Florida Estuary Research Articles

Diet Analysis of Subadult Kemp’s Ridley (Lepidochelys kempii) Turtles from West-Central Florida

Abstract The present study is the first to characterize Kemp’s ridley turtle (Lepidochelys kempii) diets between the west-central Florida estuaries of Tampa Bay to Charlotte Harbor. We analyzed the stomach contents of 20 stranded subadult L. kempii and found that their diets were primarily carnivorous, consisting mostly of calico crab (Hepatus epheliticus), stone crab (Menippe mercenaria), and blue crab (Callinectes sapidus). In addition, we found uncommon prey items including fish and horseshoe crab (Limulus polyphemus), suggesting these L. kempii are opportunistic feeders. When separated into 2 size classes (25–45 [n = 9] and > 45 [n = 11] cm straight carapace length), there was a significant difference in the turtles’ diet composition. These new insights into the ecology and life history of a critically endangered sea turtle reveal essential prey resources used by a poorly studied yet crucial subadult life stage.

Oil Characterization and Distribution in Florida Estuary Sediments Following the Deepwater Horizon Spill

Barrier islands of Northwest Florida were heavily oiled during the Deepwater Horizon spill, but less is known about the impacts to the shorelines of the associated estuaries. Shoreline sediment oiling was investigated at 18 sites within the Pensacola Bay, Florida system prior to impact, during peak oiling, and post-wellhead capping. Only two locations closest to the Gulf of Mexico had elevated levels of total petroleum hydrocarbons (TPH) and total polycyclic aromatic hydrocarbons (PAHs). These samples showed a clear weathered crude oil signature, pattern of depletion of C9 to C19 alkanes and C0 to C4 naphthalenes, and geochemical biomarker ratios in concordance with weathered Macondo crude oil. All other locations and sample times showed only trace petroleum contamination. The results of this study are consistent with available satellite imagery and visual shoreline survey data showing heavy shoreline oiling limited to sandy beaches near the entrance to Pensacola Bay and shorelines of Santa Rosa Island.

Drought Increases Consumer Pressure on Oyster Reefs in Florida, USA

Coastal economies and ecosystems have historically depended on oyster reefs, but this habitat has declined globally by 85% because of anthropogenic activities. In a Florida estuary, we investigated the cause of newly reported losses of oysters. We found that the oyster reefs have deteriorated from north to south and that this deterioration was positively correlated with the abundance of carnivorous conchs and water salinity. In experiments across these gradients, oysters survived regardless of salinity if conchs were excluded. After determining that conchs were the proximal cause of oyster loss, we tested whether elevated water salinity was linked to conch abundance either by increasing conch growth and survivorship or by decreasing the abundance of a predator of conchs. In field experiments across a salinity gradient, we failed to detect spatial variation in predation on conchs or in conch growth and survivorship. A laboratory experiment, however, demonstrated the role of salinity by showing that conch larvae failed to survive at low salinities. Because this estuary’s salinity increased in 2006 in response to reduced inputs of freshwater, we concluded that the ultimate cause of oyster decline was an increase in salinity. According to records from 2002 to 2012, oyster harvests have remained steady in the northernmost estuaries of this ecoregion (characterized by high reef biomass, low salinity, and low conch abundance) but have declined in the southernmost estuaries (characterized by lower reef biomass, increases in salinity, and increases in conch abundance). Oyster conservation in this ecoregion, which is probably one of the few that still support viable oyster populations, may be undermined by drought-induced increases in salinity causing an increased abundance of carnivorous conchs.

Climate Change: Effects on Salinity in Florida’s Estuaries and Responses of Oysters, Seagrass, and Other Animal and Plant Life

Florida’s economically important estuaries could be heavily impacted by sea-level rise and altered river flow, both caused by climate change. The resulting higher salinity, or saltiness of the water, could harm plants and animals, alter fish and bird habitat, and reduce the capacity of estuaries to provide such important services as seafood production and the protection of shorelines from erosion. This 6-page fact sheet explains the importance of estuaries, salinity in estuaries, and provides examples of stress from extreme high salinity. Then it explores the projected change in climate that could affect salinity in estuaries, how plants and animals would be affected, mitigating effects, and other impacts of climate change on estuaries. Written by Karl Havens, and published by the UF Department of Sea Grant, June 2015.
 SGEF-218/SG138: Climate Change: Effects on Salinity in Florida's Estuaries and Responses of Oysters, Seagrass, and Other Animal and Plant Life (ufl.edu)

Improved Ability to Characterize Recruitment of Gray Snapper in Three Florida Estuaries along the Gulf of Mexico through Targeted Sampling of Polyhaline Seagrass Beds

AbstractEstuarine‐dependent Gray Snapper Lutjanus griseus support extensive recreational fisheries in estuarine and coastal waters throughout the eastern Gulf of Mexico. Multiyear fisheries‐independent monitoring data collected in three Florida estuaries can be used to estimate the strength of juvenile Gray Snapper recruitment, which has been critical to assessments of other fish populations. Earlier evaluation of these data indicated that Gray Snapper inhabit polyhaline seagrass beds, which are underrepresented in ongoing monitoring efforts. During this study, in addition to the routine monitoring of shorelines and channel habitats, sampling of shoal and deepwater polyhaline seagrass habitats was implemented using 183‐m haul seines and 6.1‐m otter trawls. The incorporation of polyhaline seagrass surveys from 2008 through 2011 allowed a more thorough sampling of the Gray Snapper population, resulting in improved catch rates, increased frequency of occurrence, and a substantial reduction of the coefficient of variation for CPUE in most years and estuarine systems. Habitat‐based sampling of polyhaline seagrass habitats also provided additional data for annual abundance indices and therefore improved the ability to characterize the strength of recruitment for Gray Snapper over time. These results demonstrated that periodically reevaluating habitat‐based stratification approaches to estimate fish abundance indices from long‐term surveys can lead to more precise estimates and greater numbers of measured individuals, which are key components of successful monitoring programs.

Rare earth element cycling in a sandy subterranean estuary in Florida, USA

Rare earth element (REE) analyses were performed on 77 water samples and 5 sediment samples from the Indian River Lagoon system along the east coast of Florida. Groundwater samples were collected using nine multi-level piezometers installed along a shore-normal transect of the sandy subterranean estuary. Surface water samples were collected from Eau Gallie River and Crane Creek, the water column of the Indian River Lagoon above each piezometer, and the coastal Atlantic Ocean at Canova Beach. The REE concentrations of lagoon surface and subterranean estuary waters indicate that geochemical reactions within the subterranean estuary play a substantial role in the local REE cycle. The submarine groundwater discharge (SGD) flux of REEs calculated by using a modified form of the 1-dimensional vertical-flow equation is comprised of a nearshore heavy REE (HREE) enriched advective source chiefly composed of terrestrial SGD, and a light REE (LREE) and middle REE (MREE) enriched source that originates from reductive dissolution of Fe(III) oxides/oxyhydroxides in the subterranean estuary and subsequent transport by bioirrigation to the overlying lagoon. The total SGD flux of REEs reveals that this sandy subterranean estuary is a source for light and middle REEs and a sink for the heavy REEs to coastal waters. The SGD Nd flux is estimated at 7.69±1.02mmolday−1, which is roughly equivalent to the effective local river flux to the Indian River Lagoon. Although our re-evaluated SGD flux of Nd to the Indian River Lagoon is lower than an earlier estimate, it represents a substantial input to the coastal ocean and thus provides additional insights into the global oceanic Nd budget and the “Nd Paradox”.

Comparative ecophysiology of bloom-forming macroalgae in the Indian River Lagoon, Florida: Ulva lactuca, Hypnea musciformis, and Gracilaria tikvahiae

Macroalgal blooms are ecological responses to nutrient enrichment in shallow seagrass-dominated estuaries. For decades the Indian River Lagoon (IRL) a biodiverse estuary in east-central Florida, has experienced persistent blooms of red drift macroalgae, including Gracilaria and Hypnea spp. Since 2013, extensive blooms of green macroalgae, such as Chaetomorpha and Ulva spp., have developed. To better understand IRL nutrient effects on bloom-forming macroalgae, field and laboratory studies (2012) assessed nitrogen (N) versus phosphorus (P) limitation and morphological/physiological characteristics in relatively urbanized (Titusville, FL) versus rural (Fort Pierce, FL) IRL segments. Field studies indicated Ulva lactuca, Hypnea musciformis, and Gracilaria tikvahiae all grew fastest in Titusville (average±SD; 0.49±0.07, 0.35±0.03, and 0.14±0.05 doublings d−1, respectively). However, U. lactuca had the most rapid biomass doubling time (2days). Laboratory nutrient enrichment assays revealed 3-fold increases in rapid light curve (RLC) maximum values and 2-fold faster growth at high concentrations of N and P for U. lactuca. This superior growth and photosynthesis was attributed to higher surface area:volume ratios averaging (± coefficients of variation, %) 565.2±2.15cm2gdrywt.−1 compared to lower ratios for H. musciformis (110.7±3.97cm2gdrywt.−1) and G. tikvahiae (91.1±1.81cm2g dry wt.−1). Finely- and coarsely-branched H. musciformis and G. tikvahiae were similar photosynthetically but not morphologically based on a functional/form model. These data provide a physiological basis explaining bloom distributions and the recent success of green macroalgae in the increasingly eutrophic IRL.

South Florida Coastal Sediment Ecological Risk Assessment.

This study evaluated the degree of sediment contamination in several South Florida estuaries. During the 2010 National Condition Assessment, Florida Fish and Wildlife Research Institute collected water column, sediment and biotic data from estuaries across the entire state of Florida. Sediments were analyzed for arsenic, cadmium, chromium, lead, mercury, zinc and total polychlorinated biphenyls and were compared relative to empirically derived sediment quality guidelines. As a result of this data collection and assessment effort, it was determined that the degree of contamination with respect to sediment was low for all southern Florida estuaries assessed, except the Miami River which was determined to be considerably contaminated. However only one monitoring location was used to assess the Miami River, and as such should be viewed with caution. A low degree of contamination was determined for Biscayne Bay sediments, possibly indicating a recovery from its previously reported higher contaminant level.

Rare earth element cycling in a sandy subterranean estuary in Florida, USA

Rare earth element cycling in a sandy subterranean estuary in Florida, USA

Modeling ecosystem processes with variable freshwater inflow to the Caloosahatchee River Estuary, southwest Florida. II. Nutrient loading, submarine light, and seagrasses

Short- and long-term changes in estuarine biogeochemical and biological attributes are consequences of variations in both the magnitude and composition of freshwater inputs. A common conceptualization of estuaries depicts nutrient loading from coastal watersheds as the stressor that promotes algal biomass, decreases submarine light penetration, and degrades seagrass habitats. Freshwater inflow depresses salinity while simultaneously introducing colored dissolved organic matter (color or CDOM) which greatly reduces estuarine light penetration. This is especially true for sub-tropical estuaries. This study applied a model of the Caloosahatchee River Estuary (CRE) in southwest Florida to explore the relationships between freshwater inflow, nutrient loading, submarine light, and seagrass survival. In two independent model series, the loading of dissolved inorganic nitrogen and phosphorus (DIN and DIP) was reduced by 10%, 20%, 30%, and 50% relative to the base model case from 2002 to 2009 (2922 days). While external nutrient loads were reduced by lowering inflow (Q0) in the first series (Q0 series), reductions were accomplished by decreasing the incoming concentrations of DIN and DIP in the second series (NP Series). The model also was used to explore the partitioning of submarine light extinction due to chlorophyll a, CDOM, and turbidity. Results suggested that attempting to control nutrient loading by decreasing freshwater inflow could have minor effects on water column concentrations but greatly influence submarine light and seagrass biomass. This is because of the relative importance of Q0 to salinity and submarine light. In general, light penetration and seagrass biomass decreased with increased inflow and CDOM. Increased chlorophyll a did account for more submarine light extinction in the lower estuary. The model output was used to help identify desirable levels of inflow, nutrient loading, water quality, salinity, and submarine light for seagrass in the lower CRE. These findings provide information essential to the development of a resource-based approach to improve the management of both freshwater inflow and estuarine biotic resources.

Long-term changes in an estuarine mud crab community: evaluating the impact of non-native species

Along the US Atlantic coast, oyster reefs support a large number of estuarine species including ecologically important and abundant mud crabs. Multiple factors including environmental conditions, the introduction of non-native species, parasites, and interspecific competition can change the structure of these communities over time. To examine long-term changes in mud crab communities, crabs were sampled quarterly for ten years in a mixed oyster/mud habitat in a northeast Florida estuary. A total of 6935 individuals comprised of 10 species were collected, including two non-native crab species: Petrolisthes armatus (Gibbes, 1850) and Charybdis hellerii (Milne-Edwards, 1867). Three species (Panopeus herbstiiMilne Edwards, 1834, P. armatus, and Eurypanopeus depressus (Smith, 1869)) made up |$97.3\%$| of adult specimens collected, and were observed throughout the study period in varying abundances. Non-metric multi-dimensional scaling (MDS) conducted on species abundances revealed that the community underwent significant long-term, rather than cyclical seasonal, changes. Most noteworthy were the similarities in community assemblages observed in the years prior to, and soon after, the introduction of a non-native parasite, Loxothylacus panopaei (Gissler, 1884), which preferentially infects E. depressus. The significance of the presence/absence of the parasite on the community structure was confirmed through an analysis of similarities test (ANOSIM). While E. depressus abundance declined in the early years of the study after the introduction of L. panopaei, and never recovered, abundance of P. herbstii did not significantly change. Temperature and salinity likely only briefly impacted individual species on a seasonal or yearly basis including P. armatus, whose abundance reached an all-time low in the winter of 2010-2011 along with extreme winter temperatures.

Wave attenuation experiments over living shorelines over time: a wave tank study to assess recreational boating pressures

With sea level rise, erosion, and human disturbances affecting coastal areas, strategies to protect and stabilize existing shorelines are needed. One popular solution to stabilize while conserving intertidal habitat is the use of “living shoreline” techniques which are designed to mimic natural shoreline communities by using native plants and animals. However, little information is available on the success of living shoreline stabilization. This project evaluated the wave energy attenuation associated with living shorelines that contained Crassostrea virginica (eastern oyster) and/or Spartina alterniflora (smooth cordgrass) in a wave tank. Four living shoreline techniques were assessed, including a control (sediment only), oysters alone, cordgrass alone, and a combination of oysters plus cordgrass. Time since deployment (newly deployed, one-year after deployment) was also assessed to see how wave energy attenuation changed with natural oyster recruitment and plant growth. Wave energy was calculated for each newly deployed and one-year old shoreline stabilization treatment using capacitance wave gauges and generated waves that were representative of boat wakes in Mosquito Lagoon, a shallow-water estuary in Florida. All one-year old treatments attenuated significantly more energy than newly-deployed treatments. The combination of one-year old S. alterniflora plus live C. virginica was the most effective as this treatment reduced 67 % of the wave energy created by a single recreational boat wake, compared to bare sediment. Natural resource managers and landowners facing shoreline erosion issues can use this information to create effective stabilization protocols that preserve shorelines while conserving native intertidal habitats.

Modeling ecosystem processes with variable freshwater inflow to the Caloosahatchee River Estuary, southwest Florida. I. Model development

Variations in freshwater inflow have ecological consequences for estuaries ranging among eutrophication, flushing and transport, and high and low salinity impacts on biota. Predicting the potential effects of the magnitude and composition of inflow on estuaries over a range of spatial and temporal scales requires reliable mathematical models. The goal of this study was to develop and test a model of ecosystem processes with variable freshwater inflow to the sub-tropical Caloosahatchee River Estuary (CRE) in southwest Florida from 2002 to 2009. The modeling framework combined empirically derived inputs of freshwater and materials from the watershed, daily predictions of salinity, a box model for physical transport, and simulation models of biogeochemical and seagrass dynamics. The CRE was split into 3 segments to estimate advective and dispersive transport of water column constituents. Each segment contained a sub-model to simulate changes in the concentrations of organic nitrogen and phosphorus (ON and OP), ammonium (NH4+), nitrate-nitrite (NOx−), ortho-phosphate (PO4−3), phytoplankton chlorophyll a (CHL), and sediment microalgae (SM). The seaward segment also had sub-models for seagrasses (Halodule wrightii and Thalassia testudinum). The model provided realistic predictions of ON in the upper estuary during wet conditions since organic nitrogen is associated with freshwater inflow and low salinity. Although simulated CHL concentrations were variable, the model proved to be a reliable predictor in time and space. While predicted NOx− concentrations were proportional to freshwater inflow, NH4+ was less predictable due to the complexity of internal cycling during times of reduced freshwater inflow. Overall, the model provided a representation of seagrass biomass changes despite the absence of epiphytes, nutrient effects, or sophisticated translocation in the formulation. The model is being used to investigate the relative importance of colored dissolved organic matter (CDOM) vs. CHL in submarine light availability throughout the CRE, assess if reductions in nutrient loads are more feasible by controlling freshwater quantity or N and P concentrations, and explore the role of inflow and flushing on the fates of externally and internally derived dissolved and particulate constituents.

Assessing source contributions to particulate organic matter in a subtropical estuary: A biomarker approach

Assessing the sources and quantifying the contributions of particulate organic matter (POM) in estuaries is a challenge. Here we apply source-specific biomarkers to assess POM sources in an estuary receiving suspended material from freshwater wetlands, fringe mangroves and coastal environments. A three end-member mixing model, including terrestrial, estuarine and marine end-member contributions was developed and successfully validated to assess general OM dynamics and hydrologic processes that control POM distributions within the Shark River estuary in South Florida. Low tide and wet season conditions coincided with an enhanced signal of the freshwater end-member biomarker abundance, while high tide and dry season conditions resulted in enhanced POM input of marine origin. Incoming tide was observed to be an important factor in the re-suspension and tidal pumping of mangrove-derived POM, which seems to be the dominant source of particulate organic carbon (POC) in the estuary. The three end-member conceptual model was tested to obtain a rough estimate of POC source strength, with the ultimate goal of constraining carbon budgets in this sub-tropical estuary. Mangrove-derived POC flux of ca. 5.3×105 to 1.0×106kg/yr POC from the Shark River to the Gulf of Mexico were estimated, but end-member values used in the assessment need to be better constrained to reduce the degree of variability.

Hair mercury concentrations and fish consumption patterns in Florida residents.

Mercury exposure through the consumption of fish and shellfish represents a significant public health concern in the United States. Recent research has demonstrated higher seafood consumption and subsequent increased risk of methylmercury exposure among subpopulations living in coastal areas. The identification of high concentrations of total mercury in blood and skin among resident Atlantic bottlenose dolphins (Tursiops truncatus) in the Indian River Lagoon (IRL), a coastal estuary in Florida, alerted us to a potential public health hazard in the contiguous human population. Therefore, we analyzed hair mercury concentrations of residents living along the IRL and ascertained their sources and patterns of seafood consumption. The total mean mercury concentration for 135 residents was 1.53 ± 1.89 µg/g. The concentration of hair mercury among males (2.02 ± 2.38 µg/g) was significantly higher than that for females (0.96 ± 0.74 µg/g) (p < 0.01). Log transformed hair mercury concentration was significantly associated with the frequency of total seafood consumption (p < 0.01). Individuals who reported consuming seafood once a day or more were 3.71 (95% CI 0.84–16.38) times more likely to have a total hair mercury concentration over 1.0 µg/g, which corresponds approximately to the U.S. EPA reference dose, compared to those who consumed seafood once a week or less. Hair mercury concentration was also significantly higher among individuals who obtained all or most of their seafood from local recreational sources (p < 0.01). The elevated human mercury concentrations mirror the elevated concentrations observed in resident dolphins in the same geographical region. The current study is one of the first to apply the concept of a sentinel animal to a contiguous human population.

The potential role of benthic nutrient flux in support of Karenia blooms in west Florida (USA) estuaries and the nearshore Gulf of Mexico

The project “EcoHAB: Karenia Nutrient Dynamics in the Eastern Gulf of Mexico” (NOAA EcoHAB grant NA06NOS4780246) was designed to simultaneously quantify a wide variety of nutrient sources which can support the nearly annual blooms of Karenia brevis in the estuarine and coastal waters of west central Florida. Estuarine outflows and water column stocks of nutrients have been previously demonstrated to be insufficient to support the observed cell densities (>106cellL−1) which K. brevis can achieve. Nutrients released from sediments, however, are a nutrient source common to offshore, coastal, and estuarine environments. Prior regional measurements were generally lacking, particularly in coastal waters. Dark-only nutrient fluxes from the sediments were directly measured using large (65L, 0.27m2), in situ, opaque, stirred chambers deployed over 5–8h. Stations were located in coastal waters, a lagoonal system, and in the lower portions of two major estuaries, Tampa Bay and Charlotte Harbor, and were sampled during the fall of 2007–2009. Field procedures included triplicate chambers at each station and a water column control. Fluxes were quantified for dissolved oxygen, and dissolved ammonium, nitrate-nitrite, urea, total nitrogen, orthophosphorus, total phosphorus, and silica. Fluxes were dominated by dissolved silica (900–13,800μmolm−2d−1), ammonium (430–3360μmolm−2d−1) and ortho-phosphorus (50–1200μmolm−2d−1) and were greater than literature values which had been previously incorporated in local ecological modeling efforts. Based on literature growth rates and on cell complement data, the measured sediment flux of nutrients could have provided up to 300% of P requirements, and up to 100% of N requirements of 50,000cellsL−1 of K. brevis, modified by water depth. Flux values, derived from dark incubation and applied to Karenia cells only, likely represented an upper boundary of sediment contributions to Karenia nutrient budgets. Density stratifications common to upwelling coastal plumes and migratory behavior of K. brevis would have increased the percentage of supply afforded by sediment flux. Despite ammonium to ortho-phosphorus ratios in sediment flux substantially less than Redfield, ammonium flux provided a larger fraction of growth needs due to low levels of water column DIN concentrations (averaging 1.0μmolL−1). Fluxes enriched in P were consistent with bulk sediment P and the P-enriched geology of the region, and would have complemented N supplied by common nitrogen fixers such as Trichodesmium sp.

Ecological condition and value of oyster reefs of the Southwest Florida shelf ecosystem

The eastern oyster Crassostrea virginica is prolific and their reefs are dominant features along the estuaries and coastal areas in the Gulf of Mexico including those along the Southwest Florida coast. This paper examines the ecological and indirect economic value of oysters and the ecosystem services they provide. Drivers of change in reefs as well as various factors (pressures) that affect oyster reefs are examined. Using the monitoring data from on-going studies, this study examined various metrics of oyster health, reproduction and survival to develop an index to create an overall state of oyster reefs in the Southwest Florida estuaries. Based on existing data, oyster reefs in Southwest Florida estuaries are at “caution”, but stable. Restoration of a more natural freshwater inflow, minimizing nutrient and contaminant input as well as decreased sedimentation will enable oyster reefs to expand and thrive.

Evaluation of the use of metallothionein as a biomarker for detecting physiological responses to mercury exposure in the bonnethead, Sphyrna tiburo

Previous studies have demonstrated that sharks, perhaps more so than any other fishes, are capable of bioaccumulating the non-essential toxic metal mercury (Hg) to levels that threaten the health of human seafood consumers. However, few studies have explored the potential effects of Hg accumulation in sharks themselves. Therefore, the goal of this study was to examine if physiological effects occur in sharks in response to environmentally relevant levels of Hg exposure. To address this goal, the relationship between muscle Hg concentrations and muscle/hepatic levels of metallothionein (MT), a widely used protein biomarker of toxic metal exposure in fish, was examined in bonnetheads, Sphyrna tiburo, from three Florida estuaries. Total Hg concentrations in bonnethead muscle, as determined using thermal decomposition and atomic absorption spectrometry, ranged from 0.22 to 1.78 μg/g wet weight and were correlated with animal size. These observations were consistent with earlier studies on Florida bonnetheads, illustrating that they experience bioaccumulation of Hg, often to levels that threaten the health of these animals or consumers of their meat. However, despite this, MT concentrations measured using Western blot analysis were not correlated with muscle Hg concentrations. These results suggest that either environmentally relevant levels of Hg exposure and uptake are below the physiological threshold for inducing effects in sharks or MT is a poor biomarker of Hg exposure in these fishes. Of these two explanations, the latter is favored based on a growing body of evidence that questions the use of MTs as specific indicators of Hg exposure and effects in fish.

Soil Phosphorus Dynamics and Saltwater Intrusion in a Florida Estuary

Soils in riparian wetlands are thought to stifle eutrophication in coastal water bodies by entraining and transforming nutrients. Altered hydrology and sea level rise underscore the need to evaluate the role of salinity in nutrient cycling within these settings. We studied three intertidal wetlands along the St. Johns River estuary, Florida in order to relate soil phosphorus composition with the distribution of saltwater. Sites represented a tidal freshwater forest, a brackish marsh, and a saltmarsh. Total phosphorus and organic composition decreased along the axis of the estuary as ambient salinity increased. At upstream wetlands, porewater revealed an inverse correlation between PO4 3− and the presence of saltwater (Cl− and SO4 2−) suggesting soil efflux. During experiments, aerobic soils did not liberate PO4 3− when exposed to seawater. During anaerobic experiments, SO4 2− amended soils from a saltmarsh mobilized substantial amounts of PO4 3− but the same effect was not observed in low-salinity wetland soils. Results indicate that P availability is shaped by saltwater access in the estuary and that SO4 2− reduction may regenerate PO4 3− in the saltmarsh. We suggest this is relevant to the St. John’s river in light of ongoing eutrophication and planned surfacewater withdrawals, which may draw saline water farther upstream.

Unusual C35 to C38 alkenones in mid-Holocene sediments from a restricted estuary (Charlotte Harbor, Florida)

Unusual C35 to C38 alkenones were identified in mid-Holocene (8–3.5kyr BP) sediments from a restricted estuary in southwest Florida (Charlotte Harbor). The distribution was dominated by a C36 diunsaturated (ω15,20) ethyl ketone, identical to the one present in Black Sea Unit 2 sediments. Other unusual alkenones were tentatively assigned as a C35:2 (ω15,20) methyl ketone, a C37:2 (ω17,22) methyl ketone and a C38:2 (ω17,22) ethyl ketone. In late Holocene sediments<3.5kyr BP, the common C37 to C39 alkenones were found. Compound-specific 14C, 13C, and D isotope measurements were used to constrain the possible origin of the alkenones. Conventional radiocarbon ages of alkenones and higher plant-derived long chain n-alcohols indicated no significant difference in age between mid-Holocene alkenones and higher plant n-alcohols. Both alcohols and alkenones were offset vs. calibrated ages of shell fragments in the same sediment core, which suggests they were pre-aged by 500–800yr, implying resuspension and redistribution of the fine-grained sedimentary particles with which they are associated. The hydrogen isotopic (δD) composition (−190‰ to −200‰) of the C37 and C38 alkenones in the late Holocene sediments is in line with values for coastal haptophytes in brackish water. However, the unusual C36 and C38 alkenones from the mid Holocene sediments were enriched in D (by ca. 100‰) vs. the late Holocene alkenones. Also, δ13C values of mid-Holocene alkenones were consistently offset compared with late Holocene alkenones (−21‰ to −22‰ and −22‰ to −23‰, respectively). We suggest that the alkenones in Charlotte Harbor were produced by unknown alkenone-producing haptophyte.