A model-based estimation of nitrogen flow in the food production–supply system and its environmental effects in East Asia

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Abstract We created a numerical model to evaluate the anthropogenic nitrogen load on the environment and the nitrogen concentration in river water on a 0.5° × 0.5° scale. We estimated the nitrogen load of each country in East Asia from FAO statistics on fertilizer consumption, food balance sheet data, and grid data of NOx emissions due to fossil fuel combustion. For China, province statistic data were also adopted. Nitrogen loads of each country were distributed among grid cells on the basis of farmland and population distributions. The concentration in river water and riverine export of nitrogen were calculated by assuming a first-order reaction model in which denitrification and organic matter accumulation was a function of temperature and resident time. More than 90% of the nitrogen load originated from food production and supply. The contribution of NOx emissions was important only in Japan and South Korea. The estimated loads of nitrogen on the catchments of the major rivers were 10–30 times larger than the measured riverine export of nitrate in the literature. Estimated nitrogen concentrations in river water that also agreed well with measurements, showed that rivers close to the east coast of Northern and Central China were highly polluted with nitrogen.

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