Five-Year-Long Change in the Salinity of Soils and Sediments on Rice Fields of the Karkinit Lowland after Cessation of Irrigation

Abstract

The aim of this study is to present data on the salinity status of soils, sediments, and groundwater on irrigated rice fields of the Karkinit Lowland in Krasnoperekopskii district of Crimea in 2015–2018, 2–5 years after the irrigation stopped. Most of solonetzic microcatenas were transformed into rice paddies and irrigated by flooding during half a century; as a result, the soils were leached from soluble salts to a depth of 3–3.5 m. In 2015–2018, the groundwater table dropped below the critical level. Since 2017, a depression cone of the groundwater table has been formed at the seashore. This area is under the impact of seawater head of up to 0.8–1.1 m. The occurrence frequency of horizons with clusters of fine-grained gypsum crystals has increased in the vadose zone, and slight salinity has restored in sediments of the depression cone at a depth of 3.5–4.5 m. In rice paddies elevated by less than 2 m above seas level, the contents of soluble salts exceeded the low limit of slight salinity in the middle and deep parts of soil profiles on the fifth year after the cessation of irrigation. The maximum of soluble salts in the profile is accompanied by the appearance of calcium and magnesium chlorides in pore solutions and by the accumulation of fine gypsum grains (farinaceous gypsum).