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，生态系统氮循环的扩大不仅对区域环境产生影响，而且对全球环境产生影响。N2O排放增加导致的全球变暖、NH3沉降增加导致的酸化、NO3淋溶导致的水体污染、N负荷导致的生物多样性退化是与生态系统N循环相关的问题。本文讨论了农林生态系统中氮的最佳循环。为评价农林生态系统氮循环的最佳量，研究了以下几个方面：1)流域生态系统复群氮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温室效应气体通量。农用地剩余氮和地区处置氮是决定河流水质的主要因素。氮流模型对其评价至关重要。在流域生态系统复合体中，不同土地利用结构的氮素负荷表现出不同的特征。在降雨和融雪季节，氮负荷最多。在农田中，降雨前10天内施入农田的化肥氮主要排入溪流。虽然食用饲料和食物产生的动物和人类排泄物可以用作粪肥，但不适当的堆肥过程导致水污染。氨挥发引起森林土壤酸化，河流氮排放引起沿海生态系统富营养化。然而，它们取决于土壤质量。酸化由土壤交换性钙控制，富营养化由土壤硅供应控制。土壤形成过程将原生岩石矿物中的Ca和Si释放到土壤溶液中，是造成酸化和富营养化的重要因素。北海道是世界上农业领域N2O大量排放的特定地区。反硝化是产生大量N2O排放的主要过程。林地转为耕地增加了土地的全球变暖效应。然而，农田排水N2O排放量小于之前报道的值。基于以上结果，我们有必要利用N循环模型进行情景分析，以数值描述流域生态系统综合体中与食物和饲料生产和消费相关的N流量。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