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2: Coastal Processes

Nancy T. DeWitt, James G. Flocks, and B.J. Reynolds

U.S. Geological Survey, Florida Integrated Science Center, St. Petersburg, Florida

The Gulf Islands National Seashore (GUINS) is a series of barrier islands that provides protection along the Mississippi – Alabama coastline. These barrier islands archive 300 years of human history that the National Park Service (NPS) is responsible for preserving and protecting. The largest structure within GUINS is Fort Massachusetts, which was built on Ship Island in 1861 and is located offshore of Biloxi, MS. Due to the historical significance of the Fort and other sites on Ship Island, NPS is dedicated to preserving the structural integrity and stability of the adjacent shoreline, dunes, and vegetation. Previous studies indicate that Ship Island has continually undergone significant change. In particular is the formation of Camille Cut, an initial product of Hurricane Camille in 1969, which breached the island into what is now West and East Ship Islands. Hurricane Katrina, which passed nearby in 2005, doubled the breach in size. To provide a post-Katrina assessment of Camille Cut, the U.S. Geological Survey (USGS) conducted high-resolution single-beam bathymetry to identify, compare, and contrast shot-term bathymetric change and the influence it has on long-term bathymetric changes. High-resolution single-beam bathymetry offers a cost-effective and efficient way to measure seafloor change in shallow-water (2-3 m) areas such as Camille Cut. Over 165 km of single-beam lines were surveyed in the summer of 2007 and replicated in the summer of 2008. This report outlines the methodology for data acquisition, processing, and reports the results.

Contact Information: Nancy T. DeWitt, U.S. Geological Survey, Florida Integrated Science Center, 600 4th Street South, St. Petersburg, FL 33701; phone: 727-803-8747; email: ndewitt@usgs.gov

Emily S. Klipp1, Xan Yates1, Laurinda Travers2, Amar Nayegandhi1, John Brock3, Jamie M. Bonisteel1, and C. Wayne Wright4

1 Jacobs Technology/U.S. Geological Survey, Florida Integrated Science Center, St. Petersburg, Florida
2 Eckerd College/U.S. Geological Survey, Florida Integrated Science Center, St. Petersburg, Florida
3 U.S. Geological Survey, Coastal and Marine Geology Program, National Center, Reston, Virginia
4 U.S. Geological Survey, Florida Integrated Science Center, St. Petersburg, Florida

The USGS Coastal and Marine Geology (CMG) Program, through partnerships with the National Aeronautics and Space Administration (NASA), the National Oceanic and Atmospheric Administration (NOAA), and the National Park Service (NPS), is involved in the creation of Open-File Reports and Data Series products that consist of remotely sensed, geographically referenced elevation measurements of Lidar-derived topography. These products are used for monitoring geomorphic changes, habitat mapping, ecological monitoring, classification, and event assessment through analysis of the data. The raw data are acquired by the Experimental Advanced Airborne Research Lidar (EAARL) system, a waveform-resolving, green-wavelength laser-ranging system capable of mapping submerged and subaerial topography in a single overflight. The data are processed, filtered, and manually edited to remove any outliers or other false returns. The data are stored in a GIS-ready GeoTIFF, LAS, and xyz data format indexed through an HTML interface and are distributed on a CD/DVD and made available online. Currently, 16 of these products have been published, with six more planned for publication by the end of fiscal year 2008. The products include locations surveyed within the boundaries of the NPS Inventory & Monitoring Program for the Northeast Coastal and Barrier, Gulf Coast, and South Florida and Caribbean Networks and include any combination of bare-earth, first-surface, and submerged topography with associated metadata.

Contact Information: Emily S. Klipp, Jacobs Technology/U.S. Geological Survey, Florida Integrated Science Center, 600 4th Street South, St. Petersburg, FL 33701; phone: 727-803-8747; email: eklipp@usgs.gov

Paul O. Knorr1, Lisa L. Robbins1, and P.J. Harries2

1 U.S. Geological Survey, Florida Integrated Science Center, St. Petersburg, Florida
2 Department of Geology, University of South Florida, Tampa, Florida

Atmospheric CO2 concentrations, currently near 380 ppm, are expected to reach double pre-industrial levels of 560 ppm before the year 2100. Some models (e.g. Caldeira and Wickett, 2003) indicate that atmospheric CO2 may reach levels as high as 1,900 ppm by the year 2300. The oceanic CO2 reservoir is simultaneously absorbing increased quantities of atmospheric CO2, with concomitant increases in carbonic acid, decreases in pH, and decreases in calcium carbonate saturation state. Open-ocean pH values have decreased by 0.1 to 8.1 since pre-industrial times and are predicted to decrease 0.3 to 0.5 in the next 80 years. If atmospheric CO2 levels reach 1,900 ppm, oceanic pH levels may drop below 7.5.

This process of ocean acidification will likely modify the biogeochemical processes of calcification and carbonate sediment production. Members of the genus Halimeda, a calcareous green segmented macroalgae, are important producers of carbonate sediments in tropical, shallow-water, carbonate settings. Aragonite crystals begin to precipitate approximately 36 hours after the growth of a new segment and continue until available space within the segment is completely filled. Halimeda opuntia and Halimeda tuna were grown in a sealed aquarium containing an aragonite substrate, air bubbler, temperature and pH probes, and a CO2-injection apparatus. The water in the aquarium was maintained at pH 7.5 by controlling the levels of pCO2 in the water. Scanning electron microscopy was used to study ultrastructural details of aragonite crystal morphology of segments grown in pH 8.1 water and pH 7.5 water. As pH was decreased, a species-dependent increase in crystal growth density and a decrease in crystal width was noted.

Contact Information: Paul Knorr, U.S. Geological Survey, Florida Integrated Science Center, 600 4th Street South, St. Petersburg, FL 33701; phone: 727-803-8747; email: pknorr@usgs.gov

Lisa E. Osterman1, Richard Z. Poore1, Peter W. Swarzenski2

1 U.S. Geological Survey, Florida Integrated Science Center, St Petersburg, Florida
2 U.S. Geological Survey, Pacific Science Center, Santa Cruz, California

Hypoxia (dissolved oxygen <2 mg l-1) occurs annually on the Louisiana shelf and has been linked to increased transport of anthropogenic nutrients (fertilizer, feed lots, etc.) by the Mississippi River. The relative abundance of three species of low-oxygen-tolerant benthic foraminifers, the PEB index, in sediment cores is used to trace the initiation, spread, and spatial distribution of hypoxic conditions prior to the start of the systematic monitoring efforts begun in 1985. Nine box cores, with excess 210Pb chronologies, were collected throughout the modern “dead zone.” The PEB from the box cores indicate that the chronic seasonal hypoxia began to develop round 1920 and was well established by 1960.

The PEB results from three gravity- and box-core pairs (PE0305-1, MRD05-4 and MRD05-6) provide a cross-shelf transect of the history of earlier low-oxygen events on the continental shelf. Gravity-core chronologies are established by two basal 1000 14C dates on foraminiferal tests. The two cores collected from within the area of the modern hypoxia “dead zone” contain multiple peaks of elevated PEB species, interpreted as naturally caused episodes of low-oxygen water on the shelf over the last 1000 14C years. The gravity core collected outside of the monitored area of hypoxia contains elevated PEB values only in the last ~50 years, indicating that anthropogenically caused low-oxygen conditions have affected the benthic fauna outside of the monitored “dead zone.”

These results support the hypothesis that naturally occurring low-oxygen bottom-water events have taken place periodically on the Louisiana shelf over the last 1000 C14 years as a result of episodes of increased Mississippi River discharge and associated wetland export. The results also indicate that modern hypoxia is greater in frequency or duration and more extensive geographically than earlier naturally occurring low-oxygen bottom-water events. We conclude that the development of low-oxygen bottom water on the continental shelf is a natural process that has been significantly modified by human activities during that last ~50 years.

Contact Information: Lisa E. Osterman, U.S. Geological Survey, Florida Integrated Science Center, 600 Fourth St. South, St. Petersburg, Florida 33701; phone: 727-803-8747 x 3084; fax: 727-803-2032; email: osterman@usgs.gov

Ellen A. Raabe, Domonique K. Pope, Laura C. Roy, Melanie S. Harris, and Richard P. Stumpf

U.S. Geological Survey, Florida Integrated Science Center, St. Petersburg, Florida

The southeast region of the United States boasts many miles of coastal lowlands, buffered by barrier islands, shallow shelf gradients, and estuarine embayments. These coastal lowlands support productive fisheries and tidal wetlands and serve as a primary habitat and food resource for many aquatic and terrestrial species. Warming trends and sea-level rise under the current climate-change scenario pose a very real threat to the status quo of coastal lowland ecosystems. A geographic analysis of historic topographic charts, general land surveys, and maps of modern coastal features provides insights into the types and patterns of long-term change along the central and northern Gulf Coast of Florida. Comparison of a 20-year time series of Landsat satellite imagery sheds light on short-term changes in vegetation, biomass, and recovery patterns. Short-term biomass change seems to be episodic in response to extreme storm events, low winter temperatures, and periods of drought. Since vegetation in the coastal zone is largely resilient to such episodic events, areas lacking recovery indicate that ecosystem tolerance may have been overwhelmed by a combination of forcing factors. Evaluation of long-term change on Florida’s Gulf Coast provided verification of permanent area loss in coastal forest at almost three times the rate of area loss in tidal wetlands. Persistent loss of the coastal forest seems to be ameliorated primarily at locations with reliable freshwater flow. Habitat loss or change was exacerbated by logging activities, road construction, and alterations to hydrologic flow. A conversion from tidal marsh to mangrove forests was also documented with long-term change analysis. The tidal marsh-to-mangrove conversion may be attributable to both natural and man-made factors. The presentation will illustrate these changes in maps, diagrams, and photos as developed for several U.S. Geological Survey projects.

Contact Information: Ellen Raabe, U.S. Geological Survey, Florida Integrated Science Center, 600 4th Street South, St. Petersburg, FL 33701; phone: 727-803-8747; email: eraabe@usgs.gov

Christopher D. Reich1, James G. Flocks1, Peter W. Swarzenski2, Jeffrey B. Davis3, and David T. Rudnick4

1 U.S. Geological Survey, Florida Integrated Science Center, St. Petersburg, Florida
2 U.S. Geological Survey, Santa Cruz, California
3 St. Johns River Water Management District, Palatka, Florida
4 South Florida Water Management District, West Palm Beach, Florida

Florida Bay has been a focus of Everglades restoration because water quality in the bay and Everglades is closely linked. Prolonged algal blooms, which occurred in the 1990s and in recent years, are of particular concern. To understand causes of these blooms and predict future effects of management changes, all major sources of nutrient influx to the system need to be quantified. Quantifying groundwater as a nutrient vector is difficult because groundwater is spatially non-uniform and temporally influenced by tides and meteorological events. Resistivity surveys in Florida Bay were conducted in wet and dry seasons to elucidate fine-scale spatial variability in potential groundwater connectivity by mapping the resistivity of groundwater and surface water. Preliminary results from the wet- and dry-season surveys indicate that little variability occurs in the areas surveyed. This indicates either that water exchange is uniform annually or that the groundwater signal does not vary enough for the resistivity to identify any preferential leakage along the coastline. Continuous resistivity-profile results are comparatively uniform between the northern shore, where fresh surface water flows into the bay, and the area of southern and eastern shores, where tidal pumping drives groundwater/surface-water exchange.

Both land-based and continuous resistivity-profile surveys were conducted in a series of lakes near Orlando, FL. The objective of the lake surveys was to utilize the resistivity data to map underlying geologic lithology and framework. Geologic control on lake hydrology remains poorly understood. Most of the lakes were formed by sinkholes. Composition of the geologic material (clays vs. sand) undoubtedly has an impact on how well a lake holds water. For instance, merged resistivity profiles in Lake Prevatt indicate well-defined zones of highly resistive layers that could be indicative of sands and low resistivity units that may be representative of clays. These units seem to correlate with sediment samples obtained from split spoons in test holes drilled in the lake bottom. Subsurface structure related to karst formation was identified in Lake Prevatt and several other surveyed lakes. Thickness and lateral continuity of the clay and sand units were identified in the resistivity profiles and may be used to estimate hydrologic parameters, such as leakage, once vertical hydraulic conductivity is determined.

Contact Information: Christopher D. Reich, U.S. Geological Survey, Florida Integrated Science Center, 600 4th Street South, St. Petersburg, FL 33701; phone: 727-803-8747; email: creich@usgs.gov

Peter W. Swarzenski1, Chris Reich2, and David Rudnick3

1 U.S. Geological Survey, Santa Cruz, California
2 U.S. Geological Survey, St. Petersburg, Florida
3 South Florida Water Management District, West Palm Beach, Florida

Submarine ground-water discharge (SGD) estimates into Florida Bay remain one of the least understood and poorly constrained components in a water budget for this system. Research activities for this project included two parts. The first involved the use of a natural geochemical tracer (222Rn) to examine potential (SGD) hotspots (222Rn surveys) and to quantify total (saline water + freshwater component) SGD rates at select sites using 222Rn time-series measurements. The second research component utilized marine continuous resistivity profiling (CRP) surveys to examine the subsurface salinity structure within Florida Bay sediments. To obtain a map of the 222Rn distribution within our study site in Florida Bay, we set up a flow-through system on a small boat that consisted of a DGPS (with depth), a calibrated YSI CTD with a sampling rate of 0.5 min, and a submersible pump (z = 0.5 m) that continuously fed water into an air/water exchanger that was plumbed simultaneously into four RAD7 222Rn air monitors.

In addition to the radon measurements, we also ran continuous resistivity profiles (CRP) within our study site. This system consisted of an AGI SuperSting 8 channel receiver attached to a streamer cable that has 2 current (A,B) electrodes and 9 potential electrodes spaced 10m apart. A separate DGPS continuously sent position information to the SuperSting. To obtain local advective ground-water flux estimates, 222Rn time-series experiments were deployed strategically positioned across hydrologic and geologic gradients within our study site. These time-series stations consisted of a submersible pump, a Solinist DIVER (to record continuous CTD parameters) and two RAD7 222Rn air monitors plumbed into an air/water exchanger. Time-series 222Rn measurements were conducted for 3-4 days across several tidal excursions. Radon was also measured in the air during each sampling campaign by a dedicated RAD7. We obtained ground-water discharge information by setting up a 222Rn mass balance that accounted for lateral and horizontal exchange and an appropriate ground-water 222Rn endmember activity.

Results indicate that the 222Rn maps provide a useful gauge of relative ground-water discharge into Florida Bay. The 222Rn time-series measurements provide a reasonable estimate of site specific total (saline and fresh) ground-water discharge, and the saline nature of the shallow ground water underneath our study site, as evidenced by CPR results, indicate that most of this discharge must be recycled seawater. The CRP data show some interesting trends that appear to be corroborated with geologic and hydrologic observations. For example, some of the highest resistivity (electrical conductivity-1) values were recorded where one would expect a slight subsurface freshening (e.g., bayside Key Largo, C111 canal).

Contact Information: Peter W. Swarzenski, U.S. Geological Survey, 400 Natural Bridges Drive, Santa Crutz, CA 95060; phone: 831-427-4729; email: pswarzen@usgs.gov

Kathy A. Tedesco1, Eric J. Tappa2, Robert C. Thunell2, and Richard Z. Poore1

1 U.S. Geological Survey, Florida Integrated Science Center, St. Petersburg, Florida
2 University of South Carolina, Department of Geological Sciences, Columbia, South Carolina

A quantitative understanding of natural and anthropogenic influences on the Earth’s climate system is necessary to anticipate future changes in climate. While paleoclimate reconstructions provide information regarding the timing and magnitude of natural climate variability, the accuracy of these constructions is dependent largely on the reliability of the proxies. In January 2008, a time-series sediment trap was deployed in the northern Gulf of Mexico at 27° 31′N and 90° 21′W in 1,200 m of water to measure the sediment geochemistry (carbonate, biogenic opal, organic carbon, terrigenous material) and planktonic foraminiferal assemblage and shell chemistry (stable isotope, Mg/Ca ratios) and for comparison with concurrent hydrographic and climatic observations. The results of this study will provide improved calibration of standard climate proxies leading to enhanced interpretation and correlation between marine and terrestrial paleoclimate records.

Results will be presented from weekly sediment-trap samples collected over a 6-month period from January through July 2008. Preliminary results for the first 3 months indicate total sediment mass and planktonic foraminiferal fluxes are highest in January and February with values up to 0.30 grams m-2 day-1 and ~145 shells m-2 day-1, respectively. During this winter period, the assemblage is dominated by Globorotalia truncatulinoides, which makes up more than 60% of the assemblage, Globigerina calida, and Pulleniatina obliquiloculata. In the spring, total mass fluxes decrease to 0.07 grams m-2 day-1 and foraminiferal fluxes to ~30 shells m-2 day-1 as sea surface temperature increases. In addition, the spring assemblage is more diverse and is composed of Globorotalia crassaformis, Globigerinoides ruber (pink), G. ruber (white), Globigerina rubescens, Globigerinita glutinata, Globigerinoides sacculifer, and Neogloboquadrina dutertrei.

Contact Information: Kathy A. Tedesco, U.S. Geological Survey, Florida Integrated Science Center, 600 4th Street South, St. Petersburg, FL 33701; phone: 727-803-8747; email: ktedesco@usgs.gov