Assessing long-term and seasonal changes of post-mining lakes using multispectral remote sensing

Flooding and water reclamation of former underground and opencast workings of the former “Friendship of Nations–Babina Shaft” brown coal mine, has led to the formation of an anthropogenic lake district in Western Poland. The water reservoirs of this lake district are characterized by different origins, multicolored waters, low pH, and high concentration of iron compounds. This publication focuses on the spatiotemporal changes of 26 lakes located within the aforementioned post-mining area between 2016 and 2025. Moreover, the study paid particular attention to seasonal changes in the surface area of these artificial water bodies. The methodology proposed in this paper comprised the development of time series of spectral indices based on the Sentinel-2 mission imagery and the application of the Emerging Hot Spot method. The obtained results indicate a decrease in the surface area of water bodies between 2016 and 2025, particularly in lakes associated with former opencast mining. In addition, the conducted analyses demonstrated that the areas of the lakes vary considerably throughout the year (the largest total area of the lakes was usually observed in the spring, and the lowest in the autumn). However, no statistically significant correlations were found between these seasonal changes and the selected meteorological variables (air temperature and precipitation). This study confirms that the surface changes (rate and scale of changes) of post-mining reservoirs of various origins vary among different seasons, indicating the importance of further analysis of such anthropogenic features.