Nutrient fluxes via submarine groundwater discharge to the Bay of Puck, southern Baltic Sea

Abstract

Submarine groundwater discharge (SGD) has been recognized as an important exchange pathway between hydrologic reservoirs due to its impact on biogeochemical cycles of the coastal ocean.This study reports nutrient concentrations and loads delivered by SGD into the Bay of Puck, the southern Baltic Sea. Measurements were carried out between September, 2009 and October, 2010 at groundwater seepage sites identified by low salinity of pore water. Groundwater fluxes, measured using seepage meters, ranged from 3 to 22Lm−2day−1. Average concentrations of nutrients in groundwater samples collected were as follows: 0.4μmolL−1 nitrate (NO3), 0.8μmolL−1 nitrite (NO2), 18.2μmolL−1 ammonium (NH4) and 60.6μmolL−1 orthophosphate (PO4). Levels of NH4 and PO4 were significantly higher in samples from SGD sites than in seawater. Seawater and SGD samples showed similar NO2 concentrations but SGD samples exhibited lower NO3 levels than those observed in seawater samples. Measured seepage water fluxes and nutrient concentrations were used to calculate nutrient loads discharged into the study area while the literature groundwater flux and the measured nutrient concentrations were used to estimate nutrient loads discharged into the Bay of Puck. The estimates suggest that SGD delivers a dissolved inorganic nitrogen (DIN) load of 49.9±18.0tyr−1 and a PO4‐ load of 56.3±5.5tyr−1 into the Bay of Puck. The projected estimates are significant in comparison with loads delivered to the bay from other, well-recognized sources (705tyr−1 and 105tyr−1 respectively for DIN and PO4). Nutrient discharge input loads were projected to the entire Baltic Sea The extrapolated values indicate SGD contributes a significant proportion of phosphate load but only an insignificant proportion of DIN load. Further studies are necessary to better understand SGD contributions to the nutrient budget in the Baltic Sea.