Soil enzymes mediate organic matter decomposition and nutrient cycling, and their stoichiometry can indicate microbial nutrient demands. However, research on the variations in soil enzymes and microbial nutrient limitation under different temperate forest types still lacks insight. In this study, we sampled soils under five typical forest types (including Betula platyphylla Suk. forest, Fraxinus mandschurica Rupr forest, Larix gmelinii (Rupr.) Kuzen. forest, Populus davidiana Dode forest, and Pinus koraiensis Siebold et Zucc.forest) in the temperate climatic region of northeast China. Soil enzyme activities and soil microbial community composition and diversity were determined for each, and vector analysis was used to quantify the value of microbial limitation. The results showed that soil enzyme activity, enzyme stoichiometry, and microbial community structure were significantly different among the five temperate forest types. The ratios of soil C:N:P acquiring enzyme activity were close to 1:1:1. All the forests showed prevalent P limitation over N limitation (all vector angles > 45°), and the degree of impact varied among different forest types. Redundancy analysis (RDA) and Pearson’s test demonstrated that soil enzyme activities and microbial nutrient limitation were mainly determined by soil physical properties and microbial community. These results contribute to understanding the mechanisms that link plant composition, soil enzyme activity, and microbial nutrient limitation in temperate forests.

Drought–flood abrupt alternations (DFAAs) have a greater impact on ecosystems and socioeconomic environments than lone droughts or floods. Despite the significant impact of DFAAs, research has paid little attention to their evolutionary characteristics, particularly in relation to vegetation growth in the Heilongjiang River Basin. Therefore, this study focuses on the Heilongjiang River Basin and employs the DFAA Index to identify and analyze abrupt alternation events from 1970 to 2019. It also examines the annual and interannual distributions of vegetation growth changes from 2000 to 2019, based on the Normalized Difference Vegetation Index. Lastly, it utilizes correlation analysis to investigate the responsive relationship between vegetation growth and DFAA events. The results indicate the following: (1) Within the Heilongjiang River Basin, the number of drought-to-flood events increased over time, whereas the number of flood-to-drought events decreased over time. The frequency of mutation was relatively high in the northern region, low in the eastern region, elevated in spring and summer, and reduced in winter. (2) The Normalized Difference Vegetation Index was lowest in January, highest in July, and approximately 0 during the winter. The vegetation coverage reached its peak during the summer. (3) Vegetation changes in response to DFAAs exhibited a significant time lag. Vegetation changes in spring–summer lagged behind DFAA events by 3–4 months, while in summer–autumn, the lag was approximately 3 months. These results are of great significance for the early warning and prevention of DFAAs in the Heilongjiang River Basin.

The water-related ecological security pattern directly impacts the allocation and utilization efficiency of regional water resources, and its quantitative assessment is a core requirement for water resource management and planning. However, current assessments of water-related ecological security patterns suffer from insufficient dynamic quantitative modeling, oversimplified river network structures, and neglect of variations in cropland types. Therefore, this study employs a comprehensive approach integrating PLUS multi-scenario land-use simulation, InVEST ecosystem service flow assessment, and the MCR model to quantitatively analyze the supply-demand patterns of water ecosystem services in Jilin Province from 2000 to 2032. The results showed: 1. Persistent service deficits exist in the irrigated croplands of Baicheng and Songyuan in the northwest, while the mountainous areas of Tonghua, Baishan, and Liaoyuan in the southeast serve as primary supply units. This study identified 71 ecological corridors and 58 vulnerable nodes. These include 18 important corridors and 9 early warning nodes. 2. All three scenarios maintain the “southeast surplus-northwest deficit” pattern by 2032. Under the natural development and ecological conservation scenarios, early warning nodes clustered toward the northwest and southeast, respectively, primarily distributed along the Songhua River, the second Songhua River, and the surrounding areas of adjacent cities. Under the farmland conservation scenario, early warning nodes exhibited a strip-like distribution along the depth, with overall aquatic ecosystem health declining. 3. Model validation indicates PLUS simulation accuracy reaches 0.92 (Kappa = 0.87). The annual average aquatic production calculated by the InVEST model shows an error of approximately 2.35% compared to measured data, demonstrating reliable results. These findings contribute to optimizing the spatial configuration of aquatic ecosystems and hold significant implications for multi-scale water security assurance and sustainable water resource management.

Songhua River Basin, northeast China, has seen significant changes due to climate change and human activities from 1990 to 2000, when forests were largely reclaimed and agricultural land was taken up to change the terrestrial water cycle drastically. This paper investigates hydrological changes in three basins: the main stream basin of the Songhua River, the Second Songhua River Basin, and the Nenjiang River Basin. Machine learning and signal processing techniques have been applied to reconstruct historical river records with high accuracy, achieving determination coefficients exceeding 0.97. The physically based WEP model effectively simulates both natural hydrological patterns and human-induced hydrological processes in the northern Nenjiang region. Climate projections indicate clear temperature increases across all scenarios. The most significant warming is observed under the SSP5-8.5 scenario, where runoff increases by 8.52% to 12.02%t, with precipitation driving 62% to 78% of the changes. Summer runoff shows the most significant increase, while autumn runoff decreases, particularly in the Nenjiang Basin, where permafrost loss alters spring melt patterns. This change elevates flood risk in summer, with the rate of increase strongly dependent on the scenario. Water resources show strong scenario dependence, with the average growth rate of SSP5-8.5 being 4 times that of SSP1-2.6. A critical threshold is reached at a 2.5 °C increase in temperature, triggering system instability. These results emphasize the need for adaptation to spatial differences to address emerging water security challenges in rapidly changing northern regions, including nonlinear hydroclimatic responses, infrastructure resilience to flow changes, and cross-basin coordination.

In this study, the future snowmelt runoff in the chilly northeast region’s Tangwang River Basin was simulated and predicted using the SWAT model, which was built and used based on the NEX-GDDP-CMIP6 climate model. This study conducted a detailed analysis of the spatial and temporal distribution characteristics of snowmelt runoff using high-resolution DEM, land use, and soil data, along with data from historical and future climatic scenarios. Using box plots and the Bflow digital filtering approach, this study first determined the snowmelt runoff period before precisely defining the snowmelt periods. Sensitivity analysis and parameter rate determination ensured the simulation accuracy of the SWAT model, and the correlation coefficients of the total runoff validation period and rate period were 0.75 and 0.76, with Nashiness coefficients of 0.75 for both. The correlation coefficients of the snowmelt runoff were 0.73 and 0.74, with Nashiness coefficients of 0.7 and 0.68 for both, and the model was in good agreement with the measured data. It was discovered that while temperatures indicate an increasing tendency across all future climate scenarios, precipitation is predicted to increase under the SSP2-4.5 scenario. The SSP2-4.5 scenario predicted a decreasing trend regarding runoff, while the SSP1-2.6 and SSP5-8.5 scenarios showed an increasing trend with little overall change and the SSP5-8.5 scenario even showed a decrease of 6.35%. These differences were evident in the monthly runoff simulation projections. Overall, the findings point to the possibility that, despite future climate change having a negligible effect on the hydrological cycle of the Tangwang River Basin, it may intensify and increase the frequency of extreme weather events, creating difficulties for the management of water resources and the issuing of flood warnings. For the purpose of planning water resources and studying hydrological change in this basin and other basins in cold regions, this study offers a crucial scientific foundation. An in-depth study of snowmelt runoff is of great practical significance for optimizing water resource management, rational planning of water use, spring flood prevention, and disaster mitigation and prevention, and provides valuable data support for future research on snowmelt runoff.

Human activities have significantly altered the hydrological processes of rivers. In recent years, the increased focus on global water resource exploitation and land use changes has heightened the significance of related ecological and environmental issues. To investigate the land use changes in Hulan River Basin between 1980 and 2020, and the corresponding flow under various ecological standards, a quantitative assessment of land use changes in Hulan River Basin was conducted by analyzing the Land Use Dynamic Degree (LUD) index and the land use change matrix. Two types of models, namely natural runoff models and status quo runoff models, were developed to evaluate alterations in basin runoff. Various hydrological techniques were utilized to calculate the ecological water deficit in Hulan River Basin. The results suggest the following: (1) human consumption comprises approximately 40% of surface water resources, with Hulan River Basin exhibiting a moderate consumption level; (2) when determining the minimum ecological flow, the Distribution Flow Method (DFM) method yielded slightly higher outcomes compared to alternative methodologies; both the variable Q₉₀ method and DFM (Q₂) method satisfy 10% of the natural river flow, however, in terms of capturing the hydrological pattern, DFM exhibits a slightly lower fitting degree compared to the variable Q₉₀ (monthly average flow with 90% guarantee rate) method; (3) DFM is identified as scientifically reasonable for determining the most suitable ecological flow in comparison to other hydrological methods; (4) despite the widespread water scarcity in Hulan River Basin, the variance between most periods and the ideal ecological flow remains minimal, indicating that severe water shortages are uncommon.