【作者】 连振龙；

【导师】 刘普灵；

【作者基本信息】 中国科学院研究生院（教育部水土保持与生态环境研究中心） ， 土壤学， 2008， 硕士

【摘要】 退耕还林还草是我国西部地区进行生态恢复与治理的主要措施,在一定程度上有效改善了该地区的生态环境。本研究以黄土丘陵区典型小流域燕沟流域为研究对象,通过对天然坡面径流小区降雨产流产沙、流域把口站径流泥沙的长期观测,结合野外模拟降雨试验结果,分析了不同土地利用方式坡面产流产沙特征,计算了燕沟流域水土保持措施,特别是植被恢复措施的减沙效益;同时对流域输沙变化的影响因子进行了分析,探讨了降雨因素对流域输沙量变化的影响,主要取得如下结论:1.分析了坡面不同土地利用方式及坡度特征对产流产沙的影响在相同的雨强条件下,不同土地利用方式产沙过程与累计产沙量都明显不同,总体表现为:翻耕小区﹥刈割后的小区﹥有植被覆盖的小区。不同土地利用方式小区30min产沙量与降雨时间关系符合W=at-b的线性方程,与降雨强度之间存在W = aIb的幂函数关系。对不同坡度小区产流产沙研究表明,陡坡小区无论产流产沙的强度,还是累计产流产沙量都明显高于缓坡小区,说明大于25°坡耕地要完全退耕这一政策的必要性。2.研究了不同退耕方式、不同年限坡面植被产流产沙特征退耕以来各类土地利用方式减水减沙效益显著,各小区年产流产沙量大小关系为:坡耕地小区>草地小区>灌丛小区,草地小区径流量较坡耕地小区减少50%～60%,灌丛小区较坡耕地小区径流量减少都在70%以上;各小区减沙量都在90%以上,减沙量大于减流量。说明草灌植被都具有明显的蓄水保土作用;而不同退耕年限灌丛小区的累计产流产沙量都小于草地小区,说明在不同的降雨量及降雨强度条件下,灌丛地的水土保持作用比草地更为明显。坡面6种处理小区径流系数大小关系为:坡耕地小区>刈割草地>草地>刈割灌丛地>灌丛地>刺槐林地,随地面植被覆盖度的增加而减少,呈负相关关系。与坡耕地相比,草地、灌丛及刺槐林地小区减流量分别为51.1%、71.4%和90%,减沙量分别为99.3%,99.5%和99.6%,刺槐林地减水减沙作用最为明显,各种土地利用类型减沙作用明显大于减流作用。3.比较了草地与灌丛群落的结构特征与减沙机理草地与灌丛小区刈割处理前后产沙情况出现较大差异,刈割后草地产沙量大幅增加,而灌丛小区刈割后产沙量增加并不明显,主要原因与二者的植被结构特征有关。经过10年退耕撂荒形成的草地群落,多为一年生草本植物,且生长在近地表层,枯落物较少,容易遭受破坏;灌丛群落出现多年生的山榆、刺槐、胡枝子等多年生灌木,地表枯落物较多,地下植物根系发达,水土保持作用显著。说明处于植被演替初级阶段的近地表层草地植被减沙效益显著,但生态功能仍然比较脆弱,是需要进行封育保护的主要植被群落。4.阐明了燕沟流域植被恢复减沙效益通过对不同土地利用方式坡面小区产流产沙分析,结合定位小区观测资料,利用水保法计算了治理后的燕沟流域年均输沙模数为737 t/km2?a,减沙效益大于80%;计算输沙模数与流域把口站观测值接近,证明对燕沟流域减沙效益的计算切合实际,并进一步说明燕沟流域的综合治理具有明显的减沙效益。5.探讨了降雨变化对燕沟流域输沙量变化的影响利用相近小流域观测资料,通过时间与空间相结合的方法,对燕沟流域治理前后降雨及产沙量变化进行了分析,结果表明退耕以后,降雨变化因素造成流域输沙量平均每年减少61228t,占流域输沙量减少的25%左右,即在造成近年来实测流域输沙量减少的两大因素中,降雨变化影响约占25%,综合治理作用约占75%。更多还原

【Abstract】 Returning sloping field to woods and grass is a main measure to carry through eco-restoration, and has ameliorated the environment in some extent in the west area. As a typical watershed in the Loess Hilly Region, Yangou watershed is totally studied in this research. By observation of rainfall and run-off on the slope plot, runoff at the exit of the watershed, and analysis of the data of field simulated rainfalls, this paper analyzed the characteristics of runoff and sediment on different surface conditions on the slope, calculated the sediment reduction benefits of soil and water conservation measures, especially vegetation restoration measures in Yangou watershed, at the same time, analyzed the factors that can influence the variation of sediment production, and in the end probed into the impact of rainfall on sediment transport in the watershed. Main conclusions are made as follows:1. Analyzed the impact of different surface conditions including gradient variation on runoff and sediment production.On the condition of same rainfall intensity, the course and amount of sediment yield are different in evidence on different land use forms. Generally speaking, both of these two characteristics take on the following rule: sloping field plot>cradled plot>vegetation covered plot. The relationship between sediment yield amount of any kind of land use in 30 minutes and raining time accord with the linear equation W=at-b, while it follows the power function W = aIb with rainfall intensity.Research of runoff and sediment yield on different gradient slope show that both intensity and total amount of runoff and sediment yield on steep slopes higher than they on mild ones obviously, which prove that slope field with higher gradient than 25°must be returned to meadow or woods is necessary. 2. Studied on runoff and sediment yield characteristics of different returning forms and different years.All kinds of retuned slope fields have good benefits on sediment reduction. The amounts of sediment yield in every year have the following relationship: sloping field plot>grass plot>bush plot. Grass plot can reduce 50%～60% runoff of that produced on slope field, while bush plot can reduce more than 70%. Sediment reduction in any plot is more than 90%, which is more than runoff reduction. All account for that both grass and bush plots have the function of soil and water conservation in evidence. But the amount of runoff and sediment yield in bush plot is more than that in grass plot every year shows that bush vegetation have better function on soil and water conservation than grass, in any kind of rainfall condition.Runoff coefficients in 6 different treatment plots conform to the following relationship: sloping field plot>cradled grass plot>grass plot>cradled bush plot>bush plot>silver chain plot, all of which decreases with increasing of vegetation coverage, taking on minus correlative relationship with it. Compared with sloping fields plot, grass, shrub and silver chain plots can respectively reduce 51.1%, 71.4% and 90.0% runoff, and 99.3%,99.5% and 99.6% sediment yield. Silver chain has the best sediment and runoff reducing effect. The effect of sediment reduction is more obvious than that of runoff reduction in any kind of land use forms.3. Compared the sediment reducing mechanism between grass and shrub lands.Sediment yield in grass and shrub plot have clear diversity in comparation of before and after they are cradled. Grassplot community evolved after 10 years returned, are mostly annual herbage plants, close to the slope and with less dead woods and leaves. Elm, acacia and lespedeza appear in shrub community, which has more dead woods and leaves and more roots. Sediment yield obviously increases in cradled grass plots, while not so obvious in cradled shrub plots. That can be mainly explained by their different dimensional structure.All show that grassplot community close to the slope ground, which is in its initial stage of vegetation succession, has nice benefit in sediment reduction. However, it is still weak in its ecosystem function. So in conclusion, it is a main type of vegetation that needs essential protection.4. Clarified the total effect of vegetation recovery on sediment reduction in Yangou watershedThrough analysis of the characteristics of runoff and sediment production in different land use plots, and the data observed on long-term fixed plots, we obtain that in Yangou watershed after slope field was returned, the sediment yield modulus is about 737 t/km2·a, more than 80% of its original level. Calculated sediment reduction is very close to that observed at the exit of the watershed, which proves that the whole process of benefit calculation accords to the fact, and all show good benefits of comprehensive management on sediment reduction in evidence.5. Discussed the effect of rainfall diversity in years on sediment conveyed in Yangou watershed every year.By using the data observed in the watershed near Yangou, associated with time and space, we analyzed the diversity of rainfall and sediment yield across the vegetation recovery. Results show that after the returning of slope field to grass and woods, rainfall diversity leads to about 61228t sediment reduction every year in average, taking up about 25% of the total. That is to say, in the two factors affect the sediment reduction in recent years, rainfall diversity takes up about 25%, comprehensive management takes up about 75%.更多还原