Streamwater Quality through Years and Snowmelt Period in a Forested Inland Basin in Tohoku, Naorthern Japan

Abstract

Streamwater quality was measured for two years in a small, forested snow-covered basin in an inland part of Tohoku, Japan. The average major ion concentrations in the Himekami Experimental Basin were lower than nationwide averages. A change in streamwater quality mainly arose from the change in water discharge caused by rain or snowmelt. Positive correlations were found between discharge and pH, electrical conductivity (EC), and the Na⁺, Mg²⁺, Ca²⁺, Cl^-, HCO^3-and SiO² concentrations, and negative correlations were found between discharge and the SO₄^2- and NO₃^-concentrations. In the early stage of snowmelt, we observed a clear effect of snow coverage on the water quality, and the Na⁺, Cl^-, SO₄^2-, and NO₃^-concentration increased with snowmelt, owing to the high concentra-tions in snow. After the active stage of snowmelt, the Na⁺, Cl_-, and SiO₂ concentrations were affected by a dilution effect of the water from melting snow. By contrast, the SO₄^2- and NO₃^- concentrations also increased after the active stage of snowmelt. Increases of both ion concentrations are attributed to either outflow out of the snowpack or their elution from shallow soils. However, the response of the two ions during an event that involved both rain and melt water suggests that SO₄^2- and NO₃^- in streamwater during snowmelt were strongly affected by outflow out of the snowoack and their elution from shallow soils, resoectivelv.