Modeling early diagenesis of sediment in Ago Bay, Japan: A comparison of steady state and dynamic calculations

We modified a model of early diagenesis to study the biogeochemical processes occurring in the sediment at Ago Bay, Japan, and compared results from steady state and dynamic calculations. In the model, rate expressions describe organic matter oxidation and oxidation of reduced species formed as a product of organic matter oxidation. Organic matter oxidation is broken down into oxic respiration, denitrification, and manganese, iron, and sulfate reduction. Transport processes include advection, molecular diffusion, bioturbation and bioirrigation by benthic macrofauna. Performance of the model was evaluated against the extensive observed data available from Tategami, an area in Ago Bay. eady-state calculation reasonably reproduced the year-averaged vertical profile and our dynamic calculation also captured the overall trend of seasonal variation in the concentration of material in the sediment. These results illustrate the validity of our model of early diagenesis. We also found an interesting point that is a discrepancy between the steady-state solution and the year-averaged data obtained using the dynamic calculation. This difference was probably caused by the non-linear nature of the system (non-linear dependency on temperature) and suggests the suitability of dynamic analysis for the sediment in subtropical sea areas such as Ago Bay. ivity analysis revealed that the calculated concentration of materials in the sediment was strongly affected by changes in following parameters: the deposition flux of organic matter and iron hydroxide, transport parameters, Q10 values, and the mineralization rate of dissolved organic matter.