Ecological environmental assessment of Gobi desert open-pit mine based on time series model

Single and multi-scene remote sensing data have been usually adopted to evaluate the ecological environment in mining areas, whereas these two types of data always presented the drawbacks of inconsistent time and inaccurate evaluation. To achieve the accurate monitoring of ecological environment in mining areas, the open-pit mine in Gobi desert and its surrounding environment was selected as the research object, and CFmask algorithm+Tmask algorithm were used to obtain pure pixel reflectance. The annual remote sensing data of study area was synthesized by the time series model, and then the pressure-state-response model was used for long-term ecological environment evaluation. The results show that: ① The difference between the predicted surface reflectance values based on time series model and the surface reflectance values observed by the satellite in the corresponding local area was small, while the difference between the true color image vision was relatively small. Meanwhile, the difference between the predicted reflectance value of the impeccable pixel position and the surface reflectance value of the surrounding pure pixel in true color image vision was small. The accuracy was verified by comparing the observed and predicted values of pure pixel reflectance of each band in the study area in 2022, and the results showed that the observed values were significantly correlated with the predicted values (with the correlation coefficients greater than 0.6). The correlation between the field investigation data and the ecological environment index obtained from the time series prediction data (R²=0.450) was better than that of the single-scene ecological index (R²=0.347) and the multi-scene ecological index (R²=0.386). ② From 2013 to 2021, the overall ecological environment of the study area was poor, presenting a spatial pattern of high in the south and low in the north, high in the west and low in the east. With the increasing time, the ecological environment in the south deteriorated more seriously. The change of ecological environment inside the mining area was more stable than that outside the mining area, with the ecological environment outside the mining area degenerating rapidly. ③ The annual change rates of poor, moderate and superior ecological areas were 0.005 /a, 0.002/a and −0.007/a, respectively. The status of each ecological grade performed a trend of decreasing landscape fragmentation, decreasing landscape heterogeneity, and increasing convergence over time. The ecological superiority patch moved towards ecological medium and poor patches, and the ecological poor grade gradually became the main ecological grade of the ecological environment in the study area. The proportion of each grade within the mining area was stable, while the proportion of ecological poor level outside the mining area increased year by year. When ecological restoration would be conducted in the research area, crops planting should be avoided in the direction of semi-sunny slopes as much as possible. Moreover, it is recommended to avoid planting crops with slopes greater than 17.5° in the direction of shady slopes, semi-shady slopes, sunny slopes and semi-sunny slopes.