عنوان مقاله [English]
Land use has always been one of the most important indicators through which humans have influenced their environment. Nowadays, mining activites and related operations are parts of the activities have potential to harm the environment. The mining operations have something to do with nature and the environment with important effects on the nature. The negative effects of mining activities on changes in surface biophysical parameters such as greenness, brightness, wetness and land surface temperature (LST) depend on the type of minerals, geographical location, extraction method and other factors. Remote sensing technology provides useful information to understand temporal and spatial changes of land use/cover and land development processes.
Sungun is a large porphyry copper mine and open pit mining extraction method. The important environmental pollutions by this method of mining are land and landscape degradation, mass production of waste mineral extraction and loss of vegetation covers. Due to Sungun copper mine geographic location adjacent to the Arasbaran forests and Dezmar protected area, the activities of this mine have remarkable environmental impacts. The objective of the present study is to integrate reflective and thermal remote sensing capabilities to analyze and monitor changes in the surface biophysical parameters of the Sungun copper mine region caused by mineral activities over the past three decades.
Materials and methods
In the current study, the reflective and thermal bands of satellite images acquired by Landsat 4, 5, 7, and 8 have been used to calculate the LST and biophysical parameters. We have also used the water vapor products (MOD07) and the LST products (MOD11) of MODIS sensor of TERRA satellite, the air temperature data at the meteorological stations and ground data. In the first step, using reflective bands set of Landsat images we extracted and analyzed the land use change trends in the study area for the period 1989 to 2017. Satellite images were classified based on maximum likelihood classifier. The cross tab model was used to study land use changes trend. The changes in biophysical parameters such as greenness, brightness and wetness resulted from mineral activities have been investigated in the second step. In order to model the surface biophysical parameters of brightness, greenness and wetness for the period from 1989 to 2017, we used Albedo, NDVI and NDWI parameters, respectively. In the third step, we integrated the reflective and thermal remote sensing capabilities to extract the LST maps of different years and the trend of LST changes due to land use changes in different time periods. For LST retrieval, a single-channel (SC) algorithm was applied. Finally, the zonal analysis has been used to analyze the trend of LST changes resulted from the land use changes in the study area.
Results and discussion
Over the past two decades, with the increase in the activities of Sungun mining activites, the area of this land use has increased dramatically. The results indicate that the area of the mine class would increase from 13.41 ha in 1993 to 621.54 ha in 2017. During the same period, as a result of the expansion and development of mining activities, the area of the forests decreased from 995.94 to 594.27 ha. In this period, 2295 ha of forest area has converted into mine land use. Also, more than 2632 ha of pasture land have converted into mine land. The results demonstrated that during the period from 1989 to 2017, the mean values of Albedo, NDVI and NDWI parameters have had increase, decrease and increase, respectively. The mean surface albedo values for the study area have been increased from 0.17 in 1989 to 0.25 in 2017. Also, the mean value of the NDVI index has been decreased by almost 0.09 during the period from 1989 to 2017. The major reason for a decrease in NDVI mean values is the reduction of the forest lands and the conversion of them into the mine and pasture lands in past years. In all dates, the lowest and highest LST were related to the forest and bare land classes, respectively. In these years, the mean value of LST of the forest is, on average, 6.36 °C below the mean value of the LST of the mine land use. The results revealed that land use changes from forest to mine, pasture to mine, forest to pasture, forest to bare land and pasture to bare land have changed the LST 5.8, -0.1, -1.4, -1.6, 3.3, and 0.9 °C, respectively.
One of the most important negative impacts of human activities is the change in the surface biophysical parameters. Changes in the earth surface biophysical parameters cause a change in many natural cycles and processes of the earth, including the energy billing cycle. The results of this study are a major warning to environmental authorities to provide sound plans and solutions to reduce the negative effects of Sungun copper mining activities. The results of the study have also indicated the usefulness and efficiency of the integration of reflective and thermal remote sensing capabilities for monitoring and managing various human, environmental and natural phenomena.