Wetland restoration management under the aspect of climate change at a mesotrophic fen in Northern Germany

•Wetland restoration management has to be validated under the aspect of climate change.•We studied 15 years of water table (WT) depth development at 46 monitoring wells.•84% of WTs declined according to the trend line despite re-wetting measures.•Climate projection until 2100 indicates drier summers, which will intensify WT draw-down.

Wetland restoration management is an important tool for stakeholders and practitioners to mitigate climate change and preserve ecological functioning. Various approaches to modifying the water management of a catchment for restoration purposes exist and were performed in a preservation area in northwest Germany. To validate the effect of the re-wetting practice, a monitoring network of 46 wells was established and monthly readings were taken from 1997 onwards. A declining trend in water table depth was present at 39 wells and equaled on average a lowering of 20 cm during the study period from 1997 to 2012. So far, half of the trend lines are above 40 cm below ground, which is an indicator of an effective re-wetting practice, but they will decline below this threshold until 2032 according to linear regression analysis. The progress of water table depths might be accelerated by climate change. According to the meteorological forecast, air temperatures will rise and the annual precipitation pattern will change. Thus, the climatic water balance tends toward more negative values in the summer and positive values in the winter, favoring an earlier and more intense water table draw-down. Because root water extraction from shallow groundwater is limited to a certain depth, the forecast of water table depth development according to the recent trend depicts a worst-case scenario. Nevertheless, the results emphasize that restoration management should be validated and has to be adapted in certain ways when mitigating the impact of climate change.

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