【作者】 秦伟；

【导师】 朱清科；

【作者基本信息】 北京林业大学 ， 复合农林， 2009， 博士

【摘要】 土壤侵蚀是危及人类生存与发展的重要环境问题。黄土高原地区水资源短缺、生态环境脆弱,已成为我国乃至世界上水土流失最严重的地区之一。20世纪50年代以来,该区相继开展了一系列大规模的水土保持工程和林业生态工程。尤其是20世纪末开始大规模实施的退耕还林(草)工程,在控制水土流失、改善生态环境方面取得了显著成效。研究该区土壤侵蚀特征及其对植被重建的响应,能够为黄土高原林业生态建设和水土流失治理提供重要的理论依据与决策参考。本文以黄土高原腹地和林业生态工程的典型示范区北洛河上游为研究区,运用统计学分析方法、数字流域技术、水文学和景观生态学理论,结合多年水文气象观测数据、不同分辨率遥感影像及数字高程模型等基础资料,分析了流域降雨时空分布特征和土地利用/覆盖变化(LUCC):建立了基于数字高程模型和水流路径的沟缘线提取方法,据此探讨了流域地貌特征,进行了面向地貌特征的侵蚀风险评估;在研究流域径流、输沙变化趋势、特征时段及变化驱动因素的基础上,确定了植被重建对流域水沙的调控效应;基于高分辨率遥感影像,提取了坡面浅沟及其地形参数,分析了浅沟侵蚀的地形临界特征;在划分流域地貌单元、改进坡长因子算法、改造次降雨沟坡侵蚀模型的基础上,分别运用修正通用土壤流失方程(RUSLE)、沟坡侵蚀模型和泥沙输移分布模型(SEDD),评估了不同特征时段坡面与沟坡的侵蚀强度;通过集总侵蚀评估结果、模拟流域产沙,研究了不同地貌部位的侵蚀、产沙对植被重建的响应,建立了流域侵蚀空间分布模型,确定了不同环境因素在植被重建前后对侵蚀空间分异的相对贡献。主要获得如下结论:(1)北洛河上游年降雨量自西北向东南递增,但空间差异不显著。近十余年来,降雨量略有增加,干旱年份和极端降雨天气的发生机率略有减少。以1999年大规模开展植被重建为界,年均降雨量和降雨侵蚀力分别提高5.07%和8.64%,植被重建后气候背景具有增加径流、输沙的潜在条件。(2)研究区河网临界支撑面积介于0.5～1.0 km~2,不同级别的沟谷密度均大于0.91 km/km~2,沟间地和沟谷地分别占该区总面积的68.29%和31.7l%,表现出沟壑纵横、支离破碎的地貌特征。流域88.05%的区域存在中度以上的侵蚀风险,大部分地方具备发生较强土壤侵蚀的地形条件。(3)1986-2004间,流域植被覆盖率由56.74%提高为76.76%。其中,林地增加趋势最为明显,变化速率较快、变化程度较剧烈。不同土地利用类型中,林地和高覆盖度草地的重心向东南转移,农地和中、低覆盖度草地的重心向西北转移。景观格局呈现斑块数量增加、镶嵌度提高、同类斑块联通性下降,从而造成景观多样性显著增加、破碎度明显增大的变化特征。(4)1980-2004年间,流域径流、输沙变化分为3个阶段。其中,2001-2004年为植被重建的水沙调控效应期。4年共减少径流13 808.0万m~3、输沙14 250.8万t。单位面积新增林地年均理水、减少能力分别达2.67万m~3/km~2和2.75万t/km~2。(5)浅沟侵蚀主要受坡面坡度、长度、坡向和上坡长度等地形因素影响,其上限与下限临界坡度分别介于26～27°和15～20°,临界坡长介于50～80 m。(6)植被重建后,流域侵蚀强度由12 652.06 t/(km~2·a)下降为6 036.72 t/(km~2·a);产沙强度由3 896.99万t/a减少为1 795.50万t/a。其中,坡面侵蚀、产沙强度分别由5 770.46 t/(km~2·a)和1 308.81万t/a减少为1 437.93 t/(km~2·a)和322.46万t/a;沟坡侵蚀、产沙强度分别由28 093.92 t/(km~2·a)和2588.18万t/a减少为16 196.91 t/(km~2·a)和1473.04万t/a。坡面内,单位面积新增林地年均减少侵蚀11 752.10 t/(km~2·a)、产沙1.14万t/a。沟坡产沙比例由66.41%提高为82.04%,成为目前流域内最主要的侵蚀、产沙源。(7)植被重建前,地形、植被和降雨对流域侵蚀强度空间分异的相对贡献分别为17.30%、20.79%和61.91%;植被重建后,各类侵蚀影响因素的相对贡献率分别为15.73%、57.67%和26.60%。植被重建使得植被对流域侵蚀强度空间分异的相对贡献提高36.88%,从影响最小的因素转变为影响最大的因素。更多还原

【Abstract】 Soil erosion has turned into one of the important environmental problem endangering the existence and development of human being.The Loess Plateau is limited in water resources and vulnerable to eco-environment,has become one of regions with the most serious water and soil loss in China and even the world.Since 1950s,many of massive soil and water conservation projects and forestry ecological engineering have been executed,especially the project of returning farmland to forest and grassland begin in 1990s has been achieving obvious effect in controlling loss of soil and water and improving eco-environment.Research on characteristics of soil erosion and its response to re-vegetation in the Loess Plateau can provide an important theoretical basis and reference to decision for forestry ecological construction and controlling loss of soil and water.This thesis was carried out in the upper reaches of Beiluohehe River located in the central part of the Loess Plateau and being one of the demonstration area of forestry ecological engineering.By using the method of statistic analysis,technique of digital watershed,theories of hydrology and landscape ecology,and based on the basic materials including observed data of hydrology and meteorology, remote sensing images of different resolution and digital elevation model(DEM),the time-space distribution characteristics of rainfall and land use and land cover change(LUCC) were analyzed.The object-geomorphic erosion risk in study area was evaluated after analyzing the geomorphic feature,and establishing the method of automated extraction of shoulder line of vally based on flow path from DEM data.According to studying the change trend,characteristic stage and driving factors for variations of runoff and sediment of basin,the regulation effects of runoff and sediment of re-vegetation were calculated.A series of topographic values were extracted from high resolution remote sensing image and critical topographic characteristics of shallow gully erosion on slope were obtained.Based on dividing district for landform,mending the algorithm of L factor and modified the valley-slop erosion model of single rainfall,the intensity and distribution of soil erosion on hill-slop and on valley-slop in different period were estimated by Revised Universal Soil Loss Equation(RUSLE) and valley-slop erosion model combined with Sediment Delivery Distributed Model(SEDD),respectively.By integrating the estimated results of soil erosion on hill-slop and valley-slop,simulating sediment discharge of basin,the responses of soil erosion and sediment yield of the different geomorphic units to re-vegetation were deeply studied.Besides,the relative contributing ratios of different environmental factors to space heterogeneity of soil erosions before and after re-vegetation were determined according to established erosion spatial distribution model.The main research results are as following: The annual rainfall of the upper reaches of Beiluohebe River is lower in the northwest region than in the southeast region.Over the past decade,rainfall increased a little,and the probability of occurrence of dry year and extreme rainfall event decreased.Average annual rainfall and rainfall erosivity after 1999 when massive re-vegetation were executed increase 5.07%and 8.64%than the previous period,respectively.This indicated that there is a climate background after re-vegetation to raise the erosion intensity and sediment yield.In the upper reaches of Beiluohehe River,the critical support area of channel network is between 0.5 and 1.0 km~2.The gully densities in different levels all are more than 0.91 km/km~2.The slop-up land account for 62.29%of total area of basin,and the rest is gully land.All of these indexes present the general geomorphic characteristics that ravines and guillies criss-cross.The region existing moderate and severe erosion risk accounts for 88.05%of the total area of basin.This indicated that there is the landform condition causing severe soil erosion in most parts of study area.The vegetation coverage of basin increases form 56.74%in 1986 to 76.76%in 2004.Among different land use types,forestland presents the most obvious rising trend,fastest changing speed. Besides,gravity centers of forestland and grassland with high coverage move to southeast of basin. Conversely,gravity centers of farmland,grassland with moderate coverage and grassland with low coverage move to northwest of basin.The patch number and their mosaic degree increase,but continuity of same type patches decrease.All of these lead to the landscape pattern showing the degree of fragmentation and diversity increase obviously.From 1980 to 2004,the variation of runoff and sediment of basin could be divided into three periods.Among them,the effecting period of re-vegetation is form 2001 to 2004.In this period,the runoff and sediment of basin reduce a total of 138.08 million m~3 and 142.51 million t due to re-vegetation.The average capacities of control water and soil loss of newly increased forestland are about 26 700 m~3/(km~2·a) and 27 500 t/(km~2·a),respectively.The shallow gully erosion on slope is mainly influenced by slope degree,slope length;slop aspects up-slop length.The upper limited critical slope steepness of shallow gully erosion is between 26 and 27°,and the lower limited critical slope steepness is between 15 and 20°.In addition,the critical slope length ranges from 50 to 80 m.Taking 1980 to 1994 as the reference period and 2001 to 2004 as effecting period,the average annual intensity of soil erosion of total basin reduce from 12 652.06 t/(km~2·a) to 6 036.72 t/(km~2·a),and the average annual sediment yield reduce from 38.97 million t/a to 17.96 million t/a.Among different geomorphic units,the average annual intensity of soil erosion on hill-slop reduce from 5 770.46 t/(km~2·a) to 1 437.93 t/(km~2·a),and sediment yield reduce from 13.09 million t/a to 3.22 million t/a.At the same time,the average annual intensity of soil erosion on valley-slop reduce from 28 093.92 t/(km~2·a) to 16 196.91 t/(km~2·a),and sediment yield reduce from 25.88 million t/a to 14.73 million t/a.On the hill-slop, the average capacities of reducing erosion and sediment of newly increased forestland are about 11 752.10 t/(km~2·a) and 11 400 t/a,respectively.The proportion of sediment yield on valley-slop in total sediment yield of basin increase form 66.41%to 82.04%.The valley-slop has been as the most main source of erosion and sediment yield..Before re-vegetation,the relative contributing ratios of terrain,vegetation and rainfall to space heterogeneity of soil erosion are 17.30%,20.79%and 61.91%,respectively.After re-vegetation,the relative contributing ratios of relevant environmental factors change to 15.73%,57.67%and 26.60%。The relative contributing ratios of vegetation grows 36.88%and become the most effective factor from the least one due to re-vegetation.更多还原