強雨が森林流域における土壌浸透水の水質へ及ぼす影響

概要

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Soil infiltration process greatly contributes to the hydrological process in watershed, thus, soil infiltration water and runoff water were collected to characterize pollutant load from two planted forests. Especially, this study focused on the heavy rain which is reported to be increasing because of climate change. Glass fiber wick samplers were used to collect soil infiltration water samples, while runoff water was collected at the weir. Results showed that the wick sampler successfully collected the soil infiltration water without accumulating excess water above the device. The amounts of pollutant loads in soil infiltration water (total organic carbon; TOC, total nitrogen; TN) were positively correlated with pollutant loads in runoff water, which directly showed the contribution of soil water to runoff water. During the research period, environmental pollution load density in soil infiltration water was negatively correlated with sampled soil water volume. This could be a dilution effect caused by rainfall infiltration. However, after the heavy rainfall, soil infiltration water quality showed higher concentration than other rainfall events. The trend was clear in the long lasting strong rainfall, especially for well conductive forest slope. Because of the high permeable properties, pollutant loads from the soil surface easily reached to the depth of glass fiber wick (50cm depth), without filtering process through the soil body.