Experimental Study of Geochemical changes in a Degraded Fen Peatland during Rewetting

Organic soils such as peatlands, which form through many years of accumulation of organic matter under waterlogged conditions provide many ecological benefits such as storing ca. 30 % of the global soil carbon, acting as a sink for many nutrients and pollutants, playing a crucial role in the water cycle, and hosting numerous species of plants and animals. Drainage of many peatlands for agriculture and other activities have contribute to approximately 7 % of the total anthropogenic greenhouse gas emissions in the European Union. The conservation and management of the peatland require in depth knowledge of the hydrological processes, water chemistry, and other controlling factors. This study focuses on the geochemical changes encountered while rewetting a fen peatland located in the northeastern part of Germany that is planned for installation of photovoltaic elements, aiming to make the rewetting both ecologically and economically viable. Rewetting of peatland that has undergone years of drainage-induced degradation can result in the aqueous release and transport of trace elements and nutrients, thereby deteriorating the quality of downstream groundwater. We conducted rewetting column experiments aiming to understand the geochemical processes and reaction pathways that can be encountered while rewetting degraded peat bodies. As part of this experiment, three highly degraded peat samples and one moderately degraded peat sample of 30 cm thickness were collected from the study site that represent three different water level situations and are simulated to undergo rewetting using peat pore water obtained from the field. The columns were supplied with circulating water at a flow rate of 8.3*10^-5L*s^-1, at 10 °C, representing groundwater temperature, for a period of 100 days. Regular sampling of peat water from the column reservoir for major and trace element analyses as well as in-situ parameters measurements have contributed to understanding hydrogeochemical mechanisms and evolution. In addition, microbial analysis of the peat water and soil, before and after the rewetting experiment, will contribute insights into the influence of bacteria on the geochemical processes taking place under anoxic conditions. Analysis of the peat column after the rewetting experiments will provide crucial information on the changes of the peat geochemistry and element mobility. The experimental approach combined with geochemical modelling will enhance the understanding of the alterations in the peat water chemistry and estimate the potential impacts on downstream water resources quality.