[A-HW27] Water and material transport and cycle in watersheds: from headwater to coastal area

[AHW27-20] Active and Partial River-Groundwater Interaction and the Influence of Nutrient Cycle in the Asahi River Floodplain

*Yutaka MARUYAMA¹, Shin-ichi ONODERA¹, Mitsuyo SAITO², Koichi KITAOKA³ (1.Graduate School of Integrated Arts and Sciences, Hiroshima University, 2.Graduate School of Environmental and Life Science, Okayama University, 3.Okayama University of Scienece)

Estimation of the groundwater flux and the groundwater residence time in a local actively River-Groundwater interaction field is difficult, although it is important to understand river and groundwater quarity. In this study, to make a model of estimation of groundwater flux using temperature variation and validation of groundwater flux, to classify the River-Groundwater interaction fields using some tracers, and to estimate a nutrient mass flow. In the floodplain in the downstream area of the Asahi River watershed in Okayama prefecture, the analyzed result of the river and groundwater temeperature in 2010-2012 estimated to groundwater flux as 2.9-6.5 m/d. Simulated horizontal temperature distribution showed that there is a limit to estimate groundwater flux. Delta 18-oxygen variations and chloride concentration variations gave support to the groundwater flux estimated by the temperature model. Furthermore, these tracers teached how to classify the River-Groundwater interaction fields; Zone A-C in the waterside land; Zone D in the others. In Zone A-C, groundwater discharge is 8.2% of the river discharge, though 10% of the river nitrate nitrogen mass flow and 5.9% of the river phosphate phosphorus mass flow. It might be influence for river habitats.