黄土丘陵区生物结皮对坡面产汇流过程的影响及模拟

Biological soil crusts (biocrusts), a complex community of cyanobacteria, algae, lichens, mosses, fungi, and other bacteria that live on or just below the soil surface, are ubiquitous living covers in grasslands rehabilitated after the "Grain for Green" eco-project implemented in the Loess Plateau region, which exerted significant impacts on soil and water loss from the revegetated grasslands, with a style of soil kept but water losses. However, the impacts and mechnism of biocrusts on runoff yield and concentration process in slope scales are not clear so far，which is an obstacle to correctly predict slope runoff and evaluation of water environmental restoration after the "Grain for Green" ecosystem restoration project. To bridge the gap mentioned above, and meet the requirement of assessing the water environmental impact after the ecological construction, based on the researches that we have conducted about the distribution and succession processes of biocrusts on the Plateau, we will investigate the patches distrribution pattern and the surface physical charactoristics of varied biocrusts types on slopes.Through rainfall simulation, water releasing test and slope runoff monitoring under natural rainfall using slope runoff automatic monitor system,we will explore slope runoff yield and concentration process under the impact of biocrusts, determine the effects of biocrusts patches distribution and surface charactoristics on slope runoff yield and concentration process, identify the critical impacting factors and clarify their working mechanism. Further, the runoff yield and concentration process on biocrusts slope will be modelled. The results will provide significant reference for building runoff and soil loss model considering the impact of biocrusts, and could be a scientific base for water environment evaluation after ecological construction.

退耕封禁实施后，生物结皮成为黄土丘陵区坡面水土流失不可忽略的影响因素，形成"保土不保水"的坡面水土流失新格局。目前，生物结皮对坡面产汇流过程的影响研究较少，影响因素及作用机理不清楚，妨碍了坡面径流预报模型的精准度和以退耕封禁为主的生态恢复水环境效应的科学评估。为此，基于前期黄土丘陵区生物结皮形成分布及水分入渗特征的研究基础，本研究从生物结皮坡面斑块分布格局和生物结皮表面特征入手，采用模拟降雨、放水试验及自然降雨定位观测等方法，利用径流自动观测系统研究生物结皮影响下的坡面产汇流过程，明确生物结皮斑块格局和表面特征对坡面产汇流过程的影响方式及程度，解析主要影响因素及作用机理，进而模拟生物结皮条件下坡面产汇流过程。研究在明确生物结皮对半干旱地区地表水文过程影响的同时，可以揭示生物结皮对径流侵蚀力的影响机理，为考虑生物结皮的水土流失模型参数的选取提供科学依据。

对坡面产汇流过程影响是生物结皮水文生态功能研究的薄弱环节，妨碍了黄土高原生态恢复中水环境效应准确评估。针对这一研究中的薄弱环节，项目从坡面尺度生物结皮斑块格局和生物结皮表面特征入手，研究不同斑块格局及表面特征的生物结皮对坡面降雨入渗、产流、汇流过程的影响，探索生物结皮与典型植物斑块径流的“源-汇”效应，揭示生物结皮斑块分布格局、表面特征对坡面产汇流过程影响的方式及程度，取得以下新进展。1）黄土高原退耕地均为生物结皮-植被共同盖度，二者的镶嵌式分布，生物结皮为被镶嵌体，植物为镶嵌体。2）生物结皮较裸土土壤表面糙度降低26.9%-56.8%，十年以后的生物结皮糙度不再变化。3）生物结皮诱发土壤表面斥水性，增加了土壤的持水性和水分有效性。4）生物结皮与维管束植物对土壤水分渗透性影响差异显著，植物根基稳定入渗率较生物结皮增加60%。5）生物结皮主要通过影响产流时间、径流流速及径流在坡面的分布而影响坡面产流过程，影响程度与生物结皮的发育阶段、生物组成及其与维管束植被的分布格局有关。浅色藻结皮、深色藻结皮和混合结皮初始产流时间较裸地分别减少89.0%、96.2%和96.0%；而藓结皮则较裸地显著增加了初始产流时间。浅色藻结皮和混合结皮退水持续时间是裸地小区的2.28和2.13倍；深色藻结皮和藓结皮的径流流速较裸地分别降低29.1%和67.3%；浅色藻结皮小区的径流系数是深色藻结皮小区的2.44 倍。6）生物结皮-维管束植被间构成径流的“源-汇”关系，生物结皮是降雨-产流过程中是“源”景观。维管束植物是“汇”景观。雨强、坡长显著影响生物结皮-植被间径流的源-汇关系。植被格局对径流量的影响呈现出聚集格局>随机格局>条带格局的趋势。7）建立了生物结皮-维管束植被分布格局与坡面产汇流过程的关键参数间的关系。. 项目从产汇流的发生-发展-坡面分布-结果（产流量）4个关键环节明确了生物结皮对坡面产汇流过程的影响，建立了生物结皮-植被斑块面积比与坡面产汇流过程的关键参数间的量化关系，为建立考虑生物结皮的水土流失预报模型奠定了基础。