Variation in Short-term Temperature Fluctuations Across China During the Past 60 Years

Short-term temperature fluctuations(STFs),including amplitude and frequency fluctuations,are one of the main features of weather and play vital roles in determining the type of ecosystem present.Although temperature fluctuations at different time scales have been extensively discussed,the research on week-scale STFs is lacking.In this study,we developed a method,that can quantify the amplitude and frequency of STFs by the thresholds from all years.We used this method to quantify the amplitude and frequency of the 7-d STFs from 1951 to 2019 across China.Our results indicate that the amplitude of the STF was much higher in the eastern part of China than in the western part,while the frequency of the STF was higher in the middle part than in the southern and northern parts;further-more,the STF was highly dependent on internal factors such as topography.The long-term STF mainly showed a decreasing trend before 1990,which implies that temperature became increasingly stable from the 1950s to the 1990s.The main influencing factors were related to topography since the trends were relatively consistent in space.A case study in Taihu Lake showed that an unstable STF in winter and summer resulted in a smaller bloom area in the following spring and autumn.Our method could eliminate seasonal effects and is capable of analyzing STFs at scales ranging from days to years.Quantifications of the amplitude and frequency also make the STF indicators more comprehensive.Furthermore,the STF increased significantly across most of China after 1990,which implies that temperature is becoming increasingly unstable.The drivers of these STFs are related to human impacts since the trends are different in space.

Effects of turbulence on carbon emission in shallow lakes

Turbulent mixing is enhanced in shallow lakes. As a result, exchanges across the air–water and sediment–water interfaces are increased, causing these systems to be large sources of greenhouse gases. This study investigated the effects of turbulence on carbon dioxide（CO2）and methane（CH4） emissions in shallow lakes using simulated mesocosm experiments.Results demonstrated that turbulence increased CO2 emissions, while simultaneously decreasing CH4 emissions by altering microbial processes. Under turbulent conditions, a greater fraction of organic carbon was recycled as CO2 instead of CH4, potentially reducing the net global warming effect because of the lower global warming potential of CO2 relative to CH4. The CH4/CO2 flux ratio was approximately 0.006 under turbulent conditions, but reached 0.078 in the control. The real-time quantitative PCR analysis indicated that methanogen abundance decreased and methanotroph abundance increased under turbulent conditions, inhibiting CH4 production and favoring the oxidation of CH4 to CO2.These findings suggest that turbulence may play an important role in the global carbon cycle by limiting CH4 emissions, thereby reducing the net global warming effect of shallow lakes.