Global-change drivers that alter tidal amplitude or sea level could directly impact coastal aquifers' seawater-microbe interactions. The semidiurnal or diurnal tide can have consequences for chemical redistribution, because it deepens oxygen and nutrients penetration depth, thereby increasing O 2 depletion via microbial respiration in sediments during groundwater circulation. However, chemical and microbial distributions in tidal aquifers remain unclear, in deference to their link with depth and lateral location. By combining the microbes-accumulated equation with the traditional groundwater flow model in coastal aquifers, we explicitly unravelled the heterotrophic zonation, the salinity zonation, and the oxic zonation of tidal aquifers. According to the model estimates, salt penetrates deeper than reactive chemicals, and the heterotrophic high biomass zone is presumably 2-3 m deep. Such depth of heterotrophic distribution is 2-3 orders of magnitude higher than phototrophic distribution.Additionally, heterotrophic biomass can exhibit faint oscillations, even under the tide forces, whereas dissolved chemicals fluctuate significantly with tidal pumps. Due to

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