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 (R²=0.94; correlation coefficient). We measured the sediment temperature (256 points, 1,024 km²) 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 2.67×10⁵ml/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.

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Submarine groundwater discharge (SGD) is becoming recognized as a significant source of fresh water and chemical fluxes into the coastal oceans around the world. On the coast of eastern Toyama Bay (central Japan), land-based estimates of the water budget indicated the possible existence of SGD. The two-fold purpose of this study was to development a SGD flow measuring method with wide dynamic range and to demonstrate it by obtaining preliminary estimates of the SGD flux in Katakai River alluvial fan. A new flow rate meter was developed, named the Toyama University SGD-Flux Chamber (in collaboration with Nichiyu Giken Kogyo Co., Ltd.). Electrical conductivity and temperature sensors were mounted in a plastic chamber, conventionally used for gas flux measurements. The flow rate was calculated though the conductivity dilution velocity measured of the bottom seawater, diluted by spring groundwater from sea floor inside of the chamber (diameter: 40 cm; height: 15 cm). The initial field experiment was conducted to investigate the measurement sensitivity and accuracy of the SGD-Flux Chamber. Trial SGD water (tap water) was utilized, and two ranges of flow rate were measured: 10-50 mL/min withestimated uncertainty of±1mL (relative standard deviation: RSD=5%), and 50-400mL/min±2ml (RSD=2%). Therefore, the Flux Chamber is capable of measuring SGD flux within a large flow range, 10-400 mL/min (corresponding flow velocity values are: 5.7-458 cm/day). Flux measurements were then carried out from April to December, 2003 in the SGD area of Katakai River alluvial fan, 150-200 m seaward ofthe coastline in water depths of 8 m and 22 m. The average fluxes from April to December were 0.8-1.3 L/min/m² at 8 m and 0.5-0.8 L/min/m² at 22 m. On tidatime scales, the SGD flux increases with the dropping of the tide level with a time lag of 2 hours. There are indications the flux is controlled by changes in landward groundwater potential pressure, sea level at the SGD area, and the geotechnical condition of submarine sediment. Longer time series at multiple sites willbe required to discern the relations between the SGD flux and river flow rate, precipitation, and long-term (seasonal) changes of the landward unconfined aquifers.

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地下水の年代を把握することは地下水の循環速度や資源量を把握する上で重要である。本研究では富士山山麓に位置する5つの湧水を対象に³H/³He法による地下水年代測定を実施した。その結果，4地点の湧水について18～39年の滞留時間が得られた。この年代値は，富士山の水文地質特性や過去の研究で³⁶Cl, CFCs, SF₆から見積もられた年代と調和的であり，富士山地域の地下水年代推定における本手法の有効性を示している。

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湧水中の六フッ化硫黄（SF₆）濃度の時間変化とその要因を明らかにするため，福島県川俣町の山地源流域にて，現地水文観測とSF₆濃度等の分析を3年間実施した。無降雨時，湧水のSF₆濃度は3.6 fmol/Lから4.6 fmol/L，湧水温は8.0 ℃から13.2 ℃の範囲で変動した。また，湧水のSF₆濃度は湧水温が高いほど低い傾向を示したが，湧水温の変動幅が小さいため，流出時の大気接触の影響は小さいと判断された。さらに，湧水の流量が0.15 L/s以下では，流量が多いほどSF₆濃度が高い傾向がみられた。このことは，低流量条件下では流量が多いほど，相対的に若い地下水の寄与が多いことを示唆している。また，湧水のSF₆濃度は大気濃度から4年程度の遅れを伴って，経年的な上昇が示された。

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