Focus

The general aim of this topic is to quantify water and solute inputs from a shallow coast to the Baltic Sea. We will quantify the exchange between groundwater and sea water, taking into account the spatial distribution and temporal dynamics of submarine groundwater discharge (SGD) and sea water intrusions, and identify the governing processes and critical boundary conditions for direction and magnitude of these fluxes. This will help assessing the influence of changing climatic and hydrologic boundary conditions on nutrient export with the groundwater into the Baltic Sea.

State of the Art

Submarine groundwater discharge changes the hydrology and hydrogeochemistry of coastal waters and influences biogeochemical cycles. For the Baltic Sea, SGD has been reported from the Eckernförde Bay, Gdansk Bay, Gulf of Finland and Southern Sweden and is to be expected wherever positive hydraulic gradients prevail between groundwater and sea. Submarine groundwater discharge, which is governed by hydraulic and current-/wave-induced pressure gradients, is usually diffuse and has a large spatial (occurrence of preferential flow pathways) and temporal (tide, lunar cycle, hydrologic year) variability. Due to low flow rates, detection and quantification of SGD are difficult and laborious and a combination of experimental techniques and groundwater modeling seems to be most suitable. The interface between freshwater and brackish sea water can shift as a result of long-term changes in the marine boundary conditions as well as changing hydrologic conditions in the terrestrial environment. The groundwater situation in the Hütelmoor is a result of the inflow from the (mineral) catchment, the climatic water balance and the connection to the Baltic Sea. A transport of nutrients (N, P) into the Baltic Sea is expected especially with the shallow groundwater originating from the peat.

Work program

Groundwater observation wells will be installed in the Hütelmoor and the surroundings pre-project. Monitoring of the ground- and surface water quality in different depth will allow tracing the movement of brackish water entering the peatland both from subsurface and by flooding. Pumping tests will be conducted to characterize the hydraulic properties of the aquifer and the peat. The water exchange between aquifer and Baltic Sea will be on the one hand assessed experimentally by measuring temperature and salinity in the coastal sediments as well as using seepage meters. On the other hand, water fluxes along a 2D transect through the central Hütelmoor will be modeled to deduce the impact of changing boundary conditions.