黄河三角洲退化湿地根土混合体对水文连通的响应

Wetland degradation affects the balance and stability of the systems among vegetation, water and soil directly. In particular, hydrological connectivity within or between wetland scales is typically influenced which leads to the threat of water resources cycle due to the interrupt of hydrological connectivity. Taking the Tamarix chinensis Lour. in degraded wetland areas of Yellow River Delta as the research object, field dye tracing experiments, laboratory CT scanning analysis, data measurement and models simulation are applied to imply the time-space distribution properties of the root-soil synthesis in the research area; to show the water flow of vertical hydrological connectivity and water transformation of horizontal hydrological connectivity in the rhizosphere; and to quantify the influences of root-soil synthesis on water flow of horizontal and vertical hydrological connectivity. The results of these studies could provide theoretical and technological supports for vegetation restoration and reconstruction of degraded wetland areas.

湿地退化直接影响“植被—水体—土壤”协同作用的平衡与稳定，影响湿地内部及斑块间水文连通性，造成水文连通中断或受阻，进而对水文循环过程产生威胁。以黄河三角洲湿地退化区柽柳植被为研究对象，通过野外染色示踪、室内CT扫描、数据处理、模型构建等方法，研究退化湿地根际区根土混合体时空分布特征；揭示根际区垂向水文连通水流运动及横向水文连通水流迁移转化规律；分析根际区根土混合体对水文连通垂向和横向空间维度上水流运动影响定量关系。本研究成果将为湿地退化区植被恢复与重建提供理论和技术指导。

微观尺度连通孔隙网（土壤大孔隙、根孔隙通道、动物洞穴、土壤裂隙、根系-土壤接触面孔隙等）会直接影响水文效应，小尺度水文效应往往制约大尺度水文连通性。本项目主要针对小尺度“植被-土壤-水文”协同作用机制，在黄河三角洲国家级自然保护区不同植被群落开展研究，取得以下主要成果：（1）基于野外优先流指数和室内溶液出流构建了水文连通指数，最大贡献值染色面积比和分形维数可以准确评估水文连通指数，分形维数随着染色面积比的增加先增加后减小。（2）对不同植被群落水文连通性进行了评估，不同植被群落根际区水文连通性表现为刺槐群落>大型芦苇群落>柽柳群落>小型芦苇群落>碱蓬群落。（3）不同植被群落根际区根系总长度、总宽度、总表面积、总投影面积随着土壤深度和根系径级的增加均呈现非线性减小的趋势，根系径级D<1 mm为最大值，根系径级3<D<5 mm为最小值，根系总体积随着土壤深度的增加非线性减小，随着根系径级的增加逐渐增加。（4）土壤有机碳、有机质、全氮、全磷和有效磷显著正相关，土壤pH、电导率与土壤有机碳、有机质、全氮、全磷和有效磷负相关，土壤pH与电导率显著正相关，相关度在优先流区高于基质流区。土壤有机碳、有机质、全氮、有效磷、含水量与水文连通指数正相关，土壤全磷与水文连通指数负相关。（5）基于根系构型特征和土壤理化特性，研究了根土特性对小尺度水文连通的响应，根土混合体系中，相比根系指数，土壤指数对水文连通指数影响更大，同时与土壤化学性质相比，土壤物理性质，特别是土壤容重、土壤大孔隙度等对水文连通指数影响更大。本研究阐明了黄河三角洲湿地根际区水文过程，对于预估黄河三角洲生态系统易受侵害的状态、理解小尺度水文连通等都具有现实指导意义。