Dissolved constituent fluxes from the sediment to the water column are important in estuarine environments. Benthic nutrient source depends on the mechanisms driving advection, the advective transport rate, and the concentration of nutrients in the discharged water, all of which depend on the source of discharged water and water-solid reactions along its flow. Pore water advection has been measured at rates of 3 to 6 cm/d using seepage meters in the Banana River Lagoon, Florida. Diffusion, advection, and reaction modeling of SiO2 profiles in pore water indicate that advection and reactions are more important than diffusion in the upper 1 m of the sediments. Advection results from the recirculation of the overlying water column through the bottom sediments, oxygenating the lagoon water, while pore water lacks oxygen. As lagoon water recirculates through sediments, the subsequent loss of oxygen enhances regeneration of buried organic matter. Using measured seepage rates and average pore water concentrations of nutrients, N and P fluxes from the sediment are estimated to be 33 to 38 µg/cm2/y and 3 to 5 µg/cm2/y, respectively. On the basis of sedimentation rates and the average concentrations of N and P in the sediment, the fluxes of N and P to the sediment are estimated to be 9 to 38 µg/cm2/y and 2 to 6 µg/cm2/y, respectively. These values suggest that 100% more N and 30% more P may discharge with recirculating lagoon water than is deposited in the sediment. Because the source of most pore water is surface water, the excess nutrients appear to originate from organic matter regeneration at or near the sediment-water interface, thereby elevating their concentrations in pore waters and depleting their concentration in the buried sediment. This regeneration of nutrients appears to limit their burial rate in the lagoon.
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Vol. 2007 • No. 234