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干旱区典型城市群不透水地表扩张对土壤有机碳的影响
艳燕
学位类型博士
导师张弛
2016
学位授予单位中国科学院大学
学位授予地点北京
学位专业地图学与地理信息系统
关键词城市土壤容重 城市土壤碳 垂直格局 城市土地覆被变化 城市土壤碳储量动态 天山北坡城市群
摘要城市化对生态系统碳循环有重要影响,人工不透水地表(Impervious Surface Area,ISA)是城市地表的主要组成。由于对ISA所封存土壤有机碳(SOCISA)含量及分布格局缺乏认识,导致全球和区域碳评估中大量采用高度简化的假说来估计城市土壤碳库,这些假设直接影响到碳循环研究中对城市化效应的评估精度。为揭示不透水地表下的土壤理化性状,量化城市建设对土壤碳库的影响,本研究采集天山北坡城市群在建工程ISA下100-cm深土壤样本,并与其邻近透水面(Pervious Surface Area, PSA)所采土样,以及未受建设干扰的原位土(Original Soil)进行对比。结合遥感反演的方法提取天山北坡城市群的土地覆被及其转化,评估了城市土地覆被变化对土壤碳库的影响。 (1) 天山北坡城市群城市不透水地表下土壤容重BDISA=1.55±0.02 g cm-3;透水地表下BDPSA=1.45±0.03 g cm-3,两者之间的配对t检验结果表明碳密度前者显著高于后者约7%。不透水地表下土壤有机碳密度SOCDISA=5.74±0.40 kg C m-2;透水地表下土壤有机碳密度SOCDPSA =8.69±0.75 kg C m-2,前者显著低于后者约33.9%。城市BDISA随着深度增加而显著降低,呈现出“上紧下松”的垂直格局,而BDPSA并未表现出显著的垂直变化规律。城市两种地表下SOCD均呈现出随着深度增加而显著降低的变化趋势。 (2) 天山北坡城市群周边原位土容重BDO=1.41± 0.009 g cm-3,均低于城市两种地表下土壤BD;原位土土壤碳密度SOCDO=6.52 kg C m-2,略微高于SOCDISA,显著低于SOCDPSA。原位土SOCDO具有随着土层深度增加而降低的变化趋势。100-cm深SOCDISA总量与SOCDO相近,虽然两者的容重和SOC的垂直分布格局存在明显差异,但在考虑到建设过程中表层土(O层或A11层)被移除或因干扰导致的SOC分解流失、以及土壤压实对碳密度的影响的基础上,则可以正确模拟出原位土向不透水面下土壤转化过程。 (3) 在2000年~2014年间,天山北坡城市群土地覆被组分并未发生明显变化,城市不透水地表(ISA)主导覆被类型。然而在该时间段,ISA面积发生大幅扩张,涨幅高达41%,大面积转化了残存荒漠/裸土与农田。而在单个城市水平上,该时间段的土地覆被变化情况与整体城市群一致,以城市ISA的迅速扩张为主要类型,同时占用了其周边的残存荒漠/裸土。空间格局上,ISA的呈现出两种的增长形势,即以占用其周边农田与荒漠裸土为主的向外扩散;以及主要占用镶嵌于ISA中的零散植被的内填式增长。 (4) 在2000年与2014年时,天山北坡城市群土壤碳储量分别为4.96~4.99 Mt C,4.45 ~ 4.49 Mt C。由于ISA面积巨大,其下土壤碳储量在两个时间段均为主体土壤碳库,分别占总土壤碳储量41%与64%。2000年~2014年间,城市土地覆被变化导致约0.50 ~ 0.51Mt C的损失,该损失量为2000年总土壤碳储量的10.3%。ISA扩张转化大面积的农田、残存荒漠/裸土以及城市绿地土壤是导致土壤碳流失的主要原因。 (5) 为了阐明复杂的城市土地覆被之间相互转换对城市土壤碳库的影响,本研究以乌鲁木齐市为典型案例,将时间跨度拉长至1990年~2014年并进一步分析了土地覆被转化类型与强度对土壤碳库的影响。分类结果表明在1990年~2014年间,乌鲁木齐市ISA扩张了约三倍,其中残存荒漠/裸土、农田与城市绿地分别贡献了62%,27%和11%的面积。在该时间段,乌鲁木齐市城市土地覆被变化导致约24%土壤碳损失,其中由于ISA扩张而占用了农田、城市绿地与残存荒漠而导致的土壤碳损失量占总损失量的68%。
其他摘要Urbanization has profound impacts on ecosystem carbon cycle. Impervious surface areas (ISA) cover about 63% of the urban area and 0.9% of the land surface in China, but the biogeochemical characteristics of the soil beneath the ISA is still in lack. As the result, global and regional carbon cycle studies had to rely on over-simplified assumptions to estimate the soil organic carbon pool (SOC) beneath the ISA (SOCISA). Validities of these assumptions directly affected the assessments of the urbanization effects on regional/global carbon dynamics. To reveal the biogeochemical characteristics of the ISA soil, to evaluate the various assumptions in former studies, and to quantify the effects of ISA construction on SOC, this study, based on 100-cm-depth soil profiles taken from 27 ISA sites and the nearby pervious surface area (PSA) in the Northern Tianshan Urban Cluster in a dryland of the northwestern China, compared the soil bulk density (BD) and SOC among ISA, PSA, and the original soils undisturbed by urbanization. Meanwhile,Employing Landsat TM images acquired in 2000 and Landsat OLI images 2014, the Linear Spectral Mixture Analysis was applied to retrieve the land cover fraction images of ISA, vegetation and remnant desert/bare soil of Northern Tianshan Urban Claster. Based on SOC density data determined through field observations and literature reviews, we have evaluated the urbanization, especially the ISAexpansion on the soil orgnic Carbon pool. The main conclusions are as followes: (1) The mean regional soil bulk density BDISA=1.55±0.02 g cm-3, which was significantly higher than BDPSA=1.45±0.03 g cm-3 about 7% (p<0.01); SOCDISA = 5.74±0.40 kg C m-2 kg C m-2, which was significantly lower than SOCDPSA =8.69±0.75 kg C m-2 about 33.9% (p<0.01). The BDISA decreased significantly as the soil depth idcreased (p<0.05); however, the BDPSA did not show a significant vertical trend. Both of the SOCDISA and SOCDPSA declined as the soil depth increased significantly. (2) The mean regional original BDO=1.41 g cm-3,which was lower than that of both urban soil; mean regional SOCDO=6.52 kg C m-2,which was slightly higher than SOCDISA, but significantly lower than SOCDPSA. SOCDO declined with the increasing soil depth. Although SOCISA was close to the mean SOCDO in the study region, the vertical patter of their BDO and SOCDO did not match, our simulations indicated that it is possible to predict the changes in SOCD during ISA construction if we considered the SOCD loss due to topsoil removal and soil disturbances as well as the effects of soil compaction on SOCD. (3) The land-cover composition of Northern Tianshan Urban Cluster did not change obviously from 2000~2010, urban ISA was the dominant land-cover type. However, ISA of this region increased about 41% during this time period, which was converted large area of cropland and remnant desert. At the single city in Northern Tianshan Urban Cluster, the land-cover chage was same as the regioan land-cover pattern. Further analysis of the spatial pattern of land-cover change revealed that the impervious surface mostly sprawled outskirt displacing remnant desert/bare ground and cropland, and infilled cicyspace converting urban greenspace. (4) A total of 4.96~4.99 Mt and 4.45~4.49 Mt soil organic carbon was stored in the metropolitan area of Northern Tianshan Urban Cluster in the year of 2000 and 2014, respectively. Due to the huge area, soil organic carbon beneath the ISA was the dominant soil carbon pool in 2000 and 2014, ocuupying 41% and 64% of total soil organic carbon, respectively. The Northern Tianshan Urban Cluster lost 0.50~0.51Mt C, which was about 10.3% of the total soil organic carbon storage in 2000, due to the land-cover change during 2000~2014. The main reason of the soil carbon loss was caused by the conversion of remnant desert and cropland into ISA. (5) Because different urban land-cover types could have very different carbon storage, it is important to quantify the detailed “from-to” change trajectory information in land-use change detection. To this end, our study used the decision tree classifier to reveal the impact of complex land-covere change on urban soil organic carbon storage. This study choose the typical city of Northern Tianshan Urban Cluster—Urumqi as the case study to address the question, and increase the time period to 1990-2014. The result showed that ISA tripled from 1990-2014 displacing remnant desert and cropland. The city lost 24% of C stock from 1990-2014. About 68% of the soil organic carbon loss was caused by the conversion of remnant desert and cropland into ISA, mainly in the northern city.
学科领域地图学与地理信息系统
语种中文
文献类型学位论文
条目标识符http://ir.xjlas.org/handle/365004/14697
专题研究系统_荒漠环境研究室
作者单位中科院新疆生态与地理研究所
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艳燕. 干旱区典型城市群不透水地表扩张对土壤有机碳的影响[D]. 北京. 中国科学院大学,2016.
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