Winyah Bay Research Articles

Aboveground Carbon Stocks across a Hydrological Gradient: Ghost Forests to Non-Tidal Freshwater Forested Wetlands

Upper estuarine forested wetlands (UEFWs) play an important role in the sequestration of atmospheric carbon (C), which is facilitated by their position at the boundary of terrestrial and maritime environments but threatened by sea level rise. This study assessed the change in aboveground C stocks along the estuarine–riverine hydrogeomorphic gradient spanning salt-impacted freshwater tidal forested wetlands to freshwater forested wetlands in seasonally tidal and nontidal landscape positions. Standing stocks of C in forested wetlands were measured along two major coastal river systems, the Winyah Bay in South Carolina and the Savannah River in Georgia (USA), replicating and expanding a previous study to allow the assessment of change over time. Aboveground C stocks on these systems averaged 172.9 Mg C ha−1, comparable to those found in UEFWs across the globe and distinct from the terrestrial forested ecosystems they are often considered to be a part of during large-scale C inventory efforts. Groundwater salinity conditions as low as 1.3 ppt were observed in conjunction with losses of aboveground C. When viewed in context alongside expected sea level rise and corresponding saltwater intrusion estimates, these data suggest a marked decrease in aboveground C stocks in forested wetlands situated in and around tidal estuaries.

Forcing conditions of cross-shelf plumes on a wide continental shelf, Winyah Bay, South Atlantic Bight

Buoyant cross-shelf river plumes can extend far offshore through the combined effect of buoyancy and wind forcing, creating a critical land-ocean link in global biogeochemical cycles. On the Carolinas continental shelf, cross-shelf plume structure has been analyzed using satellite imagery, with forcing conditions represented by an estuarine Richardson number, wind stress, and alongshore pressure gradient. Three distinct cross-shelf plume patterns emerged, each occurring under an upwelling-favorable wind: (1) The separated plume, when a single filament of buoyant water spreads offshore (a prototypical cross-shelf plume structure); (2) The upwind-curving plume, which turns against the wind at some offshore distance and is created by stronger buoyancy forcing; and (3) The multi-lobe plume, which is partially trapped by the coast with multiple streaks protruding offshore and is created by stronger wind forcing, and further aided by a coincident alongshore pressure gradient force. The latter two regimes represent a low-wind, high discharge limit and a strong-wind limit of cross-shelf plumes. High-resolution satellite images reveal rich submesoscale variability associated with each plume type. Results suggest plume transport extends farthest offshore in low-energy separated plumes through a balance of weak buoyancy and weak wind forcing.

Standardization of monitoring data reassesses spatial distribution of aquatic microplastics concentrations worldwide

Microplastics are found in continental and oceanic waters worldwide, but their spatial distribution shows an intricate pattern. Their driving factors remain difficult to identify and widely discussed due to insufficient and unstandardized monitoring data. Here, based on in situ experiments and hundreds of river samples from the Qinghai-Tibet Plateau, we formulate a model to standardize aquatic microplastic measurements. The model was applied to existing data on a global scale. These data are standardized to a 20 µm mesh size, resulting in a new spatial distribution of aquatic microplastic densities, with average concentrations of 554.93 ± 1352.42 items/m3 in Europe, 2558.90 ± 4799.62 in North America and 1741.94 ± 3225.09 in Asia. Excessive contaminations (microplastic concentration > 10⁴ items/m3) are in the Yangtze River, the Charleston Harbor Estuary, the Bodega Bay and the Winyah Bay. We show that, based on these standardized concentrations, new driving factors could be used to predict the global or regional microplastic distribution in continental waters, such as the Human Development Index with a correlation of 75.86% on a global scale, the nighttime lights with a correlation of 37.26 ± 0.30% in Europe and 39.02 ± 0.54% in Asia, and the Mismanagement Plastic Waste with a correlation of 61.21 ± 19.86% in North America. Mapping standardized concentrations of aquatic microplastics enables a better comparison of contamination levels between regions and reveals more accurate hotspots to better adapt remediation efforts and future plastic pollution scenarios.

The Cross-Shelf Regime of a Wind-Driven Supercritical River Plume

Abstract River plumes are a dominant forcing agent in the coastal ocean, transporting tracers and nutrients offshore and interacting with coastal circulation. In this study we characterize the novel “cross-shelf” regime of freshwater river plumes. Rather than remaining coastally trapped (a well-established regime), a wind-driven cross-shelf plume propagates for tens to over 100 km offshore of the river mouth while remaining coherent. We perform a suite of high-resolution idealized numerical experiments that offer insight into how the cross-shelf regime comes about and the parameter space it occupies. The wind-driven shelf flow comprising the geostrophic along-shelf and the Ekman cross-shelf transport advects the plume momentum and precludes geostrophic adjustment within the plume, leading to continuous generation of internal solitons in the offshore and upstream segment of the plume. The solitons propagate into the plume interior, transporting mass within the plume and suppressing plume widening. We examine an additional ultra-high-resolution case that resolves submesoscale dynamics. This case is dynamically consistent with the lower-resolution simulations, but additionally captures vigorous inertial-symmetric instability leading to frontal erosion and lateral mixing. We support these findings with observations of the Winyah Bay plume, where the cross-shelf regime is observed under analogous forcing conditions to the model. The study offers an in-depth introduction to the cross-shelf plume regime and a look into the submesoscale mixing phenomena arising in estuarine plumes. Significance Statement In this study, we characterize a novel regime of freshwater river plumes. Rather than spreading near to or along the coast, under certain conditions river plumes may propagate away from the coast and remain coherent for tens to over 100 km offshore. Cross-shelf plumes provide a mechanism by which freshwater and river-borne materials may be transported into the open ocean, especially across wide continental shelves. Such plumes carry nutrients critical for biological productivity offshore and interact with large-scale oceanic features such as the Gulf Stream. We use high-resolution numerical modeling to examine how the cross-shelf regime arises and support our findings with observational evidence. We also study the mixing phenomena and fluid instabilities evolving within such plumes.

Striped Bass Movement in a Large Southeastern River System

Abstract Migratory behaviors of coastal Striped Bass Morone saxatilis are diverse and vary by latitude along the U.S. Atlantic Coast. Northern populations (e.g., north of Cape Hatteras, North Carolina) are anadromous, with spawning occurring in tidal freshwater/brackish rivers and adults leaving spawning locations during the winter to conduct north–south coastal migrations. The central Atlantic comprises a mixture of potamodromous and anadromous types, completing the natural continuum of behavioral modes along latitudinal ecotones. Southern populations (e.g., south of Cape Hatteras, North Carolina) are typically resident and potamodromous, completing full life cycles within river systems, and do not migrate along the Atlantic Coast. There are limited studies that have investigated daily movement of Striped Bass in the Southeast and no studies have documented movement of Striped Bass in the Great Pee Dee River, particularly with reference to spawning migrations. The objective of this study was to describe daily movement patterns and centers of attraction (e.g., spawning and resting stages) of Striped Bass in the Great Pee Dee River, South Carolina. We implanted 10 fish with hydroacoustic transmitters between 2013 and 2016. We describe daily movement and behavior using the state-space model with a two-dimensional spatial coordinate system. We recorded a total of 94,857 data points across all individuals and receivers. We observed two movement patterns. One group completed a seasonal migration (i.e., were recorded swimming upstream or downstream) that coincides with spring spawning season. A second group was present in the lower river section and Winyah Bay during the winter for 3 consecutive years but were never observed migrating up the Great Pee Dee River during the spring. One individual was documented swimming 80 river km north in the Atlantic Intracoastal Waterway, suggesting there are important overwintering locations outside their natal river. Additionally, there were significant gaps in observations for all individuals, particularly in the summer. It is possible that fish are leaving the main stem in search of thermal refuge within small tributaries. Identifying these overwintering areas and tributaries that serve as summer refuge is needed to determine stressors and fishing pressure of this important species.

Seasonal migration cues differ for dual‐spawning Atlantic Sturgeon in the Great Pee Dee River

AbstractObjectiveWe investigated environmental variables associated with spawning migration behavior for a dual‐spawning population of endangered Atlantic Sturgeon Acipenser oxyrinchus oxyrinchus in the Great Pee Dee River, South Carolina.MethodsFrom 2016 to 2021, 147 Atlantic Sturgeon were captured, implanted with acoustic transmitters, and monitored using a stationary array of 40 receivers located every 5–20 km along a 302‐km section of the Great Pee Dee River from the river mouth at Winyah Bay to the first movement barrier at Blewett Falls Dam, North Carolina.ResultWe observed 47 Atlantic Sturgeon attempting 74 spring migrations and 39 Atlantic Sturgeon attempting 76 fall migrations across 4 years of telemetry observations (2018–2021). Mixed‐effects models indicated that discharge interacted with water temperature to affect both migration initiation and upriver movement, and these interactions differed between the spring and fall runs. Spring runs were cued by rising temperatures and high river discharge, whereas fall runs were cued by falling temperatures and low discharge. Within migrations, spring‐run fish migrated further upriver when discharge was falling, and fall‐run fish moved further upriver when discharge was rising. Overall, fall‐run sturgeon migrated significantly further upriver than spring‐run sturgeon.ConclusionDifferences in migratory behavior between the two runs suggest potentially unique adaptations to ambient river conditions during the respective spawning seasons. Identifying the environmental factors that drive—and thereby limit—Atlantic Sturgeon migrations in the Great Pee Dee River informs regional recovery efforts and highlights the importance of studying and managing this species at the population level.

Contrasting trends in water quality between adjacent ocean‐ and river‐dominated estuaries: Evidence for marsh porewaters as a source of nutrient enrichment?

AbstractDegradation of estuarine water quality during the Anthropocene has largely resulted from discharges of nutrients leading to eutrophication. Recently, upstream management practices have led to comparatively reduced nutrient input into estuaries. Concurrently, climate cycles and impacts associated with anthropogenic climate warming can affect the long‐term conditions observed within estuaries. Using long‐term monitoring data from adjacent southeastern U.S. estuaries, we show that decadal‐scale trends in nutrient concentrations and phytoplankton standing stock differ between the two connected systems. These contrasting trends appear to result from differences in oceanic influence, the extent of adjacent vegetated marsh, watershed size, and upstream degradation. In the minimally impacted, ocean‐dominated North Inlet estuary, we document increasing ammonium and chlorophyll a (Chl a), while in the adjacent, river‐dominated Winyah Bay, ammonium, and Chl a concentrations are more variable but do not appear to have increased over the same time period. Surprisingly, total nitrogen exhibits the opposite pattern: temporal stability in North Inlet but increasing in Winyah Bay. We hypothesize that sea level rise associated with climate change has driven a complex set of interactions between salt marsh porewaters and tidal pumping, leading to the spillover of nutrients from salt marshes into tidal creeks in North Inlet. In Winyah Bay, this mechanism is less evident as a driver of ammonium concentrations, likely due to the outsized effect of watershed nutrient input and the narrow fringing marsh platform. The degree to which this mechanism operates in other estuaries, which vary in tidal range, the extent of vegetated marsh, watershed size, and degree of anthropogenic degradation warrants further study.

Unique biogeochemical characteristics in coastal ghost forests – The transition from freshwater forested wetland to salt marsh under the influences of sea level rise

Seawater intrusion by rising sea levels has created large areas of ghost forests along low-lying coastal wetlands in the southeastern USA, but more information is needed to better understand its soil biogeochemistry. Here, we characterized several soil and environmental parameters, including tree litterfall, surface and soil porewater quality, emissions of greenhouse gases, and microbial communities along a forest-to-marsh transect, including a freshwater forested wetland, a salt-impacted degraded ghost forest, and a salt marsh in Winyah Bay, SC, USA. General water quality parameters such as electrical conductivity, dissolved oxygen, temperature and aboveground productivity showed distinct trends along the freshwater forested wetland → degraded ghost forest → salt marsh transect, whereas there were no obvious trends in soil biogeochemical parameters. Concentrations of dissolved organic carbon (DOC) in the degraded ghost forest were generally similar to the freshwater forested wetland, but on average were higher than those in the salt marsh. More labile molecular features observed through Fourier transform ion cyclotron resonance mass spectrometry indicated an increase in the DOC biodegradability along the forest-to-marsh transect. Greater DOC biodegradability in the degraded ghost forest was observed and confirmed through its generation of the highest average electrical currents from sediment microbial fuel cells. The lowest CH4 and CO2 fluxes, but the highest degradable DOC, were observed in the degraded ghost forest, suggesting that lateral C export is important in this wetland. Moreover, the degraded ghost forest was dominated by a unique microbial community, including high abundance of Woesearchaeia, which enables carbon metabolism via symbiotic and/or fermentation-based lifestyles. Our study illustrates a ghost forest with very different characteristics compared to its parental freshwater forested wetland and its transitioned salt marsh. Data obtained from the two endmember ecosystems along the salinity gradient transect were not useful in predicting the unique biogeochemical processes in the degraded ghost forest.

Declines of methylmercury along a salinity gradient in a low-lying coastal wetland ecosystem at South Carolina, USA

Wetlands are widely regarded as biogeochemical hotspots of highly toxic methylmercury (MeHg), mainly mediated by sulfate-reducing bacteria. In low-lying coastal wetlands, sea level rise, a phenomenon caused by global climate change, is slowly degrading numerous healthy freshwater forested wetlands into salt-degraded counterparts with a nickname “ghost forests”, and eventually converting them to saltmarshes. However, little is known about the changes of mercury (Hg) methylation, bioaccumulation, and biomagnification along the forest-to-saltmarsh gradient. Here, we conducted extensive field sampling in three wetland states (healthy forested wetlands, salt-degraded forested wetlands, and saltmarsh) along a salinity gradient (from 0 to 9.4 ppt) in Winyah Bay, South Carolina, USA. We found that in our study wetland systems the saltmarshes had the lowest levels of both total Hg and MeHg in sediments and biota, as compared to healthy forested wetlands and saltwater-degraded ghost forests. Our results suggest that the slow conversion of forested wetland to saltmarsh could reduce net MeHg production in our study wetland systems, which we hypothesized that could be attributed to increased sulfate reduction and excessive buildup of sulfide in sediment that inhibits microbial Hg methylation, and/or reduced canopy density and increased photodegradation of MeHg. However, it should be noted that biogeochemical MeHg responses to salinity changes may be site-specific and we urge more similar studies in other wetland systems along a salinity gradient. Therefore, long-term salinization of coastal wetlands and the slow conversion of forests to marshes could decrease long-term exposure of toxic MeHg levels in coastal food webs that are similar to our system, and ultimately reduce human exposure to this neurotoxin.

Mission Planning for Low Altitude Aerial Drones during Water Sampling

Mission planning for small uncrewed aerial systems (sUAS) as a platform for remote sensors goes beyond the traditional issues of selecting a sensor, flying altitude/speed, spatial resolution, and the date/time of operation. Unlike purchasing or contracting imagery collections from traditional satellite or manned airborne systems, the sUAS operator must carefully select launching, landing, and flight paths that meet both the needs of the remote sensing collection and the regulatory requirements of federal, state, and local regulations. Mission planning for aerial drones must consider temporal and geographic changes in the environment, such as local weather conditions or changing tidal height. One key aspect of aerial drone missions is the visibility of the aircraft and communication with the aircraft. In this research, a visibility model for low-altitude aerial drone operations was designed using a GIS-based framework supported by high spatial resolution LiDAR data. In the example study, the geographic positions of the visibility of an aerial drone used for water sampling at low altitudes (e.g., 2 m above ground level) were modeled at different levels of tidal height. Using geospatial data for a test-case environment at the Winyah Bay estuarine environment in South Carolina, we demonstrate the utility, challenges, and solutions for determining the visibility of a very low-altitude aerial drone used in water sampling.

Offshore Spreading of a Supercritical Plume Under Upwelling Wind Forcing: A Case Study of the Winyah Bay Outflow

In this study, we present observations of the Winyah Bay (WB) plume (SC, United States) formed by high freshwater discharge and a moderate upwelling-favorable wind acting continuously for ∼1.5 days prior to the shipboard survey. If a similar wind forcing persists over a longer period, the plume turns upstream (against its natural propagation) and curves offshore forming a “filament” with minimal transverse spreading, as seen in numerous satellite images. The observed plume comprises a train of tidal sub-plumes undergoing rotational adjustment and being transported offshore by Ekman dynamics. The WB outflow is supercritical in terms of the interior Froude number. Moderate wind extends this supercritical regime farther offshore. The plume is characterized by interior fronts associated with consecutive tidal pulses. Age of the buoyant water can be distinguished by the buoyant layer mixing (evident in the layer’s thickness and salinity anomaly) along with the transformation of its TS properties. However, relatively little transverse (lateral) spreading of buoyant water occurs: the equivalent freshwater layer thickness remains surprisingly consistent, approximately 0.8 m, over more than 20 km in the direction of the bulge extension. It is hypothesized that the supercritical regime constrains the transverse spreading of a plume. Microstructure measurements reveal higher dissipation rates below the base of the older (offshore) part of the plume. This is attributed to internal wave radiation from a newly discharged tidal pulse into an older plume, with the buoyant layer acting as a waveguide. Theoretical estimations of the internal wave properties show that the interior front is highly supercritical, while the observed dissipation maximum agrees with the theoretical wave structure.

Streamflow and Tidal Dynamics in the Lower Pee Dee Basin: Hurricane Impacts

Over past years, extreme tropical storm events along the North and South Carolina coasts—and subsequent river flooding—have warranted the need for a better understanding of the hydrologic response to these events to protect life, property, businesses, and natural and cultural resources. Our focus in this study is the Pee Dee and Waccamaw River systems, which ultimately flow into Winyah Bay near Georgetown, South Carolina. River flows, coupled with the tidal nature of these freshwater systems, are complex and difficult to predict. The objective of the work is to analyze publicly available data from gauging stations along those river system as measured during Hurricanes Matthew and Florence and Tropical Storm Bertha—three uniquely different storm systems that produced varying rainfall depth, duration, and intensity across the Pee Dee Basin. The most important factor in tidal river analysis is the location of the stagnation point , where downstream river flow exactly balances upstream tidal flow. River flow only controls water level upstream of a tidal stagnation point, while ocean tide controls the water level downstream of a tidal stagnation point. An analysis of major flooding following Hurricanes Matthew, Florence, and Tropical Storm Bertha was used to determine the river flows associated with tidal stagnation at each stream gauge active during these storms. A major limitation of the analysis was a lack of flow data for the tidal channels in Georgetown County, which resulted in uncertainty in the flow associated with stagnation and uncertainty in the role played by each of the creeks that connect the Pee Dee and Waccamaw Rivers. Ignorance of the roles of these creeks most limited understanding of the relative importance of Pee Dee and Waccamaw flow to cause stagnation near Pawleys Island and Hagley gauges on the Waccamaw River and the Socastee gauge on the Atlantic Intracoastal Waterway.

A forty-seven year comparison of the vascular flora at three abandoned rice fields, Georgetown, South Carolina, U.S.A.

The vascular flora identified in 1968–1969 in three rice fields of the Winyah Bay Estuary at the Bell W. Baruch Institute for Marine Biology and Coastal Research, Georgetown County, South Carolina, abandoned in 1915, was compared with the vascular flora present in 1987–1991 and 2013–2015. Twenty vascular plant species were identified in 1968–1969 and 22 in 2013–2015 at the most saline marsh, Thousand Acre Rice Field. Forty-seven taxa were reported at Airport Marsh in 1968–1969 and 27 in 2013–2015. Fifty-six taxa were reported at Alderly in 1968–1969 with 41 identified there in 2013–2015. A parsimony algorithm was used to evaluate the distribution and co-occurrence of vascular brackish marsh species in these fields sampled at the three intervals. There was a reduction in flora at the two least saline sites, Alderly and Airport Marsh, from 1968–69 to 1987–91 and 2013–2015. Three factors—rising sea level, an increase in water salinity, and invasion by Phragmites australis—may explain this shift. There was also a shift in the flora at Thousand Acre Rice Field from 1967–1969 to 1987–1991 and 2013–2015 after the marsh was savaged by Hurricane Hugo in 1989. Invasion by non-native Phragmites australis at all sites and increase in water salinity at all sites best explain the reduction in vascular plant species at Airport Marsh and Alderly over the 47-year collection period.

Stable Isotopic Dynamics of Juvenile Elasmobranchs in a South Carolina Nursery Area

Stable isotope analysis is an increasingly utilized method for understanding resource usage and partitioning in marine species, including elasmobranch fishes. While the diet of elasmobranchs in Winyah Bay, SC, has been the subject of some preliminary research, diet and trophic relationships in this ecosystem are not yet well understood. This study addresses these knowledge gaps using δ13C and δ15N stable isotope analysis to increase understanding of isotopic niche breadth and overlap among 128 individuals representing 11 sympatric elasmobranch species present in Winyah Bay during the summer months. Overall, our findings support an understanding of Winyah Bay's elasmobranch community as trophically diverse, with some significant isotopic niche overlap among considered species, suggesting the possibility of competition for resources between co-occurring small elasmobranchs. These results suggest elasmobranch predators in the Winyah Bay ecosystem have complex and varied predator–prey relationships.

Associations Between Winter Temperatures and the Timing and Duration of Annual Larval Recruitment of a Non-native Anomuran Crab

The green porcelain crab, Petrolisthes armatus, a subtropical/tropical species, was first recorded on intertidal oyster reefs in South Carolina in 1995. Since then, its range has expanded north in a series of surges and setbacks that appear to be associated with particularly cold winters that may cause mortality. Petrolisthes armatus reproduces year-round in its native range whereas its reproductive season in the non-native range is limited to warmer months. Variation in the timing and duration of larval recruitment is not known for the non-native range and these factors may affect further range expansion. To determine whether P. armatus larval recruitment is related to temperature variation, in particular, the severity of winter temperatures, archival biweekly (every 2 weeks) larval samples collected 1994–2018 near its northern range limit in the North Inlet Winyah Bay National Estuarine Research Reserve (NERR) were examined. The goal was to determine whether the timing and duration of larval ingress varied over time and was related to temperature variation. Petrolisthes armatus larvae were first observed in samples collected in 1995. There was considerable interannual variability in the timing of the start of recruitment (coefficient of variation 29%), which ranged from the last week of March at the earliest to the last week of July at the latest, for all years but one. Earlier annual recruitment was positively correlated with a longer recruitment duration. The timing of first larval recruitment was also related to the severity of the preceding winter, with later larval recruitment occurring in years with several consecutive days of cold temperatures. Cold winter temperatures appear to affect overwintering populations and their ability to reproduce in the early spring. A decreasing frequency of severe winters along the coastal South Atlantic Bight may promote further poleward range expansion of P. armatus.

Seasonal occurrence, relative abundance, and migratory movements of juvenile sandbar sharks, Carcharhinus plumbeus, in Winyah Bay, South Carolina

In the past decade along the U.S. East coast, the overfished western North Atlantic stock of Carcharhinus plumbeus has been recovering; however, research investigating C. plumbeus habitats and seasonal habitat shifts is lacking. Accordingly, we studied the seasonal residency, catch abundance, and distribution of juvenile C. plumbeus in Winyah Bay, SC, as well as their migration patterns along the western North Atlantic. We set 303 bottom longlines from May through September in 2016 and 2017 and deployed 11 Vemco (V16-4H) acoustic transmitters in juvenile C. plumbeus. Catch abundance did not differ by month or year (p = 0.45) and was not significantly influenced by any tested water parameter (p = 0.58). C. plumbeus catches were dominated by individuals measuring 81–100 cm precaudal length, and mean size only significantly differed by year (p = 0.02) with slightly larger sharks (86.8 cm PCL) caught in 2017 than 2016 (81.4 cm PCL). Tidal stage and Bay region were positively correlated with catches (p = 0.02). From August 2016 through January 2019, juveniles were detected in Winyah Bay from April to November for 1–302 non-consecutive days (μ ± SE = 108.1 ± 32.6 days), with six juveniles exhibiting interannual return. Detection frequency and presence differed by Bay region, with most detections nearshore and in Lower Bay, fewest in Middle Bay, and none in Upper Bay. This study had two primary findings: monitored sharks utilized a previously unknown southern overwintering migration route, and Winyah Bay serves as a secondary nursery for C. plumbeus.

Hurricane Florence Flooding in Georgetown County: A Qualitative Explanation of the Interactions of Estuary and Tidal River

This paper examines data from 18 USGS gauges in the lower Pee Dee Basin in an effort to explain the behavior of the flooding following Hurricane Florence (2018) in Georgetown County, South Carolina. Despite record or near-record flooding in all the tributaries to the Winyah Bay estuary, water levels near the city of Georgetown were well below predicted heights. Floodplain storage in the lower Great Pee Dee, Lynches, and Little Pee Dee River valleys stored over 1.2 million acre-feet of floodwaters, delaying peak stage near Bucksport for five days and reducing peak flow into the Winyah Bay tidal river/estuary system by nearly 50%. An unknown amount of flow from the Winyah Bay tidal river/estuary system flowed through the Atlantic Intracoastal Water Way to Little River rather than through Winyah Bay. The resulting freshwater flow to Winyah Bay only moved the point of tidal stagnation (where upstream tidal flow balances downstream freshwater flow) to near Georgetown. Since the city of Georgetown was near the point of stagnation, water level there was driven by ocean tidal height rather than river flood stage. The lack of discharge data from the tidal rivers in Georgetown County prevents evaluation of the importance of each of these factors and will limit efforts to make quantitative predictions of future flooding in the county.

Impact of bromide exposure on natural organochlorine loss from coastal wetland soils in the Winyah Bay, South Carolina.

Naturally formed halogenated organic compounds are common in terrestrial and marine environments and play an important role in the halogen cycle. Among these halogenated compounds, chlorinated organic compounds are the most common halogenated species in all soils and freshwater sediments. This study evaluated how a previously observed phenomenon of bromination of organic matter in coastal soils due to salt-water intrusion impacts the stability and fate of natural organochlorine (org-Cl) in coastal wetland soils. The reacted solid and liquid samples were analyzed using X-ray spectroscopy (in cm and at micron scales for solids) and ion chromatography. We find that introduction of Br- species and their subsequent reactions with organic carbon are associated with an average of 39% loss of org-Cl species from leaf litter and soil. The losses are more prominent in org-Cl hotspots of leaf litter, and both aliphatic and aromatic organochlorine compounds are lost from all samples at high Br- concentrations. The combination of solid and aqueous phase analysis suggests that org-Cl loss is most likely largely associated with volatilization of org-Cl. Release of labile org-Cl compounds has detrimental environmental implications for both ecosystem toxicity, and stratospheric ozone. The reactions similar to those observed here can also have implications for the reactions of xenobiotic chlorinated compounds in soils.

Age, growth, and maturation of the Finetooth Shark, Carcharhinus isodon, in the Western North Atlantic Ocean

Many elasmobranchs display K-selected life history characteristics, making species-specific life history parameters critical to development of the most accurate stock assessment models. Age, growth, and maturity were examined for Finetooth Sharks, Carcharhinus isodon, in coastal waters of the Western North Atlantic Ocean (WNA) from Winyah Bay, South Carolina to Cape Canaveral, Florida. Ages were estimated from the vertebrae of 200 males and 232 females. The maximum observed age for males and females was 21.9 years and 22.3 years, respectively. Sizes ranged from 376 mm to 1174 mm fork length (FL) for males and 380 mm to 1282 mm FL for females. Significant differences were detected between the sexes necessitating sex-specific von Bertalanffy growth models yielding the following parameters: male, L∞ = 1140 mm FL, k = 0.29, L0 = 460 mm FL; female, L∞ = 1253 mm FL, k = 0.20, L0 = 464 mm FL. Median length (L50) at maturity was 1010 mm FL for males and 1043 mm FL for females corresponding to an age at median maturity (A50) of 6.6 years and 6.8 years, respectively. Significant differences in growth and maturity were detected between the current study and previously published parameters for the WNA and Gulf of Mexico (GOM). Observed differences in the WNA were driven by ageing methods, with current methods yielding significant differences in age estimates between studies. Results from the current study, in conjunction with previously published reproductive, tag-recapture and genetic studies, provide support for separate stocks between the WNA and GOM.

Response of a Coastal Plume Formed by Tidally Modulated Estuarine Outflow to Light Upwelling-Favorable Wind

AbstractThis study presents observations of a buoyant plume off Winyah Bay, South Carolina, which was formed under conditions of high freshwater discharge and upwelling-favorable wind forcing. Analysis of observations demonstrates that the response of the anticyclonic bulge formed by tidally modulated estuarine outflow to the light upwelling-favorable wind is more complex than the previously studied far-field response. The latter can be described by a slab-like model with mixing concentrating at the offshore edge of a buoyant layer. The observed plume depth increased from ~3 m near the mouth to 6 m at the offshore edge, with plume depth changing in a steplike fashion rather than continuously. CTD profiles near these steps revealed overturning indicative of vigorous mixing. Estimates of the gradient Richardson number confirmed the likelihood of mixing/entrainment not only at the offshore edge of the plume but also in the proximity of the observed steps. We hypothesize that these steps represent tidal fronts that undergo geostrophic adjustment and are advected offshore by the superimposed Ekman drift. Scaling analysis suggests that mixing and entrainment at the observed interior fronts can be enhanced by superposition of geostrophic and wind-induced shear.