Degraded frozen soil and reduced frost heave in China due to climate warming.

Frost heave hazard is the uneven uplift of the ground surface due to the freezing of water and the expansion of ice bodies in soil, especially in seasonally frozen soil. First, this study quantified temporal and spatial variations of frozen soil, the active layer and frost heave in China in the 2010s. Subsequently, the study predicted the changes in the frozen soil, active layer, and frost heave for the 2030s and 2050s under the SSP1-2.6, SSP2-4.5, and SSP5-8.5 climate scenarios. The permafrost will have degraded to seasonally frozen soil, and the seasonally frozen soil will have a reduced depth or even become non-frozen. By the 2050s, the area of permafrost and seasonally frozen soil will have degraded by 17.6-59.2 % and 4.8-13.5 %, respectively. There is a 19.7-37.2 % reduction in area for seasonally frozen soil when the maximum depth of the seasonally freezing layer (MDSF) < 1.0 m, 8.8-18.5 % when 2.0 < MDSF <3.0 m, and an increase up to 13 % when 1.0 < MDSF <2.0 m. The area with a frost heaving <1.5 cm, 1.5-3.0 cm, 3.0-5.0 cm will have been reduced by 16.6-27.2 %, 18.0-24.4 %, and -8.0-17.1 % in the 2050s, respectively. Areas where permafrost degrades to seasonally frozen soil require attention when managing frost heave hazards. This study will help guide engineering and environmental practices in cold regions.

Permafrost degradation alters the environmental signals recorded in tree-ring lignin methoxy group δ2H in northeastern China.

Climate warming has profoundly altered the status of permafrost and has caused extensive permafrost degradation in the Northern Hemisphere. However, long-term observations investigating the hydrological dynamics of permafrost and its ecological effects on plant growth are lacking. Previous studies have reported tree-ring stable hydrogen isotope ratios of lignin methoxy groups (δ2HLM) as an archive of hydrological signals. This study sampled tree-ring cores from a Larix gmelinii forest in Nanwenghe Forest Park, Northeastern China, and separately measured the tree-ring δ2HLM for earlywood and latewood from 1900 to 2020. Earlywood and latewood δ2HLM values, as well as the difference between them, showed no significant long-term trend from 1900 to 1987; however, they both exhibited significant increasing trends since 1988 at rates of 2.6 ‰ and 4.9 ‰ per decade, respectively. This variance changes the magnitude of the difference between the two chronologies and can be explained by the shift in source water δ2H values during tree growth. Based on a structural equation model analysis, when the influence of permafrost melting weakened due to permafrost degradation, the growing season temperature was better recorded in latewood δ2HLM through the effects of precipitation δ2H from July to September. Based on the environmental response of tree-ring δ2HLM in the permafrost region, permafrost degradation influences the source water δ2H values of trees, thereby affecting the expression of temperature signals in tree-ring δ2HLM. The novel results in this study provide a new perspective on permafrost degradation based on the dynamic responses of tree-ring δ2HLM to source water δ2H during permafrost degradation.

Unraveling of permafrost hydrological variabilities on Central Qinghai-Tibet Plateau using stable isotopic technique.

Permafrost degradation on the Qinghai-Tibet Plateau (QTP) will substantially alter the surface runoff discharge and generation, which changes the recharge processes and influences the hydrological cycle on the QTP. Hydrological connections between different water bodies and the influence of thawing permafrost (ground ice) are not well understood on the QTP. This study applied water stable isotopic method to investigate the permafrost hydrological variabilities in Beiluhe Basin (BLB) on Central QTP. Isotopic variations of precipitation, river flow, thermokarst lake, and near-surface ground ice were identified to figure out the moisture source of them, and to elaborate the hydrological connections in permafrost region. Results suggested that isotopic seasonalities in precipitation is evident, it is showing more positive values in summer seasons, and negative values in winter seasons. Stable isotopes of river flow are mainly distributed in the range of precipitation which is indicative of important replenishment from precipitation. δ18O, δD of thermokarst lakes are more positive than precipitation, indicating of basin-scale evaporation of lake water. Comparison of δI values in different water bodies shows that hydrology of thermokarst lakes was related to thawing of permafrost (ground ice) and precipitation. Near-surface ground ice in BLB exhibits different isotopic characteristics, and generates a special δD-δ18O relationship (freezing line): δD=5.81δ18O-23.02, which reflects typical freezing of liquid water. From isotopic analysis, it is inferred that near-surface ground ice was mainly recharged by precipitation and active layer water. Stable isotopic and conceptual model is suggestive of striking hydrological connections between precipitation, river flow, thermokarst lake, and ground ice under degrading permafrost. This research provides fundamental comprehensions into the hydrological processes in permafrost regions on QTP, which should be considered in investigating the influence of thawing permafrost on the hydrological cycle on QTP.

Application of annealed red mud to Mn(2+) ion adsorption from aqueous solution.

Physicochemical characteristics and Mn(2+) adsorption of annealed red mud were investigated in this study. The annealing temperature (105-900 °C) changed the mineralogical components and the point of zero charge of red mud. By comparison, annealed red mud at 700 °C (ARM700) had a better adsorption effect than other annealed samples, associated with the activated components of available Fe2O3, Al2O3, SiO2 and Na5Al3(SiO4)3CO3 (natrodavyne). The removal efficiency of Mn(2+) by ARM700 was dependent on initial pH, contact time, and initial Mn(2+) concentration of aqueous solution and was ∼56.5% with initial Mn(2+) concentration 385 mg/L at initial pH > 5. The kinetics process was predicted better by the pseudo-second-order model. The Langmuir isotherm displayed a better fitting model than the Freundlich isotherm and the Mn(2+) maximum adsorption capacity of ARM700 was 88.3 mg/g. The competing effects of Cu(2+) and Zn(2+) on Mn(2+) removal were most obvious. There was efficient Mn(2+) removal at the application of ARM700 to the leachate of electrolytic manganese residue.