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At least 163 records · Page 9Linked to original sources
USGS2017

The California Seafloor and Coastal Mapping Program – Providing science and geospatial data for California's State Waters

The California Seafloor and Coastal Mapping Program (CSCMP) is a collaborative effort to develop comprehensive bathymetric, geologic, and habitat maps and data for California's State Waters. CSCMP began in 2007 when the California Ocean Protection Council (OPC) and the National Oceanic and Atmospheric Administration (NOAA) allocated funding for high-resolution bathymetric mapping, largely to support the California Marine Life Protection Act and to update nautical charts. Collaboration and support from the U.S. Geological Survey and other partners has led to development and dissemination of one of the world's largest seafloor-mapping datasets. CSCMP provides essential science and data for ocean and coastal management, stimulates and enables research, and raises public education and awareness of coastal and ocean issues. Specific applications include: •Delineation and designation of marine protected areas •Characterization and modeling of benthic habitats and ecosystems •Updating nautical charts •Earthquake hazard assessments •Tsunami hazard assessments •Planning offshore infrastructure •Providing baselines for monitoring change •Input to models of sediment transport, coastal erosion, and coastal flooding •Regional sediment management •Understanding coastal aquifers •Providing geospatial data for emergency response

California↗
USGS2021

Lateral shoreline erosion and shore-proximal sediment deposition on a coastal marsh from seasonal, storm and decadal measurements

The persistence of coastal marsh is dependent on its ability to maintain elevation relative to sea level, particularly for marshes experiencing high rates of shoreline erosion due to wave-attack, storms, and sea level rise. Sediments eroded at the marsh edge are either delivered onto the marsh platform or into the estuary, the latter resulting in a net loss of marsh sediments and soil carbon. Knowledge on the timing, pattern, and quantity of sediment deposition versus shoreline erosion along the marsh-estuary interface is critical for evaluating the overall health and vulnerability of coastal marshes to future scenarios of sea level rise and for estimating sediment budgets . Here we examined marsh shoreline erosion and sediment deposition for marsh sites experiencing a range of shoreline erosion rates and different levels of wind-wave exposure within the Grand Bay National Estuarine Research Reserve and Wildlife Refuge in Mississippi. We developed a method for calculating an erosion-deposition sediment budget using marsh elevation profiles, shoreline erosion rate, and sediment deposition measurements. Sediment budgets were calculated at four sites with varying shoreline erosion rates. Much of the sediment eroded at the marsh edge can be accounted for as marsh platform deposition, except at the most erosive site, suggesting a possible erosion threshold where eroded sediment mass is greater than platform deposition. Consistent with other studies of marsh creeks, sediment delivery to the marsh platform appears to be largely driven by wave climate. These data suggest that for erosive bay-estuarine shorelines, sediment delivered into the marsh is largely concentrated near the marsh shoreline, although shoreline erosion does not always result in a net loss of sediments from the marsh system in either decadal or annual assessments.

Mississippi↗
USGS2025

Post-wildfire sediment fluxes and turbidity plumes in a coastal-draining watershed

Coastal watersheds impacted by wildfires experience higher erosion resulting in increased sediment delivery to the ocean that alters limiting factors (i.e., light) for marine organisms. With increasing wildfire magnitude and severity, it is critical to explore changes in riverine discharges to the ocean to assess cascading hazards associated with wildfires. In situ data, remotely sensed turbidity data, and hydrological model (Soil and Water Assessment Tool “SWAT”) simulations have been adapted to capture and investigate fire-related land use change impacts on Malibu Creek, California, USA. Modifying SWAT land cover inputs using burn severity data had minimal impact on simulations, requiring additional parameterization for acceptable model performance. Remotely sensed turbidity, in situ discharge, rating curve sediment loads, and SWAT simulated discharge and sediment loads increased following the Woolsey Fire. When compared to in situ and rating curve data in similar non-fire water years, the 2019 Woolsey Fire water year in situ discharge was 1.8 times higher, SWAT simulated discharges were 1.4–1.7 times higher, and rating curve sediment load was 1.3 times higher. However, the SWAT simulated sediment loads were slightly lower (0.8–0.9 times) than rating curve sediment loads in similar non-fire water years. Mean coastal turbidity increased to 18.2 Formazin Nephelometric Unit (FNU) during the first storm post-fire (mean background value of 4.3 FNU). Synergies between methods demonstrated rapid coastal sediment exports (remote sensing) and ongoing erosion post-fire (SWAT). These data are essential to understanding fire-related marine ecological changes and implementing effective management and conservation initiatives.

California↗
USGS2020

Hurricane sedimentation in a subtropical salt marsh-mangrove community is unaffected by vegetation type

Hurricanes periodically deliver sediment to coastal wetlands, such as those in the Mississippi River Delta Complex (MRDC), slowing elevation loss and improving resilience to sea-level rise. However, the amount of hurricane sediment deposited and retained in a wetland may vary depending on the dominant vegetation. In the subtropical climate of the MRDC, the black mangrove (Avicennia germinans) has been expanding and replacing salt marsh (Spartina alterniflora). Because these vegetation types differ in structure, their influence on sedimentation may also differ. We conducted a survey along 160 km of coastline to determine if the spatial deposition pattern in saline wetlands by Hurricanes Gustav and Ike in September 2008 was differentially influenced by vegetation type. Sampling was initiated two months after landfall at eighteen sites in the MRDC containing side-by-side stands of A. germinans and S. alterniflora along the shoreline, with S. alterniflora marsh landward. Average thickness of hurricane sediment across sites varied from 0.6 to 5.6 cm with an overall mean of 2.6 ± 0.4 cm. Within sites, hurricane-layer thickness varied from 1.3 cm at the shoreline to 4.8 cm in the marsh interior, but this pattern was unaffected by vegetation type. Despite greater canopy height, stem density (including pneumatophores), and leaf area, mangroves did not capture more hurricane sediment than salt marsh nor did they attenuate the delivery of sediment to the marsh interior. Data recorded at thirty-six monitoring stations in Louisiana's Coastwide Reference Monitoring System further showed that rates of accretion, as well as elevation change, in saline wetlands (S. alterniflora) of the MRDC were temporarily increased by Hurricanes Gustav and Ike. These findings agree with previous work showing the beneficial effects of hurricane sediments on coastal wetlands, but suggest that a climate-driven shift from S. alterniflora to A. germinans in the MRDC will not necessarily alter hurricane sediment capture.

Louisiana↗
USGS2019

Patterns of resource allocation in a coastal marsh plant (Schoenoplectus americanus) along a sediment-addition gradient

Reductions in sediment delivery to coastal marshes increase their vulnerability to relative sea-level rise. Sediment pulses from storm events and commercial dredge-spray operations (e.g., beneficial use) represent increasingly important sediment sources to otherwise sediment-deprived marshes. These sediments can stimulate plant growth by providing nutrient and elevation subsidies, with plant growth predicted to peak at intermediate sediment depths. Most sediment subsidy studies have compared plant responses among discrete sediment depths applied across a uniform marsh platform, and often assessed impacts in the years following sediment deposition. Less is known about the immediate effects of sediment additions on plant growth or the mechanisms driving differences in these responses along a sediment-addition gradient. To investigate immediate plant responses to sediment additions (i.e., within 6 months), we added sediment to Schoenoplectus americanus -dominated brackish marsh sods in a greenhouse setting. Sediment was added incrementally along a sediment addition gradient (0–20 cm) to 18 sods, which were placed in clear planting enclosures to permit monitoring of above- and below-ground responses and hydro-edaphic properties. Shoot production, which increased linearly along the sediment addition gradient, was the first observable response to sediment addition and was likely a result of apical dominance interruption. This trend continued throughout the study even as survival of those shoots declined with increasing sediment depth. At the end of the experiment, however, shoot biomass production was biphasic, responding favorably to sediment addition up to intermediate depths before collapsing at higher depths. While fine root production in sods was maximal at intermediate sediment addition levels, root production in new sediment layers was limited. There were limited differences observed for hydro-edaphic properties along the sediment addition gradient. Thus, plant resources are allocated to shoot production immediately following sediment addition at the expense of root colonization of new sediment layers, suggesting that, in certain conditions, sediment deposition can represent a stress rather than a subsidy.

Louisiana↗
USGS2019

Offshore shallow structure and sediment distribution, Point Sur to Point Arguello, central California

This publication consists of three map sheets that display shallow geologic structure, along with sediment distribution and thickness, for an about 225-km-long offshore section of the central California coast between Point Sur and Point Arguello. Each map sheet includes three maps, at scales of either 1:150,000 or 1:200,000, as well as a set of figures that contain representative high-resolution seismic-reflection profiles. The maps and seismic-reflection surveys cover most of the continental shelf in this region. In addition, the maps show the locations of the shelf break and the 3-nautical-mile limit of California’s State Waters. The seismic-reflection data, which are the primary dataset used to develop the maps, were collected to support the California Seafloor Mapping Program and U.S. Geological Survey Offshore Geologic Hazards projects. In addition to the three map sheets, this publication includes geographic information system data files of interpreted faults, folds, sediment thicknesses, and depths-to-base of sediment. The faults and folds shown on the maps have been locally simplified as appropriate for the map scales. The right-lateral San Gregorio–Hosgri Fault (SGHF) is the most significant structure in the map area. On a regional scale, the SGHF is part of a 400-km-long, right-lateral fault system that extends northwestward from Point Arguello to the area offshore of San Francisco, where it merges with the San Andreas Fault. From north to south in this part of central California, the SGHF lies offshore between the south flank of Point Sur and the north flank of Point Piedras Blancas, then comes onshore at Point Piedras Blancas, before heading offshore again between the south flank of Point Piedras Blancas and Point Arguello. Cumulative fault offset along the SGHF is as much as 150 to 160 km, decreasing to the south by transferring slip on to northwest-striking faults that converge with the SGHF both onland and offshore from the east. In the map area, the offshore-converging faults include the Los Osos Fault, the Shoreline–Point Buchon Fault, the Casmalia Fault, and the Lions Head Fault. Quaternary sediments and bedrock underlie the shelf. On the seismic-reflection profiles, we divide Quaternary shelf sediments into two units. Characterizing the younger, upper unit is a focus of this publication. This unit is inferred to have been deposited on the shelf in the last about 21,000 years during the sea-level rise that followed the last major lowstand and the Last Glacial Maximum (LGM). This upper unit overlies a transgressive surface of erosion, a commonly angular, wave-cut unconformity, and is generally characterized by low-amplitude, continuous to moderately continuous, diffuse, subparallel, generally flat reflections. Maps in this publication show both the thickness of this upper sediment unit and the depth to the base of the sediment unit. Within the map region, 11 different “domains” of post-LGM shelf sediment are delineated on the basis of sediment thickness and coastal geomorphology. Maximum sediment thickness is in the southern part of the region, offshore of the mouths of the Santa Ynez and Santa Maria Rivers. Minimum sediment thickness is found offshore of prominent rocky points, including Point Buchon and Piedras Blancas. Mean sediment thickness for the entire shelf in the map area between Point Sur and Point Arguello is 12.2 m, and total sediment volume is 24.7 million cubic meters.

California↗
USGS2019

Offshore shallow structure and sediment distribution, Punta Gorda to Point Arena, Northern California

This publication consists of two map sheets that display shallow geologic structure, along with sediment distribution and thickness, for an approximately 150-km-long offshore section of the northern California coast between Punta Gorda and Point Arena. Each map sheet includes three maps at scales of either 1:100,000 or 1:200,000, and together the sheets include 30 figures that contain representative high-resolution seismic-reflection profiles. The maps and seismic-reflection surveys cover most of the continental shelf in this region. In addition, the maps show the locations of the shelf break and the 3-nautical-mile limit of California’s State Waters. The seismic-reflection data, which are the primary dataset used to develop the maps, were collected to support the California Seafloor Mapping Program, U.S. Geological Survey Offshore Geologic Hazards projects, and National Oceanic and Atmospheric Administration’s (NOAA’s) Ocean Explorer program. In addition to the two map sheets, this publication includes geographic information system data files of faults, sediment thicknesses, and depths-to-base of sediment The map area includes the northernmost section of the right-lateral San Andreas Fault, which extends offshore from Point Arena in the south to Point Delgada in the north. The San Andreas Fault is the primary structure in the widely distributed plate boundary between the Pacific Plate and the Sierra Nevada–Great Valley Microplate, with estimates of cumulative right slip of as much as up to 450 km. South of Point Delgada, fault-related transtension has resulted in development of the Noyo Basin. North of Point Delgada, the San Andreas Fault transitions into a complex contractional zone in and (or) south of the King Range, including a possible nearshore fault that may connect with the Mattole Canyon Fault. Quaternary sediments and bedrock underlie the shelf. On the seismic-reflection profiles, we digitally traced the thickness and depth of the uppermost seismic-stratigraphic unit, which is a focus of this publication. The upper contact of this unit is the seafloor; the lower contact is a transgressive surface of erosion, a commonly angular, wave-cut unconformity characterized by an upward change to lower amplitude, more diffuse reflections. On the basis of this lower contact, this stratigraphic unit is inferred to have been deposited on the shelf in the last about 21,000 years during the sea-level rise that followed the last major lowstand and the Last Glacial Maximum (LGM). Maps in this publication show both the thickness of this upper sediment unit and the depth to the base of the sediment unit. Within the map region, five different “domains” of post-LGM shelf sediment are delineated on the basis of sediment thickness and coastal geomorphology. Maximum sediment thickness (as much as 67 m) is found in the northern part of the region, along the steep south flank of the King Range. Minimum sediment thickness (areas of exposed bedrock) is found on fault-bounded uplifts, which include Tolo bank and Punta Gorda bank. Mean sediment thickness for the entire shelf in the map area between Punta Gorda and Point Arena is 8.9 m, and total sediment volume is 12,824×10 6 m 3 .

California↗
USGS2016

Methane and sulfate dynamics in sediments from mangrove-dominated tropical coastal lagoons, Yucatan, Mexico

Porewater profiles in sediment cores from mangrove-dominated coastal lagoons (Celestún and Chelem) on the Yucatán Peninsula, Mexico, reveal the widespread coexistence of dissolved methane and sulfate. This observation is interesting since dissolved methane in porewaters is typically oxidized anaerobically by sulfate. To explain the observations we used a numerical transport-reaction model that was constrained by the field observations. The model suggests that methane in the upper sediments is produced in the sulfate reduction zone at rates ranging between 0.012 and 31 mmol m −2 d − 1 , concurrent with sulfate reduction rates between 1.1 and 24 mmol SO 4 2− m −2 d −1 . These processes are supported by high organic matter content in the sediment and the use of non-competitive substrates by methanogenic microorganisms. Indeed sediment slurry incubation experiments show that non-competitive substrates such as trimethylamine (TMA) and methanol can be utilized for microbial methanogenesis at the study sites. The model also indicates that a significant fraction of methane is transported to the sulfate reduction zone from deeper zones within the sedimentary column by rising bubbles and gas dissolution. The shallow depths of methane production and the fast rising methane gas bubbles reduce the likelihood for oxidation, thereby allowing a large fraction of the methane formed in the sediments to escape to the overlying water column.

Yucatan↗
USGS2012

The effects of wildfire on the sediment yield of a coastal California watershed

The occurrence of two wildfires separated by 31 yr in the chaparral-dominated Arroyo Seco watershed (293 km ) of California provides a unique opportunity to evaluate the effects of wildfire on suspended-sediment yield. Here, we compile discharge and suspended-sediment sampling data from before and after the fires and show that the effects of the postfire responses differed markedly. The 1977 Marble Cone wildfire was followed by an exceptionally wet winter, which resulted in concentrations and fluxes of both fine and coarse suspended sediment that were ˜35 times greater than average (sediment yield during the 1978 water year was 11,000 t/km 2 /yr). We suggest that the combined 1977–1978 fire and flood had a recurrence interval of greater than 1000 yr. In contrast, the 2008 Basin Complex wildfire was followed by a drier than normal year, and although suspended-sediment fluxes and concentrations were significantly elevated compared to those expected for unburned conditions, the sediment yield during the 2009 water year was less than 1% of the post–Marble Cone wildfire yield. After the first postfire winters, sediment concentrations and yield decreased with time toward prefire relationships and continued to have significant rainfall dependence. We hypothesize that the differences in sediment yield were related to precipitation-enhanced hillslope erosion processes, such as rilling and mass movements. The millennial-scale effects of wildfire on sediment yield were explored further using Monte Carlo simulations, and these analyses suggest that infrequent wildfires followed by floods increase long-term suspended-sediment fluxes markedly. Thus, we suggest that the current approach of estimating sediment yield from sediment rating curves and discharge data—without including periodic perturbations from wildfires—may grossly underestimate actual sediment yields.

California↗
USGS2005

Sediments in marsh ponds of the Gulf Coast Chenier Plain: Effects of structural marsh management and salinity

Physical characteristics of sediments in coastal marsh ponds (flooded zones of marsh associated with little vegetation) have important ecological consequences because they determine compositions of benthic invertebrate communities, which in turn influence compositions of waterbird communities. Sediments in marsh ponds of the Gulf Coast Chenier Plain potentially are affected by (1) structural marsh management (levees, water control structures and impoundments; SMM), and (2) variation in salinity. Based on available literature concerning effects of SMM on sediments in emergent plant zones (zones of marsh occasionally flooded and associated with dense vegetation) of coastal marshes, we predicted that SMM would increase sediment carbon content and sediment hardness, and decrease oxygen penetration (O2 depth) and the silt-clay fraction in marsh pond sediments. Assuming that freshwater marshes are more productive than are saline marshes, we also predicted that sediments of impounded freshwater marsh ponds would contain more carbon than those of impounded oligohaline and mesohaline marsh ponds, whereas C:N ratio, sediment hardness, silt-clay fraction, and O2 depth would be similar among pond types. Accordingly, we measured sediment variables within ponds of impounded and unimpounded marshes on Rockefeller State Wildlife Refuge, near Grand Chenier, Louisiana. To test the above predictions, we compared sediment variables (1) between ponds of impounded (IM) and unimpounded mesohaline marshes (UM), and (2) among ponds of impounded freshwater (IF), oligohaline (IO), and mesohaline (IM) marshes. An a priori multivariate analysis of variance (MANOVA) contrast indicated that sediments differed between IM and UM marsh ponds. As predicted, the silt-clay fraction and O2 depth were lower and carbon content, C:N ratio, and sediment hardness were higher in IM than in UM marsh ponds. An a priori MANOVA contrast also indicated that sediments differed among IF, IO, and IM marsh ponds. As predicted, carbon content was higher in IF marsh ponds than in ponds of other impounded marsh types. In contrast to our predictions, C:N ratio and sediment hardness were lowest and silt-clay fraction and O2 depth were highest in IO and IM marsh ponds. Our results indicated that SMM has affected physical properties of sediments in coastal marsh ponds. Moreover, sediments in IF marsh ponds were affected more so than were those in IO and IM marsh ponds. Our results, in conjunction with those of previous studies, indicated that sediments of marsh ponds and emergent plant zones differed greatly. We predict that changes in pond sediments due to SMM will promote greater epifaunal macroinvertebrate biomass, which in turn should attract larger populations of wintering waterbirds. However, waterbirds that filter or probe soft sediments may be negatively affected by SMM because of the expected decrease in infaunal invertebrate biomass. ?? Springer 2005.

Wetlands Ecology and Management↗
USGS2013

Use of sediment amendments to rehabilitate sinking coastal swamp forests in Louisiana

Coastal wetlands are losing elevation worldwide, so that techniques to increase elevation such as sediment amendment might benefit these wetlands. This study examined the potential of sediment amendment to raise elevation and support the production and regeneration of vegetation in coastal forests in Louisiana. Before sediment amendment, the vegetation did not differ in these Taxodium distichum–Nyssa aquatica forests with respect to herbaceous and tree seedling composition, and sapling and tree characteristics. After the application of sediment in January 2007, sediment-amended swamps had higher elevations and salinity levels than natural swamps. The layer of sediment applied to Treasure Island in Jean Lafitte National Historic Park and Preserve was relatively deep (sediment depth at Site One and Site Two: 0.89 and 0.69 m, respectively, six months after application), and may have exceeded an optimal threshold. Sediment-amended swamp with the highest elevation had some tree mortality and little tree growth of T. distichum. Also, sediment-amended swamp had higher root biomasses of ruderal species, and lower species richness and cover of herbaceous species. Nevertheless, during controlled water releases during an oil spill emergency in 2010, both sediment-amended and reference forest had higher production levels than in other years. While sediment amendment is a compelling management alternative for sinking coastal wetlands, optimal thresholds were not determined for these T. distichum–N. aquatica swamps.

Louisiana↗
USGS2023

Sediment thickness map of United States Atlantic and Gulf Coastal Plain Strata, and their influence on earthquake ground motions

With the recent successful accounting of basin depth ground-motion adjustments in seismic hazard analyses for select areas of the western United States, we move toward implementing similar adjustments in the Atlantic and Gulf Coastal Plains by constructing a sediment thickness model and evaluating multiple relevant site amplification models for central and eastern United States seismic hazard analyses. We digitize and combine existing sediment thickness data sets into a composite surface that delineates the base of Cretaceous sediments under the Atlantic Coastal Plain and the base of Mesozoic sediments under the Gulf Coastal Plain. Amplification models dependent on sediment thickness, site natural period, and source-to-site path length are compared with data sets of observed ground motions to evaluate the ability of the new models to improve ground motion estimates. We find that the amplification models can account for observed trends in sediment-thickness and period-dependent residuals, but some tuning is required. For example, the model of Chapman and Guo requires a reference V S 30 , the time-averaged shear-wave velocity within 30 m of the Earth’s surface, for non-Coastal Plain sites, which we estimate to be between about 1 and 2 km/s. Along with our sediment thickness model, we estimate a velocity profile for application to the Harmon et al. site-natural-period-based model in order to best match the Chapman and Guo period dependence for a broad range of sediment thicknesses. The Next Generation of Attenuation models for the eastern United States Gulf Coast path-based adjustment models can also account for seismic attenuation in the Coastal Plain sediments and reduce the standard deviation of total residuals. If enacted in the U.S. Geological Survey National Seismic Hazard Model, these amplification models will reduce predicted short-period (<1 s) and increase predicted long-period (>1 s) ground motions in the Coastal Plains appreciably.

Earthquake Spectra↗
USGS2004

Pocomoke Sound Sedimentary and Ecosystem History

Summary of Results: Pocomoke Sound Sediment and Sediment Processes Transport of sediment from coastal marshes. Analyses of pollen and foraminifera from surface sediments in Pocomoke Sound suggest that neither the upstream forested wetlands nor coastal marshes bordering the sound have contributed appreciably to particulate matter in the 10- to 1000-micron size range that is currently being deposited in the sound. Sediment processes derived from short-lived isotope. Analyses of beryllium-7, cesium-137 and lead-210 and redox sensitive elements from Pocomoke sediments showed that there has been a significant increase in anthropogenic elements since the late 1940's when the Delmarva Peninsula became more accessible from the Baltimore-Washington region. Cesium-137 was found to be a useful tool to determine changes in sedimentation within the system. Three major stages of sedimentation occurred. Before 1950, the system was equilibrium with the agriculture activity in the watershed, whereas urbanization and agricultural activity changes during and immediately preceding World War II resulted in increased sediment flux. Around 1970, the sediment flux diminished and there was an apparent increase in bank erosion sediment to the deeper parts of the system. Rates of sediment deposition. Radiocarbon, lead-210, and pollen dating of sediment cores from Pocomoke Sound indicate relatively continuous deposition of fine-grained sediments in the main Pocomoke channel at > ~7 m water depths. Mean sediment accumulation rates during the past few centuries were relatively high (>1 cm yr -1 ). The ages of coarser-grained sediments (sands) blanketing the shallow (< ~ 7 m water depth) flanks of Pocomoke Sound are not well constrained but were probably deposited discontinuously. Impacts of land-use on benthic biota. The Pocomoke Sound paleoecological record shows that in the 1940-50s and again in the 1970-80s, the sound experienced unprecedented changes in the benthic assemblages of both ostracodes and foraminifera that can be attributed to degradation in water quality. These changes represent perturbations to the natural variability in faunal assemblages, which are normally driven by climatically influenced changes in salinity regimes. Changes in 20th century benthic communities were characterized by the rise to dominance of facultative anaerobic taxa tolerant of hypoxia and detrital-feeding species, reflecting increased influx of organic matter, and perhaps greater turbidity. Results support the hypothesis of Orth et al. (2002) and Orth and Moore (1983) that unprecedented changes to the bay ecosystem affected submerged aquatic vegetation in the Tangiers-Pocomoke region prior to large-scale monitoring began in the 1970s and 80s. Comparison of Pocomoke paleoecological record with those from the mainstem bay indicate that environmental degradation during the 20th century was nearly synchronous bay-wide within the limits of sediment core chronology (10-20 years). Stable isotopic evidence for decadal water quality changes. Stable isotopic records from benthic foraminifera in Pocomoke Sound sediment cores, especially oxygen isotopes, document regional decadal and centennial climate processes which influence salinity and water quality over the past few centuries. These results provide indirect evidence for discharge-driven changes in freshwater and presumably river-borne sediment from the watershed to the sound. They are consistent with studies in the mainstem indicating the important influence of climatic and hydrological processes on water quality. Pollen evidence for high sedimentation and vegetation change during colonial land clearance. Pollen assemblages from sediment cores in Pocomoke Sound document high sedimentation rates (0.7->4.0 cm yr -1 ) at most sites throughout the Sound in post-Colonial time. These results confirm those from other regions of the bay that land-clearance increased the flux of river-borne sediment to certain r

Open-File Report↗
USGS2004

Documentation of revisions to the regional aquifer system analysis model of the New Jersey coastal plain

The model, which simulates flow in the New Jersey Coastal Plain sediments, developed for the U.S. Geological Survey Regional Aquifer System Analysis (RASA) program was revised. The RASA model was revised with (1) a rediscretization of the model parameters with a finer cell size, (2) a spatially variable recharge rate that is based on rates determined by recent studies and, (3) ground-water withdrawal data from 1981 to 1998. The RASA model framework, which subdivided the Coastal Plain sediments into 10 aquifers and 9 confining units, was preserved in the revised model. A transient model that simulates flow conditions from January 1, 1968 to December 31, 1998, was constructed using 21 stress periods. The model was calibrated by attempting to match the simulated results with (1) estimated base flow for five river basins, (2) measured water levels in long-term hydrographs for 28 selected observation wells, and (3) potentiometric surfaces in the model area for 1978, 1983, 1998, 1993, and 1998 conditions. The estimated and simulated base flow in the five river basins compare well. In general, the simulated water levels matched the interpreted potentiometric surfaces and the measured water levels of the hydrographs within 25 feet.

Water-Resources Investigations Report↗
USGS2017

Rare earth mineral potential in the southeastern U.S. Coastal Plain from integrated geophysical, geochemical, and geological approaches

We combined geophysical, geochemical, mineralogical, and geological data to evaluate the regional presence of rare earth element (REE)−bearing minerals in heavy mineral sand deposits of the southeastern U.S. Coastal Plain. We also analyzed regional differences in these data to determine probable sedimentary provenance. Analyses of heavy mineral separates covering the region show strong correlations between thorium, monazite, and xenotime, suggesting that radiometric equivalent thorium (eTh) can be used as a geophysical proxy for those REE-bearing minerals. Airborne radiometric data collected during the National Uranium Resource Evaluation (NURE) program cover the southeastern United States with line spacing varying from ∼2 to 10 km. These data show eTh highs over Cretaceous and Tertiary Coastal Plain sediments from the Cape Fear arch in North Carolina to eastern Alabama; these highs decrease with distance from the Piedmont. Quaternary sediments along the modern coasts show weaker eTh anomalies, except near coast-parallel ridges from South Carolina to northern Florida. Prominent eTh anomalies are also observed over large riverbeds and their floodplains, even north of the Cape Fear arch where surrounding areas are relatively low. These variations were verified using ground geophysical measurements and sample analyses, indicating that radiometric methods are a useful exploration tool at varying scales. Further analyses of heavy mineral separates showed regional differences, not only in concentrations of monazite, but also of rutile and staurolite, and in magnetic susceptibility. The combined properties suggest the presence of subregions where heavy mineral sediments are primarily sourced from high-grade metamorphic, low-grade metamorphic, or igneous terrains, or where they represent a mixing of these sources. Comparisons between interpreted sources of heavy mineral sands near the Fall Line and igneous and metamorphic Piedmont and Blue Ridge units showed a strong correspondence with rocks closest to the Fall Line and poor correspondence with rocks farther inland. This strongly suggests that the primary source of those heavy minerals, especially monazite, is the rocks that formed the rocky coast that was present during opening of the Atlantic Ocean, which in turn indicates the importance of coastal processes in forming heavy mineral sand concentrations. Furthermore, narrow radiometric eTh and K anomalies are associated with major rivers, indicating limited spatial influence of fluvial processes. Later coastal plain sediment deposition appears to have involved reworking of sediments, providing an “inheritance” of the rocky coast composition that persists for some distance from the Fall Line. However, this inheritance is reduced with distance, and sediments within ∼100 km of the coast in Georgia and Florida exhibit properties indicative of mixing from multiple sources.

GSA Bulletin↗
USGS1996

Development and evaluation of sediment quality guidelines for Florida coastal waters

The weight-of-evidence approach to the development of sediment quality guidelines (SQGs) was modified to support the derivation of biological effects-based SQGs for Florida coastal waters. Numerical SQGs were derived for 34 substances, including nine trace metals, 13 individual polycyclic aromatic hydrocarbons (PAHs), three groups of PAHs, total polychlorinated biphenyls (PCBs), seven pesticides and one phthalate ester. For each substance, a threshold effects level (TEL) and a probable effects level (PEL) was calculated. These two values defined three ranges of chemical concentrations, including those that were (1) rarely, (2) occasionally or (3) frequently associated with adverse effects. The SQGs were then evaluated to determine their degree of agreement with other guidelines (an indicator of comparability) and the percent incidence of adverse effects within each concentration range (an indicator of reliability). The guidelines also were used to classify (using a dichotomous system: toxic, with one or more exceedances of the PELs or non-toxic, with no exceedances of the TELs) sediment samples collected from various locations in Florida and the Gulf of Mexico. The accuracy of these predictions was then evaluated using the results of the biological tests that were performed on the same sediment samples. The resultant SQGs were demonstrated to provide practical, reliable and predictive tools for assessing sediment quality in Florida and elsewhere in the southeastern portion of the United States.

Ecotoxicology↗
USGS2019

Plant community establishment in a coastal marsh restored using sediment additions

A goal of wetland restoration is the establishment of resilient plant communities that persist under a variety of environmental conditions. We investigated the role of intraspecific and interspecific variation on plant community establishment in a brackish marsh that had been restored by sediment addition. Plant growth, sediment accretion, and surface elevation change in planted, not-planted, and nearby reference sites (treatments) were compared. Four perennial macrophytes were planted: Bolboschoenus robustus , Distichlis spicata , Phragmites australis , and Schoenoplectus californicus . There was 100% survival of the planted species, and all exhibited rapid vegetative spread. Intraspecific variation in stem height and cover was identified, and interspecific comparisons also indicated differences in species cover. Treatment comparisons revealed that final total cover at not-planted sites was equivalent to that at reference sites, and was highest at planted sites where P. australis became dominant. Species richness was initially highest at the reference sites, but final richness was equivalent among treatments. Soil surface elevation was greater at planted compared to not-planted and reference sites. Because of the rapid cover and increased surface elevation generated by planted species, the resiliency of restored coastal marshes may be enhanced by plantings in areas where natural colonization is slow and subsidence is high.

Louisiana↗
USGS1995

Source parameters and crustal Q for four earthquakes in South Carolina

Two three-component seismometers (one surface and one borehole) were re-installed on the Savannah River Site (SRS), South Carolina in July 1992 to determine attenuation in the Coastal Plain sediment wedge and source parameters of local earthquakes. Four earthquakes M ∼ 1.8 to 3.6 were recorded during the next 6 months. The largest event was located near Summerville within the meizoseismal area for the 1886 Charleston earthquake. Two shocks were located 50 km to the east near Neeses, and one was located 20 km north of the SRS near Aiken. Although source parameters have been determined from strong motion data and short-period regional networks for east coast earthquakes, such as the Saguenay, Nahanni, and Mt. Laurier earthquakes (e.g., Atkinson, 1993 ), these are some of the first source parameters determined from broad-band digital recorders. Seismograms for the Summerville event are also available from Chapel Hill, North Carolina and Blacksburg, Virginia, providing estimates of t * beyond 200 km. Here we determine source parameters such as moment, stress drop, and the attenuation parameter t * using a non-linear least-squares algorithm. We do not correct for site response because the deepest borehole is not below the Coastal Plain sediments (about 300m thick at this site) and because only one station is available for most of the data. Values of t* are marginally higher from seismograms recorded at the surface when compared to records from the 91m depth borehole seismograph. A value of 170-200 bars was determined for the Brune stress drop of the Summerville event using the borehole data, which is high compared to a value of 50 bars usually specified for modeling strong motion in western North America, but similar to other estimates for eastern North America. A higher stress drop leads to a higher seismic risk because peak acceleration is approximately proportional to stress drop. Moreover, mid- to upper-crustal Qs are in the range of 2,000 to 3,000, which would permit the propagation of high frequency seismic waves. A comparison of the surface records from the SRS with a record from the USGS dense array at Parkfield, CA for an event at about the same distance range and moment as the Summerville event-SRS case shows that the peak acceleration of the Summerville event is 16 times higher than that for the event from California (stress drop of 21 bars).

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