Evaluating the risk of groundwater drought in groundwater-dependent ecosystems in the central part of the Vistula River Valley, Poland

This study was focused on assessing the dynamics of groundwater-level fluctuations in shallow hydrogeological systems, that is, groundwater-dependent ecosystems (GDEs). Assessment of the range of dynamics of groundwater-level fluctuations allows for correct local water resource management, as well as aids the agricultural organizations and development/planning authorities to improve their understanding of sustainable groundwater resource management. Analysis of the dynamics of groundwater-level fluctuations in GDEs in multiannual and seasonal scales, determination of the fluctuation trends, and the values of characteristic levels allows for the identification of risks and the occurrence of groundwater (hydrogeological) drought. Observations of groundwater levels were conducted in the central part of Vistula Valley in 17 piezometers of the monitoring network (about 6600 observations). The piezometers of the monitoring network are located such that they are not under the direct influence of anthropopression, which allows for the interpretation of the results as the influence of natural factors on the quantitative state of GDEs. In conclusion, the present investigation showed that hydrogeological droughts, characteristic of the summer months, occur only during the years when the lowest groundwater levels were observed. Shallow hydrogeological droughts occur periodically, from summer to spring, and the average duration of shallow droughts was 8 weeks.