This study explores the use of microbial community analysis to evaluate the processes involved in nitrate attenuation in groundwater. Polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE) is used to identify denitrifiers based only on their 16SrRNA gene sequences, and Real-Time PCR analysis is used to quantify nitrite reducing genes (nirK and nirS). The latter suggest a new method to be used for detecting denitrification activity by comparing the gene dosage that has been detected by Real-Time PCR and the value of the nitrate (NO₃^－) δ¹⁵N and δ¹⁸O. This study focuses on a zone of significant NO₃^－ attenuation occurring at underground dam catchment area in the karstic Ryukyu limestone aquifer, which is located in the southern part of Okinawa, Japan.
As a result of microbial analysis, the bacteria were detected at all observation points which have been reported to have denitrification ability. And it has been confirmed that the bacteria has a gene nirS which is related to denitrification. In addition, the correlation was high between nirK /nirS gene dosage that has been detected by Real-Time PCR and the value of the nitrate δ¹⁵N and δ¹⁸O; therefore, this study demonstrates the effectiveness of using Real-Time PCR analysis for providing insights into the processes affecting nitrate attenuation in groundwater.

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In this study, we developed a model that represents discharge from a spring and variations in groundwater height, based on 5-years (2009-2013) of observations at Otomeyama Park in Shinjuku Ward. The model was calibrated using data from 2012-2013 and validated using data from 2009-2011. We used the model to simulate the discharge for 1998-2013 and specifically investigated the impacts of impervious land cover fraction, precipitation patterns, and water main leakage on long-term trends in the spring discharge. From Detailed Digital Information (10m Grid Land Use), it was determined that land cover/land use of the subject area has remained unchanged since the 1980’s so that it does not effect spring discharge. We found that after the 1990’s, discharge from the spring varied inter-annually owing to precipitation variability. If we take into account reduced leakage from the water main, then discharge is decreasing over time.

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A freshwater lens configuration was evaluated by using electrical conductivity data in Minami-daito Island, Japan. Groundwater levels, topographical and geological features were discussed in evaluation process.
5 significant constituents (O₁, K₁, N₂, M₂, and S₂) were detected in spectral analysis results suggesting that ocean tide has significant effect on the groundwater level. The freshwater lens was confirmed at the western side, and at the northeast side. The thickness of those lenses were 10～13m at the central low land, 5～8m at the western side, and 3～6m at the northeast side. The freshwater lens of western side showed the seasonal change due to the difference of aquifer permeability and distribution of the doline ponds or doline.

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In the floodplain composed of gravel and/or sand, the groundwater recharge from the river occurs partially and actively. To estimate the active and partial groundwater recharge from the river in the floodplain, this research examined to estimate the groundwater flux through the bypath in Okayama floodplain, using the temperature variation. Water temperature was monitored at the Asahi River and one spring at which such groundwater discharges in the Asahi River floodplain of Okayama Prefecture in Japan. Temperature variation of this spring showed the amplitude damping and the phase lag, compared with the river temperature. Results analyzed by using the one-dimensional heat transport model indicted that the Darcy flux of this groundwater was 2.9-6.5 m/d. In addition, results by inverse analysis of the horizontal temperature distribution suggested that the flow distance from the river is applicable in the range between 80 m to 1500 m. The approach by this research would be expected as the easy and simple application method to estimate groundwater recharge and groundwater resources in floodplains.

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