RI is a Tertiary aquifer at 41 m depth, RII is a Quaternary aquifer at 15.7 m depth, RIII is a Craterous aquifer at 178 m depth, H1 and W1 are Pleistocene aquifers at 170 m and 122.5 m depth respectively. In July 2013 groundwater samples were collected via push-point lances, in RG7422 each of the study sites indicated

in Figure 1. After collection, the water samples for DOC analysis were passed through 0.2 μm pre-combusted glass-fibre filters. A total of 10 ml of the filtrate was acidified with 150 μl of conc. HCl to remove carbonates and to prevent mineralisation of dissolved organic matter ( Pempkowiak 1983), then stored in the dark at 5 °C until analysis. This was carried out by means of a ‘HyPerTOC’ analyser (Thermo Electron Corp., The Netherlands), using the UV/persulphate oxidation method and non-dispersive infrared (NDIR) detection ( Kuliński

& Pempkowiak 2008). In order to remove inorganic carbon see more from samples before DOC analysis they were purged with CO2-free air. DOC concentrations in the analysed samples were derived from calibration curves based on the analysis of aqueous solutions of potassium hydrogen phthalate. Quality control for DOC analysis was performed using CRMs seawater (supplied by the Hansell Laboratory, University of Miami) as the accuracy tracer with each series of samples (average recovery was equal to 96 ± 3%). The precision, described as the Relative Standard Deviation (RSD) of triplicate analysis, was no worse than 3%. Samples for DIC analysis were collected in 40 ml glass vials, each poisoned with 150 μl of saturated HgCl2 Adenosine triphosphate solution. The analysis was carried out with a ‘HyPer-TOC’ analyser (Thermo Electron Corp., The Netherlands), using a modified method based on sample acidification and detection of the evolving CO2 in

the NDIR detector ( Kaltin et al. 2005). The DIC concentrations in the samples were calculated from the calibration curve obtained using standard aqueous solutions of Na2CO3. The recovery was 97.5 ± 1%. Each sample was analysed in triplicate. The precision assessed as RSD was better than 1.5%. DIC and DOC loads via SGD to the study area were calculated as the product of the measured groundwater fluxes and concentrations of DIC and DOC measured in the groundwater samples. To quantify the annual DIC and DOC loads delivered to the Bay of Puck, the DIC and DOC concentrations measured at the study site in the groundwater samples (salinity ≤ 0.5) and in the groundwater taken from Piekarek-Jankowska et al. (1994) (0.03 km3 yr− 1) were used. The estimate was based on hydrogeological and oceanographic methods and enabled us to evaluate the role of SGD in the water balance of the entire Bay of Puck (Piekarek-Jankowska 1994, Kozerski 2007).