【作者】 张素红；

【导师】 高尚玉； 李森；

【作者基本信息】 北京师范大学 ， 自然地理学， 2007， 博士

【摘要】 石漠化是普遍发生在亚热带喀斯特背景下的土地退化过程,其显著特征为土壤严重侵蚀、基岩裸露、植被退化、土地生产力下降,制约着当地的经济发展,被列为我国严重的生态环境问题之一。粤北岩溶山区处于我国西南岩溶区的东部边缘,北江源头及上游水源涵养区,其石漠化威胁到珠江下游地区的生态安全。本文通过遥感影像判读、解译,土壤中137Cs含量测定及损失量分析,降水侵蚀观测与模拟试验,对粤北岩溶山区近30年来石漠化时空格局特征、不同等级石漠化土地土壤侵蚀速率、侵蚀特征作了探讨。(1)以1974、1988、2004年遥感影像为基础,绘制出3期石漠化土地分布图,2004年,研究区石漠化面积534.56 km2,占研究区总面积的3.85%。30年来粤北石漠化一直处于逆转状态,比1974年减少68%,后期(1988-2004)逆转速度高于前期(1974-1988)。重度石漠化与中度石漠化土地比重持续上升,景观破碎度增大,具备较强的发展潜力和扩张趋势。(2)石漠化是岩性、地貌、坡度、土壤、植被、降水以及人为扰动等诸多因子综合作用的结果。粤北石漠化土地主要集中在碳酸盐岩分布区,其分布范围多与石灰土分布区重合,中度、重度石漠化土地与坡耕地的分布密切相关。不合理的人为活动是造成石漠化发展的最主要原因。(3)137Cs示踪法测定粤北石漠化地区多年平均土壤侵蚀模数为2433.2 t km-2 a-1,远高于喀斯特地区土壤允许侵蚀量。耕作土壤侵蚀模数高于非耕作土壤,坡耕地侵蚀模数高达4968.3 t km-2 a-1。随石漠化程度增加,土壤侵蚀速度逐渐增加,但由于可供侵蚀的土壤量有限,石漠化末期土壤侵蚀量逐渐降低。高处的土壤物质不断被流失,低凹处接受堆积。土壤分布逐渐趋于斑块化,残存在低洼之处,是维系受损的岩溶生态系统存在的基础。(4)土壤侵蚀小区一年的降水侵蚀观测记录显示,2005年5月-2006年4月一年间不同人为扰动下的土壤侵蚀量分别为:未扰动草坡,67.92 t km-2 a-1;耕地,1756.96 t km-2 a-1,是草坡侵蚀量的25.87倍;裸地,2455.37 t km-2 a-1,是草坡侵蚀量的36.15倍。虽然喀斯特地区土壤分布的特殊性决定了其绝对侵蚀量低,但在一些土层厚、土壤分布连续的小区域,土壤侵蚀模数会高于其他条件相同的非喀斯特区域。(5)有植被覆盖的未扰动草坡地及耕地的侵蚀量与次降水量的相关性高,而裸地侵蚀量则与连续30分钟最大雨强相关性更高,较好的植被覆盖可以抵御短时间的强降水。植被覆盖率是影响土壤侵蚀量高低的主要因素:裸地的次降雨土壤侵蚀量大约是草坡地的60倍,耕地次降雨土壤侵蚀量平均约是草坡地次降雨侵蚀量的15倍,因受人为耕作活动的干扰,变化幅度很大。(6)人工降雨试验结果显示研究区地表产流具有超渗产流的特征。雨强低时,地表产流量及土壤侵蚀量随降水时长增加,增量变化不大;高雨强时二者的增量很大。裸地侵蚀量的变化与可供侵蚀的土壤量相关,在短时间内迅速增大,表层土壤很快被地表径流冲刷带走,土壤面积减少,之后由于土壤源减少,土壤侵蚀量增量逐渐减小。草坡的侵蚀变化与裸地相反,降水前期土壤侵蚀量变化不大,后期地表径流量增加,流水侵蚀力超过植被保护强度,土壤侵蚀量骤增。耕地的侵蚀量随降水时间持续增加,波动不大。(7)随着石漠化的发展,表层土壤中胶结性差的松散砂粒易于随水流失,粉砂与粘粒的比重略有上升,土壤容重增大,孔隙度降低,土壤通透性下降,结构恶化。土壤侵蚀使土壤中养分迅速流失,土地退化严重。石漠化的发展导致土壤理化性质的恶化,既制约着植被的生长发育,又加大地表径流产生的可能,促进石漠化的进一步发展,形成相互反馈的恶性循环。更多还原

【Abstract】 Karst rocky desertification is a land degradation process widely occurred under the fragile karst environmental of subtropical region, which is characterized by severe soil erosion, percentage of bare rock area increasing, vegetation degenerating, and land productivity declining. It restricts the local economic development, and is ranked as one of the severe eco-environmental problems in China. Karst mountainous region of northern Guangdong locates in the watershed of Beijiang River-- the branch of Zhujiang River. Rocky desertification occurred in this region may threaten the ecological safety of the catchment area of Zhujiang River.By interpreting remote images, detecting the 137Cs activity and its loss rate in soil, observation of rainfall erosion as well as the artificial rainfall experiment, this paper discusses the temporal and spatial pattern features of rocky desertification land in karst mountainous region in northern Guangdong, the soil erosion rates and erosion characters in rocky desertification land of different degrees.(1) Based on remote images of research region in 1974, 1988 and 2004, maps of the distribution of karst desertification land are portrayed. Area of rocky desertification land and other landscape pattern indices are obtained according to the information in the maps. In 2004,the area of rocky desertification land in research region is 534.56 km2, which covers 3.85% of the total area of research region. It is in a state of reversion in recent 30 years and the area reduced by 68% than that in 1974. Its reversion speed from 1988 to 2004 is higher than that from 1974 to 1988. The ratios of moderate and severe rocky desertification lands keep rising, and their fragmentation degrees increase, which shows that moderate and severe rocky desertification lands have strong development potential and expansion tendency.(2) Rocky desertification is synthetically influenced by multi-factors such as lithologic characters, geomorphy, slope, soil features, vegetation, precipitation and human activities. In northern Guangdong, the rocky desertification lands distribute around carbonatite range, and are mostly superposed the distribution region of limestone soil. Moderate and severe rocky desertification lands are closely related with the distribution of slope-farmland. The irrational human activity is the most important factor which caused the rocky desertification.(3) The long-time average annual value of soil erosion modulus of karst mountainous region in northern Guangdong estimated by 137Cs technique is 2433.2 t km-2 a-1, which is much higher than the allowable erosion amount of karst region. Cultivated soil has a higher erosion modulus than uncultivated soil, and the soil erosion modulus of slope-farmland gets to 4968.3 t km-2 a-1. Along with the development of rocky desertification, soil erosion rate increased in early stage. Soil on upper position was kept on washing out and depositing in the low lying land. Because of the limitation of soil, the amount of soil erosion reduced gradually and ultimately stopped. The rudimental soil substance appeared in small patches and is the base of maintaining the damaged karst ecosystem.(4) According to the observation data in soil erosion sample plots from May 2004 to April 2005, the yearly amounts of soil erosion are: untouched natural grassland, 67.92 t km-2 a-1; cropland, 1756.96 t km-2 a-1, which is about 25 times higher than that in untouched natural grassland; nudation, 2455.37 t km-2 a-1, which is nearly 36 times of that in untouched natural grassland. Though the particularity of soil distribution in karst region limited its absolute amount of soil erosion, in certain samll sections where the soil distributed continuously and soil layer is thick, the soil erosion modulus may be higher than that in non-karst region where it has the same conditions with the former.(5) Soil erosive quantity on untouched natural land and cropland is most related to single rainfall, while the erosive quantity on bare-land is more related to the maximum intensity of continuous rainfall in 30 minutes. Vegetation can effectively protect land from soil erosion by short-term strong rainfall. Percentage of vegetation coverage is the main factor that influenced the amount of soil erosion: soil erosive quantity on bare-land is about 60 times higher than that on untouched natural grassland, and that the speed of soil loss on farmland 15 times higher than that on untouched natural grassland.(6) The runoff in research region has the characters of super-infiltering runoff pattern according to the results of artificial rainfall experiments. When rainfall intensity is low, the runoff yield and soil erosive quantity increased slightly along with the delay of precipitation time while they increased strongly under high rainfall intensity. The change of erosive quantity on bare-land is related to soil erodibile amount. The loss of soil on bare-land raised swiftly in short period, surface soil was soon washed away and the area of soil reduced. In later period, the change rate of soil erosive quantity minished because of the lack of soil. The change of soil loss on grassland is opposite to that on bare-land: in earlier stage of rainfall soil erosive quantity increased slowly but rised sharply in posterior stage. For the water erosive energy exceeded the vegetation protection. The change of soil loss on farmland is not obvious.(7) Along with the development of rocky desertification, the loose sand grains with low bonding capacity in surface soil runaway easily with runoff. The ratio of silt and clay ascended slightly. Soil bulk density raised, porosity reduced, permeability descended. The soil structure deteriorated. At the same time, nutrient in soil lost swiftly due to the soil erosion and land productivity declined severely.Rocky desertification results in the deterioration of physicochemical property of soil, which restrained the growth and development of vegetation and enhanced the possibility of the generation of surface runoff. It accelerated the development of rocky desertification at the same time and formed an infernal circle.更多还原