Study On Soil Moisture Movements And Features Of Hydrogen And Oxygen Isotopes In Groundwater In Luanjing Irrigation Area, Inner Mongolia

This thesis is based on the research of National natural science funds-the recharge of deep-buried phreatic from irrigation by the Yellow River and environment benefit of irrigation by the Yellow River. Inner Mongolia is one of the most dry areas in China, in arid region there is no irrigation there is no agriculture. Luanjing Irrigation Area is adjacent to the Teng Ge-li Desert where evaporation is large and precipitation is small ,so the area is seriously short of water and if we want to develop agriculture we must depend on irrigation.This article is based on reading and summing-up plenty of inner and outer literature and material, this paper mainly researched on soil moisture movements and the mechanism of groundwater recharge through indoor and outdoor experiment and theoretical analysis in Luanjing Irrigation Area.Firstly, water level observation automatic instruments were installed in the main observation wells to detect the real-time groundwater level and obtain the most intuitionistic data of the groundwater level. From the data, it can be seen that groundwater level is rising gradually in the area.Secondly, groundwater in the area were taken as samples and were analyzed of hydrogen and oxygen isotopes, this work is done to analyze the mechanism of groundwater recharge from the angle of environmental isotope. The results show as follows: 1)In the study sites, the characters of hydrogen and oxygen isotopes are consistent, which show groundwater has a same origin, mainly recharged by precipitation and the water of channel.2)With the same climate condition, the hydrogen and oxygen isotopes of groundwater have a regional trend: the groundwater in the shallow part has a enriched D and 18O.3) The hydrogen and oxygen isotopes of groundwater have a seasonal trend: the groundwater has a enriched D and a lean 18O in the winter but adverse in the summer.4)Depend on the TU of groundwater and the transformation of water level of three important observation well in the irrigation area, we get a conclusion that modern precipitation and channel water have a little proportion in the groundwater.Finally, using VS2DT software and the method of neutron instrument to model and situ-observe the soil moisture movement, we study on number 1 hole and number 3 hole where they are planting corn and sunflower respectively. The results show as follows: 1) due to the evaporation of the whole winter, the water content is very low, so the amount of seepage is very little.2) after times of plant irrigation in the growing period ,the water content is higher compared to pre-irrigation. Therefore, the fifth irrigation of corn and the third irrigation of sunflower are the main reasons that caused the leakage, meanwhile, because the corn needs five irrigation, especially the interval is short after the third irrigation, and the sunflower needs three irrigations, which interval is longer, so, the leakage amount is higher when planting corns than panting sunflower.(3)the number one pit and number three are both dual soil structure, the above soil is sand, the below layer of number 1 is grit, however, the below layer is clay-sand, because the clay-sand layer can keep more water and its permeability coefficient is lower than grit layer, so, planting in the soil which is grit in lower lay, the leakage content gets higher and its usage factor is lower than in the soil which is clay-sand below.