Longer-term monitoring of a degrading sodic lake: landscape level impacts of hydrological regime changes and restoration interventions (SE Hungary)

Abstract The diminishing number, extent and degradation of soda lakes were reported from the lowland area of the Carpathian Basin in the past two decades due to anthropogenic impact and climate change. This study provides a detailed spatio-temporal assessment of a degrading alkaline sodic lake ecosystem (13.5 ha) in Southeast Hungary. It discusses the results of spatially detailed topsoil and vegetation surveys from 2009 and 2018 to understand the changes among the current natural and anthropogenic conditions to support a future possible ecological water management. Habitat mapping and laboratory measurement of EC2.5, soda and calcium carbonate content from 199 topsoil samples provided the basis for the assessment. In 2009 the degradation of the naturalness was observed according to the vegetation survey, and the topsoil parameters reflected steppification, leaching and desalinization. Between 2009 and 2018 the loss in extent of Puccinellia swards and the spread of salt meadow species along the channel continued due to the changing salt content. According to the 2018 snapshot of the topsoil, higher salt (from 0.7 to 1.3 mS/cm) and soda content (from 0.08 to 0.12%), furthermore decreasing CaCO3 content (from 25.89 to 20.08%) were characteristic, meaning that there was a changing water and salt regime in the lakebed. The past decade was partly favourable in the point that humid years could rehabilitate the natural conditions in certain parts of the lakebed, but they did not prove to be enough to sustain this alkaline sodic lake.