Significance of submarine groundwater discharge in a semi-enclosed bay of the Baltic Sea
Please login to view abstract download link
Submarine groundwater discharge (SGD) plays a crucial role in the exchange of water and substances across the land-ocean interface and thus for coastal biogeochemistry, yet its impact remains understudied in the Baltic Sea. This study investigates the hydrogeochemistry of SGD in the Bay of Puck, southern Baltic Sea, focusing on its spatial and seasonal variability, geochemical processes, and environmental implications. SGD, groundwater and seawater samples were collected at multiple sites during several campaigns between 2009 and 2021. A one-dimensional advection-diffusion model estimates SGD rates between 1.8 × 10⁻⁷ and 2.8 × 10⁻⁷ L cm⁻² s⁻¹ in coastal areas, while at offshore sites within pockmarks, SGD varies between 4.3 × 10⁻10 and 0.5 × 10⁻⁷ L cm⁻² s⁻¹. These findings indicate that SGD is one of the most significant sources of freshwater in the study area. SGD in Puck Bay is also a key source of dissolved inorganic carbon (DIC), alkalinity (AT), and nutrients, strongly influencing coastal biogeochemistry. Under hypoxic conditions, denitrification and sulfate reduction enhance AT and DIC production; however, concentrations then decrease by 32% and 37%, respectively, due to mixing, reoxidation, and CO₂ release. Additionally, SGD has a low pH and is undersaturated with respect to the forms of the aragonite and calcite minerals of CaCO3. Therefore, SGD can potentially contribute to ocean acidification and affect the functioning of the calcifying invertebrates. Moreover, SGD in the bay serves as a potential contamination pathway, with pharmaceuticals e.g. such as carbamazepine, sulfamethoxazole, and diclofenac detected in groundwater, SGD, and coastal seawater. These findings underscore the necessity of incorporating SGD into regional water and nutrient budgets and call for further research to assess its ecological and chemical impacts on the coastal ecosystem and ecosystem services of the Baltic Sea.