Marine Geochemistry

Marine Field Station

Interstitial Water and Nutrient Flux Rates
at Several Sites in Great Bay

A consequence of the benthic community metabolism in estuaries is nutrient fluxes from sediments into the overlying water column. These fluxes support algal biomass and may contribute to eutrophication in the water column.

Stockton Marine Science Professor Gordan Grguric conducts research to determine sediment water fluxes of nutrients at selected sites within the Jacques Cousteau National Estuarine Research Reserve (JCNERR). Four to six students per semester are involved in the Marine Geochemistry field work, laboratory data analysis and results presentation.

Interstitial water from several sites has been analyzed:
Dry Bay, Little Beach Bay and Mott's Creek salt ponds.

At each site, 50 cm sediment cores are collected using plastic core liners. After transport to the Stockton Field Station, cores are sectioned and interstitial water obtained by centrifuging. The samples are then analyzed in the laboratory for:

  • Ammonia
  • Phosphate
  • Alkalinity
  • Silica
  • Chlorinity
  • Sulfate
  • Sulfide
  • Redox potential and pH are also determined

Concentration gradients of nutrients are determined using data from the top 10 cm of the sediment. Flux rates are calculated based on gradients and sediment porosity, using Fick's law:

F = f D DC where: F = flux; f = sediment porosity; q = sediment tortuosity;

q2 D Z D = molecular diffusion coefficient; DC = concentration gradient;
D Z = sediment depth

Interstitial water profiles are also used to assess the extent of denitrification and sulfate reduction in the sediments. These determinations are based on the redox potential and concentration profiles of ammonia, sulfate and sulfide.

Professor's Grguric's plans for expanding this research include comparisons of interstitial water analysis to hydrographic variables recorded from the JCNERR System Wide Monitoring program.

Methods to sample sites presently monitored by JCNERR dataloggers are being developed in hopes of developing a picture of spatial and temporal variability of sediment quality and thus benthic community metabolism in Great Bay.

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