Estimating distribution of water uptake with depth of winter wheat by hydrogen and oxygen stable isotopes under different irrigation depths

Crop root system plays an important role in the water cycle of the soil-plant-atmosphere continuum. In this study, com- bined isotope techniques, root length density and root cell activity analysis were used to investigate the root water uptake mechanisms of winter wheat （Triticum aesfivum L.） under different irrigation depths in the North China Plain. Both direct inference approach and multisource linear mixing model were applied to estimate the distribution of water uptake with depth in six growing stages. Results showed that winter wheat under land surface irrigation treatment （Ts） mainly absorbed water from 10-20 cm soil layers in the wintering and green stages （66.9 and 72.0%, respectively）; 0-20 cm （57.0%） in the jointing stage; 0-40 （15.3%） and 80-180 cm （58.1%） in the heading stage; 60-80 （13.2%） and 180-220 cm （35.5%） in the filling stage; and 0-40 （46.8%） and 80-100 cm （31.0%） in the ripening stage. Winter wheat under whole soil layers irrigation treatment （Tw） absorbed more water from deep soil layer than Ts in heading, filling and ripening stages. Moreover, root cell activity and root length density of winter wheat under TW were significantly greater than that of Ts in the three stages. We concluded that distribution of water uptake with depth was affected by the availability of water sources, the root length density and root cell activity. Implementation of the whole soil layers irrigation method can affect root system distribution and thereby increase water use from deeper soil and enhance water use efficiency.

Stable isotopes of water as a tracer for revealing spatial and temporal characteristics of groundwater recharge surrounding Qinghai Lake,China

Studying spatial and temporal characteristics of regional groundwater recharge will guide the scientific management and sustainable development of regional water resources.This study investigated stable isotopes(δ^(18)O and δ^(2) H)of precipitation,groundwater,river water and lake water during 2019-2020 in Qinghai Lake Basin to reveal the spatial and temporal characteristics of groundwater recharge.The local meteoric water line was simulated using ordinary least squares regression(δ^(2) H=7.80δ^(18)O+10.60).The local evaporation lines of the river water,lake water and groundwater were simulated asδ^(2) H=6.21δ^(18)O-0.72,δ^(2) H=5.73δ0-3.60 and δ^(2) H=6.59δ0+1.76,respectively.The δ^(2) H and δ^(18)O of river water and groundwater were in more depleted values due to the recharge by precipitation at high altitudes or precipitation effects,and theδ^(2) H andδ^(18)O of the lake water were in more enriched values because of evaporation.The relationship between the δ^(2) H and δ^(18)O of groundwater and river water was not significantly different,indicating a strong hydrological connection between the groundwater and river water surrounding Qinghai Lake.Additionally,the maximum values of δ^(18)O and the minimum values of lc-excess of groundwater in most regions were both in August,and the minimum values of δ^(18)O and the maximum values of lc-excess of groundwater in most regions were both in October.Therefore,the groundwater was recharged by soil water with strong evaporation in August and recharged by precipitation at high altitudes in October.The recharge rate of groundwater was relatively fast in areas with large slopes and large hydraulic gradients(e.g.,south of Qinghai Lake),and in areas with strong hydrological connections between the groundwater and river water(e.g.,the Buha River Valley).Those results can provide data support for protection and utilization of water resources in Qinghai Lake Basin,and provide reference for groundwater research in closed lake basins on the Qinghai-Tibet Plateau.

Application of Stable Isotope Tracing Technologies in Identification of Transformation among Waters in Sanjiang Plain,Northeast China

In order to investigate the transformation among the precipitation,groundwater,and surface water in the Sanjiang Plain,Northeast China,precipitation and groundwater samples which were collected at the meteorological station of the Sanjiang Mire Wetland Experimental Station,Chinese Academy of Sciences and the surface water which collected from the Wolulan River were used to identify the transformation of three types of water.The isotope composition of different kinds of water sources were analyzed via stable isotope(deuterium and oxygen-18) investigation of natural water.The results show a clear seasonal difference in the stable isotopes in precipitation.During the cold half-year,the mean stable isotope in precipitation in the Sanjiang Plain reaches its minimum with the minimum temperature.The δ18O and δD values are high in the rainy season.In the Wolulan River,the evaporation is the highest in August and September.The volume of evaporation and the replenishment to the river is mostly same.The groundwater is recharged more by the direct infiltration of precipitation than by the river flow.The results of this study indicate that the water bodies in the Sanjiang Plain have close hydrologic relationships,and that the transformation among each water system frequently occurs.

Stable isotope techniques in plant water sources:a review

The stable hydrogen and oxygen isotopes widely exist in various kinds of natural water.Plants have to cope with various water sources:rainwater,soil water,groundwater,sea water,and mixtures.These are usually characterized by different isotopic signatures (18O/16O and D/H ratios).Because there are relative abundance variations in water,and plant roots do not discriminate against specific water isotopes during water uptake,hydrogen and oxygen stable isotope ratios of water within plants provide new information on water sources,interactions between plant species and water use patterns under natural conditions.At present,the measurement of δD,δ18O composition of various potential water sources and stem water has become significant means to identify plant water sources.Based on previous studies,this review highlights recent advances such as theory basis,methodology,as well as different spatial and temporal scales,and existed questions and prospects.Stable isotope techniques for estimating plant water sources have provided valuable tools for conducting basic and applied research.Future studies emphasize the modification of preparing methods,isotope technique combined with other measurements,and aerial organs of plant water source should be en-couraged.

Water sources of plants and groundwater in typical ecosystems in the lower reaches of the Heihe River Basin

Stable oxygen and hydrogen isotopic compositions （δ18O and δD） of soil water and shallow groundwater of a riparian forest, an artificial shrub forest, and Gobi of the lower reaches of the Heihe River Basin are used to study the recharge water sources of those ecosystems. IsoSource software is used to determine the δ180 values for root water of Populous euphratica and Tamarix ramosissima in the riparian forest ecosystem, Haloxylon ammodendron in the artificial shrub forest, and Reaumuria soongorica in the Gobi, as well as for local soil water and groundwater, and precipitation in the upper reaches of the Heihe River Basin. Our results showed that soil water and shallow groundwater of the riparian forest and the artificial shrub forest were recharged by river water which originated from precipitation in the upper reaches, and strong evaporation occurred in the artificial shrub forest. Soil water of the Gobi was not affected by Heihe River water due to this area being far away from the river channel. The main water sources of Populous euphratica were from 40-60-cm soil water and groundwater, and of Tamarix ramosissima were from 40-80-cm soil water in the riparian forest ecosystem. In the artificial forest, Haloxylon ammodendron used 200-cm saturated-layer soil water and shallow groundwater. The Reaumuria soongorica mainly used soil water from the 175-200-cm depth in the Gobi. Therefore, soil water and groundwater are the main water sources which maintain survival and growth of the plants in the extremely arid regions of the lower reaches of the Heihe River Basin.

Study on Change Rules and Influencing Factors of Soil Moisture in Huaibei Plain

[Objectives]To study the relationship between soil water,groundwater burial depth,and precipitation for summer maize in Huaibei Plain.[Methods]The atmospheric precipitation,soil water and groundwater for the growth period of summer maize in Huaibei Plain were analyzed using the 26-year long series of data from the Wudaogou Hydrological Experimental Station,combined with the hydrogen and oxygen stable isotope tracing method.[Results]The average soil moisture content of summer maize in different growth periods showed a trend of first decreasing,then increasing and then decreasing with the increase of soil depth.The average soil moisture content was the lowest at the surface soil layer.From the characteristic values of hydrogen and oxygen isotopes of atmospheric precipitation,soil water and groundwater,it can be known that the average values ofδ18O andδD of soil water decreased with the increase of soil depth,indicating that soil moisture evaporation leads to the enrichment of soil heavy isotopes,and the degree of enrichment decreased from the surface layer to the deep layer of the soil.The seasonal variation of the stable isotope of hydrogen and oxygen in soil water declined with the increase of soil depth.The soil water changes at 30 cm and 50 cm soil depths were the most obvious.The soil was easily recharged by precipitation,and soil evaporation was relatively strong.[Conclusions]The research results are favorable for in-depth understanding of the regional water cycle process,and are expected to provide a certain scientific basis for realizing the efficient and sustainable use of regional groundwater.

Glacier meltwater runoff process analysis using δD and δ^(18)O isotope and chemistry at the remote Laohugou glacier basin in western Qilian Mountains, China

Stable hydrogen and oxygen isotope has important implication on water and mois- ture transportation tracing research. Based on stable hydrogen （6D） and oxygen （6180） isotope using a Picarro Ll102-i and water chemistry （e.g. major ions, pH, EC and TDS） meas- urement, this study discussed the temporal variation and characteristics of stable hydrogen and oxygen isotope, chemistry （e.g. TDS, pH, EC, Ca^2^, Mg2＋, Na^＋ and CI） in various water bodies including glacier meltwater runoff, ice and snow, and precipitation at the Laohugou g^acier basin during June 2012 to September 2013. Results showed that 6D and δ18O in the meltwater runoff varied obviously with the temporal change from June to September, showing firstly increasing trend and then decreasing trend, with the highest values in July with high air temperature and strong glacier melting, which could indicate the temporal change of glacier melting process and extent. Variations of 6D and δ18O in the runoff were similar with that of snow and ice on the glacier, and the values were also above the GMWL, which probably im- plied that the glacier runoff was mainly originated from glacier melting and precipitation supply The glacier meltwater chemical type at the Laohugou glacier basin were mainly composed by Ca-Na-HCO3-SO4 and Ca-Mg-HCO3-SO4, which also varied evidently with the glacier melting process in summer. By analyzing the temporal change of stable hydrogen and oxygen isotope and chemistry in the melting period, we find it is easy to separate the components of the snow and ice, atmospheric precipitation and melt-runoff in the river, which could reflect the change process of glacier melting during the melting period, and thus this work can contribute to the glacier runoff change study of large-scale region by stable isotope and geochemical method in future.

Water sources for typical desert vegetation in the Ebinur Lake basin

In arid and semi-arid environments,desert vegetation plays an important role in preventing soil erosion by wind and helps maintain the stability of desert and oasis ecosystems.Four types of typical desert vegetation,namely Populus euphratica,Haloxylon ammodendron,Nitraria sibirica,and Halostachs caspica,corresponding to different habitats(i.e.,river bank,sand dune,desert,and salt marsh)were chosen as the model vegetation in this research.Theδ^(2)H andδ^(18)O for rainwater,soil water,and plant water were applied to identify the water sources and quantify the proportions of different water sources used over the entire plant growth period(from March to October).The results showed that the precipitationδ^(2)H andδ^(18)O in the Ebinur Lake basin varied from-142.5‰to-0.6‰and from-20.16‰to 1.20‰,respectively.The largestδ^(2)H andδ^(18)O values occurred in summer and the smallest in winter.The soil waterδ^(2)H andδ^(18)O of the four habitats decreased gradually with increasing depth.Theδ^(2)H andδ^(18)O values of water extracted from the stems of the four plants had similar variation trends,that is,the maximum was observed in spring and the minimum in summer.Among the four plants,H.caspica had the highest stable isotopic values in the stem water,followed by N.sibirica,H.ammodendron,and P.euphratica.The water sources and utilization ratios of desert vegetation varied across different growth stages.Throughout the growing period,H.ammodendron mainly used groundwater,whereas the water source proportions used by N.sibirica varied greatly throughout the growing season.In spring,plants mainly relied on surface soil water,with a contribution rate of 80%-94%.However,in summer,the proportion of deep soil water used was 31%-36%;and in autumn,the proportion of middle soil water used was 33%-36%.H.caspica mainly relied on topsoil water in spring and autumn,and the proportion of soil water in the middle layer slightly increased to 20%-36%in summer.P.euphratica mainly used intermediate soil water in spring with a utilization rate of 53%-54%.In summer,groundwater was the main source,with a utilization rate of 72%-88%,and only 2%-5%came from river water,whereas in autumn,the river water utilization rate rose to 11%-21%.The results indicated that there were significant differences in water use sources during the growing period for desert vegetation in arid areas.This research provides a theoretical basis for understanding water use mechanisms,water adaptation strategies,and vegetation restoration and management in arid areas.