No.241 研究課題 / Project
多摩川上流丹波川流域における河川水質形成に及ぼす雪の効果Effect of snow on the stream chemistry in Tamagawa basin.| 学術研究 Academic Research |
No.241 |
|---|---|
| 代表研究者 Principal Investigator |
鈴木 啓介 Keisuke Suzuki |
| 所属（採択当時） Affiliation |
信州大学理学部助教授 Shinshu University |
| 研究内容要約 Research Summary |
研究対象流域では、降水量は暖候季に多く寒候季に少なくなる。表層地質が花崗岩である流域の流量と河川水中のCI、NO３、SO４２－濃度は同期的な変動を示している。いずれの場合にも寒候季に低く、暖候季に高くなる傾向を示す。ただし、融雪期には一時的な増加がみられる。河川水中のHCO３、Na+、Ca２+濃度とpHの変動は上記の溶存成分濃度と反対の変動を示していることで特徴づけられる。HCO３-、Na+、Ca２+濃度の変動には有意な季節変化は認められないが、流量が増加すると低下し、流量が低下すると増加する。一方、堆積岩の分布する流域では、暖流水中の多くのイオン濃度変動に関して、花崗岩帯を流れる暖流水質とあまり変わらない。しかし、SO４２-濃度と電導度の変動は、流量の多い暖候季に減少し、流量の少ない寒候季に増加し、花崗岩帯での変動と反対の変動傾向を示している。また、上流域に花崗岩帯を持ち、採取地点が堆積岩帯の場合は、花崗岩帯の暖流水質変動を示す。花崗岩帯に分布する各流域の平均傾斜と暖流水中の溶存成分濃度（Na+、Mg２+、Ca２+、NO３-、SO４２-、HCO３-）および土壌との関係は、HCO３-濃度以外のすべての溶存成分で、湿性褐色森林土壌の点在する流域のほうが高濃度を示している。河川水中のNO３-濃度とSO４２-濃度は流域の平均傾斜と正の相関係数を示し、HCO３-濃度は負の相関係数を示す。また、河川水中のNa+、Mg２+、Ca２+濃度と流域の平均傾斜との間にも、いずれも負の相関係数が認められる。各流域内最高高度と河川水中のHCO３-、Na+、Mg２+、Ca２+濃度の関係は、流域内の高度が高いほど、各イオン濃度は減少の傾向にある。流域の平均傾斜と最高高度の両方が河川水中のHCO３-Na+、Mg２+、Ca２+濃度に影響をおよぼしている。重回帰分析の結果からは、HCO３-、Na+、Mg２+、Ca２+濃度には、流域の平均傾斜より最高高度の影響力が強く示唆された。 In the stream basin surveyed, rainfall increases in the warm season and decreases in the cold season. In stream basins with a surface layer consisting of granite, the concentrations of Cl-, NO3-, and SO42- in the stream vary seasonally, as well as the rate of stream flow, i.e., they become low in the cold season and high in the warm season. However, they do also exhibit a temporary increase during the cold season when the snow melts. The concentrations of HCO3-, Na+, and Ca2+ and the pH of the stream water vary differently from the dissolved constituents Cl-, NO3-, and SO42-. The concentrations of HCO3-, Na+, and Ca2+ exhibit no significant seasonal variations, though the concentrations become lower or higher as the stream flow increases or decreases, respectively. In stream basins extending on sedimentary rock, the concentrations of most of the ions in the stream water do not vary greatly from those observed in the water-quality constituents in streams flowing on granitic layer. However, both the concentration of SO42- and the electric conductivity (EC) decrease in the warm season, in which stream flow is higher, and increase in the cold season, in which stream flow is lower. This pattern of change is opposite to that found in streams flowing on granitic layer. In addition, for water sampled at a point of sedimentary rock away from the upstream basin of granitic layer, the water-quality constituents exhibit the same behavior of concentration variation as the water-quality constituents in the stream on the granitic layer. Regarding the relation between the mean slope, the dissolved constituents in streams (Na+, Mg2+, Ca2+, NO3-, SO42-, and HCO3-), and the soil for stream basins extending on granitic layer, all of the constituents apart from HCO3- exhibit higher concentrations in basins containing wet brown forest soil and the concentrations of the stream water-quality constituents NO3- and SO42- indicate a positive correlation with the mean slope of basins while the concentration of HCO3- shows a negative correlation. In addition, a negative correlation is observed between the concentrations of Na+, Mg2+, and Ca2+ and the mean slope of basins. Regarding the relation between the highest altitude in individual basins and the concentrations of HCO3-, Na+, Mg2+, and Ca2+, the higher the highest altitude in a stream basin, the lower the concentrations of individual ions. This means that the mean slope of stream basins and the highest altitude both govern the concentrations of HCO3-, Na+, Mg2+, and Ca2+. The results of multiple regression analysis suggest that the concentrations of HCO3-, Na+, Mg2+, and Ca2+ are more affected by higher altitudes than by the mean slope of stream basins. |
| 共同研究者 Collaborators |
田中基樹・倉元隆之（信州大学 理学部） |
| 研究全文 Full Text |
全文をダウンロード Download (Japanese Only) |