Monitoring Soil salinity around Bakhtegan lake, Fars province, Iran, using Landsat data

Background and objectives: Primary and secondary soil salinity is one of the main reasons of land degradation and desertification in arid and semi-arid zones. Change detection of salt-affected soils, aides finding salt distribution and salinization trends. Present study was arranged for monitoring soil salinity status of agricultural lands located on southern part of Bakhtegan Lake in Fars province, Iran using remote sensing techniques in last two decades.
Materials and methods: To fulfill the goal, Electrical conductivity data from technical reports on the years 1995 and 2007 was obtained and soil sampling was done on 2014. Composite and randomly 0-30 cm soil samples were collected. Electrical conductivity of 1:2.5 soil: water extracts were measured. Landsat 5 data scanned in 1995 and 2007 and Landsat 8 data scanned in 2014 were used. Different indices and false color composite images were calculated with ILWIS 3.3 software. For year 2014, principal component analysis was done, too. Before correlation and regression analysis, digital number of satellite bands transformed to atmospheric reflectance. 80 percent of data was used for classification of imagery data and 20 percent was used for validation the images for all procedures. Salinity maps was calculated, compared and the best model was chosen.
Results: Results showed that the minimum Mahalanobis distance method (with overall accuracy of 62.5%) and maximum likelihood method (with overall accuracy of 44.8%) were the best approaches for mapping soil salinity for years 1995 and 2014, respectively, while the linear regression model (with overall accuracy of 62.5%) increased the accuracy of image classification compare to other methods. Statistical description of soil EC showed that in 1995 more than 50 percent of studied area has Electrical Conductivity less than 2 dSm-1, while in 2014 more than 50 percent of the soils have EC more than 4 dSm-1. Results also showed that during 20 years, salinity expansion was from soils around lake and center part of basin to the Neyriz city.
Conclusion: the present study showed that, during 20 years, the area of soils with salinity less than 4 dsm-1 reduced and the area of saline soils increased and salinity expansion was from Bakhtaran lake to Neyriz city. According to soil salinization, it seems, on the case of continuation of the present land management in studied area, in a short time, the existing orchards would be out of economic cycle. Therefore, to prevent the soil salinization and the loss of farm and orchards in the region, serious efforts of authorities requires.