Abstract:A numerical simulation and stationary geophysical survey at Omaehama, Japan, described the hydrogeology in a tidal flat and adjacent sea water column. The simulation of a tidally influenced aquifer with inland fresh groundwater discharges showed three circulations in the subterranean tidal flat estuary: a small, tide-induced recirculation (TIR) near the sloping beach, a deeper circulation (DC) across the interface between saltwater and freshwater, and a large, tidal flat-induced circulation (TFIC) in the offshore subterranean tidal flat and slope. The horizontal distribution of the simulated submarine groundwater discharge (SGD) showed two peaks, depending on the distance from the coast along the transect line of tidal flat; the offshore peak was quantitatively consistent with the previously observed peak based on automated seepage measurements. Time-series of the observed resistivity profiles using a marine cable (140 m) showed the structure of the fresh water/salt water interface, and indicated a salt wedge intruding from the bottom aquifer and infiltration at the surface in the beach and nearshore tidal flat. The qualitative structure of the resistivity hardly changed at each tidal stage. These results qualitatively validated the circulation patterns shown by the numerical simulation. The source of this discharging groundwater in the tidal flat is a complex mixture of fresh groundwater derived from the landward aquifer, as well as locally recycled seawater, which can contribute to the purification of the nearshore seawater.

Bacteria, including cyanobacteria, as well as some fungi, are known to deposit calcium carbonate (CaCO(3)) extracellularly in calcium-containing artificial medium. Despite extensive investigation, the mechanisms involved in extracellular formation of CaCO(3) by bacteria have remained unclear. The ability of synthetic amines to remove carbon dioxide (CO(2)) from natural gas led us to examine the role of biogenic polyamines in CaCO(3) deposition by bacteria. Here, we demonstrated that biogenic polyamines such as putrescine, spermidine, and spermine were able to react with atmospheric CO(2) and the resultant carbamate anion was characterized by using nuclear magnetic resonance (NMR) analysis. Biogenic polyamines accelerated the formation of CaCO(3), and we artificially synthesized the dumbbell-shaped calcites, which had the same form as observed with bacterial CaCO3 precipitates, under nonbacterial conditions by using polyamines. The reaction rate of calcification increased with temperature with an optimum of around 40 °C. Our observation suggests a novel scheme for CO(2) dissipation that could be a potential tool in reducing atmospheric CO(2) levels and, therefore, global warming.

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