Description: This article reports the results of a study of submarine groundwater discharge (SGD) to coastal waters of Majorca (NW Mediterranean). The overall aim is to evaluate the relevance of SGD of the island and chemically characterize the components that are supplied to the coastal waters through this pathway. Although other discharge areas are identified, we particularly focus on SGD in bays and areas of increased sea water residence time where effects of the discharges are expected to be most notable. Analysis at four selected embayments with different land-use characteristics indicated a link between human activities (mainly agriculture and urban) and compounds arriving to the coast. A pathway for these elements is the diffuse discharge along the shoreline, as suggested by the inverse relationship between salinity and nutrients in nearshore porewaters. A general survey was conducted at 46 sites around the island, and used dissolved radium as a qualitative indicator of SGD. Measurements of nutrients (P and N), pCO2 and TOC were performed to characterize the elements delivered to the coastal environment. Most nearshore samples showed 224Ra enrichment (mean ± SE, 7.0 ± 0.6 dpm 100 l−1) with respect to offshore waters (1.1 ± 0.2 dpm 100 l−1); however, 224Ra measurements along the coast were highly variable (1.0–38.1 dpm 100 l−1). Coastal samples with enhanced radium levels showed elevated pCO2 with respect to atmospheric concentrations, which together with high pCO2 in groundwater (〉5,000 ppm) indicates that SGD is an important vector of CO2 to coastal waters. Moreover, a relationship between 224Ra and phytoplankton biomass was established, suggesting an important impact of SGD on coastal productivity. The results presented here provide a first approximation of the SGD effect in the coastal waters of Majorca, and indicate that SGD could be an important source of nutrients and CO2 to the coast, strongly influencing the productivity and biogeochemical cycling of the coastal waters of Majorca.

Description: The effect of phototrophic biofilm activity on advective transport of cadmium (Cd), copper (Cu), nickel (Ni), and lead (Pb) in sandy sediments was examined using percolated columns. Cd and Ni in the effluent exhibited clear diel cycles in biofilm-containing columns, with concentrations at the end of dark periods exceeding those during illumination by up to 4.5- and 10-fold for Ni and Cd, respectively. Similar cycles were not observed for Pb or Cu. Breakthrough of the latter metals was greatly retarded and incomplete relative to Cd and Ni, and trends in biofilm treatments did not differ greatly from those in control columns. Inhibition of photosystem II by DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea) proved that diel cycles of Cd and Ni were controlled by oxygenic photosynthesis, and microsensor measurements showed that metal cycles closely matched metabolic activity-driven pH variations. The sorption edge pH for the sand/biofilm substrate followed the order Ni 〉 Cd 〉 Cu 〉 Pb, and for Ni and Cd, was within the pH 7–10 range observed in the biofilm-containing column. Adsorption dynamics over the light periods matched pH increases, but desorption during dark periods was incomplete and slower than the rate of change of pH. Over a diel cycle, desorption was less than adsorption, resulting in net binding of dissolved metals due to the biofilm metabolic activity. Extraction with selective reagents indicated that the adsorbed metals were readily exchangeable, and potentially bioavailable. Thus, phototrophic benthic biofilms can control the transport of some metals across the sand–water interface, and processes in this very thin surficial layer should be considered when evaluating chemical fluxes in permeable sediments.