Protection Effect Of Bryophytes And Lichen On The Ming Great Wall In Liangzhou

The Ming Great Wall in Liangzhou district Gansu province belongs to ramming Great Wall. It’s Appearance shape has changed greatly in the long-term weathering, such as stripping, gullying, hollowing, fissuring, sapping and sloughing disease are in the different developmental condition, and it was thanks to the industrialization of the impact on the environment in recent years that the preservation of the Great Wall has been challenged. Soil sites staff have researched the disease types and forming mechanism, strengthening methods, organic and inorganic and other reinforcing materials, all kinds of test method, and so on. Of course, they got some achievements in their work. But, the research about influence to soil sites from some other biology is very little. Under the background of "rescue reinforcement engineering of Great Wall and beacons in Liangzhou district. Gansu province", The research studied the save situation and the type of disease of the Great Wall, and the influence from bryophytes and lichens to the Great Wall.After the site investigation to the Great Wall of Ming, we found that the Great Walls were constituted by two sections, north-south direction and east-west direction. The north-south direction’s present situation was bad. The Great Wall was discontinuous and incomplete, some existing wall was buried by blown sand. All kinds of diseases, such as sapping, sloughing, stripping and gullying, had developped in both sides of the wall. The east-west direction’s present situation was better than the north-south direction. The Great Wall was continuous and not was buried by blown sand. Diseases, especially sapping, sloughing, stripping and gullying, had developed in the south side of the wall. The north side was covered by bryophytes and lichen, it had formed bryophytes crust and lichen crust. The major diseases were sapping and stripping in the bottom of the wall. Through comparing the diseases’development state of the walls that were covered by bryophytes and lichen or not we knew that the bryophytes and lichen were beneficial to protect the Great Wall.It revealed the mechanism of the bryophytes and lichen’s effect to the Great Wall when we studied bryophytes crust and lichen crust. Selected bryophytes crust and lichen crust specimen from the north side of the east-west direction, and selected no-crust specimen from the south side, and then we did the experiment as follows:particle analysis, chemical analysis, scanning electron microscopy and X-ray diffraction. The results showed the conclusions as follows:(1) Contrasted the surface electron microscopy image of the bryophytes crust, lichen crust and no-crust specimen we knew, bryophytes and lichen formed a structural plane together with soil of the Great Wall. Soil particles of the structural plane were less, pores between soil particles were filled by bryophytes or lichen or their secretions. So the structural plane effectively prevent the destruction from wind and rain because it was relatively dense.(2) Chemical analysis test showed that bryophytes and lichen selectively absorbed soluble salt that hosted in soil. Bryophytes and lichen The process decreased ions in soil, especially sodium ion,it leaded to decreasing the content of the sodium sulfate. So it stopped or retarded the enrichment of the soluble salt and decreased the destruction caused by repeated crystallization.(3) Particle analysis test showed that bryophytes and lichen had transformation effect to the Great Wall’s soil. It made soil particles become small and formed a structure layer. The cohesiveness of the soil and the anti-weathering ability of the soil site had been strengthened.(4) Both of the structural plane and the structure layer formed the system of resistance to weathering. The system effectively decreased the occurrence and development of the various diseases.