Grand Bay National Estuarine Research Research Articles

Structured Decision Making to Prioritize Regional Bird Monitoring Needs

Conservation planning for large ecosystems has multiple benefits but is often challenging to implement because of the multiple jurisdictions, species, and habitats involved. In addition, decision making at large spatial scales can be hampered because many approaches do not explicitly incorporate potentially competing values and concerns of stakeholders. After the Deepwater Horizon oil spill, establishing baselines was challenging because of (1) variation in study designs, (2) inconsistent use of explicit objectives and hypotheses, (3) inconsistent use of standardized monitoring protocols, and (4) variation in spatial and temporal scope associated with avian monitoring projects before the spill. Herein, we show how the Gulf of Mexico Avian Monitoring Network members used structured decision making to identify bird monitoring priorities. We used multiple tools and techniques to clearly define the problem and stakeholder objectives and to identify bird monitoring priorities at the scale of the entire northern Gulf of Mexico region. Although our example is specific to the northern Gulf of Mexico, this approach provides an example of how stakeholder values can be incorporated into the coordination process of broad-scale monitoring programs to address management, restoration, and scientific questions in other ecosystems and for other taxa. History: This paper was refereed. This paper was accepted for the Special Issue of INFORMS Journal on Applied Analytics—Decision Analysis. Funding: Thanks to the National Fish and Wildlife Foundation [Grant 324423], which supported A. Fournier as a postdoctoral research associate at Mississippi State University. M. Woodrey was supported by the U.S. Department of Agriculture, National Institute of Food and Agriculture, Hatch Project funds, the Mississippi Agricultural and Forestry Experiment Station, National Oceanographic and Atmospheric Administration [Grant NA16NOS4200088 to the Mississippi Department of Marine Resources’ Grand Bay National Estuarine Research Reserve], and the Mississippi Department of Marine Resources [Grant 8200025414]. This publication is a contribution of the Mississippi Agricultural and Forestry Experiment Station. T. Zenzal was supported by the National Oceanic and Atmospheric Administration RESTORE Act Science Program [Grant NA17NOS4510092].

Loss of Mississippi Diamondback Terrapin (Malaclemys terrapin pileata) Nesting Habitat in the Northern Gulf of Mexico

Diamondback terrapins (Malaclemys terrapin) are a species of turtle that occupy coastal tidal marshes and nest on sandy areas above the high-tide line. Within the Grand Bay National Estuarine Research Reserve, Mississippi diamondback terrapin (M. t. pileata) shoreline nesting habitat at Grand Battures (also known as South Rigolets Island) has decreased from a 2.34-km length of surveyable shoreline in 2014 to a 1.45-km length of shoreline in 2021. Depredated nest surveys in 2021 detected the lowest number of nests to date at this location, with increased search effort, and this is likely due to the high rates of erosion described for this area.

Lateral shoreline erosion and shore-proximal sediment deposition on a coastal marsh from seasonal, storm and decadal measurements

The persistence of coastal marsh is dependent on its ability to maintain elevation relative to sea level, particularly for marshes experiencing high rates of shoreline erosion due to wave-attack, storms, and sea level rise. Sediments eroded at the marsh edge are either delivered onto the marsh platform or into the estuary, the latter resulting in a net loss of marsh sediments and soil carbon. Knowledge on the timing, pattern, and quantity of sediment deposition versus shoreline erosion along the marsh-estuary interface is critical for evaluating the overall health and vulnerability of coastal marshes to future scenarios of sea level rise and for estimating sediment budgets. Here we examined marsh shoreline erosion and sediment deposition for marsh sites experiencing a range of shoreline erosion rates and different levels of wind-wave exposure within the Grand Bay National Estuarine Research Reserve and Wildlife Refuge in Mississippi. We developed a method for calculating an erosion-deposition sediment budget using marsh elevation profiles, shoreline erosion rate, and sediment deposition measurements. Sediment budgets were calculated at four sites with varying shoreline erosion rates. Much of the sediment eroded at the marsh edge can be accounted for as marsh platform deposition, except at the most erosive site, suggesting a possible erosion threshold where eroded sediment mass is greater than platform deposition. Consistent with other studies of marsh creeks, sediment delivery to the marsh platform appears to be largely driven by wave climate. These data suggest that for erosive bay-estuarine shorelines, sediment delivered into the marsh is largely concentrated near the marsh shoreline, although shoreline erosion does not always result in a net loss of sediments from the marsh system in either decadal or annual assessments.

Small-scale variation in herbivore abundance and grazing on Juncus roemerianus dominated salt marshes

Herbivore-plant interactions have been shown to play central roles in determining the structure of salt marsh communities. However, relatively little is known about how marsh herbivory varies over small spatial scales (e.g., < 2 km) within a single geographic region as well as the potential driving forces for such variability. Here we quantify the small-scale spatial variablity in insect grazing on three Juncus roemerianus marshes in Grand Bay National Estuarine Research Reserve, MS, USA. Sampling covered both monthly and seasonal temporal scales (February to November) to capture the well described seasonality in insect grazing in these marshes Our results show large differences in abundance of insect herbivores and intensity of herbivory across, but not within, the three marshes. In addition, the observed spatial differences in herbivory do not appear to be related to herbivore abundance or insect species, but potentially to differences in landscape context, such as proximity to upland habitats (i.e., forestland) or habitat fragmentation. These results demonstrate that insect herbivory in marshes can also vary substantially at small spatial scales and we suggest some mechanisms responsible for such differences.

Gaseous Elemental Mercury Concentrations along the Northern Gulf of Mexico Using Passive Air Sampling, with a Comparison to Active Sampling

Mercury is a toxic element that is dispersed globally through the atmosphere. Accurately measuring airborne mercury concentrations aids understanding of the pollutant’s sources, distribution, cycling, and trends. We deployed MerPAS® passive air samplers (PAS) for ~4 weeks during each season, from spring 2019 to winter 2020, to determine gaseous elemental mercury (GEM) levels at six locations along the northern Gulf of Mexico, where the pollutant is of particular concern due to high mercury wet deposition rates and high concentrations in local seafood. The objective was to (1) evaluate spatial and seasonal trends along the Mississippi and Alabama coast, and (2) compare active and passive sampling methods for GEM at Grand Bay National Estuarine Research Reserve, an Atmospheric Mercury Network site. We observed higher GEM levels (p &lt; 0.05) in the winter (1.53 ± 0.03 ng m−3) compared to other seasons at all sites; with the general pattern being: winter &gt; spring &gt; summer ≈ fall. Average GEM levels (all deployment combined) were highest at Bay St. Louis (1.36 ± 0.05 ng m−3), the western-most site nearest the New Orleans metropolitan area, and lowest at Cedar Point (1.07 ± 0.09 ng m−3), a coastal marsh with extensive vegetation that can uptake GEM. The MerPAS units compared reasonably well with the established active monitoring system, but gave slightly lower concentrations, except in the winter when the two methods were statistically similar. Both the passive and active sampling methods showed the same seasonal trends and the difference between them for each season was &lt;15%, acceptable for evaluating larger spatial and temporal trends. Overall, this work demonstrates that PASs can provide insight into GEM levels and the factors affecting them along coastal regions.

Sea-level rise thresholds for stability of salt marshes in a riverine versus a marine dominated estuary

We studied the ecological resilience of salt marshes by deriving sea level rise (SLR) thresholds in two estuaries with contrasting upland hydrological inputs in the north-central Gulf of Mexico: Grand Bay National Estuarine Research Reserve (NERR) with limited upland input, and the Pascagoula River delta drained by the Pascagoula River, the largest undammed river in the continental United States. We applied a mechanistic model to account for vegetation responses and hydrodynamics to predict salt marsh distributions under future SLR scenarios. We further investigated the potential mechanisms that contribute to salt marsh resilience to SLR.The modeling results show that salt marshes in the riverine dominated estuary are more resilient to SLR than in the marine dominated estuary with SLR thresholds of 10.3 mm/yr and 7.2 mm/yr respectively. This difference of >3 mm/yr is mainly contributed by larger quantities of riverine-borne mineral sediments in the Pascagoula River. In both systems, sediment trapping by the above-ground vegetation appears to contribute more to marsh platform accretion than organic matter from below-ground biomass based on the medians of the accretion rates. However, below-ground biomass could contribute up to 90% of accretion in the marine dominated estuary compared to only 60% of accretion in the riverine dominated estuary. SLR thresholds of salt marshes are more sensitive to vegetation biomass in the marine dominated estuary while biomass and sediment similarly affect SLR thresholds of salt marshes in the riverine dominated estuary.This research will likely help facilitate more informed decisions on conservation/restoration policies for these two types of systems in the near-term needed to minimize future catastrophic loss of these coastal marsh habitats once SLR thresholds are exceeded.

Spatially-dependent patterns of plant recovery and sediment accretion following multiple disturbances in a Gulf Coast tidal marsh

Coastal wetlands are projected to experience increases in anthropogenic and climatic disturbances, which may alter plant-sediment feedbacks critical for maintaining marsh resilience to sea level. To study the effects of disturbance on ecogeomorphic processes, we examined aboveground plant responses and sediment accretion in three locations relative to the shoreline (low, mid, and high) within a tidal marsh at Grand Bay National Estuarine Research Reserve, Mississippi, USA. This study site was affected by two hurricanes in the fall of 2008, and subsequently burned as part of a controlled experiment in January 2009, permitting examination of the effects of two disturbance types on aboveground plant responses and vertical accretion. Fire and hurricanes affected these response variables differently, with effects dependent on location within the marsh. Fire significantly reduced standing aboveground biomass, and subsequent recovery of vegetation relative to pre-burn levels was faster in low marsh plots nearest to the shore than in high marsh plots closest to the marsh-pine ecotone. Hurricanes introduced sediment to the marsh platform, resulting in greater accretion in low marsh plots that had more standing biomass and higher stem densities than high marsh plots. Collectively, these results demonstrate that disturbances can heterogeneously affect surface soil-building processes in marshes through effects on sediment and organic matter accumulation, which may have important consequences for surface elevation maintenance in coastal marshes.

Landscape genetics of the foundational salt marsh plant species black needlerush (Juncus roemerianus Scheele) across the northeastern Gulf of Mexico

ContextCommon species important for ecosystem restoration stand to lose as much genetic diversity from anthropogenic habitat fragmentation and climate change as rare species, but are rarely studied. Salt marshes, valuable ecosystems in widespread decline due to human development, are dominated by the foundational plant species black needlerush (Juncus roemerianus Scheele) in the northeastern Gulf of Mexico.ObjectivesWe assessed genetic patterns in J. roemerianus by measuring genetic and genotypic diversity, and characterizing population structure. We examined population connectivity by delineating possible dispersal corridors, and identified landscape factors influencing population connectivity.MethodsA panel of 19 microsatellite markers was used to genotype 576 samples from ten sites across the northeastern Gulf of Mexico from the Grand Bay National Estuarine Research Reserve (NERR) to the Apalachicola NERR. Genetic distances (FST and Dch) were used in a least cost transect analysis (LCTA) within a hierarchical model selection framework.ResultsGenetic and genotypic diversity results were higher than expected based on life history literature, and samples structured into two large, admixed genetic clusters across the study area, indicating sexual reproduction may not be as rare as predicted in this clonal macrophyte. Digitized coastal transects buffered by 500 m may represent possible dispersal corridors, and developed land may significantly impede population connectivity in J. roemerianus.ConclusionsResults have important implications for coastal restoration and management that seek to preserve adaptive potential by sustaining natural levels of genetic diversity and conserving population connectivity. Our methodology could be applied to other common, widespread and understudied species.

Model selection in Bayesian framework to identify the best WorldView-2 based vegetation index in predicting green biomass of salt marshes in the northern Gulf of Mexico

Coastal wetlands are among the most productive ecosystems globally but have experienced dramatic degradation and loss within the past several decades. Vegetation biomass of coastal wetlands is not only the key component of blue carbon storage but also plays an important role in vertical accretion, important for maintaining these habitats under relative sea-level rise. Remote sensing offers a cost-effective approach to study vegetation biomass at a broad spatial scale. We developed statistical models to predict peak aboveground green biomass of Spartina alterniflora and Juncus roemerianus, two dominant species of salt marshes using WorldView-2 satellite imagery at the Grand Bay National Estuarine Research Reserve (NERR) on the Mississippi coast in the northern Gulf of Mexico. The model accounted for nested data structures in the sampled biomass, assimilated uncertainties from data, parameters and model structures, and helped determine the best vegetation index among a variety of commonly-used indices to predict aboveground green biomass. We developed a series of mixed-effects models, which included different combinations of fixed effect(s), random intercept, and random slope(s). The fixed effects were species and one of the 60 vegetation indices derived from a WorldView-2 image obtained on 6 October 2012. The random effect used was site. We implemented the models in a Bayesian framework and selected the best model structure and vegetation index based on minimum posterior predictive loss and deviance information criterion. The results showed that the best vegetation index to predict peak green biomass was the green chlorophyll index derived from the reflectance values of band 8 (near-infrared) and band 3 (green), and its effect on biomass prediction varied among sites. The inclusion of species as a fixed effect improved the model prediction. The study demonstrated the need to account for spatial dependence of data in developing a robust model, and the importance of the second WorldView-2 near-infrared band (860–1040 nm) in predicting aboveground green biomass for the Grand Bay NERR. The analysis using mixed-effects modeling in Bayesian inference which coherently combined field and WorldView-2 data with uncertainties accounted for provides a robust and nondestructive tool for resource managers to monitor the status of coastal wetlands at a high spatial resolution in a timely manner. Through this study, we hope to emphasize the importance of appropriately accounting for nested data structures using mixed-effects models and promote wider application of Bayesian inference to facilitate assimilation of uncertainties in remote sensing applications.

Recording Tropical Cyclone Activity from 1909 to 2014 along the Northern Gulf of Mexico using Maritime Slash Pine Trees (Pinus elliottii var. elliottii Engelm.)

ABSTRACT Tucker, C.S.; Trepanier, J.C.; Harley, G.L., and DeLong, K.L., 2018. Recording Tropical Cyclone Activity from 1909 to 2014 along the Northern Gulf of Mexico using Maritime Slash Pine Trees (Pinus elliottii var. elliottii Engelm.). The temporally incomplete tropical cyclone (TC) observational record limits the understanding of recurrence intervals and the impacts of repeated TCs on coastal ecosystems. Growth of maritime trees near the Gulf of Mexico may be affected by high winds, precipitation, and storm surges from TCs. Proxy records, such as tree growth recorded in annual ring widths, can be used to extend TC records temporally but must be verified with the observational record first. This study develops chronologies of total ring width (TRW), earlywood ring width (ERW), and latewood ring width (LRW) from slash pine (Pinus elliottii var. elliottii Engelm.) trees located 2 km from an open saltwater bay in the Grand Bay National Estuarine Research Reserve in coastal Mississippi, U.S.A. These chron...

Seasonal and Annual Dynamics in Seagrass Beds of the Grand Bay National Estuarine Research Reserve, Mississippi

Along the mainland coastline of eastern Mississippi Sound, the seagrass species Ruppia maritima (Wigeongrass) and Halodule wrightii (Shoalgrass) co-occur in persistent and sometimes extensive beds within Grand Bay. This paper presents seasonal and annual changes in those Ruppia-Halodule beds that are part of the Grand Bay National Estuarine Research Reserve in western Grand Bay using 2005–2011 transect survey data of percent cover and 2009–2013 biomass sampling data. The seagrass beds exhibited significant interannual variation in areal coverage and seasonal variations in biomass, with peak total aboveground biomass (up to 140 g dry wt/m2) in July and August. Intact R. maritima and H. wrightii seeds were found in the sediment, with densities as high as 4160 seeds/m2. The Ruppia-Halodule beds did not show any short-term declines in their growth or abundance following 2005 Hurricanes Katrina and Rita nor the 2010 Deepwater Horizon oil spill. Resumen: A lo largo de la costa continental del este del Mississippi Sound, las especies de pastos marinos Ruppia maritima (Wigeongrass) y Halodule wrightii (Shoalgrass) coexisten en camas persistentes ya veces extensas dentro de Grand Bay. Este articulo presenta cambios estacionales y anuales en los lechos de Ruppia-Halodule que forman parte de la Reserva de Investigacion Estuarina Nacional de Grand Bay en el oeste de Grand Bay usando datos de la encuesta de transectos de 2005–2011 de cobertura porcentual y datos de muestreo de biomasa 2009–2013. Los lechos de pastos marinos mostraron una variacion interanual significativa en la cobertura aerea y las variaciones estacionales en la biomasa, con el pico de biomasa total sobre el suelo (hasta 140 g de peso seco/m2) en julio y agosto. Se encontraron semillas intactas de R. maritima y H. wrightii en el sedimento, con densidades tan altas como 4160 semillas/m2. Las camas Ruppia-Halodule no mostraron disminuciones a corto plazo en su crecimiento o abundancia despues de los huracanes Katrina y Rita en el 2005 ni en el derrame de petroleo Deepwater Horizon del 2010.

Introduction: Coastal Seagrass and Submerged Aquatic Vegetation Habitats in the Gulf of Mexico

IntroductionCoastal Seagrass and Submerged Aquatic Vegetation Habitats in the Gulf of Mexico Patrick Biber* and Hyun Jung Cho* This special issue compiles original research and reviews of previous research on an important geographic constitution at the water-land interface: the seagrass/Submerged Aquatic Vegetation (SAV) beds in the Gulf of Mexico (GoM) coastal zone. SAV are a group of vascular plants that grow underwater; and seagrass is a specialized subgroup of SAV that have adapted to live in the high salinity coastal and marine waters. Presence of, types of, and seasonality of SAV beds have substantial influences on geography, ecology, landscape, culture, and economy in the coastal zone. Healthy SAV beds help shape, maintain, and modify coastal landscapes by buffering wave energy, modifying water currents, protecting shorelines from erosion, aiding sediment deposition, consolidating substrate, and changing littoral profiles and water depth. Coastal seagrass resources are among the most productive ecosystems on Earth. Seagrass beds perform numerous vital ecological functions and provide food and shelter for commercially and ecologically important organisms, including blue crabs, shrimp, turtles, manatees, and waterfowl. Therefore, assessment of SAV distribution, composition, and abundance has been of particular interest to coastal environmental managers, scientists, developers, and recreationists as this information serves as an excellent indicator of estuarine environmental quality. Coastal areas containing seagrass and SAV beds carry geographical and historical importance in the Southeast, especially throughout the GoM. The GoM and its resources have immense ecological, economical, and historic values to the U.S. but have been going through several major environmental disturbances and disasters including, but not limited to, major hurricanes (e.g., 2005 Hurricane Katrina), the 2010 Deepwater Horizon Oil Spill, red tides, rapid subsidence, marsh erosion, threats from sea level rise, and river water diversions. Man-made levees [End Page 208] along major rivers (e.g., Mississippi River) prevent natural flooding from the rivers that historically used to deliver the necessary nutrients and sediments for coastal wetland growth and delta formation. This has resulted in coastal wetland retreat and subsidence. In addition, environmental quality has been significantly degraded, which in turn, results in the loss of ecological/economical services in the region. Loss of coastal land and environmental degradation are projected to be amplified with changing global climate, which is a growing threat to coastal SAV beds (Scavia et al. 2002, Doyle et al. 2010, Unsworth et al. 2014). The low-lying coastal areas of the GoM are particularly vulnerable to natural/anthropogenic disturbances due to the effects of sea-level rise, increases in population density, extensive landscape alternation, modification, and armoring of natural shorelines, as well as natural/man-made disasters. Documentation of habitat conditions, change over time, and interactions with the human environment are critical needs to better assess current status and predict future trends for SAV/seagrass habitats, a critical component of coastal geography. However, many regionally focused relevant studies on these habitats have not been addressed in the increasingly international scope of many pertinent scientific journals. We, the Guest Editors, agreed that compiling regional studies on a unifying topic would help enhance understanding of long-term and larger scale trends in SAV/seagrass beds of the GoM. In response, requests for manuscripts on sea-grass and other SAV occurring in tidally-influenced GoM coastal habitats were sent out to several regional seagrass/SAV scientists. In order to comply with the scope of Southeastern Geographer, the papers in this issue present studies on SAV/seagrass with a regional geography focus, particularly relating to issues of temporal variation and changes related to land use change, human alteration, and climate change. The five papers published in this special issue synergistically help to summarize change occurring across the GoM. Geographically, this special issue covers coastal habitats from Texas (the Coastal Bend and Laguna Madre), Louisiana (Terrebonne Bay, the Pontchartrain basin), areas around the borders of Mississippi and Alabama (Grand Bay National Estuarine Research Reserve), and west Florida (Tampa Bay). The topics of the papers extend from (1) evaluation of SAV for nekton habitat value in comparison to marshes during one season (Jerabek et al.), (2) test of a model to assess carbon stocks in seagrass meadows in a single year (Congdon & Dunton), (3) temporal...

Modeling Salt Panne Land-Cover Suitability under Sea-Level Rise

ABSTRACT Linhoss, A.C. and Underwood, W.V., 2016. Modeling salt panne land-cover suitability under sea-level rise. Salt pannes are an ecologically important but poorly understood feature of the salt marsh environments. Like all coastal marshes, salt pannes are threatened by sea-level rise; therefore, it is important to assess how they will be affected by rising seas. Because of a lack of understanding regarding salt panne formation and the possibly stochastic nature of their development, a traditional and purely deterministic modeling approach is unsuitable for assessing the impacts of sea-level rise on salt pannes. This research used a combination of deterministic and stochastic models to simulate the land-cover suitability for salt pannes in the Grand Bay National Estuarine Research Reserve, Mississippi, under five sea-level rise scenarios, including a rise of 0.25, 0.5, 1.0, 1.5, and 2.0 m by 2100. The Sea-Level Affecting Marshes Model (SLAMM) simulated general land-cover at the study site. However, SL...

Trace elements and heavy metals in the Grand Bay National Estuarine Reserve in the northern Gulf of Mexico

The objectives of this study are to investigate distribution of trace elements and heavy metals in the salt marsh and wetland soil and biogeochemical processes in the Grand Bay National Estuarine Research Reserve of the northern Gulf of Mexico. The results show that Hg, Cd and to some extent, As and Pb have been significantly accumulated in soils. The strongest correlations were found between concentrations of Ni and total organic matter contents. The correlations decreased in the order: Ni>Cr>Sr>Co>Zn, Cd>Cu>Cs. Strong correlations were also observed between total P and concentrations of Ni, Co, Cr, Sr, Zn, Cu, and Cd. This may be related to the P spilling accident in 2005 in the Bangs Lake site. Lead isotopic ratios in soils matched well those of North American coals, indicating the contribution of Pb through atmospheric fallout from coal power plants.

Does bird removal affect grasshopper grazing on Juncus roemerianus (black needlerush) marshes?

Grazing on J. roemerianus (black needlerush), grasshopper abundance, and black needlerush plants was examined in the presence and exclusion of marsh birds. Birds were excluded using a PVC framed exclosure wrapped with bird netting that allowed free passage of marsh grasshoppers. These measurements were taken bi-monthly from April to August 2011 in a black needlerush marsh within the Grand Bay National Estuarine Research Reserve (Moss Point, MS, USA). Grazing metrics, grasshopper abundance, and plant health metrics showed no effect of bird exclusions across all sampling dates. In contrast to other marsh systems with strong trophic cascades (e.g., Spartina alterniflora on US east coast), these results suggest that the primary consumer (grasshoppers) is not affected by the presence of their dominant predator (birds) which leads to no change in the health of the primary producer (black needlerush). Information derived from this study furthers our understanding of the trophic relationships within black needlerush marshes in the northern Gulf of Mexico.

Meteorological Modeling Using the WRF-ARW Model for Grand Bay Intensive Studies of Atmospheric Mercury

Measurements at the Grand Bay National Estuarine Research Reserve support a range of research activities aimed at improving the understanding of the atmospheric fate and transport of mercury. Routine monitoring was enhanced by two intensive measurement periods conducted at the site in summer 2010 and spring 2011. Detailed meteorological data are required to properly represent the weather conditions, to determine the transport and dispersion of plumes and to understand the wet and dry deposition of mercury. To describe the mesoscale features that might influence future plume calculations for mercury episodes during the Grand Bay Intensive campaigns, fine-resolution meteorological simulations using the Weather Research and Forecasting (WRF) model were conducted with various initialization and nudging configurations. The WRF simulations with nudging generated reasonable results in comparison with conventional observations in the region and measurements obtained at the Grand Bay site, including surface and sounding data. The grid nudging, together with observational nudging, had a positive effect on wind prediction. However, the nudging of mass fields (temperature and moisture) led to overestimates of precipitation, which may introduce significant inaccuracies if the data were to be used for subsequent atmospheric mercury modeling. The regional flow prediction was also influenced by the reanalysis data used to initialize the WRF simulations. Even with observational nudging, the summer case simulation results in the fine resolution domain inherited features of the reanalysis data, resulting in different regional wind patterns. By contrast, the spring intensive period showed less influence from the reanalysis data.

The role of light, soil and human factors on the probability of occurrence of an invasive and three native plant species in coastal transitions of coastal Mississippi, USA

Aims Understanding relationships between the distributions of species and their surrounding environment provides a basis for forecasting how species will respond to future environmental changes. In this study, we examined the effects of environmental factors and human developmental features associated with disturbances on probability of occurrence of juveniles of invasive Triadica sebifera and three native plant species, Baccharis halimifolia, Ilex vomitoria and Morella cerifera within a typical coastal transition in coastal Mississippi, USA. Methods We recorded presence of juveniles of focal species and measured environmental factors (soil salinity, canopy openness, soil texture and soil carbon to nitrogen ratio) along an 11.3 km transect located at Grand Bay National Estuarine Research Reserve. Further, we documented anthropogenic features and associated activities as a proxy for human disturbance.

Nekton and Macro-Crustacean Habitat Use of Mississippi Micro-Tidal Salt Marsh Landscapes

Salt marshes have long been recognized as productive habitats that form an important trophic link between the aquatic and terrestrial biomes through the dynamic intertidal zone. This project focused on the distribution of nekton (free-swimming organisms) and common macro-crustaceans within the intertidal to assess the breadth of habitat use by these assemblages based on geo-spatial and hydrological variables. Sampling was conducted on the flooded marsh intertidal in August and September 2011 at three sites in the micro-tidal Grand Bay National Estuarine Research Reserve, MS, using bottomless lift nets and pit traps in a landscape design. The sampled assemblage data were compared with concurrent site hydrological analyses in order to determine how distribution on the salt marsh intertidal may be influenced by defined inundation components (e.g., inundation time and frequency of inundation) and by the distance to the nearest water source. A total of 3238 organisms were collected comprising 12 fish and 13 macro-crustacean species. A two-way nested analysis of similarities (ANOSIM) indicated that the density of the assemblage varied by site (p = 0.1 %) and across the salt marsh intertidal (marsh level (MLV); p = 1.4 %). Overall, assemblages were found to be strongly influenced by the inundation characteristics along the marsh elevation gradient as well as by the unique micro-topography of each site.

Hurricane wrack generates landscape‐level heterogeneity in coastal pine savanna

Wrack (vegetation debris) deposited by storm surges of major hurricanes along the northern Gulf of Mexico produces depressant effects that vary from partial to complete mortality of groundcover vegetation in coastal savannas. As wrack decomposes or is relocated by a subsequent hurricane, patches are opened to colonization. We postulated that patterns of wrack deposition and removal, coupled with differential responses by savanna plant species should produce alternate states of groundcover vegetation. We explored extreme effects of wrack deposited by Hurricane Katrina (2005) in savannas dominated by slash pine Pinus elliottii and cordgrass Spartina patens and located above mean high tide at the Grand Bay National Estuarine Research Reserve, Mississippi, USA. In 2008, we established plots in adjacent areas with and without wrack deposits. Almost no groundcover plant species occurred in wrack deposits compared to adjacent groundcover without wrack. We simulated redistribution of wrack during a new storm surge by removing wrack from replicated plots and depositing it in plots without wrack, recording plant species in treatment and control plots before, then one month and one year after manipulations. One year later, about half the species present before wrack addition (especially dominant graminoids) grew back through redistributed wrack, suggesting that some species were resistant to burial of limited amounts of wrack. Wrack removal resulted in germination and establishment of numerous herbaceous plant species not in undisturbed groundcover, doubling total aboveground numbers of species in the pine savanna and shifting groundcover communities to alternate states not present prior to Katrina. Removal of wrack opens space colonized by resilient species, including those transported in wrack and those surviving intervals between disturbances belowground. Wrack dynamics (deposition and removal) generated alternate states that resulted from resistance‐ and resilience‐driven changes in different patches of groundcover in coastal savannas.

Mercury Speciation at a Coastal Site in the Northern Gulf of Mexico: Results from the Grand Bay Intensive Studies in Summer 2010 and Spring 2011

During two intensive studies in summer 2010 and spring 2011, measurements of mercury species including gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and particulate-bound mercury (PBM), trace chemical species including O3, SO2, CO, NO, NOY, and black carbon, and meteorological parameters were made at an Atmospheric Mercury Network (AMNet) site at the Grand Bay National Estuarine Research Reserve (NERR) in Moss Point, Mississippi. Surface measurements indicate that the mean mercury concentrations were 1.42 ± 0.12 ng∙m−3 for GEM, 5.4 ± 10.2 pg∙m−3 for GOM, and 3.1 ± 1.9 pg∙m−3 for PBM during the summer 2010 intensive and 1.53 ± 0.11 ng∙m−3 for GEM, 5.3 ± 10.2 pg∙m−3 for GOM, and 5.7 ± 6.2 pg∙m−3 for PBM during the spring 2011 intensive. Elevated daytime GOM levels (>20 pg∙m−3) were observed on a few days in each study and were usually associated with either elevated O3 (>50 ppbv), BrO, and solar radiation or elevated SO2 (>a few ppbv) but lower O3 (~20–40 ppbv). This behavior suggests two potential sources of GOM: photochemical oxidation of GEM and direct emissions of GOM from nearby local sources. Lack of correlation between GOM and Beryllium-7 (7Be) suggests little influence on surface GOM from downward mixing of GOM from the upper troposphere. These data were analyzed using the HYSPLIT back trajectory model and principal component analysis in order to develop source-receptor relationships for mercury species in this coastal environment. Trajectory frequency analysis shows that high GOM events were generally associated with high frequencies of the trajectories passing through the areas with high mercury emissions, while low GOM levels were largely associated the trajectories passing through relatively clean areas. Principal component analysis also reveals two main factors: direct emission and photochemical processes that were clustered with high GOM and PBM. This study indicates that the receptor site, which is located in a coastal environment of the Gulf of Mexico, experienced impacts from mercury sources that are both local and regional in nature.