Japan Geoscience Union Meeting 2022

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[E] Oral

A (Atmospheric and Hydrospheric Sciences ) » A-HW Hydrology & Water Environment

[A-HW23] Hydrology & Water Environment

Mon. May 23, 2022 10:45 AM - 12:15 PM 301B (International Conference Hall, Makuhari Messe)

convener:Keisuke Fukushi(Institute of Nature & Environmental Technology, Kanazawa University), convener:Takeshi Hayashi(Faculty of Education and Human Studies, Akita University), Shin'ichi Iida(Department of Disaster Prevention, Meteorology and Hydrology, Forestry and Forest Products Research Institute), convener:Sho Iwagami(Forestry and Forest Products Research Institute, Forest Research and Management Organization, National Research and Development Agency), Chairperson:Keisuke Fukushi(Institute of Nature & Environmental Technology, Kanazawa University), Takeshi Hayashi(Faculty of Education and Human Studies, Akita University), Shin'ichi Iida(Department of Disaster Prevention, Meteorology and Hydrology, Forestry and Forest Products Research Institute), Sho Iwagami(Forestry and Forest Products Research Institute, Forest Research and Management Organization, National Research and Development Agency)

10:45 AM - 11:05 AM

[AHW23-01] Hydrological impacts on nutrient transport from non-point sources in a semi-mountainous area, western Japan

★Invited Papers

*Junichiro Ide1, Ikuo Takeda2, Hiroaki Somura3, Yasushi Mori3, Yuji Sakuno4, Yasumichi Yone2, Erina Takahashi2 (1.Chitose Institute of Science and Technology, 2.Shimane University, 3.Okayama University, 4.Hiroshima University)

Keywords:conifer plantation, diffuse pollution, poor management practices

This study aimed to examine the hypothesis that coniferous forests and agricultural lands including poorly managed ones contribute to increasing nutrient concentrations in downstream rivers during storms. For this, we collected river water samples and analyzed their total nitrogen, total phosphorus, nitrate, and phosphate concentrations during the 18 years in the eight subbasins of the Hii River basin located in the semi-mountainous area, western Japan. Then, a combination of time series and linear mixed-effects model analyses were used to elucidate how the effects of land cover on nutrient concentrations in downstream rivers change depending on hydrological conditions. Results revealed that the slope of regression between nutrient concentrations and agricultural area ratio was positive and increased with daily precipitation, indicating that agricultural lands made a large contribution to increases in nutrient concentrations during storms even though they accounted for a small percentage of the basin. On the other hand, the slopes of the multiple regression analysis between nutrient concentrations and coniferous and broad-leaved forest area ratios were negative and decreased with increasing daily precipitation. This suggests that forests more contributed to the dilution of river nutrient concentrations during periods of heavier precipitation regardless of whether they were coniferous or broad-leaved.

†This presentation is based on the published paper as follows: Ide, J., Takeda, I., Somura, H., Mori, Y., Sakuno, Y., Yone, Y., & Takahashi, E. (2019). Impacts of hydrological changes on nutrient transport from diffuse sources in a rural river basin, western Japan. Journal of Geophysical Research: Biogeosciences, 124(8), 2565-2581.
https://doi.org/10.1029/2018JG004513 (free access)