Study area: The Binggou and adjacent Yakou catchments in the northeastern Tibetan Plateau. Study focus: Hillslope flow paths were studied using hydrochemical data of various water types in the spring snowmelt and summer rainfall periods based on hydrochemical tracers and endmember mixing analysis. New hydrological insights for the study region: End-member mixing analysis confirmed the dominance of surface and near-surface runoff during the spring snowmelt. Specifically, the spring Binggou stream water had 61 % surface runoff, 22 % shallow groundwater, and 17 % near-surface runoff. The spring Yakou stream water had 64 % snowmelt, 25.5 % near-surface runoff, and 10.5 % riparian saturated soil water at a depth of 20 cm. The application of end-member mixing analysis failed in the summer rainfall period, and shallow subsurface flow contributed the most to the streamflow (similar to 100 %). The average acid-neutralizing capacity of the spring Yakou stream water was 611 mu eq/L, increasing to 841 mu eq/L in the summer, and for the Binggou stream water, the values were 747 mu eq/L and 1084 mu eq/L, respectively, indicating that the thawed soil layers had a significant buffering effect on stream water chemistry. This study revealed seasonal shifts in flow paths and stream sources, with a transition from surface to subsurface flow influenced by meteorological conditions and the active layer thickness. Future climate change may enhance subsurface flow recharge, leading to less diluted streamflow and stronger water-soil interactions.

Sugar maple, an economically and ecologically important tree in the northern hardwood forest, has experienced regeneration failure that in the Northeast portion of the range has been variously attributed to soil acidification and resultant changes in soil chemistry, impacts of climate change, and effects of species composition. In a 5-year study spanning a latitudinal gradient in the state of New Hampshire, we examined evidence for these three hypotheses to explain sugar maple regeneration patterns. Overall, sugar maple seedling survival was highest in the two sites with lower sugar maple abundance. Alternatively, the two other sites with greater than 50% sugar maple relative dominance shared the following outcomes: higher seed production per area, greater foliar pest damage, lower seedling survival, lower sapling density, and higher canopy maple mortality, while the sites with lower dominance of maple had opposite outcomes. Based on field data and a common garden experiment, conspecific impacts on seedling survival were related to foliar pests and fungal pathogens rather than through soil feedbacks. These results lend support to other studies encouraging promotion of stand tree diversity and avoidance of monocultures.

Understanding and predicting plant water dynamics during and after water stress is increasingly important but challenging because the high-dimensional nature of the soil-plant-atmosphere system makes it difficult to identify mechanisms and constrain behaviour. Datasets that capture hydrological, physiological and meteorological variation during changing water availability are relatively rare but offer a potentially valuable resource to constrain plant water dynamics. This study reports on a drydown and re-wetting experiment of potted Populus trichocarpa, which intensively characterised plant water fluxes, water status and water sources. We synthesised the data qualitatively to assess the ability to better identify possible mechanisms and quantitatively, using information theory metrics, to measure the value of different measurements in constraining plant water fluxes and water status. Transpiration rates declined during the drydown and then showed a delayed and partial recovery following rewatering. After rewatering, plant water potentials also became decoupled from transpiration rates and the canopies experienced significant yellowing and leaf loss. Hormonal mechanisms were identified as a likely driver, demonstrating a mechanism with sustained impacts on plant water fluxes in the absence of xylem hydraulic damage. Quantitatively, the constraints offered by different measurements varied with the dynamic of interest, and temporally, with behaviour during recovery more difficult to constrain than during water stress. The study provides a uniquely diverse dataset offering insight into mechanisms of plant water stress response and approaches for studying these responses.

The Boltzmann growth function is introduced to study the soil consolidation behavior caused by shield construction disturbance when the lining permeability deteriorates, and the general Voigt model is used to characterize the rheological properties of saturated soft soil. Based on the Terzaghi-Rendulic theory, the governing equations for the consolidation of saturated soft soil around the tunnel were established. The shield tunnel project in Kunming's peat soft soil area is taken as an example to analyze the consolidation property. The results show the speed and curve shape of the excess pore water pressure dissipation are closely related to the leakage exacerbation mode of the lining. Increasing the number of Kelvin bodies results in slower dissipation of pore pressure, resulting in incomplete dissipation and pronounced step-like behavior.

Transmedia migration of water is the key factor influencing the bond and shear mechanical properties of the interface system between soil and concrete. In numerous engineering projects, failures often occur at the soil-concrete interface, making the study of transmedia water migration in soil-concrete interface systems highly significant. This research based on the tracer properties of fluorescein to conduct a transmedia water infiltration test on silty clay-concrete interface systems. A fluorescent quantitative method was proposed to determine the moisture content within the concrete profile. The study investigated the migration of the wetting front, changes in water content, moisture distribution across the profiles of both media, and the spatial and temporal variations of soil moisture during the transmedia water migration process. The characteristics of transmedia water migration were compared under different initial soil water contents (IWC). Results demonstrated that the water distribution law of silty clay-concrete interface systems was not monotonous; notably, the water content in the interface area increased significantly. An increase in IWC inhibited the migration of the wetting front and the water content increment of the silty clay, while promoting the progression of saturation. Additionally, the water migration in the concrete was influenced by the silty clay. The proposed fluorescent quantitative method demonstrated high measurement accuracy.

Post-construction surface settlement can be a significant proportion of the total one, ranging from 30% to 90%. This settlement does not only affect the safety of tunnels, but also causes damage to adjacent buildings and underground infrastructures, posing a number of environmental, geological and geotechnical challenges. This study delves into the consolidation behavior of a soft soil around a circular tunnel, subjected to cyclic loading at the ground level. The Boltzmann growth function is introduced to characterize the exacerbation phenomenon in the lining permeability, while the stress-strain characteristics of the soft soil are described by a generalized Kelvin model. The governing equations for the consolidation of the soft soil around the tunnel are obtained based on the Terzaghi-Rendulic theory, and the dissipation of the excess pore water pressure (EPWP) is investigated. The results indicate that higher load frequencies accelerate the disappearance of cyclic load-induced EPWP fluctuation but, overall, cyclic loading prolongs the consolidation process. The local permeability coefficient predominantly affects the EPWP dissipation in the later consolidation stages. The viscous properties of the soil lead to an incomplete dissipation, and a higher number of Kelvin bodies in the adopted rheological model is associated to a slowdown of the consolidation process. The distribution of the EPWP in the upper part of the tunnel vault is also shown to depend on the ratio between the initial permeability coefficients of the lining and of the soil.

Understanding the capacity of temperate trees to acclimate to limited soil water has become essential in the face of increasing drought risk due to climate change. We documented seasonal - or phenological - patterns in acclimation to water deficit stress in stems and leaves of tree species spanning the angiosperm phylogeny. Over 3 yr of field observations carried out in two US arboreta, we measured stem vulnerability to embolism (36 individuals of 7 Species) and turgor loss point (119 individuals of 27 species) over the growing season. We also conducted a growth chamber experiment on 20 individuals of one species to assess the mechanistic relationship between soil water restriction and acclimation. In three-quarters of species measured, plants became less vulnerable to embolism and/or loss of turgor over the growing season. We were able to stimulate this acclimatory effect by withholding water in the growth chamber experiment. Temperate angiosperms are capable of acclimation to soil water deficit stress, showing maximum vulnerability to soil water deficits following budbreak and becoming more resilient to damage over the course of the growing season or in response to simulated drought. The species-specific tempo and extent of this acclimatory potential constitutes preadaptive climate change resilience.

The optical properties of secondary brown carbon (BrC) aerosols are poorly understood, hampering quantitative assessments of their impact. We propose a new method for estimating secondary source of BrC using excitation-emission matrix (EEM) fluorescence spectroscopy, combined with parallel factor analysis (PARAFAC) and partial least squares regression (PLSR). Experiments were conducted on a collection of PM2.5 samples from urban areas in five Chinese cities during winter and summer. The humic-like component with long-emission wavelengths (L-HULIS) was identified as a secondary source tracer of BrC. This was confirmed by correlating PARAFAC components with secondary organic aerosol tracers and molecular oxidation indices obtained from Fourier transform ion cyclotron resonance mass spectrometry analysis. Using L-HULIS as a secondary tracer of BrC, it was determined that the contribution of secondary sources to water-soluble BrC (WS-BrC) in source emission samples is significantly smaller than in PM2.5 from five Chinese cities, supporting our method. In the five cities, secondary source derived via L-HULIS contributes a dominant potion (80% +/- 3.5%) of WS-BrC at 365 nm during the summer, which is approximately twice as high as during the winter (45% +/- 4.9%). Radiocarbon isotope (14C) analysis provides additional constraints to the sources of L-HULIS-derived secondary WS-BrC in urban PM2.5, suggesting that aged biomass burning is the dominant contributor to secondary WS-BrC in winter, and biogenic emission is dominant during summer. This study is the first report on identification of secondary sources of BrC using the fluorescence technique. It demonstrates the potential of this method in characterizing non-fossil source secondary BrC in the atmosphere. Brown carbon (BrC) originates from primary combustion emissions and secondary formation, with large source-dependent uncertainties of radiative forcing. Direct measurements to separate the primary and secondary BrC are challenging due to the chemical complexity. Recent online studies have shown that excitation-emission matrix fluorescence spectroscopy coupled with parallel factor (PARAFAC) analysis identified some fluorescent components that may be linked to secondary sources. However, there is a knowledge gap on whether PARAFAC components correlate closely with atmospheric secondary chemical components, particularly biogenic and anthropogenic secondary organic aerosol, as their precursors can also form secondary BrC chromophores. We established the correlations between PARAFAC components and secondary organic aerosol tracers and compound oxidations to identify the long-emission-wavelength humic-like component as a secondary source tracer of BrC. Then, we estimated non-fossil source secondary BrC in urban aerosols during the winter and summer. Our studies provide references for quantifying secondary sources of BrC in the atmosphere. A fluorescence-based method was developed to investigate secondary sources of water-soluble brown carbon in five cities in China The contribution of secondary sources to water-soluble brown carbon in the summer is approximately twice as high as during the winter This secondary water-soluble brown carbon was more associated with aging biomass burning in winter and biogenic emissions in summer

Background and aims Cover crops can increase nitrogen (N) retention in agroecosystems by taking up soil soluble N when the grain crop is absent. We examined how the combination of cover crops and variability in winter conditions can affect soil N retention and N transfer to the subsequent crop.Methods We used N-15 tracer to quantify how the presence of cover crops (both winter-hardy and winter-killed) modifies the recovery by a corn crop of soil soluble N added the previous fall, and we used snow removal to assess how increased freezing would alter N-15 recovery. We predicted snow removal would decrease N-15 recovery in corn, and this decrease would be highest for plots with winter-hardy cover crops, given they remain vulnerable to increased frost over winter.Results We used N-15 tracer to quantify how the presence of cover crops (both winter-hardy and winter-killed) modifies the recovery by a corn crop of soil soluble N added the previous fall, and we used snow removal to assess how increased freezing would alter N-15 recovery. We predicted snow removal would decrease N-15 recovery in corn, and this decrease would be highest for plots with winter-hardy cover crops, given they remain vulnerable to increased frost over winter.Conclusion Although increased soil freezing reduced grain N recovery, cover crops increased soil N retention, which indicates decreased N losses to the surrounding environment, and the potential for increased contributions to grain N in future years.

To elucidate the molecular composition and sources of organic aerosols in Central Asia, carbonaceous compounds, major ions, and 15 organic molecular tracers of total suspended particulates (TSP) were analyzed from September 2018 to August 2019 in Dushanbe, Tajikistan. Extremely high TSP concentrations (annual mean +/- std: 211 +/- 131 mu gm(-3)) were observed, particularly during summer (seasonal mean +/- std: 333 +/- 183 mu g m(- 3)). Organic carbon (OC: 11.9 +/- 7.0 mu gm(-3)) and elemental carbon (EC: 5.1 +/- 2.2 mu gm(-3)) exhibited distinct seasonal variations from TSP, with the highest values occurring in winter. A high concentration of Ca2+ was observed (11.9 +/- 9.2 mu g m(-3)), accounting for 50.8% of the total ions and reflecting the considerable influence of dust on aerosols. Among the measured organic molecular tracers, levoglucosan was the predominant compound (632 +/- 770 ng m(-3)), and its concentration correlated significantly with OC and EC during the study period. These findings highlight biomass burning (BB) as an important contributor to the particulate air pollution in Dushanbe. High ratios of levoglucosan to mannosan, and syringic acid to vanillic acid suggest that mixed hardwood and herbaceous plants were the main burning materials in the area, with softwood being a minor one. According to the diagnostic tracer ratio, OC derived from BB constituted a large fraction of the primary OC (POC) in ambient aerosols, accounting for an annual mean of nearly 30% and reaching 63% in winter. The annual contribution of fungal spores to POC was 10%, with a maximum of 16% in spring. Measurements of plant debris, accounting for 3% of POC, divulged that these have the same variation as fungal spores.