Research on soil environmental criteria is clearly demanded by laws and regulations in China. It is of great significance to provide scientific basis for soil environmental standards. Since the 1970s, during the study of soil environmental capacity and development of soil environmental quality standards, a lot of scientific researches have been carried out in the field of soil environmental criteria, and substantial results have been achieved. However, due to the inherent complexity of soil as an environmental media and its associated environmental risks, currently there are still different opinions on the concept, connotation, research content and research methods of soil environmental criteria among researchers and administrators in China. In the context that soil environmental management in China is progressing into the era of risk based management, soil environmental criteria research needs to be based on risk assessment methods, and incorporate the established methods in China's soil environmental science studies. This study explores the concept and connotation of soil environmental criteria, and recommends to define the soil environmental criteria as the content of soil contaminants that do not cause adverse effects on specific receptors, including the complete relationship between soil contaminant content (dose) and receptors' adverse effects under specific exposure conditions. At present, the focus of soil environmental criteria research in China is to establish a system of standardized research methods and to consolidate the basis of localized data.

Wetland is an essential part of global ecosystems. Wetlands store a substantial amount of environmental change information during their evolution and development process. Wetland ecosystems also store large amounts of carbon, making them as important parts of the global ecosystem carbon sink. As an indicator of climate change and a way to sequester carbon in the long-term, phytoliths have attracted much attention in paleoenvironmental and global carbon sink research. The study of phytoliths and their sequestration of organic carbon in wetland ecosystems is of great significance for exploring changes in vegetation types in wetlands, reconstructing the regional paleoecological environment, estimating the long-term carbon sequestration potential, and regulating the global carbon cycle to mitigate global warming. The relevant Chinese and international research literature have been reviewed and summarized and compared from the following three aspects: the morphology and classification, content and distribution, influencing factors and other basic researches of phytoliths, the extraction technology of phytoliths, and the applications of phytoliths in studies on wetland paleoecological environments, as well as in the studies of global carbon sink potential of wetland ecosystems. The useful future directions for phytolith research are summarized. This review could provide a reference for future researches on phytoliths and phytolith carbon sinks in wetland ecosystems.

Promoting the modernization of territory land governance with a high-level spatial planning system has increasingly become a realistic requirement for the comprehensive green transformation of current economic and social development. This paper comprehensively uses the methods of literature research, induction and deduction, and theoretical analysis, systematically combs the ideological origin of spatial planning, compares the international planning practice and exploration, and reveals the evolution of China's spatial planning system. It clarifies the basic theory and connotation of spatial planning system, and then explores the practical direction of its reform based on the new institutionalism theory. The research shows that the connotation of spatial planning presents the evolution trend of "management means - guiding theory - macro system", and the development process of China's spatial planning system forms a pattern of "initial period - development period - transformation period - reconstruction period". Ecological base point, interest midpoint and coordination node are the basis of the connotation and evolution mechanism of the overall spatial planning system. The planning model has initially formed the logical route of "basic theory and practical basis - theoretical framework and planning objectives - spatial classification and zone control - ecological restoration and key construction - planning implementation and supervision - achievements and technical requirements". In the future, the security system of spatial planning should be strengthened in terms of laws and regulations, institutional mechanisms, technological platforms, economic and social services, supervision and management.

The spatio-temporal change in land use is an essential factor driving global environmental change, which directly affect the structure and function of the ecosystem. However, the impact of ecological restoration projects on the spatio-temporal change characteristics of different land-use types remains unclear. The spatio-temporal variability characteristics of land-use change and the driving factors on the Zoige Plateau during 2000-2010 and 2010-2015 were systematically analyzed by using image data from the years 2000, 2010, and 2015. The results show that the land-use changes of 289.90 km² from 2000 to 2015 were mainly attributed to the increase in grassland and built-up land area by 37.29 and 105.27 km², respectively. Furthermore, wetland area decreased by 129.57 km² over the fifteen years. Simultaneously, the social economy development and the population growth contributed to the significant increase of the built-up land compared to the transition of other land-use types. Ecological restoration projects promoted the restoration of wetlands and decreased cropland, leading to relative stability of shrubland and forestland. In addition, ecological restoration projects were critical factors involved in the increase of wetland area in Zoige Plateau. Desertification control projects is one of the factors that slowed down the expansion of sandy land area in Ruoergai and Hongyuan counties, and climate change was a secondary factor driving land-use change in this region. Strengthening the understanding of spatio-temporal changes in land use and the influencing factors can provide a theoretical basis for optimal regional land-use management and policy making.

Clarifying the spatial and temporal evolution of landscape multifunctional characteristics in the Ancient Yellow River Basin is crucial to the improvement of the function of comprehensive improvement of mountains, water, fields, forests, lakes and grasses and the synergistic optimization of national land space. In order to explore the changes of landscape multifunctionality and trade-off-synergy relationship in the Ancient Yellow River (Suining section) from 1990 to 2020, eight landscape functions were evaluated, including primary production, habitat carrying, recreation service, carbon sequestration, water production, water purification, soil conservation and habitat maintenance. The results show that: (1) The function of the study area has changed from agricultural production to a mixed land use pattern that takes into account production, living and ecology in the past 30 years; (2) The landscape multifunctionality has increased by 21.07% in the past 30 years, among which the production and living landscape functions such as primary production, habitat-bearing and recreation services have been increasing continuously, while the carbon sequestration, water production, water purification, soil conservation and habitat maintenance functions have been increasing in a fluctuating manner; (3) Significant synergistic relationships have been observed between the functions of habitat-bearing and of water production, habitat-bearing and soil conservation, as well as carbon sequestration-habitat maintenance, while the functions between habitat-bearing and carbon sequestration, habitat-bearing and habitat maintenance, carbon sequestration and water production, water production and habitat maintenance, and water purification and soil conservation have been dominated by significant trade-off relationships. The relationships between primary production and recreation services, primary production and water production, and primary production and habitat maintenance have gradually evolved from trade-offs to synergy. This indicates that the comprehensive remediation exerts a significant positive effect on the landscape multifunction of the Ancient Yellow River Basin, and the synergy of production-life-ecology functions is an effective way to improve the adaptability and sustainability of the regional landscape in the future.

As an important place for human habitation and prosperity development in arid and semi-arid regions, the oasis's unique "cold island effect" characteristics have profound impact on the quality of the environment for human living. Based on Landsat remote sensing images, the cold island index was calculated by inverse calculation for Shihezi City's land surface temperature (LST) in 2006, 2011, 2017, and 2021 using the radiation transfer equation model, and the spatial autocorrelation of LST was then analyzed. After extracting land use information by adopting random forest classification, based on the Geodetector model, nine types of data, including five remote sensing indicators, NDVI, NDBI, MNDWI, SI, and NDMI, and land use, DEM, slope, and night lighting data, were selected to detect the spatial heterogeneity of LST in Shihezi City. The degree of coordination between town development and LST was finally determined by using the coordination model. The outcomes of the study show that, the construction land increased in all directions with the total area growing from 83.42 km² to 164.05 km² within 15 years; forest land increased gradually, while cultivated land, grassland, and water areas decreased year by year. The spatial distribution of LST is strongly influenced by land use type. The areas of extremely high temperature, high temperature, and medium temperature zones increased with the expansion of the city. The cold island index of the four periods, was 0.53, 0.47, 0.39, and 0.35, respectively, and the cold island intensity reached the highest decline rate since 2017 and slowed in 2021. The examination of the spatial autocorrelation of LST reveals that LST had a strong positive and significant spatial correlation . The results of factor detection show that the q value of NDBI was the highest, indicating that town development had a strong influence on LST; while the interaction detection results show that the influence of the two-factor interaction on LST was greater than that of the single factor, with the explanatory power of DEM∩NDMI and DEM∩NDBI on LST being the highest. Finally, in the early stage of town development, LST changes ahead of town development, but in the late stage of town development, LST and town development were restricted in some extent, and LST changes laged behind the town development.

To assess the values of ecosystem services provided by peat swamp habitats, four typical peat swamp ecosystems (Phyllostachys heteroclada peat swamp, Palhinhaea cernua peat swamp, Juncus effusus peat swamp, and Sphagnum magellanicum peat swamp) were selected in the Tianbaoyan National Nature Reserve (TNNR) in Fujian Province. Using the emergy theory, an evaluation system for the peat swamp ecosystem service values was established, and the service values of the different types of peat swamp ecosystems in TNNR were assessed. The results show that: (1) The total emergy of peat swamp ecosystem services in TNNR was 1.01×10¹⁹ sej·a^-1, with a macroeconomic value of 9.99×10⁶ yuan·a^-1. The direct service emergy value was 5.45×10¹⁷ sej·a^-1, worth 5.36×10⁵ yuan·a^-1; the indirect service emergy value was 2.73×10¹⁸ sej·a^-1, worth 2.69×10⁶ yuan·a^-1; the existing service emergy value was 6.86×10¹⁸ sej·a^-1, worth 6.76×10⁶ yuan·a^-1. (2) The order of peat swamp ecosystem service value per unit area was Sphagnum magellanicum peat swamp > Juncus effusus peat swamp > Palhinhaea cernua peat swamp > Phyllostachys heteroclada peat swamp. (3) The order of the value of each service function was culture & research (60.28%) > water purification (27.03%) > biodiversity maintenance (6.65%) > biomass increase (4.27%) > NPP increase (0.81%) > water conservation (0.74%) > peat storage (0.39%) > carbon fixation and oxygen release (0.16%). These findings provide theoretical support for the ecological compensation and differentiated protection of peat swamp wetlands.

Excessive application of chemical fertilizers has become a common phenomenon in agricultural production, and small farmers dominated management is still the main form of agricultural management in China. Therefore, exploring the internal mechanism of the excessive application of chemical fertilizers by small farmers is the focus of China's agriculture to reduce the quantity and improve the efficiency of chemical fertilizers. Based on the survey data collected from 775 rice farmers in southeast Hubei Province, the ordered logit model was employed to analyze the impact of cultivated land fragmentation and labor force aging on chemical fertilizer application intensity of paddy fields. The results indicate that: (1) Cultivated land fragmentation and labor force aging have a significantly positive effect on chemical fertilizer application intensity, and the effect of cultivated land fragmentation on chemical fertilizer application intensity is far greater than that of labor force aging; (2) The influence of labor force aging and cultivated land fragmentation on chemical fertilizer application intensity are restricted by geomorphology types. The effect of labor force aging on chemical fertilizer application intensity in the low mountain and hilly area is slightly larger than that in the downland and plain area, while the effect of cultivated land fragmentation on chemical fertilizer application intensity in the low mountain and hilly area is much greater than that in the downland and plain area; (3) Cultivated land quality and rice planting scale have significantly negative impact on chemical fertilizer application intensity, while rice commercialization rate has significantly positive impact on chemical fertilizer application intensity.

Geographical patterns of fruit type largely depend on the environmental conditions during plants' optimum growth period. In this paper, the composition and variation of fruit type in 14 sampled vegetation plots along an altitudinal gradient in Wuyishan National Park were analyzed. The results show that: (1) The proportions of dry and fleshy fruits in Wuyishan National Park were 43.41% and 56.59%, respectively. Among the 13 fruit types, drupes had the highest proportion (31.18%), followed by capsules (22.30%) and berries (15.35%). These characteristics were compatible with the mid-subtropical monsoon humid climates in Wuyishan National Park. (2) For trees, shrubs, herbs, and climbing plants, the proportions of dry fruits were 38.97%, 29.51%, 91.67%, and 30.77%, respectively, while those of fleshy fruits were 61.03%, 70.49%, 8.33%, and 69.23%, respectively. (3) With the increase of altitude, the proportion of dry fruit increased while that of fleshy fruit decreased gradually. At the altitudes of 800 to 1 700 m, the dominant fruit types were drupes, capsules and berries. At the altitude of 1 800 m, the dominant fruit types were drupes, capsules and nuts; the proportion of berries decreased or even disappeared. At the altitude of 1 900 m, the dominant fruit types were drupes, achenes and capsules. At the altitudes of 2 000 to 2 100 m, the dominant fruit types were achenes, capsules and caryopses; the proportions of berries and drupes decreased or even disappeared. (4) Drupes and capsules occurred in all the 14 plots. The proportion of drupes decreased with the rising of elevation, while that of capsules had no obvious trend along the altitudinal gradient. This study is essential for understanding the relationships between the geographical patterns of fruit type and the local climates in the Wuyi Mountains, and the adaptive evolution of terrestrial ecosystems to changes in the natural environment.

In order to provide a new idea for promoting the growth of submerged plants, photosynthetic bacteria were screened and their growth promoting effects on submerged plants were investigated. Photosynthetic bacteria were isolated from the water samples of Changdang Lake in Jiangsu. Then a hydroponics experiment was conducted to evaluate the effects of inoculation of the selected photosynthetic bacteria and plant-growth promoting bacteria Sphingomonas sanguinis YJ11 on plant growth and antioxidant enzyme activity of two kinds of submerged plants(Vallisneria natans and Vallisneria gigantea). A photosynthetic bacterium N1 was isolated, which had high efficiency in solubilizing phosphate and producing IAA and biofilm. According to 16S rDNA sequence analysis, the strain N1 belongs to Rhodopseudomonas palustris. The results show that both inoculated strains N1 and YJ11 promoted the growth of the tow plants, among which strain N1 had a more significant effect. Compared with the control, inoculation with strain N1 significantly increased the plant height, root length, fresh weight and dry weight of the two plants by 15.4%-58.8%, and also, significantly increased root activity and chlorophyll content of the two plants by 28.4%-47.5%. Further analysis show that photosynthetic bacteria N1 significantly increased the antioxidant enzyme activities of the root of the two plants and had better biofilm to colonize on root surface. Therefore, these findings demonstrate that photosynthetic bacteria N1 could promote the growth of submerged plants and can be used as elite germplasm resource for producing microbial fertilizer in the future.

Wenshan City, located in southeast of Yunnan Province, is a part of the Xishuangbanna Biodiversity Conservation Priority Area and is home to a wide range of biological species. Bozhushan is situated in the Laojunshan Area of the Wenshan National Nature Reserve and is known as the "Highest Peak in Southern Yunnan". It is an ideal place to study biodiversity patterns along elevational gradients. In this study, we aimed to study the differences in bird diversities inside and outside the Nature Reserve (Laojunshan Area) and along the elevational gradient in the Laojunshan Area. Bird surveys were conducted in breeding and non-breeding seasons in Wenshan City from July 2019 to April 2020. To do this, a total of 18 transects were placed along 5 elevational bands with an interval of 300 m inside the nature reserve, and other 41 transects were placed outside the nature reserve in 10 km×10 km grids. A total of 199 bird species (from 51 families of 16 orders) were found, with 24 of which are China's national key protected bird species. Of these, 147 species (from 47 families of 16 orders) were found outside the reserve, and 149 species (from 45 families of 12 orders) were found inside the reserve. In the breeding seasons, the Pielou index of bird communities within the reserve was significantly higher than that of outside the reserve (P=0.028, Z=-2.191). In the non-breeding season, the number of species outside the reserve (P=0.002, Z=-3.165) and the Shannon-Wiener diversity index (P=0.005, Z=-2.776) was significantly higher than that within the reserve. The non-metric multidimensional scaling method (NMDS) and permutational multivariate analysis of variance (PerMANOVA) showed significant differences among bird communities inside and outside the reserve. The peaks of bird species richness in the reserve (Laojunshan Area) are found in the elevation band of 1 700-2 000 m in both breeding season and non-breeding seasons. Meanwhile, many bird species significantly shifted their elevational ranges downslope from breeding to non-breeding seasons. The area of the reserve only accounts for 7.71％ of Wenshan, while the bird richness accounts for 74.87％ of Wenshan, underscoring the important role in the maintenance of regional bird species of the nature reserve. To protect the regional bird diversity, maintaining the forests in the nature reserve, particularly the middle elevations (i. e., 1 700-2 000 m), is the key issue. Attention should also be paid to the protection of birds and other protected species in the wetlands outside the nature reserve.

The interaction between dissolved organic matter (DOM) and soil colloidal particles will control the aggregation process of purple soil colloid, which further play an important role in soil and water conservation in the Three Gorges Reservoir Area. The effects of DOM concentrations on the zeta potentials and aggregation processes of colloidal particles,extracted from three types of purple soils in the Three Gorges Reservoir Area, were respectively determined by the zeta potential meter and light scattering techniques. The results show that (1) The aggregation of three purple soil colloids exhibited a conversion from slow aggregation (linear growth) to fast aggregation (power function growth) with increasing DOM concentrations. The total average aggregation rates (TAA) of the three purple soil colloids were significantly different, and the critical aggregation concentration (CCC) of neutral, alkaline and acidic purple soil colloids were 4.74, 2.72 and 1.77 mg·L^-1, respectively, and the CCC of neutral purple soil colloids was 1.74 and 2.68 times those of alkaline and acidic purple soil colloids, respectively. (2) With the increase of DOM concentrations, zeta potentials of neutral, alkaline and acidic purple soil colloids decreased from -20.08, -18.89 and -16.44 mV to -10.60, -6.86 and -5.62 mV, respectively. As a result, the electrostatic repulsive potential energies between colloidal particles decreased with decreasing zeta potentials (absolute value). Meanwhile, critical DOM concentration values existed for the variation of zeta potential of the three purple soil colloids, which were 5.0, 2.5 and 1.7 mg·L^-1, respectively, basically consistent with the CCC values. At the same DOM concentration, zeta potential (absolute value) of the neutral purple soil colloids was the largest, followed by that of the alkaline purple soil, and the acidic purple soil. (3) Activation energies for the three purple soils colloids aggregation decreased continuously with increasing DOM concentrations, in particular, the decreasing trend of activation energies was more obvious in the lower concentration range. Given the same DOM concentration, activation energies for aggregation showed the order of neutral purple soil > alkaline purple soil > acidic purple soil. With changed DOM concentrations, zeta potentials, activation energies as well as CCC values for purple soil colloids aggregation varied to some extent, thereby affecting the aggregation processes of purple soil colloids.

Based on a field plot experiment, the effects of straw-decomposition inoculants addition with straw returning on soil nutrient change characteristics and microbial diversity of phosphorus solubilizing bacteria in of a rice-wheat rotation system were studied, through the investigations of soil aggregates water stability, physicochemical properties, enzyme activities, phoD microbial community structure and diversity. Two treatments were set up in this experiment: conventional fertilization + straw returning (CK) and conventional fertilization + straw returning + straw-decomposition inoculants (IT). The composition of the straw-decomposition inoculants was mainly Bacillus subtills and Trichoderma harzianum, and the number of effective viable microorganism was higher than 200 million·g^-1. The results show that, under IT, the straw decomposition rate was significantly higher than that of CK by 42.1%. The water stability of soil aggregates was significantly increased, and the mean weight diameter (MWD) of soil was significantly increased by 46.7%. The number of large aggregates R_0.25 and geometric mean diameter (GMD) were increased by 62.5% and 22.2%, respectively, but there was no significant difference between CK and IT. The contents of organic matter, available nitrogen, available phosphorus and the activity of soil alkaline phosphorus were raised under IT by 11.8%, 59.8%, 62.6% and 33.8%, respectively, but there was no significant difference in pH, EC, humic acid, total nitrogen, total phosphorus, total potassium and available potassium between the two treatments. The yield of wheat was not significantly increased under IT, but the total phosphorus content of grain under IT was significantly higher than that of CK by 28.1%. Based on the comparative analysis of phoD microbial community, IT significantly increased the number of phoD community species and altered the phoD community structure significantly, but there were no significant differences in the phoD community diversity indexes between the two treatments. The results of redundancy analysis (RDA) demonstrate that phoD community structure was significantly correlated with soil pH, available nitrogen (AN) and MWD. In conclusion, the addition of straw-decomposition inoculants is conducive to improve the soil structure, increase soil available phosphorus content and optimize the soil phoD microbial community structure, so that, effectively improve the soil phosphorus supply efficiency in the rice-wheat rotation system.

In this study, paddy field, dry land, tea garden, and orchard were selected in Getang Village, Jiande City of Zhejiang Province, to investigate the soil nutrient index and heavy metal concentrations under these four different land-use patterns. Their integrated fertility index and heavy metal pollution risk were further evaluated to provide a reference for the construction of organic food production and rural ecological environment protection demonstration villages. The results show that the soil pH in the research area was slightly acidic, and the soil organic matter, total nitrogen, available nitrogen, and available phosphorus contents were at moderate or relatively abundant levels, while the available potassium content was at a deficient level. The soil fertility was significantly influenced by land-use patterns. The pH of tea garden soil was significantly lower than those of other land-use patterns; the organic matter and total nitrogen contents in the dryland soil were significantly lower than those of other land-use patterns; while the available phosphorus and available potassium contents in the orchard soil were significantly higher than those of other land-use patterns. The comprehensive soil fertility index of the orchard was 0.55, which is significantly higher than those of the other three land-use patterns. The comprehensive soil fertility index of the paddy field was at a moderate level, and those for the tea garden and dry land were at a poor level. Under different land-use patterns, the available potassium content was the main limiting factor for soil fertility in Getang Village. Additionally, the soil heavy metal concentrations under different land-use patterns in the research area were all lower than the soil pollution risk screening values for agricultural land, which indicates that it was uncontaminated by heavy metals.

Composite pollution caused by unreasonable discharge of heavy metals and residual pesticides during industrial and agricultural production is prevalent in water and sediments. To explore the remediation potential of vetiver grass (Vetiveria zizanioides) on Cd-prometryn composite polluted water, a greenhouse hydroponic simulation experiment was conducted to investigate the uptake accumulation and removal characteristics of vetiver grass on single/ composite pollutants of Cd (initial mass concentration of 0.5 mg·L^-1) or prometryn (initial mass concentration of 1 mg·L^-1) in water. The results show that with the increase of incubation time, the concentrations of Cd²⁺ and prometryn in the water of the vetiver grass planted group were significantly lower than those without vetiver grass (P<0.05). After 30 days of incubation, the relative removal rate (R₀) of Cd²⁺ in the water was 55.95% under the single Cd contamination condition, which was significantly higher than the relative removal rate of 47.33% under the Cd-prometryn composite contamination condition (P<0.05). After 30 d of incubation, the water Cd²⁺ and prometryn R₀ were significantly higher in the single Cd or single prometryn contaminated treatment than in the combined Cd-prometryn contaminated treatment (P<0.05). Compared with the control, vetiver grass planting resulted in significantly shorter (P<0.05) half-life (t_1/2) and time required to remove 99% of prometryn (t_0.99) in single prometryn contaminated and Cd-prometryn composite contaminated water. Compared with the control, the half-life of prometryn and the time required to remove 99% of prometryn were significantly shorter and the degradation rate of prometryn was significantly higher in the wate of the vetiver grass planted group (P<0.05). Compared with the composite contaminated treatment, the prometryn in the water of the single prometryn contaminated treatment had significantly shorter half-life and shorter 99% removal time and significantly higher degradation rate (P<0.05). During the incubation period, Cd²⁺ uptake by vetiver grass was mainly enriched in the root, and the Cd²⁺ content of the root was significantly higher than that of the stem and leaves (P<0.05), and the transfer coefficients of both were less than 1. The maximum transfer coefficient of prometryn in vetiver grass was 1.90 in the single prometryn treatment, while the transfer coefficients of the Cd-prometryn treatment were less than 1. Vetiver grass is able to remove both Cd and prometryn from water, and the removal effect of single pollution is better than that of composite pollution, indicating that vetiver grass can be used to remediate Cd and pesticide pollution in single/composite pollution water, which provides the theoretical basis for screening the ideal plants for remediation of heavy metal and pesticide single/composite pollution in artificial wetland.

In order to investigate the strengthening effect of biochar on the domestic sewage treatment capacity of constructed wetland (CW) as well as for the reuse of sludge, a vertical upflowed CW was constructed using zeolite and sludge biochar as substrates, with zeolite-based CW A as the control group, and two groups of wetlands B and C with different biochar dosages were set up with the top filler V(biochar)∶V(zeolite) as 1∶2 and 1∶1, respectively. The enhanced effect of sludge biochar and its dosing on nitrogen and phosphorus removal in CW, and the effect of hydraulic retention time (HRT) on pollutant removal were explored. The adsorption characteristics and mechanism of sludge biochar on TP were analyzed by static adsorption experiment and characterization data. The results indicate that the dosage of sludge biochar significantly improved the efficiency of pollutant removal. Compared with group A, group C had better removal effect on COD, TN, NH₄⁺-N, and TP, with removal rates increased by 7.56, 15.99, 11.97, and 40.77 percentage point, respectively. Longer HRT is more conducive to pollutant removal, when HRT=3 d, the removal rate presented better results. The adsorption kinetics of TP by sludge biochar corresponds to the quasi-second-order kinetic equation, while the adsorption isotherm is consistent with the Langmuir model. The maximum adsorption capacity of sludge biochar for TP is 1.42 mg·g^-1. The adsorption mechanism mainly included physical adsorption, functional group complexation, and mineral precipitation. The research has proved the high adsorption capacity and low cost of sludge biochar, along with its good application potential on wetland filler. It also extends its massive reference significance in terms of water pollution issues.

Heavy metal contamination in soil has long been a focus of attention in the global environmental field. Heavy metal passivation remediation technology is a promising treatment technology. Biochar becomes a focus of research on heavy metal contaminated soil passivation remediation methods because of its green, efficient, and low-cost treatment characteristics. Furthermore, biochar demonstrated numerous benefits in terms of improving soil pH and organic carbon content, increasing soil water-holding capacity, lowering heavy metal active ingredients, and so on. To enhance the passivation remediation ability of biochar for Pb and Cd composite contaminated soil, rice straws were used as feedstock to prepare biochar (BC), and MNBC was obtained by BC modified with manganese dioxide and amino groups. The effect of the modification method and the addition amount of biochar on the basic physical and chemical properties of soil (pH, EC, organic matter, etc.) were studied. The changes in soil heavy metal availability and heavy metal chemical form (acid-soluble state, reducible state, oxidizable state, residue state) were analyzed. The results show that with the increase of the application of MNBC, the pH, EC, and organic matter of the soil increased. Manganese dioxide/ amino modification significantly enhances the passivation performance of biochar. The application of 0.6% MNBC reduced 67.2% and 47.6% of the soil available Pb and Cd, respectively, i.e. 2.64- and 3.63-times that of BC. MNBC can effectively change the chemical forms of heavy metals by reducing 10.0% and 18.0% of soil available Pb and Cd, and increasing 12.6% and 9.1% of soil residual Pb and Cd, respectively. Overall, the addition of biochar significantly reduces the Pb and Cd in the soil and improved the physical and chemical properties of the soil. MNBC is an efficient material for passivation of Pb and Cd in soil.