The study was conducted in the Byoubusan sand dune area of Aomori prefecture of Japan with two objectives: (i) to assess the spatial and temporal variation of groundwater quality, and (ii) to evaluate the suitability of shallow groundwater as irrigation in sand dune area of northern Honshu island. Two agricultural fields of Byoubusan sand dune area in Tsugaru city of Aomori prefecture (northern Honshu island) were selected for this study which were mentioned as study filed A and B. Wheat, radish, melon, shallot, Chinese yam, water melon, burdock, potato, tobacco, garlic, asparagus, pumpkin, leek, carrot etc. are main cultivated crops of the study area.

　In study field A, three plastic tubes were installed to collect the groundwater sample from 2.0 m, 2.5 m and 3.0 m depth. On the other hand, in study field B, four plastic tubes were installed to collect the groundwater sample from 2.0 m, 2.5 m 3.0 m and 3.5 m depth. Sampling was performed every month from April 2004 to November 2005.

　For measuring the groundwater level, 12 and 14 observation bores were installed in the study field A and field B , respectively. Thermo recorders were installed at 0.1 m, 0.2 m, 0.5 m, 1.0 m, 1.5 m, 2.0 m, 2.5 m and 3.0 m depth to record soil temperature in study field A . On the other hand, in field B, thermo recorders were installed to collect air temperature and soil temperature at 0.1, 0.5 and 1.6 m depth. Platinum electrodes were installed at 0.1 m, 0.5 m, 1.5 m and 2.5 m soil depth to measure oxidation-reduction potential (Eh) in field A.

　Assessment of groundwater quality was performed on the basis of pH, electrical conductivity (EC), concentration of dissolved oxygen (DO), concentration of sodium (Na), potassium (K), calcium (Ca) and magnesium (Mg), sodium absorption ratio (SAR), total hardness (HT), ratio of calcium and magnesium, concentration of nitrate nitrogen (NO_3-N), phosphate phosphorus (PO_4-P) and iron (Fe).

　The groundwater level of the study field A was observed within a range of 1.11 m to 1.73 m throughout the investigation period. Whereas in study field B, it was observed within a range of 0.94 m to 1.55 m. Groundwater level was decreased during the cultivation period. The reasons might be the high evapotranspiration rate from April to September and the change of precipitation.

　In study field A, the soil temperatures at 0.1 m, 0.2 m 0.5 m, 1.0 m and 1.5 m depths were gradually raised with time from the month April to August. Thereafter the soil temperature was decreased sharply at the upper soil until February. On the other hand, soil temperature at 2.0 m, 2.5 m and 3.0 m depths were increased until the month of September and thereafter decreased slowly until March. These results showed that the subsoil temperature is generally warmer in winter and cooler in summer. Similar tendency was also observed in study field B.

　The Eh value was measured at 0.1 m, 0.5 m, 1.5 m and 2.5 m soil depth. Oxidation reduction potential values were observed greater than 300 mV at 0.1 m and 0.5 m depth throughout the investigation period other than in June, 2004 at 0.5 m depth. Eh value at 1.5 m depth was in the range -196 to 476 mV. Oxidation-reduction potential value at 2.5 m depth was below 300 mV throughout the investigation period, which was an indication of reduced state.

　pH values of the collected water samples were found within a range of 6.10 to 7.36 in field A, whereas in field B, it was 5.27 to 6.54. Results indicated that groundwater of field B is more acidic than that in field A. On average, the highest EC value was observed at 2.0 m depth followed by 2.5 m depth, and the lowest value at 3.0 m depth in both field A and field B. The average EC value groundwater were 0.30 mS cm^-1 and 0.33 mS cm^-1 in the study field A and field B respectively, which indicated that suitability of groundwater of the study area is doubtful for irrigation since recommended EC value for irrigation water in Japan is <0.3 mS cm^-1.

　Concentrations of Na, K, Ca and Mg in groundwater were decreased with an increase in the depth in the study area. In field A, average concentrations of Na, K, Ca and Mg were 20.91, 15.45, 26.11 and 9.92 mg L^-1, respectively, and on the other hand, in field B, concentrations were 27.56, 13.96, 24.92 and 10.36 mg L^-1, respectively. Water of Yamada river was used as a source of irrigation that contained 41.85 mg L^-1 Na. Fertilizer application might also be a source of K and Ca in ground water.

　Sodium absorption ratio is the measurement of sodium content relative to calcium and magnesium in soil-water medium, which influences soil properties and plant growth. On average, SAR of groundwater in field A was 0.90 and in field B was 1.20. Total hardness of groundwater also negatively correlated with soil depth in the study area. On average, HT in field A was 106.03 mg L^-1 and in field B 104.78 mg L^-1.

　Iron concentration was increased in groundwater with an increase in soil depth in both study fields. The low Eh value might promote the availability of Fe in water with increasing depth. On average, Fe concentration in groundwater of field A was 23.78 mg L^-1 and of field B was 21.37 mg L^-1. Groundwater of the study area was found not to be suitable for irrigation since recommended Fe concentration in irrigation water 5 mg L^-1.

　In the study area, NO_3-N concentration in groundwater identically decreased with increasing depth. Nitrate nitrogen concentration in groundwater was found between 0.0002-0.152 mg L^-1 range, and on average it was 0.030 mg L^-1 in study field A. In the study field B, NO_3-N concentration in groundwater was found within a range from 0.042 to 9.21 mg L^-1, and on average it was 2.04 mg L^-1. The results revealed that NO_3-N concentration in groundwater of study field B was identically higher than that of study field A. Nitrite nitrogen and Phosphate phosphorus in groundwater of the study field B also identically higher than that of study field A.

（和訳）

（題名）　屏風山砂丘畑の地下水の水質

　この研究は、青森県つがる市に位置する屏風山砂丘地区の２カ所（Ａ地区、Ｂ地区）の畑を用いて行われた。 この研究は、地下水の水質変動（空間的及び径時的）及び灌漑水としての適合性評価を目的とした。

　この地区は、小麦、大根、メロン、長いも、スイカ、ゴボウ、ネギなどが栽培されている。 Ａ地区では採水用の塩ビパイプを2.0ｍ、2.5mそして3.0mの深さにセットした。 他方、Ｂ地区では塩ビパイプを2.0ｍ、2.5m、3.0mそして3.5mの深さ設けた。 採水は、2004年4月から2005年11月までとした。

　地下水位測定は、A地区では12カ所、B地区では14カ所で行った。 自記温度計のセンサーの設置は、A地区では0.1m、0.2m、0.5m、1.0m、1.5m、2.0m、2.5mそして3.0m深さに、 B地区では気温、0.1、0.5m　そして2.5m深さとした。 Ａ地区には、酸化還元電位を測定する白金電極を0.1m、0.5m、1.5m、2.5m　の深さにセットした。

　地下水の水質は、ｐＨ、ＥＣ、ＤＯ、及びＮａイオン、Ｋイオン、Ｃａイオン、Ｍｇイオン、ＮＯ_３―Ｎイオン、 ＰＯ_４―Ｐイオン、ＦｅイオンそしてＳＡＲ、Ｈ_Ｔ　、CaイオンとMgイオンの割合などについて検討した。

　調査期間中の地下水位の範囲は、Ａ地区で1.10.m～1.73m、B地区では0.94～1.54mで、栽培期間中低下する傾向となった。

　A地区の0.1m、0.2m、0.5m、1.0m、1.5mでの地温は、４月から８月にかけて上昇し、その後２月まで急激に低下した。 他方、2.0m、2.5mそして3.0m深さの値は、９月まで上昇し、その後３月までゆっくり低下した。 一般に心土の地温は、気温に比べＡ地区もＢ地区も冬暖かく、夏涼しいことを意味していた。

　観測期間中の0.1m、0.5m深の酸化還元電位は300mV以上となった。 同じく、1.5m　深の酸化還元電位の範囲は-196mV～476mV、2.5m深の値は300mV以下で還元状態を示した。

　A地区の採水のｐHの値は、6.10～7.36となった。 B地区の値は5.27～6.54でA地区よりやや酸性となった。 EC値は両地区とも2.0m深、2.5m深、3.0mの順で低下した。 地下水の平均EC値は、A地区で0.3mSｃｍ^―１、B地区で0.33mSｃｍ^―１となり、 日本の灌漑水としての基準を満たす値とはならなかった。

　両地区の地下水中のNaイオン、Kイオン、Caイオン、Mgイオンの各濃度は、深度方向に低下した。 Ａ地区のNaイオン、Kイオン、Caイオン、Mgイオン濃度の平均値は、それぞれ　20.91mgL^-1、15.45 mgL^-1　26.11 mgL^-1、 9.92 mgL^-1となった。 同様にB地区のそれぞれの値は　27.56 mgL^-1、13.96 mgL^-1　24.92 mgL^-1、10.36　 mgL^-1となった。 灌漑水として用いた山田川のNa濃度は　41.85 mgL^-1で、K成分とCa成分は肥料として供給されていた。

　SARの値は、A地区で0.90、B地区で1.20となり、塩害の危険がない値であった。 H_Tの値は深度方向に低下し、概ねA地区で106.03 mgL^-1、B地区で104.78 mgL^-1となった。

　鉄イオン濃度は、両調査地区で深度方向に増加した。 Ehの値が低いことが鉄高濃度の一因と考えられる。 得られたFeイオン濃度は、A地区の地下水の平均値でほぼ23.78 mgL^-1、B地区で21.37 mgL^-1となり、 灌漑水の鉄の濃度基準5 mgL^-1を満たさないことが分かった。

　地下水中のNo_3-Nイオン濃度範囲は、0.0002 mgL^-1～0.152 mgL^-1、平均値は0.030 mgL^-1　 同様に、B地区濃度は0.042 mgL^-1～9.21 mgL^-1、平均値は2.04 mgL^-1となった。 両地区とも深度方向に濃度が低下した。硝酸、亜硝酸及びリン酸濃度もB地区はA地区よりも濃度が高くなった。