斐伊川における河川水質の時間的空間的変動

We investigated some properties of water of the Hiikawa River, which runs through the Izumo region, from April to December 2004 to determine the effects of site and climate on river water quality. Collection points of river water started from the upper reach in montane area through the middle reach in arable land and ended at the lower reach in a mixture of arable land and residential area. In addition to fresh water sample, brackish water of the Shinjiko Lake was also collected at the Aika Park. Water temperature was measured at the sites. The pH, EC, cations and anions of water sample were measured in the laboratory. As results, mean water temperature increased and mean pH decreased from upper to lower reach, respectively. EC, cations and anions increased downwardly. Water temperature raised in summer and lowered in the autumn and winter as air temperature fluctuated. In summer, EC increased at the end point of fresh water and the lake owing to increases in sodium, magnesium, chloride and sulfate ion concentration. In the fresh water of middle and upper reach, concentrations both of cations and anions were rather stable through the studied period. Brackish water might affect the quality of river water at estuarine in summer. Since climatic condition of summer in 2004 was severer than normal year, the influence of brackish water on lower reach could be greater than normal year. We should make an effort to continuously monitor water quality to clarify the characteristics of the Hiikawa River.