Assessing the recharge of peat bogs in Northern Germany using various methods

Most peatlands in Northern Germany suffer from increasing water balance deficits and decreasing groundwater levels. According to recent studies, this is not only a local trend but is observed throughout the Northern Hemisphere. Ombrotrophic bogs function as natural lysimeters and are solely rain-fed, therefore the assessment of their groundwater recharge can be a great option for the water balance evaluation of their region. From the difference between their climatic and modelled water balance, deductions about external anthropogenic effects and climate change can be drawn. This study uses environmental tracers: isotopes and major ions for the estimation of the groundwater recharge. The tracers were analysed from groundwater samples from different depths, taken from two peat bogs in Schleswig Holstein with different characteristics. The water balance can be inferred from the groundwater recharge of recent years, estimated from the depth profile of environmental tracers. Different models were applied to simulate the recharge from 2018 to 2023, based on measured and collected data: a groundwater balance method based on climatic variables estimated a 193 mm/year recharge. The modelling by Hydrus 1D estimated 420 mm/year, the cumulative method estimated 240 and 280 millimetres for the two study areas, while the isotope model estimated 162 and 173 mm/year based on the concentrations of Oxygen-18 and deuterium. However, problems with the sampling can be inferred from the results, therefore conclusions must be drawn with caution.