Apalachicola Bay Research Articles

Modeled Sea Level Rise Impacts on Coastal Ecosystems at Six Major Estuaries on Florida's Gulf Coast: Implications for Adaptation Planning.

The Sea Level Affecting Marshes Model (SLAMM) was applied at six major estuaries along Florida’s Gulf Coast (Pensacola Bay, St. Andrews/Choctawhatchee Bays, Apalachicola Bay, Southern Big Bend, Tampa Bay and Charlotte Harbor) to provide quantitative and spatial information on how coastal ecosystems may change with sea level rise (SLR) and to identify how this information can be used to inform adaption planning. High resolution LiDAR-derived elevation data was utilized under three SLR scenarios: 0.7 m, 1 m and 2 m through the year 2100 and uncertainty analyses were conducted on selected input parameters at three sites. Results indicate that the extent, spatial orientation and relative composition of coastal ecosystems at the study areas may substantially change with SLR. Under the 1 m SLR scenario, total predicted impacts for all study areas indicate that coastal forest (-69,308 ha; -18%), undeveloped dry land (-28,444 ha; -2%) and tidal flat (-25,556 ha; -47%) will likely face the greatest loss in cover by the year 2100. The largest potential gains in cover were predicted for saltmarsh (+32,922 ha; +88%), transitional saltmarsh (+23,645 ha; na) and mangrove forest (+12,583 ha; +40%). The Charlotte Harbor and Tampa Bay study areas were predicted to experience the greatest net loss in coastal wetlands The uncertainty analyses revealed low to moderate changes in results when some numerical SLAMM input parameters were varied highlighting the value of collecting long-term sedimentation, accretion and erosion data to improve SLAMM precision. The changes predicted by SLAMM will affect exposure of adjacent human communities to coastal hazards and ecosystem functions potentially resulting in impacts to property values, infrastructure investment and insurance rates. The results and process presented here can be used as a guide for communities vulnerable to SLR to identify and prioritize adaptation strategies that slow and/or accommodate the changes underway.

Baseflow response to climate variability induced droughts in the Apalachicola–Chattahoochee–Flint River Basin, U.S.A.

Droughts have been a major factor leading to the Tri-State Water Wars in the southeastern United States. One of the primary issues related to the conflict is the reduction in baseflow levels in the Flint River during droughts. This affects the availability of freshwater resources to support the endangered mussel species in the Flint and Apalachicola Rivers and threatens the shellfish industry in the Apalachicola Bay. Study of large-scale climate phenomena as well as the interactions of interannual with decadal and multidecadal oceanic–atmospheric phenomena can provide valuable information regarding regional climatic conditions such as droughts and their impact on water resources. This study was conducted to quantify the impacts of climate variability cycles on baseflow levels in the Flint River. The individual and coupled impacts of the El Nino-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), Atlantic Multidecadal Oscillation (AMO), and North Atlantic Oscillation (NAO) on baseflow were quantified. The non-parametric Joint Rank Fit (JRFit) procedure was used to provide a robust test of the significance of interactions between the phases of ENSO–PDO, ENSO–AMO and ENSO–NAO baseflows. Simple-main effect comparisons were also performed using the JRFit model to estimate significant difference between the positive and negative phase baseflows of PDO, AMO and NAO associated with El Nino or La Nina phases. The results indicate that the phases of ENSO, AMO and NAO significantly affect baseflows in the Flint River. Interaction tests showed that the PDO and AMO phases modulate ENSO phase baseflows. La Nina associated with positive phases of PDO and AMO resulted in greater decrease in baseflow levels of approximately 28% and 33%, respectively. However, La Nina associated with negative phase of AMO showed above normal baseflows. The results illustrate the importance of coupled analyses of climate variability by providing a better understanding of the severity of droughts and their impact on baseflows. The results obtained from this study can be used by water managers in the region as a guide for the issuance of drought severity-based water restrictions.

Tracing the intrusion of fossil carbon into coastal Louisiana macrofauna using natural 14C and 13C abundances

The Deepwater Horizon oil spill released a large volume of 13C and radiocarbon depleted organic matter to the northern Gulf of Mexico. Evidence of petroleum-derived carbon entering the offshore planktonic foodweb, as well as widespread oiling of coastal areas documented in previous studies suggests that hydrocarbons could have entered the near shore foodweb. To test this hypothesis, we measured radiocarbon (Δ14C%) and stable carbon isotopes (δ13C) in an assortment of fish tissue, invertebrate tissue and shell samples collected within a year of the spill at seven sites from Louisiana to Florida USA across the northern Gulf of Mexico. We observed a west–east gradient with the most depleted radiocarbon values found in Terrebonne Bay, Louisana and increasingly enriched radiocarbon values in organisms collected at sites to the east. Depleted radiocarbon values as low as −10% in invertebrate soft tissue from Terrebonne suggest assimilation of fossil carbon (2.8±1.2%), consistent with the hypothesis that organic matter from petrochemical reservoirs released during the Deepwater Horizon spill entered the coastal food web to a limited extent. Further there was a significant correlation between radiocarbon and δ13C values in invertebrate tissue consistent with this hypothesis. Both oyster tissue and hard head catfish tissue collected in impacted areas of coastal Louisiana were significantly depleted in 14C and 13C relative to organisms collected in the unaffected Apalachicola Bay, Florida (p<0.014). Alternative explanations for these results include the influence of chronic hydrocarbon pollution along the western gulf coast or that the organisms ingest carbon derived from 14C depleted organic matter mobilized during the erosion of coastal marshes in southern Louisiana.

The curious case of eastern oyster Crassostrea virginica stock status in Apalachicola Bay, Florida

Pine, W. E., III, C. J. Walters, E. V. Camp, R. Bouchillon, R. Ahrens, L. Sturmer, and M. E. Berrigan, 2015. The curious case of eastern oyster Crassostrea virginica stock status in Apalachicola Bay, Florida. Ecology and Society 20(3):46. https://doi.org/10.5751/ES-07827-200346

A National Survey of Consumer Preferences for Branded Gulf Oysters and Risk Perceptions of Gulf Seafood

Three restaurant taste panels and an online consumer survey were conducted during 2012-2013 to assess whether Gulf consumers would be willing to pay a premium for place-name specific (i.e., “branded”) Gulf oysters over typical “generic” Gulf oysters, and whether consumers in other U.S. markets would be willing to pay for branded Gulf oysters compared to other U.S. branded oysters. Panelists in the two Gulf Coast taste panels had strong preferences for local oyster varieties when they were aware of oyster variety names and harvest locations (i.e., during labeled rounds). In the absence this information (i.e., during blind rounds), panelists had no such preferences, and in the case of the Houston taste panel, actually had a significant distaste for the local Galveston Bay variety. Panelists in the Chicago taste panel had strong preferences for the Island Creek oyster, in both the blinded and labeled rounds, although during the labeled rounds, the Point aux Pins oysters fared equally well (statistically) to the Island Creeks. Additionally, during the labeled rounds, the Apalachicola Bay and Point aux Pins oysters were statistically more likely to be chosen over the San Antonio Bay oysters. Respondents to the online survey tended to have higher perceptions of quality and seafood safety regarding their own regionally-produced oysters relative to oysters from other regions. There was limited variation in perceptions from one Gulf Coast variety to another, with the exception of the Apalachicola Bay variety being rated higher in several cases, and the more general “Gulf of Mexico” category being rated lower. Online survey results indicate that, consumers living in eastern Gulf states such as Georgia and Florida may be willing to pay a premium for branded Gulf oysters, particularly oysters from Florida and Louisiana. Gulf consumers living in Alabama, Mississippi, Louisiana, and Texas, however, did not show any strong preferences for branded oysters relative to cheaper generic ones. Among non-Gulf consumers, survey results indicate that while a price discount may be needed to sell branded Gulf oysters relative to local oysters (i.e., relative to, say, East Coast oysters in East Coast markets), that Gulf oysters generally fared no worse than other non-local oysters (i.e., West Coast oysters in East Coast markets). Of the Gulf oysters tested, Atlantic Coast respondents appear to prefer Louisiana oysters. Pacific Coast respondents appear to be indifferent between most Atlantic Coast and Gulf Coast varieties. Also, it appears that relatively few respondents were concerned about the Deepwater Horizon oil spill when answering questions about oysters, although these concerns did affect preferences for Gulf Coast oysters negatively in some cases. Less than 1% of all respondents indicated any concern regarding Vibrio vulnificus, bacteria, or similar. However, such concerns, though not cited explicitly, may yet be latent in the reported perceptions of oysters from various Gulf Coast locations. These results would indicate that there is some room for opportunity for branded Gulf Coast oysters along these other two coasts in places where other non-local oysters are marketed successfully. The major challenge appears to be whether the price discount necessary to entice consumers in these other markets to buy Gulf Coast oysters relative to local varieties is yet sufficiently high as to remain a profitable enterprise for Gulf Coast producers. The price discounts estimated here in the range of $5-$10 per half-dozen sounds like a steep discount, but given the large differential in retail prices in Atlantic and Pacific markets - where oysters retail anywhere from $15 to $25 per half-dozen-- compared to Gulf Coast markets – where they retail in the neighborhood of $7 to $10 -- it is possible that even with the discounts, the prices received in these alternative markets may remain profitable.

Hydrodynamic modeling and analysis of sea-level rise impacts on salinity for oyster growth in Apalachicola Bay, Florida

In this study, a previously calibrated hydrodynamic model was applied to investigate the impacts of sea level rise on salinity variations and oyster growth in Apalachicola Bay. With available observed data (winds, tides, and river flow), a case study has been conducted for the period of June 10–July 9, 2005. In addition, sea level rise impacts under a range of river flow conditions have also been examined, which include minimum monthly flow, average monthly flow, and maximum monthly flow based on the flow data from 1977 to 2013. Referring to the case study conditions under the existing sea level, model simulations were conducted to examine salinity changes in the bay in response to the sea level rise scenarios of 0.31 m, 0.5 m and 1.0 m. SLR-induced saline water intrusion mainly enters the estuary from the large opening in the east boundary. Based on the optimal salinity range for oyster growth (20–25 at Cat Point and 17–26 at Dry Bar) in Apalachicola Bay, SLR impacts were evaluated based on the model predicted salinity at Dry Bay and Cat Point. Results indicate that sea level rise results in stronger impacts on Cat Point than Dry Bar. Under the flow conditions of average monthly flow and the observed daily flow during June 10–July 9, mean salinity at Dry Bar varies within 21–24 in the optimal salinity range under 0.31 m and 0.5 m SLR conditions; and further increase above 26.0 when SLR is equal to 1.0 m. Under the conditions of average monthly flow and the observed daily flow during June 10–July 9, the mean salinity at Cat Point is within the optimal range under existing sea level, and increases above the maximum optimal salinity of 27 under the SLR scenarios of 0.31 m, 0.5 m, and 1.0 m, respectively. Extreme low and high flow conditions have also been investigated to examine the combined effects of flow and SLR. At the same sea level rise conditions, salinity under minimum flow is much higher than those under average flow, while salinity under maximum flow is much lower than those under the average flow condition.

Dynamic Considerations of Sea-level Rise with Respect to Water Levels and Flooding in Apalachicola Bay

ABSTRACT Bacopoulos, P., and Hagen, S.C., 2014. Dynamic considerations of sea-level rise with respect to water levels and flooding in Apalachicola Bay. An examination of sea-level rise impacts on water levels and flooding extent in Florida's Apalachicola Bay and the nearby region was carried out using forcing conditions from Hurricane Dennis under multiple sea-level rise scenarios. A comparison of the modeled water levels at the inlets of the bay was conducted to determine if the trend in water levels at the inlets was linear or nonlinear in relation to increasing sea-level rise. Hydrodynamic simulations for five scenarios were performed, including a present-day (control) scenario reflecting current sea levels and four possible future sea-level rise scenarios. Water level distributions and flooding throughout the bay with either dynamic or static sea-level rise were compared, and the effects of nonlinearity in the hydrodynamic responses were measured using a normalized nonlinearity index. This analysis hi...

Sea-Level Rise Effects on Hurricane-Induced Salinity Transport in Apalachicola Bay

Huang, W.; Hagen, S.C.; Bacopoulos, P., and Teng, F., 2014. Sea-level rise effects on hurricane-induced salinity transport in Apalachicola Bay.Salinity is an important indicator for estuarine ecosystem. Estuarine salinity can be affected by hurricane and sea-level rises. In this study, hydrodynamic modeling study has been conducted to investigate the effects of sea-level rise on hurricane-induced salinity in Apalachicola Bay. By using the dataset for the Hurricane Dennis occurred in July, 2005, model simulations were conducted under different sea-level rise scenarios. Results from model simulations show the effects of sea-level rise on the estuarine salinity transport during different phases of the storm surge. Generally, the increase of water level by either storm surge or sea-level rise results in the intrusion of majority saline sea water from the east to the west through East Pass. Salinity at two oyster bars responds to the storm surge and sea-level rise differently because Cat Point is located in the east and Dry Bar is in the west of the river mouth. In Cat Point, sea-level rise can cause substantial increase of salinity because it is located between the river mouth and East Pass. Salinity at the peak of the storm surge reaches 30 ppt even without sea-level rise. While salinity at the end of the storm surge reduces to about 20 ppt under no sea-level rise condition at Cat Point, it substantially increases to 30 ppt in response to a sea-level rise of 0.2 m. However, in Dry Bar, salinity is less sensitive to the sea-level rise and the storm surge. At the peak of the storm surge, salinity in Dry Bar is 30 ppt, 28 ppt, 30 ppt., under SLR 0.2 m, 0.5 m, and 1.2 m, respectively. However, near the end of the storm surge, salinity is 22 ppt, 22 ppt, and 27 ppt under 0.2 m, 0.5 m, and 1.2 m SLR conditions, respectively. This indicates that, after the storm surge, salinity in Dry Bar can recover to the normal range (below 26 ppt) if sea-level rise is less or equal to 0.5 m.

Metagenomic assessment of the eastern oyster-associated microbiota.

Bacteria associated with the Eastern oysters (Crassostrea virginica) native to Apalachicola Bay, FL, were investigated using 16S rRNA gene amplicon metagenomic sequencing which revealed that the oyster microbiome was predominated by Cyanobacteria and Proteobacteria. We also found that the oyster tissues were predominated by the pathogenic and symbiotic Photobacterium spp. (formerly known as Vibrio damselae).

Effect of ENSO-Induced Climate Variability on Groundwater Levels in the Lower Apalachicola-Chattahoochee-Flint River Basin

<abstract> <bold><sc>Abstract.</sc></bold> Rapid population growth, urban sprawl, and increased agricultural production in the Apalachicola-Chattahoochee-Flint (ACF) river basin are threatening the availability of freshwater resources and greatly affecting the supply of freshwater to Apalachicola Bay, which supports a struggling shellfish industry. As a result, Alabama, Georgia, and Florida have been fighting over the allocation of ACF river basin water for the past three decades. The water conflict heats up every time there is drought in the basin. In the Southeast U.S., droughts are mainly caused by the La Niña phase of the seasonal-to-interannual climate variability phenomenon known as the El Niño Southern Oscillation (ENSO). Understanding and quantifying the impact of ENSO-induced climate variability on precipitation, soil moisture, streamflows, and groundwater levels can provide valuable information for sustainable management of water resources in this region. This study was undertaken to quantify the impact of ENSO on groundwater levels in the lower ACF river basin, an area highly dependent on groundwater for agricultural water use. Twenty-one observation wells with 30 years of monthly groundwater level data were used to study the ENSO-groundwater level relationship. Wavelet analysis techniques were used to study the teleconnection between ENSO and groundwater levels, while Mann-Whitney tests were conducted to quantify the impact. The effect of prolonged La Niña events on groundwater levels and their corresponding recovery periods were also studied. Results indicate a strong relationship between groundwater level fluctuations and ENSO. This relationship was found to be stronger during the recharge season (December-April) as compared to the non-recharge or agricultural irrigation season (May-November). The results obtained can be used to develop procedures for forecasting groundwater levels, which can then be used to better manage the groundwater resources of this region.

Assessment of chlorophyll-a variations in high- and low-flow seasons in Apalachicola Bay by MODIS 250-m remote sensing.

Chlorophyll-a (chl-a) is considered as a primary indicator for water quality and foods for oyster growth in Apalachicola estuarine ecosystem. Assessment of chl-a concentration variation in response to river inflow is important for estuarine environmental research and management. In this study, remote sensing analysis has been conducted to evaluate the effects of river inflow on chlorophyll concentrations in Apalachicola Bay of Florida in the northeast Gulf of Mexico. A remote sensing model for chl-a was improved and applied to map spatial distributions of chl-a by using Moderate Resolution Imaging Spectroradiometer (MODIS) 250-m resolution imageries in high-flow and low-flow seasons in 2001 and 2008. Chl-a values approximately ranged from the minimum 6μg/l to the maximum 29μg/l in the study period. Maximum chl-a concentration in high-flow season was almost twice above that in low-flow season. The averaged mean and minimum chl-a level in the high-flow season were approximately 42 and 28% higher than those in low-flow season, respectively. The remote sensing mapping of chl-a was able to show spatial variations of chl-a in the entire bay under different flow conditions, which indicated its advantage over the traditional field data sampling for monitoring water quality over a large area of estuary. The MODIS 250-m remote sensing regression model presented from this study can be used to support monitoring and assessment of the spatial chl-a distribution in the bay for environmental research and management in Apalachicola Bay.

A survey of deepwater horizon (DWH) oil-degrading bacteria from the Eastern oyster biome and its surrounding environment.

The deepwater horizon (DWH) accident led to the release of an estimated 794,936,474 L of crude oil into the northern Gulf of Mexico over an 85 day period in 2010, resulting in the contamination of the Gulf of Mexico waters, sediments, permeable beach sands, coastal wetlands, and marine life. This study examines the potential response of the Eastern oyster’s microbiome to hydrocarbon contamination and compares it with the bacterial community responses observed from the overlaying water column (WC) and the oyster bed sediments. For this purpose, microcosms seeded with DWH crude oil were established and inoculated separately with oyster tissue (OT), mantle fluid (MF), overlaying WC, and sediments (S) collected from Apalachicola Bay, FL, USA. Shifts in the microbial community structure in the amended microcosms was monitored over a 3-month period using automated ribosomal intergenic spacer region analysis, which showed that the microbiome of the OT and MF were more similar to the sediment communities than those present in the overlaying WC. This pattern remained largely consistent, regardless of the concentration of crude oil or the enrichment period. Additionally, 72 oil-degrading bacteria were isolated from the microcosms containing OT, MF, WC, and S and identified using 16S ribosomal RNA gene sequencing and compared by principal component analysis, which clearly showed that the WC isolates were different to those identified from the sediment. Conversely, the OT and MF isolates clustered together; a strong indication that the oyster microbiome is uniquely structured relative to its surrounding environment. When selected isolates from the OT, MF, WC, and S were assessed for their oil-degrading potential, we found that the DWH oil was biodegraded between 12 and 42%, under the existing conditions.

Genomic and phenotypic characterization of Vibrio cholerae non-O1 isolates from a US Gulf Coast cholera outbreak.

Between November 2010, and May 2011, eleven cases of cholera, unrelated to a concurrent outbreak on the island of Hispaniola, were recorded, and the causative agent, Vibrio cholerae serogroup O75, was traced to oysters harvested from Apalachicola Bay, Florida. From the 11 diagnosed cases, eight isolates of V. cholerae were isolated and their genomes were sequenced. Genomic analysis demonstrated the presence of a suite of mobile elements previously shown to be involved in the disease process of cholera (ctxAB, VPI-1 and -2, and a VSP-II like variant) and a phylogenomic analysis showed the isolates to be sister taxa to toxigenic V. cholerae V51 serogroup O141, a clinical strain isolated 23 years earlier. Toxigenic V. cholerae O75 has been repeatedly isolated from clinical cases in the southeastern United States and toxigenic V. cholerae O141 isolates have been isolated globally from clinical cases over several decades. Comparative genomics, phenotypic analyses, and a Caenorhabditis elegans model of infection for the isolates were conducted. This analysis coupled with isolation data of V. cholerae O75 and O141 suggests these strains may represent an underappreciated clade of cholera-causing strains responsible for significant disease burden globally.

Hydrodynamic Modeling of Hurricane Dennis Impact on Estuarine Salinity Variation in Apalachicola Bay

ABSTRACT Huang, W.; Hagen, S., and Bacopoulos, P., 2014. Hydrodynamic modeling of Hurricane Dennis impact on estuarine salinity variation in Apalachicola Bay. Hurricane Dennis made landfall in Florida on 10 July 2005 and caused a storm surge of 2.4 m in Apalachicola. Field observations of salinity, winds, and river inflows are available at a few stations in the bay during the hurricane event. Presented in this paper is a numerical modeling study that investigates the effects of Hurricane Dennis on estuarine mixing and transport. A previously calibrated three-dimensional (3D) estuarine hydrodynamic model was further validated by the field observations of salinity and water levels during the hurricane event. A large-scale storm-surge model was used to provide storm-surge hydrographs at the five estuarine boundaries for the 3D estuarine model. This model integration proved successful with the results indicating that the model predictions of storm-surge hydrographs and salinity match well with observations. M...

Genome Sequences of Clinical Vibrio cholerae Isolates from an Oyster-Borne Cholera Outbreak in Florida

Between November 2010 and April 2011, 11 cases of cholera were identified and associated with the consumption of raw oysters harvested from Apalachicola Bay, Florida. The etiological agent was the ctxAB-positive Vibrio cholerae serogroup O75. The genome sequences of the isolates provide useful information and are deposited in the public genome databases.

Phytoplankton Biomass and Composition in a River-Dominated Estuary During Two Summers of Contrasting River Discharge

Estuaries located in the northern Gulf of Mexico are expected to experience reduced river discharge due to increasing demand for freshwater and predicted periods of declining precipitation. Changes in freshwater and nutrient input might impact estuarine higher trophic level productivity through changes in phytoplankton quantity and quality. Phytoplankton biomass and composition were examined in Apalachicola Bay, Florida during two summers of contrasting river discharge. The 20 μm diatoms were an increasingly (20 to 70 %) larger component of phytoplankton biomass. Lower summer river discharges that lead to an areal contraction of lower (5–25 psu) salinity waters composed of higher phytoplankton biomass dominated by small ( 25 psu) salinity waters composed of relatively lower phytoplankton biomass and a higher percent contribution by >20 μm diatoms. A reduction in summer river discharge that leads to such a change in quantity and quality of estuarine phytoplankton available will result in a reduction in estuarine zooplankton productivity and possibly the productivity of higher trophic levels.

Seasonal and Inter-annual Patterns in Primary Production, Respiration, and Net Ecosystem Metabolism in Three Estuaries in the Northeast Gulf of Mexico

Measurements of primary production and respiration provide fundamental information about the trophic status of aquatic ecosystems, yet such measurements are logistically difficult and expensive to sustain as part of long-term monitoring programs. However, ecosystem metabolism parameters can be inferred from high frequency water quality data collections using autonomous logging instruments. For this study, we analyzed such time series datasets from three Gulf of Mexico estuaries: Grand Bay, MS; Weeks Bay, AL; and Apalachicola Bay, FL. Data were acquired from NOAA's National Estuarine Research Reserve System Wide Monitoring Program and used to calculate gross primary production (GPP), ecosystem respiration (ER), and net ecosystem metabolism (NEM) using Odum's open water method. The three systems represent a diversity of estuaries typical of the Gulf of Mexico region, varying by as much as two orders of magnitude in key physical characteristics, such as estuarine area, watershed area, freshwater flow, and nutrient loading. In all three systems, GPP and ER displayed strong seasonality, peaking in summer and being lowest during winter. Peak rates of GPP and ER exceeded 200 mmol O2 m−2 day−1 in all three estuaries. To our knowledge, this is the first study examining long-term trends in rates of GPP, ER, and NEM in estuaries. Variability in metabolism tended to be small among sites within each estuary. Nitrogen loading was highest in Weeks Bay, almost two times greater than that in Apalachicola Bay and 35 times greater than to Grand Bay. These differences in nitrogen loading were reflected in average annual GPP rates, which ranged from 825 g C m−2 year−1 in Weeks Bay to 401 g C m−2 year−1 for Apalachicola Bay and 377 g C m−2 year−1 in Grand Bay. Despite the strong inter-annual patterns in freshwater flow and salinity, variability in metabolic rates was low, perhaps reflecting shifts in the relative importance of benthic and phytoplankton productivity, during different flow regimes. The advantage of the open water method is that it uses readily available and cost-effective sonde monitoring technology to estimate these fundamental estuarine processes, thus providing a potential means for examining long-term trends in net carbon balance. It also provides a historical benchmark for comparison to ongoing and future monitoring focused on documenting the effect of human activities on the coastal zone.

Bar-built estuary as a buffer for riverine silicate discharge to the coastal ocean

River discharge is a primary source of silicates to the ocean. In this study, we show that a bar-built estuary can buffer this silicate input, which may influence the onset of the diatom spring bloom and have a leveling effect on coastal diatom production dynamics. Primary production in the northeastern Gulf of Mexico is strongly affected by the outflow of nutrient-rich water from the Apalachicola River that enters into the Apalachicola Bay. We compared the seasonal dynamics of dissolved silicate (DSi), dissolvable particulate biogenic silicate (BSi), and the total of dissolved and dissolvable silicate (DSi+BSi) in the water column and pore water at two sandy sublittoral sites located in Apalachicola Bay and the adjacent coastal Gulf of Mexico in order to determine the influence of the Bay on silicate transfer to the coastal Gulf. The one-year time series measurements in the Bay water column showed that DSi was strongly influenced by the riverine outflow, while the DSi concentrations in the nearby coastal Gulf water followed a different trend and appeared to be dominated by biological processes. The temporal changes in pore water DSi, BSi, and DSi+BSi were similar at both study sites suggesting that larger scale processes, i.e., increased sediment flushing by increased wave action in winter, controlled these changes. The sediments acted as a continuous source of DSi to the overlying water, and when the river discharge was lower during early winter, the magnitude of area-integrated DSi flux from the Bay sediments was similar to the riverine DSi input to the Bay. The Bay sediments thus functioned as a significant source of DSi for the Bay and the adjacent Gulf at the onset of the diatom spring bloom and before Apalachicola River discharge reached maximum discharge in late winter/early spring.

Regional discrimination of oysters using laser-induced breakdown spectroscopy

It is well known that eastern oysters (Crassostrea virginica) are bio-indicators and can be used to determine the elemental composition of an estuarine system. Laser-induced breakdown spectroscopy (LIBS) has been successfully used for the detect of trace elements in various environmental matrices. In this work, LIBS was used to characterize oysters collected from a total of six sites in two different coastal estuarine reserves – Grand Bay, Mississippi (4 sites) and Apalachicola Bay, Florida (2 sites). Multiple ionic and neutral elemental species of Al, C, Ca, Cu, Fe, K, Mg, Na, Si, Sr, and Zn were observed through LIBS spectral analysis of the harvested oysters. Principal component analysis, discriminant function analysis, and hierarchical cluster analysis were applied to a data matrix of identified elemental lines resulting in intra- and inter-site clustering of the oysters according to their geographical origin.

Tracking suspended particle transport via radium isotopes (226Ra and 228Ra) through the Apalachicola–Chattahoochee–Flint River system

Suspended particles in rivers can carry metals, nutrients, and pollutants downstream which can become bioactive in estuaries and coastal marine waters. In river systems with multiple sources of both suspended particles and contamination sources, it is important to assess the hydrologic conditions under which contaminated particles can be delivered to downstream ecosystems. The Apalachicola–Chattahoochee–Flint (ACF) River system in the southeastern United States represents an ideal system to study these hydrologic impacts on particle transport through a heavily-impacted river (the Chattahoochee River) and one much less impacted by anthropogenic activities (the Flint River). We demonstrate here the utility of natural radioisotopes as tracers of suspended particles through the ACF system, where particles contaminated with arsenic (As) and antimony (Sb) have been shown to be contributed from coal-fired power plants along the Chattahoochee River, and have elevated concentrations in the surficial sediments of the Apalachicola Bay Delta. Radium isotopes (228Ra and 226Ra) on suspended particles should vary throughout the different geologic provinces of this river system, allowing differentiation of the relative contributions of the Chattahoochee and Flint Rivers to the suspended load delivered to Lake Seminole, the Apalachicola River, and ultimately to Apalachicola Bay. We also use various geochemical proxies (40K, organic carbon, and calcium) to assess the relative composition of suspended particles (lithogenic, organic, and carbonate fractions, respectively) under a range of hydrologic conditions. During low (base) flow conditions, the Flint River contributed 70% of the suspended particle load to both the Apalachicola River and the bay, whereas the Chattahoochee River became the dominant source during higher discharge, contributing 80% of the suspended load to the Apalachicola River and 62% of the particles entering the estuary. Neither of these hydrologic scenarios, which were moderately low flow regimes, appeared to transport particles contaminated with arsenic and antimony to Apalachicola Bay.