UC Irvine

Seasonal remineralization rates of organic carbon are calculated in the top 20-30 cm of biologically irrigated, organic-rich sediments of Buzzards Bay, MA. Six cores were collected over a period of two years, and the pore water concentrations of the following species were measured: dissolved inorganic carbon (ΣCO2), PO3-4, ΣH2S, Alk, and Ca2+. Overall, these constituents showed large gradients with depth, which are larger in summer than in winter. Remineralization rates in the sediments were estimated by applying a non-local exchange, vertical molecular diffusion, reaction model to the ΣCO2 depth profiles. The major processes affecting the pore water concentration of ΣCO2 described in the model are diffusion, irrigation, and the oxidation of organic carbon. The calculated remineralization rates varied seasonally with the high of 7.5 × 10-9 mol/L-sec observed in August 84 and the low (0.6 × 10-9) in December 1983. The remineralization rates were dependent on the amount of irrigation in the sediments. It was possible to calculate remineralization rates between 0 and 20 cm because the amount of irrigation was well-characterized at this site. We calculated that 69 gC/m2 are oxidized annually and 5-33 gC/m2-yr are buried. It appears that there is a highly reactive portion of organic matter which is oxidized at the sediment water interface. Examination of the Alk and dissolved Ca2+ profiles indicates that there was significant production of acid which dissolved CaCO3 in the spring and early summer. © 1988.