Shanghai Urban Soil Organic Carbon, Structure And Distribution Of Spatial Variability Of Nitrogen

Soil carbon pools are impacted by severe interference of both natural factors andhuman events. Small changes of soil organic carbon density affect the variation ofglobal climate through greenhouse effect. Thus, the research on the content of soilorganic carbon is helpful for correctly evaluating the change tendency and rate of soilorganic carbon and exactly predicting climate changes, with important implicationsfor developing strategies and measures for dealing with climate changes. Soil totalnitrogen and organic matter are vital compositions of soil, the research on which issignificant for understanding the distribution of soil nutrients and nutrientmanagement. To reveal the spatial heterogeneity of soil organic carbon and nitrogenamong cities at different scales, this paper aims at Xuhui District, Minhang Districtand Fengxian District (transects of urban-rural gradient differences), studies spatialvariability of soil organic carbon and nitrogen by geo-statistics, and estimates the soilcarbon density and carbon storage in sample zones, mainly reaching followingconclusions:1. The research on soil organic carbon density and carbon storage suggests thatin sample zones the average soil carbon density is3.11kg/m2, the average paddy soilcarbon density is3.05kg/m2, the average alluvial soil carbon density is3.07kg/m2, theaverage coastal saline soil carbon density is2.87kg/m2, the average urban landsoil carbon density is3.31kg/m2. There presents a moderate variation in soil organiccarbon density of sample zones and different types of soils. The variation is listed inorder in terms of its strength, namely alluvial soil＞coastal saline soil＞paddy soil＞sample zones＞urban land. In sample zones of Shanghai, the total storage of soilorganic carbon is up to31,242.73t on0-20cm deep soils, while the organic carbonstorage of various soils is paddy soil＞coastal saline soil＞alluvial soil, where theorganic carbon storage is19,634.34t (max) on paddy soil,930.9t on alluvial soil and3,506.51t on coastal saline soil. In urban lands, the soils occupy an area of216.52km2and the organic carbon storage is7,170.98t. 2. The research on spatial distribution of organic carbon on different soils showsthat in sample zones,the soil organic carbon generally exhibits zonal andisland-shaped distribution,the content of which tends to decline from urban centers tosuburbs. In districts, the soil organic carbon shows a tendency of multi-island shapeddistribution in Minhang District. As regards tiny areas, the soil organic carbon showsa trend of island-shaped distribution in agricultural regions. The island-shaped highvalue areas locate in the southwest of agricultural regions and there is a tendency forthe content of organic carbon to decrease from island-shaped high-value centers totheir surroundings. In green lands of parks, the soil organic carbon shows a zonaldistribution, the content of which tends to decrease from northeast to southwest as awhole. High-value areas seems to be near the entrances of parks and low-value areasappear to be the deepest parts of parks. In residential areas, the soil organic carbonapparently exhibits zonal and island-shaped distribution, the content of which declinesfrom north to south, and island-shaped high value areas lie in the entrances of theseinvestigated areas. In traffic greenbelts, the soil organic carbon remarkably showszonal distribution, the content of which tends to decline from northwest to southeastand seems to be lower near the road. In industrial zones, the soil organic carbonpresents zonal distribution as a whole, the content of which has a trend to decreasefrom western high-value areas to the surroundings. On the whole, the higher theresearch scale, the higher the nugget coefficient, and thereby variables are affected bystochastic factors to a larger extent, while regional scales and size of tiny areas aremost heavily impacted by structural factors.3. The analysis on the relationship between soil organic carbon and nitrogenshows that in sample zones there exists positive correlation between soil organiccarbon and soil total nitrogen, strongly positive correlation between the content of soilorganic carbon and soil carbon/nitrogen ratio, extremely weak negative correlationbetween soil total nitrogen and carbon/nitrogen ratio, and no correlation among soilorganic carbon, total nitrogen and soil nitrate nitrogen.4. The research on spatial distribution of soil organic carbon and nitrogen insample zones suggests that the total nitrogen and soil nitrate nitrogen exhibits a trend of zonal distribution, and overall spatial variation of carbon/nitrogen ratio tends toshow multi-island shaped distribution.