富山湾東部における広域海底湧水湧出量の測定(<特集>沿岸海底湧水の地球科学)

概要

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Recently, the flow rate of submarine groundwater discharge (SGD) has been measure around the world, in order to evaluate the effect of SGD on the marine environment. However, because the flux of SGD is spatially very inhomogeneous, it is difficult to extrapolate point measurements to estimate the spatial averages necessary to infer values relevant for large scale budgets. In this study, we developed a method for calculating the SGD flow rate by using sediment temperature. The method provides an estimate of the total flow rate, and also elucidates the flow mechanism of SGD. It has been recognized that sediment temperature is highly correlated with SGD flow rate (R^2=0.94; correlation coefficient). We measured the sediment temperature (256 points, 1,024 km^2) in the Katakai alluvial fan (Toyama Bay, western central Japan) in November 2003 and used the relation to infer a SGD distribution map. High flow areas are distributed as bands, with the total flow of SGD estimated 2.67×10^5ml/min in the study area. The flow measured in August 2004 was smaller by 30 percent, with much of this reduction in the lower flow areas. It is shown that a permeable high aquifer reaches high flow locations directly, while the low flow locations are fed via higher resistance paths seeping out from the aquifer.
日本地球化学会の論文
2005-08-20