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Regional processes on land-water-air interface carbon (C) budget and balance that interconnect the land and sea are in fact C neutrality critical processes within the earth system. It is therefore essential to quantitatively analyze synergistic land-water-air interface C transport and C exchange processes to gain a deep understanding of the important role that terrestrial ecosystems play in "missing C sink". This paper systematically analyzes global land-water-air interface C migration processes as well as C budget changes and associated impact mechanisms. It also investigates the important role that these C budgets and C cycling processes play in inland water bodies, respective to C budgets at the land-water-air interface. Moreover, this study reveals the regulatory mechanisms of land-water-air interface C budgets and balances under a background of global climate change. It also quantitatively evaluates the status of China's regional land-sea-air interface C budgets as well as the C sequestration potential of its lake systems. Finally, this study concludes that the explicit quantification of anthropogenic activity impacts on land-water-air interface C transport and exchange processes is of great significance to global C balances and C neutrality. [ABSTRACT FROM AUTHOR]

The extent and mechanisms by which precipitation extremes affect hydrological processes in the critical zone (CZ) of loess possessing a thick unsaturated zone remains poorly understood. To this end, we here employed a coupled liquid‒vapor‒heat‒airflow STEMMUS (simultaneous transfer of energy, mass, and momentum in unsaturated soil) model to investigate the impact of extreme precipitation, at both event and annual scales, on CZ hydrological processes within a semiarid loess site vegetated by apple trees on China's Loess Plateau. At the event scale, the vapor flux was two orders of magnitude lower than the liquid water flux. However, the thermal vapor flux penetrated to depths of 200 cm, whereas the isothermal liquid water flux only infiltrated to 100 cm during the study period, implying that thermal‐gradient‐driven vapor transfer is an important mechanism for deep‐layer recharge (DLR). At the annual scale, the DLR below 200 cm during extremely wet years was 6.5 times larger than that during extremely dry years. In contrast, extreme changes in climate had only limited impacts on evapotranspiration; the difference between extremely wet and extremely dry years averaged only 35 mm, much less than the difference in precipitation, which averaged 310 mm. However, the extremely dry years showed a higher ratio (0.58) between transpiration and evapotranspiration than did the extremely wet years (0.51). The findings reported here improve our understanding of CZ hydrological processes related to precipitation extremes in semiarid loess regions. Key Points: Thermal‐gradient‐driven vapor transfer is an important mechanism for deep‐layer recharge (DLR) in loessThe DLR below 200 cm during extremely wet years was 6.5 times larger than that during extremely dry yearsExtreme changes in precipitation had only limited impacts on evapotranspiration [ABSTRACT FROM AUTHOR]

The effects of climate change and anthropogenic activities on the concentration of heavy metal in maize were quantitatively characterized in this study to help us better understand the complex interactions among the groundwater, vadose, plant, and atmosphere layers in the critical zone. We hypothesized that climate change and groundwater resource exploitation firstly affected the shallow groundwater level, and then the groundwater table fluctuation (GTF) impacted the concentration of heavy metal in maize through the critical zone (CZ) structure and parameters. To test our hypothesis, we collected 960 soil and 288 maize samples from the Luan River catchment in the North China Plain. The Groundwater Modeling System software was used to describe the effects of precipitation and groundwater resource exploitation on the groundwater table, and then, the structural equation method was employed to characterize the quantitative effects of GTF, precipitation, and air temperature on the concentration of heavy metal in maize. The results indicate that the influence coefficients of the effects of climate change and anthropogenic activities on the concentrations of Fe, Mn, Cr As, Pb, and Sr were 0.1595, 0.088, 0.0042, − 0.0092, 0.2219, and 0.0493 in the north plain, respectively, and 0.0256, 0.0151, 0.0816, − 0.2264, 0.1125, and − 0.0106 in the south plain of the study region, respectively. Since the human health risks of metals were mainly attributed to Fe, Mn, and Cr in the Luan River catchment, increasing the groundwater resource exploitation volume is an effective way to decrease the Fe, Mn, and Cr contents in maize by decreasing the shallow groundwater table. [ABSTRACT FROM AUTHOR]