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Lake surface morphology, an essential yet underexplored feature of hydrological systems, remains poorly understood, including its effects on water volume estimation. This study investigates north‐south surface profiles of 147 lakes worldwide using ICESat‐2 altimetry data (2018–2024). A meticulous selection process, followed by DBSCAN clustering and moving window averaging, enabled the construction of detailed elevation profiles. Based on metrics of linearity, concavity, and convexity, we classified lake surface morphology into four types: linear, concave, convex, and others. Concave surfaces were the most common (67/147 lakes), while convex surfaces were the least common (11/147 lakes). The formation of these surface types is influenced by factors such as groundwater flow, salinity gradients, and lakebed variations. Surface elevation differences ranged from 0.016 to 2.565 m, averaging 0.221 m. To address the impacts of these variations, we calculated equivalent water surface height (heq) and demonstrated that concave lakes overestimate lake surface height by an average of 0.093 m. Although the volumetric overestimation may seem small (e.g., 0.78% for Lake Victoria), 41% of lakes showed surface elevation differences exceeding their mean monthly variation, posing a risk of trend misinterpretation (e.g., Lake Victoria: elevation difference 0.59 m, standard deviation 0.16 m, monthly variation 0.044 m). These results underscore the critical importance of incorporating lake surface morphology into hydrological assessments, offering a new perspective that could lead to more accurate and comprehensive water volume estimations and ultimately improve global water resource management. Key Points Global lake surfaces are classified into concave, convex, linear, and mixed types with ICESat‐2, refining surface variability studies Wind, groundwater, salinity, and lakebed topography are suggested as factors shaping lake surface morphology Uneven lake surfaces affect volume estimation, with errors quantified using equivalent surface height

The low-resolution characteristic of Gravity Recovery and Climate Experiment (GRACE) satellite data greatly limits their application in many fields at regional or local scales. Aiming to overcome this limitation, the partial least squares regression (PLSR) model is firstly utilized to assess the importance of some independent variables that are commonly employed in GRACE downscaling research. Three kinds of downscaling models are chosen to improve the resolution of GRACE-based water storage estimates from 1 to 0.25°, namely: multivariable linear regression, random forest (RF), and NoahV2.1. Results indicate that terrestrial water storage anomalies are more closely related to four independent variables in the Haihe River Basin, China: these variables are evapotranspiration, land surface temperature, air temperature, and soil moisture. With respect to the spatial distribution, the downscaled results based on the NoahV2.1 and RF models can effectively capture the subgrid heterogeneity while preserving the water storage characteristics at the original scale. By verifying the downscaled results with measured groundwater levels, it can be observed that the correlation coefficient between the RF-based downscaled groundwater storage anomalies (GWSA) and in-situ measurements is increased by 20.55% (Beijing), 9.13% (Tianjin), and 10.48% (Hebei) relative to the downscaled results based on the NoahV2.1 model. The cross wavelet transform illustrates that the meteorological factors have a strong influence on the GWSA series in the Haihe River Basin with an approximately 12-month signal during 2003–2016. This study can provide high-resolution GWSA datasets for water resources management and also provide a reference for the selection of dominant independent variables.

In this study, the regional spatial-temporal variability of cadmium (Cd) in the topsoil of Guangxi, China from 2010 to 2016 was studied from data obtained from the China Geochemical Baseline Project (CGB Ⅰ and CGB Ⅱ). The driving forces of natural and anthropogenic variables were quantitatively analyzed using a geographically and temporally weighted regression model. The results showed that 1) soil Cd was highly enriched in 2010 and in soils of Hechi city in northwest Guangxi, a non-ferrous metal mining and metallurgy area, ~17% of the samples exceeded the soil contamination risk limit. In contrast, in 2016, the topsoil Cd content decreased significantly, with 7% of sites exceeding the soil risk limit. 2) Multiple factors jointly influenced the regional spatial variability of Cd. pH and organic carbon were found to be the main factors influencing Cd content and were strongly spatially correlated with Cd. Anthropogenic activities, including mining and industrial emissions, resulted in significant Cd enrichment in local areas, whereas agricultural and domestic pollutants were relatively weakly correlated with Cd. The weathering products of carbonates were significantly enriched in Cd; thus, the geological background played a significant role in the spatial variability of Cd. Soil-forming factors, including temperature, precipitation, and elevation influenced the spatial distribution of Cd, especially in the Cd background area. 3) Anthropogenic activities were the key factors influencing temporal changes in Cd. Mining caused significant enrichment of Cd in CGB Ⅰ, while industrial emissions were the primary factor for Cd enrichment in CGB Ⅱ. In addition, natural factors also played an important role; the increased Normalized Difference Vegetation Index suggested reduced desertification and reduction of soil erosion in the watershed and in pollutants transported from upstream.

Deep groundwater characteristics provide valuable information on oil and gas extraction and evolution of hydrosphere, and nonmetallic and metallic elements in deep groundwater are raising industrial interest. There is therefore a need for a better understanding of the origin and evolution of deep groundwater in large sedimentary basins, e.g., by using non-traditional isotopes. Here, we review the constraints of isotopes of chloride (Cl), bromine (Br), boron (B), lithium (Li), helium (He), neon (Ne), and argon (Ar) on the origin and evolution of deep groundwater in large sedimentary basins. In deep groundwater, δ 37 Cl ranges from −1.96 to + 2.07‰, δ 81 Br from −1.50 to + 3.35‰, δ 11 B from + 1.10 to + 39.99‰, and δ 7 Li from −1.00 to + 31.80‰. These values either overlap or are different compared to those in freshwater, e.g., meteoric water, river water and shallow groundwater, hydrothermal fluid, seawater, subsurface brine, lake sediment, or mineral. Noble gas isotopes such as 3 He/ 4 He, 4 He/ 20 Ne, and 36 Ar/ 40 Ar are also effective tracers for deep groundwater evolution. Integrating multiple non-traditional isotopes allows to study dissolution, sedimentation, evaporation, and mixing of different waters in deep aquifers.

It is of significance to elucidate the groundwater quality and hydrogeochemical processes for sustainable utilization of groundwater resources in water shortage regions. A total of 256 groundwater samples were collected in typical watersheds in Zhangjiakou, northern China. The hydrochemical parameters, conventional ions, and trace elements were measured, and δD and δ 18 O data were collected to delineate the groundwater quality and hydrogeochemical processes. The results showed that 32.91% of the groundwater could be directly used for drinking water sources in the Bashang Plateau, north of the study area. The F − and NO 3 − -N were the main parameters above the standard threshold for drinking water. In contrast, the groundwater quality in the Baxia River Basins, south of the study area, was of a better scenario. Nonetheless, high concentrations of F − , total hardness, and SO 4 2− were still observed. Most samples in the Bashang Plateau had relatively higher salinity than the Baxia River Basins. Both surface water and groundwater in the study area originated from local meteoric water with considerable hydraulic connections. The high-fluoride groundwater was primarily formed by dissolution of fluoride-rich minerals under conditions of high pH and Na + , low Ca 2+ , and rich in HCO 3 − . The dissolution of carbonate and silicate minerals accompanied by strong cation exchange and weak evaporation was the dominant water-rock interaction affecting the hydrochemical composition of groundwater, and anthropogenic NO 3 − input had an extra influence on hydrochemical process. This study provides a scientific guideline for the protection and allocation of local groundwater resources.

Resistance, resilience, and recovery time are critical for quantifying the stability of grasslands in response to drought disturbances. Few studies have simultaneously considered both drought intensity and duration to analyze the stability of different grassland types, which may overlook short-term extreme or long-term cumulative effects. This study used the monthly Standardized Precipitation Evapotranspiration Index (SPEI) to identify distinct drought patterns in Inner Mongolia, China, from 1998 to 2020, accounting for both intensity and duration. Grassland stability was assessed using monthly SPOT-VGT Normalized Difference Vegetation Index (NDVI) data. We focused on the vegetation response to short-term climate changes while minimizing the influence of seasonal fluctuations in vegetation growth. Six drought patterns were identified, and the resistance of grassland types under the same drought pattern followed this order: temperate desert steppe (TDS) > temperate typical steppe (TTS) > temperate meadow steppe (TMS). Resilience was ranked as TDS < TTS < TMS, while recovery time followed the reverse trend: TDS > TTS > TMS. A trade-off was observed between resilience and resistance. Most grasslands were able to recover within five months following a drought. These findings provide scientific support for enhancing ecosystem adaptability to climate change and for managing grassland resources more effectively.

Xilinhot City is a significant pastoral city in China where groundwater serves as the primary water source for the cold and arid pastoral regions. The formation and evolution of material components in groundwater, as well as groundwater quality, are directly linked to the health of pastoral residents. This study is based on the physical and chemical test results of 22 groundwater samples collected from the Xilinhot River Basin in Inner Mongolia. Various statistical analyses, including Piper and Chadha diagrams, as well as hydrogeochemical simulation methods, were employed to assess the hydrogeochemical characteristics and material composition sources of groundwater, evaluate groundwater quality and non-carcinogenic risks, and comprehensively discuss the impact of macro- and microelements on human health. The findings indicate that igneous rocks containing minerals such as potassium feldspar, plagioclase, and pyroxene contribute Na+, Cl−, and K+ to the groundwater, while sedimentary rocks containing minerals like dolomite and calcite supply ions such as Ca2+, Mg2+, and HCO3−. The groundwater quality is primarily classified as Class II–V, with F− and NO3− exhibiting varying hazard quotients for children and adults in the study area, though they do not pose a non-carcinogenic risk. Additionally, the enrichment of hardness, Ca2+, Mg2+, Na+, SO42−, and other indicators in localized areas exceeds the recommended values for drinking water, potentially impacting the digestive and urinary systems of the human body. There is a risk of excessive fluoride in areas where F levels exceed 1 mg/L. Furthermore, the content of beneficial micronutrients such as selenium (Se), zinc (Zn), boron (B), and germanium (Ge) is relatively low. Based on the elemental abundance characteristics and a comparative analysis of the chemical properties of groundwater across five regions of China, this comparison facilitates a discussion on the definition of healthy groundwater, particularly in relation to safe consumption in cold and arid regions. This study aims to highlight the health issues associated with drinking groundwater in the cold and arid regions of Mongolia. The findings serve as a valuable reference for efforts aimed at reducing the incidence of endemic diseases and enhancing human lifespan.

As an important drinking water source for Beijing, the capital of China, the water inflow of Miyun Reservoir has been decreasing year by year, which has affected the urban water supply security. To understand the variation trend of the inflow and analyze the main factors influencing the runoff change, this research focused on the watershed of Miyun Reservoir as the target. Based on the runoff data from 1984 to 2020 at the outlet of the basin, as well as the precipitation, potential evaporation intensity, NDVI (normalized difference vegetation index), population, and GDP (Gross Domestic Product) data, combined with correlation analysis methods, empirical statistical methods, the SCRCQ (Slope Change Ratio of Cumulative Quantity) method, and the GIS, the interannual variation characteristics of various elements in the basin were analyzed, the correlation between runoff and other factors was studied, and the influencing degrees of precipitation, water surface evaporation intensity, human activities, and other factors on the runoff change in the basin were quantitatively separated. The research results showed that the runoff exhibited a distinct decreasing trend, and there were two mutation points in the basin runoff from 1984 to 2020, which were 1995 and 2014, respectively. The runoff change was divided into three stages: 1984–1995 (upward trend in T1), 1995–2014 (downward trend in T2), and 2014–2020 (stable trend in T3). Runoff was significantly correlated with four indicators: the summer leaf area index of the Chaohe River and Baihe River, the regional GDP and population, among which the correlation of the summer leaf area index was the largest. Compared with the period T1, the contribution rates of climate change to the runoff reduction in T2 and T3 were 6.38% and 5.73%, and the contribution rates of human activities to the runoff reduction were 93.62% and 94.27%, respectively. Therefore, the change in annual runoff in the Miyun Reservoir watershed is mainly affected by human activities, and the contribution of climate change to the runoff attenuation is weak. This study is significant in the maintenance and enhancement of runoff in typical watershed.

The Upper Paleozoic in the southwestern Ordos Basin has significant potential for natural gas exploration. This study investigated the diagenetic fluid evolution and hydrocarbon accumulation characteristics of He 8 section from Permian Lower Shihezi formation and Shan 1 section from Shanxi formation tight sandstone reservoirs by petrographic observation, scanning electron microscope imaging, fluid inclusion study, and laser Raman spectrum analysis. The results show that He 8 section and Shan 1 section reservoirs are mainly composed of quartz sandstone, subordinate arkose quartz sandstone, and lithic quartz sandstone, with minor lithic sandstone and lithic arkose sandstone. The major pores are intergranular dissolved pores. The main diagenetic minerals include quartz overgrowth, siliceous cement, carbonate cement, illite, montmorillonite, and mixed-layer clay minerals. The overall diagenetic features show strong compaction, multistage siliceous and calcareous cements, and abundant clay minerals, strong dissolution, and well-developed fractures. Two stages of fluid inclusions developed in the He 8 and Shan 1 sections recorded the migration and accumulation of the early-stage and late-stage natural gas, respectively. The reservoir in the study area experienced early and late diagenetic stages, and its formation was simultaneous with or after its densification. The diagenetic environment changed from alkaline to acidic and again into alkaline. There are two stages of fluid activities in the study area, namely, the early diagenetic stage corresponding to hydrocarbon generation and migration and the late diagenetic stage corresponding to hydrocarbon accumulation. This study suggests that Upper Paleozoic natural gas migrated into the reservoir in Weibei Uplift, Yishan Slope, and Tianhuan Depression tectonic units during 220-197 Ma, and the large-scale migration and accumulation occurred in these tectonic units at different times. No natural gas was generated in the west margin of the basin because the temperatures of the hydrocarbon source rocks in the Upper Paleozoic were below the gas window.

The northeastern part of the Ordos Basin is the main recharge area of regional groundwater, the groundwater resources are relatively scarce. The main water supply source in the area is shallow groundwater, and there are many industrial and mining enterprises in the district. The potential groundwater pollution risk is high, and the the shallow groundwater vulnerability evaluation in the region is of great significance for groundwater resources protection.The weight of each indicator of the traditional DRASTIC model is fixed and does not change with the regional conditions, which may cause deviations in the evaluation results. This time, based on the DRASTIC model, the entropy weight coefficient method is introduced to determine the index weight, and the DRASTIC entropy weight model is established to obtain a more scientific and close to the actual conditions of the study area, and provide an important reference and basis for the protection of regional groundwater resources.