Abstract:[Subjective] Elucidating the effects of soil erosion-deposition on the soil quality of slope farmland in Mollisol region of Northeast China is crucial for protecting black soil resource and maintaining its sustainable utilization. [Methods] This paper, selecting two sloping farmlands located at Keshan county, Heilongjiang province as the study site, utilized the ¹³⁷Cs tracer technique to estimate soil erosion rates and the minimum data set (MDS) method to calculate soil quality index (SQI) to analyze impacts erosion-deposition of sloping farmland on soil quality in typical thick-layer mollic regions. [Results] 1) The soil erosion-deposition rate of slope farmland in the study area ranges from -1563.2 to 7916.1 t/km2^/a, with an average erosion rate of 2669.0 t/km2^/a. The spatial distribution of soil erosion rate along the hillslopes was characterized by intensive erosion in the middle and lower slope segment, light-moderate erosion in the top and upper slope segment, deposition at the 50 m slope segment at the foot of the slope, and the most severe slope segment of soil erosion was distributed in 120-170 m slope length. 2) The soil quality evaluation indicators based on the MDS included soil clay, soil organic carbon (SOC), total phosphorus (TP), available nitrogen (AN), soil microbial biomass carbon (MBC) and β-1,4-glucosidase (BG). Moreover, there was a significant linear positive relationship between the MDS-SQI and SQI based on the full data set (p < 0.001), indicating that the MDS could replace the full data set and really reflected the soil quality regime of the slope farmland in the study area. 3) In the study area, there was a significantly negative correlation between SQI and soil erosion rates in the erosion sites (p < 0.01); while the SQI numerally increased with deposition rates without significant difference in the depositional sites. The SQI in the erosion sites reduced by 13.3% on average compared with that in the deposition sites; and the spatial distribution of the SQI along hillslopes was opposite to that of the soil erosion rates. [Conclusion] Soil erosion in the study area is the key driving force to soil quality degradation in sloping farmland.

Abstract:[Objective] Soil saturated hydraulic conductivity (Ks) serves as a critical parameter characterizing the transport of water and solutes in soil, playing a vital role in understanding and predicting soil moisture movement and erosion processes. Studying the variation characteristics and driving factors of Ks across various vegetation restoration models in gully watershed regions of the Loess Plateau is essential for advancing regional soil erosion mitigation efforts. [Methods] Thirty-eight typical vegetation restoration plots ( 5 bare land, 3 dry land, 8 arbor forest land, 3 other forest land, 5 shrub forest land and 14 other grassland ) in Zhifanggou small watershed were selected as the research objects. The Ks, soil physical and chemical properties and root characteristics of 0-10 cm soil layer in different plots were measured. Spearman correlation analysis, partial least squares regression ( PLSR ) and multiple stepwise regression analysis were used to reveal the influence mechanism of vegetation restoration mode on Ks, and the Ks prediction model was established.[Results] Significant differences in saturated hydraulic conductivity (Ks) were observed across vegetation restoration patterns (P<0.05). The mean Ks values followed the order: shrub forest land (1.46 mm/min) > other forest land (1.36 mm/min) > other grassland (1.23 mm/min) > arbor forest land (1.04 mm/min) > dry land (0.65 mm/min) > bare land (0.15 mm/min). Spearman analysis and PLSR revealed that sand fraction, clay content, bulk density, maximum water retention, non-capillary porosity, root volumetric density, root mass density, and root mass densities in 1-2 mm and 0-1 mm diameter classes were critical determinants of Ks. Stepwise regression showed substantial improvement in model explanatory capacity upon integrating root parameters. The integrated model highlighted that intermediate roots optimized Ks through pore network expansion and compaction effect mitigation. [Conclusion] Vegetation restoration markedly elevates Ks via root-mediated soil structural modifications, particularly through pore architecture optimization. The results offer a scientific foundation for refining ecological restoration strategies and enhancing hydrological model parameterization in Loess Plateau ecosystems.

Abstract:[Objective]Land use change is an important driving factor affecting soil carbon storage changes. In order to further explore the impact of land use and cover change (LUCC) on carbon storage of specific soil types in Northeast China. [Methods]this study used land cover data to analyze the relationship between land use change and soil types in Northeast China from 1990 to 2020, and to explore its impact mechanism on soil organic carbon (SOC) sequestration. [Results]The results showed that: (1) land use change is dominated by the decrease in the area of cropland and wetland, and the increase in the area of forest and grassland (1535-4213 km2). (2) The decrease in cropland area was mainly converted into grassland (64%), other land (29%) and forest (6%). Among them, meadow soil, dark brown soil and chernozem soil were the main soil types. The areas with reduced wetlands were mainly distributed in black soil and meadow soil areas. When other land use types were converted into forest land and grassland, the main soil types involved were dark brown soil (15%-41%) and meadow soil. (3) In the past 30 years, the study area was generally in a carbon source state, and the total SOC decreased by 0.046 Pg. Specifically, the SOC storage of grassland and forest increased by 0.102 Pg and 0.283 Pg, respectively, while the SOC storage of cropland and wetland decreased by 0.111 Pg and 0.007 Pg, respectively, and the SOC storage of other land use types decreased by 0.313 Pg. (4) Long-term cultivation (main soil types: meadow soil, Aeolian sandy soil and Albic soil) caused a loss of 0.341 Pg in SOC storage; the reclamation of natural land (woodland and grassland) caused a loss of 5.79% and 4.32% in SOC, respectively. [Conclusion]In summary, the negative SOC storage in Northeast China is mainly caused by extensive land type conversion and long-term cultivation. In the future, we should focus on the restoration of long-term cultivated land (mainly meadow soil) and the protection of natural land.

Abstract:Abstract：[Objective] Spoil heaps, a major source of soil erosion in construction projects, feature a platform-slope structure, where platform runoff induces severe slope erosion in different inflow patterns. However, the response mechanisms of the slope erosion process to the inflow patterns remain unclear. [Methods] Artificially simulated scouring experiments were conducted with two inflow patterns (concentrated-flow and surfaced-flow) and three flow rates (4, 8 and 12 L/min), to reveal the effects of different inflow patterns on the sediment production and hydrodynamic characteristics of slope erosion. [Results] 1) The process of sediment and runoff production were the similar under both concentrated-flow and surfaced-flow. The process of runoff production exhibited a transition from jumping to stabilization, while the process of sediment production showed a rapid decrease and then a fluctuating reduction. Compared with the surfaced-flow, the soil erosion rate showed stronger volatility in concentrated-flow, with the coefficient of variation of 71.49%~111.94%. 2) Mean flow velocity in concentrated-flow was significantly increased 28.15%~52.85% compared with surfaced-flow (p< 0.05), with increasing in flow rate. 3) Runoff conditions under both concentrated-flow and surfaced-flow were transitional flow and turbulent flow, while there was a significant difference in runoff state, which was rapid flow in concentrated-flow and tranquil flow in the surfaced-flow. 4) Soil erosion rate was positively correlated with the Reynolds number, resistance coefficient, shear stress, runoff power, and runoff unit energy under the two inflow patterns (p< 0.01). However, the optimal hydrodynamic indicators differed, with runoff power (R2= 0.68) for surfaced-flow and runoff shear (R2= 0.80) for concentrated-flow. 5) Compared with surfaced-flow, soil erodibility indexes Kτ, Kω and Kε in concentrated-flow increased by 166.67%, 81.25% and 113.86%, respectively, and the corresponding critical hydrodynamic thresholds (τ0, ω0, ε0) increased by 19.78%, 40.70%, and 42.11%, respectively. [Conclusion] The concentrated-flow shows stronger turbulence, has higher erosion energy, and triggers serious soil erosion. This study reveals the influence mechanism of inflow patterns on the slope erosion process and provides an important theoretical basis for the development of slope erosion prediction models under different inflow patterns for spoil heaps.

Abstract:[Objective]Driven by global climate change and the continuous intensification of human social and economic activities, we explored the imbalance between supply and demand of ecosystem services in Anhui Province, and provided reliable basis for regional ecological security construction.[Methods]Anhui Province was selected as the research area, and the InVEST model and hotspot analysis method were integrated to systematically evaluate the supply and demand capacity of the four key services of water yield, habitat quality, carbon storage and soil conservation and the comprehensive cold hotspot distribution pattern in Anhui province from 2003 to 2023. From the perspective of ecosystem service supply and demand, we constructed the ecological supply and demand pattern of Anhui province with the help of circuit theory[Reults]1) From 2003 to 2023, water yield would first decrease and then increase, with a spatial distribution of "more in the south and less in the north". Carbon storage showed a decreasing trend. The habitat quality was higher in the south than in the north and decreased year by year. The amount of soil retention decreased first and then increased, with an overall upward trend.2) From 2003 to 2023, the demand for water production service, carbon sequestration service and habitat demand would generally show an upward trend. The overall demand for soil conservation services (soil erosion) in Anhui province showed a significant downward trend.3) The hotspots of comprehensive ecosystem services supply in Anhui Province were characterized by "high in the south and southwest, and low in the north". The hot spots of comprehensive demand were high in the northwest and low in the southeast. The comprehensive supply-demand ratio showed the characteristics of "high in the south and low in the north".4) The research consensus included 40 supply sources and 36 demand sources; There were 93 supply corridors and 96 demand corridors. Forming an ecological supply and demand pattern of "southern screen and northern link, river basin through".[Conclusion]From the perspective of supply and demand relationship, we constructed a multi-objective coordinated ecological supply and demand network, provided scientific basis for the optimal allocation of regional resources and sustainable ecosystem management, and formed a decision-making support system with both theoretical value and practical guidance.

Abstract:[Objective] The study aims to explore the impact of future climate and land use changes on runoff prediction and its influencing mechanisms in lake basins, which helps to understand hydrological response patterns, optimize water resource allocation, and formulate adaptive management strategies. [Methods] Taking the Erhai Lake Basin as the study area, the research integrates CMIP6 climate data and land use data, coupling the PLUS model and SWAT model to construct a framework for predicting runoff under future climate and land use change scenarios. This framework predicts runoff in the Erhai Lake Basin based on three climate scenarios (SSP1-1.9, SSP2-4.5, and SSP5-8.5) under different Shared Socioeconomic Pathways (SSPs) and future land use change scenarios. The optimal parameter geographical detector is used to reveal the main driving factors and their interactions affecting runoff in the Erhai Lake Basin. [Results] 1) Cultivated land, forest land, and grassland are the dominant land use types in the Erhai Lake Basin over the long term. From 2010 to 2020, urbanization drove the expansion of construction land, encroaching on cultivated land and forest land. By 2030, construction land is expected to reach 18396 hm2, with an additional 1427 hm2 of new construction land, mainly converted from cultivated land, reflecting pressures from population growth and infrastructure demands. 2) The runoff in the Erhai Lake Basin in 2030 shows certain variations under the three scenarios. The highest runoff is observed under the SSP5-8.5 scenario (19.592 m3/s), followed by the SSP1-1.9 scenario (18.013 m3/s), and the lowest under the SSP2-4.5 scenario (17.387 m3/s). Despite variations under different emission scenarios, the overall trend remains relatively stable. 3) The geographical detector results indicate that wind speed exhibits strong independent explanatory power in most years, while the combination of precipitation and other factors shows highly significant interactive explanatory power across all years. [Conclusion] The runoff in the Erhai Lake Basin in 2030 remains relatively stable across different scenarios, with the annual average runoff following the trend of SSP5-8.5 > SSP1-1.9 > SSP2-4.5. Wind speed has the greatest impact on runoff under all three scenarios in 2030, while the combination of precipitation and other factors outperforms other combinations in influencing runoff.

Abstract:[Objectives] Compared to natural-formed tropical coral islands, newly-constructed coral islands exhibit distinct compactied clay layers due to the hydraulic filling and deposition during formation processes. To explore the hydraulic properties and hydrological conditions effects on rainfall infiltration, subsurface flow and coral sand transport. [Methods] This study focuses on the clay compaction layer in coral sand profiles. Through in-situ field investigations and sampling, we characterized the textural type and hydro-physical properties of coral sand at different depth. Laboratory rainfall simulation experiments were conducted to investigate hydrological responses and sand transport processes under varying profile compositions, comparing homogeneous slopes with those containing clay compaction layers. [Results] These results showed that coarse coral sand has a high hydraulic conductivity, whereas the clay compaction layer exhibits extremely low permeability. The saturated hydraulic conductivity of clay compaction layer was only 8% of the other coarse coral sand. The homogeneous slopes allowed complete rainwater infiltration without surface runoff generation, while clay compaction layers redirect 87% of rainfall as subsurface flow, triggering coral sand particle loss. Hydrological condition shifts from free drainage to saturated and seepage flows amplify the rates and total amount of subsurface runoff and sand transport, though the compaction layer with low-permeability may mitigates coral sand loss under seepage condition. [Conclusion] The clay compaction layer can significantly alter hydrological processes and sand transport, leading to shallow hydrological processes and the development of dissolution fissures. These findings have critical implications for improving our understanding of freshwater cycling processes and guiding eco-friendly engineering practices in coral islands.

Abstract:[Objective] To elucidate the influence mechanisms of the physicochemical properties of soil aggregates with different particle sizes on cadmium (Cd) speciation, this study investigated the distribution characteristics of aggregates in typical paddy soils and the effects of different aggregate size fractions on Cd environmental behavior. [Methods] Two Cd-contaminated paddy soils were selected, including granitic sandy soil (developed from granite) and eel clayey soil (developed from shale and slate). Soil aggregates were separated into four size fractions using the wet-sieving method: macroaggregates (2–8 mm), intermediate aggregates (0.25–2 mm), microaggregates (0.053–0.25 mm), and silt-clay particles (<0.053 mm). The adsorption effects of different-sized aggregates on Cd were analyzed after removing organic matter and free iron oxides. [Results] Both soils were dominated by macroaggregates. The aggregate structure of the eel clayey soil was more stable than that of the granitic sandy soil, with higher mean weight diameter (MWD) and geometric mean diameter (GMD). The granitic sandy soil had a higher proportion of fine aggregates, with looser structure and lower stability, mainly due to the lower contents of organic matter and free iron oxides in its parent material. As aggregate size decreased, the contents of organic matter, free iron oxides, and cation exchange capacity (CEC) significantly increased. Cd adsorption capacity progressively enhanced with reduced aggregate size, reaching maximum adsorption in silt-clay particles. The removal of organic matter significantly reduced the Cd adsorption capacity, whereas the removal of free iron oxides had a relatively smaller effect. [Conclusion] The compositional and structural stability differences in aggregates from distinct soil types significantly affect Cd adsorption and speciation patterns. These findings provide scientific basis for deciphering the evolution of heavy metal pollution in paddy fields and formulating remediation strategies.

Abstract:[Objective] Against the backdrop of persistent global warming impacts on climate systems, this study investigates the evolving trends and spatial patterns of climatic elements across China under different warming scenarios, aiming to provide a scientific foundation for formulating differentiated climate adaptation strategies. [Methods] Using NASA Earth Exchange Global Daily Downscaled Projections (NEX-GDDP) CMIP6 high-resolution data, this study evaluates the changes in climate elements across China under global warming scenarios of 1.5?°C to 5?°C, with a focus on analyzing trends and spatial distribution of six key climate variables. [Results] China's land surface warms faster than the global average, exhibiting amplified warming relative to global temperature rise. At 1.5?°C global warming, China’s annual mean temperature increases by approximately 1.3?°C, escalating to 5.92?°C under 5?°C warming. The minimum temperatures rises even more markedly, reaching 6.21?°C. The warming is particularly significant in Northeast China, North China, and the Qinghai-Tibet Plateau. Precipitation increases notably, with 70% of regions experiencing annual precipitation increases exceeding 50?mm relative to the baseline period under 3?°C warming, while the Tibetan Plateau and Northwest China receive over 100?mm more. Extreme high-temperature and extreme precipitation events are projected to intensify in both frequency and magnitude under higher warming scenarios. Wind speed and relative humidity display declining trends, potentially affecting wind energy utilization and regional moisture cycles. At 1.5?°C warming, wind speed decreases by about 0.15?m/s, nearly doubling to 0.32?m/s under 5?°C warming. Relative humidity declines by 0.34% compared to the baseline period at 5?°C warming, though substantial inter-model uncertainties persist. [Conclusion] These findings provide scientific support for climate adaptation and mitigation policies in China, emphasizing the critical need to constrain global temperature rise to address potential climate challenges and reduce future climate risks.

Abstract:The meadow soil in the Tibetan Plateau is highly susceptible to freeze-thaw changes under future climate conditions, and hence this study aims to elucidate the responses of meadow soil microbial activities to increasing number of freezing-thawing cycles. [Methods] A meadow soil was collected from the seasonal FT region of the Tibetan Plateau. Five different FT scenarios respectively with 1, 3, 5, 7 and 9 FT cycles (hereafter termed as C1, C3, C5, C7 and C9) were simulated and compared with the non-FT treatment (N9), to identify the varying responses of dissolved organic carbon (DOC), NO3-N, NH4-H, soil microbial biomass carbon (SMBC) and nitrogen (SMBN), as well as CO2 and N2O emission rates. [Results] 1) Compared with the non-FT N9, the SMBC was significantly decreased by 23.64% after C9, while the DOC significantly increased by 10.7%, cumulatively releasing 71.10% and 321.40% more CO2 and N2O; 2) With increasing number of FT cycles, the DOC and the activities of β-glucosidase and leucine aminopeptidase showed nonlinear patterns, which declined first to the lowest values after C5 and then gradually increased at C7 and C9. The CO2 emissions rates peaked after C2 (1.83 times of that from the non-FT soil), whilst the N2O emission rates roared up after C5 (reaching 8.01 ~ 25.43 times of that from the non-FT soil). 3) With the increasing number of FT cycles, the SMBN did not vary significantly, yet the NO3-N and acetylaminoglucosidase activities gradually increased, while the NH4-N steadily decreased. [Conclusion] The effects of multiple freeze-thaw cycles on soil microorganisms were not just repetitions of a single freeze-thaw event. After five freeze-thaw cycles in alpine meadow soils, the changes in pore structure and microbial deaths induced by soil water freezing and swelling had been basically stabilized, while the surviving microbial communities gradually adapted to the new temperature conditions and revived their activities in further freeze-thaw cycles. This casted a new light to help advance our current understanding as to how soil microbes overwinter in the seasonal freeze-thaw regions.