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Ecosystem services (ESs) serve as a fundamental cornerstone for upholding global biodiversity and promoting human well-being. ESs trade-off and synergy are supposed to be significantly affected by climate change (CC) and land use/cover change (LULC). However, the limited availability of finely classified future land-use data and integrated landscape change models incorporating climate change scenarios has hindered our understanding of the trade-off and synergistic patterns and controls of ESs at multiple scales, particularly in arid areas. Here, a future multi-scenario ESs trade-off/collaborative assessment framework (SD-PLUS-InVEST model) for multi-scale conversion and refined land-use classification was developed by coupling the patch-generated land-use simulation (PLUS) model, system dynamics (SD) model, InVEST model, geographically weighted regression (GWR) model, optimal parameter geographical detector (OPGD) model, and structural equation model (SEM). The four ESs, namely carbon storage (CS), habitat quality (HQ), water conservation (WC), and soil conservation (SC), were assessed. Further, multi-scale ESs were evaluated under different climate change and development scenarios (i.e., the SSP1-2.6 and ecological protection scenario, SSP1-2.6-EP; SSP2-4.5 and natural development scenario, SSP2-4.5-ND; SSP5-8.5 and economic growth scenario, SSP5-8.5-EG). The results demonstrated that the arid region of northwest China (ANWC) was experiencing a significant and continuous warming trend accompanied by increased humidity. There will be a significant decrease in the areas occupied by paddy fields, natural forests, and permanent glaciers among the 24 LULC types. Conversely, there will be a substantial increase in dry land, high-coverage grassland, and urban construction land areas. According to the SSP1-2.6-EP, SSP2-4.5-ND, and SSP5-8.5-EG scenarios, the comprehensive land-use dynamic degrees were estimated to reach 2.58%, 4.08%, and 4.74%, respectively. The LULC resulting from CC exacerbates the differences in the four ESs of ANWC. In particular, CS and HQ experience significant reductions in 2100. Conversely, WC and SC show notable increases during the same period. The changes in CS, HQ, WC, and SC reach 11.36 × 108 m3, 1735.25 × 108 t, −1.29 × 108 t, and −0.009, respectively. The four ESs of CS, HQ, WC, and SC in ANWC display a synergistic relationship. This synergy is influenced by the heterogeneous spatial distribution of CS, HQ, WC, and SC, with the strongest synergy observed between CS and HQ and the weakest between CS and WC. Interestingly, the distribution differences in ESs synergy were amplified at watershed, county, and grid scales in mountainous areas, with the most significant detection differentiation occurring at the grid scale. Furthermore, the detection of spatial heterogeneity in the four ESs can be attributed to various factors. These factors include the drought index (q = 0.378), annual average precipitation (q = 0.375), economic density (q = 0.095), vegetation coverage (q = 0.262), and soil bulk density (q = 0.077). Our results highlight the importance of CC in influencing ESs. The spatial variations in ESs trade-offs and coordination at different scales, particularly the pronounced differences observed in mountainous areas, underscore the need to prioritize the conservation of arid mountainous regions in terms of future policy making. [ABSTRACT FROM AUTHOR]

As the transition zone between the Tibetan Plateau and arid region, the Qilian Mountains are important ecological barriers and source regions of inland rivers in northwest China. In recent decades, drastic changes in the cryosphere have had a considerable impact on the formation process of water resources in the Qilian Mountains. In this study, 2164 environmental isotope samples were used to quantify the runoff components of 11 major rivers in the Qilian Mountains and investigate the influence of cryosphere changes on mountain runoff. The results show that the mountain runoff primarily originates in the cryosphere belt, which contributes approximately 82 %, 71 %, and 80 % to the Hexi inland water system, the upper stream of the Yellow River system, and the Qinghai inland river system, respectively. The maximum contribution ratio of glacier and snow meltwater to runoff occurred in May. The contribution of supra-permafrost water to runoff gradually increased from May and reached approximately 40 % in some rivers in October. Cryosphere degradation in the Qilian Mountains after the 1990s has caused a rapid increase in runoff, changes in the peak runoff time, and an increase in winter runoff. These changes in the hydrological processes bring opportunities and challenges to managing inland river water resources, and various adaptive measures to seek advantages and avoid disadvantages have been proposed. The findings from the environmental isotope analysis provide insights into understanding water resources and realizing the nexus of life, agriculture, industry, and ecological water use. [ABSTRACT FROM AUTHOR]

Accurate daily streamflow forecasts remain challenging in arid regions. A Bayesian model averaging (BMA) ensemble learning strategy was proposed to forecast 1-, 2-, and 3-day-ahead streamflow in Dunhuang Oasis, northwest China. The efficiency of BMA was compared with four decomposition-based machine learning and deep learning models. Satisfactory forecasts were achieved with all proposed models at all lead times; however, based on Nash-Sutcliffe efficiency values of 0.976, 0.967, and 0.957, BMA achieved the greatest accuracy for 1-, 2-, and 3-day-ahead streamflow forecasts, respectively. Uncertainty analysis confirmed the reliability of BMA in yielding consistently accurate streamflow forecasts. Thus, BMA could provide an efficient alternative approach to multistep-ahead daily streamflow forecasting. The incorporation of data decomposition techniques (e.g. variational mode decomposition) and deep learning algorithms (e.g. deep belief network) into BMA may provide worthy technical references for supervised learning of streamflow systems in data-scarce regions. [ABSTRACT FROM AUTHOR]

Purpose: Soil organic carbon (SOC) in alpine regions is characterized by a strong local heterogeneity, which may contribute to relatively large uncertainties in regional SOC stock estimation. However, the patterns, stock, and environmental controls of SOC in semiarid alpine regions are still less understood. Therefore, the purpose of this study is to comprehensively quantify the stock and controls of SOC in semiarid alpine regions. Materials and methods: Soils from 138 study sites across a typical semiarid alpine basin (1755–5051 m, ~1 × 104 km2) are sampled at 0–10, 10–20, 20–40, and 40–60 cm. SOC content, bulk density, soil texture, and soil pH are determined. Both a classical statistical model (i.e., a multiple linear regression, MLR) and a machine learning technique (i.e., a random forest, RF) are applied to estimate the SOC stock at a basin scale. The study further quantifies the environmental controls of SOC based on a general linear model (GLM) coupled with the structural equation modeling (SEM). Results and discussion: SOC density varies significantly with topographic factors, with the highest values occurring at an elevation zone of ~3400 m. The results show that the SOC is more accurately estimated by the RF compared to the MLR model, with a total stock of 219.33 Tg C and an average density of 21.25 kg C m−2 at 0–60 cm across the study basin. The GLM approach reveals that the topography is seen to explain about 58.11% of the total variation in SOC density at 0–10 cm, of which the largest two proportions are attributable to the elevation (44.32%) and the aspect factor (11.25%). The SEM approach further indicates that, of the climatic, vegetative, and edaphic factors examined, the mean annual temperature, which is mainly shaped by topography, exerts the most significant control on SOC, mainly through its direct effect, and also, through indirect effect as delivered by vegetation type. Conclusions: The results of this study highlight the presence of high stocks of organic carbon in soils of semiarid alpine regions, indicating a fundamental role played by topography in affecting the overall SOC, which is mainly attained through its effects on the mean annual temperature. [ABSTRACT FROM AUTHOR]

Purpose: Soil organic carbon (SOC) in mountainous regions is characterized by strong topography-induced heterogeneity, which may contribute to large uncertainties in regional SOC stock estimation. However, the quantitative effects of topography on SOC stocks in semiarid alpine grasslands are currently not well understood. Therefore, the purpose of this research study is to determine the role of topography in shaping the spatial patterns of SOC stocks. Materials and methods: Soils from the summit, shoulder, backslope, footslope, and toeslope positions along nine toposequences within three elevation-dependent grassland types (i.e., montane desert steppe at ~ 2450 m, montane steppe at ~ 2900 m, and subalpine meadow at ~ 3350 m) are sampled at four depths (0–10, 10–20, 20–40, and 40–60 cm). SOC content, bulk density, soil texture, soil water content, and grassland biomass are determined. The general linear model (GLM) is employed to quantify the effects of topography on the SOC stocks. Ordinary least squares regressions are performed to explore the underlying relationships between SOC stocks and the other edaphic factors. Results and discussion: In accordance with the present results, the SOC stocks at 0–60 cm show an increasing trend in respect to the elevation zone, with the highest stock being approximately 37.70 g m−2 in the subalpine meadow, about 2.07 and 3.41 times larger than that in the montane steppe and montane desert steppe, respectively. Along the toposequences, it is revealed the SOC stocks are maximal at toeslope, reaching to 14.98, 31.76, and 49.52 kg m−2, which are also significantly larger than those at the shoulder by a factor of 1.38, 2.31, and 1.44, in montane desert steppe, montane steppe, and subalpine meadow, respectively. Topography totally is seen to explain about 84% of the overall variation in SOC stocks, of which 70.61 and 9.74% are attributed to elevation zone and slope position, while the slope aspect and slope gradient are seen to plausibly explain only about 1.84 and 0.01%, respectively. Conclusions: The elevation zone and the slope position are seen to markedly shape the spatial patterns of the SOC stocks, and thus, they may be considered as key indicating factors in constructing the optimal SOC estimation model in such semiarid alpine grasslands. [ABSTRACT FROM AUTHOR]

Abstract Land degradation results from the interactions among multiple climate and human factors. Solving the problem requires a holistic strategy that deals with all significant factors simultaneously. However, it is difficult to solve such problems because few researchers have studied the simultaneous effects of these interactions, making it difficult to develop a truly holistic strategy. To help land managers find such a strategy, we have proposed and tested a new approach for ecological restoration in which we calculated the simultaneous contributions of multiple factors during vegetation cover change in Yan'an City, Shaanxi Province, China, from 2000 to 2016. After implementing the new approach, the vegetation cover increased by 35.7% during the study period, which is 2.3 times the rate in the rest of Shaanxi Province, where only the national Grain for Green program was implemented. The new approach accounted for 74.0% of the increased vegetation cover in the first year, and comparable values in the second and third years. Our results provide important information to guide sustainable development in China, and our approach can be adapted for use in other nations that are facing similar problems. Graphical abstract Image 1 Highlights • Ecological restoration must account for climate and human factors simultaneously. • Restoration through socioeconomic development will be sustainable in the long term. • Alleviating poverty significantly improves the effects of ecological restoration. [ABSTRACT FROM AUTHOR]

Highlights • Afforestation is an important land use option decision for arid and semi-arid regions. • The effect of stand type and stand age on soil carbon storage (SC) was investigated. • The SC for the apricot stand with 40 yrs and 16 yrs was 88.36 Mg ha−1, and 56.16 Mg ha−1, respectively. • The SC for the poplar stand with 40 yrs was 79.07 Mg ha−1. • For afforestations in arid and semi-arid regions, a tradeoff between SC and soil water is required. Abstract Afforestation implemented on available lands that have a poor fertility with a low primary productivity is considered to be a significant land use change issue globally, especially in the current phase of increasing atmospheric CO 2 concentrations. However, different stand types and stand ages, where afforestation is initiated, may have a different effect on soil carbon storage. Two stand types, including the apricot and poplar stand, both with 40 years, and two stand ages, including the apricot stand with 40 years and apricot stand with 16 years were sampled on the Loess Plateau, to explore the differences in soil carbon storage between both of them, respectively. The results showed that the total soil carbon storage up to the 1.0 m soil depth for the poplar stand was 79.07 Mg ha−1, and for the apricot stand with 40 years was 88.36 Mg ha−1, while for the apricot stand with 16 years, it was 56.16 Mg ha−1. About 50% the soil carbon was stored in the 0-0.4 m soil layer for all these forested lands. This ascertains that the soil carbon was very sensitive to climate change and anthropogenic disturbances. Based on these results, if we are interested in combating global warming issue, the apricot trees can be a preferred option for future plantations. However, these plants are likely to consume more water than any other vegetation types. Since water is a limited resource both in arid and semi-arid regions, a tradeoff between soil carbon and soil water should also be considered in future afforestation policy options. [ABSTRACT FROM AUTHOR]

Abstract: Cultivated oases play an important role in supporting human civilization in arid regions. Few quantitative analyses have been conducted on the influence of natural disturbances and human interventions on this fragile system over a long timescale. This paper presents an empirical study to investigate the quantitative relationship between cultivated oasis evolution and a set of natural and human factors in Heihe River Basin (HRB) over a timeframe of approximately 2,000 years (206  BC–1949 AD). Multiple data sources, including documentary records, historical atlas reconstruction data, and published papers, were used. Stepwise multiple linear regression analysis was adopted to quantify any significant contributions of the selected variables. The results showed that cultivated oasis in the HRB had experienced substantial fluctuations. Population size, agricultural policies, military clashes, and grain yield per unit area were 4 major human related factors determining historical cultivated oasis development, while flood was the only significant natural factor. In combination of similar studies in recent decades, this study shows that the dynamics of oasis development and its transition is important for determination of the sustainable size of a cultivated oasis in the HRB. [ABSTRACT FROM AUTHOR]

In this study, the characteristics of energy flux partitioning and evapotranspiration of P. euphratica forests were examined in the extreme arid region of Northwest China. Energy balance closure of the ecosystem was approximately 72% (H + LE = 0.72 ∗ (Rn-G)+7.72, r2=0.79, n=12095), where Rn is the net radiation, G is the soil heat flux, H is the sensible heat flux, and LE is the latent heat flux. LE was the main term of energy consumption at annual time scale because of higher value in the growing season. The ratios of the latent (LE) and sensible (H) heat fluxes to net radiation were 0.47 and 0.28 throughout the year, respectively. Moreover, the yearly evapotranspiration of P. euphratica forests was 744 mm year−1. And the mean daily ET was 5.09 mm·d−1 in the vibrant growing season. In particular, a small spike in the actual evapotranspiration distribution occurred during the soil ablation period due to the higher temperature and sufficient soil moisture associated with soil thawing. This period is accompanied by a series of physical processes, such as moisture transfer and heat exchange. [ABSTRACT FROM AUTHOR]

Soils in alpine regions associated with complex topography are characterized by large variability in the spatial distribution of soil organic carbon (SOC). However, the patterns and topographic controls on SOC at the hill scale in semiarid alpine regions are not well understood. In this study, the effects of slope aspects and depths on SOC were quantified based on field investigations in a mainly undisturbed region of the Qilian Mountains in northwestern China. Soil samples were collected at 0–10, 10–20, 20–40 and 40–60 cm on south-, southwest-, west-, and north-facing slopes of three hills. Results showed that the SOC density at 0–60 cm varied from 9.73 to 35.21 kg m − 2 , and increased from the south- to north-facing slopes. The average SOC density on the north-facing slopes was about 3.2, 2.9 and 1.9 times larger than on the south-, southwest- and west-facing slopes. Both the general linear model and mixed linear model suggested that, at the hill scale, the slope aspects and soil depths explained the main variations of SOC concentration in our study. The profile pedotransfer function method indicated that the SOC varied predictably with soil depths and aspects, and the prediction functions well predicted the SOC data from literature. Our results highlight the importance of slope aspect as an indicator of the SOC, and demonstrate that the transformed aspect is a good continuous variable in predicting the SOC in the semiarid alpine region. [ABSTRACT FROM AUTHOR]

The nitrate pollution of groundwater in arid areas subject to human activity, and especially agricultural activity, is of immense environmental concern. Groundwater is the main water source in arid areas, once an aquifer is polluted, the impact upon the security of the water supply becomes all the more serious. The process of nitrate transformation is also different from that of humid areas, therefore, it is very important to identify and quantify the nitrate sources in aquifers. Using the hydrochemical, stable isotope tracers of 194 groundwater samples, and combining these with the MixSIAR model, the spatial distribution of groundwater nitrates in the Shiyang River Basin (SRB), China, was mapped. The relative contributions made by nitrate sources to different aquifers, and their key transformation processes, were identified. It was found that, shallow groundwater is seriously polluted, with NO 3 − concentrations ranging from 1.1 to 438.7 mg L−1. In the SRB, NO 3 − concentrations of 23% and 73% in shallow groundwater samples exceed the NO 3 − concentration limits found in natural sources (13.3 mg L−1), and the World Health Organization (WHO) nitrate limits for drinking water (50 mg L−1). Furthermore, the nitrates found in confined aquifers indicate that these are also affected by anthropogenic sources, with concentrations ranging from 1.6 to 44.7 mg L−1. Soil organic nitrogen (51.9%) and NH 4 + fertilizer (20.8%), wastewater and manure (20.5%) are the main sources of groundwater nitrates; NO 3 − fertilizer (4.4%) and precipitation (2.3%) have a relatively insignificant effect on groundwater nitrates. The process of nitrification is the main factor affecting changes in nitrate concentrations in aquifers. Other than the denitrification observed in the shallow aquifers of the Minqin Basin (MQB), there was no significant denitrification in the other sub-basins of the SRB. Anthropogenic sources, especially agricultural sources, are now major contributors to the increases in groundwater nitrate concentrations observed in the SRB. This study provides data that can be used to help prevent groundwater pollution and enhance water resources management in arid areas. [Display omitted] • Except Jinchang sub-basin, nitrate pollution in groundwater is obvious in other sub-basins of SRB. • Nitrate concentrations in confined aquifer have also been affected by anthropogenic sources. • The process of nitrification is the main factor affecting changes in nitrate concentrations in aquifers. • A denitrification process that would alleviate the nitrate pollution of groundwater bodies is relatively lacking in SRB. [ABSTRACT FROM AUTHOR]

Aims: As deep water uptake is limited by the low densities of fine roots at the subsoil layer at high evaporative demand, hydraulic redistribution (HR) is another possible mechanism that could account for the lack of water stress experienced by desert riparian phreatophytes during dry periods. The objectives of this study were to search for evidence that the roots of two desert riparian phreatophytes, Populus euphratica Oliv. and Tamarix ramosissima Ledeb., carry out HR and to investigate the pattern of this phenomenon in the broader scheme of plant water uptake by roots. Methods: To demonstrate HR, we present data on patterns of sap flow in the stems or branches and lateral roots of those two phreatophyte species and soil volumetric moisture content where these species grow. Results: During the dry season, we observed reverse or acropetal flow in the lateral roots of P. euphratica, a pattern consistent with hydraulic lift. With the onset of heavy rains, this pattern reversed, indicating water movement from moist topsoil to dry subsoil, i.e. hydraulic descent. After lateral irrigation by creek, water moved downward to dry subsoil and outward to opposite sides, suggesting lateral hydraulic redistribution via roots at night and during the day, which may be mediated by stem tissues and, by inference, the radial sectoring in the xylem. Although no direct evidence indicated reverse sap flow of lateral roots and associated HR in T. ramosissima, several factors indicate that HR is occurring: (1) diel fluctuations of volumetric moisture content in the upper soil layer and (2) the identification of primary water sources as groundwater and vadose zone water through stable isotope studies. As a result, we inferred that HR occurs in T. ramosissima via adventitious roots with diameters of 2-5 mm and length of 60-100 cm in the upper soil layer, rather than via lateral roots; further investigation is needed to substantiate this. Conclusions: We confirm and extend previous knowledge on HR patterns of P. euphratica and add a new species, T. ramosissima, to the wide list of existing species involved in HR. However, these two desert riparian phreatophytes exhibit remarkable differences in their patterns and pathways of HR that are possibly associated with root architecture. [ABSTRACT FROM AUTHOR]

Ecosystem services in arid inland regions are significantly affected by climate change and land use/land cover change associated with agricultural activity. However, the dynamics and relationships of ecosystem services affected by natural and anthropogenic drivers in inland regions are still less understood. In this study, the spatiotemporal patterns of ecosystem services in the Hexi Region were quantified based on multiple high-resolution datasets, the InVEST model and the Revised Wind Erosion Equation (RWEQ) model. In addition, the trade-offs and synergistic relationships among multiple ecosystem services were also explored by Pearson correlation analysis and bivariate spatial autocorrelation, and redundancy analysis (RDA) was also employed to determine the environmental drivers of these services and interactions. The results showed that most ecosystem services had a similar spatial distribution pattern with an increasing trend from northwest to southeast. Over the past 40 years, ecosystem services in the Hexi Region have improved significantly, with the water retention and soil retention increasing by 87.17 × 108 m3 and 287.84 × 108 t, respectively, and the sand fixation decreasing by 369.17 × 104 t. Among these ecosystem services, strong synergistic relationships were detected, while the trade-offs were found to be weak, and showed significant spatial heterogeneity in the Hexi Region. The spatial synergies and trade-offs in the Qilian Mountains were 1.02 and 1.37 times higher than those in the Hexi Corridor, respectively. Human activities were found to exacerbate the trade-offs between ecosystem services by increasing water consumption in the Hexi Corridor, with the exception of carbon storage. In particular, there were significant tradeoffs between food production and water retention, and between soil retention and habitat quality in the oases of the Hexi Corridor, which is affected by rapid population growth and cropland expansion. Additionally, precipitation, temperature and vegetation cover in the Qilian Mountains have increased significantly over the past four decades, and these increases significantly contributed to the enhancements in water retention, carbon storage, habitat quality, soil retention and food production. Nevertheless, the amount of sand fixation significantly decreased, and this was probably associated with the reduction in wind speed over the past four decades. Our results highlighted the importance of climate wetting and water resource management in the enhancement of ecosystem services and the mitigation of food production trade-offs for arid inland regions. [ABSTRACT FROM AUTHOR]

• A SOTE-WNN model to study s , C s and E x dynamics in cold/arid agricultural regions is introduced. • Soil degradation risks and crop production losses induced by C s and E x are aggravating in the SRW. • Trade-offs between irrigation water quality and GTD need to be emphasized in arid agro-ecosystems. Salinity and sodicity posing large risks to soil hydroecological functioning and agricultural production. However, a comprehensive investigating of the long-term salinity and sodicity dynamics and how these contribute to soil degradation risk and plant response in intensive irrigated agro-ecosystems is still scarce, especially in cold/arid agricultural regions. To quantify long-term soil degradation risk and plant response as driven by rainfall, irrigation and groundwater in seasonally-frozen arid regions, taking into account the influence of capillary flux from shallow brackish groundwater and annual soil freezing-thawing cycles and snowmelt infiltration to soil moisture (s), salinity (C s) and sodicity (E x), we coupled the Salt of the Earth (SOTE) model and the Wavelet Neural Network (WNN) model (i.e. SOTE-WNN model) as well as improved the Crop Response to the Soil Environment (ANSWER) model. The long-term dynamics of root zone s , C s and E x and therefore soil degradation risks and plant responses in irrigated agro-ecosystems in three different hydrological regions (i.e. ADFO: alluvial-diluvial-fan oasis; APOU: alluvial-plain oasis in the upper part; and APOL: alluvial-plain oasis in the lower part) in the Sangong River watershed (SRW) of northwestern China were investigated. The SOTE-WNN model was calibrated and validated using field comprehensive observations during April 2018–April 2021. The simulated results of root zone s , C s and E x resulted in a good agreement with the observed values in the SRW. Results showed that the s in the three hydrological regions has a similar periodic steady state with sawtooth pattern; the C s is the largest in the APOL and corresponding the crop relative yield is the lowest; in the APOU the E x is the largest and corresponding the soil degradation risk is the highest. Carried out sensitivity analysis revealed that the increase in rainfall and snowfall can clearly alleviate soil degradation by reducing soil alkalization in the root zone. The irrigation water quality is one of the primary controls on long-term dynamics of root zone s , C s and E x , and imposing adverse impact on soil hydraulic conductivity and agricultural crop productivity. The shallow groundwater table and quality have non-monotonic effects on the root zone s , C s and E x dynamics, the 2–3 m is the critical water table interval that limits soil salinization and alkalization hazards in the SRW. The results highlight that the trade-offs between irrigation water quality and water table need to be emphasized at appropriate spatial and temporal scales when promoting intensive irrigation practices in arid/cold climate regions. [ABSTRACT FROM AUTHOR]

The Ecological Water Transfer and Rehabilitation Project in the arid inland area of northwest China is an important measure in restoring a deteriorated ecosystem. However, the sustainability of the project is affected by many socio-economic factors. This article examines the attitudes of the local populace toward the project, its impact on the livelihood of the people, and the positive effects of water-efficient agricultural practices in Ejina County. Related data were collected through questionnaire surveys and group discussions. The results identified three critical issues that may influence the sustainability of the project in the study area. The first issue relates to the impact of the project on the livelihood of local herdsmen. The potential for the sustainability of the project is compromised because the livelihood of the herdsmen greatly depends on the compensation awarded by the project. The second issue is that the project did not raise the water resource utilization ratio, which may undermine its final purpose. Finally, the compensation provided by the project considers losses in agriculture, but neglects the externalities and public benefit of eco-water. Thus, appropriate compensation mechanisms should be established and adopted according to local economic, environmental, and social conditions. Some recommendations for improving the sustainability of the project are provided based on the results of this study. [ABSTRACT FROM AUTHOR]

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

• The calculated initial abstraction ratios varied from 0.18 to 0.89, with a median of 0.51. • Using initial abstraction ratio of 0.2 was not appropriate for runoff prediction of green roofs. • Using initial abstraction ratio of 0.05 was highly improved the accuracy of runoff prediction. • Median CN value was modified to 96 while using the optimal initial abstraction ratio of 0.05. • Incorporating antecedent substrate moisture into initial abstraction ratio was needed. The widespread adoption of green roof technology in urban stormwater management practices requires the use of adequate modelling and evaluating tools. Soil Conservation Service-Curve Number (SCS-CN) method is the most common adopted and simple method for runoff prediction of green roofs. However, the standard initial abstraction ratio is the most ambiguous assumption and requires dedicated adjustments in runoff prediction. In this study, the initial abstraction ratios of green roofs in SCS-CN method were determined using rainfall-runoff event analysis from the simulated rainfall experiments for runoff plots of green roofs. Influences of the standard and modified initial abstraction ratios on runoff estimation of green roofs were investigated and evaluated. Results showed that the calculated I a / S ratios varied from 0.18 to 0.89, with a median of 0.51. The SCS-CN method for initial abstraction ratios using 0.5 and 0.2 values were underestimated runoff volume, thus they were not appropriately used for runoff prediction of green roofs. However, evaluated results revealed that runoff prediction using I a / S = 0.05 was significantly improved than that predicted using I a / S = 0.2. The estimation of green roof runoff using I a / S = 0.05 provided the best model efficiency MAE, RMSE, NSE and WI among the predictions using the modified initial abstraction ratios of 0.2, 0.5, 0.05 and 0.02. Particularly, the NSE and WI values of I a / S = 0.05 were improved to 0.88 and 0.97 respectively. Accordingly, the median CN value was modified to 96 while using I a / S = 0.05. A significantly negative relationship was found between antecedent substrate moisture and I a / S ratios of green roofs. These results suggested that an optimal initial abstraction ratio of 0.05 with modified CN values used in the SCS-CN method can highly improve the accuracy of runoff prediction for green roofs. [ABSTRACT FROM AUTHOR]

• The hydrology changes is sensitive to energy in high-altitude. • The hydrology changes is controlled by water limitation in low-altitude area. • The water-energy coupling relation highly relies on altitudinal gradient. • Climate change dominate the hydrological shifts in alpine region. Hydrology heterogeneity refers to the different water regimes or hydrological processes in response to heterogeneous in topography, landscapes, land cover, soil properties, geology and meteorology reflecting as the spatial variation of precipitation, evapotranspiration and water yield along with landscape, elevation, terrain and climate variation. However, the hydrology heterogeneity in the alpine region of inland river basin has remained unclear to date, which limits the understanding of the hydrology and landscape interaction mechanism and affects the rational utilization of regional water resources. In this study, we combined the soil and water assessment tool (SWAT) and water-energy coupling framework to detect the hydrology heterogeneity in the arid alpine region of Heihe River Basin (HRB). We applied SWAT model to present the hydrological processes and regimes at different landscapes and elevation bands by using field measured parameters, and investigate the hydrology heterogeneity as well as the response to the changes in recent climate and land surface in the perspective of water-energy coupling framework. The results indicate that SWAT is indeed a robust tool in representing the streamflow process in alpine region with accurate performance. The distribution of landscapes reflect the comprehensive effect of regional water-energy coupling, which highly rely on the altitudinal gradient. The hydrology heterogeneity in high-altitude area is sensitive to energy and in low-altitude area is sensitive to water limitation (drought stress). Climate change is the dominate factor that driving the hydrology heterogeneity shifts in alpine region of HRB, while, the effect of land surface change is gradually strengthening over the past 50 years, reflecting with the contribution of land surface change on hydrology shifts is gradually increasing. [ABSTRACT FROM AUTHOR]

• Soil salinity negatively affected soil bacterial diversity. • The community structure in solonchak was simpler and more prone to damage. • Rare taxa were as important as abundant taxa for co-occurrence network stability. • Community assembly was gradually dominated by stochasticity as salinity increased. Soil salinization has become the most expansive form of soil degradation in arid and semiarid regions, and the management of soil salinization is imperative for achieving sustainable development. Soil microorganisms are supposed to play an integral role in controlling soil salinization, and the effects of high-salt environments on microbial community have been widely investigated, but there is currently limited comprehensive study on taxon co-occurrence patterns and assembly processes under different salt intensities. Here, based on high-throughput sequencing technologies, we analysed bacterial community structure and assembly mechanism under salt intensity in arid and semiarid regions. The results demonstrated that bacterial diversity was negatively correlated with soil salinity, and community structure also varied with changes in salt intensity. Solonchaks (soils with high soluble salt accumulation) had the lowest average degree of bacterial co-occurrence network, and there was a lower level of connectivity and correlation among bacteria in solonchaks compared to other salt-affected soils. The highest competitive connections among soil bacteria were detected in light-intensity saline soils, whereas overall collaborative connections increased with soil salinity. For co-occurrence network stability, the rare taxa (with each taxon's relative abundance < 0.1%) were more essential than the abundant taxa (> 1%). As soil salinity increased, stochastic processes gradually dominated the community assembly, and the dispersal limitation contributed from 45.18% to 58.73%. These findings offered valuable information about how soil salt intensity affected soil bacterial community and would be useful in controlling soil salinization. [ABSTRACT FROM AUTHOR]

• MNC contributed the most to SOC in dry sub-humid zone than other climate zones. • BNC contributed more to SOC than FNC for semi-arid zones. • Aridity shifts cause divergent impacts on MNC and MNC:SOC with varied soil environments. Microbial necromass is supposed to play fundamental role in contributing to soil organic carbon (SOC) stabilization, while variations and controls of grassland soil microbial necromass carbon (MNC) accumulation along aridity gradients remains unclear. In this study, we obtained data for 201 MNC concentrations in grasslands, and divided them into four categories according to aridity for further synthesized data analysis, i.e., humid, dry sub-humid, semi-arid and arid zones. Results showed that soil MNC was an essential contributor to SOC in grasslands, accounting for 47% to 66% of the SOC contents with the highest proportion in dry sub-humid zones compared with humid, semi-arid and arid zones. Bacterial necromass carbon (BNC) contributed more to SOC than fungal necromass carbon (FNC) for semi-arid zones, while FNC was more important in other climate zones. As for contributions of necromass carbon to SOC, soil pH and textures played more important roles in semi-arid and arid zones than climate did, while climate mattered in humid and dry sub-humid zones. Structural equation modelling analysis indicated that soil pH not only had a direct negative effect on soil FNC but also indirectly affected soil BNC by altering SOC. Mean annual temperature and soil C:N could also significantly affect soil FNC, BNC and MNC by regulating SOC and pH. Our results highlighted that aridity shifts may cause divergent impacts on MNC and the proportion of necromass carbon to SOC in grasslands with varied soil environments. [ABSTRACT FROM AUTHOR]

• VWC variations of green roofs among different structural configurations were remarkably varied. • Average substrate moisture loss rate in summer and autumn was 1.35 and 1.22 mm/day, respectively. • The differences of mean VWC among substrate materials and vegetation types were all significant. • Relative humidity was the most significant factor on VWC, followed by ADWP and precipitation. • Crop coefficient and water holding capacity were the key parameters for moisture content simulation. Substrate moisture condition is crucial for hydrological performance, water management and plant survival of green roofs. To date, the behaviour of long-term substrate moisture of green roofs in various climate regions has not been well understood. In this study, 24 months continuous field monitoring of substrate moisture content within nine extensive green roof modules with varies structural configurations was conducted to investigate the impacts of structural configurations and meteorological factors on substrate moisture content, and identify the key parameters for simulating the long-term substrate moisture dynamics. Results showed that green roofs planted with Sedum Spectabile have the highest mean volumetric water content (VWC) (0.12–0.15 m3/m3) compared to other plant species considered. Green roofs with 5-cm substrate depth had lower mean VWC (0.07–0.08 m3/m3) than other substrate depths. The average substrate moisture loss rate of green roofs in summer and autumn seasons was 1.35 and 1.22 mm/day, respectively, which was higher than the spring (0.73 mm/day) and winter (0.64 mm/day) seasons for 2021. There were significant differences in mean VWC of green roofs among substrate material types. The mean VWC of green roofs was gradually enhanced from 0.12 to 0.14 m3/m3 as the substrate depth increased from 5 cm to 15 cm. The differences of mean VWC among vegetation types were all extremely significant (p < 0.001). The relative humidity was the most significant influencing factor on the average VWC level (correlation coefficient r = 0.42), with antecedent dry weather period (ADWP) had less significant effects on substrate VWC (r = 0.33), and followed by precipitation depth (r = 0.27). However, there was no significant relationship between air temperature and average VWC level of green roofs as well as total solar radiation. Nash-Sutcliffe efficient (NSE) values of the model simulations ranged from 0.70 to 0.81, and the mean absolute relative error (MAE) values ranged from 1.25 to 2.36, which indicated the model can adequately simulate the long-term substrate moisture content dynamics of green roofs. The crop coefficient and maximum water holding capacity of the substrate were the key parameters affecting long-term moisture content simulation of green roofs. These results could provide scientific suggestions for selecting suitable structural configuration to enhance water holding capacity of extensive green roofs in arid climates. [ABSTRACT FROM AUTHOR]

Soil organic carbon (SOC) storage in arid inland regions is significantly affected by land use and land cover change (LUCC) associated with climate change and agricultural activities. A systematic evaluation to the LUCC effects on SOC storage could enable us to better manage soil carbon pools in arid inland regions. Here, we evaluated the effects of LUCC on SOC storage in the Hexi Regions based on high-resolution SOC and LUCC maps derived from Landsat imagery and digital soil mapping using machine learning algorithm and environmental covariates. The results showed that SOC generally increased from northwest to southeast over the Hexi Regions with an average stock of 7.15 kg C m−2 at a soil depth of 100 cm and a total storage of 2783.05 Tg C. The SOC stock and storage in the Qilian Mountains (mountains) was about 3.90 and 4.55 times higher than that in the Hexi Corridor (plains), respectively. It was estimated that LUCC over the past four decades caused a net increase of 23.41 and 18.19 Tg C in total SOC storage for the Qilian Mountains and Hexi Corridor, respectively. Specifically, the development in grasslands quality as well as the land-use category conversion from the bare land to grassland mainly contributed to the increase in SOC storage of the Qilian Mountains, where the LUCC was mainly driven by climate change. By contrast, the SOC storage change in the Hexi Corridor was mainly associated with the conversion from sandy land and low-cover grassland to cropland as well as sandy land to grassland, being mainly affected by intense cropland expansion and desertification control. Our results highlighted the importance of climate change and cropland expansion in enhancing SOC storage of the Qilian Mountains and Hexi corridor, respectively. • The high-resolution soil organic carbon (SOC) and land use change maps was used. • The Hexi Regions SOC show an increasing trend caused by land use change during 1980–2018. • The climate change and cropland expansion enhanced SOC storage of the Qilian Mountains and Hexi Corridor, respectively. • The local should balance agricultural and ecological water to further enhance SOC storage. [ABSTRACT FROM AUTHOR]

Salinization is considered a significant threat to soil ecosystem and plant growth in arid and semiarid regions. Soil microorganisms are supposed to be essential in relieving soil salinization and enhancing plant salt tolerance. However, although the responses of soil fungal diversity and community structure to salt stress have been investigated, major knowledge gaps remain in the interactions and community assembly of abundant and rare fungal taxa, and fungal functional characteristics under different salt intensities. Here, next-generation sequencing technology were used to investigate the response of all, abundant and rare fungal taxa to salt stress in arid and semiarid regions. The results demonstrated that high salt stress reduced the complexity and stability of fungal networks and increased fungal collaborations. Rare taxa held a key position in the co-occurrence network and exhibited greater proficiency in collaborating with intermediate and rare taxa, thereby augmenting the resistance of the community and maintaining its stability. Notably, with increasing salt stress, the importance of rare taxa gradually enhanced, while the importance of abundant taxa decreased. Moreover, fungal communities were manipulated by stochastic processes under salt stress, while were also influenced by deterministic processes (heterogeneous selection), especially for rare taxa. Furthermore, low salinity conditions promoted the colonization of saprophytic and symbiotic fungi and inhibited the growth of pathogenic fungi. Functional groups associated with fungal parasite-soil saprotroph-undefined saprotroph function were extremely sensitive to soil salinity and exerted a pivotal influence in sustaining community stability. Our findings may broaden our understanding of how abundant and rare fungi react to salt stress, making it easier to forecast the possible loss of biodiversity due to soil salinization, and offering microbial references for the development of saline-alkaline soil. [Display omitted] • Fungal networks were less stable but more collaborative under salt stress. • Rare taxa were more robust in sustaining community stability than abundant taxa. • Rich and rare taxa's importance gap in sustaining network increased as salinity rose. • Stochastic processes gradually dominated community assembly as salinity increased. • Heterogeneous selection contributed more to rare taxa assembly than to abundant taxa. [ABSTRACT FROM AUTHOR]

Desertification control and oasis management are of strategic importance for the protection of ecological security and the achievement of sustainable development in arid regions. However, the role of soil microorganisms in desertification and oasification has been historically overlooked, especially for the influence of microbial communities on landscape change and the stability of soil-vegetation system in desert-oasis ecosystems. Here, using an environmental sampling approach combined with functional annotation, the landscape differentiation of soil bacterial diversity, community structure and functional traits, as well as the bacteria-soil-vegetation interactions were investigated in desert, oasis and desert-oasis ecotone habitats. The results showed that soil bacterial diversity increased significantly from desert, ecotone to oasis, and the highest spatial differentiation of bacterial diversity was observed in desert. The simplest and unique bacterial composition was detected in desert, which was dominant by Arthrobacter , Streptomyces , Burkholderia , etc. However, the phyla Actinobacteria, Proteobacteria, Acidobacteria, Chloroflexi, and the genus Candidatus_Nitrososphaera were the crucial biomarkers for distinguishing the composition differences across different landscapes. In terms of bacterial composition shift, it was far more challenging to go from ecotone to oasis than from desert to ecotone. Meanwhile, the most stable functional network was exhibited in oasis, while the simplest network was detected in ecotone rather than in desert. Relatively high soil moisture, total nitrogen, organic carbon, total phosphorus, and silt and clay proportions played decisive roles in improving microbial diversity, community structure and functional service, which would enhance the stability and diversity of desert-oasis ecosystems. Furthermore, increase in the relative abundances of functional genes, which were related to metabolism, environmental information processing, and organismal systems, may be harmful to nitrogen cycling and vegetation growth. These results conclude that the landscape differentiation of soil bacteria in desert, ecotone and oasis identifies the central role of bacterial interactions in ecosystem processes and highlights the importance of landscape stability control, forming a novel perspective of microbial behaviour in controlling landscape stability in desert-oasis ecosystems. • The highest spatial differentiation of soil bacterial diversity was observed in desert. • Shift in bacterial composition from desert to ecotone was much easier than that from ecotone to oasis. • Functional network in desert was more stable than in ecotone. • Increase in the relative abundances of some functional genes may be harmful to nitrogen cycling and vegetation growth. [ABSTRACT FROM AUTHOR]

Abstract: There is little information regarding the sustainability of the high yield agroecosystem with double ridges and furrows mulched with plastic film in semi-arid areas. In this study, we explored the sustainability of this agroecosystem with different mulching time during two growing seasons over 2006 and 2007. Three treatments were designed: (i) plastic film mulching applied at sowing and film removed at harvest (CK); (ii) mulching applied 30 days before sowing and removed at harvest (M1); and (iii) mulching applied at sowing and film left on field after harvest and used continually for mulching in the second season (M2). Microbial biomass C (MBC) and ratio of MBC to soil organic C (SOC) (MBC/SOC) were higher in M1 and M2 than in CK in 2007 growing season. The reduction rates of the ratios of light fraction of organic C (LFOC) to SOC (LFOC/SOC) with sampling dates were 0.0020, 0.0047 and 0.0045 for CK, M1 and M2, respectively. A larger value means a faster reduction rate of LFOC/SOC with sampling dates, and implying farming system would face a higher unsustainable risk. MBC correlated negative significantly with LFOC (R = −0.939, P = 0.0001) and mineral N (R = −0.835, P = 0.0007) due to low soil C pool. Accordingly, film mulched ridge and furrow system would threaten the sustainability of soil ecosystem via MBC increase a semi-arid agroecosystem. The practices of mulching applied 30 d before sowing (M1) and use of plastic film once every two years (M2) lead to increased environmental risk for the farming system. [Copyright &y& Elsevier]