Brock, J.C.; Barras, J.A., and Williams, S.J., 2013. Introduction to the Special Issue on “Understanding and Predicting Change in the Coastal Ecosystems of the Northern Gulf of Mexico”. In: Brock, J.C.; Barras, J.A., and Williams, S.J. (eds.), Understanding and Predicting Change in the Coastal Ecosystems of the Northern Gulf of Mexico, Journal of Coastal Research, Special Issue No. 63, pp. 1–5. Coconut Creek (Florida), ISSN 0749-0208.

The coastal region of the northern Gulf of Mexico owes its current landscape structure to an array of tectonic, erosional and depositional, climatic, geochemical, hydrological, ecological, and human processes that have resulted in some of the world's most complex, dynamic, productive, and threatened ecosystems. Catastrophic hurricane landfalls, ongoing subsidence and erosion exacerbated by sea-level rise, disintegration of barrier island chains, and high rates of wetland loss have called attention to the vulnerability of northern Gulf coast ecosystems, habitats, built infrastructure, and economy to natural and anthropogenic threats. The devastating hurricanes of 2005 (Katrina and Rita) motivated the U.S. Geological Survey Coastal and Marine Geology Program and partnering researchers to pursue studies aimed at understanding and predicting landscape change and the associated storm hazard vulnerability of northern Gulf coast region ecosystems and human communities. Attaining this science goal requires increased knowledge of landscape evolution on geologic, historical, and human time scales, and analysis of the implications of such changes in the natural and built components of the landscape for hurricane impact susceptibility. This Special Issue of the Journal of Coastal Research communicates northern Gulf of Mexico research results that (1) improve knowledge of prior climates and depositional environments, (2) assess broad regional ecosystem structure and change over Holocene to human time scales, (3) undertake process studies and change analyses of dynamic landscape components, and (4) integrate framework, climate, variable time and spatial scale mapping, monitoring, and discipline-specific process investigations within interdisciplinary studies.

Poore, R.Z.; Tedesco, K.A., and Spear, J.W., 2013. Seasonal flux and assemblage composition of planktic foraminifers from a sediment-trap study in the northern Gulf of Mexico. In: Brock, J.C.; Barras, J.A., and Williams, S.J. (eds.), Understanding and Predicting Change in the Coastal Ecosystems of the Northern Gulf of Mexico, Journal of Coastal Research, Special Issue No. 63, pp. 6–19, Coconut Creek (Florida), ISSN 0749-0208.

Sediment-trap samples from the northern Gulf of Mexico reveal that Globorotalia truncatulinoides, Neogloboquadrina dutertrei, Pulleniatina spp. (includes P. obliquiloculata and P. finalis), and the Globorotalia menardii group (includes Gt. menardii, Gt. tumida, and Gt. ungulata) generally occur in cold months. Globigerinoides ruber (white and pink varieties) and Globigennoides sacculifer occur throughout the year. The seasonal occurrence of individual taxa of planktic foraminifers in the Gulf of Mexico have important differences with the seasonal occurrence of the same taxa observed in a 6-year sediment-trap dataset from the western Sargasso Sea. Thus information on the ecologic preferences of individual taxa determined in one region cannot necessarily be applied directly to another area. In the northern Gulf of Mexico ∼90% of the total flux of Globorotalia truncatulinoides tests to sediments occurs in January and February. Mg/Ca and d¹⁸Ο; measurements indicate that nonencrusted forms of Gt. truncatulinoides calcify in the upper-surface-mixed zone. Thus, analyses of nonencrusted Gt. truncatulinoides in sediments of the northern Gulf of Mexico have potential for monitoring past conditions in the winter-surface-mixed layer. The relatively low overall abundance of Globigerinoides ruber (white) in sediment-trap samples is anomalous because Gs. ruber (white) is one of the most abundant foraminifers in>150 µm census data from northern Gulf of Mexico Holocene sediment core samples. Globigerinoides ruber (pink) is a relatively persistent and common component of the sediment-trap samples. Thus Gs. ruber (pink) has potential as a proxy for mean annual sea-surface temperature in the Gulf of Mexico.

Flannery, J.A. and Poore, R.Z., 2013. Sr/Ca proxy sea-surface temperature reconstructions from modern and Holocene Montastraea faveolata specimens from the Dry Tortugas National Park In: Brock, J.C.; Barras, J.A., and Williams, S.J. (eds.), Understanding and Predicting Change in the Coastal Ecosystems of the Northern Gulf of Mexico, Journal of Coastal Research, Special Issue No. 63, pp. 20–31, Coconut Creek (Florida), ISSN 0749-0208.

Sr/Ca ratios from skeletal samples from two Montastraea faveolata corals (one modern, one Holocene, ∼6 Ka) from the Dry Tortugas National Park were measured as a proxy for sea-surface temperature (SST). We sampled coral specimens with a computer- driven triaxial micromilling machine, which yielded an average of 15 homogenous samples per annual growth increment. We regressed Sr/Ca values from resulting powdered samples against a local SST record to obtain a calibration equation of Sr/Ca = -0.0392 SST 10.205, R = -0.97. The resulting calibration was used to generate a 47-year modern (1961–2008) and a 7-year Holocene (∼6 Ka) Sr/Ca subannually resolved proxy record of SST. The modern M. faveolata yields well-defined annual Sr/Ca cycles ranging in amplitude from ∼0.3 and 0.5 mmol/mol. The amplitude of ∼0.3 to 0.5 mmol/mol equates to a ∼10–15°C seasonal SST amplitude, which is consistent with available local instrumental records. Summer maxima proxy SSTs calculated from the modern coral Sr/ Ca tend to be fairly stable: most SST maxima from 1961–2008 are 29°C ± 1°C. In contrast, winter minimum SST calculated in the 47-year modern time-series are highly variable, with a cool interval in the early to mid-1970s.

The Holocene (∼6 Ka) Montastraea faveolata coral also yields distinct annual Sr/Ca cycles with amplitudes ranging from ∼0.3 to 0.6 mmol/mol. Absolute Sr/Ca values and thus resulting SST estimates over the ∼7-year long record are similar to those from the modern coral. We conclude that Sr/Ca from Montastraea faveolata has high potential for developing subannually resolved Holocene SST records.

Twichell, D.C.; Flocks, J.G.; Pendleton, E.A., and Baldwin, W.E., 2013. Geologic controls on regional and local erosion rates of three northern Gulf of Mexico barrier island systems. In: Brock, J.C.; Barras, J.A., and Williams, S.J. (eds.), Understanding and Predicting Change in the Coastal Ecosystems of the Northern Gulf of Mexico, Journal of Coastal Research, Special Issue No. 63, pp. 32–45, Coconut Creek (Florida), ISSN 0749-0208.

The stratigraphy of sections of three barrier island systems in the northeastern Gulf of Mexico (Apalachicola, Mississippi, and Chandeleur) have been mapped using geophysical and coring techniques to assess the influence of geologic variations in barrier lithosomes and adjoining inner shelf deposits on long-term rates of shoreline change at regional and local scales. Regional scale was addressed by comparing average geologic characteristics of the three areas with mean shoreline-change rates for each area. Regionally, differences in sand volume contained within the part of the barrier lithosome above sea level, sand volume on the inner shelf, and to a lesser extent, sediment grain size correlate with shoreline change rates. Larger sand volumes and coarser grain sizes are found where erosion rates are lower. Local scale was addressed by comparing alongshore variations in barrier island and inner shelf geology with alongshore variations in shoreline change. Locally, long-term shoreline change rates are highest directly shoreward of paleovalleys exposed on the inner shelf. While geology is not the sole explanation for observed differences in shoreline change along these three coastal regions, it is a significant contributor to change variability.

Reich, C.D.; Poore, R.Z., and Hickey, T.D., 2013. The role of vermetid gastropods in the development of the Florida Middle Ground, northeast Gulf of Mexico. In: Brock, J.C.; Barras, J.A., and Williams, S.J. (eds.), Understanding and Predicting Change in the Coastal Ecosystems of the Northern Gulf of Mexico, Journal of Coastal Research, Special Issue No. 63, pp. 46–57, Coconut Creek (Florida), ISSN 0749-0208.

The Florida Middle Ground is a complex of north to northwest trending ridges that lie approximately 180 km northwest of Tampa Bay, Florida. The irregular ridges appear on the otherwise gently sloping West Florida shelf and exhibit between 10–15 m of relief. Modern studies interpret the ridges as remnants of a Holocene coral-reef buildup that today provide a hard substrate for growth of a variety of benthic organisms including hydrocorals, scleractinians, alcyonarians, and algae. Recent rotary coring reveals that the core of the eastern ridge of the Florida Middle Ground complex consists of unconsolidated marine calcareous muddy sand that is capped by a boundstone composed primarily of the sessile vermetid gastropod Petaloconchus sp., and overlays a weathered, fossiliferous limestone. Accelerator Mass Spectrometry radiocarbon ages (uncalibrated) on the 3.6-m thick vermetid worm rock indicate that it developed during a sea-level stillstand in the early Holocene (8,225 ±30–8,910 ± 25 yr B.P.). Our observations suggest that the Florida Middle Ground is a remnant of a series of shore parallel bars that formed in the early Holocene and were capped by a 3.6-m thick unit of vermetid gastropods. During a rapid sea-level rise that began ∼8,000 yr B.P. the vermetids growth ceased and the worm rock preserved the ridges structure. Diver observations document that the edges of the ridges are currently being eroded and undermined by biological activity and current action, leading to calving of large capstone blocks.

Couvillion, B.R. and Beck, H., 2013. Marsh collapse thresholds for coastal Louisiana estimated using elevation and vegetation index data. In: Brock, J.C.; Barras, J.A., and Williams, S.J. (eds.), Understanding and Predicting Change in the Coastal Ecosystems of the Northern Gulf of Mexico, Journal of Coastal Research, Special Issue No. 63, pp. 58–67, Coconut Creek (Florida), ISSN 0749-0208.

Forecasting marsh collapse in coastal Louisiana as a result of changes in sea-level rise, subsidence, and accretion deficits necessitates an understanding of thresholds beyond which inundation stress impedes marsh survival. The variability in thresholds at which different marsh types cease to occur (i.e., marsh collapse) is not well understood. We utilized remotely sensed imagery, field data, and elevation data to help gain insight into the relationships between vegetation health and inundation. A Normalized Difference Vegetation Index (NDVI) dataset was calculated using remotely sensed data at peak biomass (August) and used as a proxy for vegetation health and productivity. Statistics were calculated for NDVI values by marsh type for intermediate, brackish, and saline marsh in coastal Louisiana. Marsh-type specific NDVI values of 1.5 and 2 standard deviations below the mean were used as upper and lower limits to identify conditions indicative of collapse. As marshes seldom occur beyond these values, they are believed to represent a range within which marsh collapse is likely to occur. Inundation depth was selected as the primary candidate for evaluation of marsh collapse thresholds. Elevation relative to mean water level (MWL) was calculated by subtracting MWL from an elevation dataset compiled from multiple data types including light detection and ranging (lidar) and bathymetry. A polynomial cubic regression was used to examine a random subset of pixels to determine the relationship between elevation (relative to MWL) and NDVI. The marsh collapse uncertainty range values were found by locating the intercept of the regression line with the 1.5 and 2 standard deviations below the mean NDVI value for each marsh type. Results indicate marsh collapse uncertainty ranges of 30.7–35.8 cm below MWL for intermediate marsh, 20–25.6 cm below MWL for brackish marsh, and 16.9–23.5 cm below MWL for saline marsh. These values are thought to represent the ranges of inundation depths within which marsh collapse is probable.

Smith, C.G.; Osterman, L.E., and Poore, R.Z., 2013. An examination of historical inorganic sedimentation and organic matter accumulation in several marsh types within the Mobile Bay and Mobile—Tensaw River delta region. In: Brock, J.C.; Barras, J.A., and Williams, S.J. (eds.), Understanding and Predicting Change in the Coastal Ecosystems of the Northern Gulf of Mexico, Journal of Coastal Research, Special Issue No. 63, pp. 68–83, Coconut Creek (Florida), ISSN 0749-0208.

Mass accumulation rates (MAR; g cm^-2 y^-1), linear sedimentation rates (LSR; cm y^-1), and core geochronology derived from excess lead-210 (²¹⁰Pb) profiles and inventories measured in six sediment cores collected from marsh sites from the MobileTensaw River Delta and Mobile Bay region record the importance of both continuous and event-driven inorganic sedimentation over the last 120 years. MAR in freshwater marshes varied considerably between sites and through time (0.24 and 1.31 g cm^-2 y^-1). The highest MARs occurred in the 1950s and 1960s and correspond to record discharge events along the Mobile and Tensaw Rivers. In comparison, MAR at salt marsh sites increased almost threefold over the last 120 years (0.05 to 0.18 g cm^-2 y^-1 or 0.23 to 0.48 cm y^-1). From 1880 to 1960, organic accumulation remained fairly constant (∼20%), while intermittent pulses of high inorganic sedimentation were observed following 1960. The pulses in inorganic sedimentation coincide with several major hurricanes (e.g., Hurricanes Camille, Fredric, Georges, and Ivan). The nearly threefold increase in MAR in salt marshes during the last 120 years would thus appear to be partially dependent on inorganic sedimentation from storm events. This study shows that while hurricanes, floods, and other natural hazards are well-known threats to human infrastructure and coastal ecosystems, these events also transport sediment to marshes that help abate other pressures such as sea-level rise (SLR) and subsidence.

Nunnally, C.C.; Rowe, G.T.; Thornton, D.C.O., and Quigg, A., 2013. Sedimentary oxygen consumption and nutrient regeneration in the Gulf of Mexico hypoxic zone. In: Brock, J.C.; Barras, J.A., and Williams, S.J. (eds.), Understanding and Predicting Change in the Coastal Ecosystems of the Northern Gulf of Mexico, Journal of Coastal Research, Special Issue No. 63, pp. 84–96, Coconut Creek (Florida), ISSN 0749-0208.

Seasonal summer stratification and enhanced nutrient loading of the Louisiana continental shelf (U.S.A.) west of the Mississippi River create hypoxic regions that affect large areas of the benthos. Total sediment oxygen uptake and nutrient recycling were measured during different, (e.g. pre, early, late and post) hypoxic regimes using shipboard Batch Micro-Incubation Chambers (BMICs) in 2004 to 2005 and again in 2007 to 2009. Sediment community oxygen consumption during oxic regimes (dissolved oxygen > 63 µmol L^-1) was -9.5 ± 0.7 mmol O₂ m^-2 d^-1 (mean ± SE), almost twice that measured (-5.8 ± 0.6 mmol O₂ m^-2 d^-1) during suboxic conditions. During the summer when hypoxia occurred, the benthos consumed nitrate and nitrite (-0.14 ± 0.04 and -0.10 ± 0.02 mmol N m^-2 d^-1 respectively) and produced ammonium (1.6 ± 0.39 mmol N m^-2 d^-1). Elevated sediment community oxygen consumption and nutrient remineralization occurred near terrestrial river inputs associated with the Mississippi and Atchafalaya Rivers. Net release of dissolved inorganic nitrogen, in the form of ammonium, peaked during late summer. Released ammonium may be a source of nutrients for primary production in bottom waters, and can also provide reduced nitrogen for nitrification and microbial respiration, both of which may reinforce the intensity and duration of hypoxia. Based on chamber results, sediments actively scavenged phosphate from the bottom waters (-98.4 ± 21.3 µmol P m^-2 d^-1) and released silicate (2.62 = 0.31 mmol Si m^-2 d^-1). The addition of reactive nitrogen and removal of phosphorous due to benthic community metabolism could potentially be accentuating phosphorous limitation on the continental shelf.

Palaneasu-Lovejoy, M.; Kranenburg, C.; Barras, J.A., and Brock, J.C., 2013. Land loss due to recent hurricanes in coastal Louisiana, U.S.A.. In: Brock, J.C.; Barras, J.A., and Williams, S.J. (eds.), Understanding and Predicting Change in the Coastal Ecosystems of the Northern Gulf of Mexico, Journal of Coastal Research, Special Issue No. 63, pp. 97–109, Coconut Creek (Florida), ISSN 0749-0208.

The aim of this study is to improve estimates of wetland land loss in two study regions of coastal Louisiana, U.S.A., due to the extreme storms that impacted the region between 2004 and 2009. The estimates are based on change-detection-mapping analysis that incorporates pre and postlandfall (Hurricanes Katrina, Rita, Gustav, and Ike) fractional-water classifications using a combination of high-resolution (<5 m) QuickBird, IKONOS, and GeoEye-1, and medium-resolution (30 m) Landsat Thematic Mapper satellite imagery. This process was applied in two study areas: the Hackberry area located in the southwestern part of chenier plain that was impacted by Hurricanes Rita (September 24, 2005) and Ike (September 13, 2008), and the Delacroix area located in the eastern delta plain that was impacted by Hurricanes Katrina (August 29, 2005) and Gustav (September 1, 2008). In both areas, effects of the hurricanes include enlargement of existing bodies of open water and erosion of fringing marsh areas. Surge-removed marsh was easily identified in stable marshes but was difficult to identify in degraded or flooded marshes. Persistent land loss in the Hackberry area due to Hurricane Rita was approximately 5.8% and increased by an additional 7.9% due to Hurricane Ike, although this additional area may yet recover. About 80% of the Hackberry study area remained unchanged since 2003. In the Delacroix area, persistent land loss due to Hurricane Katrina measured approximately 4.9% of the study area, while Hurricane Gustav caused minimal impact of 0.6% land loss by November 2009. Continued recovery in this area may further erase Hurricane Gustav's impact in the absence of new storm events.

Suir, G.M.; Evers, D.E.; Steyer, G.D., and Sasser C.E., 2013. Development of a reproducible method for determning quantity of water and its configuration in a marsh landscape. In: Brock, J.C.; Barras, J.A., and Williams, S.J. (eds.), Understanding and Predicting Change in the Coastal Ecosystems of the Northern Gulf of Mexico, Journal of Coastal Research, Special Issue No. 63, pp. 110–117, Coconut Creek (Florida), ISSN 0749-0208.

Coastal Louisiana is a dynamic and ever-changing landscape. From 1956 to 2010, over 3,734 km² of Louisiana's coastal wetlands have been lost due to a combination of natural and human-induced activities. The resulting landscape constitutes a mosaic of conditions from highly deteriorated to relatively stable with intact landmasses. Understanding how and why coastal landscapes change over time is critical to restoration and rehabilitation efforts. Historically, changes in marsh pattern (i.e., size and spatial distribution of marsh landmasses and water bodies) have been distinguished using visual identification by individual researchers. Difficulties associated with this approach include subjective interpretation, uncertain reproducibility, and laborious techniques. In order to minimize these limitations, this study aims to expand existing tools and techniques via a computer-based method, which uses geospatial technologies for determining shifts in landscape patterns. Our method is based on a raster framework and uses landscape statistics to develop conditions and thresholds for a marsh classification scheme. The classification scheme incorporates land and water classified imagery and a two-part classification system: (1) ratio of water to land, and (2) configuration and connectivity of water within wetland landscapes to evaluate changes in marsh patterns. This analysis system can also be used to trace trajectories in landscape patterns through space and time. Overall, our method provides a more automated means of quantifying landscape patterns and may serve as a reliable landscape evaluation tool for future investigations of wetland ecosystem processes in the northern Gulf of Mexico.

Steyer, G.D.; Couvillion, B.R., and Barras, J.A., 2013. Monitoring vegetation response to episodic disturbance events by using multitemporal vegetation indices In: Brock, J.C.; Barras, J.A., and Williams, S.J. (eds.), Understanding and Predicting Change in the Coastal Ecosystems of the Northern Gulf of Mexico, Journal of Coastal Research, Special Issue No. 63, pp. 118–130, Coconut Creek (Florida), ISSN 0749-0208.

Normalized Difference Vegetation Index (NDVI) derived from MODerate-resolution Imaging Spectroradiometer (MODIS) satellite imagery and land/water assessments from Landsat Thematic Mapper (TM) imagery were used to quantify the extent and severity of damage and subsequent recovery after Hurricanes Katrina and Rita of 2005 within the vegetation communities of Louisiana's coastal wetlands. Field data on species composition and total live cover were collected from 232 unique plots during multiple time periods to corroborate changes in NDVI values over time. Aprehurricane 5-year baseline time series clearly identified NDVI values by habitat type, suggesting the sensitivity of NDVI to assess and monitor phenological changes in coastal wetland habitats. Monthly data from March 2005 to November 2006 were compared to the baseline average to create a departure from average statistic. Departures suggest that over 33% (4,714 km²) of the prestorm, coastal wetlands experienced a substantial decline in the density and vigor of vegetation by October 2005 (poststorm), mostly in the east and west regions, where landfalls of Hurricanes Katrina and Rita occurred. The percentage of area of persistent vegetation damage due to long-lasting formation of new open water was 91.8% in the east and 81.0% and 29.0% in the central and west regions, respectively. Although below average NDVI values were observed in most marsh communities through November 2006, recovery of vegetation was evident. Results indicated that impacts and recovery from large episodic disturbance events that influence multiple habitat types can be accurately determined using NDVI, especially when integrated with assessments of physical landscape changes and field verifications.

Kish, S.A. and Donoghue, J.F., 2013. Coastal response to storms and sea-level rise: Santa Rosa Island, northwest Florida, U.S.A.. In: Brock, J.C.; Barras, J.A., and Williams, S.J. (eds.), Understanding and Predicting Change in the Coastal Ecosystems of the Northern Gulf of Mexico, Journal of Coastal Research, Special Issue No. 63, pp. 131–140, Coconut Creek (Florida), ISSN 0749-0208.

The western panhandle coast of northwest Florida is wave dominated and microtidal. Major storms are infrequent but have a significant effect on coastal morphology. Santa Rosa Island, a 75-kilometer long barrier, is the major coastal feature of the region. The island is narrow, with an average width of 500 meters. During most of the historical period, prominent foredunes, ranging as high as 7 meters, have helped keep the island's sediment budget in near equilibrium. This investigation compiled and georeferenced nearly two dozen historical shoreline positions from surveys and aerial photos, dating from the 1850s to the present. Time intervals between shoreline positions ranged from 30 years to multiple datasets per year. The U.S. Geological Survey's Digital Shoreline Analysis System (DSAS) was used to analyze the shoreline data. Analysis of the dataset reveals that storms have heavily influenced shoreline position. Shoreline retreat during the period from 1851—present has averaged less than 1 meter per year. Periods of more rapid retreat have been associated with the occurrence of major storms. A six-decade period of relative quiescence during the mid-20^th century resulted in modest advance of the island's coastline. A cluster of three major storms during the period 1995–2005 had a major impact on the morphology and stability of the island. Much of the foredune complex was lost and rates of coastal retreat increased significantly. The historical shoreline data therefore underscore the dominant influence of storm frequency and intensity in determining coastal change.

Morang, A.; Rosati, J.D., and King, D.B., 2013. Regional sediment processes, sediment supply, and their impact on the Lousiana coast. In: Brock, J.C.; Barras, J.A., and Williams, S.J. (eds.), Understanding and Predicting Change in the Coastal Ecosystems of the Northern Gulf of Mexico, Journal of Coastal Research, Special Issue No. 63, pp. 141-165, Coconut Creek (Florida), ISSN 0749-0208.

Coastal Louisiana is geologically unique in the United States because its complex shallow geologic structure is the result of fluvial deposition (Mississippi and Atchafalaya Rivers) and marine reworking over thousands of years. Other characteristics include the preponderance of fine sediment, relative youth, and shallow nearshore slope. It has been impacted by more than 150 years of project-focused designs that have modified regional sediment transport. Because of engineering and commercial activities on the upper Mississippi River and the delta, the system is now suffering from innumerable geomorphic changes, which have produced profound social and economic consequences. Sediment to this coast has been almost totally supplied by the Mississippi's distributaries, with deltaic lobes changing over the centuries. Sediment delivery has diminished by over 50% during the last 150 years because of up-river engineering activities such as dam construction, bank stabilization, dredging, and levees. The ultimate implication of reduced sediment and rapid relative sea-level rise is that the delta can no longer grow as it did before urbanization and development of the continent. A sediment budget has been developed for the Louisiana coast based on multiyear data preceding Hurricanes Katrina and Rita. The budget is based on numerous sources and dredging data from the U.S. Army Corps of Engineers, New Orleans District. Despite the typically low-wave energy climate, sediment is transported alongshore between some cells. Also, there is significant loss offshore, possibly a consequence of storm impacts, sediment consolidation, and rapid relative sea-level rise.

Byrnes, M.R.; Rosati, J.D.; Griffee, S.F., and Berlinghoff, J.L., 2013. Historical sediment transport pathways and quantities for determining an operational sediment budget: Mississippi Sound barrier islands. In: Brock, J.C.; Barras, J.A., and Williams, S.J. (eds.), Understanding and Predicting Change in the Coastal Ecosystems of the Northern Gulf of Mexico, Journal of Coastal Research, Special Issue No. 63, pp. 166–183, Coconut Creek (Florida), ISSN 0749-0208.

Historical shoreline and bathymetric survey data were compiled for the barrier islands and passes fronting Mississippi Sound to identify net littoral sand transport pathways, quantify the magnitude of net sand transport, and develop an operational sediment budget spanning a 90-year period. Net littoral sand transport along the islands and passes is primarily unidirectional (east-to-west). Beach erosion along the east side of each island and sand spit deposition to the west result in an average sand flux of about 400,000 cy/yr (305,000 m³/yr) throughout the barrier island system. Dog Keys Pass, located updrift of East Ship Island, is the only inlet acting as a net sediment sink. It also is the widest pass in the system (about 10 km) and has two active channels and ebb shoals. As such, a deficit of sand exists along East Ship Island. Littoral sand transport decreases rapidly along West Ship Island, where exchange of sand between islands terminates because of wave sheltering from the Chandeleur Islands and shoals at the eastern margin of the St. Bernard delta complex, Louisiana. These data were used to assist with design of a large island restoration project along Ship Island, Mississippi.

Williams, S.J., 2013. Sea-level rise implications for coastal regions. In: Brock, J.C.; Barras, J.A., and Williams, S.J. (eds.), Understanding and Predicting Change in the Coastal Ecosystems of the Northern Gulf of Mexico, Journal of Coastal Research, Special Issue No. 63, pp. 184–196, Coconut Creek (Florida), ISSN 0749-0208.

Sea-level rise, a dominant driving force of change for coastal regions, is becoming increasingly important as a hazard to humans and urban areas in the coastal zone worldwide as global climate change takes effect. The geologic record shows that sea level, due to past natural climate factors, has been highly variable, as much as 6-8 m higher than present during the last interglacial warm period and 130 m lower during the last glacial period. Sea level was fairly stable for the past 3,000 years until about the mid- 19^th century. During the 20^th century, sea level began rising at a global average rate of 1.7 mm/yr. The current average rise rate is 3.1 mm/yr, a 50% increase over the past two decades. Many regions are experiencing even greater rise rates due to local geophysical (e.g., Louisiana, Chesapeake Bay) and oceanographic (Mid-Atlantic coast) forces. A few regions experience rise rates less than the global average due to land uplift. Observations show the increase of carbon emissions since the Industrial Revolution has increased global mean temperature of the air and ocean, which is responsible for sea-level rise due to ice sheet melting and steric expansion, and many related environmental changes. Sea-level rise, with high regional variability, is exhibiting acceleration and is expected to continue for centuries unless mitigation is enacted to reduce atmospheric carbon. Low-lying coastal plain regions, deltas, and most islands are highly vulnerable. Adaptation planning on local, state and national scales for projected sea-level rise of 0.5–2 m by A.D. 2100 is advisable. Sustained global rise in sea level of 4 m to as much as 8 m is possible, but not likely until well after A.D. 2100.

Gesch, D.B., 2013. Consideration of vertical uncertainty in elevation-based sea-level rise assessments: Mobile Bay, Alabama case study, In: Brock, J.C.; Barras, J. A., and Williams, S.J. (eds.), Understanding and Predicting Change in the Coastal Ecosystems of the Northern Gulf of Mexico, Journal of Coastal Research, Special Issue No. 63, pp. 197–210, Coconut Creek (Florida), ISSN 0749-0208.

The accuracy with which coastal topography has been mapped directly affects the reliability and usefulness of elevationbased sea-level rise vulnerability assessments. Recent research has shown that the qualities of the elevation data must be well understood to properly model potential impacts. The cumulative vertical uncertainty has contributions from elevation data error, water level data uncertainties, and vertical datum and transformation uncertainties. The concepts of minimum sealevel rise increment and minimum planning timeline, important parameters for an elevation-based sea-level rise assessment, are used in recognition of the inherent vertical uncertainty of the underlying data. These concepts were applied to conduct a sea-level rise vulnerability assessment of the Mobile Bay, Alabama, region based on high-quality lidar-derived elevation data. The results that detail the area and associated resources (land cover, population, and infrastructure) vulnerable to a 1.18-m sea-level rise by the year 2100 are reported as a range of values (at the 95% confidence level) to account for the vertical uncertainty in the base data. Examination of the tabulated statistics about land cover, population, and infrastructure in the minimum and maximum vulnerable areas shows that these resources are not uniformly distributed throughout the overall vulnerable zone. The methods demonstrated in the Mobile Bay analysis provide an example of how to consider and properly account for vertical uncertainty in elevation-based sea-level rise vulnerability assessments, and the advantages of doing so.

Glick, P.; Clough, J.; Polaczyk, A.; Couvillion, B., and Nunley, B., 2013. Potential effects of sea-level rise on coastal wetlands in southeastern Louisiana. In: Brock, J.C; Barras, J.A., and Williams, S.J. (eds.), Understanding and Predicting Change in the Coastal Ecosystems of the Northern Gulf of Mexico, Journal of Coastal Research, Special Issue No. 63, pp. 211-233, Coconut Creek (Florida), ISSN 0749–0208.

Coastal Louisiana wetlands contain about 37% of the estuarine herbaceous marshes in the conterminous United States. The long-term stability of coastal wetlands is often a function of a wetland's ability to maintain elevation equilibrium with mean sea level through processes such as primary production and sediment accretion. However, Louisiana has sustained more coastal wetland loss than all other states in the continental United States combined due to a combination of natural and anthropogenic factors, including sea-level rise. This study investigates the potential impact of current and accelerating sea-level rise rates on key coastal wetland habitats in southeastern Louisiana using the Sea Level Affecting Marshes Model (SLAMM). Model calibration was conducted using a 1956–2007 observation period and hindcasting results predicted 35% versus observed 39% total marsh loss. Multiple sea-level-rise scenarios were then simulated for the period of 2007–2100. Results indicate a range of potential wetland losses by 2100, from an additional 2,188.97 km² (218,897 ha, 9% of the 2007 wetland area) under the lowest sea-level-rise scenario (0.34 m), to a potential loss of 5,875.27 km² (587,527 ha, 24% of the 2007 wetland area) in the highest sea-level-rise scenario (1.9 m). Model results suggest that one area of particular concern is the potential vulnerability of the region's baldcypress-water tupelo (Taxodium distichum-Nyssa aquatica) swamp habitat, much of which is projected to become permanently flooded (affecting regeneration) under all modeled scenarios for sea-level rise. These findings will aid in the development of ecosystem management plans that support the processes and conditions that result in sustainable coastal ecosystems.

Thatcher, C.A.; Brock J.C., and Pendleton, E.A., 2013. Economic Vulnerability to Sea-Level Rise Along the Northern U.S. Gulf Coast. In: Brock, J.C.; Barras, J.A., and Williams, S.J. (eds.), Understanding and Predicting Change in the Coastal Ecosystems of the Northern Gulf of Mexico, Journal of Coastal Research, Special Issue No. 63, pp. 234–243, Coconut Creek (Florida), ISSN 0749–0208.

The northern Gulf of Mexico coast of the United States has been identified as highly vulnerable to sea-level rise, based on a combination of physical and societal factors. Vulnerability of human populations and infrastructure to projected increases in sea level is a critical area of uncertainty for communities in the extremely low-lying and flat northern gulf coastal zone. A rapidly growing population along some parts of the northern Gulf of Mexico coastline is further increasing the potential societal and economic impacts of projected sea-level rise in the region, where observed relative rise rates range from 0.75 to 9.95 mm per year on the Gulf coasts of Texas, Louisiana, Mississippi, Alabama, and Florida. A 1-m elevation threshold was chosen as an inclusive designation of the coastal zone vulnerable to relative sea-level rise, because of uncertainty associated with sea-level rise projections. This study applies a Coastal Economic Vulnerability Index (CEVI) to the northern Gulf of Mexico region, which includes both physical and economic factors that contribute to societal risk of impacts from rising sea level. The economic variables incorporated in the CEVI include human population, urban land cover, economic value of key types of infrastructure, and residential and commercial building values. The variables are standardized and combined to produce a quantitative index value for each 1-km coastal segment, highlighting areas where human populations and the built environment are most at risk. This information can be used by coastal managers as they allocate limited resources for ecosystem restoration, beach nourishment, and coastal-protection infrastructure. The study indicates a large amount of variability in index values along the northern Gulf of Mexico coastline, and highlights areas where long-term planning to enhance resiliency is particularly needed.

Yáñez-Arancibia, A.; Day, J.W., and Reyes, E., 2013. Understanding the coastal ecosystem-based management approach in the Gulf of Mexico. In: Brock, J.C.; Barras, J.A., and Williams, S.J. (eds.), Understanding and Predicting Change in the Coastal Ecosystems of the Northern Gulf of Mexico, Journal of Coastal Research, Special Issue No. 63, pp. 244–262, Coconut Creek (Florida), ISSN 0749–0208.

The Gulf of Mexico (GOM) is a shared ecosystem in which problems and solutions are a common responsibility among governments, primarily the United States and Mexico. Concepts about management of coastal systems suggest that GOM ecosystem-based management approaches should be coupled with ecological risk assessment and that quantitative modeling is a valuable tool for ecosystem-based management, which results in sound sustainable management. Sustainable management requires the consideration of a number of processes and issues. These include definition of ecological regions, description of processes controlling primary productivity, wetland restoration and coastal fisheries, and an understanding that pulsing is a fundamental characteristic of coastal systems, that climate change must be taken into consideration in management, and that environmental sustainability and socioeconomic development are strongly related. Throughout the 6,134 km of coastline stretching from Florida to Quintana Roo, there are several major geographic regions that include the warm-temperate GOM, the tropical GOM, and the Caribbean coast connected to the GOM. Within each geographic region, discrete complex systems can be defined as geographic/hydrological subregions, characterized by the interactions of geology, geomorphology, oceanography, climate, freshwater input, biogeochemistry, coastal vegetation, wildlife, estuary-shelf interactions, and human factors. We conclude: (a) system functioning should serve as a basis for sustainable coastal management; and (b) to sustain environmental and socioeconomic conditions, the GOM must be maintained as a healthy, productive, and resilient ecosystem. The challenge for future coastal management in the GOM should be towards an integration of coastal management with large marine ecosystem management.