Against the background of a warming and humidifying climate on the Qinghai–Tibet Plateau, increasing attention has been paid to the sustainability of water resources and ecosystems in the Qinghai Lake Basin. Investigating the characteristics of precipitation stable isotopes and moisture sources provides critical insights into the driving mechanisms of the regional hydrological cycle. In this study, precipitation samples collected at the Qinghai Lake Wetland Ecosystem National Observation and Research Station from June 2023 to October 2024 were analyzed for hydrogen (δ²H) and oxygen (δ¹⁸O) stable isotopes. The temporal variations of δ²H, δ¹⁸O, and deuterium excess (d-excess) were characterized, and their relationships with air temperature and precipitation amount were examined. In addition, a backward trajectory model was employed to identify the moisture sources of precipitation during the observation period. The results indicate that: (1) precipitation stable isotopes and d-excess exhibit pronounced seasonal variability, characterized by enrichment in summer and depletion in spring and autumn; (2) the Local Meteoric Water Line (LMWL) for the basin is defined as δ²H = 8.15δ¹⁸O + 38.71 (R² = 0.93), with both slope and intercept exceeding those of the Global Meteoric Water Line (GMWL); (3) precipitation isotopes show a discernible temperature effect but are jointly controlled by multiple moisture sources and meteorological factors; and (4) backward trajectory analysis combined with d-excess values reveals that precipitation moisture is primarily derived from westerly transport, while locally recycled moisture and continental air masses also exert significant influences. Overall, these findings reveal the multi-source driving mechanisms of the regional hydrological cycle and provide critical scientific support for understanding hydrological processes in alpine inland basins and their responses to future climate change, thereby contributing to the sustainable management of regional water resources.

To elucidate the recharge relationships and hydrological processes among different water bodies in the Qinghai Lake Basin, precipitation, river water, groundwater, and lake water samples were collected from April to November 2024. The hydrogen and oxygen stable isotope compositions (δ²H and δ¹⁸O) were determined to characterize their spatiotemporal variations, and the MixSIAR model was applied to quantitatively evaluate the recharge contributions among different water bodies. The results show significant differences in stable isotope compositions among the various water bodies. Overall, lake water exhibited the most enriched isotopic signatures, whereas groundwater was the most depleted and isotopically stable, while precipitation displayed the largest variability. Precipitation isotopes exhibited pronounced seasonal effects. River water showed a depletion–enrichment–depletion pattern, reflecting the important recharge contributions from wet season precipitation and frozen-soil meltwater. Groundwater exhibited relatively weak seasonal variations and a distinct smoothing effect. In contrast, the isotopic composition of lake water was jointly controlled by evaporative fractionation and multiple recharge sources, with the highest enrichment occurring in spring and gradual depletion during wet season and dry season. Spatially, significant isotopic differences were observed among rivers. Groundwater was relatively enriched in the western part of the basin and depleted in the eastern part, whereas lake water exhibited an opposite pattern, characterized by enrichment in the east and depletion in the west. The Local Meteoric Water Line (LMWL) of the Qinghai Lake Basin was defined as δ²H = 8.07δ¹⁸O + 37.48 (R² = 0.96). Both the slope and intercept were higher than those of the Global Meteoric Water Line (GMWL), indicating that locally recycled evaporated moisture played an important role in regional precipitation formation. The river water line showed characteristics similar to those of the groundwater line, suggesting strong hydraulic connectivity between river water and groundwater. In contrast, the lake water line deviated markedly from the meteoric water line, indicating significant evaporative fractionation of lake water. The MixSIAR results indicate that the contributions of river water, groundwater, and precipitation to lake water were 37.5%, 33.9%, and 28.6%, respectively. These findings reveal the complex hydrological connections and transformation processes among multiple water bodies in the Qinghai Lake Basin and provide a scientific basis for water resource management and ecological environmental protection in inland basins of the Qinghai–Tibet Plateau.

Desert steppe is a typical ecosystem in arid and semi-arid regions and an important component of the global carbon cycle. Under the background of global climate change, the increasing frequency of extreme precipitation events and changes in precipitation patterns can significantly affect water- and heat-sensitive desert steppe ecosystems, thereby regulating soil CO₂ flux; however, the underlying mechanisms remain unclear. To investigate the effects of precipitation changes on soil CO₂ flux and their roles in carbon cycling and ecological sustainability, this study was conducted in a desert steppe. Seven precipitation treatments were established, including a control (CK) and ±15%, ±30%, and ±45% precipitation gradients. Based on the static chamber-gas chromatography method, combined with principal component analysis (PCA), correlation analysis, random forest modeling, and stepwise regression, the main influencing factors and their diurnal variation patterns of soil CO₂ flux were analyzed over 24 h periods from June to August. The results show that CO₂ flux ranged from −68.33 to 77.59 mg·m⁻²·h⁻¹. During the study period, CO₂ flux exhibited a diurnal pattern characterized by daytime emissions and weak nighttime emissions or uptake, along with clear seasonal variation. The ±30% precipitation treatment showed the largest fluctuation in CO₂ flux. Soil hydrothermal factors were identified as the key drivers of CO₂ flux. With changes in precipitation intensity, the combined effects of multiple factors increased ecosystem complexity, and the controlling factors showed clear seasonal differences. The results from different analytical methods were generally consistent, providing a reference for predicting CO₂ flux, developing carbon sink strategies, and supporting sustainable ecological management in desert steppe regions.

Cold alpine salt-affected soils may retain carbon through mineral protection or suppressed microbial decomposition, but these processes remain difficult to distinguish. We measured soil physicochemical properties, four extracellular enzyme activities, soil organic carbon (SOC), and its dissolved (DOC), particulate (POC), and mineral-associated (MAOC) fractions across five soil types on the Qiangtang Plateau. Multivariate analyses and five XGBoost models interpreted using Shapley additive explanations (SHAP) characterized carbon-enzyme associations and identified leading predictors and nonlinear response transition points. Model performance varied among response variables (CV-R² = 0.4094–0.8815). Soda (SD) soil had a distinct carbon-pool composition, and no significant carbon-enzyme correlations remained after Benjamini–Hochberg correction. pH was the leading predictor of SOC and its fractions, whereas total nitrogen and total phosphorus ranked highest for overall enzyme activity. The fitted SHAP contributions changed from negative to positive between pH 8.50 and 9.00 for the carbon variables and at a total nitrogen concentration of 0.71 g·kg⁻¹ for enzyme activity. These model-dependent transition points indicate that carbon-pool restructuring and nutrient-related changes in enzyme activity occur over different environmental ranges. SD soil contained the highest carbon concentrations but the smallest MAOC proportion and the largest POC and DOC proportions, indicating relative enrichment of labile carbon fractions. By jointly analyzing carbon fractions and enzyme activity within an interpretable XGBoost-SHAP framework, this study helps distinguish high carbon stocks from stable sequestration and shows why total SOC alone may overestimate long-term carbon stability in alpine salt-affected soils.

As a vital ecological security barrier and climate regulator in northwestern China, the Qinghai Lake Basin (QLB) holds significant strategic value for regional ecological conservation and national park development. This study, utilizing land use data from 2010 to 2023 and integrating the InVEST and GeoDetector models, systematically investigated the spatiotemporal dynamics of soil conservation (SC) and its underlying driving mechanisms. The results indicate the following: (1) During the study period, SC services exhibited a gradual declining trend across the selected years, with total SC decreasing from 14.64 × 10³ t to 7.49 × 10³ t. Spatially, high-value areas were predominantly concentrated in the high-altitude forest–grassland ecotones along the basin margins, whereas low-value areas were mainly distributed in the low-altitude zones surrounding the lake and in the northwestern corner of the basin. (2) Among different land use types, forestland, bare land, and grassland constituted the dominant contributing categories, with bare land exhibiting the highest sediment export (SE) intensity (ranging from 8.93 to 19.13 t·hm⁻²·a⁻¹), thereby serving as the primary erosion source area. Along the elevational gradient, the mid-to-high elevation zones (3500–4500 m) contributed the most to total SC, with SC intensity increasing progressively with rising elevation. With respect to slope classes, total SC was predominantly concentrated in the gentle-to-moderate slope zones (5–25°), whereas SC intensity exhibited a non-linear increase with increasing slope steepness. (3) Slope was identified as the single factor with the strongest explanatory power regarding the spatial heterogeneity of SC, and the coupled interactions of “topography–soil–vegetation” exerted a synergistic regulatory effect on SC function. It is recommended that priority attention be given to the mid-to-high elevation contribution zones (3500–4500 m), the total SC contribution zones on gentle-to-moderate slopes (5–25°), and the extremely steep slope areas (>35°) with high erosion risk, so as to implement differentiated soil and water conservation measures. These findings provide a scientific basis for ecological protection, soil and water conservation strategy formulation, and sustainable development in the QLB.