Anomalous stable hydrogen-oxygen isotope characteristics and water vapor sources of autumn precipitation in the Weihe River basin, Northwest China.

The extreme changes in autumn rain have significant impacts on the ecological environment of Weihe River basin. Based on 117 autumn rain samples and corresponding meteorological data from 2015 to 2021 at Yangling located in the middle of Weihe River basin, we investigated the stable hydrogen and oxygen isotope composition and water vapor sources of precipitation. The results showed that, (1) extreme changes in autumn rainfall in the study area occurred frequently in recent years, which could be divided into extreme-high autumn precipitation year (HAP, 2021), general autumn precipitation year (GAP, 2015-2017, 2019-2020) and extreme-low autumn precipitation year (LAP, 2018) based on the autumn rain index (ARI); (2) the stable isotopes of different types of precipitation differed significantly, with a pattern of LAP>GAP>HAP for both δ2H and δ18O values. the variations of d-excess values and the slopes and intercepts of the meteoric water lines of autumn rain showed opposite trends. The main factor controlling autumn rain anomaly was not the local meteorological parameters, but the El Nino-Southern Oscillation and the Indian Ocean dipole events, which could explain 99% and 93% of the autumn rain isotopic variations, respectively. These coupling phenomena affected water vapor transport intensity of the marine air mass to the northwest inland, which determined autumn rainfall amount and the stable hydrogen-oxygen isotope composition. Our results would be helpful for improving the understanding of autumn rain anomalies in West China, and provide basic data and theoretical support for regional hydrological model building, would thereby better serve water resources management and disaster prevention and reduction.

[Hydrochemistry and Its Controlling Factors and Water Quality Assessment of Shallow Groundwater in the Weihe and Jinghe River Catchments].

The Weihe and Jinghe Rivers catchments are important tributaries of the Yellow River, where it is of great significance to evaluate groundwater hydrochemistry and quality for ecological protection and sustainable development. Piper diagrams, Gibbs, Na-normalized molar ratios, and ion correlation methods were used to analyze the chemical composition of groundwater in these two catchments. Furthermore, the WQI method, Wilcox diagrams, USSL diagrams, and Doneen diagrams were used to evaluate the suitability of groundwater quality for drinking and irrigation. The results showed that the Weihe and Jinghe River catchments are dominated by fresh and weakly alkaline water. Groundwater ion concentration in the Weihe River are higher than in Jinghe River except for Na+, and the major groundwater types are HCO3-Ca-Mg(accounted for 50%), and HCO3-Ca-Mg and HCO3-Na-K (accounted for 32.5%), respectively. The hydrochemistry of the Weihe and Jinghe River catchments is mainly controlled by rock weathering, primarily silicate weathering. Moreover, the groundwater chemistry in the research area is affected by mining and chemical fertilizer application for agriculture. Furthermore, the hydrochemistry of the Weihe River catchment is affected by cation exchange, although this was not obvious in some regions of the Jinghe River catchment. The overall groundwater quality of the two catchments was good, with the Jinghe River water quality being better than in the Weihe River catchment. Based on SSP, SAR, and PI, the groundwater in some parts of the study area cannot be directly used for irrigation as this would result in salinization and, thus, inhibit plant growth. Overall, the groundwater quality in the south of the study area is better than in the north, and is better in the Jinghe River catchment than in the Weihe River catchment according to these three indicators. This study provides a basis for the sustainable development of two catchments, providing baseline data for groundwater quality management.

[Hydrochemical and Isotopic Characteristics in the Shallow Groundwater of the Fenhe River Basin and Indicative Significance].

The Fenhe River basin is the second largest tributary of the Yellow River. Piper diagrams, Gibbs, PCA, correlation analysis and forward derivation modeling were used to analyze the distribution characteristics and the controlling factors of the groundwater chemistry and stable isotopes in the Fenhe River basin, which revealed the water cycle and water quality evolution process. The results indicated that the groundwater is a weakly alkaline, micro-hard water, the dominant anions and cations are HCO3- and Ca2+, the major groundwater types are Mg-Ca-HCO3 and Mg-Ca-Cl-SO4, the groundwater quality is good, and more than 94% of the samples belong to classes Ⅰ-Ⅲ. The average values of δD and δ18O of the Fenhe River groundwater are -70.2‰ and -9.6‰, which are similar to the isotope values of the precipitation from July to September, indicating that the groundwater may have originated from this period and that the groundwater recharge mode (dominant flow and piston flow) has a spatial variation. Rock weathering is the dominant source of ions in the groundwater, with an average contribution of 87%, while the contributions of atmospheric input and human activity are 8% and 5%, respectively. For rock weathering, silicate, evaporate, and carbonate rock contribute equally to the groundwater solutes, accounting for 32%, 28%, and 26%, respectively. The results of this study provide the basis for promoting the sustainable development and utilization of groundwater resources in the Fenhe River basin.

[Analysis of Hydrogen and Oxygen Stable Isotope Characteristics and Vapor Sources of Precipitation in the Guanzhong Plain].

To improve the understanding of hydrogen and oxygen stable isotope characteristics and vapor sources in the Guanzhong Plain, we collected 98 precipitation samples and corresponding meteorological data between 2015 and 2018 in Yangling, Shanxi Province, which is located in the central area of the Guanzhong Plain. The composition characteristics of the local hydrogen and oxygen stable isotopes of precipitation (δ2H, δ18O, and δ17O) and their environmental controls were analyzed, and the local meteoric water line (LMWL) and the meteoric water line of the triple oxygen isotopes were established. Three indicators (δ18O, d-excess, and 17O-excess) were used to explore the possible vapor sources of local precipitation and to quantify the contributions of ocean-source and inland-source water vapor to the precipitation. The results showed that there were obvious seasonal changes in the hydrogen and oxygen stable isotopes of precipitation in the Yangling area:water isotopes were depleted in the wet season (May to October) and enriched in the dry season (November to April of the next year). Both the slope (7.7) and intercept (9.1) of the LMWL were lower than those of the global meteoric water line (GMWL), indicating that the annual precipitation in the research area experienced variable degrees of secondary evaporation under cloud cover. The slope of the meteoric water line of the triple oxygen isotopes is 0.528, which is between that of seawater equilibrium fractionation (0.529) and water vapor diffusion into dry air (0.518), consistent with the fact that the Guanzhong area is located on the migration path of marine air mass to inland arid regions. Comprehensive analysis of δ18O, d-excess, and 17O-excess confirmed that the precipitation in the study area is jointly contributed to by the warm and humid air mass from the southeast monsoon and the dry and cold air mass from the westerly wind. Of these, approximately 55%-79% of the precipitation water vapor comes from the ocean, mainly in June to August, and about 21%-45% of the water vapor comes from inland and local evaporation, mainly from October to April. The water vapor sources of precipitation in May and September are complex and may intermittently originate from ocean and inland water vapor.

[Effects of extraction methods on soil water isotope and plant water source segmentation.] / æå–æ–¹æ³•å¯¹åœŸå£¤æ°´åŒä½ç´ å’Œæ¤ç‰©æ°´æºåˆ†å‰²çš„å½±å“.

We used two types of soil with different physicochemical properties (loam and sand), oven-dried them, and then added the known isotopic composition mineral water that was reference water to compose the soil-water mixture with different soil water contents (loam: 0.15, 0.20, 0.30 g·g-1; sand: 0.10 g·g-1). After that, we set up different equilibrium time (loam: 3, 6, 12, 24, 48, 72, 96 h; sand: 96 h) to ensure that the dry soil particles were well mixed with the added water. The soil water was extracted by mechanical centrifugation and cryogenic vacuum extraction after equilibrium, and their isotope composition was analyzed. Results showed that the isotopic values of soil water extracted by mechanical centrifugation method had no significant difference in same water content with different equilibration times, but were more enriched compared with the reference water isotopic value. The maximum enrichment for hydrogen and oxygen isotope was 7.38‰ and 1.24‰, respectively. In contrast, cryogenic vacuum extraction method resulted in more depleted soil water isotopes than reference water, with the maximum depletion for hydrogen and oxygen isotope being 6.27‰ and 1.03‰, respectively. Moreover, the degree of depletion increased with the increases of equilibrium time (less than 24 h) at low water content, and became stable after 24 h. With the increases of soil water content, the isotopic composition of the extracted soil water was less affected by the two extraction methods. The water isotope value of loam that had high clay content, was more sensitive to the extraction method than the sandy soil that had low clay content. The difference of isotopic composition caused by extraction methods did not affect the plant water source segmentation.

[Profile Distribution of Soil Organic and Inorganic Carbon Under Different Land Use Types in the Loess Plateau of Northern Shaanxi].

Carbon storage in the Loess Plateau is affected by land use. In order to assess the differences in soil organic carbon (SOC) and soil inorganic carbon (SIC) under different land use patterns in deep soil profiles, we investigated the distribution characteristics of SOC and SIC at 0-20.0 m soil depth at three locations in the northern Shaanxi province (i.e., an economical plantation in Mizhi, a reforestation area in Shenmu, and a wind break and sand fixation forest district in Yuyang). The results showed that the order for SOC content was:pruning jujube tree (2.00 g·kg-1) > jujube tree (1.54 g·kg-1) > Caragana (0.97 g·kg-1) > degraded artificial grassland (0.81 g·kg-1) > pine forests (0.70 g·kg-1) > natural grass field (0.45 g·kg-1), which indicated significant differences between SOC content and land use types (P<0.05). Similarly, the order of SIC content was:pruning jujube tree (11.66 g·kg-1) > jujube tree (11.59 g·kg-1) > Caragana (9.62 g·kg-1) > degraded artificial grassland (8.07 g·kg-1) > pine forests (4.32 g·kg-1) > natural grass field (0.47 g·kg-1). There were no significant differences between SIC content and soil profiles under the economical plantation of Mizhi and the reforestation area of Shenmu. There were significant differences for SIC content between an artificial economic forest, an area returning farmland to a forest (grass) profile, and a windbreak and sand fixation forest (P<0.05). The SIC densities for pruning jujube tree, jujube tree, Caragana, degraded artificial grassland, pine forest, and natural grass field were 6.19, 7.71, 10.70, 10.78, 5.91, and 1.03 times that of its corresponding SOC density, respectively. It has been concluded that the soil carbon storage was significantly different for different land use patterns, and the SIC content was much higher than the SOC content in the soil profile.

[Effects of land use types on deep soil water content in the loess hilly area of the north Shaanxi Province, China]. / 黄土丘陵区不同土地利用模式对深层土壤含水量的影响.

This study explored the differences of soil water content at 0-20 m soil depth at three locations, including economical plantation in Mizhi, reforestation area in Shenmu, and wind break and sand fixation forest district of Yuyang, and for clarifying the impacts of different land use types on deep soil water distribution and storage characterization, as well as its eco-environmental effect on the loess hilly area. The results showed that in the soil profile of 0-20 m, land use patterns had a significant impact on soil moisture distribution. There were significant differences of soil water sto-rage for the economical plantation, pruning Ziziphus jujuba plantation ＞ Z. jujuba plantation with 587.9 mm difference. There was no significant difference in soil water storage between Caragana korshinskii plantation and degraded artificial vegetation or between pine forests and natural grass field, degraded artificial grassland ＞ C. korshinskii plantation with 98.8 mm difference at Shenmu, and natural grassland ＞ Pinus sylvestris var. mongolica plantation with 7.5 mm difference at Yuyang. The pruning Z. jujuba tree reduced soil water consumption and was beneficial to sustainable use of soil water due to the decreased crown width and thus reduced transpiration. There were no obvious differences of soil water content between C. korshinskii plantation and degraded artificial grassland due to the historical alfalfa planting which was characterized by high water consumption due to its deep root distribution and large biomass. In contrast, P. sylvestris var. mongolica plantation and na-tural grassland had similar and low averaged soil water contents with 3.4% and 3.6%, respectively, mainly due to the sandy soil texture and weak soil water holding capacity. In addition, with increa-sing soil depth, soil water content increased in this area, indicating the effect of plants on water moisture of deep soil was very limited. Except for the underlying control of soil texture on soil water content in the soil profile, different vegetation played a key role in the dynamics of soil water content due to the difference of root zones. It was very important to choose the suitable type of vegetation regarding the protection and sustainable use of deep soil water.

A user-friendly modified pore-solid fractal model.

The primary objective of this study was to evaluate a range of calculation points on water retention curves (WRC) instead of the singularity point at air-entry suction in the pore-solid fractal (PSF) model, which additionally considered the hysteresis effect based on the PSF theory. The modified pore-solid fractal (M-PSF) model was tested using 26 soil samples from Yangling on the Loess Plateau in China and 54 soil samples from the Unsaturated Soil Hydraulic Database. The derivation results showed that the M-PSF model is user-friendly and flexible for a wide range of calculation point options. This model theoretically describes the primary differences between the soil moisture desorption and the adsorption processes by the fractal dimensions. The M-PSF model demonstrated good performance particularly at the calculation points corresponding to the suctions from 100 cm to 1000 cm. Furthermore, the M-PSF model, used the fractal dimension of the particle size distribution, exhibited an accepted performance of WRC predictions for different textured soils when the suction values were ≥100 cm. To fully understand the function of hysteresis in the PSF theory, the role of allowable and accessible pores must be examined.

Measuring solid percentage of oil sands mature fine tailings using the dual probe heat pulse method.

The reclamation of mature fine tailings (MFT) is a critical challenge for the oil sands industry in western Canada, and a nonradioactive, automated, and inexpensive method to monitor the MFT solidification is needed. The objective of this paper is to evaluate the feasibility of a dual-probe heat pulse (DPHP) method to measure MFT solid percentage. Dual-probe heat pulse measurements were performed on three MFT samples, each at various solid percentages. A linear relationship ( = 0.9495 + 0.0558) was established between the DPHP-measured solid percentage () and that of oven-dry method (). Six additional MFT samples were collected and measured to validate the DPHP method. The specific heats of the six MFT solids were measured independently using a modulated differential scanning calorimetry method, and the sensitivity of DPHP-measured MFT solid percentage to the specific heat of MFT solids was evaluated. The result shows that the DPHP method can be used to accurately measure MFT solid percentages, and the accuracy can be further improved if the specific heat of the MFT solids is measured independently.

Wetting properties of fungi mycelium alter soil infiltration and soil water repellency in a γ-sterilized wettable and repellent soil.

Soil water repellency (SWR) has a drastic impact on soil quality resulting in reduced infiltration, increased runoff, increased leaching, reduced plant growth, and increased soil erosion. One of the causes of SWR is hydrophobic fungal structures and exudates that change the soil-water relationship. The objective of this study was to determine whether SWR and infiltration could be manipulated through inoculation with fungi. The effect of fungi on SWR was investigated through inoculation of three fungal strains (hydrophilic -Fusarium proliferatum, chrono-amphiphilic -Trichoderma harzianum, and hydrophobic -Alternaria sp.) on a water repellent soil (WR-soil) and a wettable soil (W-soil). The change in SWR and infiltration was assessed by the water repellency index and cumulative infiltration respectively. F. proliferatum decreased the SWR on WR-soil and slightly increased SWR in W-soil, while Alternaria sp. increased SWR in both the W-soil and the WR-soil. Conversely T. harzianum increased the SWR in the W-soil and decreased the SWR in the WR-soil. All strains showed a decrease in infiltration in W-soil, while only the F. proliferatum and T. harzianum strain showed improvement in infiltration in the WR-soil. The ability of fungi to alter the SWR and enmesh soil particles results in changes to the infiltration dynamics in soil.

A novel method for identifying hydrophobicity on fungal surfaces.

Fungal surface hydrophobicity has many ecological functions and water contact angles measurement is a direct and simple approach for its characterization. The objective of this study was to evaluate if in-vitro growth conditions coupled with versatile image analysis allows for more accurate fungal contact angle measurements. Fungal cultures were grown on agar slide media and contact angles were measured utilizing a modified microscope and digital camera setup. Advanced imaging software was adopted for contact angle determination. Contact angles were observed in hydrophobic, hydrophilic and a newly created chronoamphiphilic class containing fungi taxa with changing surface hydrophobicity. Previous methods are unable to detect slight changes in hydrophobicity, which provide vital information of hydrophobicity expression patterns. Our method allows for easy and efficient characterization of hydrophobicity, minimizing disturbance to cultures and quantifying subtle variation in hydrophobicity.