Storms cause peatland flooding and paint it black: Sulfur biogeochemistry of a rewetting temperate coastal area

Land-ocean interactions in the coastal zone are of particular interest regarding the exchange of substances, like nutrients, carbon, sulfur, metals, and water. The rising sea level is and will enhance the pressure of salty solutions on previously fresh water ecosystems. Currently coastal areas in the North Eastern part of Germany under increasingly rewetted by the connection with the brackish Baltic Sea. We present results on the isotope biogeochemistry of a modern rewetted wetland, at the southern Baltic Sea, the Huetelmoor, that is under impact by event-type flooding by brackish seawater. These events lead to an enhancement of sulfate availability for microbial carbon transformations. Sediment cores on transects within the wetland were investigated for the pore water and soil composition, together with selected ground water wells and surface waters from the channeling system. Different fractions of the soils were analyzed for the elemental composition, mineral micro-textures, and the stable sulfur (and oxygen) isotope composition of different sulfur fractions to understand the water and biogeochemical carbon-sulfur-metal cycles and the geochemical signatures in authigenic mineral phases and organic matter. Adding sulfate creates space for mineral authigenesis and organic matter sulfurization. The soils are impacted by different intensities in sulfur cycling as reflected by isotope and textural signals. Further mechanistic investigations consider the role of DOS upon changing sulfur substrate availability. Results allow for a transfer of proxy information to other modern and past coastal organic-rich peatlands.

Acknowledgement for support by DFG Research Training Group BALTIC TRANSCOAST, ERASMUS, and DAAD