Coastal regions represent a transition between land and sea. From the hydro(geo)logical point of view freshwater and saltwater are coming together here. The groundwater discharge which discharges directly into the sea is called submarine groundwater discharge (SGD). At the regional scale, SGD is often measured indirectly based on tracers. At the local scale, SGD flux over time can be measured directly, e.g. using seepage meters. However, this method only represents the punctual source of discharge. Especially to record the diffusive discharge locations, a new method which focuses on the puddles in intertidal areas as potential diffusive discharge locations was developed. There, the salinity and water depth were observed at different puddle locations over time. Moreover, photos were taken in order to get information about the changing area of the puddle. From these data we calculated a water budget to show how much submarine groundwater discharges at the measured puddle. The results show a geographically and temporal variability of the SGD in the mudflat of the south of Königshafen on Sylt. The diffusive discharge locations were primarily located at the beginning of the intertidal zone. In order to support the new method, two additional pore water measurements were conducted at each puddle. The salinity of the pore waters were freshening with increasing depth here. The presented method can help to transfer the observed data of SGD to a regional scale.
Sebastian Janßen1, Alexandra Nozik1, Ulf Mallast2, Nils Moosdorf1,3
1ZMT, Germany; 2UFZ, Germany; 3CAU Kiel, Germany