The seasonality of nutrient regeneration in an organic‐rich coastal sediment: Kinetic modeling of changing pore‐water nutrient and sulfate distributions

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Abstract
Measured pore‐water concentration profiles for dissolved ammonium, phosphate, total inorganic carbon, and sulfate show a distinct seasonal cycle in response to the temperature dependence of rates of microbially mediated organic matter oxidation in sediments at Cape Lookout Bight, N.C. The depth and temperature dependence of measured production and consumption rates, adsorption coefficients, apparent diffusion coefficients, and sediment porosities were combined to construct a diagenetic model of ammonium production, ΣCO2 production, and sulfate reduction that was time‐temperature‐ and depth‐dependent. Numerical predictions of pore‐water concentrations from a set of initial spring conditions agree well with measured pore‐water profiles through summer and fall—the period of greatest change in reaction rates in response to seasonal fluctuations in temperature. Modeling also indicates that inclusion of complex, porosity‐dependent terms, even in the time‐ and temperature‐dependent case, is probably unnecessary in these sediments; simpler, constant‐porosity models give results that generally deviate <4% from the predictions of complex models.

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