Ocean City Inlet Research Articles

Characteristics of Surface Currents in a Shallow Lagoon–Inlet–Coastal Ocean System Revealed by Surface Drifter Observations

The circulation in a shallow lagoon–inlet–coastal ocean system is significant to material transports (e.g., debris, pollutants, and larvae). To study surface flows in this system, we deployed 35 surface drifters at various tidal phases and wind conditions during 2017 and 2018 in the Maryland Coastal Bays system (MCBs). Given that winds and tides are two important drivers of estuarine and coastal circulation, their influences on surface drifter trajectories were analyzed. Observations indicate that surface drifters exit (enter) the lagoon mostly during ebb (flood) currents, and clockwise circular movements at a length scale of 1.5 km formed at the outer edge of Ocean City Inlet (OCI). Under weak wind conditions, tides are primarily responsible for drifter movements near OCI, whereas both the long-fetch winds and tides are important near the relatively larger Chincoteague Inlet and backbays. Under strong wind conditions, surface drifter movements generally follow wind directions. In the shallow lagoonal system, relative effects of winds on surface drifters gradually become stronger in the regions further away from the adjacent inlet as tides are weaker. Further investigations indicate that the fastest and slowest surface drifters are near the small OCI and backbays with the weakened tides, respectively. The direct surface drifter observations that cover a wide spatial range and long time series can provide strong support to surface current simulations. Enhanced understanding of coastal physical oceanography in the MCBs can be beneficial to similar systems and coastal ocean communities.

Stratification variability in a lagoon system in response to a passing storm

AbstractShallow lagoon systems with limited river flow and precipitation are often regarded as being well‐mixed; however, stratification can occasionally occur in shallow lagoons in response to intense river runoffs and precipitation. Understanding the stratification behaviors of a shallow lagoon system is critical for future environmental assessment and management strategies. Thus, in this study, stratification and mixing mechanisms in a shallow lagoon system (the Maryland Coastal Bays) were investigated on an episodic scale during Hurricane Sandy (2012) by using a numerical model. The strength of stratification (Brunt‐Väisälä frequency, N in s−1) in the lagoon system varied spatially; and was determined by river flow, precipitation, winds, and remote forcing. During the pre‐Sandy period (October 25–28, 2012), the bays were relatively mixed without sufficient river flow and precipitation. Driven by intense river flow from the northern creeks (peak: 82.47 m3 s−1), high precipitation (peak: 3.29 × 10−6 m s−1), and strong storm winds (mean: 12.15 m s−1) during the Sandy period (October 28–31, 2012), the water column in the northern creeks of the bays became stratified (mean N2: ~ 0.01 s−2). During the post‐Sandy period (October 31–November 3, 2012), the St. Martin River among the northern creeks showed strong stratification (mean N2: ~ 0.03 s−2) due to weaker winds (mean: 5.70 m s−1) and residual high river flow and precipitation from the Sandy period. The wind was found to be the most dominant source of mixing in the bays, while remote forcing and wind regulated the stratification near the Ocean City Inlet.

Analysis of Estrogenic Activity in Maryland Coastal Bays Using the MCF-7 Cell Proliferation Assay.

Contaminants of Emerging Concern (CECs) with estrogenic or estrogenic-like activity have been increasingly detected in aquatic environments and have been an issue of global concern due to their potential negative effects on wildlife and human health. This study used the MCF-7 cell proliferation assay (E-Screen) to assess the estrogenic activity profiles in Maryland Coastal Bays (MCBs), a eutrophic system of estuaries impacted by human activities. Estrogenic activity was observed in all study sites tested. Water samples from MCBs increased MCF-7 cell proliferation above the negative control from 2.1-fold at site 8, located in Sinepuxent Bay close to the Ocean City Inlet, to 6.3-fold at site 6, located in Newport Bay. The proliferative effects of the sediment samples over the negative control ranged from 1.9-fold at the Assateague Island National Seashore site to 7.7-fold at the Public Landing site. Moreover, elevated cell proliferation (p < 0.05) was observed when cells were co-exposed with 17ß-Estradiol (E2), while reduction in cell proliferation was observed when cells were co-exposed with the antagonist ICI 182, 780 suggesting that cell proliferative effects were primarily mediated by the estrogen receptor (ER). These results suggest the occurrence of some estrogenic or hormonal-like compounds in the MCBs and are consistent with our previous findings based on vitellogenin analyses.

Carbon and nitrogen stable isotopes of copepods in a tidal estuarine system in Maryland, USA

The carbon and nitrogen stable isotope ratios of copepods, particularly Acartia tonsa and suspended particulate organic matter (SPOM) samples, collected seasonally (2014 to 2017) from 13 sites in the tidal estuaries of Maryland were analyzed. We hypothesized that copepods at sites close to the mouths of lagoon tributaries have more depleted δ13C than copepods at sites near the inlets, and that variations in the δ13C values of copepods mirror that of the SPOM. Copepod δ13C values ranged from −27.8‰ to −19.4‰, and that of SPOM from −26.8 to −20.3‰. Mean copepod δ13C value (−21.8‰±0.4) at a site close to the ocean was the highest, whereas the lowest value (−24.4‰±0.5) occurred at a site located at the mouth of St. Martin River. δ15N copepod values varied from 2.9‰ to 13.0‰ (mean=9.2‰±0.1); that of SPOM was −0.58 to 10.51‰ (mean=5.7‰±0.2). Reduction in the δ15N mean values from a site near the Ocean City inlet (10.2±0.4‰) to a site close to the tributaries (8.5±0.6‰) suggests that copepods at the site near Ocean City inlet likely fed on food items that contained more marine phytoplankton with enriched δ15N and heterotrophic protists, than copepods at a site near the river mouth. The highest (−21.9‰±0.4) and lowest (−25.8‰±0.3) mean copepod δ13C values were observed in summer 2015 and winter 2017, whereas the highest (10.8‰±0.2) and lowest (7.1‰±0.7) mean copepod δ15N values were recorded in winter and fall 2016, respectively. δ15N enrichment between copepods and SPOM ranged from 1.0‰ to 8.9‰ (mean: 3.4‰). The highest enrichment observed in February 2016 stemmed from a reduction in SPOM δ15N values, after a major storm event, which was unaccompanied by a decrease in Acartiaδ15N. Copepod and SPOM δ13C and δ15N values, displayed similar spatial patterns and were positively correlated; enrichment at sites near the ocean and depletion near the river mouth indicating that SPOM composition influenced copepods diets in the lagoons.

Population Structure of the Blue Crab Callinectes sapidus in the Maryland Coastal Bays

The population structure of the blue crab Callinectes sapidus was examined in the Maryland Coastal Bays (MCB) from 2014 to 2016. Crabs were sampled from April to December of each year. Size–frequency distributions showed a strong seasonal cycle, with small crabs being abundant in April, increasing in size through September, with adult crabs observed in the highest proportions from August through October of each year. A subsample of crabs was assayed for hemolymph ecdysone concentrations to examine molting patterns in field-collected blue crabs. Molting was observed throughout the sampling season, peaking in April for immature crabs, with lows in all size classes occurring in October. The mean size at maturity (L50) for females collected in this study was 116 mm carapace width (CW), which is comparable to that reported for the lower Chesapeake Bay (CB) and suggests crabs in the MCB are not significantly smaller as previously thought; however, large crabs (>127 mm CW) appear to make up a smaller proportion of the total population in the MCB than in CB. Ovigerous females were observed at two distinct locations depending on the season, with 13/15 (86.7%) in southern Chincoteague Bay in April and May and 24/41 (58.5%) nearest to the Ocean City Inlet in July and August, indicating two potentially distinct spawning grounds and periods. This work suggests that blue crab reproductive success and general population trends are similar across both systems, with fishing pressure or disease in the MCB potentially explaining the low abundance of adult male crabs.

Spatial and Temporal Patterns of δ13C and δ15N of Suspended Particulate Organic Matter in Maryland Coastal Bays, USA

The suspended particulate organic matter (SPOM) in transitional waters such as the Maryland Coastal Bays (MCBs) is derived from allochthonous and autochthonous sources. Little is known, however, about the contribution of terrestrially derived organic matter to SPOM in the MCBs. The sources of SPOM in the MCBs were evaluated using stable isotope ratios of nitrogen (δ15N) and carbon (δ13C), and C/N molar ratios. The values of SPOM δ15N, δ13C and C/N ratios from samples collected seasonally (July 2014 to October 2017) at 13 sites ranged from −0.58 to 10.51‰, −26.85 to −20.33‰, and 1.67 to 11.36, respectively, indicating a mixture of terrestrial SPOM transported by tributaries, marine organic matter from phytoplankton, and sewage. SPOM δ13C levels less than −24‰, suggesting the dominance of terrestrially derived carbon, occurred mainly at sites close to the mouths of tributaries, and were less depleted at sites near the ocean. The mean value of SPOM δ13C was higher in October 2014 (−22.76‰) than in October 2015 (−24.65‰) and 2016 (−24.57‰) likely due to differences in river discharge. Much lower values (&lt;4‰) of δ15N observed in February 2016 coincided with a high freshwater inflow that accompanied a major storm, indicating a strong influence of untreated sewage. Results from a two end-member mixing model suggest that on average, the SPOM in the MCBs is composed of 44% terrestrial materials with the highest percent contributions in October 2015 and 2016 (61%), and lowest (28%) in July 2015. The contribution of terrestrial materials to the SPOM was highest (58%) near the mouth of St. Martin River and lowest (25%) near the Ocean City inlet. SPOM composition and distribution in MCBs are, therefore, a function of land use, freshwater inflow, and water circulation that influence in situ phytoplankton production, and the transport and distribution of terrestrially derived materials.

The Study of the Hurricane-Induced Storm Surge and Bay-Ocean Exchange Using a Nesting Model

Lagoon systems are more heavily impacted by hurricanes, whereas the relevant storm surge modeling studies have been paid little attention to lagoon systems and the storm-induced exchange in lagoon systems is even less understood. To address this gap, a three-dimensional unstructured grid-based model was configured for the Maryland Coastal Bays, a typical lagoon system with two unique inlets (Ocean City Inlet (OCI) and Chincoteague Inlet (CI)), to investigate how Hurricane Sandy impacted inlet dynamics. A nesting model framework was applied to provide the necessary remote forcing from a large model domain and maintain the intricate shoreline and bathymetry of an inner model domain. Results indicated that the flux patterns varied in response to the change in wind direction and rising/falling high water levels from the coastal ocean, rather than a single flow pattern during the passage of Sandy. From October 29 05:00 to 17:00 UTC, mild (> 10 m/s) and strong (> 15 m/s) northerly winds accompanied by the rising high water level from the coastal ocean promoted a mean inflow pattern at the OCI and a mean outflow pattern at the CI. Strong southwesterly winds (> 15 m/s) dominated in the bays from October 30 03:00 to 15:00 UTC. Under strong southwesterly winds and falling high water levels from the coastal ocean, flux was transported landward at the CI and seaward at the OCI. Sensitivity experiments on various storm temporal scales showed that a net inflow pattern occurred in the bays, and the net exchange amounts became smaller in response to longer storm durations. Residual effect of relatively high river flow from Sandy could still influence the salinity at the OCI, whereas the CI salinity was not affected by river flow owing to a long distance between the CI and river locations.

Dynamics of Mesozooplankton Assemblage in Relation to Environmental Factors in the Maryland Coastal Bays

The mesozooplankton composition and dynamics in coastal lagoons of Maryland, mid-Atlantic region, USA have received little scientific attention despite the fact that the lagoons have undergone changes in water quality in the past two decades. We compared mesozooplankton abundance and community structure among sites and seasons, and between 2012, a year of higher than average salinity (33.4), and 2013 with lower than average salinity (26.6). It was observed that the composition, diversity, and abundance of mesozooplankton in 2012 differed from those of 2013. Barnacle nauplii were abundant in 2012 contributing 31% of the non-copepod mesozooplankton abundance, whereas hydromedusae were more dominant in 2013 and contributed up to 83% of non-copepod zooplankton abundance. Gastropod veliger larvae were more abundant in 2013 than in 2012 while larvae of bivalves, polychaetes, and decapods, in addition to cladocerans and ostracods had higher abundances in 2012. The abundance and diversity of mesozooplankton were explained by variations in environmental factors particularly salinity, and by the abundance of predators such as bay anchovy (Anchoa mitchelli). Diversity was higher in spring and summer 2012 (dry year) than in 2013 (wet year). The reduction of salinity in fall 2012, due to high freshwater discharge associated with Hurricane Sandy, was accompanied by a decrease in mesozooplankton diversity. Spatially, diversity was higher at sites with high salinity near the Ocean City Inlet than at sites near the mouth of tributaries with lower salinity, higher nutrient levels and higher phytoplankton biomass. Perhaps, the relatively low salinity and high temperature in 2013 resulted in an increase in the abundance of hydromedusae, which through predation contributed to the reduction in the abundance of bivalve larvae and other taxa.

Influence of temperature on the occurrence and distribution of the sand shrimp Crangon septemspinosaSay, 1818 (Decapoda: Caridea: Crangonidae) in polyhaline lagoons in Maryland, USA

Abstract Sand shrimp, Crangon septemspinosaSay, 1818, is one of the most abundant decapod crustaceans in estuaries and coastal waters of the northwestern Atlantic Ocean, though little is known about its population dynamics in polyhaline lagoons of the mid-Atlantic region. Seasonal and spatial patterns of abundance and distribution of C. septemspinosa were evaluated in relation to temperature, salinity, and dissolved oxygen in Maryland coastal bays (MCBs) using monthly data (April to October 1994 to 2012). We tested the hypothesis that temperature influences the occurrence and distribution of sand shrimp in the lagoons. A consistent pattern of high relative abundance of shrimp in spring and its scarcity in summer and early fall was observed. Shrimp abundance was highest in the northern bays and at sites closest to the Ocean City Inlet during April, but lowest at sites in the upper parts of Chincoteague Bay and MCBs tributaries. As mean temperature increased from April (12.2–17.1 oC) to June (21.8–26.7 oC), the relative abundance of the shrimp decreased substantially at most sites except at two sites where mean water temperature was comparatively low (21.8–23.3 oC). By July, when mean temperature was at its maximum (23.1–28.9 oC) in the bays, shrimp were rarely caught in trawls even in early fall in spite of the decline in temperature. It is likely that shrimp moved into nearshore waters with cooler temperature or suffered high mortality due to high temperature during this period. Generalized linear models suggest that temperature, and temperature and dissolved oxygen combined, were the most important abiotic factors examined that influenced the spatial distribution of C. septemspinosa in May and June, respectively. Considering their trophic importance, the spatio-temporal variations in the occurrence and abundance of the shrimp have implications for food web dynamics in the MCBs.

Wave–current dynamics and interactions near the two inlets of a shallow lagoon–inlet–coastal ocean system under hurricane conditions

Inlet wave–current dynamics and interactions are vital to the physical exchanges in a lagoon–inlet–coastal ocean system. A wave–current coupled model was calibrated and validated against observational data, and then applied to investigate the complex dynamics in the Maryland Coastal Bays during Hurricane Irene (2011). With the inclusion of wave–current interactions, skill in simulating the maximum total water surface elevation was improved under hurricane conditions. Major processes of wave–current interactions include the radiation stress-induced setup and current, and water depth variation-induced wave breaking. Wave-induced bottom friction and sea surface roughness are of secondary importance to nearshore dynamics. Further investigations reveal that tidal currents and ocean swells dominate inlet circulation and wave dynamics, respectively. Physical dynamics within the paired inlets are regulated by local winds, wave–current interactions, and unique inlet characteristics. However, wave dynamics in the lagoon and behind inlets are dominated by local winds and modulated by the shallow bathymetry. With the hypothetical closure of any inlet, wave–current dynamics and interactions behind the corresponding inlet are strongly altered, whereas they are weakly influenced from a remote one. Occasionally, the circulation near the narrow Ocean City Inlet area is influenced moderately by artificially shutting down the relatively wider Chincoteague Inlet. The finding from this work on the Maryland Coastal Bays can be beneficial to understanding similar lagoon–inlet–coastal ocean systems elsewhere.

Dynamics of water and salt exchange at Maryland Coastal Bays

The exchange processes between the Maryland Coastal Bays system (MCBs) and their adjacent coastal ocean were simulated using a three-dimensional unstructured-grid based hydrodynamic model, which was validated by observed data including water level, current velocity and salinity. Idealized experiments were then carried out to investigate the impact of wind forcing on water exchange and salt flux. Through these experiments, the exchanges between the MCBs and coastal ocean were investigated at two inlets (Ocean City Inlet and Chincoteague Inlet). Given that winds and tides are two key external forces known to impact estuarine dynamics, the effect of each individual force on the exchange processes was studied to evaluate the corresponding influence on the inlet dynamics. It was found that wind forcing significantly impacts the inlet dynamics: the effect of wind directions on exchange processes under strong wind speeds is substantial; for example, northwesterly winds push flux to the southern part of the bays, while southwesterly winds pile up flux towards northern Chincoteague Bay. The effect of wind forcing on the exchange dynamics becomes stronger with the augmentation of its speed. Meanwhile, tidal forcing is the major driver of exchange dynamics at weak wind speeds (e.g., 3 m/s), and its effect on exchange process gradually weakens with stronger wind speeds (e.g., 7 m/s, 15 m/s). In addition, sensitivity tests elucidated that closing either inlet results in a significant impact on the water elevation, current velocity and salinity nearby the relevant cut-off inlet areas.

Grain‐size distributions and coastal morphodynamics along the southern Maryland and Virginia barrier islands

AbstractThis study examined grain‐size distributions to address questions regarding geological and oceanographic controls on island morphodynamics along one of the longest undeveloped, mixed‐energy barrier island systems in the world. In particular, statistical analyses (i.e. analysis of variance, Tukey honest significant difference multiple comparison tests, nonparametric statistics and linear regression analysis) of 230 barrier island samples from Ocean City Inlet, Maryland, to the mouth of the Chesapeake Bay and 134 nearshore samples (d ≤ 10 m) identified grain‐size trends related to the morphodynamic characteristics of these systems. In general, the Virginia barrier islands north of Wachapreague Inlet and Assateague Island form a statistically different subset of grain sizes (medium‐grained to coarse‐grained sand) from the islands south of Wachapreague Inlet (fine‐grained sand). These textural trends corroborate the Pleistocene headlands of the Delmarva coastal compartment as the sediment source and indicate that some of the coarse‐grained to medium‐grained sediment bypasses the large sinks in the net southward longshore sediment transport system (i.e. Fishing Point and Chincoteague Inlet). This research also demonstrates that the preferential accumulation of coarse‐grained to medium‐grained sand on the ebb‐tidal delta at Wachapreague Inlet probably controls the erosional morphodynamics of the islands located downdrift (south) of the inlet. These results suggest that an increase in tidal prism, set up by sea‐level rise and/or a shift in wave climate/refraction patterns, may lead to barrier island fragmentation and a runaway transgression of this predominantly natural barrier island system. Consequently, a grain analysis of major coastal compartments, across multiple driving forces, can be used to assess coastal morphodynamics and the potential impact of climate change on coastal systems.

Restoration of overwash processes creates piping plover (Charadrius melodus) habitat on a barrier island (Assateague Island, Maryland)

On Assateague Island, an undeveloped barrier island along Maryland and Virginia, a foredune was constructed to protect the island from the erosion and breaching threat caused by permanent jetties built to maintain Ocean City Inlet. Scientists and engineers integrated expertise in vegetation, wildlife, geomorphology, and coastal engineering in order to design a habitat restoration project that would be evaluated in terms of coastal processes rather than static features. Development of specific restoration targets, thresholds for intervention, and criteria to evaluate long-term project success were based on biological and geomorphological data and coastal engineering models. A detailed long-term monitoring plan was established to measure project sustainability. The foredune unexpectedly acted as near-total barrier to both overwash and wind, and the dynamic ecosystem underwent undesirable habitat changes including conversion of early-succession beach habitat to herbaceous and shrub communities, diminishing availability of foraging habitat and thereby reducing productivity of the Federally-listed Threatened Charadrius melodus (piping plover). To address these impacts, multiple notches were cut through the constructed foredune. The metric for initial geomorphological success—restoration of at least one overwash event per year across the constructed foredune, if occurring elsewhere on the island—was reached. New overwash fans increased island stability by increasing interior island elevation. At every notch, areas of sparse vegetation increased and the new foraging habitat was utilized by breeding pairs during the 2010 breeding season. However, the metric for long-term biological success—an increase to 37% sparsely vegetated habitat on the North End and an increase in piping plover productivity to 1.25 chicks fledged per breeding pair—has not yet been met. By 2010 there was an overall productivity of 1.2 chicks fledged per breeding pair and a 1.7% decrease in sparsely vegetated habitat. Ideally, overwash restoration will sustain the availability of foraging habitat, but future foredune modifications may be necessary to maintain or increase overwash processes and piping plover habitat in the project area.

Concepts in Sediment Budgets

ROSATI, J.D., 2005, Concepts in sediment budgets. Journal of Coastal Research, 21(2), 307‐322. West Palm Beach (Florida), ISSN 0749-0208. The sediment budget is fundamental in coastal science and engineering. Budgets allow estimates to be made of the volume or volume rate of sediment entering and exiting a defined region of the coast and the surplus or deficit remaining in that region. Sediment budgets have been regularly employed with variations in approaches to determine the sources and sinks through application of the primary conservation of mass equation. Historically, sediment budgets have been constructed and displayed on paper or maps. Challenges in constructing a sediment budget include determining the appropriate boundaries of the budget and interior cells; defining the possible range of sediment transport pathways, and the relative magnitude of each; representing the uncertainty associated with values and assumptions in the budget; and testing the sensitivity of the series of budgets to variations in the unknown and temporally-changing values. These challenges are usually addressed by representing a series of budget alternatives that are ultimately drawn on paper, maps, or graphs. Applications of the methodology include detailed local-scale sediment budgets, such as for an inlet or beach fill project, and large-scale sediment budgets for the region surrounding the study area. The local-scale budget has calculation cells representing features on the order of 10s to 100s of meters, and it must be shown separately from the regional sediment budget, with cells ranging from 100s of meters to kilometers. This paper reviews commonly applied sediment budget concepts and introduces new considerations intended to make the sediment budget process more reliable, streamlined, and understandable. The need for both local and regional sediment budgets is discussed, and the utility of combining, or collapsing, cells is shown to be beneficial for local budgets within a regional system. Collapsing all cells within the budget creates a ‘‘macrobudget,’’ which can be applied to check for overall balance of values. An automated means of changing the magnitude of terms, while maintaining the same dependency on other values within the sediment budget, is presented. Finally, the need for and method of tracking uncertainty within the sediment budget, and a means for conducting sensitivity analyses, are discussed. These new concepts are demonstrated within the Sediment Budget Analysis System with an application for Long Island, New York, and Ocean City Inlet, Maryland.

Reservoir Model of Ebb-Tidal Shoal Evolution and Sand Bypassing

A mathematical model is presented for calculating the change in volume and sand-bypassing rate at ebb-tidal shoals. Conceptually and mathematically, the ebb-tidal shoal is distinguished from bypassing bars that emerge from it and from attachment bars where the bypassing bars merge with the beach. The volumes and bypassing rates of these morphologic entities are calculated by analogy to a reservoir system, where each reservoir can fill to a maximum (equilibrium) volume. The ratio of the input longshore sand transport rate and the equilibrium volume of the morphologic feature is found to be a key parameter governing morphologic evolution. The analytical model gives explicit expressions for the time delays in evolution of the bypassing bar and the attachment bar, which are directly related to the delays in sand bypassing. Predictions of morphology change agree with observations made at Ocean City Inlet, Md. Examples of extension of the model by numerical solution are given for a hypothetical case of mining of an ebb-tidal shoal and for an idealized case of bidirectional longshore sand transport, in which updrift and downdrift bypassing bars and attachment bars are generated.