Abstract
Managing the rapidly changing saline-alkali land under cultivation in the coastal areas of China is important not only for mitigating the negative impacts of such land on the environment, but also for ensuring long-term sustainability of agriculture. In this light, setting up rapid monitoring systems to assist decision-making in developing sustainable management plans is therefore an absolute necessity. In this study, we developed a new interpretation system where symbols are used to grade and classify saline-alkali lands in space and time, based on the characteristics of plant cover and features of remote sensing images. The system was used in combination with the maximum likelihood supervised classification to analyze the changes in cultivated lands under saline-alkali conditions in Huanghua City. The analysis revealed changes in the area and spatial distribution of cultivated under saline-alkali conditions in the region. The total area of saline-alkali land was 139,588.8 ha in 1992 and 134,477.5 ha in 2011. Compared with 1992, severely and moderately saline-alkali land areas decreased in 2011. However, non/slightly saline land areas increased over that in 1992. The results showed that the salinization rate of arable lands in Huanghua City decreased from 1992 to 2011. The moderately saline-alkali land southeast of the city transformed into non/slightly saline-alkaline. Then, severely saline-alkali land far from the coastal zone west of the city became moderately saline-alkaline. Spatial changes in cultivated saline-alkali lands in Huanghua City were such that the centers of gravity (CG) of severely and non/slightly saline-alkali land moved closer the coastline, while that of the moderately saline-alkali land moved from southwest coastal line to northwest. Factors influencing changes in cultivated lands in the saline-alkali ecosystem included climate, hydrology and human activity. Thus, studies are required to further explore these factors in order to build a better understanding into the relative contributions of the changes saline-alkali state on the functions of coastline ecosystems.
Highlights
Some 83 million hectares of land is affected by salt, with a wide range of distribution in five continents and over 100 countries [1]
Where X and Y are the gravity center coordinate for cultivated land under saline-alkali conditions in the Huanghua City ( ̋), Pj is the area of the jth patch, Xj and Yj are gravity center coordinate of the jth patch ( ̋), and n is the number of patches in the cultivated lands under saline-alkali conditions
The results showed that salinization of cultivated lands in the Huanghua city study area dropped during the period from 1992 to 2011 [24]
Summary
Some 83 million hectares of land is affected by salt, with a wide range of distribution in five continents and over 100 countries [1]. Soil salinization is so much so extensive that it spreads at the rate of two million hectares per year [2,3] This requires the development of effective preventive and management measures, including rapid reliable means of getting information on spatial and temporal distributions of saline-alkali lands across the globe. Dwivedi and Rao [7] noted that the combination of Landsat TM bands 1, 3 and 5 was most suitable for the interpretation of salt-affected soils. The spatial and temporal distributions of soil salinization in Jiefangzha Irrigation Sub-district were determined by analyzing remote sensing images acquired at the end of March. We used remote sensing images acquired at the end of May or the beginning of June to determine the spatial and temporal variability of soil salinity in a coastal area in Huanghua City. The interpretation system was integrated with the maximum likelihood supervised classification method to derive relevant on saline-alkali soils
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