Chemical inputs from a karstic submarine groundwater discharge (SGD) into an oligotrophic Mediterranean coastal area

Abstract

The impacts of nutrient and other chemical inputs released by a submarine groundwater discharge (SGD) on the marine environment of an oligotrophic Mediterranean coastal area (Messiniakos Gulf, SE Ionian Sea) are investigated through a multidisciplinary approach. Nutrients and organic pollutants associated with the SGD are presented to study the chemical characteristics of the SGD and to investigate its effect on the marine ecosystem in comparison to freshwater discharges of the water bodies of Messinia Prefecture. Nutrient and organic pollutant fluxes were calculated from (214)Bi-based SGD estimates. An average of 22×10(3) mol of silicate per month and 8×10(3) mol of nitrate per month were released via the SGD. Nutrient concentrations at the mouth of the SGD were three times higher than in Messiniakos Gulf, and NO3(-) was the primary Dissolved Inorganic Nitrogen form discharged by SGD. Organic pollutant concentrations associated with agricultural activities were low at the SGD. The implementation of a Eutrophication Index (E.I.) showed that the water column at the SGD site corresponds to Moderate/Bad ecological quality, whereas the status switches rapidly to Good at a small distance from the SGD. Coastal areas influenced by river or sewage discharge correspond to a Moderate/Good ecological status. The BENTIX index used for the classification of the ecological quality status of the benthic macroinvertebrate communities showed that the SGD has a minor influence compared to the other freshwater discharges in Messiniakos Gulf. Though the SGD has a considerable outflow, morphology and hydrodynamics of the area favor the rapid dispersion of the upwelling water and degrades the SGD's effect even on a regional scale.

Keywords: BENTIX index; Ecological quality status; Eutrophication index; Nutrient fluxes; SGD.