Physiological acclimation strategies of riparian plants to environment change in the delta of the Tarim River,China

The occurrence and development of riparian forests, which were mainly dominated by mesophytes species related closely with surface water. Since there was no water discharged to the lower reaches of Tarim River in the past three decade years, the riparian forests degrade severely. The groundwater table, the saline content of the groundwater, as well as the content of free proline, soluble sugars, plant endogenous hormones (abscisic acid (ABA), and cytokinins (CTK)) of the leaves and relative rates of sap flow of the Populus euphratica Oliv. (arbor species), Tamarix ramosissima Ldb. (bush species), and Apocynum venetum L. (herb species) were monitored and analyzed at the lower reaches of the Tarim River in the study area where five positions on a transect were fixed at 100 m intervals along a sampling direction from riverbank to the sand dunes before and after water release. The physiological responses and acclimation strategies of three species to variations in water and salinity stress were discussed. It was found that A. venetum population recovered to groundwater table ranging from −1.73 to −3.56 m, and when exposed to saline content of the groundwater ranging from 36.59 to 93.48 m mol/L; P. euphratica appeared to be more sensitive to the elevation of groundwater table than the A. venetum and T. ramosissima at groundwater table ranging from −5.08 to −5.80 m, and when exposed to saline content of the groundwater ranging from 42.17 to 49.55 m mol/L. T. ramosissima tended to be the best candidate species for reclamation in this hyper-arid area because it responded to groundwater table ranging from −1.73 to −7.05 m, and when exposed to saline content of the groundwater ranging from 36.59 to 93.48 m mol/L. These results explained the distribution patterns of desert vegetation in the lower reaches of the Tarim River. Understanding the relationships among ecological factors variables, physiological response and acclimation strategies of plant individuals could provide guidance to sustainable management, reclamation and development of this and similar regions.     

The influence of 10 years of water conveyances on groundwater and juvenile Populus euphratica of the lower Tarim River

The changes in the depth of groundwater were studied from the period before water conveyance through 2010, and the TDS of groundwater was analyzed in the lower reaches of the Tarim River during the period 2001–2010. Besides, the numbers of juvenile P. euphratica were investigated in the lower reaches of the Tarim River during the period 2001–2010. The findings indicate that: (1) the hydrological environment of the lower reaches has slowly deteriorated again; and (2) few juvenile P. euphratica were observed along the channel. These results show that the positive influence of the ecological water conveyance project on the ecosystem of the lower Tarim River should be beneficial in the long term; however, the long-term stability of the ecosystem cannot be achieved by the current water diversion scheme.     

Response of groundwater chemistry to water deliveries in the lower reaches of Tarim River,Northwest China

In this paper, we analysed the monitored data from nine groundwater-monitoring transects in the lower reaches of Tarim River during the five times of stream water deliveries to the river transect where the stream flow ceased. The results showed that the groundwater depth in the lower reaches of Tarim River rose from −9.30 m before the conveyances to −8.17 and −6.50 m after the first and second conveyances, −5.81 and −6.00 m after the third and fourth the conveyance, and −4.73 m after the fifth. The horizontal extent of groundwater recharge was gradually enlarged along both sides of the channel of conveyance, i.e., from 250 m in width after the first conveyance to 1,050 m away from the channel after the fourth delivery. With the rising groundwater level, the concentrations of major anions Cl⁻, SO₄²⁻ and cations Ca²⁺, Mg²⁺, Na⁺, as well as total dissolved solids (TDS) in groundwater underwent a significant change. The spatial variations in groundwater chemistry indicated that the groundwater chemistry at the transect near Daxihaizi Reservoir changed earlier than that farther from it. In the same transect, the chemical variations were earlier in the monitoring well close to watercourse than that farther away from the stream. In general, the concentration of the major ions and TDS at each monitoring well increased remarkably when the water delivery started, and decreased with the continued water delivery, and then increased once again at the end of the study period. Hence, the whole study period may be divided into three stages: the initial stage, the intermediate stage and the later stage. According to the three stages of groundwater chemistry reaction to water delivery and the relationships between groundwater chemical properties and groundwater depths, we educe that under the situation of water delivery, the optimum groundwater depth in the lower reaches of the Tarim River should be −5 m.     

Groundwater depth affects the daily course of gas exchange parameters of Populus euphratica in arid areas

In this case study, the diurnal courses of gas exchange in Populus euphratica at different groundwater depths in the lower reaches of Tarim River were investigated to understand the effects of soil hydrology on photosynthesis and water use efficiency (WUE) of vegetation in arid desert area. It was found that the photosynthetic rate (P _N) was not sensitive to the change of groundwater depth (GD) within the range of 4.2?C6.8?m. Compared to stomatal conductance (g _s) and transpiration rate (E) of P. euphratica grown at GD 4.2, 5.6 and 5.8?m, g _s and E at GD 6.8?m both markedly declined in June, suggesting that P. euphratica at deeper GD can avoid overall water loss by stomatal adjustment. The intrinsic water use efficiency of P. euphratica first decreases with the increasing GD, but when GD increased to 6.8?m, intrinsic WUE increased by 1.2?C2.2 fold, compared with the WUE of P. euphratica at GD 4.2?C5.8?m, indicating that intrinsic WUE of P. euphratica will increase when the plant suffers from moderate drought stress.     

Physiochemical conditions of Folsomia candida occurrence in a shallow coastal Lake Michigan aquifer

An insect, Folsomia candida, was found in a shallow aquifer along the southwestern coast of Michigan. F. candida is a standard organism for soil toxicity testing but its occurrence in groundwater is uncommon to rare, or has been under-reported in the literature. Attempts to correlate the presence of F. candida to water and soil parameters yielded: (1) F. candida is present in the upper 15–25 cm of topsoil, but absent in the underlying vadose zone except directly above the water table, regardless of the presence in groundwater; (2) F. candida is most abundant in groundwater 4.3–5.0 m below land surface; (3) Most F. candida occur in wells with dissolved oxygen ranging from 4 to 5 ppm; (4) F. candida is most abundant in water between about 14 and 18°C; (5) F. candida is abundant in groundwater with high concentrations of Cl⁻, Na⁺, and K⁺; and, (6) Small differences in pore space volume determine the feasibility of F. candida occupancy, but not the presence of F. candida in the study area.     

Photosynthesis and water use efficiency of Populus euphratica in response to changing groundwater depth and CO2 concentration

Changes of stomatal conductance (g _s), net photosynthetic rates (P _N) and water use efficiency (WUE) were investigated in Populus euphratica grown on sites with different groundwater depths (GDs) under two CO₂ concentrations in the lower reaches of Tarim River, Xinjiang, northwestern China. P _N in P. euphratica only slightly decreased when the groundwater depth increased from 4.12 to 7.74 m below the ground surface. P _N values significantly increased in response to an elevated CO₂ concentration at all GDs except at GD of 4.12 m for its good availability of groundwater. WUE values decreased with an initial increase in the groundwater depth, but increased when the groundwater depth reached 7.74 m especially under the elevated CO₂ concentration. The g _s values measured at 4.12 and 4.74 m both decreased indistinctively by only 3% due to CO₂ enrichment; however, when GDs increased to 5.54 and 7.74 m, the g _s values decreased significantly by about 10%. It shows that the response of g _s in P. euphratica to elevated CO₂ is weaker under lower groundwater depth (mild drought stress) but stronger under deeper groundwater depth (moderate drought stress). Results from this study suggest that groundwater depth could determine the response of photosynthesis to future CO₂ enrichment in P. euphratica in arid desert areas.     

Statistical analysis of groundwater chemistry of the Tarim River lower reaches,Northwest China

This study applied a comprehensive quantitative approach including statistical, principal component and gray relation analyses to assess the groundwater chemistry based on monitored data from 840 samples collected from the lower reaches of Tarim River from 2000 to 2009. The main findings were: (1) there were six types of groundwater chemistry in the lower reaches of Tarim River where Cl·SO₄–Na·Mg was the dominant type accounting for 73.57% in all samples. There were linear relationships among chemical parameters, where TDS had significant multiple correlations with Na⁺, K⁺, Mg²⁺, Ca²⁺ and Cl⁻, respectively. (2) Three principal components (PC1, PC2 and PC3) were extracted. They included comprehensive measurements for salinization, alkalinity and pH, respectively. Most parameters showed decreasing trends during the period of 2000–2009, as well as the scores on PC1, because the concentrations of various chemical substances were diluted due to the uplift of the groundwater table in the lower reaches and the implementation of the ecological water delivery project in 2000. (3) HCO₃ ⁻ was the most sensitive chemical parameter affected by the groundwater table followed by TA, Mg²⁺, TH, SO₄²⁻, K⁺, TDS and TS. PC2 was the most sensitive principal component to the change of the groundwater table followed by PC1 and PC3.     

Environmental effects of water resource development and use in the Tarim River basin of northwestern China

The unbridled development and use of water resources in the Tarim River basin over the last 50 years have led to a serious degradation of soil (>12×10³ km² of land desertified between the 1960s and 1990s) and water quality (rise in maximum salinity was from 1.3 g l^–1 in 1960, to 4.0 g l^–1 in 1981–1984, and to 7.8 g l^–1 in 1998). Approximately 300 km of the lower reaches of the river course dried up between the 1950s and 1970s, seriously altering the downstream hydrological processes (a 4–6 m drop in groundwater levels from the 1960s to the 1980s, and 0.2 m yr^–1 thereafter) and ecosystems (67% and 50% decrease (1958–1978) in Populus euphratica forest acreage and biomass, respectively). Between the 1950s and 1990s, 3820 km² of P. euphratica forest and 200 km² of shrub- and grassland were lost in the lower reaches of the Tarim River. In this study, based on estimates of soil organic carbon in desertified lands, it has been found that in the last 30 years (1970–2000), approximately 112 Tg of organic carbon (28% originating in the 0–1.0 m soil profile) has been released into the atmosphere as a result of soil degradation in the Tarim River basin. Intensive anthropogenic disturbance has been one of the foremost factors leading to the deterioration of water resources in this region. The key to solving these problems is to enhance the scientific and technical level of monitoring, management, and restoration of water resources and associated water and soil components of local ecosystems.     

A Geochemical study of the groundwater in the Misli basin and environmental implications

The aim of this study was to determine geochemical properties of groundwater and thermal water in the Misli Basin and to assess thermal water intrusion into shallow groundwater due to over-extraction. According to isotope and hydrochemical analyses results, sampled waters can be divided into three groups: cold, thermal, and mixed waters. Only a few waters reach water–rock chemical equilibrium. Thermal waters in the area are characterized by Na⁺–Cl⁻–HCO₃⁻, while the cold waters by CaHCO₃ facies. On the basis of isotope results, thermal waters in the Misli basin are meteoric origin. In particular, δ¹⁸O and δ²H values of shallow groundwater vary from −10.2 to −12.2‰ and −71.2 to −82‰, while those of thermal waters range from −7.8 to −10.1‰ and from −67 to −74‰, respectively. The tritium values of shallow groundwater having short circulation as young waters coming from wells that range from 30 to 70 m in depth vary from 10 to 14 TU. The average tritium activity of groundwater in depths more than 100 m is 1.59 ± 1.16, which indicates long circulation. The rapid infiltration of the precipitation, the recycling of the evaporated irrigation water, the influence of thermal fluids and the heterogeneity of the aquifer make it difficult to determine groundwater quality changes in the Misli Basin. Obtained results show that further lowering of the groundwater table by over-consumption will cause further intrusion of thermal water which resulted in high mineral content into the fresh groundwater aquifer. Because of this phenomenon, the concentrations of some chemical components which impairs water quality in terms of irrigation purposes in shallow groundwaters, such as Na⁺, B, and Cl⁻, are highy probably expected to increase in time.     

The threshold of soil moisture and salinity influencing the growth of Populus euphratica and Tamarix ramosissima in the extremely arid region

The drought and salt tolerance of two pioneer species, Populus euphratica and Tamarix ramosissima, were studied by monitoring the stem and leaf water potentials under various soil moisture and salinity at depths of 0–180 cm. The plants are naturally distributed in arid environment in the lower reaches of the Tarim River in Xinjiang, China. The results showed that P. euphratica can withhold water by prolonging dewatering and adapt to the dry desert weather by reducing water consumption. The lowest soil moisture that would unfavorably influence its growth was found to be 7% soil moisture. T. ramosissima was found to have low water potential and high transpiration efficiency. It is capable of absorbing water from the soil by keeping a low water potential, so there is no critical limit of soil moisture for T. ramosissima. In terms of salt resistance, P. euphratica was found to secrete salt from its body by discharging salty water through portals in its trunks and leaves. A soil salinity of 20% was the minimum concentration at which the salt secretion mechanism of P. euphratica was activated. T. ramosissima secreted salt by storing the accumulated salt in the vacuoles of its salt secretion glands for separation. Thus, it has no minimum soil salinity limit. T. ramosissima was found to have better resistance to drought and salt stress than P. euphratica.     

Transport,fate, and infectivity of <Emphasis Type="Italic">Cryptosporidium parvum</Emphasis> oocysts released from manure and leached through macroporous soil

A major mode of transmission of Cryptosporidium parvum, a widespread waterborne pathogen, is via contaminated drinking and recreational waters. Oocyst transport to surface water can occur by deposition of manure directly in the water or by wash off in surface runoff. Oocyst transport to groundwater is less straightforward and requires that the oocysts move through soil and bedrock to reach the water table. The purpose of this study was to determine the relative concentration and infectivity of C. parvum oocysts released from manure and leached through columns of undisturbed, macroporous karst soil. Modeling the fate of oocysts in this system over time can provide baseline data for evaluating real world events. Substantially more oocysts leached from undisturbed soil columns than disturbed soil columns. Oocyst survival studies using BALB/c neonatal suckling mice showed that about 85% of oocysts were infective at the beginning of leaching experiments. The oocyst infectivity decreased to about 20% after 12 weeks of leaching from soil columns maintained at 10°C. Cool (10°C) temperatures appear to increase survivability and maintain infectivity of many oocysts for 3 months or longer. Cool temperatures also appear to increase rates of release of oocysts from manure and leaching through soil. This study demonstrated that leaching is an important mechanism of oocyst transport in karst soils where infiltration capacities are high and long, continuous macropores exist. Karst groundwater systems might be especially vulnerable to contamination by leached oocysts, because of the prevalence of shallow soils and rapid groundwater movement. Oocysts leaching from soils into the epikarst could accumulate and remain viable for months until hydrological conditions are right for flushing the oocysts into the conduit flow system.     

Spatial distribution characteristics of stable carbon isotope compositions in desert plant Reaumuria soongorica (Pall.) Maxim

In order to investigate the distribution characteristics of stable carbon isotope ratios (δ ¹³C) in the desert plant Reaumuria soongorica, the δ ¹³C values of leaves were measured in 407 individuals of 21 populations. Soil physicochemical properties including soil water content, soil total dissolved solids, soil total nitrogen, soil total phosphorus and soil organic content were also analyzed in order to survey the major factors influencing δ ¹³C values on spatial variation. Leaves and soil samples were simultaneously collected from the ten major distribution areas in Northwest China at altitudes from 394 m to 1 987 m above sea level, at latitudes from 36°10′N to 44°33′N, and at longitudes from 81°43′E to 106°37′E. These ten areas include Shihezi, Baicheng, Yiwu areas in Xinjiang Uygur Autonomous Region; Anxi, Zhangye, Baiyin, Lanzhou areas in Gansu Province; Shapotou, Yinchuan areas in Ningxia Hui Autonomous Region; and Alashan County in Inner Mongolia Autonomous Region. The results show that the δ ¹³C value of R. soongorica ranges from −22.77‰ to −29.85‰ with an average of −26.52‰. Foliar d13C values in R. soongorica are not significantly correlated with altitude, latitude or longitude, and a spatial distribution trend of d13C values of R. soongorica is not obvious on a large scale. However, when d13C values of two R. soongorica populations under the same climate conditions are compared, δ ¹³C values increase obviously from east to west and from north to south. As none of the soil total dissolved solids, soil total nitrogen, soil total phosphorus, and soil organic content shows a uniform trend from east to west and from north to south, we suppose that the small-scaled spatial distribution pattern of δ ¹³C values of R. soongorica is mainly controlled by the soil water content. Translated from Quaternary Sciences, 2006, 26(6): 947–954 [译自: 第四纪研究]     

The effects of human activities on oasis climate and hydrologic environment in the Aksu River Basin,Xinjiang, China

Under the influence of human activities, the differences in climate changes emerged obviously in the Aksu Oasis. The summer air temperature in Aksu City increased at a rate of 0.20°C·(10 annum)⁻¹, while the air temperature in Aler in summer decreased at a rate of −0.27°C·(10 annum)⁻¹. Human intervention has become the dominant factor in the the changes of water resources in the Aksu Oasis. Compared with the Xidaqiao hydrological station, which is located on the upper reaches of the Aksu River, the runoff ratio at the Aler hydrological station increased in summer and decreased in spring. Though the natural water inflow has increased in the last 50 years, irrigation diversion and water consumption for human activities have increased unceasingly due to the increased reclamation of land and the development of extensive agriculture. The water quality at the Xidaqiao station is in Grade I at different periods, and the water quality at the Aler station of the Tarim River is good because the river did not suffer from human disturbance before the large-scale development of oasis agriculture; but the salinity of river water increased from 0.67 g L⁻¹ in 1960 to 5.27 g L⁻¹ in 2000 at the Aler station after farmland development, reclamation and salt washing in the oasis. The geographic distribution of surface water resources has changed due to human activities and in turn affected groundwater replenishment, bringing about changes to groundwater table and quality.     

Research on the water use efficiency and foliar nutrient status of <Emphasis Type="Italic">Populus euphratica</Emphasis> and <Emphasis Type="Italic">Tamarix ramosissima</Emphasis> in the extreme arid region of China

Seasonal variations in foliar stable carbon composition (δ¹³C) and nitrogen (N), phosphorus (P) and potassium (K) concentrations of Populus euphratica Olivier and Tamarix ramosissima Ledeb, as well as correlations between foliar δ¹³C values and N, P and K concentrations were studied in the Ejina oasis in the lower reaches of the Heihe River, northwestern China. Foliar δ¹³C values, and P and K concentrations significantly differed between species. Foliar δ¹³C signatures in T. ramosissima were significantly more enriched than those in P. euphratica, but P and K concentrations of P. euphratica were higher. The seasonal variations and patterns of these were similar. The total foliar δ¹³C values and N, P and K concentrations in both P. euphratica and T. ramosissima showed a descending trend. There were significantly positive correlations between foliar δ¹³C values and N and P concentration of both P. euphratica and T. ramosissima. For the relationship between foliar δ¹³C and K concentration, there appeared oppositely positive and negative correlations in P. euphratica and T. ramosissima, respectively, but they were not significant. The simple positive correlations of δ¹³C–P% and δ¹³C–N% suggested that N and P in P. euphratica and T. ramosissima behave in a similar manner. This study also showed that there were nutrient deficiencies; N and P nutriments were the co-limiting factors in P. euphratica, while it was P nutriment in T. ramosissima.     

Hydrogeochemical processes in the groundwater environment of Heihe River Basin,northwest China

The Heihe River Basin is a typical arid inland river basin for examining stress on groundwater resources in northwest China. The basin is composed of large volumes of unconsolidated Quaternary sediments of widely differing grain size, and during the past half century, rapid socio-economic development has created an increased demand for groundwater resources. Understanding the hydrogeochemical processes of groundwater and water quality is important for sustainable development and effective management of groundwater resources in the Heihe River basin. To this end, a total of 30 representative groundwater samples were collected from different wells to monitor the water chemistry of various ions and its quality for irrigation. Chemical analysis shows that water presents a large spatial variability of chemical facies (SO₄ ²⁻–HCO₃⁻, SO₄ ²⁻–Cl⁻, and Cl⁻–SO₄ ²⁻) as groundwater flow from recharge area to discharge area. The ionic ratio indicates positive correlation between the flowing pairs of parameters: Cl⁻ and Na⁺(r = 0.95), SO₄ ²⁻ and Na⁺ (r = 0.84), HCO₃ ⁻ and Mg²⁺(r = 0.86), and SO₄ ²⁻ and Ca²⁺ (r = 0.91). Dissolution of minerals, such as halite, gypsum, dolomite, silicate, and Mirabilite (Na₂SO₄·10H₂O) in the sediments results in the Cl⁻, SO₄ ²⁻, HCO₃ ⁻, Na⁺, Ca²⁺ and Mg²⁺ content in the groundwater. Other reactions, such as evaporation, ion exchange, and deposition also influence the water composition. The suitability of the groundwater for irrigation was assessed based on the US Salinity Laboratory salinity classification and the Wilcox diagram. The results show that most of the groundwater samples are suitable for irrigation uses barring a few locations in the dessert region in the northern sub-basin.     

A study of turbulent characteristics of atmospheric boundary layer over monsoon trough region using Kytoon and Doppler sodar

As a part of the MONTBLEX-90 observational programme, Kytoon and Doppler sodar observations were taken at Kharagpur. These data are analysed to study the turbulent characteristics of the atmospheric boundary layer in terms of stability, temperature structure function (C _T ² ) and velocity structure function (C _v ² ).C _T ² follows aZ ^−4/3 law on most of the days, whereas the variation ofC _V ² is not systematic.C _V ² andC _T ² values are found to vary between 10⁻⁵−10⁻¹ m^4/3s⁻² and 10⁻⁵−10⁻²°C² m^−2/3 respectively.     

Effects of light intensity on the growth of <Emphasis Type="Italic">Cryptomonas</Emphasis> sp. (Cryptophyceae)

Laboratory culture experiments have been conducted to evaluate the effects of light intensity on the growth of Cryptomonas sp. (Cryptophyceae) and the discrepancy in absorption of iron and phosphorus under different light conditions. Results show that there is an exponential correlation between algal growth rate and light intensity. The saturating and semi-saturating light values for Cryptomonas sp. cells are 150 and 47 μmol photons m⁻² s⁻¹, respectively. More uptake of Fe, P, and other trace elements such as Zn, Mn, Co, and Mo is observed in the low light cultures, although the algal growth rates are slow. The growth rate at 10 μmol photons m⁻² s⁻¹ is only 10% of that at 150 μmol photons m⁻² s⁻¹, whereas Fe and P uptake increases by 150 and 100%, respectively. These results suggest potential implications of differentiation in absorption of iron and phosphorus at different light intensities for the occurrence of harmful algal blooms (HABs). The mechanisms of light intensity regulating nutrient uptake as well as the occurrence of HABs are also discussed.     

The role of deuterium excess in determining the water salinisation mechanism: A case study of the arid Tarim River Basin,NW China

Understanding the water salinisation mechanism is the basis for regional salt management. Mineral dissolution, evaporation and transpiration are the main factors controlling natural water salinity in arid inland basins; however, the two are difficult to differentiate. Because deuterium excess decreases during evaporation and is unrelated to the isotopic composition of the initial water, it is a potential tool for determining the contribution of the evapoconcentration of a given water body using the relationship between deuterium excess and salinity rather than between δ¹⁸O (or δ²H) and salinity. In this paper, the relationship between the residual water fraction and deuterium excess was derived from the Rayleigh distillation equation. The contribution of evapoconcentration and mineral dissolution and/or transpiration for a given water body can be determined by comparing the residual water fraction and salinity between the initial water and the evapoconcentrated water. The extremely arid Tarim River Basin in NW China is taken as an example to demonstrate deuterium excess and salinity evolution from the source stream to river water, lake/reservoir water and groundwater. The results show that mineral dissolution contributes most of the salinity (67–77%) for Boston Lake and the Kongque and Tarim rivers relative to the source stream. Mineral dissolution and/or transpiration contribute greater salinity (73–99.6%) to the groundwater recharged by the river water in the middle and lower reaches of the Tarim River. The study provides a method for determining the salinisation mechanism and is important for salt movement and management.     

Spatio-temporal variations of δ<Superscript>2</Superscript>H and δ<Superscript>18</Superscript>O in precipitation and shallow groundwater in the Hilly Loess Region of the Loess Plateau,China

Groundwater is of utmost significance to socio-economic development and ecological recovery for the Loess Plateau. However, studies regarding the mechanism governing groundwater recharge over this area appear to be inadequate. This study is to examine the spatio-temporal variations of δ²H and δ¹⁸O in precipitation and shallow groundwater. On the basis of this, the mechanisms governing shallow groundwater recharge were explored. Precipitation and groundwater were sampled monthly from May to October during the period 2004–2006 at 13 sites in the Chabagou Catchment (187 km²). In the Caopingxigou Experimental Watershed (0.1 km²), meteorological variables were observed and rainfall larger than 5 mm was sampled immediately after each rain event. Across the area, 90% of the precipitation occurred from May to September primarily in the form of heavy rains or rainstorms with great spatial variability. There were about 30 localized rains in each year. It was indicated that there existed notable seasonality and pronounced spatial variability in precipitation isotopic compositions. Contributing factors and indications of isotopic compositions, as well as their climatic indications such as monsoon intensities and mixing processes of water vapor, were investigated. The δ²H–δ¹⁸O relation of groundwater was found to be δ²H = 3.22 × δ¹⁸O − 38.1, deviating from the local meteoric water line δ²H = 7.57 × δ¹⁸O + 3.9. The range of δ values in groundwater is shrunken to be 15–21% of that in individual precipitations, and groundwater in the middle reaches shows a wider range of δ values. Isotopic results showed that groundwater originates from precipitation with hydrogen and oxygen isotopic compositions being −69 and −9.7‰, respectively, and most groundwater experiences serious evaporation and adequate mixing with old water during infiltration or percolation in the aerated zone. It was also founded that obvious fluctuations of isotopic compositions in groundwater mainly appear in the middle reaches especially at sites that are close to valleys, suggesting varying sources of groundwater from precipitation, precipitation runoff, isotopically enriched surface water and/or lateral recharge of adjacent groundwater.     

Equation of state,structural behaviour and phase diagram of synthetic MgFe<Subscript>2</Subscript>O<Subscript>4</Subscript>, as a function of pressure and temperature

The behaviour of synthetic Mg-ferrite (MgFe₂O₄) has been investigated at high pressure (in situ high-pressure synchrotron radiation powder diffraction at ESRF) and at high temperature (in situ high-temperature X-ray powder diffraction) conditions. The elastic properties determined by the third-order Birch–Murnaghan equation of state result in K₀=181.5(± 1.3) GPa, K=6.32(± 0.14) and K= –0.0638 GPa^–1. The symmetry-independent coordinate of oxygen does not show significant sensitivity to pressure, and the structure shrinking is mainly attributable to the shortening of the cell edge (homogeneous strain). The lattice parameter thermal expansion is described by _a0+_a1*(T–298)+_a2/(T–298)², where _a0=9.1(1) 10^–6 K^–1, _a1=4.9(2) 10^–9 K^–2 and _a2= 5.1(5) 10^–2 K. The high-temperature cation-ordering reaction which MgFe-spinel undergoes has been interpreted by the ONeill model, whose parameters are = 22.2(± 1.8) kJ mol^–1 and =–17.6(± 1.2) kJ mol^–1. The elastic and thermal properties measured have then been used to model the phase diagram of MgFe₂O₄, which shows that the high-pressure transition from spinel to orthorombic CaMn₂O₄-like structure at T < 1700 K is preceded by a decomposition into MgO and Fe₂O₃.