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Sustaining water quality is an important component of coastal resilience. Floodwaters deliver reactive nitrogen (NOx) to sensitive aquatic systems and can diminish water quality. Coastal habitats in flooded areas can be effective at removing reactive nitrogen through denitrification (DNF). However, less is known about this biogeochemical process in urbanized environments. This study assessed the nitrogen removal capabilities of flooded habitats along an urban estuarine coastline in the upper Neuse River Estuary (NRE), NC, USA under two nitrate concentrations (16.8 µM and 52.3 µM NOx, respectively). We also determined how storm characteristics (e.g., precipitation and wind) affect water column NOx concentrations and consequently DNF by flooded habitats. Continuous flow-through sediment core incubation experiments quantified gas and nutrient fluxes across the sediment-water interface in marsh, swamp forest, undeveloped open space, stormwater pond, and shallow subtidal sediments. All habitats exhibited net DNF. Additionally, all habitats increased DNF rates under elevated nitrate conditions compared to low nitrate. Structured habitats with high sediment organic matter had higher nitrogen removal capacity than unstructured, low sediment organic matter habitats. High precipitation-high wind storm events produced concentrations significantly lower than other types of storms (e.g., low precipitation-high wind, high wind-low precipitation, low wind-low precipitation), which likely results in relatively low DNF rates by flooded habitats and low removal percentages of total dissolved nitrogen loads. These results demonstrate the importance of natural systems to water quality in urbanized coastal areas subject to flooding.

When prey alter behavioral or morphological traits to reduce predation risk, they often incur fitness costs through reduced growth and reproduction as well as increased mortality that are known as nonconsumptive effects (NCEs). Environmental context and trophic structure can individually alter the strength of NCEs, yet the interactive influence of these contexts in natural settings is less understood. At six sites across 1000 km of the Southeastern Atlantic Bight (SAB), we constructed oyster reefs with one, two, or three trophic levels and evaluated the traits of focal juvenile oysters exposed to predation risk cues. We monitored environmental variables (water flow velocity, microalgal resources, and oyster larval recruitment) that may have altered how oysters respond to risk, and we also assessed the cost of trait changes to oyster mortality and growth when they were protected from direct predatory loss. Regardless of trophic structure, we found that oyster shell strength and natural oyster recruitment peaked at the center of the region. This high recruitment negated the potential for NCEs by smothering and killing the focal oysters. Also independent of trophic structure, focal oysters grew the most at the northernmost site. In contrast to, and perhaps because of, these strong environmental effects, the oyster traits of condition index and larval recruitment were only suppressed by the trophic treatment with a full complement of risk cues from intermediate and top predators at just the southernmost site. But at this same site, statistically significant NCEs on oyster growth and mortality were not detected. More strikingly, our study demonstrated environmental gradients that differentially influence oysters throughout the SAB. In particular, the results of our trophic manipulation experiment across these gradients suggest that in the absence of predation, environmental differences among sites may overwhelm the influence of NCEs on prey traits and population dynamics.

The Defense Coastal/Estuarine Research Program (DCERP) was a 10-year multi-investigator project funded by the Department of Defense to improve understanding of ecosystem processes and their interactions with natural and anthropogenic stressors at the Marine Corps Base Camp Lejeune (MCBCL) located in coastal North Carolina. The project was aimed at facilitating ecosystem-based management (EBM) at the MCBCL and other coastal military installations. Because of its scope, interdisciplinary character, and duration, DCERP embodied many of the opportunities and challenges associated with EBM, including the need for explicit goals, system models, long-term perspectives, systems complexity, change inevitability, consideration of humans as ecosystem components, and program adaptability and accountability. We describe key elements of this program, its contributions to coastal EBM, and its relevance as an exemplar of EBM.

Environmental changes can alter the interactions between biotic and abiotic ecosystem components in tidal wetlands and therefore impact important ecosystem functions. The objective of this study was to determine how saltwater intrusion affects wetland nutrient biogeochemistry, with a specific focus on the soil microbial communities and physicochemical parameters that control nitrate removal. Our work took place in a tidal freshwater marsh in South Carolina, USA, where a 3.5-year saltwater intrusion experiment increased porewater salinities from freshwater to oligohaline levels. We measured rates of denitrification, soil oxygen demand, and dissimilatory nitrate reduction to ammonium (DNRA) and used molecular genetic techniques to assess the abundance and community structure of soil microbes. In soils exposed to elevated salinities, rates of denitrification were reduced by about 70% due to changes in the soil physicochemical environment (higher salinity, higher carbon:nitrogen ratio) and shifts in the community composition of denitrifiers. Saltwater intrusion also affected the microbial community responsible for DNRA, increasing the abundance of genes associated with this process and shifting microbial community composition. Though rates of DNRA were below detection, the microbial community response may be a precursor to increased rates of DNRA with continued saltwater intrusion. Overall, saltwater intrusion reduces the ability of tidal freshwater marshes to convert reactive nitrogen to dinitrogen gas and therefore negatively affects their water quality functions. Continued study of the interrelationships between biotic communities, the abiotic environment, and biogeochemical transformations will lead to a better understanding of how the progressive replacement of tidal freshwater marshes with brackish analogues will affect the overall functioning of the coastal landscape.

Living shorelines are nature-based solutions to coastal erosion that can be constructed as salt marshes with fringing oyster reefs. Each of these habitats can decrease the potential for eutrophication through increased nitrogen (N) removal via denitrification. However, the development of N cycling over time has not been studied in living shorelines. This research measured denitrification rates in a chronosequence of living shorelines spanning 0–20 years in age in Bogue Sound, NC. Analyses were conducted seasonally from summer 2014 to spring 2015 along an elevation transect through the salt marsh, oyster reef, and adjacent sandflat at all sites. Gas fluxes (N2 and O2) from sediment core incubations were measured with a membrane inlet mass spectrometer (MIMS) to assess denitrification and sediment oxygen demand. Fluxes of dissolved nutrients and the greenhouse gas N2O were measured. Sediment properties, inundation frequency, oyster filtration rates, and marsh grass stem density were also quantified. There was no significant difference in denitrification rates among habitats. N removal consistently increased from the 0- to 7-year-old sites. Denitrification efficiency was always greater than 50% and positive N2O fluxes were negligible. Our results suggest that living shorelines increase net N removal within a relatively short time period following construction, without introducing deleterious greenhouse gas emissions. This demonstrates that living shorelines can play an important role in estuarine N cycling and management.

Velinsky, D.J.; Paudel, B.; Quirk, T.; Piehler, M., and Smyth, A., 2017. Salt marsh denitrification provides a significant nitrogen sink in Barnegat Bay, New Jersey. In: Buchanan, G.A.; Belton, T.J., and Paudel, B. (eds.), A Comprehensive Assessment of Barnegat Bay-Little Egg Harbor, New Jersey. Denitrification in salt marshes can be an important removal mechanism for inorganic nitrogen, particularly in coastal estuaries subject to high nutrient loading and eutrophication. Barnegat Bay, New Jersey has had high nutrient loading in the northern part of the Bay and has exhibited symptoms of eutrophication. The first goal of this study was to examine seasonal denitrification, other N fluxes, and sediment oxygen demand in salt marshes of Barnegat Bay where inputs and concentrations of nutrients vary spatially within the Bay. Second, differences in N process rates among emergent vegetated marsh and permanently flooded isolated ponds were investigated. Finally, the percentage of the N load to the Bay re...

Wet ponds have been used extensively for stormwater control throughout the US, including coastal areas. Despite the widespread application of these water control structures, few studies have investigated how watershed-scale implementation of wet ponds affects downstream water quality or how the pollutant removal efficacy of wet ponds changes over time in a coastal setting. This study utilizes a seven year data set of nutrient, total suspended solid, and chlorophyll-a concentration data collected during baseflow and stormflow from two coastal headwater streams draining a developed (28% impervious) and an undeveloped (1.2% impervious) watershed. The seven year record encompasses before, during, and after a large construction project and concurrent implementation of wet ponds in the developed watershed that drain 97% of the watershed area. Additional nutrient, total suspended solid, and chlorophyll-a concentration data were collected from within a wet pond in the developed watershed during baseflow over a single spring and summer. A comparison of stream water quality before and after the construction project and wet pond implementation in the developed watershed showed that mean chlorophyll-a, nitrate-nitrite (NOx−), organic nitrogen, and total suspended solid concentrations significantly increased, the mean orthophosphate (PO43−) concentration significantly decreased, and the mean ammonium (NH4+) concentration did not change. Over a three year time period after construction and pond implementation, developed stream chlorophyll-a, ammonium, and organic nitrogen concentrations decreased, and nitrate-nitrite, orthophosphate, and total suspended solid concentrations increased compared to the reference stream during the same period, indicating changes in pollutant removal capacity. A comparison of baseflow and stormflow samples during the Post period and samples from a wet pond in the developed watershed indicated that ponds were functioning as sources of chlorophyll-a and total suspended solids to the stream and sinks for nitrate-nitrite. Overall, watershed-scale implementation of wet ponds in the developed watershed failed to mitigate many negative water quality impacts caused by increased development. This study suggests that centralized stormwater management may not be optimal for maintaining water quality in coastal environments, and that pond retrofits combined with frequent excavation could improve pollutant removal by wet ponds. Further research on the effects of nutrient cycling in coastal wet ponds and wet pond maintenance is needed.

A comprehensive carbon budget was constructed to quantify carbon flows through the freshwater-marine continuum of a temperate, microtidal estuary. We performed coordinated measurements of dissolved inorganic carbon and total organic carbon fluxes to resolve spatial variability between and along the channel and shoals and diel variability across the entire estuary for 2 yr. Net ecosystem metabolism (NEM) was the most significant control on carbon flow within estuary regions. However, metabolic rates were spatially coupled such that counteracting fluxes across the channel-shoal gradient or along the river-ocean gradient resulted in system-wide NEM that was closely in balance (–3.0 ± 3.3 to 1.1 ± 4.4 molC m−2 yr−1). Similarly, large diel and seasonal variability in air–water CO2 fluxes were observed during 72 spatial surveys, but these short-term variations generally cancelled out when aggregated to annual budget terms. Although atmospheric exchanges were small (–0.2 ± 0.1 to 2.0 ± 0.4 molC m−2 yr−1), they were subject to large errors (± 4 molC m−2 yr−1) if diel variability was neglected. Internal mechanisms that maintained balanced carbon flows were strongly impacted by river discharge and were only apparent by separately quantifying channel and shoal fluxes. Notably, metabolic responses of the shoal to river forcing outweighed the responses of the channel, and the net impact was contrary to prior relationships derived from synthesis of lower-resolution carbon budgets. Our budget demonstrates that resolution of carbon fluxes at appropriate scales, including channel-shoal and diel variability, is critical to characterizing ecosystem function and the fate of carbon within the river-ocean continuum.

Biotic interactions can structure ecological communities and influence ecosystem functioning. As ecosystem engineers and filter feeders, bivalves often have disproportionately large effects on ecosystem functioning. They also utilize numerous morphological and behavioral responses to reduce predation, which can include changes in their filtration rates. To test the response of Crassostrea virginica filtration rates to the presence of predators, juvenile and adult oysters were separately exposed to varying types of predation risk from Callinectes sapidus and Panopeus herbstii in outdoor mesocosms. Water column chlorophyll a concentrations and crab behavior were measured over the duration of the experiment. Predation risk had no effect on oyster reef drawdown of chlorophyll a, which suggests that this important ecosystem function of oyster reefs is not mediated by behaviorally induced predator effects. Therefore, efforts to model how oyster predators influence filtration rates and associated ecosystem services should focus primarily on the factors that influence oyster mortality rather than predator effects on oyster behavior.

Predators can influence prey traits and behavior (nonconsumptive effects [NCEs]), often with cascading effects for basal resources and ecosystem function. But critiques of NCE experiments suggest that their duration and design produce results that describe the potential importance of NCEs rather than their actual importance. In light of these critiques, we re-evaluated a toadfish (predator), crab (prey), and oyster (resource) NCE-mediated trophic cascade. In a 4-month field experiment, we varied toadfish cue (NCE) and crab density (approximating variation in predator consumptive effects, CE). Toadfish initially benefitted oyster survival by causing crabs to reduce consumption. But this NCE weakened over time (possibly due to prey hunger), so that after 2 months, crab density (CE) dictated oyster survivorship, regardless of cue. However, the NCE ultimately re-emerged on reefs with a toadfish cue, increasing oyster survivorship. At no point did the effect of toadfish cue on mud crab foraging behavior alter oyster population growth or sediment organic matter on the reef, which is a measure of benthic-pelagic coupling. Instead, both decreased with increasing crab density. Thus, within a system shown to exhibit strong NCEs in short-term experiments (days) our study supported predictions from theoretical models: (a) within the generation of individual prey, the relative influence of NCEs appears to cycle over longer time periods (months); and (b) predator CEs, not NCEs, drive longer-term resource dynamics and ecosystem function. Thus, our study implies that the impacts of removing top predators via activities such as hunting and overfishing will cascade to basal resources and ecosystem properties primarily through density-mediated interactions.

Improving mechanistic prediction of shoreline response to sea level rise is currently limited by 1) morphologic complexity of tidal creek shorelines that confounds application of mechanistic models, and 2) availability of suspended sediment measurements to parameterize mechanistic models. To address these challenges we developed a metric to distinguish two morphodynamic classes of tidal creek and tested whether this metric could be used to predict suspended sediment concentration. We studied three small tidal creeks in North Carolina, U.S.A. We collected suspended sediment at one non-tidal and two tidal sites in each creek and measured the wetland and channel width using a geographic information system. In each creek, tidal harmonics were measured for one year, sediment accretion on the salt marsh was measured for three years, and shoreline erosion was measured from aerial photographs spanning 50 years. Additional total suspended solids measurements from seven creeks reported in a national database supplemented our analysis. Among the three intensively studied creeks, shoreline erosion was highest in the most embayed creek (having a wider channel than the width of adjoining wetlands) and lowest in the wetland-dominated creek (having a channel narrower than the width of adjoining wetlands). Wetland sediment accretion rate in the wetland-dominated creek was four times higher than the accretion in the embayed creek. The wetland-dominated tidal creek had over twice the suspended sediment as the most embayed creek. Based on these results, we conclude that our metric of embayed and contrasting wetland-dominated creek morphology provides a guide for choosing between two types of morphodynamic models that are widely used to predict wetland shoreline change. This metric also allowed us to parse the 10 tidal creeks studied into two groups with different suspended sediment concentrations. This relationship between suspended sediment concentration and creek morphology provides a method to estimate sediment concentration for individual tidal creek shorelines from spatial data alone, enabling more accurate parameterization of shoreline change models.

Although species interactions are often assumed to be strongest at small spatial scales, they can interact with regional environmental factors to modify food web dynamics across biogeographic scales. The eastern oyster (Crassostrea virginica) is a widespread foundational species of both ecological and economic importance. The oyster and its associated assemblage of fish and macroinvertebrates is an ideal system to investigate how regional differences in environmental variables influence trophic interactions and food web structure. We quantified multiple environmental factors, oyster reef properties, associated species, and trophic guilds on intertidal oyster reefs within 10 estuaries along 900 km of the southeastern United States. Geographical gradients in fall water temperature and mean water depth likely influenced regional (i.e., the northern, central and southern sections of the SAB) variation in oyster reef food web structure. Variation in the biomass of mud crabs, an intermediate predator, was mostly (84.1%) explained by reefs within each site, and did not differ substantially among regions; however, regional variation in the biomass of top predators and of juvenile oysters also contributed to biogeographic variation in food web structure. In particular, region explained almost half (40.2%) of the variation in biomass of predators of blue crab, a top predator that was prevalent only in the central region where water depth was greater. Field experiments revealed that oyster mortality due to predation was greatest in the central region, suggesting spatial variation in the importance of trophic cascades. However, high oyster recruitment in the middle region probably compensates for this enhanced predation, potentially explaining why relatively less variation (17.9%) in oyster cluster biomass was explained by region. Region also explained over half of the variation in biomass of mud crab predators (55.2%), with the southern region containing almost an order of magnitude more biomass than the other two regions. In this region, higher water temperatures in the fall corresponded with higher biomass of fish that consume mud crabs and of fish that consume juvenile and forage fish, whereas biomas of their prey (mud crabs and juvenile and forage fish, respectively) was generally low in the southern region. Collectively, these results show how environmental gradients interact with trophic cascades to structure food webs associated with foundation species across biogeographic regions.

The rapid growth of the aquaculture industry to meet global seafood demand offers both risks and opportunities for resource management and conservation. In particular, hatcheries hold promise for stock enhancement and restoration, yet cultivation practices may lead to enhanced variation between populations at the expense of variation within populations, with uncertain implications for performance and resilience. To date, few studies have assessed how production techniques impact genetic diversity and population structure, as well as resultant trait variation in and performance of cultivated offspring. We collaborated with a commercial hatchery to produce multiple cohorts of the eastern oyster (Crassostrea virginica) from field-collected broodstock using standard practices. We recorded key characteristics of the broodstock (male : female ratio, effective population size), quantified the genetic diversity of the resulting cohorts, and tested their trait variation and performance across multiple field sites and experimental conditions. Oyster cohorts produced under the same conditions in a single hatchery varied almost twofold in genetic diversity. In addition, cohort genetic diversity was a significant positive predictor of oyster performance traits, including initial size and survival in the field. Oyster cohorts produced in the hatchery had lower within-cohort genetic variation and higher among-cohort genetic structure than adults surveyed from the same source sites. These findings are consistent with "sweepstakes reproduction" in oysters, even when manually spawned. A readily measured characteristic of broodstock, the ratio of males to females, was positively correlated with within-cohort genetic diversity of the resulting offspring. Thus, this metric may offer a tractable way both to meet short-term production goals for seafood demand and to ensure the capacity of hatchery-produced stock to achieve conservation objectives, such as the recovery of self-sustaining wild populations.

Functional trait variation within and across populations can strongly influence population, community, and ecosystem processes, but the relative contributions of genetic vs. environmental factors to this variation are often not clear, potentially complicating conservation and restoration efforts. For example, local adaptation, a particular type of genetic by environmental (G*E) interaction in which the fitness of a population in its own habitat is greater than in other habitats, is often invoked in management practices, even in the absence of supporting evidence. Despite increasing attention to the potential for G*E interactions, few studies have tested multiple populations and environments simultaneously, limiting our understanding of the spatial consistency in patterns of adaptive genetic variation. In addition, few studies explicitly differentiate adaptation in response to predation from other biological and environmental factors. We conducted a reciprocal transplant experiment of first-generation eastern oyster (Crassostrea virginica) juveniles from six populations across three field sites spanning 1000 km in the southeastern Atlantic Bight in both the presence and absence of predation to test for G*E variation in this economically valuable and ecologically important species. We documented significant G*E variation in survival and growth, yet there was no evidence for local adaptation. Condition varied across oyster cohorts: Offspring of northern populations had better condition than offspring from the center of our region. Oyster populations in the southeastern Atlantic Bight differ in juvenile survival, growth, and condition, yet offspring from local broodstock do not have higher survival or growth than those from farther away. In the absence of population-specific performance information, oyster restoration and aquaculture may benefit from incorporating multiple populations into their practices.

We examined seasonal and spatial patterns in dissolved organic carbon (DOC) and chromophoric dissolved organic matter (CDOM) in the Chowan River watershed, North Carolina, a blackwater river which discharges into the second largest estuary in the United States, the Albemarle–Pamlico Estuarine System. From April 2008 to May 2010, DOC concentration did not significantly vary across seasons (range 7.69–30.39 mg L−1); however, CDOM molecular size and aromaticity increased throughout the spring, decreased during the summer and fall, and remained relatively low in the winter. Spectral slope ratios suggested microbial processing of CDOM in the spring and photodegradation of CDOM in the summer and fall. Spatially, DOC and CDOM concentrations were similar in the mainstem and at the mouths of two tributaries, Bennetts Creek and Wiccacon River, but were significantly higher upstream on the tributaries. DOC concentration was positively correlated with CDOM absorbance coefficients at 254 and 350 nm; however, these optical proxies explained only ~60 % of the variance. DOC and CDOM absorption loads to the Albemarle Sound ranged from 2.63 × 1010 g year−1 and 9.84 × 1010 m2 year−1, respectively, in a dry year and 7.9 × 1010 g year−1 and 2.2 × 1011 m2 year−1, respectively, in a wet year, which are comparable to non-blackwater rivers with larger watersheds. Blackwater rivers may therefore represent “hotspots” in coastal carbon chemistry, with seasonal variations in the quality and quantity of DOC and CDOM influencing estuarine food web dynamics and net ecosystem metabolism.

Coastal plain streams in the southeastern United States supply carbon that supports important coastal ecosystems, but the effects of urbanization on carbon export from these streams have not been extensively studied. This study aimed to determine how urbanization changes coastal plain stream organic matter quality, rates of carbon export, and dissolved oxygen dynamics that have implications for stream ecosystem function. Organic matter quality, organic carbon export, and dissolved oxygen concentrations were measured for multiple years (2009 & 2013-2015) in North Carolina coastal plain streams that spanned a gradient of urbanization. Based on spectral characteristics, dissolved organic matter (DOM) quality appeared to shift from characteristic blackwater in minimally impacted streams to clear streamwater in urban streams due to large reductions in chromophoric DOM concentrations, aromaticity, and molecular weight. Differences in spectral indices and characteristics of dissolved organic carbon export suggest that urbanization reduced natural sources of DOM and provided various urban sources of DOM that were likely more bioavailable. Particulate organic matter in the urban streams was indicative of more labile autochthonous sources than that of the less impacted streams, and rates of particulate carbon export increased and shifted to higher flows with watershed impervious surface cover. Diel variation of dissolved oxygen increased with watershed impervious surface cover, indicating that urbanization and associated changes in carbon and nutrient cycling altered stream function. While the effects of urbanization on carbon export were similar to previous studies in other regions, the unique blackwater state of natural streams and receiving waters in the study area make them especially susceptible to negative ecological impacts from altered carbon and nutrient export. Management actions that conserve or restore natural carbon sources to the stream may help mitigate multiple negative effects of urbanization in southeastern US coastal plain streams.

Stormwater control measures (SCMs) have the potential to mitigate negative effects of watershed development on hydrology and water quality. Stormwater regulations and scientific literature have assumed that SCMs are important sites for denitrification, the permanent removal of nitrogen, but this assumption has been informed mainly by short-term loading studies and measurements of potential rates of nitrogen cycling. Recent research concluded that SCM nitrogen removal can be dominated by plant and soil assimilation rather than by denitrification, and rates of nitrogen fixation can exceed rates of denitrification in SCM sediments, resulting in a net addition of nitrogen. Nitrogen cycling measurements from other human-impacted aquatic habitats have presented similar results, additionally suggesting that dissimilatory nitrate reduction to ammonium (DNRA) and algal uptake could be important processes for recycling nitrogen in SCMs. Future research should directly measure a suite of nitrogen cycling processes in SCMs and reveal controlling mechanisms of individual rate processes. There is ample opportunity for research on SCM nitrogen cycling, including investigations of seasonal variation, differences between climatic regions, and trade-offs between nitrogen removal and phosphorus removal. Understanding nitrogen dynamics within SCMs will inform more efficient SCM design and management that promotes denitrification to help mitigate negative effects of urban stormwater on downstream ecosystems.

Restoration of degraded ecosystems is an important societal goal, yet inadequate monitoring and the absence of clear performance metrics are common criticisms of many habitat restoration projects. Funding limitations can prevent adequate monitoring, but we suggest that the lack of accepted metrics to address the diversity of restoration objectives also presents a serious challenge to the monitoring of restoration projects. A working group with experience in designing and monitoring oyster reef projects was used to develop standardized monitoring metrics, units, and performance criteria that would allow for comparison among restoration sites and projects of various construction types. A set of four universal metrics (reef areal dimensions, reef height, oyster density, and oyster size–frequency distribution) and a set of three universal environmental variables (water temperature, salinity, and dissolved oxygen) are recommended to be monitored for all oyster habitat restoration projects regardless of their goal(s). In addition, restoration goal-based metrics specific to four commonly cited ecosystem service-based restoration goals are recommended, along with an optional set of seven supplemental ancillary metrics that could provide information useful to the interpretation of prerestoration and postrestoration monitoring data. Widespread adoption of a common set of metrics with standardized techniques and units to assess well-defined goals not only allows practitioners to gauge the performance of their own projects but also allows for comparison among projects, which is both essential to the advancement of the field of oyster restoration and can provide new knowledge about the structure and ecological function of oyster reef ecosystems.

Rapid population growth and coastal development are primary drivers of marine habitat degradation. Although shoreline hardening or armoring (the addition of concrete structures such as seawalls, jetties, and groins), a byproduct of development, can accelerate erosion and loss of beaches and tidal wetlands, it is a common practice globally. Here, we provide the first estimate of shoreline hardening along US Pacific, Atlantic, and Gulf of Mexico coasts and predict where future armoring may result in tidal wetland loss if coastal management practices remain unchanged. Our analysis indicates that 22 842 km of continental US shoreline – approximately 14% of the total US coastline – has been armored. We also consider how socioeconomic and physical factors relate to the pervasiveness of shoreline armoring and show that housing density, gross domestic product, storms, and wave height are positively correlated with hardening. Over 50% of South Atlantic and Gulf of Mexico coasts are fringed with tidal wetlands that...

Summary Like many ecosystem functions in marine and terrestrial environments, nutrient processing varies dramatically over small spatial scales, making efforts to apply findings within and across ecosystems challenging. In estuaries, information on the influence of habitat context on sediment nutrient cycling is lacking even though this is an important estuarine function with high societal value. We collected triplicate intact sediment cores from restored oyster reefs located in different habitat contexts (adjacent to salt marshes, seagrass beds and mudflats), as well as salt marshes, seagrass beds and mudflats without reefs (controls). Sediment denitrification and fluxes of dissolved inorganic nitrogen were measured under ambient and experimentally elevated water column nitrate levels. Under ambient nitrate, oyster reefs enhanced sediment denitrification by 18–275% over the controls, with highest rates of denitrification in the mudflat context. With experimentally elevated nitrate, the rate of denitrification was higher for oyster reefs compared to the controls in all contexts. This suggests that oyster reefs prime sediments to denitrify nitrate pulses by providing a labile carbon source for denitrifying bacteria. There was a weak positive relationship between oyster density and denitrification under ambient nitrate concentrations and a positive relationship with denitrification that became negative beyond ∼2400 individuals m−2 with elevated nitrate concentrations. The effect of the oyster reef on sediment denitrification was most pronounced in the mudflat context, due to the absence of other structured habitats and higher oyster density, compared to the other two habitat contexts investigated. The consistency of denitrification efficiency across the habitats and lack of difference between habitats with reefs and those without (controls) suggest oyster-mediated denitrification is an effective sink for nitrogen in coastal systems. Synthesis and applications. Our study indicates that oyster-mediated denitrification is dependent on the habitat context of the oyster reef, and variation in oyster density and the relative functional redundancy of oyster reefs where other structured habitats exist (e.g. seagrass and salt marshes) may explain this pattern. Efforts to model and predict ecosystem services provided through oyster reef restoration such as the removal of anthropogenically derived nitrogen should incorporate how habitat context influences ecosystem functions.

Physical-biological coupling helps structure aquatic communities, yet physical factors can vary widely across large, biogeographic scales. The eastern oyster (Crassostrea virginica) is an ecosystem engineer that creates intertidal reefs, filters water, promotes denitrification, stabilizes shorelines, and provides habitat throughout the inner waters of the U.S. South Atlantic Bight (SAB). We quantified physical variables (temperature, salinity, duration and depth of water inundation), oyster reef properties (slope, vertical relief), and oyster recruitment, density, and biomass over a 1500 km scale across the SAB for one year. All oyster-level and many reef-level variables exhibited unimodal patterns with latitude that peaked in Georgia and South Carolina estuaries. Of the physical variables, salinity and duration of water inundation over reefs were similar across all sites, and temperature declined linearly with increasing latitude, except during summer when it had no relationship with latitude. Depth of water inundation over reefs was the only physical variable with a prominent unimodal distribution that may explain the oyster’s biological responses. Similar durations of water inundation across all reefs coupled with higher water depths in the mid-latitude sites collectively indicate that these sites experience higher flow velocity, energy and net water volume delivery per unit time. The resultant higher accumulation of oyster biomass and heightened reef structure in areas of higher tidal energy emphasize that the physical forcing of the SAB (especially large cross-shelf gradients in tidal amplification) affects the biology of the eastern oyster, including its reef properties, with potential implications for community structure and ecosystem service delivery across a biogeographic scale.

Wet ponds are a common type of stormwater control measure (SCM) in coastal areas of the southeastern US, but their internal nitrogen dynamics have not been extensively studied. Using flow-through intact sediment core incubations, net sediment N2 fluxes before and after a nitrate addition from five wet ponds spanning a range of ages (3.25-10years old) were quantified through membrane inlet mass spectrometry during early summer. Multiple locations within a single wet pond (6.16years old) were also sampled during ambient conditions in late summer to determine the combined effects of depth, vegetation, and flow path position on net N2 fluxes at the sediment-water interface. All pond sediments had considerable rates of net nitrogen fixation during ambient conditions, and net N2 fluxes during nitrate-enriched conditions were significantly correlated with pond age. Following a nitrate addition to simulate storm conditions, younger pond sediments shifted towards net denitrification, but older ponds exhibited even higher rates of net nitrogen fixation. The pond forebay had significantly higher rates of net nitrogen fixation compared to the main basin, and rates throughout the pond were an order of magnitude higher than the early summer experiment. These results identify less than optimal nitrogen processing in this common SCM, however, data presented here suggest that water column mixing and pond sediment excavation could improve the capacity of wet ponds to enhance water quality by permanently removing nitrogen.

The eastern oyster (Crassostrea virginica) is a foundation species providing significant ecosystem services. However, the roles of oyster microbiomes have not been integrated into any of the services, particularly nitrogen removal through denitrification. We investigated the composition and denitrification potential of oyster microbiomes with an approach that combined 16S rRNA gene analysis, metabolic inference, qPCR of the nitrous oxide reductase gene (nosZ), and N2 flux measurements. Microbiomes of the oyster digestive gland, the oyster shell, and sediments adjacent to the oyster reef were examined based on next generation sequencing (NGS) of 16S rRNA gene amplicons. Denitrification potentials of the microbiomes were determined by metabolic inferences using a customized denitrification gene and genome database with the paprica (PAthway PRediction by phylogenetIC plAcement) bioinformatics pipeline. Denitrification genes examined included nitrite reductase (nirS and nirK) and nitrous oxide reductase (nosZ), which was further subdivided by genotype into clade I (nosZI) or clade II (nosZII). Continuous flow through experiments measuring N2 fluxes were conducted with the oysters, shells, and sediments to compare denitrification activities. Paprica properly classified the composition of microbiomes, showing similar classification results from Silva, Greengenes and RDP databases. Microbiomes of the oyster digestive glands and shells were quite different from each other and from the sediments. The relative abundance of denitrifying bacteria inferred by paprica was higher in oysters and shells than in sediments suggesting that oysters act as hotspots for denitrification in the marine environment. Similarly, the inferred nosZI gene abundances were also higher in the oyster and shell microbiomes than in the sediment microbiome. Gene abundances for nosZI were verified with qPCR of nosZI genes, which showed a significant positive correlation (F1,7 = 14.7, p = 6.0x10-3, R2 = 0.68). N2 flux rates were significantly higher in the oyster (364.4 ± 23.5 μmol N-N2 m-2 h-1) and oyster shell (355.3 ± 6.4 μmol N-N2 m-2 h-1) compared to the sediment (270.5 ± 20.1 μmol N-N2 m-2 h-1). Thus, bacteria carrying nosZI genes were found to be an important denitrifier, facilitating nitrogen removal in oyster reefs. In addition, this is the first study to validate the use of 16S gene based metabolic inference as a method for determining microbiome function, such as denitrification, by comparing inference results with qPCR gene quantification and rate measurements.

Enhancingpopulations ofsuspension feedingbivalves,particularlythe easternoyster,Crassostreavirginica, has been proposed as a means of mitigating eutrophication in coastal waters. Review of studies evaluating the effects of C. virginica on nitrogen (N) cycling found that oysters can have effects on water quality that vary by orders of magnitude among sites, seasons, and growing condition (e.g., oyster reefs, aquaculture). Nitrogen contained in phytoplankton consumed by oysters may be returned to the water column, assimilatedintooystertissue and shell,buriedin the sediments,orreturnedtothe atmosphereas dinitrogen gas, primarily via denitrification. Accurately quantifying oyster-related N removal requires detailed knowledge oftheseprimaryfatesofNincoastalwaters.Areviewofexistingdatademonstratedthatthecurrentstateof knowledgeisincompleteinmanyrespects.Nitrogenassimilatedintooystertissueandshellpergramofdry weight was generallysimilaracrosssitesand in oysters growingon reefscomparedto aquaculture.Data on long-term burial of N associated with oyster reefs or aquaculture are lacking. When compared to suitable reference sites, denitrification rates were not consistently enhanced. Depending on environmental and oyster growing conditions, changes in denitrification rates varied by orders of magnitude among studies and did not always occur. Oyster aquaculture rarely enhanced denitrification. Unharvested oyster reefs frequently enhanced denitrification rates. Incorporating oysters into nutrient reduction strategies will require filling gaps in existing data to determine the extent to which relationships between N removal and environmental and/or growing conditions can be generalized.

Denitrification in tidal freshwater river channels and their adjoining freshwater wetlands greatly affects nitrogen export from river networks, yet the relative importance of these two habitats to nitrogen export has not been examined. Knowledge of how these habitats contribute to denitrification of the river nitrogen load is critical for improving models of nitrogen transport. Denitrification rates were measured in sediments from the channel, bank, and floodplain at upstream and downstream sites of two forested tidal freshwater zones (TFZs) in North Carolina, the New River and Newport River, using membrane inlet mass spectrometry to measure N2 production. Denitrification rates did not usually differ statistically between the channel, bank, and floodplain, although denitrification was highest on the floodplain at the upstream site in the Newport River. When these rates were extrapolated across the entire area of the TFZ, the channel contributed more to the N2 flux than the riparian zone. These results indicate that denitrification rates are comparable between the channel and riparian zone in forested TFZs, and that the importance of the channel versus the riparian zone depends on channel and floodplain morphology.

Multiple stressors affect estuarine shorelines including erosion, sea level rise and impacts from human development of adjacent lands. Increasingly common features of coastal development are vertical shoreline stabilization structures such as bulkheads. Bulkheads are designed to prevent land loss and flooding through the construction of a vertical wall anchored to the land. However, they break the connection between land and water and are barriers to upland plant migration. This disconnect can affect hydrology, alter nutrient and sediment supplies, and lead to marsh loss. We measured the effects of bulkheads on sediment nitrogen fluxes, including denitrification (DEN), at three representative estuarine shoreline types: natural marsh (no bulkhead), bulkhead without marsh, and bulkheads with marshes of varying widths. Sediment cores were taken mid-marsh or, 2 m seaward of bulkhead in sites lacking marsh in northern, central and southern coastal regions of North Carolina. Concentrations of N2 and O2 were measured using a membrane inlet mass spectrometer. In addition, sediment organic matter and inorganic nitrogen concentrations were quantified. Average DEN rate was 93.1 ± 7.0 µmol N m−2 h−1 with the highest rates in the summer and lowest rates in the winter. Sediment oxygen demand was positively correlated with DEN rate (R2 = 0.43, p

The introduction of non-native species occurs within a context of other anthropogenic impacts: thus a holistic approach is needed to understand interactive effects. Installation of shoreline protection structures is increasing in response to rising sea levels and increasing frequency of intense storms. Shoreline hardening structures can facilitate establishment of non-native species with multiple potential consequences. We measured abundances of both native and non-native Codium, a green macroalga, on natural hard substrates (oyster reefs) and artificial substrates (bulkheads and revetments) in two estuaries and assessed the effects of each Codium species on nitrogen fixation and net N2 fluxes. Native C. decorticatum was the most abundant (86 %) Codium on oyster reefs, while exotic C. fragile dominated (99 %) artificial substrates. N2 production via denitrification was greater than nitrogen fixation for both species and the net N2 production associated with non-native C. fragile was greater than with native C. decorticatum. Comparing our results with surveys conducted in the 1940s before C. fragile had invaded, indicates that non-native Codium has outcompeted native Codium on artificial substrates, but that natural substrate provided by oyster reefs remains a refuge for native Codium. Although shoreline hardening with artificial structures can reduce ecosystem services provided by coastal marsh and other habitats, an unexpected beneficial consequence was the N2 production associated with the non-native Codium, which has the potential to mitigate anthropogenic nutrient loading. Our results illustrate that the interaction between multiple anthropogenic impacts can be positive, and indicate that non-ephemeral macroalgae could be an overlooked component in nitrogen removal from marine ecosystems by enhancing denitrification.

The role of habitat-providing species in facilitating associated species abundance and diversity is recognized as a key structuring force in many ecosystems. Reciprocal facilitation by associates, often involving multiple species, can be important for the maintenance of the host species. As with other multi-species interactions (e.g. multiple predator effects), non-additive relationships may be common among these associates, yet relatively few studies have examined potential interactions among multiple facilitator species. We combined field surveys and a mesocosm experiment to examine the independent and interactive effects of two co-occurring facilitator species, ribbed mussels Geukensia demissa and fiddler crabs Uca pugilator, on their host salt marsh plant species, cordgrass Spartina alterniflora. We also experimentally examined how these relationships varied across different host plant genotypes. Overall, facilitator effects increased with increasing facilitator density. There was a significant interaction between mussel and fiddler crab presence, indicating that the effects of each species on cordgrass were dependent on the presence of the other facilitator species. In addition, there were strong interactions among mussels, fiddler crabs, and plant genotype, with greater variation in the performance of individual genotypes when fiddler crabs were absent. Our work reinforces the importance of considering multiple responses when assessing the functional redundancy of co-occurring facilitators, as species are seldom completely redundant across the range of services they provide. It also highlights that the strength and direction of species interactions can vary due to genetic variation within the interacting species.

Drivers of large-scale variability in parasite prevalence are not well understood. For logistical reasons, explorations of spatial patterns in parasites are often performed as observational studies. However, to understand the mechanisms that underlie these spatial patterns, standardized and controlled comparisons are needed. Here, we examined spatial variability in infection of an important fishery species and ecosystem engineer, the oyster (Crassostrea virginica) by its pea crab parasite (Zaops ostreus) across 700 km of the southeastern USA coastline. To minimize the influence of host genetics on infection patterns, we obtained juvenile oysters from a homogeneous source stock and raised them in situ for 3 months at multiple sites with similar environmental characteristics. We found that prevalence of pea crab infection varied between 24 and 73 % across sites, but not systematically across latitude. Of all measured environmental variables, oyster recruitment correlated most strongly (and positively) with pea crab infection, explaining 92 % of the variability in infection across sites. Our data ostensibly suggest that regional processes driving variation in oyster recruitment similarly affect the recruitment of one of its common parasites.

We hypothesized that mats of a nonnative macroalga, Gracilaria vermiculophylla, which is often found incorporated several centimeters into intertidal mudflat sediments, would increase net denitrification rates relative to bare sediments. At moderate densities (, 40 g dry weight [dry wt] m22), net denitrification rates in June (182.37 6 16.87 mmol N-N2 m22 h21), July (213.19 6 16.30 mmol N-N2 m22 h21), and September (124.82 6 11.17 mmol N-N2 m22 h21) were higher than rates previously documented with macroalgal mats. Compared with rates from bare sediment in June (25.48 6 15.09 mmol N-N2 m22 h21) and September (46.47 6 15.79 mmol N-N2 m22 h21), net denitrification was significantly higher when G. vermiculophylla was present. Rates measured on bare sediment in July (254.81 6 19.86 mmol N-N2 m22 h21) were not significantly different from G. vermiculophylla counterparts, most likely because of highly reduced conditions in G. vermiculophylla cores, which could have limited nitrification. July incubations also demonstrate that at higher densities (, 120 g dry wt m22 G. vermiculophylla), denitrification rates can drop, suggesting a potential biomass threshold for macroalgal enhancement of denitrification.

In shallow photic systems, the benthic filter, including microphytobenthos and denitrifiers, is important in preventing or reducing release of remineralized NH4 + to the water column. Its effectiveness can be impacted by climate-related drivers, including temperature and storminess, which by increasing wind and freshwater delivery can resuspend sediment, reduce salinity and deliver nutrients, total suspended solids, and chromophoric dissolved organic matter (CDOM) to coastal systems. Increases in temperature and freshwater delivery may initiate a cascade of responses affecting benthic metabolism with impacts on sediment properties, which in turn regulate nitrogen cycling processes that either sequester (via microphytobenthos), remove (via denitrification), or increase sediment nitrogen (via remineralization, nitrogen fixation, and dissimilatory nitrate reduction to ammonium). We conducted a seasonal study at shallow stations to assess the effects of freshwater inflow, temperature, wind, light, and CDOM on sediment properties, benthic metabolism, nitrogen cycling processes, and the effectiveness of the benthic filter. We also conducted a depth study to constrain seasonally varying parameters such as temperature to better assess the effects of light availability and water depth on benthic processes. Based on relationships observed between climatic drivers and response variables, we predict a reduction in the effectiveness of the benthic filter over the long term with feedbacks that will increase effluxes of N to the water column with the potential to contribute to system eutrophication. This may push shallow systems past a tipping point where trophic status moves from net autotrophy toward net heterotrophy, with new baselines characterized by degraded water quality.

How does river hydrology and morphology change due to tidal influence? We contend that this is a question of particular consequence to many earth surface disciplines, but one that has not been adequately addressed. Previous studies have relied on gradients in channel morphology and stratigraphy to infer energy regime of channels. However, in tidal rivers geomorphology influences the energy regime while the energy regime influences morphology; thus, geomorphic and stratigraphic patterns do not fully resolve the mechanisms which lead to change. We addressed this problem by comparing measurements of hydraulic energy and channel morphology along a tidal gradient to predictions of these characteristics in the absence of tides, and attributed the differences to tidal processes. Measurements of discharge, channel area, and energy dissipation (in kJ day–1) were made over a 24·8 hour period at four sites spanning the non-tidal to tidal freshwater Newport River, NC. We then predicted those characteristics under non-tidal conditions using hydraulic geometry relationships and literature values from coastal plain rivers. Discharge was enhanced more than 10-fold by tide, and this tidal effect increased from upstream to downstream along the tidal gradient. Cross-sectional area increased three-fold due to tide. Energy dissipation measured in the upper tidal river was four-fold lower than predicted to occur in the absence of tide because tides decreased average velocity and discharge. Energy dissipation measured downstream was similar to that predicted to occur without tides, although there was large uncertainty in predicted values downstream. While this limited dataset does not permit us to make broad generalizations for definitive models, it does provide a proof-of-concept for a new approach to addressing a critical problem at the interface of fluvial and coastal morphology. Copyright © 2013 John Wiley & Sons, Ltd.

Functional trait variation within and across populations can strongly influence population, community, and ecosystem processes, but the relative contributions of genetic vs. environmental factors to this variation are often not clear, potentially complicating conservation and restoration efforts. For example, local adaptation, a particular type of genetic by environmental (G*E) interaction in which the fitness of a population in its own habitat is greater than in other habitats, is often invoked in management practices, even in the absence of supporting evidence. Despite increasing attention to the potential for G*E interactions, few studies have tested multiple populations and environments simultaneously, limiting our understanding of the spatial consistency in patterns of adaptive genetic variation. In addition, few studies explicitly differentiate adaptation in response to predation from other biological and environmental factors. We conducted a reciprocal transplant experiment of first‐generation eastern oyster (Crassostrea virginica) juveniles from six populations across three field sites spanning 1000 km in the southeastern Atlantic Bight in both the presence and absence of predation to test for G*E variation in this economically valuable and ecologically important species. We documented significant G*E variation in survival and growth, yet there was no evidence for local adaptation. Condition varied across oyster cohorts: Offspring of northern populations had better condition than offspring from the center of our region. Oyster populations in the southeastern Atlantic Bight differ in juvenile survival, growth, and condition, yet offspring from local broodstock do not have higher survival or growth than those from farther away. In the absence of population‐specific performance information, oyster restoration and aquaculture may benefit from incorporating multiple populations into their practices.

The use of ecological network analysis (ENA) in the study of nutrient cycling in general and N cycling in particular has been less developed than for carbon flow through food webs. No standard rules have been applied to the construction of the N cycling networks, although there appears to be two general forms: those that try to focus on biogeochemical processing and those that track N through the food web. Many of the N cycling networks, especially the biogeochemical ones, address aspects of eutrophication. While food web N cycling networks have not directly addressed eutrophication, they have extended the concepts of nutrient limitation and sufficiency beyond that for primary producers alone. Also, new concepts of organization and control of material cycling are being evaluated through these networks. Here we review the history and state of ecological network analysis within coastal ecosystems in the context of better understanding N cycling.

Valuation of ecosystem services can provide evidence of the importance of sustaining and enhancing those resources and the ecosystems that provide them. Long appreciated only as a commercial source of oysters, oyster reefs are now acknowledged for the other services they provide, such as enhancing water quality and stabilizing shorelines. We develop a framework to assess the value of these services. We conservatively estimate that the economic value of oyster reef services, excluding oyster harvesting, is between $5500 and $99,000 per hectare per year and that reefs recover their median restoration costs in 2–14 years. In contrast, when oyster reefs are subjected to destructive oyster harvesting, they do not recover the costs of restoration. Shoreline stabilization is the most valuable potential service, although this value varies greatly by reef location. Quantifying the economic values of ecosystem services provides guidance about when oyster reef restoration is a good use of funds.

Assessing nitrogen dynamics in the estuarine landscape is challenging given the unique effects of individual habitats on nitrogen dynamics. We measured net N2 fluxes, sediment oxygen demand, and fluxes of ammonium and nitrate seasonally from five major estuarine habitats: salt marshes, seagrass beds (SAV), oyster reefs, and intertidal and subtidal flats. Net N2 fluxes ranged from 332 ± 116 μmol N-N2 m−2 h−1 from oyster reef sediments in the summer to −67 ± 4 μmol N-N2 m−2 h−1 from SAV in the winter. Oyster reef sediments had the highest rate of N2 production of all habitats. Dissimilatory nitrate reduction to ammonium (DNRA) was measured during the summer and winter. DNRA was low during the winter and ranged from 4.5 ± 3.0 in subtidal flats to 104 ± 34 μmol 15NH 4 + m−2 h−1 in oyster reefs during the summer. Annual denitrification, accounting for seasonal differences in inundation and light, ranged from 161.1 ± 19.2 mmol N-N2 m−2 year−1 for marsh sediments to 509.9 ± 122.7 mmol N-N2 m−2 year−1 for SAV sediments. Given the current habitat distribution in our study system, an estimated 28.3 × 106 mol of N are removed per year or 76 % of estimated watershed nitrogen load. These results indicate that changes in the area and distribution of habitats in the estuarine landscape will impact ecosystem function and services.

Summary 1. Coastal rivers can have long tidally influenced reaches that are affected by tides but do not contain saline water. These tidal freshwater reaches have steep geomorphic gradients where the river transitions from narrow, heavily shaded streams to wide, unshaded channels. The influence of these gradients on river ecosystem production is poorly understood. 2. We characterised gradients in irradiance, geomorphology, water clarity and chlorophyll a along 9- to 16-km tidal freshwater reaches of the Newport and White Oak Rivers in North Carolina, USA, and examined the effect of nutrient enrichment on phytoplankton growth in the Newport River. Underwater irradiance was modelled at 2–4 week intervals along both rivers using measurements of the above-canopy irradiance, canopy cover, water column light attenuation (Kd) and water depth. Suspended material (TSS), dissolved organic carbon (DOC) and chlorophyll a were sampled at 2-week interval at five sites on the Newport River and on four dates at four sites on the White Oak River over the course of one year. 3. Phytoplankton nutrient limitation was assessed at three locations along the tidal gradient. River water was collected during March, April, June and October, and incubated in 10-L plastic outdoor containers under ambient water temperature and sunlight. Additions of inorganic nitrogen and phosphorus served as treatments; growth rate during the 4 days of incubation was calculated from the change in chlorophyll a concentration over time. 4. Canopy cover decreased from more than 90% to

This research details changes in lake algal community structure that occurred during dystrophication. We conducted a paleolimnological investigation of Pungo Lake, a shallow, dystrophic system near the coast of North Carolina, USA. Multiple chemical and biological proxies were measured on a sediment core, including sedimentary photosynthetic pigments, lignin-phenols, nutrients, and δ13C. Data analysis identified three zones of algal community structure corresponding to three regimes of organic matter inputs. Predystrophic conditions represented a period of low organic inputs but substantial algal abundance (diatoms and other algal types). The period of dystrophication preceded European settlement (1850) and showed an increase in organic matter deposition, lignin, and a change in lignin type. Lignin-phenols and δ13C signatures of organic matter indicated that terrestrial organic matter inputs increased during this period, possibly as a result of wetland expansion. Dystrophication also corresponded to an increase in algal groups that favor low light environments (cyanobacteria and cryptophytes).

Tidal freshwater wetlands (TFW) alter nitrogen concentrations in river water, but the role of these processes on a river’s downstream nitrogen delivery is poorly understood. We examined spatial and temporal patterns in denitrification in TFW of four rivers in North Carolina, USA and evaluated the relative importance of denitrification rate and inundation on ecosystem-scale N2 efflux. An empirical model of TFW denitrification was developed to predict N2 efflux using a digital topographic model of the TFW, a time series of water level measurements, and a range of denitrification rates. Additionally, a magnitude-frequency analysis was performed to investigate the relative importance of storm events on decadal patterns in N2 efflux. Spatially, inundation patterns exerted more influence on N2 efflux than did the range of denitrification rate used. Temporal variability in N2 efflux was greatest in the lower half of the tidal rivers (near the saline estuary) where inundation dynamics exerted more influence on N2 efflux than denitrification rate. N2 efflux was highest in the upper half of the rivers following storm runoff, and under these conditions variation in denitrification rate had a larger effect on N2 efflux than variability in inundation. The frequency-magnitude analysis predicted that most N2 efflux occurred during low flow periods when tidal dynamics, not storm events, affected TFW inundation. Tidal hydrology and riparian topography are as important as denitrification rate in calculating nitrogen loss in TFW; we present a simple empirical model that links nitrogen transport in rivers with loss due to denitrification in TFW.

Relative fitness of three bloom-forming and potentially toxic cyanobacteria from the subtropical St. John's River, Florida was investigated under a range of nutrient conditions, during a bloom dominated by Cylindrospermopsis raciborskii. Nitrogen (N) was the primary nutrient limiting phytoplankton primary productivity and biomass. Phytoplankton biomass was also enhanced by phosphorus (P) added either alone or jointly with N, suggesting different components of the phytoplankton experienced distinct nutrient limitations. Based on quantitative PCR, the diazotrophic cyanobacteria Anabaena sp. and C. raciborskii were responsible for the primary production response to P additions, while the nondiazotrophic Microcystis aeruginosa appeared to benefit from N released from the diazotrophs. Cylindrospermopsis raciborskii maintained high net growth rates under diazotrophic and nondiazotrophic conditions, while Anabaena sp. growth was significantly reduced under DIN enrichment. C. raciborskii appears to be a generalist with regard to N source, a lifestyle traditionally not considered a viable ecological strategy among diazotrophs. Using facultative diazotrophy, C. raciborskii gains a growth advantage under fluctuating DIN conditions, such as systems that are under the influence of anthropogenic N loading events. The described niche differentiation may be a key factor explaining the recent global expansion of C. raciborskii.

Carolina bays are nearly ubiquitous along ~ 1300 km of the North American Atlantic Coastal Plain, but relatively few bays have been examined in detail, making their formation and evolution a topic of controversy. The Lake Mattamuskeet basin, eastern North Carolina, USA, is a conglomeration of multiple Carolina bays that form a > 162 km2 lake. The eastern shoreline of the lake is made up of a 2.9-km-wide plain of parabolic ridges that recorded rapid shoreface progradation. The lower shoreface deposit contains abundant charcoal beds and laminae dated 6465–6863 cal yr BP, corresponding with initiation of a lacustrine environment in the eastern part of the lake. A core from the western part of the lake sampled a 1541–1633 cal yr BP charcoal bed at the base of the lacustrine unit, indicating formation of this part of the basin postdates the eastern basin. Lake Mattamuskeet has no relationship to the Younger Dryas or a linked impact event because rim accretion significantly postdates 12,000 cal yr BP. The shoreline progradation, and association of charcoal beds with the oldest lake sediment in both main parts of the basin, suggest that fire and subsequent hydrodynamic processes were associated with initial formation of these Carolina bays.