[A-HW24] Material transportation and cycling at the land-sea interface: from headwaters to the ocean

[AHW24-P13] Seasonal variation in groundwater quality and greenhouse gas in agricultural areas

*Mitsuyo Saito¹, Shin-ichi Onodera², Riku Kameyama³, Yusuke Tomozawa², Toru Iwata¹ (1.Graduate School of Environmental and Life Science, Okayama University, 2.Graduate School of Advanced Science and Engineering, Hiroshima University, 3.Faculty of Environmental Science and Technology, Okayama University)

Keywords:Groundwater quality, Greenhouse gases , Agricultural area

The purpose of this study is to clarify the characteristics of seasonal variations in groundwater quality and greenhouse gases in agricultural areas. Groundwater quality including nutrients and concentrations of greenhouse gases in the atmosphere have been continuously measured at Hachihama paddy field (HPF) and the coastal Ikuchijima Island covered by citrus farms (IKC). Groundwater table locates near the land surface in HPF and both upward and downward movement of groundwater occurred between the 50cm and 1m deep observation boreholes. While the water table at 3m deep borehole has been a few meters below the ground in IKC throughout the observation period. The groundwater has been more anaerobic condition in IKC than HPF and nitrate concentration has been significantly low throughout the observation period. While the variation ranges of nutrients including nitrite and ammonium were larger in HPF. Totally higher concentrations of greenhouse gases in HPF than IKC suggests the higher emission of them in HPF. Especially for the nitrous oxide gas, it is suggested that the denitrification process and upward groundwater discharge may cause the significant nitrous oxide gas transport to the atmosphere in HPF.

Acknowledgement: This research was supported by JSPS Grant-in-Aid for Scientific Research (A) (No. 18H04151, PI: Shin-ichi Onodera) and JSPS Grant-in-Aid for Scientific Research (B) (No. 21H03650, PI: Mitsuyo Saito).