Soil Salinization Map of the Ust’-Orda Buryat Okrug, Irkutsk Oblast

A series of soil salinization maps of the Ust’-Orda Buryat okrug of Irkutsk oblast on a scale of 1 : 300 000 was compiled for the first time on the basis of the GIS project in the ArcInfo environment. The maps enabled us to answer a number of questions about the distribution of saline and solonetzic soils and the chemical composition of salts. These maps were used to calculate the areas of salt-affected soils taking into account the depth and degree of salinization and the chemical composition of salts. The maps were compiled on the basis of a cross-analysis of 73 soil maps: 68 large-scale soil maps of farms on a scale of 1 : 25 000 for six districts of the okrug, two medium-scale soil maps of the okrug, and three small-scale soil maps, and two small-scale maps of soil salinization. The boundaries of mapping areas were delineated with due account for remote sensing data (RSD), topographic maps, and digital elevation model (SRTM). The compiled maps were verified using 136 georeferenced soil pits with analytical information on salinization. We identified 346 mapping areas containing different proportions of saline soils with a total area of 364 300 ha. Slightly saline soils sulfate salinization in the surface layer predominated. Sulfate salinization with gypsum and sulfate salinization with toxic alkalinity determined by magnesium bicarbonate were identified on the maps for the first time. Alkalinity associated with soda rarely occurs in soils with predominating alkaline sulfate–chloride salinization. Predominantly chloride salinization is also not widespread. Soils saline in the upper 1-m-thick layer occupy 45 200 ± 17 300 ha (slightly saline) and 17 800 ± 7900 ha (moderately and strongly saline), and the area of solonchaks is 4700 ± 2500 ha. The area of solonetzes is 2800 ± 2200 ha, and solonetzic soils occupy 25 100 ± 12 500 ha.