We report preliminary results from geochemical characterization of a coastal multi-aquifer groundwater system, which has been carried out in the framework of the project "Modelling of the impact of the agricultural holdings and land-use structure on the quality of inland and coastal waters of the Baltic Sea set up on the example of the Municipality of Puck region – Integrated info-prediction Web Service WaterPUCK", funded by National Centre for Research and Development (NCBR), Poland, (BIOSTRATEG3/343927/3/NCBR/2017). One of its main aims is to quantify the presence of nutrients (nitrogen and phosphorus compounds) in groundwater and their potential impact on seawater quality in the Puck Bay, which is a part of the Baltic Sea adjacent to the Polish coast and separated from the open sea by the Hel Peninsula.
The investigation area is covered by young glacial sediments and consists of moraine uplands and deep cut ice marginal valleys. Groundwater occurs in form of small perched aquifers on top of glacial till, as well as two main Quarternary aquifers, which have their outcrops in the sea bottom of Puck Bay, within 1-5 km from the coast. The land is used mostly for agriculture and forestry.
Groundwater samples were taken from 85 sampling points, including dug wells (mostly in perched aquifers), drilled wells (mostly in the shallow Quarternary aquifer), springs and boreholes. There are clear differences in nitrate (NO3) concentration between the shallow dug wells (10 to 90 mg/L) and deeper drilled wells (generally below 2 mg/L). The concentrations of ammonium (NH4) are similar in both groups of wells, while the concentrations of phosphorus (PO4) are mostly between 0.1 and 10 mg/L, with the average value slightly higher in the shallow wells. In this work we will present a detailed analysis of spatial and time distribution of the concentrations of nutrients and major ions in the area and we will discuss the potential impact of groundwater on the seawater quality.