风化花岗岩侵蚀坡地表层流水流动态及携氮磷流失特征研究

There is great difference in surface soil particle composition and the soil profile level is not well developed and simple configuration due to strong water erosion. So that has a great effect on rainfall runoff infiltration, the surface flow formation and the topsoil nutrition loss. Based on this phenomenon, we have taken water flow dynamic of water erosion slope developing from weathered granite and its characteristics of carrying nitrogen and phosphorus as objects of study. Therefore, erosion slopes including 3 kinds of surface soil compositions red soil, sandy soil and debris were chosen to build runoff plots. Also, we have adopted method of artificial rainfall simulation with dyeing tracer and regularly collected the flow from surface soil. Then we calculated dynamic parameters of simulation in different rainfall intensity and diachronic combination、loss intensity and leach coefficient and analyzed morphological characteristics of nitrogen and phosphorus loss. So we studied surface water flow characteristics and its influence mechanism of morphology and strength of nitrogen and phosphorus loss to reveal the relationships among them. Meantime, we analyzed characteristics and strength of the nitrogen and phosphorus loss in surface runoff and calculated proportion of nitrogen and phosphorus loss in surface runoff of total loss to discuss its influence to soil quality degradation. Besides, the achievements could provide reference data for artificial control to nitrogen and phosphorus loss and pollution.

强烈水力侵蚀致使暴露于地表的土层质地粗细构成差异很大、土体剖面层次不发育而构型简单，对降水产流入渗、表层流形成、表土层养分流失的影响很大。基于此思考，本项目以风化花岗岩侵蚀坡地表层流的水流动态及携氮磷流失特征为研究对象，选择3种地表组成物质（红土层、砂土层和碎屑层）的侵蚀坡地修建试验径流小区，采用野外原位人工模拟降雨配以染色示踪的试验方法，定时分层采集表层流出流水样，通过不同雨强、不同历时多重组合降雨试验过程中表层流各动态参数的计算、氮磷流失形态特征的分析、流失强度和淋失系数的计算，研究不同坡面土壤质地和孔隙结构特性情况下的表层流水流特征，以及对氮磷流失形态和强度的影响机理，进而揭示它们的相互作用关系；分析表层流携氮磷流失形态和强度随降雨特征的变化规律；计算表层流携氮磷流失占总流失量的比重，探讨其对表层土质量退化的影响；研究成果将能为坡地氮磷流失、地表水氮磷污染的人为控制提供参考。

在项目执行期间，经项目组全体人员的共同努力，完成了原定研究内容并达到了预期目标。本项目主要关注了风化花岗岩残积母质上发育的坡地土壤易侵蚀、易漏肥漏水的特点，以不同侵蚀程度风化花岗岩坡地为研究对象，开展了原状土柱的CT扫描和土壤样品的X荧光射线化学全量测试，研究了不同侵蚀强度坡面土壤层质地和孔隙结构特性差异。由于实地坡面监测在雨强控制上的缺陷，项目组采用了搬迁典型坡地土壤原状土的方式，在室内开展了变雨强和变坡度的组合试验，共进行了55场人工模拟降雨试验，完成了3种侵蚀坡面不同地表物质（表土层、红土层、和砂土层）构成的模拟径流小区产流、产沙及氮、磷、碳流失的监测和测试。计算了多重组合条件下坡面径流和壤中流的产流率，不同侵蚀强度3种坡面径流和壤中流携氮、磷、碳流失量占总流失量比重的差异；分析了坡面径流和壤中流携氮、磷、碳流失形态和强度的变化规律。结论：在强烈侵蚀的花岗岩风化残积坡地土壤发育过程较弱，侵蚀强度越大土壤发育越差。坡地土壤结构均以大孔隙为主，大孔隙度大于均值的层位分布在0-30cm之间。土壤侵蚀强度越大，大孔隙占比越大，孔隙结构性越差，漏肥漏水越严重。在砂土层露出的坡地，壤中流所占总径流量的比重均大于坡面径流。侵蚀产沙量与坡度之间的关系可以用幂函数表示，与雨强之间为指数函数关系。壤中流是坡面总氮流失的主要途径，流失比例可达91.26%—99.61％。坡地磷素流失主要以侵蚀相为主，并以坡面径流携带流失为主，壤中流磷素流失量较小。在大雨强情况下，在坡面径流中总碳流失量都随着雨强的增大而增大，而壤中流中总碳流失量在减小。成果：发表标注有项目资助的论文15篇，获得授权发明专利4项，实用新型专利3项，培养毕业研究生3名，在读研究生3名。参加国内外会议6次，参会人员在会议上发表讲演15场次。研究成果可为我国南方风化花岗岩母质土壤径流携带养分流失量的估算提供计算方法，对坡地氮、磷、碳流失控制提供科学依据。