【作者】 韩建刚；

【导师】 李占斌；

【作者基本信息】 西北农林科技大学 ， 土壤学， 2005， 博士

【摘要】 土壤及养分流失机制与预测模型研究是当前土壤侵蚀和非点源污染研究领域的核心内容,也是多学科目前共同关注的焦点。紫色土是主要分布于我国且集中分布于长江中上游地区的一种侵蚀型的高生产力岩性土,该区域是我国重要的粮食基地,但强烈的水土及养分流失不仅导致该地区土地生产力退化,而且给下游水体带来了日趋严重的泥沙和化学污染等环境问题,同时为长江防洪安全及水利设施安全埋下了隐患。本研究结合中欧合作项目,以川中紫色土丘陵区三个具有不同集水面积、物理特征和土地利用方式的典型小流域为研究对象,通过对流域三年间野外降雨、径流、土壤及养分流失等过程连续的全方位的观测,结合流域土地利用的变化,从流域尺度揭示了紫色土丘陵区径流产生机制,阐明了土壤及养分流失对不同雨型、空间尺度、土地利用和流域种植模式变化等的响应特征,分析了其主要影响因子,并提出了相应的预测模型,旨在为紫色土丘陵区小流域水土及养分流失治理和非点源污染的管理、评价与调控提供科学依据。通过研究,取得的主要结论及创新点如下: 1. 紫色土丘陵区小流域降雨产流机制为典型的蓄满产流机制,径流成分包括地表径流、壤中流和地下径流。次降雨径流过程表现为与高强度降雨过程相对应的大流量短历时的单峰形地表径流与滞后于地表径流低流量长历时的壤中流和地下径流过程的复合形式,壤中流和地下径流的各单峰以24 小时为周期出现。2. 通过对0~2.5 cm,0~5 cm,0~10 cm土层土壤养分含量的测定与对比,论证了监测紫色土丘陵区小流域地表径流过程土壤养分流失时的土样采集深度。监测林地利用为主小流域地表径流过程土壤养分流失时的土样采集深度以小于2.5 cm为佳;对于其他土地利用类型的流域而言,除土壤磷素流失监测时要求与林地的相似外,其他种类养分的监测可选用0~5 cm的采样深度。3. 紫色土丘陵区小流域次降雨径流过程含沙量变化表现为锯齿状平缓下降形、对数递减形和峰状起伏形三种形式;间歇型降雨侵蚀过程中径流含沙量最高(9.58±10.90更多还原

【Abstract】 Mechanism and simulation of soil and nutrient losses have been an interdisciplinary focus with evolvement of soil erosion and expansion of non-point source pollution in recent years. Purple soil is a lithologic soil with high productivity but characterized by severe erosion. It is mostly distributed in upper stream region of Yangtze River. The region is an important food bases in China, however, unreasonable reclamation and land use methods have accelerated soil erosion process and losses of soil nutrient. This had not only caused the irreversible loss of soil resources and thus limited the increase of land productivity, but also threaten downstream water environmental quality and water conservancy. Three small agro-watersheds with different catchments area, physical characteristic and land use type were employed to investigate mechanism of soil and nutrient losses in purple soil region in the middle of Sichuan province combining closely with Euro-Chi cooperation projects. Three-year natural rainfall events, corresponding runoff process, soil, and nutrient loss process together with change of planting pattern were sequentially observed. The mechanisms of runoff generation were discovered from watersheds scale. The characteristics of soil and nutrient losses in response to rainfall type, spatial scale variability, land use change and planting pattern were set out. Based on the response and the key influential factors, the forecasting model was put forward. The objectives were to serve for reducing, controlling soil, and nutrient loss and evaluating the status of non-point source pollution in agro-watersheds of this region. The main conclusions and innovations were following. 1. The mechanisms of runoff generation in purple hilly area could be characterized by saturation-excess with the components of surface runoff, subsurface runoff and base flow. The process of runoff behaved a compound type of single-peak-shape hydrograph of surface runoff with higher flow rate and shorter duration, which response the high intense rainfall process, and the following multi-peak-shape hydrograph of subsurface runoff and base flow with lower flow rate and longer duration. The peak period during the processes of subsurface runoff and base flow was 24 hour. 2. The reasonable depth for soil sampling during forecasting the loss of soil nutrient by surface runoff was demonstrated through the measurement and analysis of nutrient content among 0~2.5 cm, 0~5 cm and 0~10 cm soil layers. The depth of 2.5 cm below was proved to be reasonable for taking soil sample to forecast the loss of soil nutrient by surface runoff in woodland-dominated watershed, while 0~5 cm was feasible for other watersheds but to forecast soil phosphorus loss, which should be 2.5 cm below. 3. Sediment concentration behaved three types as indention and descending trend, logarithm-decreasing trend and peak-shape undulation trend in purple soil watersheds. The sediment concentration was highest (9.58±10.90 g.l-1) under the erosion of IM-type rainfalls (the duration is discontinuous, having obvious segmentation phenomenon during rainfall process). While the lowest sediment concentration (1.13±0.58 g.l-1) was found during the erosion of PP-type rainfalls (the high-intensity-rainfall duration appeared in the prophase of rainfall process). The peak flow rate was proved to be the main influential factors of soil loss in woodland-dominated watersheds. While the main factors are rainfall erosivity factor in other watersheds. Based on the flow rate, power function was put forward to forecast sediment concentration in surface runoff during erosion of a rainfall event. 4. Nitrate nitrogen was the main form of N loss, which accounting above 80 percent of N loss by surface runoff. The peak flow rate was proved to be the main influential factors of nitrate nitrogen losses in woodland-dominated watersheds, while the main factors in other watersheds are total runoff amount. Based on the flow rate, Logarithm-decreasing function was put forward to forecast nitrate nitrogen concentration in surface runoff during erosion of a rainfall event. The loss of soil ammonium nitrogen was strongly affected by the change of plantingpattern and vegetation cover degree. The concentration of ammonium nitrogen in surface runoff in interplant pattern was much higher than that of in monoculture pattern. With the increase of vegetation cover degree, the loss of soil ammonium nitrogen increased in woodland-dominated watershed but decreased in farmland-dominated watershed. The average concentration of nitrogen in surface runoff in farmland-dominated watershed and the average concentration of water-solute phosphorus in watersheds with various landscape structures were remarkable high, which exceeded 10 to 24 times than nitrogen critical value of eutrophication and 2 to 19 times than phosphorus critical value of eutrophication, respectively. 5. Relationships of the concentrations of ammonium nitrogen and water-solute phosphorus in surface runoff and flow rate both took on power function decreasing in woodland-dominated watersheds, while they showed logarithm decreasing and power function increasing relationship with sediment concentration in farmland-dominated watersheds, respectively. During the erosion of two rainfalls with a short interval period (less than 5 days), the concentration of sediment and water solute phosphorus in surface runoff during erosion of the latter rainfall were lower than that of the former. In farmland-dominated watershed, the concentration of nitrate nitrogen in surface runoff of the latter rainfall was significantly higher than that of the former. No significant difference was found for the loss of ammonium nitrogen in the two rainfalls.更多还原