Stable Isotope Characters Of Soil Water Movement In Shijiazhuang City

The problem of the north China plain water resources is becoming increasingly serious, especially some developed urban have a large population, decrease precipitation, shortage water, fragile ecosystem, among which Shijiazhuang is representative. Due to the underground water level decline year by year, the soil water plays a very important role in the water resources reasonable use and the water cycle of ecological system.In this study we analyzed the stable hydrogen and oxygen isotope values of precipitation, soil water, irrigation water that collected in Shijiazhuang from April 2013 to May 2014 to investigate the changing rule of the stable isotopes in different soil profiles and the process of soil water movement according to using the isotope tracer technique and combining with the analysis of soil mechanical composition.The results showed that :In 2013,the whole year’s precipitation is 596.55 mm.The local meteoric water line(LMWL) equation is y=6.547x-1.667(R2=0.941,p<0.001), the mean excess deuterium is 6.1885‰, which reflected that precipitation in Shijiazhuang mainly comes from the marine water vapor,and also has certain local evaporation. Precipitation is the main soil water sources and it is much enough to supply the soil in rainy season, the irrigation water has a supplementary role of alleviating drought at the early stage of the rainy season.The measurement results of soil mechanical composition of Shijiazhuang show that,in this area,0-100 cm soil texture are loam layer, there into the 0-70 cm soil is the coarse sand loam and the 80-100 cm soil is the fine powder soil. The 70-80 cm soil is an obvious soil transition layer which is prone to soil water accumulation.From the different time scales of soil sampling, we can make an analysis of soil moisture migration process. The results prove that:(1) In April, After a large precipitation, the soil infiltration rate is not uniform. The soil infiltration rate between 40-70 cm is 100mm/d, and between 70-80 cm is 33mm/d. Under the influence of soil texture, precipitation and precipitation time, The soil water vertical infiltration rate is from fast to slow in this process. The soil at 70 cm is always a blocked layer.(2)From May, the soil water semimonthly observation show that :The stable oxygen isotopes at 10cm-100 cm depth decreased with theincrease in depth;maximum depth of evaporation in the rainy season reached 40 cm, in may and September, due to the less rainfall, the evaporation of soil water is most obvious, which reaches 40 cm depth of evaporation. The peak of stable oxygen isotopes of soil water pushed down along the profile, and the soil between 0-70 cm is easier to be affected by soil water infiltration than that between 80-100 cm, and this process which was infected by the interaction of the precipitation infiltration and the mixing water.