Geochemical characteristics and transport mechanisms of elements of river water in Akita Prefecture

Abstract

Based on the distribution of concentrations and isotope ratios of elements in river water and variations in the chemical forms of elements in river water, the controlling factors of river water quality and transport mechanisms of elements were clarified for river water in Akita Prefecture. The distribution of concentrations and isotope ratios indicates that river water in Akita Prefecture is formed under the influence of air masses that form precipitation, water/rock reactions when the river water exists as groundwater, and thermal water. The variations in the chemical forms of Fe and Al indicate that Fe and Al in river water exist in dissolved and particulate fractions at pH below 6, and that most of the particulate fraction is precipitated, while Fe exists in particulate and microcolloidal fractions and Al in suspended fraction at pH above 7. In river systems with many stagnant water bodies such as dams, the decrease in the amount of T-Al is large. This indicates that in river systems with stagnant water bodies such as dams, elements that are easily precipitated are precipitated in the stagnant water bodies.