湖北师范大学

The occurrence of metalimnetic hypoxia in deep lakes poses a significant threat to the structural and functional integrity of lake ecosystems.As a reservoir of nearly 50％of China's Class Ⅰ freshwater resources,Lake Fuxian plays a critical role in nation-al water security.However,the spatiotemporal evolution and key drivers of metalimnetic hypoxia in Lake Fuxian under ongoing cli-mate warming remain inadequately understood.Based on high-frequency monitoring data from 2021 to 2024 and a process-based hydrodynamic-ecological model(GOTM-WET),this study reconstructed the evolution of metalimnetic hypoxia in Lake Fuxian spanning the period from 1945 to 2024.Scenario simulations were further conducted to elucidate the regulatory roles of key biogeo-chemical oxygen-consuming processes.Results reveal that metalimnetic hypoxia has occurred frequently during the stratified season since the 1980s.Relative to 1980,dissolved oxygen(DO)concentration in the hypoxic zone declined at a rate of(0.20±0.03)mg/(L·10 a),while its depth shoaled by(0.45±0.21)m/10 a and its thickness increased by(1.07±0.17)m/10 a.The volu-metric proportion of the hypoxic zone relative to the metalimnion rose by(6.44±0.98)％/10 a,and its annual duration extended by(31.20±5.08)days/10 a.These trends were significantly correlated with warming-induced intensification of thermal stratifica-tion,including increases in Schmidt stability,metalimnion thickness,and stratification duration.Model simulations indicated that phytoplankton respiration and dissolved organic matter(DOM)mineralization were the dominant oxygen-consuming processes,ac-counting for 34.6％and 27.5％of total oxygen consumption,respectively,followed by particulate organic matter(POM)minerali-zation(19.7％)and nitrification(16.7％),with sediment oxygen demand(SOD)contributing minimally(1.5％).Scenario ana-lyses further identified DOM mineralization and phytoplankton respiration as the primary drivers of hypoxia initiation,whereas POM mineralization,nitrification,and SOD played important roles in regulating the concentration,persistence,and vertical distribution of metalimnetic hypoxia.In summary,this study demonstrates that metalimnetic hypoxia in Lake Fuxian under climate warming is synergistically controlled by physical(thermal stratification)and biogeochemical(oxygen consumption)processes,offering scientif-ic support for understanding deep-lake ecosystem responses to climate change and informing management strategies.

In bullying incidents,the behaviors of bystanders who support and defend the victims play a significant role.Many studies have focused on the influencing factors and positive effects of defending behavior,but there is a lack of comprehensive understanding of its negative effects on the bullied.Based on the nature and style of defending behavior,this paper proposes a four-type structure of defending behaviors and sorts out their positive and negative effects.Then,based on the general aggression model,this paper proposes the mechanism linking the double-edged sword effect of defending behaviors on the bullying victims'psychosocial adjustment,considering both cognitive and emotional aspects and their interconnections.Finally,it proposes that future research should explore the intervention effects of different defending behaviors,identify ways to mitigate their negative impacts on victims,clarify the mechanisms linking defending behavior to psychosocial adjustment,and investigate the subsequent behaviors of victims and bystanders within social networks.

Tibetan Plateau is particularly sensitive to climate change and is a hotspot for studying ecosystem responses to global change.Currently,there is much controversy surrounding studies of aquatic biota response to climate change in this region,requi-ring further investigation.In our study,the evolution of the lake ecosystem over the last 300 years was investigated by paleolimno-logical methods in Lake Xingyicuo on the southeastern Tibetan Plateau.The results showed that the lake and surrounding environ-ment had undergone limited changes before 1930.Since 1930,weathering and erosion had increased in the area leading to in-creased nutrient levels in the lake.Principal component analysis revealed significant ecological changes in rare diatom species after 1930,while the dominant species remained stable.Our study indicated that climate change was the primary cause of increased weathering and erosion in the Lake Xingyicuo watershed,with human grazing activities having a possible exacerbating effect.Al-though the current environmental changes have not yet caused significant changes in the aquatic ecosystems,our studies found rare species in the lakes responded quickly to climate changes since the 1930s.In the future,the lake ecosystems in this region may face a risk of rapid change if environmental pressures continue to increase.