using wireline or direct push technology. Geophysical logging is one of the primary methods of collecting subsurface information for hydrogeologic investigations. Groundwater scientists and engineers should have a basic understanding of borehole geophysics and how it is applied in the characterization of aquifer systems. In this book, the different types of geophysical logs and equipment used in hydrogeologic investigations are reviewed. Applications and analysis methods are illustrated by specific examples in both unconsolidated deposits and bedrock settings. Key references for further exploration of the methods and applications are provided. Hands-on exercises are included for students to develop and practice log-analysis skills.

Book↗

USGS2023

Bedform distributions and dynamics in a large, channelized river: Implications for benthic ecological processes

Sand bedforms are fundamental habitat elements for benthic fish in large, sand-bedded rivers and are hypothesized to provide flow refugia, food transport, and ecological disturbance. We explored bedform distributions and dynamics in the Lower Missouri River, Missouri, with the objective of understanding the implications of these features for benthic fish habitat, particularly for the endangered pallid sturgeon (Scaphirhynchus albus) and shovelnose sturgeon (Scaphirhynchus platorynchus) during their early life stages. We mapped bathymetry in a 3-kilometer-long reach of the highly engineered Lower Missouri River 22 times over a three-year period from 2019-2021 using a multibeam echosounder. Surveys included precise water surface and bed elevations over discharges ranging from 1,360-8,550 cubic meters per second. This included weekly surveys during a large flood event with a peak of 9,290 cubic meters per second in the spring and summer of 2019. Velocity was mapped with an acoustic Doppler current profiler during 11 of the 22 multibeam surveys. The dataset illustrates how bedforms are distributed in a typical Missouri River reach and how they evolve with changes in discharge. We measured a variety of bedform characteristics, including height, length, lee-slope angle, and crest orientation, and examined their relationship to larval sturgeon catch in the reach in 2020 and 2021. Bedform shapes are controlled by depositional environment and discharge and range in size from less than a meter in wavelength and amplitude to greater than 4 meters high and 75 meters long and generally have low angle lee-slopes. Small dunes were located in lower velocity regions on the inside of a bend and behind wing-dikes, as well as superimposed on larger dunes. Larger dunes were generally located in the channel thalweg and were associated with higher flow velocities. However, bedform size did not necessarily scale with discharge over the course of the 2019 flood, possibly due to sediment supply limitations and hysteresis effects. Changes in bedform size over the course of the flood event were most pronounced in the thalweg; less change in bedform size occurred behind wing dikes on the inside of channel bends, indicating some degree of habitat stability. Despite rarely getting caught in the thalweg, larval sturgeon drift in the thalweg until they are intercepted into off-channel habitats in wing dike fields, where they are caught in much higher numbers. Bedform orientations were affected by flow expansion around wing dikes, indicative of the role of wing dikes in influencing exchange of material between the thalweg and channel margins. Increased understanding of bedform distributions and dynamics will inform future sampling and habitat restoration designs for larval pallid sturgeon and contribute to increased understanding of their influence on benthic ecological processes.

Conference Paper↗