The Geochemistry of Selenium and Sulfur in a Coastal Salt Marsh

Investigation of the various chemical forms of selenium and sulfur in sediments and pore waters can provide information about various oxidation/reduction processes. Five cores were obtained from the Great Marsh, from April 1985 to June 1986. Sampling times coincided with the seasonal redox cycle known to occur within the marsh system. Sediments were analyzed for various selenium and sulfur phases. Iron monosulfides and elemental sulfur both display large seasonal changes in concentration and distribution with depth, indicating a coupling with redox conditions. In contrast, the depth distribution of greigite did not show appreciable changes with season. Pyrite underwent large concentration changes in the upper 15 cm of sediment during spring, but remained relatively constant with respect to concentration and distribution below this zone. Using a mass balance approach for the upper marsh sediment (0-15 cm), sulfur needed for the observed rapid pyritization is found to be derived from elemental sulfur, iron monosulfide, and sulfate reduction. In the deeper sediments (15-30 cm), diagenetic modeling confirms that greigite is an intermediate in pyrite formation. The depth distribution of total sedimentary selenium shows minor variations with season. Concentrations are generally higher in the surface layers and then decrease with depth. Elemental selenium exhibits a trend with depth similar to total selenium. Chromium reducible selenium was generally undetectable in most cores and shows little seasonality. In contrast, sedimentary (selenite + selenate) shows marked seasonality. In spring, sedimentary is less than 10% of the total sedimentary selenium throughout the profile. However in summer, a broad maximum (30% of the total selenium) occurs just above the redoxcline. Below the redoxcline sedimentary accounts for less than 10% of the total sedimentary selenium. Pore water selenium exhibits a seasonal trend, concurrent with the cyclic changes in sedimentary. Diagenetic modeling shows that the loss of total sedimentary selenium is controlled by the decrease in elemental selenium. Mass balance modeling indicates that the major export of selenium from the marsh sediment is either gaseous emissions of selenium or the flux of Spartina alterniflora litter from the marsh system. Gaseous selenium is a potentially important source of selenium to the atmosphere

Sources and cycling of dissolved and particulate organic radiocarbon in the northwest Atlantic continental margin

Continental shelves and slopes are productive and dynamic ocean margin systems that also regulate the fluxes of terrestrial, riverine, and estuarine materials between the continents and oceans. In order to evaluate the ages, potential sources, and transformations of organic matter in an ocean margin system, we measured the radiocarbon (Delta (14)C and delta (13)C distributions of total dissolved organic carbon (DOC), suspended particulate organic carbon (POC), and dissolved inorganic carbon (DIC) in waters of the Middle Atlantic Bight (MAB) continental shelf and slope in April-May 1994. The Delta (14)C of DOC was greatest (as high as -39 parts per thousand) in surface waters of the shelf, decreasing rapidly offshore and with depth, even in relatively shallow (25-50 in depth) shelf waters. The lowest Delta (14)C-DOC values were observed in deep slope waters, where they were significantly lower than values measured previously for the deep Sargasso Sea. There was a strong inverse relationship between Delta (14)C-DOC and delta (-13)C-DOC in all shelf and surface slope waters of the MAB, which is likely attributable to varying contributions of young, (14)C-enriched organic matter of terrestrial and/or riverine origin. The more highly (14)C-depleted DOC in deep : slope waters (as low as -442 parts per thousand) generally had a correspondingly lower delta (13)C (as low as -22.3 parts per thousand) component. However, this must originate from relic terrestrial material either in the MAB itself or be discharged to the MAB from rivers and estuaries. The isotopic signatures of POC were clearly differentiable from DOC and indicate that this pool also contained a broad range of both old and young material of terrestrial (delta (13)C as low as -24.9 parts per thousand) and marine (delta (13)C as high as -19.9 parts per thousand) origin throughout the MAB shelf and slope. The highest Delta (14)C-POC values (up to 78 parts per thousand) were observed in shallow shelf waters of the southern MAR Conversely, the lowest Delta (14)C-POC values (as low as -394 parts per thousand) were found in MAB deep slope waters and were also significantly more depleted in (14)C than POC from the central north Atlantic (Sargasso Sea). A multiple-source isotopic mass balance model employing both (14)C and (13)C was used to evaluate the relative contributions of both young and old terrigenous versus marine organic matter to DOC and POC in the MAR The results indicate that shelf and slope DOC is comprised of an old marine fraction (represented by offshore Sargasso Sea material) and either a young terrestrial/riverine/estuarine (TRE) component (in shelf and shallow slope waters) or a relic TRE component (in deep and some shallow slope waters). In contrast, suspended POC from the MAB appears to originate predominantly from a mixture of recent MAB primary production and an old, TRE component, similar to that observed in one of the major subestuaries of the Chesapeake Bay. These results suggest that both young and old sources of terrestrial and riverine organic matter can comprise a significant fraction of the DOC and POC in ocean margins. Preliminary calculations indicate that the export of this compositionally unique DOC and suspended POC may be significant terms in the organic carbon budgets of the MAB and other margin systems

Accuracy and precision of tidal wetland soil carbon mapping in the conterminous United States

© The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Scientific Reports 8 (2018): 9478, doi:10.1038/s41598-018-26948-7.Tidal wetlands produce long-term soil organic carbon (C) stocks. Thus for carbon accounting purposes, we need accurate and precise information on the magnitude and spatial distribution of those stocks. We assembled and analyzed an unprecedented soil core dataset, and tested three strategies for mapping carbon stocks: applying the average value from the synthesis to mapped tidal wetlands, applying models fit using empirical data and applied using soil, vegetation and salinity maps, and relying on independently generated soil carbon maps. Soil carbon stocks were far lower on average and varied less spatially and with depth than stocks calculated from available soils maps. Further, variation in carbon density was not well-predicted based on climate, salinity, vegetation, or soil classes. Instead, the assembled dataset showed that carbon density across the conterminous united states (CONUS) was normally distributed, with a predictable range of observations. We identified the simplest strategy, applying mean carbon density (27.0 kg C m−3), as the best performing strategy, and conservatively estimated that the top meter of CONUS tidal wetland soil contains 0.72 petagrams C. This strategy could provide standardization in CONUS tidal carbon accounting until such a time as modeling and mapping advancements can quantitatively improve accuracy and precision.Synthesis efforts were funded by NASA Carbon Monitoring System (CMS; NNH14AY67I), USGS LandCarbon and the Smithsonian Institution. J.R.H. was additionally supported by the NSF-funded Coastal Carbon Research Coordination Network while completing this manuscript (DEB-1655622). J.M.S. coring efforts were funded by NSF (EAR-1204079). B.P.H. coring efforts were funded by Earth Observatory (Publication Number 197)

Routine monitoring of toxics in New Jersey fish: Fourth year (2007) of routine monitoring program Atlantic Coastal Region

Describes results of sampling program performed to assess status and trends in fish contamination

Routine monitoring of toxics in new jersey fish: Third year (2006) of routine monitoring program

Describes results of sampling program performed to assess status and trends in fish contamination

Determination of the isotopic composition of ammonium-nitrogen at the natural abundance level from estuarine waters

Abstract A method was developed to measure the stable nitrogen isotope ratio of dissolved ammonium (NH4+) at the natural abundance level from estuarine waters. This method employed rapid steam distillation with collection of ammonium on zeolite via ion-exchange. The steam distillation step had a recovery of 103±5%; subsequent exchange of the ammonium on zeolite had a yield of 96.4±1.6%. The zeolite with exchanged ammonium was converted to N2 in quartz tubes at 910°C with CuO and Cu and the isotopic composition of the gas was measured in an isotope ratio mass spectrometer. When analyzing 200 μg of N the accuracy using isotopic standards was within 4% of the true ratio, with an overall precision of ±0.5%. A benefit of this method is that samples can be distilled and preserved onboard ship, thereby minimizing storage artifacts. This method was used in a seasonal study of the isotopic composition of dissolved ammonium from the Delaware Estuary

Routine monitoring of toxics in fish-year 4 - Atlantic Coastal Inland Region: Office of Science research project summary

The Routine Monitoring for Toxics in Fish Program is a 5-year, geographically based rotating program to generate data on chemical contaminants in fish for the issuance, update and revision of fish consumption advisories. The monitoring program design is built upon fish contaminant research conducted by NJDEP since the early 1980’s. In order to investigate regional patterns in fish contamination the program includes rotating sample collections among geographic regions within the state. In addition to analyze fish contaminant temporal trends and to identify unknown hotspots, re-sampling selected waterbodies and sampling “new” (not previously sampled) locations was part of the sampling regime. This Year 4 study provides the results for the Atlantic Coastal Inland Region. The study design incorporated a variety of considerations, including sampling species that are important to recreational fishing, targeting fish species of specific trophic position that are known to bioaccumulate mercury and/or organic chemical contaminants, consider the target species body lipid content (important in organic contaminants), as well as species longevity and/or lifestyle proximity to bottom sediments. The data generated through this study are useful in developing credible consumption risk assessments, since they include the size ranges and species that are generally targeted by recreational anglers and can be used in an evaluation of contaminant trends in this region and comparable throughout the state. The results show that mercury in fish concentrations varied among species, but typically increased with fish size and are usually higher in predatory fish, such as chain pickerel and largemouth bass. Mercury levels in chain pickerel were highest in waters with pH less than 7, and for largemouth bass in lakes with pH between 5 and 6. The highest mercury concentrations were observed at drainage sites within and marginal to the Pine Barrens. As observed in this and previous studies lower pH waterbodies typically reflect conditions promoting high mercury bioavailability through methylation, and sources of mercury in the environment are both natural and anthropogenic. PCB levels in the fish sampled, however, showed a different contamination pattern with only relatively low to moderate PCB concentrations identified from these same locations. In general, PCBs and OCPs were typically higher in samples of American eel than other fish species examined. DDXs showed high variability within all sites of the study area, with some of the lowest and highest average concentrations observed when compared to previously studied regions. The variations in these xenobiotics (PCBs, OCPs, DDX) may highlight the differing contaminant sources and geo-chemistry of these contaminants, and may also reflect legacy industrial practices of production, disposal and/or use. Although these xenobiotic concentrations were variable among sites, the highest average concentrations were seen in fish from Deal Lake (PCBs and chlordanes), North Branch Metedeconk River (DDXs and chlordanes), Maurice River (PCBs), and several other smaller lakes (DDXs). Although there are large differences in contaminant concentrations in samples within regions, a comparison of fish tissue chemical data among sites from the previous studies on the Passaic and Raritan Regions, and this study show some regional contaminant differences. In general concentrations of mercury were higher in the Atlantic Coastal Region while PCBs were higher in the Raritan Region. Where comparisons between 1992 and 2007datasets for this study were possible, there was no clear trend in contaminant concentrations at previously sampled locations. When comparing these data to available health criteria, with the exception of mercury, few of the samples analyzed exceeded the USFDA action levels for advisories on commercial fish. However, the NJDEP/DHSS use USEPA supported risk-based health criteria, in establishing consumption advisories for recreationally caught fish. These criteria are typically lower than FDA thresholds for mercury, PCBs, dioxins, and OCPs. The majority of the fish samples tested in this study exceeded the various individual NJDEP/DHSS/USEPA contaminant risk-based thresholds and several samples examined exceeded thresholds for multiple contaminants. The data from this study were used by NJDEP/DHSS to develop the most recent fish consumption advisories for a variety of recreationally caught fish in New Jersey