In shallow ecosystems, the microphytobenthos is considered as an important driver in modulating several biogeochemical processes through their activities. However, their inclusion in benthic ecosystem models is only discussed in a few studies. Here we implement a new model that extends a classic early diagenesis model (OMEXDIA) to include phosphorus dynamics and detailed MPB processes describing their complex physiological behavior. We investigated the role of microphytobenthos and other physical forcings on the biogeochemical dynamics within the sediment. This was done by considering four scenarios with varying degree of complexity involving light and tide effects. Our results show that inclusion of MPB can introduced fine-scale diurnal variability in several processes. Total mineralization was enhanced by 71.53% in the presence of MPB because of the input of fresh labile organic matter. This increased the depth of the oxic layer resulting in an increased coupled nitrification-denitrification process. Imposing the influence of tide effect resulted in high surface nutrient (ammonium, nitrate, phosphate) accumulation when the sediment was exposed, and that was quickly exchanged with the overlying water upon immersion. Thus, the sediment acts as a source of nutrient to the bottom water. The different scenarios explored in the model showed the complex behavior exhibited by MPB under dynamically changing environments which have significant biogeochemical ramifications.
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