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Abstract:

There are many shallow, environmentally sensitive salt-affected lakes in the Danube-Tisza Interfluve, Hungary. Because of long-term tendencies in regional and local hydrological and meteorological conditions (e.g. channelization, precipitation extremities, consecutive droughts) significant changes occurred in the state of these shallow lakes (or soda pans) in the last decades. In the example of Lake Szappanos the changes were studied that have taken place over the last three decades, such as the quality of surface water, groundwater and soil condition, transformation of vegetation, in 2014/2015 - repeating a survey in 1982. In the observed points, the average depth of groundwater level slightly dropped, away from the lake the differences became more pronounced, while the extension of the lake surface decreased. The soluble salt content of the groundwater decreased by one order of magnitude. The saline groundwater lies deeper, getting to lose its role as the source of salt. The rainfed near-surface water can act as a „freshwater cushion”, which results in freshwater-like conditions, accompanied by changes in the vegetation. The „desalinization” process can be reversed to some extent and the Smaroglay’s (1939) lake-evolutionary stages („white” to „black” lake toward freshwater marsh) could be interchangeable in both directions by changing the influencing factors.