After the flood: Impact of salt water intrusions on the isotope biogeochemistry of a rewetted coastal peatland
Authors: Winski Lucas , Rach Benjamin , Jenner Anna-K. , Westphal Julia , Schmiedinger Iris , von Ahn Cátia M.E. , Zeller Mary , Malik Christoph , Böttcher Michael E. 
Published: March 2021

&lt;p&gt;&lt;span&gt;Land-ocean interactions in the coastal zone (LOICZ) are of particular interest regarding the exchange of water and elements, like nutrients, carbon, sulfur, and metals. &lt;/span&gt;&lt;span&gt;Processes impacting &lt;/span&gt;&lt;span&gt;groundwater&lt;/span&gt;&lt;span&gt; fluxes at these boundaries belong to the still unsolved problems in hydrology (Bl&amp;#246;schl et al., 2019). &lt;/span&gt;&lt;span&gt;Stable isotope signatures (H, C, O, S), major and trace element contents in surface waters of a rewetted coastal peatland were investigated to understand the impact of storm-induced flooding by brackish seawater on hydrology and biogeochemical element cycling.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;The study area is the H&amp;#252;telmoor, a wetland located at the coastline of the southern Baltic Sea. The area is characterized by a continuous release of fresh water to the Baltic Sea via submarine groundwater discharge (Jurasinski et al., 2018). Surface water is partly drained to a nearby river, but the introduction of brackish waters into the peatland is typically precluded by a small dune and limited to storm-induced flooding events. In the present study, the spatially distributed composition of surface waters was investigated briefly after a flooding event. The results are compared with previous campaigns without actual salt water impact. &lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;Conservative elements and water isotopes demonstrate the importance of seasonal variations due to varying evapotranspiration during pre-flood times and allow for a quantification of mixing processes in the post-flood waters. The impact of soil respired CO&lt;/span&gt;&lt;sub&gt;&lt;span&gt;2&lt;/span&gt;&lt;/sub&gt;&lt;span&gt;, and/or the mineralization of organic matter or methane on the surface waters is indicated by a shift of the C isotope composition of DIC towards lighter data. The S and O isotopic composition of dissolved sulfate indicates an impact by solutions modified by net microbial sulfate reduction on pre-flood surface waters and a potential oxidation of reduced sulfur species in post-flooding solutions. &lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;Previous flooding events already impacted element cycling in the peatland&amp;#8217;s past and are also reflected by a sulfidization of peat layers (Fern&amp;#225;ndez-Fern&amp;#225;ndez et al., 2017) and the observation of local areas with enhanced dissolved concentrations in the central part of the peatland.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;The study is supported by DFG during GK Baltic TRANSCOAST, DAAD, and Leibniz IOW.&lt;/span&gt;&lt;/p&gt;&lt;p align=&quot;justify&quot;&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;span&gt;References:&lt;/span&gt;&lt;/p&gt;&lt;ul&gt;&lt;li&gt;&lt;span&gt;Bl&amp;#246;schl G. et al. (2019) Twenty-three unsolved problems in hydrology (UPH) &amp;#8211; a community perspective. Hydrol. Sci. J. 64, 1141-1158.&lt;/span&gt;&lt;/li&gt;
&lt;li&gt;&lt;span&gt;Jurasinski G. et al. (2018) Understanding the coastal ecocline: Assessing sea-land-interactions at non-tidal, low-lying coasts through interdisciplinary research. Front. Mar. Sci. 5, 1-22&lt;/span&gt;&lt;span&gt;.&lt;/span&gt;&lt;/li&gt;
&lt;li&gt;Fern&amp;#225;ndez-Fern&amp;#225;ndez L.E. et al. &lt;span&gt;(2017) Sulfur isotope biogeochemistry of soils from an episodically flooded coastal wetland, southern Baltic Sea. Geophys. Res. Abs. 19, EGU2017-14335&lt;/span&gt;&lt;span&gt;.&lt;/span&gt;&lt;/li&gt;
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