The Densities, Components And Temporal-spatial Variations Of Soil Organic Carbon In Urban Soils In Kaifeng City

With the industrialization in most countries, Urbanization carried out in global area. The long–term and continuous land expansion changed the land use and land cover, what had profound influence on soil organic carbon. The early researches of the urban soils focused on the fertility, including the characteristics and chemical components. Afterwards, with the serious situation of global environment, soil organic carbon of urban soils were concerned. The current researches concerned on the topsoil and sub–surface layer of soil, ignoring the vertical distribution of soil organic carbon; concerned on the soil covered by vegetation, ignoring the soil with no vegetation cover; concerned on the total organic carbon, ignoring the components; and the researches on temporal variation of soil organic carbon were not enough. Therefore, to be familiar with the influence of urbanization on soil organic carbon depended on deeper and wider researches. Taking Kaifeng city which had about 2700 yrs city–building history as the research object, the components, storage and temporal–spatial variations of soil organic carbon were studied based on the sampling and experiment. 25 norm soil profiles in greenlands, 8 soil profiles in lands with non–vegetation cover and 112 topsoil samples were set, collecting 91 profile samples in greenlands, 79 profile samples with non–vegetation cover and 112 topsoil samples. The samples were experimented on physical–chemical property, organic carbon, humus, light fraction organic carbon, Particulate organic carbon, Readily oxidizable carbon, water–soluble organic carbon and black carbon. There were nine chapters in the paper, including five sections:The first section was introduction(the first chapter), including the background, survey, existing problems, trend of urban soil organic carbon; main contents and significance of this paper.The second section was material and methods(the second chapter), including natural and socioeconomic status , environmental pollution situation; setting and collection of soil samples; experimental methods of items; data processing method; technical route of this paper.The third section was the components, storage and temporal–spatial variations of urban soils(the third, fourth, fifth and sixth chapter), including storage, difference among functional districts, horizontal and vertical distribution of soil organic carbon, active organic carbon, carbon in humus(carbon in humic acid, fulvic acid and humin) and black carbon. The fourth section was the temporal variations and variations along transaction line from urban areas to suburbs(the seventh and eighth chapter), including the difference of soil organic carbon in topsoil and profile along the time; the difference of soil organic carbon and active organic carbon in topsoil among different–aging greenlands; variations of soil organic carbon and the components between urban areas and suburbs, and along the transaction line from the center of urban area to suburbs.The fifth section was conclusion and discussion(the ninth chapter), including the conclusion, deficiency and prospect of this research.The main results were as follows:(1)The contents and densities of soil organic carbon in topsoil of urban areas were higher than soils with non–vegetation cover and soils in suburbs. Urban soils had 1.15–fold more densities of soil organic carbon(SOCD) in profiles than suburbs. The storage of soil organic carbon in greenlands was higher than lands with non–vegetation cover; the values of POC and LFOC in urban soils were higher than that in suburbs, the situation of ROC and WSOC were the opposite. The storage of humus in urban soils was lower than that in suburbs, and the percentage of carbon in humus in total organic carbon in urban soils was lower than that in suburbs by 10.76%. The contents of carbon in humic acid and humin were higher in urban soils than that in suburbs, the contents of carbon in fulvic acid in urban soils was lower than that in suburbs by 31%. The value of HA/FA in urban soils was 0.09 higher than that in suburbs. The value of E4/E6 in urban soils was 0.03 lower than that in suburbs. The urban soils had 1.34–fold more BC in topsoil than suburbs.(2) The storage of soil organic carbon, active organic carbon, carbon in humus and BC were different among functional districts. The order of the contents and densities of topsoil were all industrial district > administrative district> traffic district > residential district > cultural/educational district >recreational district. The SOCD in profile followed the order of cultural/educational district> traffic district >industrial district > residential/administrative district > recreational district. Industrial district and administrative district had the higher storage of POC, ROC and LFOC; cultural/educational district and recreational district had the lower storage of them. However, the storage of WSOC in recreational district was the highest among functional districts, and the storage WSOC in industrial district and administrative district were lower. The storage of carbon in humus and its components were the highest in industrial districts, the lowest in recreational district. The value of HA/FA was the highest in recreational district, the lowest in industrial districts. The order of the value of E4/E6 was cultural/educational district <industrial district< administrative district< traffic district. BC in topsoil of urban soils followed the order of industrial district> administrative district> cultural/educational district> traffic district> recreational district> residential district.(3) The storage of soil organic carbon in bare land was higher than that in land with building and road cover. The contents and densities of POC, ROC and LFOC in topsoil all followed the orders of bare lands> lands covered by buildings> land covered by road. The content of WSOC followed the order of bare lands> lands covered by buildings> land covered by road. However, the soils in land covered by road had 1.33–fold and 1.50–fold more density of WSOC than bare lands and lands covered by buildings, respectively.(4) The horizontal distribution of soil organic carbon, active organic carbon and carbon in humus were different. The shape of horizontal distribution of soil organic carbon was annular, and the contents declined from the east area to northwestern area. The distribution of POC took on a string shape, and the contents declined from southeastern area to northwestern area. The content of ROC declined from the southern area to northern area. The shape of WSOC's distribution was speckle, with three high value centers in southeastern area and western area in urban area, western area and southeastern area in suburbs, respectively. The value of LFOC declined from eastern area to western area. The value of carbon in humus declined from eastern area to western area, and from the center of urban area to northern area, and to southern area, respectively.(5) The contents of soil organic carbon, carbon in humus and active organic carbon in greenlands declined with the depth. They were mainly distributed within the scope of 0³0cm, with about 40⁶0% of soil organic carbon, 46.59% of LFOC, 56.41% of POC, 50.31% of ROC. The storage of WSOC in the scope of 0³0cm and 30⁶0cm were closed, with the percentages of 30.62% and 30.08%, respectively. The components of humus declined with the depth, and the order of regularity was carbon in humin>carbon in humic acid> fulvic acid. There was no obvious variation of HA/FA in vertical distribution. The vertical distribution of E4/E6 followed the regularity of power function(R²=0.448⁰.988,p<0.05). The soil organic carbon and BC in topsoil of lands covered with no vegetation declined with the depth.(6) The contents and densities in topsoil and densities in profile increased with the time, with the increasing range of 0.99～28.19 g kg^–1, 0.12～3.39 kg m^–2 and 0.39～7.59 kg m^–2, respectively. Period I(before the early of 20th century) had 1.19–fold more content of soil organic carbon and 1.08–fold more SOCD in topsoil than period II(after the early of 20th century), respectively. The contents of LFOC, POC, ROC and carbon in humus of period I were 1.15, 1.35, 1.44 and 1.16 times more than periodâ…¡, respectively. There was no obvious rise of WSOC. The value of HA/FA of periodâ… was lower than periodâ…¡.(7) The storage of soil organic carbon in topsoil and in profile in urban area were higher than that in suburbs along the transaction line. The storage of soil organic carbon declined from the center of urban area to suburbs. There was obvious variation of the contents of carbon in humus along the transaction line. however, the percentage of it in total organic carbon was followed the order suburbs>old urban area> new urban area, and the percentage increased along the transaction line from the center of urban area to suburbs. There was no obvious variation of HA/FA in this line. The value of E4/E6 in urban area was higher than that in suburbs. The storage of LFOC, POC and BC in urban area were higher than that in suburbs, and they all declined from the center of city to suburbs. The storage of WSOC in urban area was lower than that in suburbs, increasing with the distance. The storage of ROC in urban area was similar to that in suburbs, and took on a complicated variation in transaction line. The contents of BC in urban area was higher than that in suburbs, and it declined with the distance.