Lake Water Quality and Dynamics Assessment during 1990-2020 (A Case Study: Chao Lake, China)

Settlements along the coastlines of oceans and lakes, which are among the world's most densely populated areas, are in immediate danger due to stressors brought on by climate change and dangers posed by human activities. This study investigates the water changes of Chao Lake during the last 30 years by using Landsat 5, 7 and 8 time-series images and water indices, including Normalized Difference Water Index (NDWI), Normalized Difference Turbidity Index (NDTI), Green Normalized Difference Vegetation Index (GNDVI) and Normalized Sea Surface Temperature (SST). The gathered data demonstrates that each estimated indicator's value has increased with time. Thus, over the course of the 30-year research period, the NDWI, NDTI, GNDVI and SST annual average values show increases of 112.10%, 242.42%, 112.82% and 119.42%, respectively. The NDWI index underwent these fluctuations, evidenced with the biggest amount (681.8%) in the winter and the lowest amount (28.13%) in the fall. The most NDTI changes (480%) and the least (only 50%) occurred in summer and fall, respectively. The largest increases in GNDVI (180%) and SST values (537.86%) were observed in winter; the smallest changes in GNDVI (43.48%) and GNDVI (68.76%) in fall. The outcomes also demonstrated a strong link between all four estimated factors. In the majority of the analyzed months, the correlation between the 2 measures, GNDVI and NDTI, was considerably greater and near to 1. The findings of this study may be utilized by managers, decision-makers and local planners for the purpose of environmental planning and reducing water pollution in Chao Lake (and other water regions), as well as reducing the risk of environmental hazards due to water pollution.

Automated summary

Coastal and lakeside settlements, which are heavily populated, are at immediate risk due to climate change and human activities. This study analyzed the water changes in Chao Lake over the past 30 years using time-series images and water indices. The results showed an increase in each estimated indicator's value over time, with the largest fluctuations observed in winter and the smallest in fall. The study also found a strong correlation between the estimated factors, particularly between GNDVI and NDTI. The findings can contribute to environmental planning and efforts to reduce water pollution and environmental hazards in Chao Lake and other water regions.