Characteristics of Ion Components in River Water with Multivaraite Analysis and Piper Diagram in Agricultural Area

抄録

The Tokachi and Nemuro areas are large-scale agricultural land, and are located in Eastern Hokkaido. Increases in nitrogen concentrations in the river water caused by the outflow of excess nitrogen from an agricultural land in the Tokachi and Nemuro area have been reported. Here we considered the characteristics of the origin of river water quality with multivariate analysis and piper diagram in the Tokachi and Nemuro areas with different agricultural land use. The main agricultural land uses in the Tokachi area are upland and dairy farming. It is an area mainly of dairy farming in the Nemuro area. The investigation was carried out in late August 2005. We analyzed the following ion parameters: Cl^-, NO₃^-, NO₂^-, SO₄^2-, HCO₃^-, CO₃^-, PO₄^3-, NH₄⁺, Na⁺, K⁺, Ca²⁺ and Mg²⁺ by liquid chromatography. NO₃^- and SO₄^2- were higher in the Tokachi area; the values of NO₃^- and SO₄^2- were 0.71-31 mg/L and 1.9-39 mg/L in the Tokachi area and 0.44-9.7 mg/L and 2.0-19 mg/L respectively. On the other hand, HCO₃^- and Na⁺ were higher in the Nemuro area; 6.4-31 mg/L and 3.3-9.9 mg/L in the Tokachi area and 13- 42 mg/L and 5.8-15 mg/L in the Nemuro area respectively. The plot in piper diagram showed that most of the river water samples in the Tokachi area fall in the field of mixed Ca-Mg-Cl type of water. Some samples are also representing Ca-Cl and Ca-HCO₃ types. The most of the samples in the Nemuro area fall in the field of Ca-HCO₃ types, and some samples also representing Na-Cl types. This result suggests that the outflow of excess nitrogen from the agricultural land affected river water quality in the Tokachi area while the mixing of seawater and geological component affected river water quality in the Nemuro area.