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The foothill areas of eastern Turkey are an arid and semiarid region with natural salinization, where calcareous alluvial saline soils (Calcaric Fluvisols) are circulated as a result of floods of the Aras River. In this study, the effects of salinity and alkalinity on soil aggregate size distribution and enzyme activities at different aggregate size were investigated. For this purpose, soil samples were collected with three replicates at saline, alkaline, saline-alkaline and non-saline–alkaline areas and passed through into different sieves (2, 1, 0.850, 0.425, 0.106 and 0.02 mm) by dry sieving method for determining aggregate weight distribution in each macro (2–0.45 mm) and micro (0.45–0.02 mm) aggregates. For determining aggregate size distribution, sieves were shaken using a horizontal shaking machine (Retsch, AS 200 basic, Haan, Germany). The soil enzymes were determined in these aggregate sizes (2–1, 1–0.850, 0.850–0.425, 0.425–0.106, 0.106–0.02 mm) for all soil types. All soils belonged to the clay loam with the carbon content in the range of 0.5–0.8%, while the percentage of exchangeable sodium for the non-saline–alkaline and alkaline–saline soils was from 3.5 to 22%, but the pH diapason from 8.3 to 8.9. Results showed that soil salinity and alkalinity decreased the weight of macro aggregates and increased the weight of micro aggregates, besides soil salinity and alkalinity decreased soil enzyme activities. But soil salinity decreased enzyme activity more than alkalinity. Furthermore, the highest urease and catalase activities were in macro aggregates (0.850–0.425 mm aggregate size) for all soil types. The reason may be that macro aggregates contain higher organic matter and organic carbon than micro aggregates. Consequently, the highest enzyme (urease and catalase) activities were detected in macro aggregates. [ABSTRACT FROM AUTHOR]