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城镇化背景下三峡库区农村土地利用变化及其生态环境效应——以重庆市万州区为例
Alternative Titleural Land Use Change and Eco-environmental Effects of Ubanization in Three Gorges Reservoir Area: A Case Study of the Wanzhou District, Chongqing
陈颖锋
Subtype博士
Thesis Advisor王玉宽
2017
Degree Grantor中国科学院大学
Place of Conferral北京
Degree Discipline自然地理
Keyword城镇化 劳动力转移 土地利用变化 耕地撂荒 生态环境效应
Abstract中国城镇化发展过程中产生的区域生态环境问题已经引起全社会的广泛关注。快速的城镇化发展吸引了大量人口由农村转移到城镇,导致城镇地区不透水地表迅速扩张和农村地区耕地撂荒现象日趋严重,土地利用发生显著改变,这对区域生态环境和社会经济产生了重要影响。三峡库区地处四川盆地与长江中下游平原的结合部,内部人口密度较大且土地后备资源较为不足,城镇化的发展一方面使库区大量的耕地被不断扩张的城镇用地所占用,另一方面也使大量的农村劳动力发生转移,库区的人地关系趋于紧张。此外,三峡工程的建设使库区产生了大量移民,这改变了库区原本的人口分布,使库区城镇化水平在短时期内发生了跨越式的发展,库区内部生态环境也随之发生显著改变。因此,研究三峡库区城镇化发展背景下劳动力转移和土地利用变化以及生态环境的变化状况,对研究山区的城镇化发展有重要的理论和现实意义。本研究选择位于三峡库区中部的万州,在已有的理论基础上,分析万州区的城镇化发展水平,并结合遥感调查、问卷调查和样地监测等手段,在不同尺度上分析与万州建成区近、中、远等不同区域的农村土地利用的变化状况和农村劳动力的转移规律,并分析城镇化影响下农村地区的生态环境的变化状况。主要结论有:(1)万州区城镇化发展迅速。2000-2014年间城镇化率从36.3%增加至61.1%,增幅68.32%,同时城市建成区面积扩张4.02倍,全区建设用地面积增长4.56倍。调查问卷表明,有48.20%的农村劳动力较大部分时间在外进行务工等行为活动,常年转移至省外、重庆其他区县、万州主城区、万州其他乡镇和本地乡镇的比例分别占总人数的24.92%、5.72%、10.05%、0.94%和6.56%,外省和万州主城区是劳动力最主要的转移目的地。劳动力转移具有多尺度特征。在乡镇尺度,随着与人口聚集中心(万州建成区)距离的增加,劳动力转移的比例随之降低,其中转移至万州主城区的人口主要来自近城区,近城区平均有14.16%的劳动力转移至万州建成区,远高于而中间区和远城区;中间区平均有31.3%的劳动力转移至外省,高于近城区和远城区的转移比例。(2)城镇化带来了土地利用的剧烈变化,主要表现为建设用地的增加和耕地的减少,同时土地利用方式和强度也发生较大的变化。2000-2015年间万州最为主要的土地利用变化类型是耕地和林地转变为建设用地,以及农村耕地的撂荒。不同区域发生转变的强度也有所不同,变化强度表现为近城区>中间区>远城区,近城区耕地减少面积占近城区面积的5.79%,大于中间区的4.38%和远城区的4.03%;近城区建设用地增加面积占近城区面积的5.46%,明显高于中间区的3.35%和远城区的1.64%。林地、耕地和撂荒地是万州农村地区主要的土地利用类型,在调查的20个典型小流域中,土地利用以耕地和林地为主。分别占流域面积的32.51%和41.45%,而土地撂荒现象突出。撂荒地占15.05%,平均撂荒比例为30.38%。撂荒的区域差异明显,总体而言,撂荒比例呈现近城区<中间区<远城区。不同区域土地利用强度也有所不同,中间区的平均耕地复种指数最高,近城区次之,远城区最低;随着距中心城区距离的增加,化肥用量呈明显的减少趋势,而农家肥用量呈明显增加趋势。劳动力转移是影响耕地撂荒的重要因素,其中劳动力转移的去向和撂荒状况显示出较好的相关性,转移至较远地区的劳动力比例对该区域撂荒具有重要的影响。当劳动力大量转移至较远的区域,当地的撂荒风险就会增大,而劳动力就近转移则可以降低撂荒的风险。此外,土地流转则有效缓解了耕地撂荒,特别在偏远地区。大规模的耕地流转可以改变耕作方式、耕作强度和农田管理模式,甚至影响当地劳动力的转移。(3)城镇化的发展导致区域景观格局趋于破碎,但生态系统服务有所提升。2000-2015年间,万州区不同景观类型均受到了不同程度的干扰,总体而言,在全区尺度,受到干扰强度最大的是耕地和建设用地。其中,近城区受到的干扰强度最大,中间区受到的干扰强度小于近城区,但大于远城区;在流域尺度,近城区破碎的程度最高,远城区最低。耕地撂荒之后的生态服务发生了较大变化,产水量、土壤保持量和洪水缓解量均得到不同程度的提升。其中,产水量平均增加2.99%;潜在土壤侵蚀量平均减少0.22%,实际土壤侵蚀量平均减少17.7%;减洪量平均增加8.41%,提升程度表现为中间区>近城区>远城区。(4)研究区生态环境总体呈现好转的趋势,但仍有新的污染问题。撂荒导致区域土壤理化性质发生改变,各地类的平均砂粒含量均表现为近城区>中间区>远城区,表明随着城镇化影响能力的减弱,土壤颗粒呈明显的细化趋势。撂荒对控制径流的氮磷流失起到了一定的作用,同时增加了土壤的容重,粗化了土壤机械组成,万州区撂荒地土壤容重平均为1.55g/cm3,大于耕地和果园的平均土壤容重;撂荒地土壤平均砂粒含量为25.7%,颗粒相比耕地和果园较粗。撂荒使土壤的有机质含量升高,同时使氮素、磷素和钾素的含量有所下降,撂荒地的土壤重金属含量较耕地和果园也有明显的下降。随着近年来流域撂荒比例持续增加,流域地表径流的氮、磷浓度持续下降,特别是撂荒比例达到50%后,流域出口断面污染大幅降低,耕地中撂荒比例每增加5%,氮浓度降低8.20%,磷浓度降低10.48%。但城镇化的发展促进了水产养殖业的发展,导致养殖型的库大量涌现,使塘库氮磷含量增加。
Other AbstractThe regional ecological and environment problems resulted from urbanization has aroused wide concern of the whole society. Rapid urbanization attracted a large number of population transfer from rural to urban, which leads to growing abandonment of arable land, rapid expansion of urban impervious surface and significant change of land use, and this has a great impact on regional ecological environment and social economy.The Three Gorges reservoir area is an important part of upper reaches of the Yangtze River Economic Zone, and the urbanization process thereof is different from the evolution process of other regions in China. The construction of the Three Gorges project resulted in a large number of immigrants and changed the original population distribution of reservoir area, and the urbanization of reservoir area presented leapfrog development within a short period of time. The Three Gorges reservoir area is densely populated and short of land reserve resources. The urbanization of reservoir area occupies a lot of land and also transfers a large number of rural labors to city, making the man-land relationship in reservoir area strained. Therefore, studying population transfer, changes of regional land use and changes of ecological environment in the Three Gorges Reservoir area under the urbanization background has great theoretical and practical significance to the study on urbanization of mountainous region.Based on existing theories, this study analyzed the urbanization development level, land use change, population transfer and ecological environment changes of Wanzhou District in combination with remote sensing investigation, questionnaire survey and sample monitoring and made the following main conclusions:(1) The urbanization is rapidly developed in Wanzhou District. The urbanization rate was increased from 36.3% to 61.1% from 2000 to 2014, with the increasing range being 68.32%, meanwhile, the urban built-up area was expanded by 4.02 times, and the construction land area in whole district was increased by 4.56 times. The questionnaire showed that 48.20% of rural population spent most of their time working outside; the ratio of population transferred to other province, other counties in Chongqing Province, main urban area of Wanzhou, other towns of Wanzhou, and local towns to total population is 24.92%, 5.72%, 10.05%, 0.94% and 6.56%; and other provinces and the main urban area of Wanzhou are the most popular transfer destination for laborers. The population transfer has multi-scale characteristics. In the township scale, with the increase of distance from the population center, the labor transfer ratio is decreased, wherein the population transferred to the main urban area of Wanzhou is mainly from near urban areas; an average of 14.16% of laborers in near urban area transfer to Wanzhou built-up area, which is greatly higher than that of the middle urban area and the far urban area; and an average of 31.3% of the laborers in middle urban area transfer to other provinces, which is higher than the transfer ratio of near urban area and far urban area.(2) The urbanization has brought drastic changes in land use, mainly manifested as the increase of construction land and the decrease of cultivated land, as well as great changes of land use pattern and intensity. From 2000 to 2015, the most popular land use change types in Wanzhou were changing cultivated land and forest land to construction land, and abandoning rural farmland. The change degrees in different areas are different and decreasingly ranked from near urban area, middle urban area to far urban area, wherein the ratio of arable land decreasing area in near urban area to the area of near urban area is 5.79% and greater than 4.38% of middle urban area and 4.03% of far urban area, and the ratio of construction land increasing area in near urban area to the area of near urban area is 5.46% and significantly higher than 3.35% of middle urban area and 1.64% of far urban area. Woodland, arable land and abandoned land are main land use types in rural areas of Wanzhou, in 20 typical small watersheds in the survey, the land use is focused on arable land and woodland which account for 32.51% and 41.45% of watershed area, respectively, while land abandonment phenomenon is prominent, the abandoned land accounted for 15.05% of watershed area, and the average abandonment ratio is 30.38%. The abandonment shows obvious regional difference, the abandonment ratio is increasingly ranked from near urban area, middle urban area to far urban area. Different areas also shows different land use intensities, the middle urban area has the highest average arable land multiple crop index, successively followed by near urban area and far urban area. With the increase of distance from the city center, the fertilizer consumption is decreased significantly, while the manure consumption is significantly increased. The labor transfer is an important factor affecting the abandonment of arable land, wherein the labor transfer destination shows a good correlation of abandonment status; the labor ratio transferring to far regions has an important influence on the abandonment in local region, that is to say, when a large number of laborers transfer to the far regions, the abandonment risk in local region will increases, and the nearest labor transfer can reduce the abandonment risk. In addition, the land circulation effectively alleviates the abandonment of arable land, especially in remote areas. The large-scale arable land circulation can change the cultivation mode, cultivation intensity and farmland management pattern, even affect the local labor transfer.(3) The urbanization development leads to the fragmentation trend of regional landscape pattern but improves the ecosystem services at certain extent. Different landscape types have been disturbed by different degrees, wherein the interference intensity is decreasingly ranked from near urban area, middle urban area and far urban area; and as to the watershed scale, the near urban area suffers the highest fragmentation degree, while the far urban area suffers the lowest fragmentation degree. The abandonment of arable land changes the ecological service greatly, the water production, soil conservation and flood mitigation are increased at different extents, wherein the water production is increased by 2.99% on average, the potential soil erosion is reduced by 0.22% on average, the actual soil erosion is reduced by 17.7% on average, the flood mitigation is increased by 8.41% on average, and the improvement degree is decreasingly ranked from middle urban area, near urban area to far urban area.(4) The ecological environment in the study area is generally improved, but there are still new pollution problems. The abandonment changes the physical and chemical properties of regional soil, the average sand content of all types of soil is decreasingly ranked from near urban area, middle urban area to far urban area, and this shows that, with the weakening of urbanization influence, the soil particles present obvious trend of refinement. The abandonment plays a certain role on controlling nitrogen and phosphorus loss of runoff, but also increases the soil bulk density and coarsens the soil mechanical composition, wherein the average soil bulk density of abandoned land in Wanzhou District is 1.55g/cm3 which is higher than the average soil bulk density of arable land and orchard, and the average sand content of abandoned land soil is 25.7% and the sand particles in abandoned land are thicker than those in arable land and orchard. The abandonment increases the organic matter content of soil and reduces the nitrogen, phosphorus and potassium content, meanwhile, the soil heavy metal content in abandoned land is obviously lower than that in arable land and orchard. With the continuous increase of abandonment ratio of watershed and the continuous decrease of nitrogen and phosphorus concentration of watershed surface runoff in recent years, especially after the abandonment ratio reaches 50%, the outlet section pollution of watershed is greatly reduced, and 5% increase of abandonment ratio of arable land will reduce 8.20% decrease of nitrogen concentration and 10.48% decrease of phosphorus concentration. However, the urbanization development promoted the development of aquaculture industry, resulting in the emergence of a large number of aquaculture ponds, and this increases the nitrogen and phosphorus content of ponds.
Pages128
Language中文
Document Type学位论文
Identifierhttp://ir.imde.ac.cn/handle/131551/24581
Collection山区发展研究中心
Affiliation中国科学院成都山地灾害与环境研究所
First Author Affilication中国科学院水利部成都山地灾害与环境研究所
Recommended Citation
GB/T 7714
陈颖锋. 城镇化背景下三峡库区农村土地利用变化及其生态环境效应——以重庆市万州区为例[D]. 北京. 中国科学院大学,2017.
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