Water in the Mogao Grottoes,China:where it comes from and how it is driven

The Dunhuang Mogao Grottoes in China was designated as a world heritage site by UNESCO in 1987 and is famous for its cultural relics. Water is the most active factor that harms the relics in the caves as it damages the grotto murals and painted sculptures. Thus, determining the water sources and driving forces of water movement is a key issue for protecting these cultural relics. These issues have troubled relics protectors for a long time. In this study, the authors chose a representative cave in the Mogao Grottoes and, by completely sealing the cave to make a closed system, measured the water vapor from the surrounding rock. This was accomplished by installing a condensation-dehumidification temperature-humidity control system for the collection of water vapor. The results show that there is continuous evaporation from the deep surrounding rock into the cave. The daily evaporation capacity is determined to be 1.02 g/（d·m2）. The water sources and driving forces of water movement were further analyzed according to the character of the water evaporation and by monitoring the temperature and humidity of the surrounding rock. It was found that the water vapor in the cave derives from phreatic water. Moreover, the yearly fluctuation of temperature in the surrounding rock and geothermal forces are the basic powers responsible for driving phreatic evaporation. Under the action of the yearly temperature fluctuations, decomposition and combination of bound water acts as a ＂pump＂ that drives phreatic water migration and evaporation. When the temperature rises, bound water decomposes and evaporates; and when it falls, the rock absorbs moisture. This causes the phreatic water to move from deep regions to shallow ones. Determining the source and dynamic foundation of the water provides a firm scientific basis for protecting the valuable cultural relics in the caves.

GSPAC water movement in extremely dry area

Under an extremely arid condition,a PVC greenhouse was built on the top of Mogao Grottoes in gobi area.The results of 235-day constant extraction of condensed water on the greenhouse film and soil water content showed that 2.1 g/（m2·d） groundwater moved up and exported into the soil,and a phreatic water evaporation existed in the extreme dry area where the groundwater is buried deeper than 200 m.After a prolonged export,the soil water content in the greenhouse was not lower but obviously higher than the original control ones.According to the monitored parameters including relative humidity and absolute humidity of soil,and temperature outside and inside the greenhouse,it was found that there is the available condition and mechanism for the upward movement of groundwater,and also it can be sure that the exported water was not from the soil and atmosphere outside the greenhouse.Phreatic water,an important source for soil water,interacts with atmosphere moisture via soil respiration.Soil salinity also has important effects on soil water movement and spatial-temporal heterogeneity.The extremely dry climate,terrestrial heat and change of upper soil temperature are the fundamental driving forces of water transportation and phreatic water evaporation in the Groundwater-Soil-Plant-Atmosphere Continuum（GSPAC） system.

Overall efficiency of a V-shaped nylon net fence in preventing sand damage to the Mogao Grottoes

A V-shaped nylon net fence installed in 1990 on top of the Mogao Grottoes is shown to be effectively resisting aeolian sand damage to the grottoes. The structure guides and causes deposition of sand from westerly wind （the primary hard wind）, but to some extent hinders the inverse function of easterly wind carrying sand away from the grottoes toward Mount Mingsha. The gobi side by the fence experiences higher wind speed, so that on which are easily formed undercutting pits, and the deposited sands on it generally form double-peak structures due to abundant sand sources. If the earth surface characteristics in gobi areas by both sides of the fence are quite varied, the erosion and deposition features of the accumulating sand section are similar in different seasons; however, if the earth surface characteristics are similar, the features become irregular in different seasons. Sand depositions with long slope feet are formed along the south and north sides of V-shaped nylon net fence. Disrupted by strong westerly wind and northwesterly wind, sand accumulations by north of the fence are in form of single peaks. Although the operation duration of the V-shaped nylon net fence has exceeded its design life （10 years）, our observations indicate that it is still effective in reducing wind-driven sand damages to the Mogao Grottoes, so it should not be withdrawn.

Seasonal variation of airborne fungi of the Tiantishan Grottoes andWestern Xia Museum,Wuwei,China

In this study,a systematic survey of cultural airborne fungi was carried out in the occurrence environments of wall paintings that are preserved in the Tiantishan Grottoes and the Western Xia Museum,China.A bio-aerosol sampler was used for sampling in four seasons in 2016.Culture-dependent and-independent methods were taken to acquire airborne fungal concentration and purified strains;by the extraction of genomic DNA,amplification of fungal ITS rRNA gene region,sequencing,and phylogenetic analysis,thereafter the fungal community composition and distribution characteristics of different study sites were clarified.We disclosure the main environmental factors which may be responsible for dynamic changes of airborne fungi at the sampling sites.The concentration of cultural airborne fungi was in a range from 13 to 1,576 CFU/m^(3),no significant difference between the two sites at the Tiantishan Grottoes,with obvious characteristics of seasonal variation,in winter and spring were higher than in summer and autumn.Also,there was a significant difference in fungal concentration between the inside and outside of the Western Xia Museum,the outside of the museum was far more than the inside of the museum in the four seasons,particularly in the winter.Eight fungal genera were detected,including Cladosporium,Penicillium,Alternaria,and Filobasidium as the dominant groups.The airborne fungal community structures of the Tiantishan Grottoes show a distinct characteristic of seasonal variation and spatial distribution.Relative humidity,temperature and seasonal rainfall influence airborne fungal distribution.Some of the isolated strains have the potential to cause biodeterioration of ancient wall paintings.This study provides supporting information for the pre-warning conservation of cultural relics that are preserved at local sites and inside museums.

麦积山石窟赋存环境中空气细菌的时空分布特征

【目的】空气微生物沉降及污染与文化遗产的微生物退化密切相关,本文对世界文化遗产地麦积山石窟赋存环境空气中细菌浓度和群落结构的季节性变化特征进行了系统研究,为石窟环境监测预警和文物预防性保护提供依据。【方法】利用生物气溶胶采样器,在2016年春、夏、秋和冬季分别采集空气样品;基于传统培养方法获得空气中细菌浓度及纯培养菌株;通过提取基因组DNA、扩增细菌16S rRNA、测序和系统发生树等分子技术研究细菌群落时空动态变化规律;结合环境监测数据,分析影响遗产地空气细菌变化的主要因素。【结果】监测期内,空气细菌浓度在(281.20–1409.20)CFU/m3之间,最高浓度出现在MJ4处的夏季,最低浓度出现在MJO处的春季;具有明显季节性变化特征,在空间层位分布上有所差异,但不显著(P>0.05)。培养的细菌菌株经鉴定属于4个门11个属;芽孢杆菌属(Bacillus)、Paenarthrobacter、节杆菌属(Arthrobacter)、薄层菌属(Hymenobacter)和考克氏菌属(Kocuria)等为优势属。【结论】麦积山石窟空气细菌群落结构具有明显的季节性和空间分布动态变化特征;在石窟不同层位,空气中细菌群落分布与相对湿度、温度与降雨量相关;部分细菌种属如芽孢杆菌属、微球菌属(Micrococcus),为壁画及彩塑生物腐蚀的潜在病害菌;麦积山石窟及周边环境空气细菌的监测可为石窟保护和旅游开放管理提供重要参考。

莫高窟PM_(10)浓度与气象要素的关系

采用2018年敦煌莫高窟第16窟窟内与窟区PM_(10)浓度及气象数据,分析PM_(10)时空分布特征及其影响因素。结果表明:(1)两处监测点PM_(10)浓度主要分布在50μg·m^(-3)以下,受重污染天气影响较小;春、冬、秋、夏季依次降低,窟区PM_(10)浓度在春、冬季高于窟内,夏、秋季反之。(2)PM_(10)浓度3月最高,9月最低,5—9月窟内月均值高于窟区。PM_(10)污染日数窟内5月最多,而窟区3、5月较多。(3)PM_(10)浓度日变化曲线在春季和秋季呈“双峰”型,夏季和冬季呈“单峰”型。(4)在半封闭环境的洞窟内,沙尘暴发生前后,PM_(10)浓度达到极值及恢复至原来水平的时间均滞后于窟区。(5)在不同季节PM_(10)浓度与气温、风速和降水呈负相关。除秋季外,PM_(10)浓度与相对湿度、气压呈正相关。(6)窟区全年主风向为ESE,在冬春两季,此风向PM_(10)浓度最高,PM_(10)主要来自三危山前的戈壁滩、干涸的大泉河河道以及窟前裸露的地表积尘。