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In the United States (US), salt marshes are especially vulnerable to the effects of projected sea level rise, increased storm frequency, and climatic changes. Sentinel-2 data offer the opportunity to observe the land surface at high spatial resolutions (10 m). The Sentinel-2 data, encompassing Cumberland Island National Seashore, Fort Pulaski National Monument, and Canaveral National Seashore, were analyzed to identify temporal changes in salt marsh presence from 2016 to 2020. ENVI-derived unsupervised and supervised classification algorithms were applied to determine the most appropriate procedure to measure distant areas of salt marsh increases and decreases. The Normalized Difference Vegetation Index (NDVI) was applied to describe the varied vegetation biomass spatially. The results from this approach indicate that the ENVI-derived maximum likelihood classification provides a statistical distribution and calculation of the probability (>90%) that the given pixels represented both water and salt marsh environments. The salt marshes captured by the maximum likelihood classification indicated an overall decrease in salt marsh area presence. The NDVI results displayed how the varied vegetation biomass was analogous to the occurrence of salt marsh changes. Areas representing the lowest NDVI values (−0.1 to 0.1) corresponded to bare soil areas where a salt marsh decrease was detected. [ABSTRACT FROM AUTHOR]

Salt marshes are dynamic ecosystems that change in response to local geographic and geologic factors as well as sea level changes. Most east coast salt marshes are the result of rising sea levels since the end of the last ice age, about 20,000 ybp. To compound this natural process, anthropogenic manipulations for farming, development and other purposes have occurred for centuries. Alterations to salt marshes for the purpose of controlling larval mosquitoes at their source, at least along the east coast of the United States, have occurred since the early twentieth century. These alterations have included large-scale manipulations such as extensive parallel grid-ditching and impounding. Within the last 50 years, more selective source reduction methods such as Open Marsh Water Management (OMWM) have been employed with fewer deleterious impacts to marsh resources. Even more recently, the more holistic approach of Integrated Marsh Management (IMM) has been used with considerable success particularly in the northeastern and Mid-Atlantic states. IMM not only uses OMWM techniques but incorporates the judicious use of mosquito control pesticides, tidal flow restoration, impoundment management, wildlife habitat enhancement, invasive plant control, and selective shallow ditching ("runneling") depending on local conditions and management plans. As many marshes are becoming wetter and either drowning or migrating inland (where possible) due to the effects of increasing rates of sea level rise, the compounding long-term impacts of parallel grid-ditching and past manipulations on marsh surface elevation and hydrology are being more intently studied. These changes in saltmarsh dynamics have had and will continue to have impacts on where saltmarsh mosquitoes are produced, which could have corollary effects on public health and quality of life near coastal communities. As salt marshes continue to change, mosquito control agencies can play a significant role in providing input for salt marsh restoration and management in addition to their primary objective of vector control and enhancing quality of life. [ABSTRACT FROM AUTHOR]

The coastal ecosystems of temperate North America provide a variety of ecosystem services including high rates of carbon sequestration. Yet, little data exist for the carbon stocks of major tidal wetland types in the Pacific Northwest, United States. We quantified the total ecosystem carbon stocks (TECS) in seagrass, emergent marshes, and forested tidal wetlands, occurring along increasing elevation and decreasing salinity gradients. The TECS included the total aboveground carbon stocks and the entire soil profile (to as deep as 3 m). TECS significantly increased along the elevation and salinity gradients: 217 ± 60 Mg C/ha for seagrass (low elevation/high salinity), 417 ± 70 Mg C/ha for low marsh, 551 ± 47 Mg C/ha for high marsh, and 1,064 ± 38 Mg C/ha for tidal forest (high elevation/low salinity). Soil carbon stocks accounted for >98% of TECS in the seagrass and marsh communities and 78% in the tidal forest. Soils in the 0–100 cm portion of the profile accounted for only 48%–53% of the TECS in seagrasses and marshes and 34% of the TECS in tidal forests. Thus, the commonly applied limit defining TECS to a 100 cm depth would greatly underestimate both carbon stocks and potential greenhouse gas emissions from land‐use conversion. The large carbon stocks coupled with other ecosystem services suggest value in the conservation and restoration of temperate zone tidal wetlands through climate change mitigation strategies. However, the findings suggest that long‐term sea‐level rise effects such as tidal inundation and increased porewater salinity will likely decrease ecosystem carbon stocks in the absence of upslope wetland migration buffer zones. [ABSTRACT FROM AUTHOR]

Foundation plant species play a critical role in coastal wetlands, often modifying abiotic conditions that are too stressful for most organisms and providing the primary habitat features that support entire ecological communities. Here, we consider the influence of climatic drivers on the distribution of foundation plant species within coastal wetlands of the conterminous USA. Using region-level syntheses, we identified 24 dominant foundation plant species within 12 biogeographic regions, and we categorized species and biogeographic regions into four groups: graminoids, mangroves, succulents, and unvegetated. Literature searches were used to characterize the level of research directed at each of the 24 species. Most coastal wetlands research has been focused on a subset of foundation species, with about 45% of publications directed at just one grass species—Spartina alterniflora. An additional 14 and 8% have been directed, respectively, at two mangrove species—Rhizophora mangle and Avicennia germinans. At the national scale, winter temperature extremes govern the distribution of mangrove forests relative to salt marsh graminoids, and arid conditions can produce hypersaline conditions that increase the dominance of succulent plants, algal mats, and unvegetated tidal flats (i.e., salt flats, salt pans) relative to graminoid and mangrove plants. Collectively, our analyses illustrate the diversity of foundation plant species in the conterminous USA and begin to elucidate the influence of climatic drivers on their distribution. However, our results also highlight critical knowledge gaps and identify emerging research needs for assessing climate change impacts. Given the importance of plant-mediated processes in coastal wetland ecosystems, there is a pressing need in many biogeographic regions for additional species- and functional group-specific research that can be used to better anticipate coastal wetland responses to rising sea levels and changing temperature and precipitation regimes. [ABSTRACT FROM AUTHOR]

Plant sexual reproduction is an important driver of plant community maintenance, dispersal, and recovery from disturbance. Despite this, sexual reproduction in habitats dominated by clonally spreading perennial species, such as salt marshes, is often ignored. Communities dominated by long-lived perennial species can still depend on sexual reproduction for recolonizing large disturbed patches or for establishing in new patches, such as restored sites. We investigated the influence of restoration and elevation on flowering phenology, potential seed and seedling production, and insect flower damage of the dominant salt marsh grass, Spartina alterniflora, in reference and restored marshes in southeastern Louisiana, USA. We additionally tested whether elevation gradients or soil parameters could explain differences in sexual reproduction between sites. We demonstrate that sediment-slurry amendment restoration may not affect flowering phenology or insect flower damage at ecologically relevant levels, but that restoration activity increases sexual reproductive output at the patch scale. Restoration activity affected reproductive dynamics more often than changes in elevation alone. Restoration of subsiding salt marsh habitat by altering the soil environment may increase sexual reproductive capacity of these wetlands. [ABSTRACT FROM AUTHOR]

In coastal marsh ecosystems, porewater salinity strongly affects vegetation distribution and productivity. To simulate marsh porewater salinity, an integrated, spatially explicit model was developed, accounting for tidal inundation, evaporation, and precipitation, as well as lateral and vertical exchanges in both surface waters and the subsurface. It was applied to the Duplin River marsh, Sapelo Island, USA, over a 3-year period, which covered both drought and wet conditions. Simulated porewater salinity in the low and high marsh correlated with Duplin River salinity, with evapotranspiration and precipitation leading to substantial variations in porewater salinities across seasons, in particular in the high marsh. The model revealed substantial interannual variability in marsh soil conditions, and--due to its processbased approach linked to external forcings--can be used to explore effects of sea level rise and changes in hydrological forcings on marsh soil conditions. [ABSTRACT FROM AUTHOR]

Species distribution models have been applied across a wide range of spatial scales to generate information for conservation planning. Understanding how well models transfer through space and time is important to promote effective species-habitat conservation. Here, we assess model transferability in coastal tidal marshes of the southeastern United States using count data of a widespread marsh bird: the Clapper Rail (Rallus crepitans). We developed species-habitat models at a state level in both South Carolina and Georgia, and then assessed how well top models from each state predicted abundance in the other state. Internally (locally) validated models performed well with reasonable fit (SC: R2 = 0.35, GA: R2 = 0.14), and high significance (P = 0.0005); however, both models performed poorly when predicting abundance from the other state (R2 = 0.03 and 0.003). To assess the consequences of this lack of transferability, we applied the South Carolina- and Georgia-derived parameter estimates to habitat features in South Carolina and identified the top 25% of tidal marsh habitat that each model predicted within the state. There was minimal overlap between model habitat quality predictions (<5%). Our results address the predictive power and uncertainties that arise from using habitat associations and climate models to predict species distributions or abundance in locations without training data. We discuss potential reasons model transferability was not successful and address the need for better regional datasets and the importance of intraspecific variability in response to environmental gradients. [ABSTRACT FROM AUTHOR]

Salt marsh losses have been documented worldwide because of land use change, wave erosion, and sea-level rise. It is still unclear how resistant salt marshes are to extreme storms and whether they can survive multiple events without collapsing. Based on a large dataset of salt marsh lateral erosion rates collected around the world, here, we determine the general response of salt marsh boundaries to wave action under normal and extreme weather conditions. As wave energy increases, salt marsh response to wind waves remains linear, and there is not a critical threshold in wave energy above which salt marsh erosion drastically accelerates. We apply our general formulation for salt marsh erosion to historical wave climates at eight salt marsh locations affected by hurricanes in the United States. Based on the analysis of two decades of data, we find that violent storms and hurricanes contribute less than 1% to long-term salt marsh erosion rates. In contrast, moderate storms with a return period of 2.5 mo are those causing the most salt marsh deterioration. Therefore, salt marshes seem more susceptible to variations in mean wave energy rather than changes in the extremes. The intrinsic resistance of salt marshes to violent storms and their predictable erosion rates during moderate events should be taken into account by coastal managers in restoration projects and risk management plans. [ABSTRACT FROM AUTHOR]

Tidal salt marshes provide important ecological services, habitat, disturbance regulation, water quality improvement, and biodiversity, as well as accumulation and sequestration of carbon dioxide (CO) in vegetation and soil organic matter. Different management practices may alter their capacity to provide these ecosystem services. We examined soil properties (bulk density, percent organic C, percent N), C and N pools, C sequestration and N accumulation at four marshes managed with open marsh water management (OMWM) and four marshes that were not at U.S. Fish and Wildlife National Wildlife Refuges (NWRs) on the East Coast of the United States. Soil properties (bulk density, percent organic C, percent N) exhibited no consistent differences among managed and non-OMWM marshes. Soil organic carbon pools (0-60-cm depth) also did not differ. Managed marshes contained 15.9 kg C/m compared to 16.2 kg C/m in non-OMWM marshes. Proportionately, more C (per unit volume) was stored in surface than in subsurface soils. The rate of C sequestration, based on Cs and Pb dating of soil cores, ranged from 41 to 152 g/m/year. Because of the low emissions of CH from salt marshes relative to freshwater wetlands and the ability to sequester C in soil, protection and restoration of salt marshes can be a vital tool for delivering key ecosystem services, while at the same time, reducing the C footprint associated with managing these wetlands. [ABSTRACT FROM AUTHOR]

Most salt marshes in the USA have been degraded by human activities, and coastal managers are faced with complex choices among possible actions to restore or enhance ecosystem integrity. We applied structured decision making (SDM) to guide selection of monitoring variables and management priorities for salt marshes within the National Wildlife Refuge System in the northeastern USA. In general, SDM is a systematic process for decomposing a decision into its essential elements. We first engaged stakeholders in clarifying regional salt marsh decision problems, defining objectives and attributes to evaluate whether objectives are achieved, and developing a pool of alternative management actions for achieving objectives. Through this process, we identified salt marsh attributes that were applicable to monitoring National Wildlife Refuges on a regional scale and that targeted management needs. We then analyzed management decisions within three salt marsh units at Prime Hook National Wildlife Refuge, coastal Delaware, as a case example of prioritizing management alternatives. Values for salt marsh attributes were estimated from 2 years of baseline monitoring data and expert opinion. We used linear value modeling to aggregate multiple attributes into a single performance score for each alternative, constrained optimization to identify alternatives that maximized total management benefits subject to refuge-wide cost constraints, and used graphical analysis to identify the optimal set of alternatives for the refuge. SDM offers an efficient, transparent approach for integrating monitoring into management practice and improving the quality of management decisions. [ABSTRACT FROM AUTHOR]

The Gulf Killifish ( Fundulus grandis) is one of the most abundant nekton species in the US Gulf of Mexico (GOM) salt marshes, providing an important trophic link in these systems. Recently, the use of F. grandis as an indicator species of salt marsh health in the region has been suggested because its Atlantic coast congener, the Mummichog ( Fundulus heteroclitus) has filled such a role due to its demonstrated high site fidelity and small-scale movements. Given the similar life histories between species, F. grandis was assumed to exhibit the same type of small-scale movements, although this has not been documented. During summer 2013, we collected and marked 1,719 fish from a northern Gulf of Mexico estuary, recapturing 959 (56 % recapture rate). Of these recaptured fish, only 31 moved from their original tagging location, and of these, 29 moved only 100 m between sites connected by salt marsh. Based on these results, F. grandis appears to exhibit high site fidelity and make only small-scale movements, similar to F. heteroclitus, supporting its role as an indicator species. [ABSTRACT FROM AUTHOR]

Tidal inundation extent and duration, and water drainage and retention by marsh peat - marsh hydrology - determine most physical and ecological characteristics of salt marsh systems. Ditching, installed across nearly all marshes on the US east coast by 1940 to control mosquitoes, alters marsh hydrology. Two linchpin papers are used here as springboards to review the literature that describes the resulting effects, which clearly include reduced water table height for most marshes and changes in avian populations. Effects on invertebrate populations, including mosquitoes, are generally less, although to a smaller degree than is sometimes reported. Impacts on nekton are not clear, although probably negative. Tidal range and the degree of tide asymmetry appear to have greater effects on intermarsh variations in effects from ditching than has generally been appreciated or studied. Overall, although changed patterns of nutrient releases and promotion of Phragmites australis invasions are important ecological effects extending beyond individual sites, and salt marsh aesthetics are marred, ditching impacts are less than certain other anthropogenic alterations of coastal processes that affect salt marshes and estuarine ecology to a much greater extent. [ABSTRACT FROM AUTHOR]

Abstract: Salt marshes can be a significant source of MeHg in coastal marine organisms, however the sources and cycling of Hg in salt marsh sediments, and in coastal environments in general, remain unclear. We analyzed surface and cored sediments from a salt marsh and adjacent upland sand dune in Cabretta Island, Georgia, USA, for total mercury (HgT), Hg isotopes and trace metal concentrations to better constrain the sources of Hg in this coastal environment. HgT concentrations are lower in the upland sands (1–6ng/g) than in the marsh sediments (6–16ng/g). HgT shows a positive correlation with total organic content (TOC) and increasing proportion of fines in the sediments. Trace metal concentrations also show a positive correlation with HgT in the marsh sediments regardless of chemical affinity (i.e. chalcophile, siderophile or lithophile). All these data are consistent with surface adsorption (either directly on to sediments or on to organic matter) as a dominant mechanism of Hg and metals accumulation in the marsh sediments. The surface sediments show significant mass independent fractionation (MIF) of odd Hg isotopes: the upland dune sands have zero to slightly negative Δ199Hg (−0.07‰ to −0.14‰) and the marsh surface sediments have positive Δ199Hg (0.48‰ to 0.79‰). As in the surface samples, well-sorted sand layers in the cored sediments have low Hg concentrations and zero to slightly negative Δ199Hg, whereas fine particle-rich layers have higher Hg concentrations and positive Δ199Hg values. In the absence of any evidence for MIF of Hg isotopes by bacteria mediated methylation–demethylation reactions, the observed Hg isotope differences between marsh and upland sands can be explained by different sources of Hg. We suggest that local atmospheric Hg deposition dominates the Hg budget in the ombrotrophic upland sand, while the positive MIF in the marsh sediments are consistent with Hg dominantly of seawater origin. While in situ processes, like photoreduction and evasion can overprint the Hg depositional isotope signature, their effect on the sediments is currently unconstrained. Nevertheless, our data show that Hg isotopes can delineate different sources of Hg in a pristine coastal environment and at small spatial scales. Thus natural background isotope variability should be assessed as a baseline when Hg isotopes are used as tracers of Hg in anthropogenically-influenced sites. [Copyright &y& Elsevier]

Abstract: Remote-sensing based cover mapping has a long history of use in natural resource management for a wide-range of applications. In order to be effectively employed, remote-sensing based cover maps must be accurate and meet the spatial scale inherent to the phenomena of interest. In this study, we employed the Random Forests algorithm in a supervised classification approach to construct a fine-scale (i.e., 1.0meter pixel resolution) remote-sensing based cover map of coastal dune and salt marsh ecosystems at Cape Cod National Seashore, USA. We achieved high overall classification accuracies (i.e., 75.1% and 86.8% correct classification rate for the dune and salt marsh study areas, respectively) with a large proportion of the misclassified holdout validation assessment points being errors of commission between overlapping and/or ecologically similar cover classes. In addition, we were able to considerably reduce the predictor variable set by using a forward selection variable reduction method while achieving modestly higher classification accuracies compared to the global model. Our results suggest that coastal dune and salt marsh ecosystems can be mapped at a fine spatial resolution with reasonably high classification accuracy using a supervised Random Forests-based approach such as ours. [Copyright &y& Elsevier]

Abstract: We have constructed a database of Holocene relative sea level (RSL) observations for the Atlantic coast of the United States. The database contains 492 index points, which locate the position of RSL in time and space, and 344 limiting dates, which constrain the minimum or maximum limit of former sea level. The majority of the index points in the database are from 6 ka BP to present, with only 7% older than 6 ka BP. Spatially, index points are distributed between Maine and South Carolina, but there is an absence of data from Georgia and the Atlantic coast of Florida. The database is sub-divided into 16 regions based on the distance from the former Laurentide Ice Sheet and are classified depending upon their susceptibility to compaction. The index points and limiting data demonstrate that RSL did not exceed present (0 m) during the Holocene except potentially in regions 1 and 2 (Eastern Maine and Southern Maine). Rates of RSL change were highest during the early Holocene and have decreased over time, due to the diminishing response of the Earth’s mantle to glacial isostatic adjustment and reduction of ice equivalent meltwater input. Along the Atlantic coast of the United States the linear rate of RSL rise prior to 4 ka BP ranged from 0.5 to 4.5 mm a−1, compared to 0.6–1.8 mm a−1 from 4 ka BP to AD 1900. The database suggests minimal (<0.3 mm/yr) changes in these rates of RSL rise during the late Holocene. Deglaciation of the Laurentide Ice Sheet caused the spatial variability captured by the database. The maximum rate of late Holocene (and ongoing) RSL rise occurred in mid-Atlantic regions (New Jersey and Inner Delaware) because of collapse of the peripheral forebulge. [Copyright &y& Elsevier]

The effects of bioturbation by the mud fiddler crab ( Uca pugnax) on salt marsh seedling recruitment were investigated experimentally in this study. Burrowing and foraging activity caused a large amount of soil disturbance, which in turn negatively impacted the establishment of seedlings. Either seeds did not germinate or seedlings were uprooted or buried. Although the majority of the published literature suggests a positive influence of Uca spp. on salt marsh plant growth, at high densities they have the potential to hinder the re-colonization of areas made bare by previous disturbance. This study illustrates the perhaps underappreciated role that bioturbators can have on vegetation patterns in salt marshes and other ecosystems. [ABSTRACT FROM AUTHOR]

The article discusses research on trait-mediated indirect interaction (TMII) between top predators and dominant vascular plants in U.S. salt marshes. Field observations show that marsh periwinkle Littoraria irrorata tend to graze extensive monocultures of Spartina alterniflora in the ecosystems studied. Experimental details which include the selection of a marsh area, measurement of grazer habitat use, and evaluation of longitudinal grazing scars seen on Spartina leaves are reported.

We present new sea-level reconstructions for the past 2100 y based on salt-marsh sedimentary sequences from the US Atlantic coast. The data from North Carolina reveal four phases of persistent sea-level change after correction for glacial isostatic adjustment. Sea level was stable from at least BC 100 until AD 950. Sea level then increased for 400 y at a rate of 0.6 mm/y, followed by a further period of stable, or slightly falling, sea level that persisted until the late 19th century. Since then, sea level has risen at an average rate of 2.1 mm/y, representing the steepest century-scale increase of the past two millennia. This rate was initiated between AD 1865 and 1892. Using an extended semiempirical modeling approach, we show that these sea-level changes are consistent with global temperature for at least the past millennium. [ABSTRACT FROM AUTHOR]

The article discusses a study completed in 2010 on how changing sea levels affect Saltmarsh Sparrows, Ammodramus caudacutus in Latin. It states that climate change has an impact on coastal areas where the birds make their nests. To study that impact, it reports that researchers observed 191 nests at two salt marshes in the northeastern part of the U.S., monitoring where nests were made, tide height and frequency of flooding. They found that less than 20% were spared from flooding and rising waters, making the birds vulnerable to sea level changes.

The shrub Iva frutescens, which occupies the terrestrial border of U.S. Atlantic Coast salt marshes, supports a food web that varies strongly across latitude. We tested whether latitudinal variation in plant quality (higher at high latitudes), consumption by omnivores (a crab, present only at low latitudes), consumption by mesopredators (ladybugs, present at all latitudes), or the life history stage of an herbivorous beetle could explain continental-scale field patterns of herbivore density. In a mesocosm experiment, crabs exerted strong top-down control on herbivorous beetles, ladybugs exerted strong top-down control on aphids, and both predators benefited plants through trophic cascades. Latitude of plant origin had no effect on consumers. Herbivorous beetle density was greater if mesocosms were stocked with beetle adults rather than larvae, and aphid densities were reduced in the "adult beetle" treatment. Treatment combinations representing high and low latitudes produced patterns of herbivore density similar to those in the field. We conclude that latitudinal variation in plant quality is less important than latitudinal variation in top consumers and competition in mediating food web structure. Climate may also play a strong role in structuring high-latitude salt marshes by limiting the number of herbivore generations per growing season and causing high overwintering mortality. [ABSTRACT FROM AUTHOR]

Abstract: We described the distributions of foraminifera from ten physiographically distinct salt marshes in the Albemarle–Pamlico estuarine system, North Carolina using 193 surface samples. We defined elevation-dependent ecological zones at individual sites using cluster analysis and detrended correspondence analysis. Additionally, seven principal biozones of salt-marsh foraminifera were identified that have distinctive spatial distributions reflecting a pattern of salinity regimes caused by the current configuration of barrier-island inlets. High salinity sites along the southern Outer Banks are associated with sub-tidal calcareous assemblages, low marshes dominated by Miliammina fusca and high marsh environments defined by Haplophragmoides wilberti, Trochammina inflata and Arenoparrella mexicana. In contrast, lower salinity marshes have Ammobaculites spp. in sub-tidal settings, Miliammina fusca-dominated low marshes and high marsh settings characterized by Jadammina macrescens. Spatial variation of foraminiferal populations and the potential for biozones to migrate in response to changing inlet configuration and salinity, suggests that datasets of modern salt-marsh foraminifera from multiple environments would be appropriate for reconstructing Holocene relative sea level in North Carolina. [Copyright &y& Elsevier]

Recently, strong top-down (consumer) control of cordgrass (Spartina alterniflora) has been demonstrated. Here, we manipulated the densities of cordgrass consumers, acridid grasshoppers (Melanoplus bivittatus and Melanoplus femurrubrum), to examine their impact on cordgrass in the Plum Island Estuary (PIE), MA, USA. After 1 month, there was no detectable effect of grasshopper density on S. alterniflora biomass and grasshoppers at the highest densities (34 individuals per square meter) consumed only ~14% of the standing stock biomass. However, significant impacts of grasshopper density on grazing damage were seen. For example, plant damage and scarring length increased by 160% and 6,156%, respectively, at the highest grasshopper densities relative to exclusion (zero grasshoppers) densities. Plant height was significantly reduced with increasing grasshopper densities, although this may be a function of leaf tip removal instead of reduced plant growth. No other strong consumers of cordgrass (e.g., Littoraria irrorata, Prokelisia marginata) were observed in PIE and we suggest that consumer regulation of cordgrass is weak in this system. [ABSTRACT FROM AUTHOR]

Abstract: Plant-flow interactions on the surface of tidal wetlands result in flow characteristics that are profoundly different from non-vegetated flows. Reductions in mean flow velocity and turbulence, especially the vertical components, limit vertical mixing and may impact a wide range of processes including geochemical exchanges at the sediment water interface, larval recruitment and dispersion, and sediment deposition and retention. The goal of this paper is to quantify horizontal and vertical components of velocity, turbulence intensity and total turbulent kinetic energy in Spartina alterniflora canopies in southeastern North Carolina and to relate flow characteristics to particulate transport on the marsh surface. Another aim of this paper is to assess the extent to which the distribution of standing biomass affects mean flow and turbulence by comparing S. alterniflora data to other canopy types and through a series of canopy manipulations which altered canopy height and stem densities. The results of this study indicate that flow velocity, turbulence intensity, and total turbulent kinetic energy (TKE) are significantly reduced within the vegetated canopy and that this reduction is inversely related to the amount of biomass present in the water column. Within the canopy, approximately 50% of the initial mean velocity and TKE is reduced within 5m of the canopy edge. Within the canopy, mean velocity and TKEhoriz usually exceeded vertical velocity or TKEvert and the vertical components of flow were attenuated more strongly than the horizontal. These results suggest that within the vegetation, turbulence contributes more to lateral advection than to vertical mixing. As a result, total suspended solid concentrations were shown to decrease logarithmically with distance from the canopy edge and to decrease at a faster rate in more densely vegetated regions of the canopy (i.e. lower TKEvert) as compared to areas of sparser vegetation (i.e. higher TKEvert). [Copyright &y& Elsevier]

Ecological interactions may vary geographically as a function of diversity, density, or per capita interaction strengths, but we know little about the relative importance of these three mechanisms. We examined variation in species richness, abundance, and interactions among leaf-chewing herbivores and the dominant salt-marsh plant Spartina alterniflora along the Atlantic Coast of the United States. High-latitude S. alterniflora plants are more palatable to herbivores than are low-latitude plants. Within this range of latitude, diversity and density of the dominant leaf-chewing consumers, snails and grasshoppers, in Spartina-dominated portions of the marsh varied little. Low-latitude plants, however, experienced much greater levels of leaf damage from consumers than did high-latitude plants. Per capita feeding rates of low-latitude snails (Littoraria irrorata) and grasshoppers (Orchelimum fidicinum) in the laboratory were greater than feeding rates of high-latitude snails (Melampus bidentatus) and grasshoppers (Conocephalus spartinae). In field experiments, low-latitude snails strongly suppressed S. alterniflora growth, but high-latitude snails had no effect on primary production. Thus, latitudinal differences in the effect of herbivores on plants (i.e., interaction strength), driven by differences in per capita effects among species, rather than differences in diversity or density, may contribute to selection for latitudinal differences in plant palatability. Because geographical differences in interaction strength can occur in the absence of differences in diversity or density, linking biogeography with community ecology will require experimental studies that explicitly measure interaction strength at multiple geographic locations. [ABSTRACT FROM AUTHOR]

Analysis of aerial photographs and historic charts indicates that the barrier beach at Brigantine, NJ has migrated landward 300 to 400 m since 1869, primarily as a result of overwash during hurricanes and winter storms. A series of vibracores from the backbarrier salt marsh reveals a millennial-scale stratigraphic record of overwash deposition. Carbon-14 (C-14) and Cesium-137 (Cs-137) radioisotopic methods were used to date overwash deposits (washovers). The ages of recent washovers are consistent with deposition during intense storms in 1938, 1944, 1950, and 1962. An additional overwash deposit recovered in five of the sediment cores was likely deposited by an intense hurricane strike in 1821 or possibly in 1788. Two prehistoric overwash fans were likely deposited by intense storms striking the New Jersey Coast in the 7th to 14th centuries and 6th to 7th centuries A.D. The landward barrier migration indicates that the older overwash sediments were likely transported a considerably greater distance than the more recent overwash fans. The greater distance of transport may indicate that the prehistoric storms that deposited overwash fans across the study site were more intense than the most intense storm to strike this coast in the historic period, the hurricane of 1821. The spatially variable occurrence of overwash deposition at this site points to a need for multisite stratigraphic surveys of extensive stretches of the coast in order to develop reliable records of past intense storm frequency from backbarrier environments. [Copyright &y& Elsevier]

Twelve salt marshes in south Louisiana (USA) were classified as either ‘impaired’ or ‘healthy’ before a summer sample collection of above- and below-ground biomass and determination of sediment accretion rates. The above-ground biomass of plant tissues was the same at both impaired and healthy salt marshes and was not a good predictor of marsh health. However, below-ground root biomass in the upper 30 cm was much lower in the impaired marshes compared to the healthy marshes. Compromises to root production apparently occur before there is an obvious consequence to the above-ground biomass, which may quickly collapse before remedial action can be taken. The subsequent change in vertical position of the marsh surface may be equivalent to many years of accretion, and be irreversible within decades without considerable effort. These results are consistent with the hypothesis that it is the plant's below-ground accumulation of organic matter, not inorganic matter that governs the maintenance of salt marsh ecosystem in the vertical plane. Reversing the precursor conditions leading to marsh stress before the collapse of the above-ground biomass occurs is therefore a prudent management objective and could be easier than restoration. [ABSTRACT FROM AUTHOR]

Submarine groundwater discharge (SGD) generally occurs through permeable sediments where the hydraulic head of an aquifer is above sea level, and often includes a recirculated seawater component. In order to determine SGD to the Great Sippewissett Marsh, West Falmouth, MA, we measured the activities of four radium isotopes (226Ra, 228Ra, 223Ra, 224Ra) at the marsh inlet in July 1999 and 2001 and compared our data with Ra activities measured at the same location in 1983 and 1985. A radium-based approach for estimating SGD to the marsh yielded a summer average of 3900 m3 day−1. This flux was in good agreement with independent estimates from the literature, which ranged from 600 to 23,000 m3 day−1. Radium activities of the long-lived isotopes (226Ra, 228Ra) were on average more than two times higher in 1999 than during the three other time periods. These results suggest that drought conditions leading to enhanced seawater–sediment interactions may be an important mechanism in delivering certain dissolved substances to coastal waters. [Copyright &y& Elsevier]

Dredging is a large-scale anthropogenic disturbance agent in coastal and estuarine habitats that can profoundly affect water quality. We examined the impact of a small-scale dredging operation in a salt marsh in South Carolina by comparing nutrient levels (NH4+, NOx, PO4−) and total suspended solid concentrations before and during dredging activities. Nutrient enrichment was evaluated within the context of tidal, seasonal, and inter-annual variability by using long-term water chemistry data provided by the North Inlet–Winyah Bay National Estuarine Research Reserve. The conditions of the dredging permit (i.e., its relatively small scale), the season chosen for the work (fall–winter), the nature of the sediments dredged (coarse-grained), and the amount of natural variability in the estuary’s water chemistry (even on a daily time-scale) all minimized the impact of the dredging activities. Results of this study will add to the limited body of empirical data that should be considered in evaluating future dredging permit applications related to shallow estuarine waterways. [Copyright &y& Elsevier]

Abstract In 1980 the State of Connecticut began a tidal marsh restoration program targeting systems degraded by tidal restrictions and impoundments. Such marshes become dominated by common reed grass (Phragmites australis ) and cattail (Typha angustifolia and T. latifolia ), with little ecological connection to Long Island Sound. The management and scientific hypothesis was that returning tidal action, reconnecting marshes to Long Island Sound, would set these systems on a recovery trajectory. Specific restoration targets (i.e., pre-disturbance conditions or particular reference marshes) were considered unrealistic. However, it was expected that with time restored tides would return ecological functions and attributes characteristic of fully functioning tidal salt marshes. Here we report results of this program at nine separate sites within six marsh systems along 110 km of Long Island Sound shoreline, with restoration times of 5 to 21 years. Biotic parameters assessed include vegetation, macroinvertebrates, and use by fish and birds. Abiotic factors studied were soil salinity, elevation and tidal flooding, and soil water table depth. Sites fell into two categories of vegetation recovery: slow, ca. 0.5%, or fast, more than 5% of total area per year. Although total cover and frequency of salt marsh angiosperms was positively related to soil salinity, and reed grass stand parameters negatively so, fast versus slow recovery rates could not be attributed to salinity. Instead, rates appear to reflect differences in tidal flooding. Rapid recovery was characterized by lower elevations, greater hydroperiods, and higher soil water tables. Recovery of other biotic attributes and functions does not necessarily parallel those for vegetation. At the longest studied system (rapid vegetation recovery) the high marsh snail Melampus bidentatus took two decades to reach densities comparable with a nearby reference marsh, whereas the amphipod Orchestia grillus was well established... [ABSTRACT FROM AUTHOR]

Abstract Tidal flow to salt marshes throughout the northeastern United States is often restricted by roads, dikes, impoundments, and inadequately sized culverts or bridge openings, resulting in altered ecological structure and function. In this study we evaluated the response of vegetation and nekton (fishes and decapod crustaceans) to restoration of full tidal flow to a portion of the Sachuest Point salt marsh, Middletown, Rhode Island. A before, after, control, impact study design was used, including evaluations of the tide-restricted marsh, the same marsh after reintroduction of tidal flow (i.e., tide-restored marsh), and an unrestricted control marsh. Before tidal restoration vegetation of the 3.7-ha tide-restricted marsh was dominated by Phragmites australis and was significantly different from the adjacent 6.3-ha Spartina -dominated unrestricted control marsh (analysis of similarities randomization test, p < 0.001). After one growing season vegetation of the tide-restored marsh had changed from its pre-restoration condition (analysis of similarities randomization test, p < 0.005). Although not similar to the unrestricted control marsh, Spartina patens and S. alterniflora abundance increased and abundance and height of Phragmites significantly declined, suggesting a convergence toward typical New England salt marsh vegetation. Before restoration shallow water habitat (creeks and pools) of the unrestricted control marsh supported a greater density of nekton compared with the tide-restricted marsh (analysis of variance, p < 0.001), but after one season of restored tidal flow nekton density was equivalent. A similar trend was documented for nekton species richness. Nekton density and species richness from marsh surface samples were similar between the tide-restored marsh and unrestricted control marsh. Fundulus heteroclitus and Palaemonetes pugio were the numerically dominant fish and decapod species in all sampled habitats. This study provides an example of a... [ABSTRACT FROM AUTHOR]

Abstract A growing number of studies have assessed the functional equivalency of restored and natural salt marshes. Several of these have explored the use of functional trajectories to track the increase in restored marsh function over time; however, these studies have disagreed as to the usefulness of such models in long-term predictions of restored marsh development. We compared indicators of four marsh functions (primary production, soil organic matter accumulation, sediment trapping, and maintenance of plant communities) in 6 restored and 11 reference (matched to restored marshes using principal components analysis) salt marshes in the Great Bay Estuary. The restored marshes were all constructed and planted on imported substrate and ranged in age from 1 to 14 years. We used marsh age in a space-for-time substitution to track constructed salt marsh development and explore the use of trajectories. A high degree of variability was observed among natural salt marsh sites, displaying the importance of carefully chosen reference sites. As expected, mean values for constructed site (n = 6) and reference site (n = 11) functions were significantly different. Using constructed marsh age as the independent variable and functional indicator values as dependent variables, nonlinear regression analyses produced several ecologically meaningful trajectories (r 2 > 0.9), demonstrating that the use of different-aged marshes can be a viable approach to developing functional trajectories. The trajectories illustrated that although indicators of some functions (primary production, sediment deposition, and plant species richness) may reach natural site values relatively quickly (<10 years), others (soil organic matter content) will take longer. [ABSTRACT FROM AUTHOR]

Abstract For an estuarine restoration project to be successful it must reverse anthropogenic effects and restore lost ecosystem functions. Restoration projects that aim to rehabilitate endangered species populations make project success even more important, because if misjudged damage to already weakened populations may result. Determining project success depends on our ability to assess the functional state or “performance” and the trajectory of ecosystem development. Mature system structure is often the desired “end point” of restoration and is assumed to provide maximum benefit for target species; however, few studies have measured linkages between structure and function and possible benefits available from early recovery stages. The Salmon River estuary, Oregon, U.S.A., offers a unique opportunity to simultaneously evaluate several estuarine restoration projects and the response of the marsh community while making comparisons with a concurring undiked portion of the estuary. Dikes installed in three locations in the estuary during the early 1960s were removed in 1978, 1987, and 1996, creating a “space-for-time substitution” chronosequence. Analysis of the marsh community responses enables us to use the development state of the three recovering marshes to determine a trajectory of estuarine recovery over 23 years and to make comparisons with a reference marsh. We assessed the rate and pattern of juvenile salmon habitat development in terms of fish density, available prey resources, and diet composition of wild juvenile Oncorhynchus tshawytscha (chinook salmon). Results from the outmigration of 1998 and 1999 show differences in fish densities, prey resources, and diet composition among the four sites. Peaks in chinook salmon densities were greatest in the reference site in 1998 and in the youngest (1996) site in 1999. The 1996 marsh had higher densities of chironomids (insects; average 864/m2 ) and lower... [ABSTRACT FROM AUTHOR]

Abstract Since 1972 over 940 ha (2,300 ac) of leveed former salt marsh sites around San Francisco Bay have been restored to tidal action, purposely or through natural processes. The evolution of these sites can inform predictions of rates of marshplain evolution and establishment of tidal channel systems. A review of the history of 15 re-flooded sites ranging in size from 18 to 220 ha (45 to 550 ac) and in age from 2 to 29 years indicates that marshplain vegetation with more than 50% cover was established at nine of the sites within 4 to 20 years. The remaining six sites aged 2 to approximately 20 years continue to be less than 50% vegetated. The evolution of these sites is consistent with the following simple conceptual model of the physical evolution of restored tidal marshes in subsided breached sites. Initially, deposition of estuarine sediment builds up mudflats that allow vegetation establishment once elevations are high enough for vegetation to survive. Sites that are initially lower in the tidal frame take longer to vegetate than those that are initially higher. Three factors appear to retard the time frame for vegetation establishment: limited estuarine suspended sediment supply, erosion of deposited estuarine muds by internally generated wind waves, and restricted tidal exchange. These factors affect evolution more significantly in larger sites. The comparatively short time frame for vegetation colonization and marshplain evolution experienced in earlier, smaller, and/or less subsided breached levee restorations may not necessarily be replicable by simple levee breaching on larger subsided restoration sites now being planned. Our review of the 15 sites also indicates that the formation of tidal channels within the marshes is greatly dependent on whether and how high the site was filled before breaching. Filled sites at high intertidal elevations (above approximately 0.3 m below mean higher high water) can vegetate quickly but after several decades may... [ABSTRACT FROM AUTHOR]

One of the world's largest tidal wetland restoration projects was conceived to offset the loss of nekton to once-through cooling at a power plant on Delaware Bay, USA. An aggregated food chain model was employed to estimate the area of tidal salt marsh required to replace these losses. The 5040 ha was comprised of two degraded marsh types – Phragmites-dominated marshes and diked salt hay farms – at eleven locations in oligo-mesohaline and polyhaline reaches of the estuary. At a series of `summits' convened with noted experts in the field, it was decided to apply an ecological engineering approach (i.e., `self design', and minimal intrusion) in a landscape ecology framework to the restoration designs while at the same time monitoring long-term success of the project in the context of a `bound of expectation'. The latter encompassed a range of reference marsh planforms and acceptable end-points established interactively with two advisory committees, numerous resource agencies, the permitting agency and multiple-stakeholder groups. In addition to the technical recommendations provided by the project's advisors, public health and safety, property protection and public access to the restored sites were a constant part of the dialogue between the utility, its consulting scientists and the resource/permitting agencies. Adaptive management was used to maintain the restoration trajectories, ensure that success criteria were met in a timely fashion, and to protect the public against potential effects of salt intrusion into wells and septic systems, and against upland flooding. Herbicide spray, followed by prescribed burns and altered microtopography were used at Phragmites-dominated sites, and excavation of higher order channels and dike breaching were the methods used to initiate the restorations at the diked salt hay farms. Monitoring consisted of evaluating the rate of re-vegetation and redevelopment of natural drainage networks, nekton response to the restorations, and focused research on nutrient flux, nekton movements, condition factors, trophic linkages, and other specific topics. Because of its size and uniqueness, the Estuary Enhancement Program as this project is known, has become an important case study for scientists engaged in restoration ecology and the application of ecological engineering principles. The history of this project, and ultimately the Restoration Principles that emerged from it, are the subjects of this paper. By documenting the pathways to success, it is hoped that other restoration ecologists and practitioners will benefit from the experiences we have gained. [ABSTRACT FROM AUTHOR]

The recent population explosion along the coastal zoneof the southeast United States and the Gulf of Mexicohas accelerated the development rate of waterfrontproperty, and particularly along the Gulf Coast ofMississippi. We compared use of pristine and alteredshoreline habitat by early life-history stages of fishand crustaceans to assess the potential effects ofthis development. Monthly beam trawls were taken at13 sites along shoreline habitats characterized by Juncus/Spartinamarsh, natural beach, and areasaltered by bulkheads and rubble. A total of 52,068fish (n = 48 taxa) and 288,715 crustaceans (n = 24taxa) were collected during a two year study. The mostabundant fish groups included gobiids, sciaenids,clupeids, and engraulids. Crustaceans, excluding thecopepods, were numerically dominated by mysids, bothcaridean and penaeid shrimps, and crabs ( Callinectesspp.). Demersal residents were dominatedby Gobiosoma boscand Palaemonetessp.whereas clupeiformes, sciaenids and penaeid shrimpswere dominant among the nektonic and demersaltransient species. These taxa were least abundantalong stretches of shoreline altered with bulkheads orrubble, and were generally most abundant in shorelinehabitats fringed with Juncus/Spartinagrasses.This general pattern in nekton relative abundanceparallel the low diversity (reciprocal of Simpson'sDominance Index) values adjacent to altered marsh tohigh values adjacent to pristine marsh or beachhabitats, suggesting that habitats adjacent to alteredmarsh sites are less frequently used as nurseryhabitat compared to natural sites. These data supportthe hypothesis that shorelines adjacent to marshhabitat are critical to various life history stages ofecologically- and commercially-important species,illustrate the influence of altering natural marshhabitat on resident/transient nekton, and providequantitative data for resource managers in thecontinued efforts to preserve the complex estuarinemarsh landscape. [ABSTRACT FROM AUTHOR]

A new species, Porphyra rediviva (Bangiales, Rhodophyta), is described from the northeast Pacific based on morphological, cytological, reproductive, ecological, and molecular characters. This species occurs at high intertidal levels in salt marshes along the coasts of Washington, Oregon, and northern California and exhibits a growth optimum at reduced salinity. It is further distinguished by a distinct demarcation between male and female sectors of the gametophytic thalli of epilithic specimens. The species is found most commonly in the drift or trapped in Salicornia beds, but these detached blades never have been found with sporangia or gametangia. Molecular analyses using restriction fragment length polymorphism patterns polymerase chain reaction-amplified ribosomal DNA (rDNA) show that this salt marsh Porphyra is conspecific throughout its range and is distinct from other Pacific Porphyra species with similar reproductive patterns. Based on molecular data, P. rediviva is related most closely to P. purpurea from the North Atlantic. Fixed rDNA polymorphisms between the two taxa, however, support ecological and cytological evidence that they should be considered different species. [ABSTRACT FROM AUTHOR]

Primary production roles of edaphsc algae associated with the sediments beneath four monospecific canopies of vascular plants were determined over an annual cycle in a Mississppi salt marsh. The edaphic algal flora was dominated by small, motile pennate diatoms. Algal production (as measured by [SUP14]C uptake) was generally highest in spring-early summer and lowest in fall. Hourly rates ranged from a lou of 1.4 mg C/m[SUP2] in Juncus roemerianus Scheele to a high of 163 mg C/m[SUP2] beneath the Scirpus olneyi Gray canopy. Stepwise multiple regressions identified a soil moisture index and chlorophyll a as the beat environmental predictors of hourly production; light energy reaching the marsh surface and sediment and ate temperature proved of little value. Adding the relative abundances of 13 diatom taxa to the set of independent variables only slightly increased R[SUP2]; however, virtually all variables selected were diatom taxa. R[SUP2] was only 0. 38 for the Spartina alterniflora Loisel. habitat but ranged from 0. 70 to 0.87 for the, remaining three vascular plant zones. Annual rates of algal production (g C/m[SUP2] were estimated as follows: Juncus (28). Spartina (57). Distichlis spicata L. Greene (88). and Scirpus(151). The ratio of annual edaphic algal production to vascular plant net aerial production (EAP/VPP) was 10-12% for the first three habitata and 61% for Scirpus. Chlorophyll a concentrations, annual algal production rates, and EAP / VPP values were comparable to those determined in Texas. Delaware, and Massachusetts salt marshes but lower than those reported for Georgia and particularly California marshes. [ABSTRACT FROM AUTHOR]

Edaphic diatoms were collected on a seasonal basis from beneath five monospecific stands of spermatophytes on Graveline Bay Marsh (Mississippi) from 14 October 1976 through 21 June 1977. Of the 119 diatom taxa encountend, only seven were restricted to a single edaphic habitat, and five of these accounted for 17.2% of the individuals comprising the community associated with Distichlis spicata (L.) Greene. The single most abundant diatom was Navicula tripunctata (Müll.) Bory, which accounted for 21.5% of all individuals counted during the study. Based on a 2-way ANOVA of species diversity (H[SUP1]) and the number of taxa in a sample, edaphic diatom community diversity was highest beneath D. spicata and Spartina patens (Ait.) Muhl. Lowest beneath Sp. Alterniflora Loisel: and Juncus roemerianus Scheele, and somewhat intermediate for the Scirpus olneyi Gray habitat. Structural differences between selected community pairs were quantified using a similarity index (SIMI) and the values generated were exceedingly variable. A multiple regression analysis revealed that structural differences amongst edaphic diatom communities were related to differences in elevation, far red light energy, ammonia nitrogen, soil moisture, and tentatively, height of the spermatophyte canopy. [ABSTRACT FROM AUTHOR]

Although there is mounting evidence that biodiversity is an important and widespread driver of ecosystem multifunctionality, much of this research has focused on small-scale biodiversity manipulations. Hence, which mechanisms maintain patches of enhanced biodiversity in natural systems and if these patches elevate ecosystem multifunctionality at both local and landscape scales remain outstanding questions. In a 17 month experiment conducted within southeastern United States salt marshes, we found that patches of enhanced biodiversity and multifunctionality arise only where habitat-forming foundation species overlap—i.e. where aggregations of ribbed mussels (Geukensia demissa) form around cordgrass (Spartina alterniflora) stems. By empirically scaling up our experimental results to the marsh platform at 12 sites, we further show that mussels—despite covering only approximately 1% of the marsh surface—strongly enhance five distinct ecosystem functions, including decomposition, primary production and water infiltration rate, at the landscape scale. Thus, mussels create conditions that support the co-occurrence of high densities of functionally distinct organisms within cordgrass and, in doing so, elevate salt marsh multifunctionality from the patch to landscape scale. Collectively, these findings suggest that patterns in foundation species' overlap drive variation in biodiversity and ecosystem functioning within and across natural ecosystems. We therefore argue that foundation species should be integrated in our conceptual understanding of forces that moderate biodiversity–ecosystem functioning relationships, approaches for conserving species diversity and strategies to improve the multifunctionality of degraded ecosystems. [ABSTRACT FROM AUTHOR]

Despite long-term monitoring of water quality in the coastal lagoonsof California, USA, the fate of organochlorines discharged from agricultural and urban sources to salt marsh habitats has received littleattention. We measured organochlorine concentrations in Upper Newport Bay marsh and channel sediments and salt marsh plants. Sediment grain-size analyses show that organochlorines are fractionated and concentrated in the organic material traveling with the clay fraction of the washload discharged into the bay from San Diego Creek. Hydrophobiccompounds such as DDT are not associated with the sand and silt fractions. The most frequently detected analyte was p,p'- I,1-dichloro-2,2-bis(4-chlorophenyl)ethylene (DDE), occurring in 100% of the sediment samples and 87% of the plant root samples. Maximum concentrations in sediment were 122 ng/g (dry wt) for DDE and 162 ng/g DDT plus metabolites (Sigma DDT) in salt marsh deposited since 1980. Ratios of DDT to its metabolites suggest that anaerobic degradation of DDT occurs in the cordgrass (Spartina fnliosa Trin.) sediments. Cordgrass and pickleweed (Saticornia virginica L.) partition organochlorine residues to the root epidermis, attaining values of 50,000 ng/g lipid for SigmaDDT and 80,000 ng/g lipid for heptachlorepoxide (1,4,5,6,7,8,8-heptachloro-2.3-epoxy-3Alpha,4,7,7a lpha-tetrahydro-4,7-methanoindan). [ABSTRACT FROM AUTHOR]

Twenty-eight tidal creeks along the South Carolina coast were sampled during the summer of 1995 to determine the levels of sediment contamination including organic chemicals (i.e., polycyclic aromatic hydrocarbons [PAHs], polychlorinated biphenyls [PCBs], and DDT and its metabolites) associated with different types and varying levels of watershed development (i.e., industrial/urban, suburban, forested, and salt marsh). Organic analysis utilized high-performance liquid chromatography (HPLC) with fluorescence detection and capillary gas chromatography-ion trap mass spectrometry (GC-ITMS) for PAHs, and gas chromatography with electron capture detection (GC-ECD) for pesticides and PCBs. Results indicated that creeks with industrial/urban watersheds hadsignificantly higher concentrations of PAHs, PCBs, and DDT compared with creeks with suburban and forested (reference) watersheds. The suburban watershed class of creeks had concentrations of half the PAH analytes and the total PCBs which exceeded the concentrations found inthe forested watershed class of creeks. The spatial distribution of organic contaminants was evaluated in four of these tidal creek-salt marsh systems representing urban/industrial, suburban, and forested watersheds, from the creek channel to the adjacent uplands. The distribution of organic contaminants within each representative creek was not concordant with the total organic carbon or the clay content of the sediment. The representative industrial/urban creek-marsh system, Diesel Creek, had the highest concentration of PAHs in the creek channel and the highest concentration of PCBs and DDT on the marsh surface, primarily in the upper portion of the system. The representative suburban creek-marsh system, Shem Creek, had elevated levels of both PAHs and PCBs throughout the entire system. This system also had one site with a total PAH concentration of 324,000 ppb and a total DDT concentration that was 20-100 times higher than the other sites. One of the [ABSTRACT FROM AUTHOR]

Twenty-eight tidal creeks were sampled along the South Carolina coast in the summer of 1995 to determine the levels of sediment trace metal contamination associated with different types and varying levels of human development in their watersheds. The particle size and total organic carbon (TOC) content of creek sediments in developed watersheds (i.e., industrial, urban, and suburban) were similar to that in watersheds with little or no development (i.e., forested or reference).Those trace metals commonly associated with urban and industrial sources, including Cu, Cr, Pb, Zn, Cd, and Hg, were in significantly higher concentrations in tidal creeks located in industrial/urban watersheds compared to the suburban and forested watersheds. Sediment tracemetal concentrations were similar for creeks located in suburban andforested watersheds and 2 to 10 times lower than the creeks located in industrial/urban watersheds. Concentrations of trace metals primarily associated with the natural weathering of basement rock, including Al, Fe, As, Ni, and Mn, were not significantly different among watershed types. Four of the tidal creek-salt marsh systems were extensively sampled from the creek channel to the marsh-upland interface to characterize sediment trace metal spatial distributions within creek-marsh systems. Sediment particle size, TOC, and trace metal concentrations varied spatially within each creek-marsh system depending on thetype of development in the watershed and the probable source of metals. The creek-marsh system selected to represent the industrial development had significantly higher 'anthropogenic' trace metal concentrations compared to the other creek-marsh systems. This system also hadtrace metal distributional patterns that appeared to be associated with several localized sources of metals on the marsh surface. Both the 'anthropogenic' and 'natural' trace metal concentrations andspatialdistributions were similar among and within the forested and suburban cree [ABSTRACT FROM AUTHOR]

Salt marsh ecosystems in Louisiana are at high risk of an oil contamination event while remediation of these systems is mainly limited tointrinsic bioremediation due to the physical sensitivity of salt marshes. This study investigated both the intrinsic and nutrient enhanced rates of crude oil degradation both in microcosm and core studies. In addition, limiting elements, loading rates and optimum nitrogen forms (NH4^+ or NO3^-) were determined. Salt marshes have relatively low intrinsic degradation rates (0-3.9% day-1) of the alkane component (C11-C44) but high rates (8-16% day-1) of degradation of the polycyclic aromatic hydrocarbon (PAH) fraction (naphthalene, C1, and C2-Naphthalene and Phenanthrene, C1, and C2-Phenanthrene). Additions of nitrogen statistically enhanced degradation of many alkanes and total PAHs while naturally present phosphorous was found to be sufficient. Nitrogen was found to be mosteffective if applied as NH4^+ in the range of 100-500-N mg kg-1 of soil producing a pore water range of 100-670-N mg L-1. Core studies indicate that similar trends are observed when applying fertilizers to intact portions of salt marsh. [ABSTRACT FROM AUTHOR]