Search Results (39)

Water use strategies reflect the ability of plants to adapt to drought caused by climate change. However, how these strategies change with stand development and seasonal drought is not fully understood. This study used stable isotope techniques (δD, δ¹⁸O, and δ¹³C) combined with the MixSIAR model to quantify the seasonal changes in water use sources and water use efficiency (WUE) of Eucalyptus urophylla S.T.Blake × E. grandis (E. urophylla × E. grandis) at four stand ages (2-, 4-, 9- and 14-year-old) and to identify their influencing factors. Our results showed that the young (2-year-old) and middle-aged (4-year-old) stands primarily relied on shallow soil water throughout the growing season due to the limitations of a shallow root system. In contrast, the mature (9-year-old) and overmature (14-year-old) stands, influenced by the synergistic effects of larger and deeper root systems and relative extractable water (REW), exhibited more flexibility in water use, mainly relying on shallow soil water in wet months, but shifting to using middle and deep soil layer water in dry months, and quickly returning to mainly using shallow soil water in the episodic wet month of the dry season. The WUE of E. urophylla × E. grandis was affected by the combined effect of air temperature (T), vapor pressure deficit (VPD), and REW. WUE was consistent across the stand ages in the wet season but decreased significantly with stand age in the dry season. This suggests that mature and overmature stands depend more on shifting their water source, while young and middle-aged stands rely more on enhanced WUE to cope with seasonal drought stress, resulting in young and middle-aged stands being more vulnerable to drought stress. These findings offer valuable insights for managing water resources in eucalyptus plantations, particularly as drought frequency and intensity continue to rise. Full article

In comparison with conventional hydrological parameters such as water levels and temperatures, geochemical changes induced by earthquakes have become increasingly important. It should be noted that hydrogen (δ²H) and oxygen isotopes (δ¹⁸O) offer the greatest potential as precursor proxies of earthquakes. Here, we conducted high-resolution sampling (weekly, 59 samples), measuring consecutive δ²H and δ¹⁸O levels at the two sites of the WLY well and SS spring in the Yan-Huai Basin of Beijing from June 2021 to June 2022. During the period of this sampling, several small earthquakes of ML > 1.6 occurred in Beijing. We used statistical methods (analysis of variance) to test the significant differences, used Self-Organizing Maps (SOMs) for data clustering, and then used Bayesian Mixing Models (MixSIAR) to calculate the proportions of the source contributions. We found significant four-stage patterns of change processes in δ²H and δ¹⁸O at both sites. The WLY well exhibited a distinct four-stage variation pattern: initial stable development (WT1) followed by a rapid rise (WT2) and sudden fall (WT3) before the small earthquakes, and finally gradual stabilization after earthquakes (WT4). In contrast, the SS spring displayed an inverse pattern, beginning with stable development (ST1), then undergoing a rapid falling (ST2) and sudden rising (ST3) before the small earthquakes, and finally stabilizing through stepwise reduction after the earthquakes (ST4). The most likely mechanisms were differences in the time of rupture between the carbonate in WLY and granite in SS under sustained stress. The stress induced source mixing of fluid from the surface or deeper groundwater-source reservoirs. The hypothesis was supported by the MixSIAR model, calculating the variational proportion of source contributions in the four stages. This work permitted the use of high-resolution isotopic data for statistical confirmation of concomitant shifts during the earthquakes, provided the mechanisms behind them, and highlighted the potential for the consecutive monitoring of hydrogen and oxygen isotopes indicators in earthquake-prediction studies. Full article

Nitrate (NO₃⁻) pollution resulting from anthropogenic activities represents one of the most prevalent environmental issues in karst spring catchments of northern China. In June 2021, a comprehensive study was conducted in the Jinan Spring Catchment (JSC), where 30 groundwater and surface water samples were collected. The sources and spatial distribution of nitrate pollution were systematically investigated through hydrochemical analysis combined with dual-isotope tracing techniques (δ¹⁵N_NO3 and δ¹⁸O_NO3). Analytical results revealed that the predominant anion and cation sequences were HCO₃⁻ > SO₄²⁻ > Cl⁻ > NO₃⁻ and Ca²⁺ > Na⁺ > Mg²⁺ > K⁺, respectively, with HCO₃·SO₄-Ca identified as the primary hydrochemical type. Notably, the average NO₃⁻ concentration in groundwater (46.62 mg/L) significantly exceeded that in surface water (4.96 mg/L). Among the water samples, 11 locations exhibited substantial nitrate pollution, demonstrating an exceedance rate of 42%. Particularly, the NO₃⁻-N concentrations in both the upstream recharge area and downstream drainage area were markedly higher than those in the runoff area. The spatial distribution of NO₃⁻ concentrations was primarily influenced by mixing processes, with no significant evidence of denitrification observed. The isotopic compositions ranged from −1.42‰ to 12.79‰ for δ¹⁵N_NO3 and 0.50‰ to 15.63‰ for δ¹⁸O_NO3. Bayesian isotope mixing model (MixSIAR) analysis indicated that domestic sewage and manure constituted the principal nitrate sources, contributing 37.1% and 56.9% to groundwater and surface water, respectively. Secondary sources included soil organic nitrogen, rainfall and fertilizer NH₄⁺, and chemical fertilizers, while atmospheric deposition showed the lowest contribution rate. Additionally, potential mixing of soil organic nitrogen with chemical fertilizer was identified. Full article

Nitrate contamination poses a significant global environmental threat, impacting the water quality in surface and groundwater systems. Despite its considerable impact, there remains a lack of comprehensive understanding of nitrate sources and discharge patterns, particularly in the Lake Victoria basin of East Africa. To address this gap, a study was conducted in the Kagera River basin, responsible for 33% of Lake Victoria’s surface inflow. This study utilized δ¹⁵N and δ¹⁸O isotope analysis in nitrate, hydrochemistry, and the Bayesian mixing model (MixSIAR) to identify and quantify nitrate sources. Spatiotemporal data were collected across three seasons: long rains, dry season, and short rains, in areas with diverse land uses. Nitrate isotopic data from water and potential sources were integrated into a Bayesian mixing model to determine the relative contributions of various nitrate sources. Notable spatial variations were observed at sampling sites with concentrations ranging from 0.004 to 3.31 mg L⁻¹. Spatially and temporally, δ¹⁵N-NO₃⁻ values ranged from +6.0% to +10.2‰, whereas δ¹⁸O-NO₃⁻ displayed significant spatial differences with mean ranges from −1% to +7‰. MixSIAR analysis revealed important contributions from manure and sewage sources ranging between 49% and 73%. A boron analysis revealed manure was the main source of nitrates in the manure and sewage. These results show that it is necessary to implement improved manure and sewage management practices, especially through proper waste treatment and disposal systems, to enable informed policy decisions to enhance nitrogen management strategies in riparian East Africa, and to safeguard the region’s water resources and ecosystems. Full article

To explain one of the reasons why two adjacent deep-rooted desert plants can coexist over long periods, mutual water supply between species was investigated. The study focused on δD and δ¹⁸O stable isotopic characteristics of root water and soil water near the roots of Tamarix ramosissima Ledeb. and Alhagi sparsifolia Shap. in the Tarim River Basin in China during the growing season. The direct comparison method and the Mix SIAR model were employed to analyze the water sources of the plants and the contribution rates of each water source. A similarity proportional index was used to assess the hydraulic connections between plant species. The water sources of T. ramosissima and A. sparsifolia were soil water found at depths of 40 to 90 cm and 220 to 300 cm (a total contribution rate of 58.85%) and 130 to 190 and 240 to 300 cm (a total contribution rate of 81.35%) with groundwater depths of 2.5 to 3.0 m, respectively. When the groundwater depth increased to 4 m, the water sources for both T. ramosissima and A. sparsifolia were soil water at depths of 20 to 100 (a contribution rate of 70.60%) and 20 to 120 cm (a contribution rate of 49.60%), respectively. Both A. sparsifolia and T. ramosissima could lift water from deep soil or groundwater for their own growth needs and supply some water to each other, which suggests that desert plants were allowed to achieve mutual benefits and coexistence through hydraulic connections. These results enrich the theoretical understanding of desert plant coexistence and provide a scientific basis for desert vegetation restoration. Full article

Phosphorus is the primary contributor to eutrophication in water bodies, and identifying phosphorus sources in rivers is crucial for controlling phosphorus pollution and subsequent eutrophication. Although phosphate oxygen isotopes (δ¹⁸O_P) have the capacity to trace phosphorus sources and cycling in water and sediments, they have not been used in small- to medium-sized watersheds, such as the Xiaodongjiang River (XDJ), which is located in an agricultural watershed, source–complex region of southern China. This study employed phosphate oxygen isotope techniques in combination with a land-use-based mixed end-member model and the MixSIAR Bayesian mixing model to quantitatively determine potential phosphorus sources in surface water and sediments. The δ¹⁸O_P values of the surface water ranged from 5.72‰ to 15.02‰, while those of sediment ranged from 10.41‰ to 16.80‰. In the downstream section, the δ¹⁸O_P values of the surface water and sediment were similar, suggesting that phosphate in the downstream water was primarily influenced by endogenous sediment control. The results of the land-use–source mixing model and Bayesian model framework demonstrated that controlling phosphorus inputs from fertilizers is essential for reducing phosphorus emissions in the XDJ watershed. Furthermore, ongoing rural sewage treatment, manure management, and the resource utilization of aquaculture substrates contributed to reduced phosphorus pollution. This study showed that isotope techniques, combined with multi-model approaches, effectively assessed phosphorus sources in complex watersheds, offering a theoretical basis for phosphorus pollution management to prevent eutrophication. Full article

Riparian zones, acting as transitional areas between aquatic and terrestrial ecosystems, boast a rich diversity of plant species. However, alterations in river hydrological regimes can significantly impact plant growth and distribution. In this study, seven typical reaches of Yongding River Basin were selected, and xylem water, soil water at different depths, and river water were collected in May and August. By measuring δ²H and δ¹⁸O values and combining with MixSIAR model, the proportion of water utilization by plants from different sources was quantified. The findings revealed that δ²H and δ¹⁸O values of river water, soil water, and plant xylem water were higher in August compared to May. While there was no significant difference in δ²H and δ¹⁸O values between river and soil water during different periods (p > 0.05), significant differences were observed in δ¹⁸O in plant xylem water (p = 0.022). Regardless of whether it was May or August, herbaceous plants utilized river water more extensively than trees and shrubs, and hydrophytes exhibited a higher dependence on river water compared to mesophytes and xerophytes. Some hygrophytes (P. anserina, etc.) utilized river water for over 90% of their total water intake. There were significant differences between herbs and trees and shrubs in the proportion of river water usage in August (p = 0.001). Moreover, considerable variations existed in the proportion of river water usage among different water ecotypes in both May (p = 0.005) and August (p < 0.001). Our findings provide a scientific basis for the rational allocation of plants in the process of riparian vegetation restoration. Full article

The Gobi Desert is one of the harsh terrestrial ecosystems distributed on the Mongolian Plateau and northwest China. Water is the key restricting environmental factor for the Gobi Desert plants’ growth. Exploring the annual dynamic of water sources for the vulnerable plants in the Gobi Desert helps to understand their adaptation to the arid climate and is fundamental for their conservation, e.g., the vulnerable plant Ammopiptanthus mongolicus (Maxim. ex Kom.) S. H. Cheng. The water source of the dominant and companion shrubs in a Gobi Desert A. mongolicus community was determined by comparing the δD and δ¹⁸O values of their xylem water and different layers of soil water using the MixSIAR model from spring to autumn over two years. The results showed that A. mongolicus mainly utilized 50–150 cm of middle and deep soil water. However, it also used 10 or 25 cm of surface soil water after heavy rains in the early spring and moderate rains in the autumn of 2021 and after heavy rains in the summer of 2022. Three companion shrubs (Nitraria sphaerocarpa Maxim, Caragana korshinskii Kom, and Convolvulus tragacanthoides Turcz.) had similar main water sources, competing for relatively reliable deep soil water with the dominant A. mongolicus during droughts in 2021 and 2022. Moreover, A. mongolicus utilized more deep soil water in 2021 with less rain. However, C. tragacanthoides used more shallow soil water during the growing season of 2022 with more rain. Therefore, four xerophytic shrubs in the A. mongolicus community utilized soil water in different layers based on their ability to adapt to the annual fluctuation of rain in the Gobi Desert. Full article

Water resources are crucial factors that limit vegetation recovery, and rational planning of silvicultural patterns is essential for the efficient utilization of water in arid and semi-arid regions. This study examined the water utilization strategies of pure shrubs (pure stands of Artemisia ordosica and pure stands of Salix psammophila) and mixed shrubs (mixed stands of A. ordosica S. psammophila, and mixed stands of A. ordosica Caragana korshinskii) from the rainy to dry seasons using stable isotope techniques and MixSIAR modeling in the Mu Us Sandy Land in the semi-arid region of China. Mixed shrubs were significantly more effective than pure shrubs in utilizing the primary water sypply from the soil layer. During the rainy season in August, shallow soil water was used to a greater extent, contributing 33.78 ± 2.18%, with no significant difference in the contribution proportion. After a brief drought during the transition period in September, there was a significant increase in the use of the primary water-absorbing soil layer across all vegetation types, with a maximum increase of 39.53%. Conversely, during the dry season in October, after an extended drought, the contribution of the primary water supply layer to vegetation water absorption decreased compared with the transition period, with a maximum increase of only 17.88%. The results of this study revealed that variations in water conditions and vegetation configurations influence the water utilization patterns of the vegetation. This study offers a scientific basis and theoretical support for understanding ecological water use, the rationale behind vegetation establishment, and an assessment of plantation community stability in sandy regions. Full article

Nitrate is among the most widely occurring contaminants in groundwater on a global scale, posing a serious threat to drinking water supplies. With the advancement of urbanization and mountainous agriculture, the nitrate in the groundwater of Wanzhou District in the Three Gorges Reservoir Area has formed a complex combination of pollution sources. To more accurately identify the sources of nitrate in groundwater, this study integrates hydrochemical methods and environmental isotope techniques to analyze the sources and transformation processes in shallow groundwater nitrate under different land-use types. Furthermore, the Bayesian isotope mixing model (MixSAIR) is employed to calculate the contribution rates in various nitrate sources. The results indicate that nitrate is the primary form of inorganic nitrogen in shallow groundwater within the study area, with nitrate concentrations in cultivated groundwater generally higher than those in construction land and forest land. The transformation process of nitrate is predominantly nitrification, with little to no denitrification observed. In cultivated shallow groundwater, nitrate mainly originates from chemical fertilizers (36.3%), sewage and manure (35.4%), and soil organic nitrogen (24.7%); in forested areas, nitrate primarily comes from atmospheric precipitation (35.3%), chemical fertilizers (31.3%), and soil organic nitrogen (22.1%); while in constructed areas, nitrate mainly derives from chemical fertilizers (46.0%) and sewage and manure (32.2%). These results establish a scientific foundation for formulating groundwater pollution control and management strategies in the region and serve as a reference for identifying nitrate sources in groundwater in regions with comparable hydrogeological features and pollution profiles. Full article

Air pollution can induce diseases and increase the risks of death, and it also has close links with climate change. Carbonaceous matter is an important component of aerosols, but studies quantifying the source apportionment of carbonaceous compositions in different-sized aerosols from a stable carbon isotopic perspective remain scarce. In this study, fine (particulate size < 2.5 μm) and coarse (particulate size 2.5~10 μm) particles were collected from December 2021 to February 2022 (winter) and from June to August 2022 (summer) in the tropical city of Haikou; the concentrations of water-soluble inorganic ions (WSIIs) and total carbonaceous matter (TC) and the stable carbon isotope of TC (δ¹³C-TC) values in both fine and coarse particles were analyzed. Higher concentrations of TC, SO₄²⁻, NO₃⁻, and NH₄⁺ but lower δ¹³C-TC values in fine particles than those in coarse particles in both winter and summer indicated that combustion-related emissions dominate fine particulate TC sources. The δ¹³C-TC values coupled with the stable isotope mixing model in R (SIAR) results showed that combustion-related emissions contributed 77.5% and 76.6% to the TC of fine particles in winter and summer, respectively. Additionally, the lowest δ¹³C-TC values were observed in summertime fine particles; plant physiological activity was identified as an important source of fine particulate TC in summer and contributed 12.4% to fine particulate TC. For coarse particles, higher δ¹³C-TC values and Ca²⁺ and Na⁺ concentrations but lower TC concentrations implied significant contributions from natural emissions (29.2% in winter and 44.3% in summer) to coarse particulate TC. This study underscores that instead of fossil fuels and biomass, clean energy can decrease 45–78% of aerosol TC at Haikou. In addition, our results also provide a dataset for making environmental policy and optimizing the energy structure, which further favors the sustainable development of air quality. Full article

The South China Sea (SCS) is a crucial region for studying atmospheric aerosols, given its unique geographical location and the interaction of various natural and anthropogenic sources. In this study, we measured the isotopic characteristics of sulfate and nitrate in PM_2.5 and utilized a Bayesian isotope mixing model (SIAR) to analyze their sources and formation pathways. Sulfur isotopic values in sulfate (δ³⁴S-SO₄²⁻) were 8.7 ± 1.8‰, while nitrogen and oxygen isotopic values in nitrate (δ¹⁵N-NO₃⁻ and δ¹⁸O-NO₃⁻) were −0.9 ± 2.4‰ and 52.3 ± 7.3‰, respectively. The results revealed that sulfate was primarily influenced by marine biogenic sulfur emissions (mostly dimethyl sulfide, DMS), fossil fuel combustion, and biomass burning. Nitrate formation was dominated by the NO₂ + •OH pathway (accounting for 69.8–85.7%), with significant contributions from vehicle emissions, biomass burning, and lightning. These findings offer key insights into the complex interactions between natural and anthropogenic aerosol sources in the SCS, contributing to a broader understanding of marine aerosol chemistry. Full article

Elucidating the water utilization strategy of trees during forest succession is a prerequisite for predicting the direction of forest succession. However, the water utilization characteristics of trees in forests across a successional gradient remain unclear. Here, we utilized the hydrogen and oxygen stable isotopes combined with the Bayesian mixed model (MixSIAR) to analyze the water utilization of dominant trees (Pinus massoniana, Castanea henryi, and Schima superba) in forests along a successional gradient in the Dinghushan Biosphere Reserve of China. Furthermore, we determined the primary factor affecting the water utilization of various trees based on variation partitioning analysis and a random forest model. Our results illustrated that in the early-successional forest, the water utilization ratios from shallow soil layers by P. massoniana were significantly lower than that in the mid-successional forest (51.3%–61.7% vs. 75.3%–81.4%), while its water utilization ratios from deep soil layers exhibited the opposite pattern (26.1%–30.1% vs. 9.0%–15.0%). Similarly, the ratios of water utilization from shallow soil layers by C. henryi (18.9%–29.5% vs. 32.4%–45.9%) and S. superba (10.0%–25.7% vs. 29.2%–66.4%) in the mid-successional forest were relatively lower than in the late-successional forest, whereas their water utilization ratios from deep soil layers showed the contrary tendency. Moreover, our results demonstrated that the diverse water utilization of each tree in different successional forests was mainly attributed to their distinct plant properties. Our findings highlight the increased percentage of water utilization of trees from shallow soil layers with forest succession, providing new insights for predicting the direction of forest succession under changing environments. Full article

Nitrate pollution is a major environmental problem threatening rivers, and nitrogen and oxygen isotopes have proved to be an effective means of analyzing the sources and transformations of nitrate in rivers. However, a low monitoring frequency cannot accurately reflect the changes in nitrate. In this study, the sources and transformations of nitrate in the middle reaches of the Yellow River and its tributaries during the dry season and the wet season were analyzed based on water quality parameters and nitrate isotopes. Stable isotope analysis conducted using the R (SIAR) model was used to estimate the proportions of different nitrate sources. The results showed that the main nitrate sources in the main stream were soil nitrogen (40.95–45.83%) and domestic sewage and manure (30.93–32.60%), respectively, with little variation between the dry season and wet season because of the large flow of the Yellow River. During the dry season, the nitrate sources of the two tributaries were mainly domestic sewage and manure (45.23–47.40%), followed by soil nitrogen (31.35–34.00%). However, the primary nitrate source of T2 (Qin River) became soil nitrogen (40.05%) during the wet season, a phenomenon that was mainly caused by the significant increase in river discharge and in soil erosion in the basin. During the wet season, the concentrations of total nitrogen (TN) and nitrate (NO₃⁻) significantly decreased in the main stream and tributaries, and nitrification and denitrification processes occurred in both the main stream and tributaries of the Yellow River. In addition, the T2 tributary (Qin River) was also significantly affected by mixed dilution. High-frequency sampling can reflect the isotopic information of nitrate in the river more comprehensively, which helps us to understand the conversion process of nitrate more accurately. Full article

One of the crucial challenges of our time is climate change. The consequences of rising sea levels and drought greatly impact water resources, potentially worsening seawater intrusion. Characterizing coastal aquifers is an essential step in devising strategies to address these phenomena. Seawater intrusion poses a critical socio-economic and environmental issue in the coastal plain of Muravera, southeastern Sardinia (Italy). This coastal plain is an important agricultural area in Sardinia, and the health of the crops is compromised by the increasing salinization of shallow groundwater. To enhance our understanding of the hydrogeological conceptual model, which is essential for a sustainable resource management system, hydrogeological investigations were conducted and complemented by the chemical and multi-isotopic analyses of groundwater. The main objectives of this study were to identify groundwater recharge areas, understand salinization mechanisms and trace the evolution of water chemistry. Within this framework, a monthly survey monitoring piezometric level and electrical conductivity was carried out for one year. This survey was integrated with chemical and isotope analyses, including δ¹⁸O_H2O and δ²H_H2O, δ¹¹B, δ¹⁸O_SO4, δ³⁴S_SO4, and ⁸⁷Sr/⁸⁶Sr. Hydrochemistry analysis results revealed the occurrence of seawater–freshwater mixing, extending up to 4 km inland. H₂O isotope analysis confirmed the mixing processes and indicated the meteoric origin of recharge waters for both shallow and semi-confined aquifers. The strontium isotopes ratio facilitated the identification of four main groundwater flow paths, confirmed by the SIAR model. The results of this combined hydrogeological–geochemical–isotopic survey provide essential elements for the future implementation of an integrated and sustainable management system. These findings enable interventions to slow the process of seawater intrusion and meet the economic needs for the development of local communities. Full article