Iron plaque, naturally iron-manganese (hydr)oxides adhered to the surface of rice roots, controls the sequestration and accumulation of arsenic (As) and cadmium (Cd) in the paddy soil-rice system. However, the effects of the paddy rice growth on the iron plaque formation and As and Cd accumulation of rice roots are often neglected. This study explores the distribution characteristics of iron plaques on rice roots and their effects on As and Cd sequestration and uptake via cutting the rice roots into 5 cm segments. Results indicated that the percentages of rice root biomass of 0-5 cm, 5-10 cm, 10-15 cm, 15-20 cm, and 20-25 cm are 57.5 %, 25.2 %, 9.3 %, 4.9 %, and 3.1 %, respectively. Iron (Fe) and manganese (Mn) concentrations in iron plaques on rice roots of various segments are 41.19-81.11 g kg^-1 and 0.94-3.20 g kg^-1, respectively. Increased tendency of Fe and Mn concentrations from the proximal rice roots to the distal rice roots show that iron plaque is more likely to deposit on the distal rice roots than proximal rice roots. The DCB-extractable As and Cd concentrations of rice roots with various segments are 694.63-1517.23 mg kg^-1 and 9.00-37.58 mg kg^-1, displaying a similar trend to the distribution characteristics of Fe and Mn. Furthermore, the average transfer factor (TF) of As (0.68 ± 0.26) from iron plaque to rice roots was significantly lower than that of Cd (1.57 ± 0.19) (P < 0.05). There was a significant positive correlation between the Cd sequestration in iron plaque and the Cd accumulation in rice roots (R = 0.97, P < 0.01). Still, a similar correlation wasn't observed between As sequestration in iron plaque and As accumulation in rice roots (R = -0.04, and P > 0.05). These results indicated that the formed iron plaque might act as a barrier to As uptake by rice roots and a facilitator to Cd uptake. This study provides insight into the role of iron plaque in the sequestration and uptake of As and Cd in paddy soil-rice systems.

A simply synthetic ferrihydrite-modified biochar (Fh@BC) was applied to simultaneously remove As(III) and Cd(II) from the aqueous solution, and then to explore the mutual effects between As(III) and Cd(II) and the corresponding mechanisms. The Langmuir maximum adsorption capacities of As(III) and Cd(II) in the single adsorbate solution were 18.38 and 18.18 mg g⁻¹, respectively. It demonstrated that Fh@BC was a potential absorbent material for simultaneous removal of As(III) and Cd(II) in aqueous solution. According to the XRF, SEM–EDS, FTIR, XRD, and XPS analysis, the mechanisms of simultaneous removal of As(III) and Cd(II) by Fh@BC could be attributable to the cation exchange, complexation with R-OH and Fe-OH, and oxidation. Moreover, the mutual effect experiment indicated that Cd(II) and As(III) adsorption on Fh@BC in the binary solution exhibited competition, facilitation and synergy, depending on their ratios and added sequences. The mechanisms of facilitation and synergy between Cd(II) and As(III) might include the electrostatic interaction and the formation of both type A or type B ternary surface complexes on the Fh@BC.

The aim of this study was to explore the effects of temperature and light on microalgal growth and nutrient removal in turtle aquaculture wastewater using a single-factor experiment method. Results showed that the growth process of Desmodesmus sp. CHX1 in turtle aquaculture wastewater exhibited three stages, namely adaptation, logarithmic, and stable periods. Temperature and light significantly influenced the growth and protein and lipid accumulation of Desmodesmus sp. CHX1. The optimal conditions for the growth and biomass accumulation of Desmodesmus sp. CHX1 included a temperature of 30 °C, a photoperiod of 24L:0D, and a light intensity of 180 μmol photon/(m²·s). Increased temperature, photoperiod, and light intensity enhanced nutrient removal efficiency. Maximum nitrogen removal was achieved at a temperature of 30 °C, a photoperiod of 24L:0D, and a light intensity of 180 μmol photon/(m²·s), with the removal efficiency of 86.53%, 97.94%, 99.57%, and 99.15% for ammonia, nitrate, nitrite, and total phosphorus (TP), respectively. Temperature did not significantly affect TP removal, but increased photoperiod and light intensity improved the removal efficiency of TP. The development of microalgae biomass as a feed rich in protein and lipids could address feed shortages and meet the nutritional needs of turtles, offering a feasible solution for large-scale production.

The relationship between land use changes and regional carbon storage is closely linked. Identifying evolving trends concerning and influencing factors on carbon storage under future scenarios is key in order to achieve the “dual carbon” goals. Using Chongqing as a case study, this study integrated the advantages of the PLUS model, InVEST model, and a geographic detector model. It conducted simulations of land use type data under scenarios of natural development (ND) and ecological protection (EP), and identified evolving trends and influencing factors regarding carbon storage. The results were as follows: (1) the PLUS model demonstrated excellent simulation performance, with a Kappa coefficient above 0.85 and an overall accuracy above 0.90. During the study period, significant changes occurred for cultivated land, forested land, water bodies, and construction, which were closely related to carbon storage; (2) carbon storage in Chongqing showed a decreasing trend, with a decrease of 10.07 × 10⁶ t C from 2000 to 2020. Under the ND scenario, carbon storage was projected to decrease by 10.54 × 10⁶ t C in 2030 compared to 2020, and it was expected to stabilize from 2030 to 2050. At the county level, Youyang, Fengjie, and Wuxi had the highest carbon storage, while Nanchuan, Jiangbei, and Dadukou had the lowest; (3) the spatial distribution of carbon storage presented an “eastern hotspot western cold spot aggregation” pattern. The proportions of regions with a decreased, unchanged, and increased aggregation of carbon storage in Chongqing during 2000–2010 and 2010–2020 were 2.99%, 95.95%, 1.06%; and 4.39%, 92.40%, 3.21%, respectively. The trend indicated a decrease in the aggregation of carbon storage, and future carbon storage was expected to stabilize; (4) elevation, terrain fluctuation, NDVI, annual average temperature, annual average precipitation, and nighttime light index had influence values of 0.88, 0.81, 0.61, 0.86, 0.77, and 0.81 on carbon storage, respectively, with different combinations of influencing factors having a greater impact. In the future, ecological priority and green development concepts should be followed, and comprehensive improvement of regional development conditions should be pursued to enhance carbon storage, thereby promoting the achievement of the “dual carbon” goals. This study provided an analytical path and data support for formulating optimized carbon storage policies at the regional level.

Biochar has received increased research attention due to its effectiveness in mitigating the potential risks of mercury (Hg) in agricultural soils. However, there is a lack of consensus on the effect of pristine biochar on the net production, availability, and accumulation of methylmercury (MeHg) in the paddy rice-soil system. As such, a meta-analysis with 189 observations was performed to quantitatively assess the effects of biochar on Hg methylation, MeHg availability in paddy soil, and the accumulation of MeHg in paddy rice. Results suggested that biochar application could significantly increase the production of MeHg in paddy soil by 19.01%; biochar could also decrease the dissolved and available MeHg in paddy soil by 88.64% and 75.69%, respectively. More importantly, biochar application significantly inhibited the MeHg accumulation in paddy rice by 61.10%. These results highlight that biochar could decrease the availability of MeHg in paddy soil and thus inhibit MeHg accumulation in paddy rice, although it might facilitate the net production of MeHg in paddy soil. Additionally, results also indicated that the biochar feedstock and its elementary composition significantly impacted the net MeHg production in paddy soil. Generally, biochar with a low carbon content, high sulfur content, and low application rate might be beneficial for inhibiting Hg methylation in paddy soil, meaning that Hg methylation depends on biochar feedstock. These findings suggested that biochar has great potential to inhibit MeHg accumulation in paddy rice, and further research should focus on selecting biochar feedstock to control Hg methylation potential and determine its long-term effects.

Rural green development is a concrete practice of rural revitalization. Currently, research on quantitative evaluation methods for rural green development levels are not well developed. In this study, an evaluation model of the rural green development level in Chongqing City, China was developed based on the parameters of ecology, living, and production. An entropy weight method, Theil index, optimal scale regression model, and GIS were used to analyze the spatio-temporal characteristics, trends, and influencing factors of the rural green development level from 2018 to 2020 in Chongqing City. The results showed that: (1) the overall “ecology, living, and production” dimensions and the comprehensive index of the development level in the city were generally increasing, and the proportion of counties at a high-level increased from 23.68% in 2018 to 81.58% in 2020; (2) the Theil index of the city in was 0.0185, 0.0121, and 0.0114 in 2018, 2019, and 2020 respectively, indicating that the differences in development level among regions decreased as the development level increased; (3) the level of rural green development showed a clear upwards trend, and the proportion of counties with low-speed growth, medium-speed growth, and high-speed growth from 2018 to 2020 was 5.26%, 81.58%, and 13.16%, respectively; and (4) the optimal scale regression analysis showed that the factors with greater impacts on the rural green development level are social security and employment expenditure level of government finance, health expenditure level of government finance, with their contributions is 40.3% and 26%, respectively. The results from this study demonstrate the significance of exploring research methods for rural green development and ways to improve the level of rural green development.