Extensive study on forest runoff water chemistry over east Asia

The chemistry of runoff waters from 13 forested watersheds in six regions (four regions from Japan, one from southern China and one from northern Thailand) was evaluated. The Cl− concentrations in runoff waters were higher in those watersheds which had closed canopies and were nearer to the ocean. The NO3 − concentrations were higher in those watersheds having the developed soils and high moisture conditions, but were lower in tropical and subtropical regions for those watersheds which had high rates of nitrogen uptake and for watersheds with large areas of saturated soils. The SO4 2− concentrations were affected by SO4 2− adsorption properties of the soils: at Shibecha, Jiulianshan, and Chiang Mai with high adsorption capacities SO4 2− concentrations in streams were low. High SO4 2− concentrations were found at Mt. Hiei and Kagawa due to the weathering of sulfur minerals and high levels of atmospheric sulfur deposition. Within regions SO4 2− concentrations were inversely related to NO3 − concentrations. A comparison among the watersheds suggested H+ consumption in deeper soil that increased pH and HCO3 − concentrations of the runoff waters of some watersheds. Anion concentrations increased with low H.I. (Humidity Index) values suggesting that dry conditions increased concentrations due to high rates of evapotranspiration.