The Research About Water Environmental Isotope In Yuanmou Dry-hot Valleys

In dry-hot valleys, the typical vulnerable ecological areas, afforestation is the traditional ecology recovery manner. However, whether and how it works are disputed greatly. So it's necessary to have a research on the ecology effect of afforestation. This research also provide a isotope view about the dry of this area. Moreover, Yuanmou as a well-developed agriculture country it's crop irrigation closely relies on the under grounder water. Whether the under ground water can recycle healthy or not is a serious problem. We analyzed the isotope composition of the Yuanmou precipitation and under ground water samples. With the IsoSource model, the naturally occurring concentration gradients in oxygen and hydrogen stable isotopes in soil water of different depths and plant stem or tracheophyte water were used to determine the sources of water used by typical artificial vegetation, shrubs, and native herbs. The soil-water environment of two representative vegetation of hot-dry valleys also had been surveyed by determining the soil water content of12layers in5m deep soil profiles. The main results of this study are as follows:(1) Compared with GMWL and KMMWL, there is a heavy isotope fractionation in Yuanmou precipitation, and it results from the factors of dry and hot in this area. δD and δ18O values show some kind of precipitation effect and temperature effect, such as poor in rain season and rich in dry season.(2) With values of deuterium excess calculated by δD and δ18O values, we can estimate that the main water source of precipitation is the precipitation recycle result from the evaporation from local water.(3) The water source of Yuanmou under ground water is precipitation. The δD and δ18O values are stable all the year except in rainy season because of the precipitation supply for it.(4) The soil water content in dry season is not optimism which in natural vegetation of grass is barely enough the wilting moisture9%while in reforestation is far from it, even doesn' t reach a half of9%.(5) We calculated that the mainly potential water source of trees are around or under the layer of3m-depth soil water except Salix myrtillacea is from the water within1m. The herb's water source is the superficial soil water within lm from the surface.(6) The negative impact of artificial forestation may degenerate the situation of drought in this region. So whether the afforestation befits the dry-hot valleys needs more consider and discuss.