Excessive arsenic in soil and groundwater will not only seriously affect the growth of plants, but also endanger human health through the food chain. However, there are few studies on the effects of metalloid speciation and anion competition on the toxicity of arsenate [As(V)]. To investigate the effects of accompanying anions and pH on the toxicity of As(V) on wheat root elongation, wheat roots were exposed to the concentrations of As(V) in the solution ranged from 0 to 500 mM and different levels of pH (4.5-8.0) and different accompanying anions (H2PO4-, SO42-, NO3- and Cl-) for five days. The root length of wheat was measured and the biotic ligand model (BLM) was developed to predict the potential toxicity of As(V) speciation to wheat roots. The results illustrated that EC50 of total As(V) (EC50{As(V)(T)}) values increased from 6.88 to 33.9 mu M with increasing pH values from 4.5 to 8.0, suggesting that increasing pH alleviated As(V) toxicity. The EC50{AsO43-} and EC50{HAsO4 } values increased from 0.001 to 4342 mu M and from 0.0214 to 27.4 mu M, respectively, while the EC50{H2AsO4-} and EC50 {H3AsO4} values sharply decreased from 6.62 to 2.68 mu M and from 41.8 mu M to 5.34 nm, respectively, when pH increased from 4.5 to 8.0. The toxicity of As(V) decreased as the H2PO4- and SO4 activities increased but not when the activities of NO3- and Cl- increased, indicating that SO4 and H2PO4- showed competitive effects with As (V) on the binding sites. Based on BLM theory, the stability constants were obtained: logK(AsO4BL)= 3.70; logK(HAsO4BL)= 4.08; logK(H2AsO4BL)= 4.77; logK(H3AsO4BL)= 6.50; logK(H2PO4BL)= 2.09 and log(KSO4BL)= 1.86, with f(AsBL)(50%) = 0.30 and beta = 1.73. Results implied that BLM performed well in As(V) toxicity prediction when coupling toxic species AsO43-, HAsO42-, H2AsO4-, and H3AsO4, and the competition of SO4 and H2PO4- for binding sites. The current study provides a useful tool to accurately predict As(V) toxicity to wheat roots.

Soil erosion is one of the causes of ecosystem fragility in the Yellow River Delta. Plant roots can improve soil shear strength and effectively prevent soil erosion. However, there are no studies on soil shear strength in the Yellow River Delta. In this study, Phragmites australis (PA) root–soil composites with different root area ratios (RARs) (RARs = 0%, 0.06%, 0.14%, 0.17%, 0.19%, 0.24%, 0.36%) were prototypically sampled from the Yellow River Delta. Direct shear tests of root–soil composites were performed by a ZJ-type (three-speed) strain-controlled direct shear apparatus. The normal stresses were 25, 50, 100, and 200 kPa, and the shear rate was 1.2 mm/min. The results showed that PA roots significantly increased soil shear strength and cohesion with maximum growth rates of 219.0% and 440.1%, respectively. An optimal RAR of 0.14% in the range of 0~0.36% maximized the shear strength and cohesion of the root–soil composites. The internal friction angles of root–soil composites with different RARs did not differ significantly from those of the rootless soil. This indicates that the increase in shear strength was mainly due to an increase in cohesion. In addition, overall shear failure was the primary failure mode of rootless soil, with the roots pulled out of the soil in the root–soil composite failure mode. It is important to note that the root is deflected during shear in the direction opposite to the direction of the shear stress. These findings deepen our understanding of the effect of vegetation roots on soil shear characteristics and provide a scientific basis for the protection of bank slopes, soil and water conservation, and vegetation restoration in the Yellow River Delta.

Net primary productivity (NPP) reflects the carbon sequestration capacity of terrestrial ecosystems and it is used as an important indicator for measuring ecosystem quality. However, due to the effects of “warming and humidification” and “oasisization”, the spatiotemporal evolution and driving mechanisms of the NPP of vegetation in the northern slope of the Tianshan Mountains (NSTM), a typical arid area in China, are still unclear. Thus, in this study, we used remote sensing data and meteorological data to construct a Carnegie–Ames–Stanford–Approach (CASA) model for estimating the NPP of vegetation in the study area. Trend analysis, partial correlation analysis, and optimal parameter-based geographic detector (OPGD) methods were combined to explore the spatiotemporal evolution and driving mechanisms to changes in the NPP. The results showed that from 2001 to 2020, the annual average NPP on the NSTM exhibited an overall significant upward trend, increasing from 107.33 gC⋅m⁻²⋅yr⁻¹ to 156.77 gC⋅m⁻²⋅yr⁻¹, with an increase of 2.47 gC⋅m⁻² per year and 46.06% year-on-year. Over the past 20 years, climate change and human activities generally positively affected the changes in NPP in the study area. Human activities in the study area are mainly manifested in the large-scale conversion of other land use types into farmland, with a total increase of 16,154 km² in farmland area, resulting in a net increase of 6.01 TgC in NPP. Precipitation has the strongest correlation with NPP in the study area, with a partial correlation coefficient of 0.30, temperature and solar radiation have partial correlation coefficients with NPPs of 0.17 and 0.09, respectively. Therefore, increases in precipitation, temperature, and solar radiation have a promoting effect on the growth of NPP on the NSTM. During the study period, the land use type and soil moisture were the main factors that affected the spatial differentiation of vegetation NPP, and the effects of human interference on natural environmental conditions had significant impacts on vegetation NPP in the area. Therefore, in this study, we accurately determined the spatiotemporal variations in the NPP on the NSTM and comprehensively explored the driving mechanisms to provide a theoretical basis for sustainable development in arid areas and achieving carbon neutrality goals.

Worldwide solar dimming from the 1960s to the 1980s has been widely recognized, but the occurrence of solar brightening since the late 1980s is still under debate—particularly in China. This study aims to properly examine the biases of urbanization in the observed sunshine duration series from 1987 to 2016 and explore the related driving factors based on five meteorological stations around Hangzhou City, China. The results inferred a weak and insignificant decreasing trend in annual mean sunshine duration (−0.09 h/d decade⁻¹) from 1987 to 2016 in the Hangzhou region, indicating a solar dimming tendency. However, large differences in sunshine duration changes between rural, suburban, and urban stations were observed on the annual, seasonal, and monthly scales, which can be attributed to the varied urbanization effects. Using rural stations as a baseline, we found evident urbanization effects on the annual mean sunshine duration series at urban and suburban stations—particularly in the period of 2002–2016. The effects of urbanization on the annual mean sunshine duration trends during 1987−2016 were estimated to be −0.16 and −0.35 h/d decade⁻¹ at suburban and urban stations, respectively. For urban stations, the strongest urbanization effect was observed in summer (−0.46 h/d decade⁻¹) on the seasonal scale and in June (−0.63 h/d decade⁻¹) on the monthly scale. The notable negative impact of urbanization on local solar radiation changes was closely related to the changes in anthropogenic pollutions, which largely reduced the estimations of solar radiation trends in the Hangzhou region. This result highlights the necessity to carefully consider urbanization impacts when analyzing the trend in regional solar radiation and designing cities for sustainable development.

The iron-modified coal gasification slag (Fe-CGS) material has excellent performance in purifying heavy-metal-contaminated water due to its good surface properties and adsorption capacities. However, it is unclear whether it can provide long-term simultaneous stabilization of Cd and As in composite-contaminated soils in extreme environments. This study investigated the long-term stabilization of Cd and As in acidic (JLG) and alkaline (QD) soils by simulating prolonged heavy rainfall with the addition of Fe-CGS. Multiple extraction methods were used to analyze the immobilization mechanisms of Cd and As in soil and their effects on bioavailability. The results indicate that the stabilization efficiency was related to the dosage of Fe-CGS. The concentrations of Cd and As in the JLG soil leachate were reduced by 77.6% (2.0 wt%) and 87.8% (1.0 wt%), respectively. Additionally, the availability of Cd and As decreased by 46.7% (2.0 wt%) and 53.0% (1.0 wt%), respectively. In the QD soil leachate, the concentration of Cd did not significantly change, while the concentration of As decreased by 92.3% (2.0 wt%). Furthermore, the availability of Cd and As decreased by 22.1% (2.0 wt%) and 40.2% (1.0 wt%), respectively. Continuous extraction revealed that Fe-CGS facilitated the conversion of unstable, acid-soluble Cd into oxidizable Cd and acid-soluble Cd. Additionally, it promoted the transformation of both non-specifically and specifically adsorbed As into amorphous iron oxide-bound and residual As. Fe-CGS effectively improved the soil pH, reduced the bioavailability of Cd and As, and blocked the migration of Cd and As under extreme rainfall leaching conditions. It also promoted the transformation of Cd and As into more stable forms, exhibiting satisfactory long-term stabilization performance for Cd and As.