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

[AHW24-15] Nitrogen and phosphorus ratios in various groundwater in Japanese agricultural areas

*Shin-ichi Onodera¹, Mitsuyo Saito², Masayuki Tamura⁴, Takuya Ishida¹, Yuta Shimizu³ (1.Graduate School of Advanced Science and Engineering, Hiroshima University, 2.Graduate School of Environmental and Life Science, Okayama University, 3.Western Region Agricultural Research Center, National Agriculture and Food Research Organization, 4.School of Integrated Arts and Sciences, Hiroshima University)

Keywords:Groundwater, N/P ratio, Agricultural areas

Biogeochemical cycling in underground environment is important in proper land management and understanding of natural systems. Nitrogen and phosphorus in groundwater is originated by both natural and anthropogenic processes. Especially for the groundwater in agricultural areas, it is significantly influenced by the inputs of chemical fertilizer and manure. However, the mechanisms of controlling N/P ratio in the groundwater system have not been fully clarified. In this study, we aimed to clarify the effects of lithology and human activity, especially agriculture, on the N/P ratios of groundwater in several agricultural areas in Japan.
We reviewed the previous papers, made a data base and compared all information. The geological factor was significant for phosphate concentrations, on the other hand agricultural factor such as fertilizer application and crop was for inorganic nitrogen concentrations. We confirmed variations of DIN and DIP, from 0 to 30 and from 0 to 3 mg/l, respectively. In addition, N/P ratios were indicated to be from 10 to around 150. The highest phosphate were found in Hachiro-gata, and Ikuchi-shima underlain by alluvial deposit and granitic rock, respectively.
* This research was supported by JSPS Projects (18H04151 and 21KK0192) and APN Project (CRRP2019-09MY-Onodera), in which PI were S.Onodera, respectively.