Using modified remote sensing imagery to interpret changes in cultivated land under saline-alkali conditions

Abstract

Managing the rapidly changing saline-alkali land under cultivation in the coastal areas ofChina is important not only for mitigating the negative impacts of such land on the environment, butalso for ensuring long-term sustainability of agriculture. In this light, setting up rapid monitoringsystems to assist decision-making in developing sustainable management plans is therefore anabsolute necessity. In this study, we developed a new interpretation system where symbols areused to grade and classify saline-alkali lands in space and time, based on the characteristics ofplant cover and features of remote sensing images. The system was used in combination with themaximum likelihood supervised classification to analyze the changes in cultivated lands undersaline-alkali conditions in Huanghua City. The analysis revealed changes in the area and spatialdistribution of cultivated under saline-alkali conditions in the region. The total area of saline-alkaliland was 139,588.8 ha in 1992 and 134,477.5 ha in 2011. Compared with 1992, severely and moderatelysaline-alkali land areas decreased in 2011. However, non/slightly saline land areas increased over thatin 1992. The results showed that the salinization rate of arable lands in Huanghua City decreased from1992 to 2011. The moderately saline-alkali land southeast of the city transformed into non/slightlysaline-alkaline. Then, severely saline-alkali land far from the coastal zone west of the city becamemoderately saline-alkaline. Spatial changes in cultivated saline-alkali lands in Huanghua City weresuch that the centers of gravity (CG) of severely and non/slightly saline-alkali land moved closerthe coastline, while that of the moderately saline-alkali land moved from southwest coastal line tonorthwest. Factors influencing changes in cultivated lands in the saline-alkali ecosystem includedclimate, hydrology and human activity. Thus, studies are required to further explore these factors inorder to build a better understanding into the relative contributions of the changes saline-alkali stateon the functions of coastline ecosystems.