# Centennial Lake Environmental Evolution Reflected by Diatoms in Yilong Lake, Yunnan Province, China
## 5 Conclusions  
1. The average deposition rate of Yilong Lake was 0.77 cm/a. The pH value and eutrophication were the two main environmental factors that affected the environmental change of Yilong Lake, which was in a high pH and eutrophication state for a long time.
2. In Yilong Lake, the main diatom species indicated a high pH value were _A. exigua_, _N. meniscus_, _N. viridula_, _F. inflata_, and _N. denticule_. Meanwhile, _A. exigua_, _N. meniscus_, and _N. viridula_ could be used for the index of eutrophication. On the contrary, _A.islandica_ and _E. sorex_ could be considered indicators for lower eutrophication in the lake.
3. According to the pH value and eutrophication curves obtained from PCA, the evolution of Yilong Lake from 1938 to 2020 could be divided into six major stages. Though high pH value and eutrophication had been the main characteristics for a long time, the quality of Yilong Lake was gradually improved through planned treatment in the last decades.
4. Different stages of evolution in Yilong Lake corresponded to different natural changes and human activities. Due to the influence of lithology and sedimentation, the pH value of Yilong Lake was relatively low, and there were few affections by human activities in the preliminary stage. Since 1984, eutrophication has rapidly increased due to the increasing population and accompanying human activities such as agricultural development, deforestation, and land reclamation. After 1980, the water quality of Yilong Lake continued to improve due to planned treatment such as building sewage treatment plants, restoring forests, dredging, and planting lakeside wetlands.
5. The sediment diatom records provided effective information on the pH value and eutrophication of Yilong Lake, reflecting the history of the lake over the past century. In addition to the changes in nature, especially the drying up of the lake caused by drought, which might lead to the high pH value and eutrophication, human activities had also played an important role in the lake environment. The irrational human development in the lake basin caused abnormal changes in pH values and eutrophication, while the planned and targeted treatment could restore the natural state of the lake. This provided a scientific basis for research on the evolution of plateau lakes such as Yilong Lake, as well as for lake governance and protection.  
**Supplementary Materials:** The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app13095288/s1](https://www.mdpi.com/article/10.3390/app13095288/s1)]([https://www.mdpi.com/article/10.3390/app13095288/s1](https://www.mdpi.com/article/10.3390/app13095288/s1)), Table S1: Relative percentage of diatoms in Yilong Lake.  
**Author Contributions:** Conceptualization, Y.H., H.S. and R.M.; methodology, Y.H., H.S. and R.M.; software, R.M.; validation, Y.H.; formal analysis, Y.H., H.S. and R.M.; investigation, Y.H.; resources, J.L.; data curation, J.L.; writing--original draft preparation, H.S. and S.T.; writing--review and editing, Y.H. and R.M.; visualization, R.M. and S.T.; project administration, J.L.; funding acquisition, J.L. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was funded by Science and Technology Department of Yunnan Province (No. 202203 AC100002), and the National Natural Science Foundation of China (No. U220220245).  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The data used to support the findings of this study are available from the corresponding author upon request.  
**Conflicts of Interest:** The authors declare no conflict of interest.