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Study on Groundwater Recharge from Irrigated Lands in Xinjiang Based on Stable IsotopeCN

宋浩

长安大学

Abstract:Xinjiang Uygur Autonomous Region is located in the arid area of Northwest China,with little rainfall and strong evaporation.Agricultural development in arid area often requires groundwater irrigation to meet the needs of crop growth.Unreasonable exploitation and utilization of groundwater resources often leads to many environmental problems.In order to improve the irrigation efficiency of groundwater,it is urgent to explore the infiltration and migration regularities of soil water in vadose zone of arid area.As a key link between surface water and groundwater,the study of water movement in vadose zone has always been a hot issue in groundwater science.Hydrogen and oxygen stable isotopes can move with water,and can characterize water infiltration,evaporation and other processes.Therefore,stable isotope technology has become an important means to study water transport and exchange in vadose zone in recent years.In this paper,irrigation areas of Huocheng County(Yili Valley)and Shawan County(Manas River Basin)in Xinjiang were used as experimental sites.In order to study the effects of different lithological conditions and crop types on water migration in vadose zone,bare soil,desert and farmland were selected according to different site conditions(farmland includes corn field and cotton field according to different crop cultivation)as test sites.Field experiments were combined with laboratory experiments.Stable isotope techniques and numerical model were used to analyze soil water infiltration and migration regularities under different field conditions.On this basis,the irrigation infiltration recharge coefficients of each test site were calculated using stable isotope mass conservation method,water conservation method,fixed flux method and numerical model method.The following results were achieved:(1)In bare soil,desert,corn field,and cotton field,the moisture content of clay profile in the corn field was the largest before and after irrigation,and the stable hydrogen and oxygen isotopes enrichment of fine sand profile in the desert was the highest.Thereafter,on the basis of the hydraulic head curve,it is found that zero flux surface was formed at 40 cm,38 cm and30 cm in bare soil area,corn field and cotton field respectively.The isotope fractionation effect above zero flux surface was obvious,while the isotope in lower part was relatively stable;Zero flux surface was formed at 40 cm and the isotope fractionation effect in upper and lower part of zero flux surface was obvious in desert,indicating that the isotope fractionation ability of the fine sand profile is stronger than of the clay profile under evaporation conditions.(2)According to the soil evaporation curves(correlation betweenδD andδ18O)of different experimental sites,the evaporation capacity of bare soil area was the strongest(the slope of evaporation line is 1.58),followed by desert,cotton field and arable area.The reason is the natural section of bare soil area.It is concluded that compared with lithology,temperature gradient has greater influence on soil evaporation capacity,and the reason of the large drift of the 18O in bare soil area may be that the the soil particles are more attractive to heavy molecules.(3)Compared with different irrigation sources,the hydrogen and oxygen stable isotope enrichment in soil water under surface water irrigation was stronger than that under groundwater irrigation.The proportion of irrigation water in bare soil(groundwater irrigation)and cotton field(surface water irrigation)were 29.3%and 40.5%respectively.Comparing different lithological profiles,the stable isotope fractionation ability of fine sand profile was stronger than that of clay profile in soil water.Comparing the corn field and the cotton field,the soil moisture content of maize field was smaller than that of cotton field in 30 cm below the surface,while that of maize field was larger than that of cotton field below 40 cm,indicating that the water requirement of maize field is greater than the cotton field.(4)The recharge coefficient of field irrigation was estimated by different methods.The results of stable isotope method,water conservation method and fixed flux method were close.The recharge coefficient of irrigation infiltration was 0.29-0.31 in bare soil 12 days after irrigation,0.37-0.39 in corn field 13 days after irrigation,0.26-0.27 in desert 10 days after irrigation,and 0.34-0.40 in cotton field 11 days after irrigation.The recharge coefficient of the second time irrigation was about 0.39 calculated by numerical model method,further indicating that high-quantity and high-frequency cotton field irrigation may make irrigation water infiltrate into deep soil and crops may be failed to fully absorb it,resulting in waste of surface water or groundwater resources.
  • Series:

    (D) Agriculture

  • Subject:

    Agricultural Engineering

  • Classification Code:

    S274

Tutor:

王文科;

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