毛乌素沙地南缘固沙灌丛下地表凝结水特征

Effects of surface dew under different types of sand-fixing shrubs in the southern margin of Mu Us Sandy Land,Northern China

尽管凝结水在干旱生态系统中所发挥的重要作用已被广泛关注,但对其在固沙灌丛下时空变化特征的研究仍然比较薄弱。为探明固沙灌丛对地表凝结水的影响,在毛乌素沙地南缘沙区选择3种典型固沙灌丛(沙柳Salix psammophila、柠条Caragana korshinskii和油蒿Artemisia ordosica),以无固沙灌丛影响的裸沙作为对照,用微型蒸渗仪测定了固沙灌丛下不同位置(根部、1/2冠幅和外缘)和不同方向(东、南、西、北)上地表凝结水的形成和蒸发特征。结果表明:(1)与对照相比,固沙灌丛的存在显著降低了地表凝结水量,沙柳、油蒿和柠条灌丛下凝结水量分别降低了29%、32%和33%;(2)不同类型固沙灌丛下地表凝结水量由里向外均呈显著增加的趋势,但不同方向上地表凝结水量差异不显著;(3)固沙灌丛的存在减缓了凝结水的形成和蒸发过程,即凝结水自19:00开始形成,到次日08:00基本结束,至13:00—15:00蒸发殆尽,其形成过程整体上表现出增加—平缓—增加的趋势,柠条和油蒿灌丛下地表凝结水在03:00—05:00甚至有少量蒸发,而蒸发过程呈稳定下降趋势;(4)凝结水的形成过程与空气相对湿度显著正相关,与空气温度和地表温度显著负相关。固沙灌丛通过拦截太阳辐射来缓冲地表温度变化以减缓水分凝结和蒸发过程。

Although the important role of dew in arid system has been widely recognized,its characteristics of temporal and spatial variation under sand-fixing shrubs has been paid less attention.To better understand the influence of surface dew under sand-fixing shrubs,three typical artificial sand-fixing shrubs(Salix psammophila,Caragana korshinskii and Artemisia ordosica)on the southern edge of the Mu Us Sandy Land,Northern China were selected and the bare sand without the effect of sand-fixing shrubs was used as the control in this study.The deposition and evaporation characteristics of surface dew in different positions(root,1/2 crown width and periphery crown width)and directions(east,south,west and north)under sand-fixing shrubs were measured by micro-lysimeter.The results showed:(1)compared with the control,the presence of sand-fixing shrubs significantly reduced the amount of surface dew,and the amount of dew under Salix psammophila,Artemisia ordosica and Caragana korshinskii decreased by 29%,32%and 33%respectively.(2)The amount of surface dew under different types of sand-fixing shrubs showed a significant increasing trend from the inside to the outside,but the difference in the amount of surface dew in different directions was not significant.(3)The existence of sand-fixing shrubs slowed down the deposition and evaporation of surface dew,that was,the formation of dew started at 19:00 at night,ended at 08:00 the next day,and evaporated from 13:00-15:00.The deposition process of dew showed an overall trend of increasing,fluctuating and increasing.The surface dew under Caragana korshinskii and Artemisia ordosica even evaporated a little from 03:00 to 05:00,and the evaporation process showed a steady downward trend.(4)The formation process of dew had a significant positive correlation with relative humidity,and a significant negative correlation with atmospheric temperature and surface temperature.Sand-fixing shrubs buffered surface temperature changes by intercepting solar radiation to slow down the deposition and evaporation processes of dew.