Changes of Nitrogen Flow in Agro-Ecosystems of China and Its Effects on Water Environment

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  • 中国農村地域における窒素フローの変動および水環境への影響評価
  • チュウゴク ノウソン チイキ ニ オケル チッソ フロー ノ ヘンドウ オヨビ ミズ カンキョウ エ ノ エイキョウ ヒョウカ

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Abstract

The present study aimed to quantitatively clarify the impact of human activity (with regard diet habits, waste disposal and farming method) on the nitrogen flow of agro-ecosystem and the water environmental problem by both statistical material and field investigation. According to our estimates, the total amount of nitrogen transported to the surface waters increased from 1.98 Tg-N in 1980 to 3.03 Tg-N in 1990 and to 4.50 Tg-N in 2000, showing a 2.3-fold increase between 1980 and 2000. The areas that exported large amounts of riverine nitrogen expanded widely from the Changjiang lower plain to the Changjiang middle plain and surrounding areas between 1980 and 2000. The high rate of nitrogen fertilizer application and the low fertilizer use efficiency were implicated as major causal factors of increased riverine N transport. Regarding per-capita annual potential nitrogen loading from human excrement, approximately 1.02 kg-N is returned to farmland and 5.49 kg-N is discharged into rivers in urban area. In rural regions, on the other hand, approximately 4.33 kg-N is returned to farmlands and 1.60 kg-N is directly discharged into rivers. Furthermore, the economic growth and urbanization lead to an increased proportion of meat in the diet, greater use of flush toilets, less recycling of human and animal wasters onto agricultural land, which makes rural communities more dependent on chemical fertilizer and imported animal feeds. China is facing serious water pollution problems; therefore, increasing organic matter recycling rate and decreasing chemical fertilizer application rate requires consideration.

Journal

  • ENVIRONMENTAL SCIENCE

    ENVIRONMENTAL SCIENCE 23 (4), 259-267, 2010

    SOCIETY OF ENVIRONMENTAL SCIENCE, JAPAN

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