Chanton Jeffrey P.

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Jeffrey P.

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  • Preprint
    Assessment of groundwater discharges into West Neck Bay, New York, via natural tracers
    ( 2006-05-21) Dulaiova, Henrieta ; Burnett, William C. ; Chanton, Jeffrey P. ; Moore, Willard S. ; Bokuniewicz, Henry J. ; Charette, Matthew A. ; Sholkovitz, Edward R.
    A field experiment to compare methods of assessing submarine groundwater discharge (SGD) was held on Shelter Island, NY, in May 2002. We evaluated the use of radon, radium isotopes, and methane to assess SGD rates and dynamics from a glacial aquifer in the coastal zone. Fluxes of radon across the sediment-water interface were calculated from changes in measured surface water inventories following evaluation and correction for tidal effects, atmospheric evasion, and mixing with offshore waters. These fluxes were then converted to SGD rates using the measured radon concentration in the groundwater. We used the short-lived radium isotopes to calculate a horizontal mixing coefficient to assess radon loss by mixing between nearshore and offshore waters. We also made an independent calculation of SGD using the Ra-derived mixing coefficient and the long-lived 226Ra concentration gradient in the bay. Seepage rates were calculated to range between 0 and 34 using the radon measurements and 15 as indicated by the radium isotopes. The radiotracer results were consistent and comparable to SGD rates measured directly with vented benthic chambers (seepage meters) deployed during this experiment. These meters indicated rates between 2 and 200 depending on their location. Both the calculated radon fluxes and rates measured directly by the automated seepage meters revealed a clear reproducible pattern of higher fluxes during low tides. Considering that the two techniques are completely independent, the agreement in the SGD dynamics is significant. Methane concentration in groundwater was very low (~30 nM) and not suitable as SGD tracer at this study site.
  • Preprint
    Biomass transfer subsidizes nitrogen to offshore food webs
    ( 2013-03-17) Nelson, James A. ; Stallings, Christopher D. ; Landing, William M. ; Chanton, Jeffrey P.
    We evaluated the potential contribution of allochthonous biomass subsidies to the upper trophic levels of offshore food webs in the northeastern Gulf of Mexico (GOM). We made this evaluation considering nitrogen, an essential and often limiting nutrient in coastal ecosystems, to estimate the potential production of within-ecosystem biomass relative to the known import of biomass from an adjacent seagrass dominated ecosystem. When adjusted for trophic transfer efficiency, we found the biomass subsidy from a single species (pinfish, Lagodon rhomboides) from neashore seagrass habitat to the offshore GOM to be greater than the amount of nitrogen exported by a two major rivers and local submarine ground water discharge. Our calculations show that seagrass-derived biomass accounts for ~25% of the total potential production in the northeastern GOM. This estimate is in agreement with a previous study that found 18.5-25% of the biomass in a predatory reef fish was derived from seagrass biomass inputs. These results indicate that all of the sources we consider account for the majority of the nitrogen available to the food web in the northeastern GOM. Our approach could be adapted to other coupled ecosystems to determine the relative importance of biomass subsidies to coastal ocean food 48 webs.