Water Level Fluctuation Rather than Eutrophication Induced the Extinction of Submerged Plants in Guizhou’s Caohai Lake: Implications for Lake Management

The intensifying global decline in submerged aquatic lake plants is commonly attributed to lake eutrophication, while other drivers such as water levels are seldom considered. This study focused on the sudden extinction of the submerged plants in Caohai Lake, Guizhou, and employed long-term data and a whole-lake water level manipulation experiment to explore the impacts of nutrients and water level changes on the decline in submerged plants. The results indicated that over the past 40 years, the total nitrogen and ammonia nitrogen in the water did not change significantly, while the total phosphorus showed a significant decreasing trend. In recent years, however, the water level rose. The biomass of submerged plants continuously increased until a sudden large-scale extinction occurred in 2021; chlorophyll a also significantly increased. It is speculated that the large-scale extinction of the submerged plants was caused by water level fluctuations rather than eutrophication. After the restoration of the natural hydrological regime of low water levels in winter and spring and high levels in summer and autumn, the submerged plants gradually recovered, with the biomass increasing to 922.6 g/m2 in 2023. The structural equation modeling indicated that the water depth and bottom light availability were the main drivers for the changes in the submerged plants. However, in lake protection and management, more attention is often paid to controlling nutrients, while other influencing factors are neglected. These findings confirm the importance of water levels in the decline in and restoration of submerged plants in shallow lakes, suggesting a focus on water level management in lake protection and aquatic vegetation restoration

Control of soil organic carbon under karst landforms: A case study of Guizhou Province, in southwest China

Global karst landforms account for about 15 % of the land area. The development of karst landforms in southwest China accounts for>1/3 of the country's land area, and is considered to be an important carbon storage with considerable carbon sequestration potential to alleviate global warming. Clarifying the response mechanism of soil organic carbon (SOC) to different controlling factors is of great significance to formulate and implement regional carbon sink strategies. Based on 517 soil samples in Guizhou Province, this study used geostatistical methods to analyze the spatial heterogeneity of SOC in Guizhou Province. The effects of altitude, land use, soil type, slope direction, slope position, slope gradient and rock exposure rate on the spatial variability of SOC in karst areas were quantitatively compared by statistical analysis methods. The results showed that the mean value of SOC content in Guizhou Province was 19.59 g/kg, and the coefficient of variation was 69.11 %, showing moderate-intensity variation. Spatially, the SOC content in Guizhou Province showed a declining trend from west to east, with the low-value areas predominantly distributed in the south and north areas. The semi-variogram model showed that the nugget coefficient C0/(C0 + C) was  slope gradient (0.255) > rock exposure rate (0.166) > land use (0.08) > slope position (0.059) > slope direction (0.043) > soil type (0.041). This research suggests that the provincial government should pay attention to the control of rocky desertification and the development of modern low-carbon agriculture in the work of increasing soil carbon sequestration