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Hurricane Harvey (Harvey) struck the Texas coast 25–27 August, 2017, and produced massive flooding of the Galveston Bay tributaries. The slow release of floodwaters from the Barker and Addicks Reservoirs, west of Houston, produced a 48-day flood across metro-Houston through via Buffalo Bayou, through the San Jacinto Estuary (SJE), before flowing into Galveston Bay. To quantify the thickness and mass of sediment which was delivered to Galveston Bay as well as the mass of mercury (Hg), a series of 56 pushcores were collected from across Galveston Bay, including the San Jacinto Estuary, Trinity Bay, Galveston Bay, East Galveston Bay, Clear Lake, and Dickinson Bayou. X-radiographs of each core was used to quantify the thickness of the flood layer and average water content of the cores was used to estimate bulk density of the cores in the estimation the flood deposit mass. Using average Hg concentrations from each core, combined with the bulk densities, Hg mass calculations were made for the sub-bays and the entire bay system. Within Galveston Bay and the SJE, Harvey deposited 131.34 × 106 t of sediment, representing 31 years of average annual sediment load to the bay. The combined Galveston Bay and SJE Harvey deposit contains 5.09 t of Hg. This Hg was primarily sourced from legacy Hg which had been archived in lower Buffalo Bayou and the SJE due to elevated land subsidence and as a result of historical releases from industrial wastewater, primariy from Patrick Bayou, a small tributary of lower Buffalo Bayou. Harvey flooding eroded nearly the entire upper 0.5 cm of lower SJE, resulting in the erosion of 16.4 × 106 t of sediment, containing at least 3.43 t of Hg, from the SJE and Patrick Bayou, dispersing it within Galveston Bay. The floodwater during peak discharge rapidly exited Galveston Bay into the Gulf of Mexico. In contrast, the slow release from the Barker and Addicks Reservoirs resulted in prolonged hydraulic trapping of both floodwaters and suspended sediment within Trinity and upper Galveston Bay. The prolonged hydraulic trapping contributed to the broad dispersal of Hg across Galveston Bay and also increased the potential exposure of marine organisms to the elevated concentrations of Hg within the suspended sediment. With the increase in slow-moving storms and the archiving of legacy contaminants within urbanized estuaries, especially where there is elevated land subsidence, suggests that the impact and dispersal of legacy contaminants within Galveston Bay by Harvey is a harbinger of things to come for other urbanized estuaries throughout the world.

Reconstructing the provenance of siliciclastic marine sediment is important for understanding sediment pathways and constraining palaeoclimate and erosion records. However, physical fractionation of different size fractions can occur during sediment transport, potentially biasing records derived from bulk sediment. In this study, records of radiogenic Sr and Nd isotopic composition and K/Al ratio of the separated clay fraction, as well as bulk grain size, are presented, measured from deep-sea sediments recovered from International Ocean Discovery Program (IODP) Sites U1456 and U1457 in the Arabian Sea. These new records are compared with published bulk sediment records to investigate the influence of sediment transport on these proxies and to constrain provenance evolution and its relationship to climate variability since middle Miocene time. Correlations between grain size and the bulk sediment isotopic composition confirm that transport processes are influencing the bulk sediment record. This relationship, although present, is not as strong in the clay-fraction isotopic records. Heterogeneity of bulk sediment likely drives differences between bulk and clay records, thought to be largely controlled by sediment transport processes. The isotopic records reveal variations in provenance that correlate with climatic change at 8–7 Ma, as well as an increase in overall provenance variability beginning at c. 3.5 Ma, likely linked to monsoon strength and glacial–interglacial cycles. The clay-fraction records highlight the potential value of measuring proxy records from multiple size fractions to help constrain provenance records as well as investigate sediment transport and/or weathering and erosion processes recorded in deep-sea sediment archives.

To understand siltation processes within the North Port of Incheon, Korea, this study estimated the sedimentation rate and then determined the dominant mechanisms for the siltation. The sedimentation rate was estimated by comparing bathymetric surveys adjusted with the dredged volume, and verified by the penetration depth of 11 gravity cores to the previous dredging surface. The average sedimentation rate was 64 cm/year but varied from 10 cm/year in the interior to about 100 cm/year at the entrance. To determine the dominant mechanisms for siltation, two ADCPs were deployed at the entrance and the interior end of the harbor over a month to estimate sediment flux. Detailed sediment transport processes were examined by two 13-h CTD profiling surveys near the entrance and interior end of the harbor. High siltation at the entrance is attributable to the influx of high turbidity water, the decrease of current velocity, and the formation of an eddy. Low sedimentation inside the harbor was attained by the slow settling of microflocs of about 20–30 mg/l concentration that are maintained regardless of time and space.

The geochemical behavior of Pb in terrestrial and coastal water systems significantly influences Pb biogeochemical cycling and pollutant exchange at the land-sea continuum. An ideal case study of Pb environmental geochemistry is Galveston Bay, an anthropogenic estuary exposed to industrial runoff, wastewater and shipping vessel spills but also fed by natural rivers. Here, sediments from Galveston Bay were measured for Pb isotope ratios and abundances to constrain Pb sources and fluxes and understand Pb pollution history in the bay. Lead isotopes have been established as source tracers of environmental pollution and allow Pb sources to be reliably fingerprinted and identified. Sediments were leached to distinguish authigenic sediment coatings from lithogenic residual sediments, in addition to bulk sediment digestions. Total Pb concentrations ranged from 1.76 µg/g–29.19 µg/g in bulk digests, which are below federal toxicity thresholds and aligns well with prior measurements of Pb in Galveston Bay sediments in the 20th century. Lead concentrations are spatially constrained by flocculation in eastern bay areas where the Trinity River enters the bay and positively temporally correlated to freshwater discharge. Sediment 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios range between 18.338–19.777±0.002, 15.557–15.755±0.002 and 37.913–43.340±0.005, respectively, and were used in an advanced Bayesian isotope mixing model to identify Pb sources in the Galveston Bay sediment fractions analyzed. Anthropogenic sources supply approximately 83.8%, 16.6% and 25.5% of Pb to the leachates, residues and bulk sediments, respectively. This study showcases the importance of estuaries in moderating terrestrial and marine Pb distribution and provides insight for future contaminant studies in Galveston Bay and other estuarine systems around the world. MAIN FINDINGS Pb isotope ratio and abundance measurements of Galveston Bay sediments demonstrate significant anthropogenic Pb inputs to the estuary despite low Pb levels.

Galveston Bay is an anthropogenic-influenced estuary where industrial runoff, wastewater, and shipping vessel discharges enter the bay alongside natural freshwaters. Here, heavy metal concentrations in Galveston Bay surface sediment (2-year quarterly time-series) and a single sediment core are presented to explore the anthropogenic and geochemical controls on the spatiotemporal distributions, fluxes, sources, and potential toxicity of metals within this estuary. Samples were leached to distinguish authigenic sediment coatings from geogenic crystalline material. Spatial differences dominate the observed concentration variability, with higher metal concentrations in eastern vs. western bay sediments, as the eastern bay is where metals are flocculated from the dissolved phase and/or sediments are hydrodynamically trapped. Temporal variations are a secondary controlling factor, with sediment metal concentrations positively correlated with Trinity River discharge. Core data indicate stable Fe, Pb Ni, Cd and Hg levels during the 20th century but increasing Cu and Zn levels in recent years. Galveston Bay sediments are potentially toxic for As, Cd, Cr, Cu, Ni, Sb, Zn and Hg, based on federal toxicity standards. Enrichment factors and statistical analyses suggest that Ni and Cr originate from natural sources, while anthropogenic sources dominate supply of As, Cd, Hg, Ni, Pb, Sb, and Zn. This unique time-series shows that major flooding events, such as Hurricane Harvey in 2017, affect surface sediment metal distributions in Galveston Bay, but not any more than the natural geochemical controls on spatiotemporal distributions of metals in anthropogenic-influenced estuaries.

Hurricane Harvey led to a broad redistribution of sediment throughout Galveston Bay and the Houston Ship Channel (GB/HSC), but the resulting changes in chemical contaminant distributions have yet to be characterized. To address this question, we collected and analyzed post-Harvey sediment for concentrations of the EPA 16 Priority Pollutant polycyclic aromatic hydrocarbon (PAHs), determining the extent to which the spatial distribution and sourcing of contaminants may have changed in contrast to historical surface sediment data (5 cm) from the National Oceanic Atmospheric Administration (NOAA) available for the years 1996-2011. We found a small, but detectable increase from pre- to post-Harvey in PAH concentrations, with PAH diagnostic sourcing indicating combustion origins. Of the detected PAHs, none exceeded Sediment Quality Guideline values. Overall, we have added to the understanding of PAH spatial trends within the GB/HSC region, and developed a reference PAH baseline to inform future studies.

Background: Given the time and monetary costs associated with traditional analytical chemistry, there remains a need to rapidly characterize environmental samples for priority analysis, especially within disaster research response (DR2). As PAHs are both ubiquitous and occur as complex mixtures at many National Priority List sites, these compounds are of interest for post-disaster exposures. Objective: This study tests the field application of the KinExA Inline Biosensor in Galveston Bay and the Houston Ship Channel (GB/HSC) and in the Elizabeth River, characterizing the PAH profiles of these region's soils and sediments. To our knowledge, this is the first application of the biosensor to include soils. Methods: The biosensor enables calculation of total free PAHs in porewater (C free), which is confirmed through gas chromatography-mass spectrometry (GC-MS) analysis. To determine potential risk of the collected soils the United States Environmental Protection (USEPA) Agency's Regional Screening Level (RSL) Calculator is used along with the USEPA Region 4 Ecological Screening Values (R4-ESV) and Refined Screening Values (R4-RSV). Results: Based on GC-MS results, all samples had PAH-related hazard indices below 1, indicating low noncarcinogenic risks, but some samples exceeded screening levels for PAH-associated cancer risks. Combining biosensor-based C free with Total Organic Carbon yields predictions highly correlated (r > 0.5) both with total PAH concentrations as well as with hazard indices and cancer risks. Additionally, several individual parent PAH concentrations in both the GB/HSC and Elizabeth River sediments exceeded the R4- ESV and R4-RSV values, indicating a need for follow-up sediment studies. Conclusions: The resulting data support the utility of the biosensor for future DR2 efforts to characterize PAH contamination, enabling preliminary PAH exposure risk screening to aid in prioritization of environmental sample analysis.

Over the past three decades, particle-reactive cosmogenic 7Be (t1/2 = 53.3 d) has frequently been used to quantify recent fluvial sediment inputs to estuaries and coastal marine environments, providing an important tool to understand the timing and pathways of sediment dispersal. This study utilizes a 2-year high-resolution time series collected from the Copper River, Alaska, to examine the seasonal fluctuation in 7Be activity of suspended sediments near the river mouth. We show that there is considerable variability (particulate 7Be = ≤ 3.3–47 Bq kg−1) throughout the hydrograph, with a significant negative correlation to discharge and suspended sediment concentration. This variability is interpreted to be driven by a combination of fluctuations in atmospheric deposition, water aging, and dilution by 7Be-depleted sediments, reflecting erosion within the streambed/watershed and/or differing freshwater/sediment source. Particularly within this high-latitude setting, seasonal differences in provenance (snowpack/glacial melting vs. rainfall) likely influence 7Be activities. Importantly, 7Be was below detectable limits in river suspended sediments during peak discharge periods in both years, indicating that the flood signal in adjacent coastal environments will be negligible at this time. These results suggest that 7Be will not be an effective tracer of fluvial sediment deposition in some coastal environments.

Galveston Bay is the second largest estuary along the northern Gulf of Mexico coast, with a watershed containing one of largest concentrations of petroleum and chemical industries globally, as well as Houston, the fifth largest metropolitan area in the USA. Throughout the last century, extensive groundwater extraction to support these industries and an expanding population has resulted in significantly enhanced land subsidence (0.6–3.0 cm yr−1). The highest subsidence rates observed in the bay are within the lower 15 km of the San Jacinto River/Houston Ship Channel region (SJR/HSC), with distal areas in East and West Galveston Bays having subsidence rates on the order of 0.2 cm yr−1. In order to investigate the impacts of subsidence on sedimentation, a series of 22 vibracores were collected throughout the bay, and 210Pb and 137Cs radioisotope geochronologies and grain size distributions were determined. Sediment accumulation rates are highest (1.9 ± 0.5 cm yr−1) in the SJR/HSC, and decrease (

Sedimentological and geochemical investigation of sediment cores collected in the deep (>400 m) central basin of Prince William Sound, along with geochemical fingerprinting of sediment source areas, are used to identify earthquake-generated sediment gravity flows. Prince William Sound receives sediment from two distinct sources: from offshore (primarily Copper River) through Hinchinbrook Inlet, and from sources within the Sound (primarily Columbia Glacier). These sources are found to have diagnostic elemental ratios indicative of provenance; Copper River Basin sediments were significantly higher in Sr/Pb and Cu/Pb, whereas Prince William Sound sediments were significantly higher in K/Ca and Rb/Sr. Within the past century, sediment gravity flows deposited within the deep central channel of Prince William Sound have robust geochemical (provenance) signatures that can be correlated with known moderate to large earthquakes in the region. Given the thick Holocene sequence in the Sound (~200 m) and correspondingly high sedimentation rates (>1 cm year−1), this relationship suggests that sediments within the central basin of Prince William Sound may contain an extraordinary high-resolution record of paleoseismicity in the region.

Extreme precipitation events are projected to occur more frequently under a warming climate, posing increasing threats to coastal ecosystems. Hurricane Harvey (2017), the wettest tropical cyclone in the U.S. history causing a 1000-year flood in the Houston metropolitan area, provides an opportunity to study the response of coastal ecosystems to extreme events. As sessile, epibenthic filter-feeding organisms, oysters are inherently sensitive to changes in environmental and water quality conditions, making them a good indicator for ecosystem health. Oyster measurements at 130 sites in Galveston Bay show that the mean oyster mortality drastically increased from 11% before Harvey to 48% after Harvey. Post-Harvey oyster mortality exhibited large spatial variability and was up to 100% at some major reef complexes. For all the oyster sampling sites, brown shells were dominant, while black shells indicating mud burial were rare. Considering the little impact from sediment deposit, we hypothesized the low-salinity exposure as the main cause for the massive oyster kill. The hypothesis is supported by a multidisciplinary (biological-geological-physical) analysis of bay-wide oyster mortality and sediment-core data and results of a previously-validated high-resolution hydrodynamic model. Oyster mortality was found to be significantly and positively correlated with the bottom low-salinity exposure time (duration of bottom salinity continuously less than 5 PSU), while there was no significant relationship with the thickness of storm-induced sediment deposit. The physiological aspects for the impact of low-salinity exposure, the underlying physical mechanisms for the prolonged salinity recovery, and wider implications of oyster kill in Galveston Bay in the context of global oyster reef conditions were discussed. The worldwide reported oyster kills following extreme weather events suggest additional pressure posed by future climate on the native coastal oyster reefs that are already at the brink of functional extinction due to centuries of resource extraction and coastal habitat degradation.

Meteorological frontal passages are recognized as important mechanisms for remobilizing sediment in estuaries along the northern Gulf of Mexico, but few studies have addressed factors beyond wind speed as a predictor for resuspension. To better understand resuspension mechanisms during these events, this study investigated the effects of wind, waves, and currents on suspended sediment concentration near the seabed during frontal passages in the shallow, micro-tidal West Galveston Bay located along the Texas coast. In late January and early February 2013, two multi-day deployments of instrumented pods (an acoustic Doppler velocimeter, and an acoustic wave and current profiler) were conducted to capture two separate frontal passages. The results indicate that the bed shear stress under the combined effect of waves and currents showed a much stronger relationship to sediment resuspension (R2 = 0.90) than wind stress alone (R2 = 0.55), or currents alone (R2 = 0.72). Increases in the bed shear stress due to the combined effects of waves and currents resulted from increased wave height, which is strongly related to fetch within the bay. Therefore, understanding fetch-limited wave heights as a function of wind speed and direction, in conjunction with basin geometry, may be a better way to predict sediment resuspension during meteorological frontal passages in the shallow bays of the northern Gulf of Mexico.

Extreme episodic events have the capacity to transport large amounts of terrestrial material to the coastal ocean. While estuaries and deltas are typically thought to trap most of this material, some escapes these coastal features and is transported to distal depocenters along the continental shelf. Distal shelf depocenters can act as the ultimate sink for event deposits, yet event sedimentation and the impact of terrestrial carbon burial within these shelf deposits remains understudied. Therefore, this study investigated event sedimentation within the Texas Mud Blanket (TMB), a distal shelf depocenter of the Brazos River located in the northwestern Gulf of Mexico. Using a core that was collected from the TMB during a months-long elevated discharge event in late 2015 to early 2016 we applied a multi-proxy approach to delineate the event deposit. We utilized physical sediment properties (fabric, texture, and bulk density), radioisotopes (7Be and 210Pb), and organic geochemical properties (ẟ13C, C/N, and lignin-phenols) to identify a 10 cm event layer at the surface of the core. Within this 10 cm layer, we also distinguished two sub-layers associated with separate extreme discharge periods in the winter and spring, respectively. Using these event layer characteristics, we identified three other earlier potential event deposits in the core that we have attributed to events in 2010, 2007, and 2000–2001. From these results, this study has demonstrated that the TMB may be an archive for event deposits over multi-decadal time periods, in particular the transition from periods of prolonged drought to extreme wetness associated with the Brazos River. This event-dominated sedimentation regime can enhance long-term carbon burial, potentially increasing current estimates of carbon burial significantly in the TMB and other similar distal shelf depocenters. Ultimately this study highlights the potential for distal shelf depocenters as organic carbon burial “hotspots,” and postulates that this role may expand in the future as climate change increases the intensity and frequency of extreme events.

Hurricane Harvey (Harvey), a slow-moving storm, struck the Texas coast as a category 4 hurricane. Over the course of 53 days, the floodwaters of Harvey delivered 14 × 109m3 of freshwater to Galveston Bay. This resulted in record flooding of Houston bayous and waterways, all of which drained into the San Jacinto Estuary (SJE,) with its main tributaries being Buffalo Bayou and the San Jacinto River. The lower SJE and lower Buffalo Bayou has experienced up to 3m of land subsidence in the past 100 years and, as a result, prior to Hurricane Harvey, up to 2m of sediment within the upper seabed contained an archive of high concentrations of Total Hg (HgT) and other particle-bound and porewater contaminants. Within the SJE, Harvey eroded at least 48 cm of the sediment column, resulting in the transport of an estimated 16.4 × 106 tons of sediment and at least 2 tons of Hg into Galveston Bay. This eroded sediment was replaced by a Harvey storm deposit of 7.73 × 106 tons of sediment and 0.96 tons within the SJE, mostly sourced from Buffalo Bayou. Considering that the frequency of slow-moving tropical cyclones capable of delivering devastating rainfall may be increasing, then one can expect that delivery of Hg and other contaminants from the archived sediment within urbanized estuaries will increase and that what happened during Harvey is a harbinger of what is to come., Graphical Abstract

Hurricane Harvey, one of the worst hurricanes that hit the United States in recent history, poured record-breaking rainfall across the Houston metropolitan area. Based on a comprehensive set of data from various sources, we examined the dramatic responses in hydrodynamic and sedimentary processes of Galveston Bay to this extreme event. Using a freshwater fraction method that circumvents the uncertainties in surface runoff and groundwater discharge, the freshwater load into the bay during Harvey and the following month was estimated to be 11.1 × 109 m3, about 3 times the bay volume, which had completely refreshed the entire bay. Harvey also delivered 9.86 × 107 metric tons of sediment into the bay, equivalent to 18 years of average annual sediment load. At a site inside the San Jacinto Estuary, acute bed erosion of 48 cm followed by deposition of 22 cm of new sediment was observed from the sediment cores. Slow salinity recovery (~2 month) and a thick flood deposit (~10.5 cm average over the entire bay) had likely impacted the ecosystem in the bay and the adjacent inner shelf. Estuaries with similar bathymetric and geometric characteristics, i.e., shallow bathymetry with narrow outlets, are expected to experience similar dramatic estuarine responses while extreme precipitation events are expected to occur more frequently under the warming climate.

The rapid economic growth of the Republic of Korea (S. Korea) within the last half-century has resulted in a pronounced increase in anthropogenic Hg emission from coal combustion, oil refining, cement production, and waste incineration. The record of increasing atmospheric sources have been investigated with a historical reconstruction of Hg accumulation in 30 sediment cores collected from the Yeongsan Estuary. Within the last several decades, this region has undergone severe anthropogenic alteration, including the construction of an estuarine dam forming the Yeongsan Lake, and installation of numerous seawalls that eliminated vast tidal flats and restricted estuarine circulation. Total mercury concentrations (T-Hg) measured in sediments deposited after 1980 (23.2 ± 9.6 ng g−1; n = 273), were significantly higher than those reported for pre-industrial sediments (i.e. background values: 8.6 ± 2.7 ng g−1; n = 274). An extensive survey of surface samples show that T-Hg concentrations are highest above the dam, with a gradient to lower values further offshore. The concomitant timing of enrichment of T-Hg within the sedimentary record and increased National emissions in Korea suggests that regional sources dominate the input to the Yeongsan Estuary. This indicates that with sufficient regional historic emission data, T-Hg might be utilized as a geochronologic tool to aid in corroborating traditional radioisotopic methods.

Globally, deltas are increasingly threatened by anthropogenic activities. As a result, deltas now evolve through the combined effects of natural and human-induced processes occurring throughout the fluvial–deltaic system. The Brazos River delta, located along the Texas coast in the northwestern Gulf of Mexico, and its watershed have been impacted by direct and indirect human activities since the late 19th century. This provides an opportunity to investigate how such alterations have shaped the evolution of a delta in the Anthropocene, a time when humans are drivers of geological change. Historic alteration to the delta and watershed include extensive agricultural activity, jetty construction at the mouth in the late 1890s, mouth diversion ~10 km to the southwest in 1929, and reservoir construction throughout the early and mid 20th Century. Three subaerial deltaic geometries provided the framework to connect subaerial deltaic responses, to the anthropogenic alterations, to the resulting stratigraphic characteristics observed in the subaqueous delta. This study utilized high-resolution geophysical data (swath bathymetry, side scan sonar, CHIRP subbottom profiling) on the subaqueous delta to investigate the subaqueous delta stratigraphy and infer the processes that shaped the deltaic record over time. The results showed distinct areas across the subaqueous delta that were dominated by erosion and deposition. Erosional areas corresponded to earlier growth phase depocenters being exposed at the surface, while the depositional areas corresponded to areas with the most recent growth phase depocenter overlying the earlier depocenters. These results highlight that the subaqueous depocenter has migrated westward over time, consistent with the observed changes to the subaerial delta. Additionally, the data showed that evidence for these past growth phases and depocenters may be preserved within the subaqueous delta, even after subaerial portions of the delta returned to pre-Anthropocene configurations. In general, this study showed that the subaqueous delta, similar to the subaerial delta, is impacted by human-driven alterations to the fluvial–deltaic system, and may preserve a more complete record of the evolution of deltas during the Anthropocene.

Previous sedimentological work has shown that throughout the last half-century, average sediment accumulation of 2–6 cm yr− 1 occurred due to the emplacement of estuarine dams and land reclamation in the Nakdong Estuary of South Korea (Williams et al., 2013). To investigate the timing and rate of sedimentation, two sonar altimeters were deployed for nearly a year. In the West Nakdong River, where there is no freshwater discharge from the dam, 4 cm of gradual sedimentation was observed, corresponding to the long-term average accumulation. On the other hand, episodic sedimentation of 6 cm, which also corresponds to the long-term accumulation rate, was observed during two months of summer discharge in the main East Eulsuk Channel. To examine the mechanisms of sedimentation, Acoustic Doppler Current Profilers at three sites measured current velocity and acoustically-derived suspended sediment concentration during increased discharge and wave activity events, and through spring and neap tidal cycles. Sediment flux was decomposed into tidal pumping and advection terms to determine the primary factors controlling sedimentation throughout the estuary. Downstream sediment fluxes were dominated by mean advection, particularly during large discharge events. The difference in the magnitude between the upper and lower stations has been determined to be the main mechanism for convergence of flux (deposition) in the central estuary. In the absence of strong discharge, residual sediment transport caused a flux into the estuary, suggesting the primary mechanism for gradual deposition throughout the year in the West Nakdong River where discharge is entirely blocked.

The Brazos River is second only to the Mississippi River in terms of sediment load discharged to the Gulf of Mexico (GOM). This study focused on the interaction between a salt wedge and suspended sediment in the lower Brazos River, and the implications for sediment export to the coastal ocean. Salinity and turbidity (optical backscatter sensor) data with depth, swath bathymetry, and CHIRP sub-bottom profiling data were collected from 2007 to 2012 over various river discharge stages. Sampling locations included the lower-most 15 km river reach and the coastal ocean proximal to the mouth. Results indicated that during low to moderate river discharges a salt wedge was present in the lower river, but absent during elevated fluvial discharge. Quantitative analysis showed the salt wedge within the river modulated sediment export to the GOM by trapping sediment along the lower most 9 km reach. Within this reach the trapped sediment formed a decimeter-thick mud layer observed in the CHIRP and bathymetric data. At elevated fluvial discharges the salt wedge was no longer observed in the river, and the lower river reach transitioned from depositional to erosional. Based on the observations and analysis from this study, a fluvial discharge threshold where the salt wedge is not present in the river and sediment export to the coastal ocean was maximized was estimated. This threshold has been met or exceeded only ~ 10% of time since the 1960s. These conditions imply that sediment transport to the coastal ocean is highly variable, and occurs during irregular, pulsed events. This study highlights how estuarine conditions at the river mouth can impact terrestrial material flux to the coastal ocean.

During the 20th century the impacts of industrialization and urbanization in Galveston Bay resulted in significant shifts in trace metals (Hg, Pb, Ni, Zn) and vascular plant biomarkers (lignin phenols) recorded within the surface sediments and sediment cores profile. A total of 22 sediment cores were collected in Galveston Bay in order to reconstruct the historical input of Hg, Pb, Ni, Zn and terrestrial organic matter. Total Hg (T-Hg) concentration ranged between 6 and 162 ng g−1 in surface sediments, and showed decreasing concentrations southward from the Houston Ship Channel (HSC) toward the open estuary. Core profiles of T-Hg and trace metals (Ni, Zn) showed substantial inputs starting in 1905, with peak concentrations between 1960 and 1970's, and decreasing thereafter with exception to Pb, which peaked around 1930–1940s. Stable carbon isotopes and lignin phenols showed an increasing input of terrestrial organic matter driven by urban development within the watershed in the early 1940s. Both the enrichment factor and the geoaccumulation index (Igeo) for T-Hg as a measure of the effectiveness of environmental management practices showed substantial improvements since the 1970s. The natural recovery rate in Galveston Bay since the peak input of T-Hg was non-linear and displayed a slow recovery during the twenty-first century.

Over the last half-century, coastal zones within the Republic of Korea (S. Korea) have experienced a wide range of engineered coastal modifications including construction of seawalls, extensive land reclamation, and installation of estuarine dams. The Yeongsan Estuary has experienced all of these modifications and provides an ideal case study on how sedimentation changes within a macrotidal estuary in response to these alterations. Combined, these alterations have considerably modulated the timing and intensity of river discharge, prevented natural tidal exchange, modified the shoreline profile, and altered the transport of sediment and organic matter within the coastal zone. These impacts have been investigated using 30 gravity cores analyzed for 210 Pb radioisotope geochronology, laser diffraction particle size analyses, δ 13 C and δ 15 N isotope ratio mass spectrometry, and X-radiography. Average sediment accumulation rates range from 0.9 ± 0.6 cm yr − 1 to 10.0 ± 2.9 cm yr − 1 , with the highest rates proximal to the downstream side of the dam, and some areas determined to be either actively eroding or recently dredged. These results are supported by comparison of multiple bathymetric surveys, and CHIRP seismic data suggest an order of magnitude increase from average Holocene sediment accumulation rates. Side scan sonograms collected adjacent to the dam reveal distinctive scouring, transitioning to areas accumulating fine-grained sediments. Shifts in the organic matter source inputs are apparent in pre/post-dam sediments and reflect the occluding of tidal influence above the dam, resulting in increasingly terrestrial dominated signatures. Additionally, a time series of cores collected during periods of limited and high discharge analyzed for 7 Be, indicates sediment deposition occurs episodically corresponding to high discharge dam releases. Our observations record a shift in depositional environments as a response to an extensive array of anthropogenic alterations. Ultimately, land reclamation and dam construction have severely altered the fate and transport of sediment within the estuarine system. As a consequence, sedimentation rates have increased dramatically and depositional events are primarily controlled by discharges from the estuarine dam.

The Brazos River Delta is located in the northwestern Gulf of Mexico. Sedimentation on the Brazos River subaqueous delta has been largely understudied. Swath bathymetry data collected across the subaqueous delta reveals a noticeable asymmetry with much deeper water depths and greater cross-shelf slopes along the eastern, up drift side of the delta than along the western, down-drift side. End-member sampling reveals that Brazos River derived sediment is red, red-brown, or brown in color, exhibits increased bulk density, and is enriched in calcium a function of carbonate-rich areas of the watershed, whereas the Gulf of Mexico inner shelf muds are gray to black and have a relatively lower calcium content. Analyses of a series of 33 submersible vibra cores collected across the subaqueous delta reveal alternating beds of Brazos River derived sediment and Gulf of Mexico shelf dominated sediment. Excess 210Pb geochronologies of select cores reveal that sediment accumulation has been a combination of fluvial flood event deposition, and deposition of remobilized sediment from the proximal shelf and older portions of the delta rather than steady state accumulation. Because the Brazos River is susceptible to local climatic cycles, fluvial flood events that create the event layers are intermittent between prolonged periods where marine processes drive accumulation. Results also show that the primary depocenter of the subaqueous delta has migrated southwestward over time, and the erosion of earlier depocenters and proximal shelf sediment has contributed to accumulation on the delta. Over the past ~ 50 years the subaqueous delta has reached an equilibrium where flood event beds can be completely remobilized within a year, and net accumulation approximates relative sea level rise. This study highlights relatively rapid clinoform migration due to natural and anthropogenic changes to the system, and demonstrates subaqueous delta growth through a combination of direct fluvial and marine-derived sediment input.

The Naples–Dollar Bay Estuarine System (NDBES), situated in southwestern Florida, has undergone extensive modifications caused directly and indirectly by anthropogenic influences. These alterations include: (1) the substitution of mangrove-forested shorelines with concrete bulkheads and installation of residential canals; (2) installation of a regionally extensive navigational channel; and (3) canalization of the watershed, resulting in annexation of a heavily altered drainage basin ten times the size of the pre-alteration basin and with a significantly different soil and bedrock. The NDBES consists of northern Naples Bay, southern Naples Bay, and Dollar Bay, whose shorelines range from highly developed to undeveloped, respectively. This project explored the geological response of the system to these alterations using data from side-scan sonar, sediment grab samples, and vibracores. In highly urbanized northern Naples Bay, benthic substrates consist primarily of muddy sand with few oyster reefs. Southern Naples Bay and Dollar Bay, however, consist of coarser sediment, and are characterized by extensive mangrove shorelines and numerous fringing oyster reefs. The impact of anthropogenic alterations has significantly shifted sediment distributions in northern Naples Bay from a relatively coarser to a relatively fine grained substrate; to a lesser degree in southern Naples Bay, and Dollar Bay, this transition has not taken place due to the general lack of anthropogenic modifications made to this part of the system.

The Nakdong Estuary, located within the coastal zone of Busan, South Korea, has been subjected to a series of engineered alterations typical of many eastern Asian estuaries. The construction of two estuarine dams (1934 and 1983) and numerous seawalls associated with land reclamation projects has altered the timing and flux of sediment, and resulted in three contrasting discharge energy regimes. Additionally, the impoundments have appreciably reduced the tidal prism by at least 50%. Consequently, vast geomorphologic changes have occurred including the development of five new barrier islands. In order to assess the impacts of these modifications, 19 vibracores were obtained throughout the estuary. The dispersal and accumulation of sediment was evaluated utilizing 210 Pb and 137 Cs radioisotope geochronology of 6 cores. Average sediment accumulation rates range from 2.19 cm yr − 1 adjacent to the first constructed dam to as high as 6.55 cm yr − 1 in the middle region of the estuary. These high rates are further supported by comparison of bathymetric survey data from 1985 to 2009. Laser diffraction grain size analyses and X-radiographs revealed distinctive changes associated with dam construction, and correlation of events between cores conveys the episodic sedimentation corresponding to floodgate releases. Ultimately, anthropogenic alterations have resulted in a shift from a tide-dominated to a wave-dominated estuary. The increase in sediment trapping efficiency that has ensued resulting from extensive coastal construction provides the basis for reevaluating traditional facies models for estuaries. A conceptual model is developed here to characterize the alterations in sediment depositional patterns according to relative discharge energy of the adjacent floodgate.

Coastal regions, such as the Texas–Louisiana shelf, are subject to seasonal hypoxia that strongly depends on the magnitude of freshwater discharge from local and regional river systems. We have determined benthic foraminiferal fauna and isotopic compositions in two 210 Pb dated box cores (BR4 and BR5) to examine the evidence for nearshore hypoxia and freshwater discharge on the Texas shelf during the last 100 years. The 210 Pb chronologies of both cores reveal sedimentation rates of 0.2 and 0.1 cm yr −1 , translating to ∼60 and ∼90 year records. The fauna of both cores were almost exclusively composed of Ammonia parkinsoniana and Elphidium excavatum , indicating euryhaline ambient waters. The Ammonia – Elphidium (A–E) index, a qualitative measure of low oxygen conditions, shows an increase from values between 20 and 50 to near 100 in both cores, suggesting low oxygen conditions between 1960 and the core top. Between 1950 and 1960 (9–10 cm), low A–E values in BR4 coincide with high δ 18 O and δ 13 C values greater than 0‰ and −1‰ respectively. This event corresponds to severe drought (the Texas Drought of Record) over the Brazos River drainage basin and considerably reduced river discharge from 1948 to 1957. High A–E values prior to this event imply low-oxygen conditions were prevalent prior to anthropogenic exacerbation of Louisiana shelf hypoxia and at least since the dredging of a new Brazos River delta in 1929. Elphidium excavatum δ 13 C values are very low (−4‰) and indicative of significant vital effect. The δ 13 C values of A. parkinsoniana average −3‰ and exhibit little variability, most likely reflecting pore waters influenced by aerobic and anaerobic respiration. The association of lowered Brazos River discharge with more oxygenated shelf bottom waters suggests Brazos River discharge and shelf hypoxia are linked, but the influence of Mississippi–Atchafalaya discharge can also contribute to shelf stratification.

We investigated the habitat associations of sea otters (Enhydra lutris) during resting and feeding in an area with a predominately soft- and mixed-sediment benthos supporting infaunal prey populations in a fjord in Alaska during the summer months of 2001–2003. Water depth and benthic sediments were sampled, analyzed, and mapped throughout the bay. Sea otter locations and behavior were determined during boat surveys, and water depth, benthic sediment type, and position in the bay (peripheral compared to central) were determined for each animal location. We used logistic regression analysis to determine whether the use of habitat by sea otters was nonrandom according to these variables. Water depth was the most significant habitat association for feeding behavior, with 39% of feeding dives occurring in water 0–10 m deep. Feeding behavior was not strongly associated with sediment type. Position in the bay was the most significant habitat association for resting behavior, with the majority (63%) of otters resting in the central areas of the bay. Overall, habitat associations were nonrandom, a possible reflection of selective pressure to maximize energy intake, minimize energy expenditure, and avoid terrestrial predators.

123 km of high-resolution 2-D seismic lines and 6 sediment cores up to 16 m in length were collected from Copano Bay, Texas. These data were used to examine the role of climate and sea-level changes in the evolution of the bay. Paleogeographic maps of the bay were constructed to show how the bay evolved through time. The overall transgression was punctuated by five environmental changes within Copano Bay over the past 9.6 ky. The largest environmental change occurred at 8.2 ka when the bay-head delta back-stepped approximately 7.5 km as a result of a 0.4–1.2 m rapid rise in sea level. With a well constrained model of how the bay changed through time, textural data from the most continuous record of middle-bay deposits was used to produce a proxy for wind strength over the last 8.2 ky. Our wind strength proxy reveals that Copano Bay experienced relatively tranquil winds during the early Holocene followed by its windiest conditions from 5.2 to 4.1 ka and a return to more tranquil winds during the late Holocene. The wind strength proxy was compared with other published paleo-climatic records for the region and a reasonable correlation was found between periods of higher wind energy and drier climate. This study illustrates that despite their complex depositional systems and many sediment and water sources, a system-wide approach to studying an estuary can still be used to extract paleoclimate archives from estuarine deposits.

The COAstal STorm Rapid Response (COASTRR) system has been implemented to measure hydro-dynamic, morphodynamic, and sedimentary processes occurring along coastlines during storm impact and subsequent recovery. Relatively few measurements are available to evaluate the physical processes shaping coastal systems during extreme storm events, nor to assess post-storm system recovery (e.g. Sherwood et al., 2014). Prior to landfall of Hurricane Harvey, instruments to collect high-resolution in-situ hydrodynamic measure-ments across two different barrier island transects on the upper Texas Gulf Coast were deployed before and recovered after the storm. Hurricane Harvey struck the central Texas Gulf Coast as a Category 4 storm on August 25, 2017 causing severe infrastructure damage and erosion near its landfall location but generating mostly accretional features at the two field sites on Hog Island and Follets Island, respectively, which were located more than 160 miles northeast of Harvey’s landfall location.

We investigated the assemblage structure of fishes associated with different habitats (inshore mud, shell bank, and offshore mud) over a drowned barrier island, Freeport Rocks Bathymetric High, on the inner continental shelf of the northwestern Gulf of Mexico (NW Gulf). Density data from otter trawls were used to examine spatial (habitat and site) and temporal differences in fish assemblage structure using multi- and univariate procedures. Eight species accounted for 69% of the total composition and in order of decreasing abundance included shoal flounder (Syacium gunteri), dwarf sand perch (Diplectrum bivittatum), red snapper (Lutjanus campechanus), least puffer (Sphoeroides parvus), silver seatrout (Cynoscion nothus), largescale lizardfish (Saurida brasiliensis), silver jenny (Eucinostomus gula), and sand seatrout (Cynoscion arenarius). Multivariate results indicated fish assemblage structure differed among habitats (ANOSIM; Global R = 0.190, P < 0.001) and survey dates (ANOSIM; Global R = 0.541, P < 0.001); however, differences among sites were negligible (ANOSIM; Global R = −0.015, P = 0.749). Highest densities of dwarf sand perch and least puffer were found on the shell bank, while densities of shoal flounder, largescale lizardfish, and silver jenny were highest on offshore mud. In addition, smallest sizes and highest densities of six of the eight abundant species were found in July, suggesting an important period for juvenile fishes. Diversity indices also varied relative to habitat with highest Shannon diversity (H′) and species richness (S) values for fishes associated with the shell bank. Results of this study highlight the importance of a mosaic of habitat types to fish assemblages on a drowned barrier island in the NW Gulf.

Surficial sediment distribution within Simpson Bay is a function of antecedent bedrock and recently deposited glacial geology, as well as active physical processes both within Simpson Bay and Prince William Sound (PWS). Simpson Bay is a turbid, outwash fjord located in northeastern PWS, Alaska. Freshwater from heavy precipitation, and the melting of high alpine glaciers enter the bay through bay head rivers and small shoreline creeks. The catchment has a high watershed/basin surface area ratio (∼8:1), and easily erodible bedrock that contribute to high sediment loads. The system can be divided into three discrete basins, each with specific morphologic and circulatory characters. Side scan sonar, swath bathymetry, and seismic profiles reveal that bathymetric highs are areas of outcropping glacial surfaces. High backscatter coupled with surface grab samples reveal these surfaces to be composed of coarse sediment and bedrock outcrops. Bathymetric lows are areas of low backscatter, and grab samples reveal these areas to be ponded deposits of organic-rich estuarine muds. The data provide evidence of terminal morainal bank systems, and glacial grounding line deposits at the mouth of the bay and rocky outcrops were identified as subsurface extensions of aerial rocky promontories. Radioisotope analyses of short cores reveal that the bay has an average accumulation rate of approx. 0.5 cm year−1, but that this varies in function of the watershed/basin surface area ratios of the different basins. The interaction of tidal currents and sediment source drives sediment distribution in Simpson Bay. Hydrographic data reveal high spatial variability in surface and bottom currents throughout the bay. Subsurface currents are tide dominated, but generally weak (5–20 cm s−1), while faster currents are found along shorelines, outcrops, and bathymetric highs. Bathymetric data reveal steep slopes with little to no modern sediment throughout the bay, suggesting lack of deposition due to tidal currents.

To address the relative importance of shrimp trawling on seabed resuspension and bottom characteristics in shallow estuaries, a series of disturbance and monitoring experiments were conducted at a bay bottom mud site (2.5 m depth) in Galveston Bay, Texas in July 1998 and May 1999. Based on pre- and post-trawl sediment profiles of 7Be; pore water dissolved oxygen and sulfide concentration; and bulk sediment properties, it was estimated that the trawl rig, including the net, trawl doors, and “tickler chain,” excavate the seabed to a maximum depth of approximately 1.5 cm, with most areas displaying considerably less disturbance. Water column profile data in the turbid plume left by the trawl in these underconsolidated muds (85–90% porosity

A process-oriented sedimentary facies model is developed for the York River estuary, a sub-estuary of the lower Chesapeake Bay. This facies model was based on 210Pb and grain-size profiles, as well as X-radiographs taken from kasten cores and box cores collected in a series of across-river transects. Throughout most of the energetic microtidal York River, the seabed is characterized by physical mixing to depths of 25–200 cm. A strong cross-estuary gradient in processes is observed with one side, including channel, flank and shoal, dominated by frequent deep erosion and redeposition (physical mixing), while physical mixing is reduced on the other side, resulting in a greater preservation of biological mixing signatures. Within the physically dominated side of the river, the mixed layer is characterized by ‘stair-stepped’ 210Pb profiles with one or more segments (∼25–200 cm thick) of nearly uniform excess activity. X-radiographs reveal that, although a record of limited biogenic sediment modification is preserved, sedimentary structures within the mixed layer are dominated by centimeter to decimeter scale units of finely to coarsely laminated strata bounded by hiatal surfaces. This demonstrates that mixing results primarily from erosion, resuspension and deposition. Reduced salinity limits the number of benthic species in the York River. Physical disturbance leads to an impoverishment of this community, which is composed primarily of small, opportunistic species with a paucity of larger macrofauna. As a result, mixing in the biologically dominated side of the river is generally on the order of a few centimeters, but may be as deep as 40 cm, and 210Pb geochronology yields low biodiffusion rates (0.43–3.35 cm2 yr−1). X-radiographs reveal the presence of some laminations which suggest that although the mixing is controlled by biological processes the mixing intensity is relatively low. Based on 210Pb geochronologies, residence time estimates for particles within the mixed layer are on the order of centuries. Residence time calculations based on the sediment mass in the physically mixed layer is equivalent to 70 yr of river sediment yield, consistent with century-scale residence times from core data. The frequency and intensity of seabed mixing appears to differ between the lower and upper river. The lower York River is wider and deeper, and is more susceptible to large storms and sea surges, which we suspect drives much of the recorded seabed mixing. Within the upper river, longer-term events (storms) may cause the deepest mixing, but much of this record is destroyed by shorter-term, high-frequency events which produce shallow to mid-depth (

The effects of shrimp trawling on sediment oxygen consumption and the sediment–water exchange fluxes of nutrients (ammonium, phosphate and silicate) and trace metals (Mn, Ni, Cu, Cd and Pb) were determined for two separate experiments conducted during July 1998 and May 1999. Oxygen microelectrode measurements showed that during the 1998 experiment, the surface sediments were oxic down to depths of approximately 15 mm suggesting that the study area had not been recently trawled. However, after passage of the trawl gear oxygen was present to depths of only 5 mm. This suggests resuspension of the upper 1 cm of sediment and resulted in ammonium and manganese fluxes increasing by a factor of 2–3, which was attributed to a similar mechanism, i.e. a strengthening of the diffusive gradient. The measured fluxes of oxygen, phosphate and the trace metals Ni, Cu and Pb were not affected by trawling, while the flux of Cd was affected. During the 1999 shrimp trawl experiment, pre- and post-trawl oxygen penetration was limited to the upper 1 mm of sediment suggesting the area had been recently trawled. The diffusive fluxes of oxygen were in agreement with directly measured oxygen fluxes, both prior to and after trawling; further indication that trawling had little to no effect on the exchange of oxygen across the sediment–water interface during this time. Macrofaunal abundance was significantly reduced during 1999 and consistent with sediment oxygen consumption rates, which were also lower during this time. This resulted in the fluxes of oxygen, which were enhanced by biological processes during 1998, becoming diffusion controlled during 1999. This resulted in pre- and post-trawl fluxes of oxygen, ammonium, silicate, Mn, Ni, Cu and Pb, when considering the measurement error, which did not differ significantly. Cd again seemed affected by shrimp trawling activities. An increase or decrease in a trace metal's turnover time (the time in days required to replenish the water column concentration) can have important implications towards the overall health of an estuary. In Galveston Bay, trace metal turnover times averaged 0.4±0.5, 52±32, 27±15, 22±23 and 5.3±3.0 d for Mn, Ni, Cu, Cd and Pb, respectively. These relatively short turnover times indicate that the sediments can be an important source of trace metals to the overlying water column, especially during low-flow periods of the Trinity River, which can sometimes last more than 1 yr. This, in turn, could possibly lead to the non-conservative mixing behaviors, for both nutrients and trace metals, previously reported for the Trinity Bay region of Galveston Bay, as conservative mixing is observed in the lower estuary. Our study shows that the effects of shrimp trawling are largely dependent on the prevailing sediment redox conditions due to the shallow penetration depth of both oxygen and the trawl gear. Therefore, it is unlikely that trawling activities adversely affect the overall health of Galveston Bay. However, repeated trawling with removal of the upper oxic sediment layers could trend surface sediments towards anoxia and ultimately lead to changes in benthic–pelagic coupling.

The Sepik River, with an estimated annual sediment load of ∼85×106 t yr−1, empties directly into a submarine canyon that transverses a narrow continental shelf (

Sediments and porewaters from two cores, one from the East River, New York and one from Newark Bay, New Jersey, were sampled for polycyclic aromatic hydrocarbons (PAHs) and other geochemical markers including 210 Pb specific activities. Despite what appears to be similar sources of PAHs to sediments within each core as inferred by ratios of alkylated to non-alkylated PAHs and PAH isomer ratios, sediments and associated PAHs have undergone distinctly different depositional processes at each site. Sediments from the core in the East River appear to have been subject to intense physically driven resuspension, resulting in selective depletion of low molecular weight PAHs within the core presumably due to processes such as enhanced desorption and scouring of particle surfaces. Although sediment PAH concentrations were higher in the East River core compared to the Newark Bay core, porewaters were depleted of the majority of PAHs analysed in the East River core relative to the Newark Bay core, precluding quantifying sediment porewater PAH distribution coefficients in this core. Sedimentary variables such as C/N ratio, particle surface area, and sedimentary soot carbon were not related to organic carbon normalized PAH distribution coefficients (K OC ) obs . Rather in the core from the Newark Bay site, (K OC ) obs were influenced by sediment mixing and porewater dissolved organic carbon (DOC). Results indicate that in urban coastal areas, the physical factors influencing time scales of sediment resuspension and deposition may be of primary importance over particle geochemistry in determining whether PAHs will likely equilibrate between sediments and pore waters.

Biologically dominated lower Chesapeake Bay and the physically dominated York River subestuary are contrasted in terms of the dynamics of sediment mixing, strata formation and sea-bed particle residence times. Two lower bay sites were examined; both are located within the bay stem plains and are characterized by muddy sand and an abundance of large, deep-dwelling organisms. X-radiographs indicate extensive biological reworking of sediments, with no long-term preservation of physical stratification.210Pb profiles reveal low sediment accumulation rates at both lower bay sites ( 80vs6–30 cm2year−1). In contrast, the York River site, located within a partially-filled palaeochannel, is predominantly mud with a depauperate benthic community dominated by small, short-lived, shallow-dwelling organisms. Although210Pb accumulation rates at the York River site (

[1] Sediment cores from the continental shelf adjacent to the Mississippi River delta immediately after the passage of Hurricane Katrina were used to examine the magnitude, and implications for the carbon budget, of sediment and particulate organic carbon (POC) remobilized by the storm on the river-dominated continental shelf. POC was sourced from incision of the innermost continental shelf ( 5000 yBP) POC eroded from the seafloor, has major implications for the remineralization versus burial of POC in deltas. The scale of erosional deflation of the shelf in water depths beyond seasonal wave-current conditions suggests that, over millennia, tropical cyclones may be responsible for partly removing prodeltaic strata from the geologic record in low-to-mid latitude deltas.