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The complex relationships within desert ecosystems and their environmental conditions are reflected in patterns of plant water use. Thus, understanding the sources of water used by plants in these areas is crucial for effective resource management. In this study, we investigated the water use pattern of Haloxylon ammodendron in Semnan province, in the central plateau of Iran, using the stable isotope analysis. We employed a simple, homemade cryogenic vacuum distillation (CVD) system to directly extract water from soil samples and different plant components for subsequent analysis by mass spectrometer. The contribution of each possible water source to the plant xylem water was estimated using the IsoSource mixing model. The pattern of δ 18O values in the xylem water of H. ammodendron indicated its reliance on groundwater as a primary water resource during the wet season. Additionally, the correlation of sand particles with both δ2H and δ18O was found to be 0.32. Moreover, the δ 18O values of H. ammodendron xylem water were mainly similar to those of groundwater, suggesting the species' dominant use of groundwater. The findings of this study provide valuable insights for strategically planting H. ammodendron to mitigate impacts on groundwater resources and ensure long-term sustainability in arid and semi-arid regions. [ABSTRACT FROM AUTHOR]

In this study, three typical plants capable of restoring in the Heidaigou open-pit mine dump, namely, Pinus sylvestris var. mongolica, Caragana korshinskii, and Medicago sativa, were taken as the research objects. The δ2H and δ18O values of atmospheric precipitation, soil water, stem water, and leaf water were measured using the stable isotope technique, and the distribution characteristics of the δ2H and δ18O values of different water sources were identified. The IsoSource model (version1.3.1) was used to calculate the contribution rate of different water sources to the plants, and the differences and dynamic changes in the water sources for P. sylvestris var. mongolica, C. korshinskii, and M. sativa during the rainy season were examined. Results showed that the water source of the three plants was found to be mainly soil water, and the utilization of each potential water source varied in different periods of the rainy season. In June, when SWC was sufficient, P. sylvestris var. mongolica and M. sativa primarily absorbed and utilized shallow and middle soil water, with relative utilization ratios of 55.5% and 59%, respectively, while C. korshinskii has a more balanced utilization ratio of soil water in each layer, with shallow soil water utilization at 33.7%, middle soil water at 34.2%, and deep soil water at 32.2%. In August, when SWC decreased, P. sylvestris var. mongolica, C. korshinskii, and M. sativa were all transferred to deep soil water, with utilization ratios of 75.8%, 78.8%, and 71.1%, respectively. The values showed that these three typical plants are capable of restoring can respond to external water changes through the plastic transformation of water absorption sources. Among them, C. korshinskii can flexibly use soil water in each layer, has stronger survival competitiveness in drought, and can better adapt to the fragile ecological environment of a mining dump. [ABSTRACT FROM AUTHOR]

Understanding water absorption mechanisms of sand-fixing plants is important for the rational establishment of plant community structures, thereby providing a scientific basis for desertification control and the efficient utilization of water resources in sandy areas. Based on the hydrogen and oxygen isotopic compositions of precipitation, soil water, xylem water, and groundwater, coupled with soil water-heat dynamics, annual water consumption characteristics of vegetation, using the multi-source linear mixing model (IsoSource), we analyzed the differences in water sources between Salix psammophila and Artemisia ordosica, during winter and the growing season. We further examined the effects of groundwater depth (2 m and 10 m), soil freezing-thawing, and drought on their water utilization to elucidate water absorption mechanisms of those species. The results showed that: 1) During soil freezing-thawing period (January to March), S. psammophila mainly utilized soil water in 60-120 cm depths below the frozen layer (69.1%). In the green-up season (April and May), soil water from the 0-60 cm layers could satisfy the water demand of S. psammophila ( 30.9%-87.6%). During the dry period of the growing season (June), it predominantly utilized soil water at the depth of 120-160 cm (27.4%-40.8%). Over the rainy season (July and September), soil water in 0-60 cm depths provided 59.8%-67.9% of the total water required. A. ordosica, with shallow roots, could not utilize soil water after complete freezing of root zone but could overwinter by storing water in rhizomes during autumn. During the growing season, it primarily relied on 0-40 cm soil layer (23.4%-86.8%). During the dry period, it mainly utilized soil water from 40-80 cm and 80-160 cm soil layers, with utilization rates of 14.6%-74.4% and 21.8%-78.2%, respectively. 2) With decreasing groundwater depth, vegetation shifted its water absorption depth upward, with water source of S. psammophila transitioning from 120-160 cm to 60-160 cm layers, while A. ordosica shifted water absorption depth from 80-160 cm to 0-40 cm. S. psammophila' s utilization of soil water is influenced by transpiration, adopting an "on-demand" approach to achieve a balance between water supply and energy conservation, whereas A. ordosica tends to utilize shallow soil water, exhibiting a higher dependence on water sources from a single soil layer. [ABSTRACT FROM AUTHOR]

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To study the contribution of moisture from different straw-treated and irrigated soil layers to the water consumption of winter wheat in dry farming, a 2-year straw treatment and regulated deficit irrigation experiment was implemented. The field experiment was carried out with 0% (S0), 1% (S1), and 2% (S2) straw returning amounts, and 75 mm (V3), 60 mm (V2), and 45 mm (V1) irrigation volumes. This experiment involved nine treatments, used to quantitatively analyze the ratio and variation of soil water use from different soil layers via the direct contrast method (DCM) and the multiple linear mixed model (MLMM). The results show the following: (1) The distribution of precipitation isotope compositions displayed a repeated trend of first decreasing and then increasing during the study period. Regression analysis showed that the local meteoric water line (LMWL): δD = 6.37δ18O − 3.77 (R2 = 0.832). (2) With increasing soil depth, the δ18O value decreased gradually, and the maximum δ18O value of the soil water within each growth period was distributed at 10 cm. (3) Under the same irrigation amount, δ 18O increased with increasing straw return at 0–20 cm and decreased with increasing straw return at 20–80 cm. (4) The comparison results of the DCM and MLMM were consistent. During the jointing and flowering stages, 0–30 cm soil water was the main source of water for winter wheat. The contribution of soil water below 30 cm had a decreasing trend from the jointing stage to the flowering stage. The average contribution rates of the 0–30 cm soil layer during the jointing and flowering stages were 23.07% and 23.15%, respectively. These findings have important implications for studying the soil water cycle in the context of farming. [ABSTRACT FROM AUTHOR]

Accurate identification of nitrate (NO3−) sources is critical to addressing groundwater pollution, especially in highly vulnerable karst aquifers. The groundwater hydrochemistry and δ15NNO3 and δ18ONO3 isotopes were analyzed in samples taken from the Jinan Spring Catchment, which has been affected by urbanization and agricultural activities. The study highlighted the use of hydrochemistry, environmental isotopes, and a multisource linear mixed model for NO3− source identification and apportionment. The results showed that, controlled by carbonate rocks, the hydrochemical types in both rainy and dry seasons were highly consistent, and HCO3·SO4−Ca was the dominant type, accounting for 60%. Except for Ca2+, Mg2+ and HCO3−, the coefficients of variation of other ions were all greater than 0.5 in rainy and dry seasons. The chemical composition of groundwater was mainly controlled by water–rock interaction. Ca2+ and HCO3− were mainly derived from carbonate rock dissolution; K+, Na+, SO42−, NO3− and Cl− were partially derived from atmospheric precipitation. The IsoSource model quantitatively revealed that the majority of the groundwater and surface water was influenced by manure and sewage (M&S) contributing 39.3% and 52.3% in the rainy season, and 37.1% and 56.9% in the dry season, respectively. The NO3− source fraction rates were in the order M&S > SON > AF > CF > AD. In addition, nitrate pollution control measures and suggestions for different areas are put forward. In rural residential areas, the free discharge of livestock manure and sewage should be strictly controlled. In agricultural planting areas, chemical fertilizers and pesticides should be used rationally to prevent non-point source pollution. In urban areas, the centralized treatment of industrial and residential sewage should be strengthened to prevent point source pollution. [ABSTRACT FROM AUTHOR]

Copyright of Arid Zone Research / Ganhanqu Yanjiu is the property of Arid Zone Research Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Arid Zone Research / Ganhanqu Yanjiu is the property of Arid Zone Research Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Understanding the hydrogen and oxygen stable isotope composition and characteristics of different water bodies in soil-plant-atmosphere continuum is of significance for revealing regional hydrological processes and water cycle mechanisms. In this study, we analyzed the stable isotopic composition, relationship and indicative significance of precipitation, soil water (0∼l00 cm depth) and xylem water of Qinghai spruce (Picea crassifolia) forest in the eastern Qilian Mountains, and explored the circulation process among different water bodies. The results show that the stable isotopes of precipitation vary greatly during the entire observation period. The values of δ2H and δ18O in the precipitation in the warm season are richer than those in the cold season, and the slope and intercept of local meteoric water line (LMWL, δ2H = 6.79δ18O+7.13) are both smaller than global meteoric water line (GMWL, δ2H=8.17δ18O+10.56). The stable isotopes of soil water at different depths underwent different degrees of evaporative fractionation, and the δ18O and δ2H of shallow soil water varied greatly, while the deep soil water tended to be similar. The topsoil (0∼10 cm) can respond quickly to precipitation, and the response of the deep soil has a time lag. In the whole growing season, 0∼30 cm and 60∼100 cm soil water are the main water sources of Qinghai spruce. The water source of Qinghai spruce was from all soil layers in May and September, mainly from the shallow soil layer (0∼30 cm) in August and October, and mainly from the deep soil layer (60∼100 cm) in June and July. [ABSTRACT FROM AUTHOR]

Moisture conditions are important ecological factors limiting plant growth in karst areas. In karst areas, because bedrock exposure and permeability are significant and soils are dispersed—without spatial continuity—and shallow, the water storage required for plant uptake and growth in rock fissures as well as shallow soils is very limited, and therefore, water conditions are an important factor influencing plant growth. In order to discover the sources of water used by plants in the karst zone ecosystem of southwest China and the differences in plant water use under different lithological conditions, this study selected limestone and dolomite in the karst ecological test site of Maocun, Guilin, Guangxi, for comparison with the clastic rock area. By measuring the δD and δ18O composition of plant stem water and the potential water sources (soil water, groundwater and precipitation) of the dominant species in the study area, and using the IsoSource and soil water excess (SW-excess) models, we analyzed the proportion of water utilization by different vegetation types under different lithological conditions. The results showed that (1) the slope and intercept of the local rainfall line (LMWL) and soil water line (SWL) in the study area were smaller than those of the global rainfall line (GMWL), and also smaller than those of the local atmospheric precipitation line in Guilin (δD = 8.8δ18O + 17.96), indicating that the local rainfall is influenced by evaporation and is formed by nonequilibrium fractionation of isotopes; (2) in general, the plant water sources in the dolomite, limestone, and clastic areas were dominated by rainfall, groundwater, and soil water, respectively; and (3) the fluctuation range of SW-excess in karst areas was significantly greater than that in nonkarst areas, the xylem water of plants in karst areas was more depleted in δD than soil water, and groundwater was more enriched in δD than soil water, indicating that there might be an ecological–hydrological separation phenomenon in karst areas, i.e., the "two water worlds" hypothesis. The results of this study provide scientific data for hydrological regulation in the ecological restoration of karst areas. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Agro-Environment Science is the property of Journal of Agro-Environment Science Editorial Board and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Nitrate (NO3−) pollution is a common phenomenon in karst underground rivers, which are important water sources in karst landscapes. For drinking water safety and environmental protection, it is crucial to accurately identify NO3− sources and their migration and transformation processes in the Lihu Underground River. In this study, water samples of the Lihu Underground River in Guangxi were collected in May 2014, October 2014, January 2015, and July 2015, and water chemical and dual isotopic (δ15N-NO3− and δ18O-NO3−) approaches were used to evaluate the NO3− characteristics and sources in the Lihu Underground River. The concentration of NO3− in the Lihu Underground River ranged from 1.16 to 19.78 mg·L−1, with an average of 9.30 mg·L−1, which is more than 37% of the WHO standard (10 mg·L−1). The concentrations of NO3− in the wet season (May 2014 and July 2015) were slightly lower than those in the dry season (from October 2014 to January 2015) at most sampling sites due to dilution effects. The migration and transformation processes of NO3− were analyzed by comparing the measured and calculated concentrations of NO3− in the Lihu Underground River. In the dry season (from October 2014 to January 2015), the variation in NO3− concentration upstream and midstream of the Lihu Underground River was affected by exogenous input and nitrification. From midstream to the outlet of Xiaolongdong, it is affected by self-purification factors, including physical processes, chemical processes, and biological processes. In the wet season (May 2014 and July 2015), the dilution and mixing effects were the main factors controlling the variation in NO3− concentration in the Lihu Underground River. The contribution rates of potential NO3− sources (incl. atmospheric precipitation (AP), NO3− fertilizer (NF), NH4+ in fertilizer and rainfall (NFA), soil organic nitrogen (SON), and manure and sewage (M&S)) were quantitatively evaluated by using the IsoSource model. The results showed that in May 2014, the main sources of NO3− were M&S and NF, with contribution rates of 46% and 41%, respectively. In October 2014, NO3− sources were M&S with a contribution rate of 47%, followed by NFA with a contribution rate of 31%. In January 2015, NO3− sources in groundwater were M&S, with a contribution rate of 53%, followed by NFA (34%). In July 2015, the main NO3− sources were M&S and NF, whose contribution rates were 54% and 39%, respectively. [ABSTRACT FROM AUTHOR]

Located along the northeastern edge of the Qinghai‐Tibet Plateau in China, the Qilian Mountains are an important ecological barrier in Northwest China. Therefore, it is of great significance to study the plant water sources in subalpine habitats for understanding the ecological and hydrological processes in the Qilian Mountains. Here, based on the samples of precipitation, xylem water, soil water, river water, and spring water collected during May–October 2019 from subalpine habitats on the northern slope of the Qilian Mountains and the measured hydrogen and oxygen stable isotope values (δ2H and δ18O, respectively), the present study gained further insight into plant water sources in this region using the IsoSource model. Water absorption characteristics of shrubs were similar in subalpine habitats. Specifically, plants absorbed water primarily from the topsoil layer (0–30 cm) and rarely from the deep soil layers. Nevertheless, in the dry and growing seasons with high water demand, subalpine shrubs competed for water resources at similar depths. As a result of this competition, the utilization rate of deep soil water improved in some shrubs, expanding the differences in water sources of subalpine shrubs within the same habitat. In addition, in the dry and growing seasons, the water sources of the same subalpine shrub varied across different habitats. Compared with other subalpine shrubs, Salix cupularis Rehder, Salix oritrepha Schneid., Potentilla fruticosa L., Salix sclerophylla Anderss., Rhododendron anthopogonoides Maxim., and Rhododendron przewalskii Maxim. could alter their water use strategies with variations in water conditions, exhibiting a greater drought tolerance. These findings provide valuable information for understanding the subalpine region's eco‐hydrological processes and contribute to the selection of suitable species for the restoration of the subalpine ecological environment under the background of global change. [ABSTRACT FROM AUTHOR]

The situation of water pollution in the Maobanqiao Reservoir is not optimistic, and the cause of pollution is not clear. In order to identify the present situation of water environment and pollution sources of the Maobanqiao Reservoir, combined with historical data collection and on-site investigation, this study analyzed the main over-standard factors of the water body. The contribution of different pollution sources to nitrate were quantitatively calculated through the analysis of nitrate-nitrogen and oxygen isotope (515N-NCV and 518O-NO3). The results show that the ratio up to the standard of water quality was 60.5% in Maobanqiao Reservoir national control section, based on class III standard of the National Surface Water Environmental Quality Standards (GB3838-2002) in China, while the main over-standard factors of water quality were TP, BOD5, and COD. With the on-site investigation in July 2019, the TN concentrations fluctuated between 0.91 and 1.96mg/L, with an average value of 1.29mg/L, and the nitrogen pollution was relatively serious. With IsoSource model analysis, the nitrate in the Maobanqiao Reservoir mainly comes from soil nitrogen (68%), followed by chemical fertilizer (18%) and domestic sewage (14%). Therefore, the agricultural planting and domestic sewage input by non-point source pollution should be controlled in the upper reaches of the Longchuan River to effectively reduce the pollution load of pollutants into the Maobanqiao Reservoir. [ABSTRACT FROM AUTHOR]

Moisture conditions are important ecological factors limiting plant growth in karst areas. In karst areas, because bedrock exposure and permeability are significant and soils are dispersed—without spatial continuity—and shallow, the water storage required for plant uptake and growth in rock fissures as well as shallow soils is very limited, and therefore, water conditions are an important factor influencing plant growth. In order to discover the sources of water used by plants in the karst zone ecosystem of southwest China and the differences in plant water use under different lithological conditions, this study selected limestone and dolomite in the karst ecological test site of Maocun, Guilin, Guangxi, for comparison with the clastic rock area. By measuring the δD and δ18O composition of plant stem water and the potential water sources (soil water, groundwater and precipitation) of the dominant species in the study area, and using the IsoSource and soil water excess (SW-excess) models, we analyzed the proportion of water utilization by different vegetation types under different lithological conditions. The results showed that (1) the slope and intercept of the local rainfall line (LMWL) and soil water line (SWL) in the study area were smaller than those of the global rainfall line (GMWL), and also smaller than those of the local atmospheric precipitation line in Guilin (δD = 8.8δ18O + 17.96), indicating that the local rainfall is influenced by evaporation and is formed by nonequilibrium fractionation of isotopes; (2) in general, the plant water sources in the dolomite, limestone, and clastic areas were dominated by rainfall, groundwater, and soil water, respectively; and (3) the fluctuation range of SW-excess in karst areas was significantly greater than that in nonkarst areas, the xylem water of plants in karst areas was more depleted in δD than soil water, and groundwater was more enriched in δD than soil water, indicating that there might be an ecological–hydrological separation phenomenon in karst areas, i.e., the “two water worlds” hypothesis. The results of this study provide scientific data for hydrological regulation in the ecological restoration of karst areas.

Understanding water absorption mechanisms of sand-fixing plants is important for the rational establishment of plant community structures, thereby providing a scientific basis for desertification control and the efficient utilization of water resources in sandy areas. Based on the hydrogen and oxygen isotopic compositions of precipi-tation, soil water, xylem water, and groundwater, coupled with soil water-heat dynamics, annual water consumption characteristics of vegetation, using the multi-source linear mixing model (IsoSource), we analyzed the differences in water sources between Salix psammophila and Artemisia ordosica , during winter and the growing season. We further examined the effects of groundwater depth (2 m and 10 m), soil freezing-thawing, and drought on their water utilization to elucidate water absorption mechanisms of those species. The results showed that: 1) During soil freezing-thawing period (January to March), S. psammophila mainly utilized soil water in 60-120 cm depths below the frozen layer (69.1%). In the green-up season (April and May), soil water from the 0-60 cm layers could satisfy the water demand of S. psammophila (30.9%-87.6%). During the dry period of the growing season (June), it predominantly utilized soil water at the depth of 120-160 cm (27.4%-40.8%). Over the rainy season (July and September), soil water in 0-60 cm depths provided 59.8%-67.9% of the total water required. A. ordosica , with shallow roots, could not utilize soil water after complete freezing of root zone but could overwinter by storing water in rhizomes during autumn. During the growing season, it primarily relied on 0-40 cm soil layer (23.4%-86.8%). During the dry period, it mainly utilized soil water from 40-80 cm and 80-160 cm soil layers, with utilization rates of 14.6%-74.4% and 21.8%-78.2%, respectively. 2) With decreasing groundwater depth, vegetation shifted its water absorption depth upward, with water source of S. psammophila transitioning from 120-160 cm to 60-160 cm layers, while A. ordosica shifted water absorption depth from 80-160 cm to 0-40 cm. S. psammophila 's utilization of soil water is influenced by transpiration, adopting an "on-demand" approach to achieve a balance between water supply and energy conservation, whereas A. ordosica tends to utilize shallow soil water, exhibiting a higher depen-dence on water sources from a single soil layer.

Copyright of Chinese Journal of Applied Ecology / Yingyong Shengtai Xuebao is the property of Chinese Journal of Applied Ecology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Chinese Journal of Applied Ecology / Yingyong Shengtai Xuebao is the property of Chinese Journal of Applied Ecology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To understand habitat associated differences in desert plant water-use patterns, water stable oxygen isotope composition was used to determine water source and leaf carbon isotope composition ( δ C) was used to estimate long-term water-use efficiency in three typical habitats (saline land, sandy land and Gobi) in Dunhuang. The primary findings are: (1) in the three habitats, plant species used mainly deep soil water (>120 cm), except for Kalidium foliatum in the saline land, which relied primarily on 0-40 cm soil water; (2) in the saline land and Gobi habitat, Alhagi sparsifolia had the most negative foliar δ C; in the sandy land, Elaeagnus angustifolia leaf was enriched in C than the other three species in 2011, but no species differences in foliar δ C was observed among the four species in 2012; (3) common species ( Tamarix ramosissima and A. sparsifolia) may alter their water sources to cope with habitat differences associated changes in soil water availability with deeper water sources were used in the Gobi habitat with lower soil water content (SWC) compared to in the saline land and sandy land; (4) we detected significant habitat differences in foliar δ C in A. sparsifolia which may have resulted from differences in SWC and soil electrical conductivity. However, no habitat differences in foliar δ C were observed in T. ramosissima, which may attribute to the strong genetic control in T. ramosissima or the ability to access stable deep soil water. Overall, the results suggest that extremely arid climate, root distribution and soil properties worked together to determine plant water uptake in Dunhuang area. [ABSTRACT FROM AUTHOR]

How to quantify the root water uptake from different soil layers under alternate furrow irrigation (AFI) condition accurately, is still of great challenge. In this study, the stable hydrogen and oxygen (δD and δ 18 O) isotopes of soil water, stem water, rainfall and irrigation water (groundwater) in the maize field system under AFI condition were measured during 2013–2014. The root water uptake was estimated by the multi-source mass balance method (IsoSource model). Results showed that δ 18 O distribution varied significantly between the ridge (R) and furrow (F) near soil surface, and between ridge surface and wet furrow under AFI. δ 18 O in stem water had better response to soil water variation at wet side, and soil water in wet side was firstly absorbed by maize root and then transported to the dry side. Maize water uptake was mainly from the depths of 20–40 cm at the late jointing stage, 40–60 cm at the late heading stage and 40–80 cm at the filling stage, with relative contribution of 84, 80 and 66%, respectively. Maize water uptake from different soil zones varied remarkably at AFI. For example, at the filling stage, 16–52% of maize water uptake was from the depth of 60–80 cm below the ridge (dry side) before irrigation, 32–78 and 14–64% from the surface soil (0–20 cm) of wet furrow and the ridge at 1 day after irrigation, 14–60 and 8–54% from the depths of 20–40 cm below the ridge side and 40–60 cm below wet furrow at 3 day after irrigation, and 6–80 and 30–60% from the depths of 60–80 cm below the ridge and 40–60 cm below the ridge side at 7 day after irrigation. Thus maize root water uptake was from deeper soil with the advance of growth stage, and it was mainly from the deeper soil in dry side and the shallow soil in wet side under AFI. [ABSTRACT FROM AUTHOR]

• The MixSIAR model outperformed the IsoSource model in the Yellow River source area for runoff generation simulations during the permafrost thaw period. Both models showed the dominance of subsurface runoff. • The influence of permafrost on hydrological processes diluted significantly as the watershed scale increased, and there was no clear relationship between runoff component contributions and watershed scale. • The influence of permafrost on the runoff mechanism of the watershed is controlled by the shape of the watershed itself, especially the topography plays a decisive role. In the Yellow River source area (SAYR), a large-scale isotope hydrological monitoring effort of landscape heterogeneity was implemented. To assess and determine whether permafrost has a controlling influence on hydrological processes in the watersheds, the IsoSource and MixSIAR models were used to partition runoff during permafrost thaw season in five nested basins (from 20,930 km2 to 121,972 km2). The analysis results showed that there were significant differences in the factors controlling runoff generation in the five basins, as well as significant differences in runoff sources between upper watersheds with predominantly permafrost cover and lower watersheds with predominantly seasonal frozen soil cover. The influence of permafrost on runoff generation was significantly reduced with increasing basin size. Soil permeability was influenced by permafrost thawing which impacted runoff generation in the permafrost zone. However, this only became effective under a specific combination of landscape characteristics and topography. In basins with less permafrost cover, the topographic characteristics and conditions of the catchment itself controlled the runoff generation mechanism. In general, the presence of permafrost influences the runoff generation, but the extent of the influence depends on the characteristics of the basin itself and, in particular, the control of topography increases with the scale of the basin. [ABSTRACT FROM AUTHOR]

Aims: Haloxylon ammodendron and Haloxylon persicum are the dominant species in the Gurbantonggut Desert, China, with the former grows at inter-dune lowland and the later grows at the sand dune. This study aims to investigate the dynamics of water usage of the two species and their responses to the soil water fluctuations resulting from summer precipitation. Methods: Oxygen isotope ratios ( δO) were measured for xylem water, soil water in different soil layers (0-300 cm), precipitation water and groundwater. Four potential water sources were identified: shallow (0-40 cm), middle (40-100 cm) and deep soil water (100-300 cm), as well as groundwater. The water sources used by the two species were calculated using the IsoSource model. Results: When the upper soil water was abundant in early spring, H. ammodendron mainly used shallow soil water while H. persicum mainly used middle soil water; when the upper soil water was depleted in summer, H. ammodendron mainly used groundwater while H. persicum mainly used deep soil water. Both species were conservative in using shallow soil water following the relatively large summer precipitations. Conclusions: The two Haloxylon species had distinct water use patterns during the growing season, which reflects their adaptations to their specific habitats in this water-limited desert environment. Large precipitations in dry summer hardly altered their water use patterns, which mean that these species are rather conservative in water use strategy. [ABSTRACT FROM AUTHOR]

The impoundment in the Three Gorges Reservoir Area (TGRA) was first reached 175 m in 2010. To approach the influence of this impoundment on the food web energy sources of fishes in the tributaries of TRGA, an analysis was made on the food web energy sources of seven economically important fishes (Carassius auratus, Cyprinus carpio, Silurus asotus, Culter mongolicus mongolicus, Mystus macropterus, Pelteobagrus vachelli, and Pelteobagrus nitidus) in the backwater area of Xiaojiang River by using stable isotope method in combining with IsoSource Model. The results showed that before this impoundment (July 2010), microalgae were the main energy sources for the seven species. After this impoundment (December 2010), the contribution ratio of the microalgae decreased somewhat, while the relative contribution of terrestrial C4 plants had an obvious increase. Especially for crucian carp (C. auratus) and catfish (S. asotus), the contribution rate of the C4 plants reached 38-54% and 32-50%, respectively. After the impoundment, at least 30% of the energy resources of these two fishes were come from terrestrial C4 plants, suggesting that the impoundment in TGRA increased the contribution rate of exogenous terrestrial C4 plants as the energy sources of fishes. [ABSTRACT FROM AUTHOR]

Large seasonal water-level fluctuations may influence isotopic signatures of primary producers and the types and amounts of these potential food sources accessible to aquatic fauna of Poyang Lake, the largest freshwater lake in China. In this study, the isotopic signatures of primary producers and consumers were determined, stable carbon and nitrogen isotope analysis and mixing models were combined to investigate the influence of water levels on the diet and isotopic composition of Poyang Lake fish and invertebrates. Five potential food sources (seston, benthic organic matter, aquatic macrophytes, attached algae, and terrestrial plants), 4 species of invertebrates, and 10 species of fish were collected from the lake area during dry and wet seasons between January 2009 and April 2010. The δC values of invertebrates and most fish were within the range of δC values of the potential food sources for both seasons. The δC values of invertebrates and most fish were lower in the dry season than in the wet season, whereas the δN values exhibited different patterns for different species. Mixing models indicated that the most important food sources for common lake fauna were seston in the dry season and aquatic macrophytes and terrestrial plants in the wet season. The fauna were more omnivorous in the wet season than in the dry season. The food web dynamics of Poyang Lake are strongly influenced by changes in the abundance and accessibility of different basal food sources that occur because of seasonal flood pulses. The trophic links within the aquatic communities of Poyang Lake are modified by water-level fluctuations. [ABSTRACT FROM AUTHOR]

We used stable carbon and nitrogen isotope analyses to estimate the relative proportions of three putative food sources (1) algae, (2) allochthonous organic matter (but including also heterotrophic bacteria and green-sulphur bacteria having similar isotopic values) and (3) methane-oxidizing bacteria (MOB) in the diets of crustacean zooplankton in five small boreal lakes representing a gradient of dissolved organic carbon (DOC) concentration from ca. 5 to 40 mg C l. The lakes were sampled in May, after establishment of stratification, and again in October during autumnal mixing of the water column. IsoSource mixing model outputs indicated that the proportion of algae in the diets of zooplankton was generally higher in May than in October, and that bacteria contributed to the diets of both cladocerans and copepods. Our results indicate that bacteria, especially MOB, can make an appreciable contribution to zooplankton diets in these small lakes, even in those with relatively low DOC concentrations. [ABSTRACT FROM AUTHOR]

Sustained whole-lake additions of 13C-enriched dissolved inorganic carbon (DIC), intehded to increase experimentally the δ13C of DIC in the epilimnion of a small lake with high dissolved organic carbon (DOC), were made during three seasonal periods (spring, summer, and autumn). Coupled with carbon and nitrogen stable isotope analysis of zooplankton and several of their putative food sources, these additions were used to investigate seasonal changes in the relative contributions of different food sources to zooplankton diet in the lake. Four main potential food sources were considered: phytoplankton, heterotrophic bacteria (HB), methanotrophic bacteria (MO B), and green sulfur bacteria (GSB). Because the number of potential food sources exceeded the number of isotopes analyzed, a computer program (IsoSource) was used to estimate the range of possible contributions of the various food sources. During all three periods the added inorganic 13C quickly increased the epilimnetic DIC δ13C by between 18‰ and 21‰ above the initial value of approximately -21‰. This 13C enrichment of DIC was rapidly transmitted to the particulate organic matter (POM), which included photosynthetic phytoplankton. In spring and summer, δ13C of both adult and juvenile Daphnia increased by -10‰, indicating that Daphnia utilized autochthonous carbon. However, this 13C labeling of Daphnia was not so obvious during the autumn period, when their δ13C generally decreased. According to the IsoSource model outputs based on both δ13C and δ15N values, Daplinia utilized all four potential food source types during spring, summer, and autumn, but in different proportions. The possible contribution of phytoplankton to Daphnia diet was substantial (25-71%) in all seasons. The possible contributions of the bacterial food sources were more variable. The possible contribution of GSB was minor (0-20%) at all times and negligible in autumn. The possible contribution of HB was higher but very variable. Methanotrophic bacteria always made a significant contribution to Daphnia diet and were likely the single most important food source in autumn. Since both HB and MOB in this high-DOC lake probably depend largely on allochthonous organic carbon, our results highlight the seasonal variability in the potential importance of ecosystem subsidies in lake food webs. [ABSTRACT FROM AUTHOR]

Plants are vital components of the nitrogen (N) cycling in the riparian zones. Understanding of N uptake strategies of riparian plants, including N sources and preference in N forms (ammonium (NH 4 +) vs. nitrate (NO 3 −)), is essential to advance our knowledge on the role that plants play in regulating nutrient biogeochemical cyclings in the riparian areas. In this study, stable N isotopes (δ 15 N) of three riparian plants, including Acorus calamus , Canna indica and Phragmites australis , and the δ 15 N of NH 4 + and NO 3 − in different sources were measured during the plant growing season (June–September) in the Taihu Lake Basin. The dissolved inorganic N (DIN) from river water, groundwater, rainwater and soil were considered as the major N sources for plants in the riparian ecosystem. Our results indicated that soil was the largest source for plant N nutrition, with significantly different (P < 0.05) contributions from soil observed among plant species (80.5 ± 4.1, 73.9 ± 2.8 and 58.7 ± 6.1% for A. calamus , C. indica , and P. australis , respectively). Meanwhile, complex water networks, shallow water tables, and high DIN content in rainwater lead to nonignorable N contributions from river water, groundwater and rainwater to plants. Groundwater contributed more percentage of N to P. australis (12.8 ± 3.2%) than A. calamus (6.1 ± 1.9%) and C. indica (8.0 ± 1.5%), which is likely attributed to the deeper roots of P. australis. All plants showed similar N preference for NO 3 − during the growing season. External environmental conditions and plant characteristics and adaption to more abundant soil NO 3 − content are possible explanations. Our research could provide important information for vegetation selections during the process of riparian ecological restoration. Reasonable choice of vegetation is essential to plant growth and water quality management, especially in agricultural watersheds where N concentrations are relatively high in agricultural runoff due to the wide uses of N fertilizers. Unlabelled Image • Order of N source contributions: soil > river water > groundwater > rainwater • The contribution of N sources to three plants was significantly different. • Riparian plants mainly utilized NO 3 − and showed same N preference for NO 3 −. • P. australis had a different N uptake strategy compared to the other two plants. [ABSTRACT FROM AUTHOR]

• Water use pattern was investigated for Caragana korshinskii on sunny and shady slopes. • Caragana korshinskii seasonally switched its water sources from different soil layers. • Caragana korshinskii on sunny slope used shallower soil water than that on shady slope. • Root distribution and soil moisture affect water use pattern of Caragana korshinskii. Flexible water use patterns are of great importance for the survival of vegetation in dryland regions. Our study aimed to investigate the influences of season and slope aspect on the water use patterns of Caragana korshinskii on typical shady and sunny slopes on the Loess Plateau in China. We collected xylem water, soil water from the 0–200 cm soil layers, and precipitation in May, July, September and November 2018 and measured their hydrogen (δD) and oxygen (δ18O) isotope compositions. The root distribution of C. korshinskii in the 0–200 cm soil layer on both slopes was also investigated. The 0–20, 20–80, and 80–200 cm soil layers were identified as three potential water sources for C. korshinskii , and their proportional contributions to the plant water supply were calculated using a linear mixed model. The results showed that C. korshinskii on the sunny slope absorbed 89.3% of their water from the 0–20 cm soil layer in May but mainly utilized water from the 0–20 and 20–80 cm soil layers in both July and September, and the total contribution percentages of these layers were 84.5% and 89.2%, respectively. However, C. korshinskii on the shady slope extracted water evenly from all three soil layers in May. Thereafter, the plants absorbed water from the 20–80 and 80–200 cm soil layers in both July and September, and the total contribution percentages of these layers were 96.0% and 91.8%, respectively. In November, C. korshinskii absorbed 84.8% and 78.0% of their water from the 80–200 cm soil layer on the shady and sunny slopes, respectively. The generally shallower soil water use of C. korshinskii on the sunny slope than on the shady slope may be due to the larger fine-root (d < 2 mm) length density in the 0–80 cm soil layer on the sunny slope (1.12 ± 0.28 mm/cm3) than on the shady slope (0.57 ± 0.16 mm/mm3) (P < 0.05). This study indicates that C. korshinskii on both shady and sunny slopes seasonally switched their water sources from different soil water layers during the growing season. However, due to their reliance on soil water at the 0–20 cm depth, which is supplied by unstable rainfall, C. korshinskii on sunny slopes may be more vulnerable to future climatic warming and drying on the Loess Plateau. Our findings provide valuable information related to optimal water management in the afforested shrublands in this region. [ABSTRACT FROM AUTHOR]

Due to the vulnerability of karst hydrological systems, nitrate pollution in karst groundwater has become a global common and serious environmental problem. In order to ensure drinking water safety, it is very important to accurately identify groundwater nitrate sources. The groundwater hydrochemistry and δ 15 N-NO 3 - isotopes were analyzed in samples taken from a suburb of Chongqing:the Longfeng karst trough-valley, which is mainly affected by agricultural activities, and the Longche karst trough-valley, which is primarily affected by urbanization. The IsoSource model was then used to quantify the groundwater nitrate sources. The results showed that:① The NO δ 18 O-NO 3 - isotopes were analyzed in samples taken from a suburb of Chongqing:the Longfeng karst trough-valley, which is mainly affected by agricultural activities, and the Longche karst trough-valley, which is primarily affected by urbanization. The IsoSource model was then used to quantify the groundwater nitrate sources. The results showed that:① The NO 3 - concentration in groundwater ranged from 19.31 mg·L -1 to 37.01 mg·L -1 (mean of 28.21 mg·L -1 ) in the Longfeng karst trough-valley, and from 2.15 mg·L -1 to 27.69 mg·L -1 (mean of 10.31 mg·L -1 ) in the Longche karst trough-valley. The groundwater NO 3 - concentration exhibited an obvious seasonal variation in both valleys. ② The δ 15 N-NO 3 - and δ 18 O-NO 3 - isotopes in groundwater in the Longfeng karst trough-valley ranged from 3.29‰ to 11.03‰ (mean of 6.74‰) and 0.88‰ to 7.51‰ (mean of 3.18‰), respectively. In contrast, groundwater in the Longche karst trough-valley presented higher δ 15 N-NO 3 - and δ 18 O-NO 3 - values that ranged from 5.25‰ to 11.40‰ (mean of 7.95‰) and 2.90‰ to 19.94‰ (mean of 11.18‰), respectively. The lower values of δ 15 N-NO 3 - and δ 18 O-NO 3 - in groundwater in the Longfeng karst trough-valley suggest that groundwater NO 3 - was mainly sourced from agricultural N fertilizer, while the higher values of δ 15 N-NO 3 - and δ 18 O-NO 3 concentration in the Longche karst trough-valley primarily originated from domestic sewage in both seasons. ③ The results of the IsoSource model indicated that the nitrification of NH - in groundwater in the Longche karst trough-valley indicate that groundwater NO 3 - was primarily sourced from domestic sewage. Moreover, such δ 15 N-NO 3 - and δ 18 O-NO 3 - values in groundwater indicate that nitrification was the primary process for nitrogen conversion in both valleys. Meanwhile, significant seasonal differences in groundwater δ 15 N-NO 3 - and δ 18 O-NO 3 - were observed in both valleys; the δ 15 N-NO 3 - and δ 18 O-NO 3 - values were higher during the dry season (means of 8.83‰ and 2.79‰, respectively) than during the rainy season (means of 4.64‰ and 3.58‰, respectively) in the Longfeng karst trough-valley, whereas the δ 15 N-NO 3 - and δ 18 O-NO 3 - values were lower during the dry season (means of 9.79‰ and 14.56‰, respectively) than during the rainy season (means of 5.12‰ and 7.8‰, respectively) in the Longche trough-valley. This suggests that there were differences in the seasonal NO 3 - sources to groundwater in both valleys. During the rainy season, the groundwater NO 3 - concentration in the Longfeng karst trough-valley was mainly due to the nitrification of NH 4 + in precipitation and fertilizer as well as organic nitrogen in soil, whereas during the dry season, the groundwater NO 3 - concentration primarily originated from domestic sewage. In contrast, the groundwater NO 3 - concentration in the Longche karst trough-valley primarily originated from domestic sewage in both seasons. ③ The results of the IsoSource model indicated that the nitrification of NH 4 + from fertilizer and rainwater was the primary NO 3 - source to groundwater (44.63% of the total) in the Longfeng trough valley, and was followed by domestic sewage (29.5%), soil organic nitrogen (22.38%), and NO 3 - from rainwater and fertilizer (<10%). During the rainy season, the groundwater NO 3 - concentration was mainly due to the nitrification of NH 4 + from fertilizer and rainwater (52.25% of the total) in Longfeng trough-valley, while groundwater NO 3 - concentration primarily originated from domestic sewage during the dry season (41% of the total). In contrast, the groundwater NO 3 - concentration was mainly from domestic sewage (36.17%) in Longche karst trough-valley, and was followed by the nitrification of NH 4 + from fertilizer and rainwater (23.5%), soil organic nitrogen (22.5%), and NO 3 - from rainwater and fertilizer (<10%). The groundwater NO 3 - concentration in the Longche karst trough-valley primarily originated from domestic sewage in both seasons, and accounted for 47% and 25% during the rainy season and dry season, respectively.

The objectives of this study were to reveal the sources of nitrate and the ratio of karst in an agricultural basin based on a 15 N and 18 O isotope technique and quantitative calculation of the IsoSource model. From May to October 2017, six sampling points in the Qingmuguan river basin, Chongqing, were monitored every 24 d. Results showed that there was a great risk of nitrate pollution in the underground river system, because most NO 3 - -N concentrations of the sampling points exceeded the threshold. Spatially, NO 3 - -N concentrations in the underground river increased from upstream to downstream. Temporally, NO 3 - -N concentrations of Fishpond and Yankou Ponor upstream and Jiangjia Spring downstream were impacted by agricultural fertilizer from May to June and fluctuated from June to September due to precipitation. With decreased agricultural activities, NO 3 - -N concentrations gradually decreased after September. NO 3 - -N concentrations were high in midstream soil water. Daluchi, in the middle and lower reaches, maintained relatively low NO 3 - in precipitation were the main nitrate sources in the outlet. Nitrate source contribution of the outlet was calculated with the IsoSource model. The calculation results showed that manure and sewage, soil organic nitrogen, NH 15 N and 18 O isotopic compositions suggested that the upstream nitrates were derived from soil organic nitrogen and a mixture of manure and sewage. The midstream nitrates originated from soil organic nitrogen and NH 4 + from fertilizer and rain. Nitrates in the middle and lower reaches were derived from the mixing of manure and sewage, soil organic nitrogen, and NH 4 + from fertilizer and rain. Jiangjia Spring, the outlet of the underground river, was seriously polluted by nitrates. It is believed that soil organic nitrogen, NH 4 + in fertilizer and rain, the mixing of manure and sewage, and NO 3 - in precipitation were the main nitrate sources in the outlet. Nitrate source contribution of the outlet was calculated with the IsoSource model. The calculation results showed that manure and sewage, soil organic nitrogen, NH 4 + in fertilizer and rain, and NO 3 - in precipitation contributed 46.4%, 32.6%, 18.6%, and 2.4%, respectively.

This study aimed to qualify the potential water sources and their responses to seasonal precipitations for the system of Platycladus orientalis and Vitex negundo var. heterophylla by IsoSource model based on stable hydrogen and oxygen isotopic analysis in Jiufeng Mountain area of Beijing. The results showed that the 18 O of water from 0-20 cm soil layer was enriched, whereas that was depleted as the soil layer deepened. P. orientalis used water mainly from 0-30 cm soil la-yer, being composed of rainwater 2-3 days before at the beginning of dry season. The water absorbed by P. orientalis and V. negundo sourced from 0-10 cm and 10-30 cm soil layer, which was fed on recent rainwater at the end of dry season. In wet season P. orientalis mainly accessed the soil water (from 0-40 cm layer, 59.3%) and recent rainwater (12.5%), while V. negundo drank the water from 0-30 cm soil layer derived from recent heavy rain. P. orientalis actively uptook the deeper soil water with time, until the end of growing season (November), its available water was from 60-80 cm soil layer and sourced from the rainwater happened 2-3 days before. Meanwhile, V. negundo completed its growing cycle and was on the brink of death. This system faced less competition for water use, stating its vertical water availability for climate adaptation in this region, which could reduce water and soil loss and minimize the instantaneous damage under heavy rainstorm attack.

Tamarix chinensis, the dominant species of plant communities in the coastal wetlands of the Yellow River Delta, was selected to study the water use strategy of coastal plants at different habitats during a drought year. The Δ 18 O values for xylem water of T. chinensis were analyzed. Potential contributions by different water sources to T. chinensis were estimated using the IsoSource model. The contributions were analyzed to reveal the adaptation mechanism of T. chinensis to water stress at different habitats. The results showed that the main water sources for T. chinensis during a drought year were soil water and groundwater rather than precipitation. However, the water use strategies of T. chinensis changed significantly with different micro-topographies. For dune crests, 72.6%-95.4% water of T. chinensis came from deeper soil water (40-100 cm) and groundwater. However, near the high tide line, T. chinensis absorbed 40.7%-97.3% of the water from the upper soil (0-40 cm) to avoid the salt stress caused by sea water and shallow groundwater. This provided T. chinensis with a competitive advantage related to water consumption and improved its water use efficiency in the coastal ecosystem, which led to mono-dominant shrub community of T. chinensis in this area.