Evaluation of Nitrogen Cycling in a Basin Associated with Forest, Grassland and Animal Husbandry, Hokkaido, Japan

随着人类活动的增加，生态系统中N循环的扩大不仅对区域环境，而且对全球环境都有影响。全球变暖导致的N2O排放增加、酸化导致的NH3沉降量增加、NO3淋溶造成的水污染、生物多样性随N负荷的退化是生态系统中与N循环相关的问题。本文讨论了农林复合生态系统中氮素的最佳循环问题。为了评价农林复合生态系统中氮素循环的最佳数量，我们研究了以下内容：1)流域生态系统复合体中氮素循环对河流水质的影响；2)大气氮沉降对森林土壤生态系统的影响；3)流域生态系统复合体中温室效应气体通量。农田剩余氮和区域处置氮是决定河流水质的主要因素。氮流模型对它们的评价是至关重要的。在流域生态系统复合体中，每个土地利用结构都表现出独特的N负荷。大多数…降雨季和融雪季氮负荷较大。在农田中，在雨前10天内提供给农田的化肥N主要排放到溪流中。虽然饲料和食物消费产生的动物和人类排泄物可以用作粪便，但堆肥过程不充分导致了水质污染。氨挥发导致森林土壤酸化，河流氮排放导致沿海生态系统富营养化。然而，它们取决于土壤质量。酸化受土壤交换性钙控制，富营养化受土壤供硅控制。成土过程将原生岩石矿物中的钙和硅同时释放到土壤溶液中，是导致土壤酸化和富营养化的重要因素。北海道是世界上农田N2O排放量较大的特定地区。反硝化是N2O大量排放的主要过程。退耕还林增加了土地的全球变暖效应。然而，农田排放的N2O比以前报告的数值要小。根据上述结果，我们有必要利用N循环模型进行情景分析来评价最佳N循环，以数值描述流域生态系统复合体中与食物和饲料生产和消费相关的N流。较少

Expansion of N cycling in ecosystems with increase of human activity impacts on not only regional environments but also global environments. Global warming with increasing emission of N2O, acidification with increasing of NH3 deposition, water pollution with NO3 leaching, degradation of bio-diversity with N load are the problems associated with N cycling in ecosystems. This report discussed about optimum N cycling in agro-forested ecosystems. In order to evaluate optimum amount of N cycling in agro-forested ecosystems, we studied following topics: 1) Impact of N cycling in basin ecosystem complexes on stream water quality; 2) Impact of atmospheric N deposition on forest soil ecosystems; 3) Green house effect gas fluxes in basin ecosystem complexes. Surplus N in agricultural lands and disposal N in regions are major factor determining stream water quality. N flow model was crucial for their evaluation. Unique N load was shown in each land use structure in a basin ecosystem complex. Most … More N load occurred during rainfall and snow melt season. In agricultural land, chemical fertilizer N, which was supplied to the fields within a 10-day before rain, was mainly discharged to the stream. Although animal and human excreta produced with the consumption of feed and food can be used as manure, inadequate composting process resulted in water pollution. Ammonium volatilization induced acidification of forest soils and stream N discharge induces eutrophication of coastal ecosystems. However they depended on soil quality. Acidification was controlled by exchangeable Ca in soils and eutrophication was controlled by Si supply from soils. Soil forming process, which releases both Ca and Si from primary rock minerals to soil solution, was quite important factor for occurrence of both acidification and eutropication. Hokkaido was the specific area in the world for occurrence of large N2O emission from agricultural fields. Denitrification was major process for large N2O emission. Conversion of forested land to crop land increased global warming effect of the land. However, N2O emission through water discharge from agricultural fields was smaller than the values reported previously. According to the above results, it is necessary for us to evaluate optimal N cycling with scenario analysis using N cycling model to describe numerically N flow associated with production and consumption of food and feed in basin ecosystem complex. Less