Study On Hydrologic Effects Of Slope Protection By Herb-shrub Vegetation In Frigid And Arid-semiarid Loess Area

The stems and leaves of plants play an important role in intercepting rainfall, decreasing erosion andrefraining water flow for protecting slope. The roots of plants can absorb water on the slope, lead and expendwater, decrease water pressure of soil pore and strengthen soil anti-erosion ability.In this study, the hydrologic effects of the stems, leaves and roots of4herbs and4shrubs planted in thesilt slope of the experiment field are studied by a large amount of indoor and outdoor observations andexperiments. The conclusions are as follows:4herbs and4shrubs with strong adaptability, rapid growth speed, dense root system, abundant stemsand leaves and strong coverage areas for protecting slope were selected to be planted in the experiment field.The results showed that, with the growing time passing, the plants height, tiller, leaf branch, plot coverageareas increase. Elytrigia repens increases the fastest among the four herbs; next, Elymus dahuricus; then,Agropyron trachycaulum; Leymus secalinus increases the slowest. Atriplex canescens and Zygophyllumxanthoxylon increase faster than Caragana korshinskii and Nitraria tangutorum. After growing for5months, the coverage rate of4herbs is28～49%and that of4shrubs,32～45%.Adopting soaping and artificial rainfall method, the interception experiment of4herbs and4shrubswere conducted. The results showed: the interception volume of the stems and leaves of4herbs is0.34～0.99g and the absorbing water rate is10.0～33.6%; while the interception volume of4shrubs is0.35～0.53gand the absorbing water rate,12.6～28.7%. For the4herbs, the order of interception rainfall water ability isElytrigia repens＞Elymus dahuricus＞Agropyron trachycaulum＞Leymus secalinus; while for4shrubs,Atriplex canescens＞Zygophyllum xanthoxylon＞Caragana korshinskii＞Nitraria tangutorum.The results of the transpiration experiment showed that the transpiration rate of the leaves of4herbs is43.9～64.0mg/m2·min; while that of4shrubs is27.4～44.5mg/m2·min. After evaporating for30minutes,moisture evaporation rate of soil-root composite for Elytrigia repens, Elymus dahuricus, Agropyrontrachycaulum, Leymus secalinus increases respectively by1.08%,0.67%,0.52%and0.37%larger than that ofsoil, while for Atriplex canescens, Zygophyllum xanthoxylon, Caragana korshinskii and Nitraria tangutorum,the evaporation rates increases0.35%,0.26%,0.22%and0.11%respectively. The order of the evaporationeffects of4herbs is Elytrigia repens＞Elymus dahuricus＞Agropyron trachycaulum＞Leymus secalinus;while for4shrubs, Atriplex canescens＞Zygophyllum xanthoxylon＞Caragana korshinskii＞Nitraria tangutorum.The evaporation rate of soil-root composite of4herbs and4shrubs in the experiment field graduallyincreases with evaporation time passing. The moisture content of herbs and shrubs soil-root composite leaksfaster than that of soil, with the increasing of evaporation time. The order of the leaking of moisture contentof soil-herbs’ root composite is Elytrigia repens＞Elymus dahuricus＞Agropyron trachycaulum＞Leymussecalinus; while for4shrubs is Atriplex canescens＞Zygophyllum xanthoxylon＞Caragana korshinskii＞Nitraria tangutorum. This indicates that root system of herbs and shrubs in the experiment field have greatability in absorbing and dissipating water on slopes. The more developed the root system is, the morepowerful the dissipating ability is.The permeable experiments showed that the penetrating time of the soil-root composite for4herbs and4shrubs is shorter than that of soil and the permeability coefficient is higher than that of soil, too. Thepermeability coefficient of soil-root composite of Elytrigia repens, Elymus dahuricus, Agropyrontrachycaulum and Leymus secalinus is0.39mm/s,0.27mm/s,0.23mm/s and0.02mm/s higher than that of soilrespectively. The permeability coefficient of soil-root composite for Atriplex canescens, Zygophyllumxanthoxylon, Caragana korshinskii and Nitraria tangutorum is0.32mm/s,0.16mm/s,0.11mm/s and0.04mm/s higher than that of soil respectively. This indicated, the more developed the root is, the stronger itspower in leading water is.Considering comprehensive factors about the above ground growth characteristics of herbs and shrubs,stem and leaf interception volume, evaporation rate and leading water ability, the appraisal system forhydrologic effects of slope protection by herb-shrub vegetation in frigid and arid-semiarid loess area isestablished and further studies on mechanism of slope protection by vegetation were conducted, whichprovides the scientific rules for evaluating the effects of slope protection by vegetation and screeningdominant socials with better hydrologic effects, so it has significance in both theory and practice. Based onthe appraisal system of hydrologic effects, among4herbs, Elytrigia repens is the best; among4shrubs,Atriplex canescens is the best. Therefore, it is ideal to select above ground herbs and shrubs with abundantstems and leaves, higher interception volume, evaporation rate and good leading water ability for protectingslopes in frigid and arid-semiarid loess area, such as Elytrigia repens and Atriplex canescens.