北海道の市町村を単位とした窒素環境容量に基づく地下水の硝酸汚染リスクの評価  [in Japanese] Risk Assessment of Nitrate Pollution in Groundwater Based on the Environmental Nitrogen-Assimilation Capacity of Agricultural Lands in Hokkaido  [in Japanese]

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Abstract

各種統計資料などを用いて北海道の市町村を単位とした窒素環境容量（作物による窒素持出量と余剰水量からみた硝酸性窒素の残存許容量の合量）および窒素投入量を試算し、地下水の硝酸性窒素濃度との関係を検討した。1．窒素環境容量の平均値は183kgha-1で、94-308kgha-1の幅が認められ、農地利用形態別では草地（218kgha-1）＞畑地（169kgha-1）＞水田（157kgha-1）の傾向にあった。2．窒素投入量の平均値は185kgha-1で、草地（212kgha-1）＞畑地（186kgha-1）＞水田（151kgha-1）の順に多かった。3．窒素環境容量に対する窒素投入量の超過分を超過窒素量とすると、その平均値は2kgha-1で、畑地（18kgha-1）＞水田・草地（一6kgha-1）の順に多く、45％の市町村がプラスの値を示した。4．北海道環境生活部の調査結果から整理した地下水（深さ20m未満）硝酸性窒素濃度（全道平均値±標準偏差）は4.0±3.9mgL-1で、畑地（6.5mgL-1）＞草地（2.5mgL-1）＞水田（2.4mgL-1）の順に高かった。5．各市町村について超過窒素量と地下水中硝酸性窒素濃度の関係を検討した結果、両者の間には1％水準で有意な正の相関が認められた。また、窒素投入量が窒素環境容量を上回る市町村の一部において地下水中の硝酸性窒素濃度が環境基準（10mgL-1）を超過する場合が認められた。6．以上のことから、窒素環境容量は農業に由来する地下水の硝酸汚染を防止するための、農地への窒素投入上限量の目安を把握するうえで、有効な指標になると考えられた。

A trial calculation was performed of the environmental nitrogen-assimilation capacity and the amount of nitrogen input based on various statistical data, which were compiled from each city, town and village in Hokkaido prefecture. The relationship between the excess quantity of nitrogen, after nitrogen input, and the environmental nitrogen-assimilation capacity and the nitrate-nitrogen concentration of the groundwater was considered. Environmental nitrogen-assimilation capacity =nitrogen output by the crops+acceptable level of residual nitrate in the soil profile. It is calculated by the amount of nitrate (precipitation-evapotranspiration)×10 (mg L^<-1>). 1) The average value of the environmental nitrogen-assimilation capacity in Hokkaido Prefecture was observed to be 183 kg ha^<-1>. The maximum and minimum values of the environmental nitrogen-assimilation capacity were 308 kg ha^<-1> and 94 kg ha^<-1>, respectively. When the average value of the environmental nitrogen-assimilation capacity with respect to main agricultural land use was compared across municipalities, it was largely in the following order : grassland (218kg ha^<-1>), upland (169kg ha^<-1>), and paddy land (157kg ha^<-1>). 2) The average value of the amount of nitrogen input in Hokkaido Prefecture was 185kg ha^<-1>. This value was largely in the following order : grassland (212kg ha^<-1>), upland (186kg ha^<-1>), and paddy land (151kg ha^<-1>). 3) The average value of the excess quantity of nitrogen, i.e., the difference between the nitrogen input and the environmental nitrogen-assimilation capacity, in Hokkaido Prefecture was 2 kg ha^<-1>. This value was largely in the following order : upland (18kg ha^<-1>), paddy land (-6kg ha^<-1>), and grassland (-6kg ha^<-1>). 4) The average value of the nitrate-nitrogen concentration investigated in groundwater was 4.0mg L^<-1> at a depth of 20 m or less. This value was largely in the following order : upland (6.5mg L^<-1>), grassland (2.5mg L^<-1>), and paddy land (2.4mg L^<-1>). 5) Significant positive correlation was obtained between the difference between the nitrogen input and the environmental nitrogen-assimilation capacity and nitrate-nitrogen concentration of groundwater. A case where the nitrate-nitrogen concentration of groundwater exceeded the environmental standards of water quality (10mg L^<-1>) was in one part of encountered municipality in Hokkaido Prefecture ; in such a case, the nitrogen input exceeds the environmental nitrogen-assimilation capacity. 6) Based on these results, it was concluded that the environmental nitrogen-assimilation capacity is an effective guideline for nitrogen input in agricultural lands and helps in the prevention of nitrate pollution in groundwater derived from agricultural land.

Journal

  • Japanese journal of soil science and plant nutrition

    Japanese journal of soil science and plant nutrition 77(1), 17-24, 2006-02-05

    Japanese Society of Soil Science and Plant Nutrition

References:  33

Cited by:  3

Codes

  • NII Article ID (NAID)
    110006280006
  • NII NACSIS-CAT ID (NCID)
    AN00195767
  • Text Lang
    JPN
  • Article Type
    Journal Article
  • ISSN
    00290610
  • NDL Article ID
    7826407
  • NDL Source Classification
    ZR7(科学技術--農林水産--農産)
  • NDL Call No.
    Z18-331
  • Data Source
    CJP  CJPref  NDL  NII-ELS  IR 
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