沙漠固结层与植被复构条件下风蚀调控机理研究

The desert area and the area vulnerable to desertification is enormous in China. Despite of the significant achievement having been made in desertification control, desertification is still facing the situation of "partly controlled but whole worsen". The desertification process has not been effectively controlled yet, being a serious threat to ecological security and a severe restriction to socio-economic sustainable development. Therefore, exploring new technologies and methods for desertification control is still an urgent task. The project is mainly based on the effectiveness of fly ash and polyacrylamide (PAM) in improving soil physico-chemical characteristics and their effective gelation. Appropriate amounts of fly ash and PAM are mixed in proportion and applied to the desert surface to form a consolidated layer similar to the soil which can not only prevent wind erosion but also preserve sandy soil moisture and promote plants growth. Indoor wind tunnel simulation, pot experiments and field vegetation restoration are conducted on different wind regime conditions to study the threshold wind speed of the sand grains of the consolidated soil layer, their motion characteristics and the sand fixation mechanism as well as to determine the best application amount and mixture proportion of fly ash and PAM, to select the kind of plants suitable for the consolidated soil layer growing environment, to establish vegetation ecological system on the consolidated soil layer of the desert surface and to overall evaluate the effect of desertification control. The project will put forward a new technology and method for desertification control by using fly ash and PAM and provide a scientific basis for the ecological establishment in the desert area.

我国沙漠面积和潜在的沙漠化面积十分巨大，虽然我国沙漠化治理取得了巨大成就，但沙漠化仍然呈现"局部治理，整体恶化"的严峻态势，沙漠化的进程没有得到有效的遏制，严重威胁生态安全并制约社会经济的可持续发展，探索沙漠化防治新技术和新方法仍是十分迫切的任务。本项目充分利用粉煤灰和和高分子化合物聚丙烯酰胺（PAM）可改善土壤物化性质和胶凝作用的特性，用一定的粉煤灰和PAM混合比例施加在沙漠的表层，生成既能防止风力吹蚀又能保持沙土水分和有利于植物生长发育的类似土壤固结层。通过室内风洞模拟、盆栽和野外植被恢复试验，研究土壤固结层在不同风况条件下的沙粒的起动与运动规律以及固沙的机理，寻找粉煤灰和PAM最佳使用量和混合比例，筛选适宜土壤固结层生长环境的植物，构建沙漠表层土壤固结层及植被生态系统，整体评估沙漠化治理的效果。本项目将提出粉煤灰和PAM的沙漠化治理技术和方法，为沙漠区生态建设提供科学依据。

本项目利用粉煤灰与聚丙烯酰胺(PAM)的物化性质，构造与土壤性质相似的沙土固结层研究沙土固结层对沙土风蚀的抑制作用。室内风洞模拟实验表明，沙土固结层可以提高沙土的起动风速；增加粉煤灰和PAM添加量可以降低沙土风蚀量；粉煤灰(10%)和PAM(0.1%)形成的固结层效果最好。野外沙土模拟实验表明，沙土固结层在野外环境下可以有效的抵抗风蚀作用。野外环境中，风速是主要影响沙土固结层风蚀率的主要因素，并且沙土、粉煤灰和PAM搅拌形成的沙土固结层抗风蚀性能更好。在植被复构条件下，沙土固结层具有一定的保水性，不同深度处沙土固结层含水率高于沙土，同时含水率较高的沙土固结层中植被长势更好，风蚀率更稳定。在植被、粉煤灰及PAM的共同作用下，沙土固结层受到风速的影响较小。土壤结皮发育实验采集不同发育阶段的土壤结皮，分析其物理化学性质和生物学性质。粉煤灰和PAM的改良实验，选取粉煤灰施用比例分别为低、中、高3种，PAM施用比例2种，探讨粉煤灰和 PAM 改良沙土对柠条生长的影响。结果表明，随着结皮的发育，结皮厚度、水分含量、微生物量和酶活性逐渐增加，土壤结皮容重下降。土壤的pH和电导率随粉煤灰施加量的增加而增加，适量比例的粉煤灰和PAM促进柠条的生长。