JpGU-AGU Joint Meeting 2017

Presentation information

[EE] Poster

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

[A-HW32] [EE] Biodiversity, nutrients and other materials in ecosystems from headwaters to coasts

Sat. May 20, 2017 1:45 PM - 3:15 PM Poster Hall (International Exhibition Hall HALL7)

convener:Noboru Okuda(Research Institute for Humanity and Nature), Shin-ichi Onodera(Graduate School of Integrated and Arts Sciences, Hiroshima University), Tohru Ikeya(Research Institute for Humanity and Nature), Adina Paytan(University of California Santa Cruz)

[AHW32-P10] Effect of groundwater recycle system on nitrate load distribution in an agricultural area, Japan

*JIAHUI BAI1, Shin-ichi Onodera1, Guangzhe Jin1, Mitsuyo Saito2, Yuta Shimizu3 (1.Graduate School of Integrated Art and Science, Hiroshima University, 2.Graduate School of Environment and Life Science, Okayama University, 3.National Agriculture and Food Research Organization Western Region Agricultural Research center)

Keywords:groundwater recycle, nitrate load, SWAT model

As one of the major elements for crops, nitrogen directly affects the agricultural production. However, the excess application of fertilizers leads to a lot of environmental problems such as groundwater and surface water contamination. Especially, groundwater contamination by nitrate (NO3-) has been an important issue in agriculture areas. Ikuchijima island, located on the Seto Inland Sea of western Japan is one of the most famous and important agricultural island in Japan, with citrus groves cover 42% of the island. Groundwater is one of important water resources in the area because of low annual rainfall and relatively high risk of drought in the area. To maintain and improve crop yields, nitrogen fertilizer is applied over the whole year at a rate of ~2,400 kg ha-1 yr-1. Consequently, most of the groundwater of the agricultural area are significantly contaminated by NO3-, and are considered in “eutrophic” condition. Therefore, the recycle of high NO3- groundwater to the irrigation on the catchment scale is effective strategy for saving both fertilizer usage and groundwater resource in the area.
In this study, we estimated nitrogen load from the catchments in Ikuchijima island using the SWAT (Soil and Water Assessment Tool) model. Especially, we tried to simulate the effect of reducing fertilizer application on nitrogen load assumed the recycle of NO3- in groundwater. The results showed that NO3- loads were highest near the coastal areas, which is related to the distribution of citrus farms. 42% of nitrogen load was from citrus farms in the north region of the island, and it ups to 60 % in the south region. It indicates fertilizer is the major source of nitrogen load in the island. Higher average nitrogen loadings also occurred in high density of residential area. The total nitrogen load from whole island was estimated to be 82507kg/yearwhen the annual nitrogen fertilizer application is 240kg/ha/year. However, it decreased to 42548kg/year when the fertilizer application was reduced to 160kg/ha/year.