RMZ - Materials and Geoenvironment, Vol. 52, No. 1, 35-39, 2005 35

Geochemical characterization of the submarine spring of Izola (Gulf of , N )

JADRAN FAGANELI1, NIVES OGRINC2, LYNN M. WALTER3, JOŽE ŽUMER4

1Marine Biological Station, National Institute of Biology, Fornaèe 41, 6330 , ; [email protected] 2Department of Environmental Sciences, “J. Stefan” Institute, Jamova 39, 1000 Ljubljana, Slovenia; [email protected] 3University of Michigan, Dept. of Geological Sci., 1018 C.C. Little Building Ann Arbor, MI 48109-1063, USA 4 Diving center Port of , Koper, Slovenia

Abstract: First results of the geochemical research performed in a submarine spring near Izola are presented. It was found that the spring discharge of nutrients to the southern part of the Gulf is of less importance relative to the other freshwater discharges, repre- senting <4 % of the total freshwater nutrient input.

Key words: groundwater, coastal zone, discharge, measurements

INTRODUCTION

Submarine groundwater springs are a wide- ary (MOORE, 1999). In subterranean estuar- spread coastal phenomena which occur wher- ies, geochemical reactions between the ever hydrogeological gradients enable lateral mixed waters and host aquifer materials can and upward groundwater transport enhance sediment/water geochemical ex- (JOHANNES, 1980). Karstic coastlines (BACK change and significantly affect the coastal ET AL., 1979; PAULL ET AL., 1990), modern water mass balance of nutrients and other and paleo-river channels (CHAPELLE, 1997), reactive constituents (SWARZENSKI ET AL. 2001 geopressured aquifires (MANHEIM, 1967; and references therein). KOHOUT ET AL., 1976), geothermal aquifers (KOHOUT, 1967), mountainous shorelines The aim of the present study is to determine with large tidal amplitudes and lagoons with the complete geochemical composition of a heightened evaporation (SIMMS, 1984) are submarine spring located 0.8 km offshore of most important locales for submarine Izola (, northern Adriatic Sea) groundwater discharges. A submarine spring to identify the source(s) of spring water and derived from meteoric and seawater mixing to determine via comparison with conserva- within an aquifier can be considered a sub- tive tracers (e.g. Cl, Mg) the significance of terranean estuary because it displays many geochemical reactions occurring at the mix- of the key chemical features of surface estu- ing zone.

Short scientific paper 36 FAGANELI, J. ET AL.

Figure 1. Parametric acoustic profile of Izola submarine spring (Courtesy of Harphasea Koper, Slovenia)

MATERIALS AND METHODS

Samples - Water samples were collected in (GRASSHOFF ET AL., 1986). Analyses of the November 2003 at the Izola submarine following elements (Ca, Mg, Na, K, Sr, Ba, spring (45° 32.911 N, 13° 38.752 W). To B, Mn, Fe, Zn, Si, Li and Al) were performed obtain the most pristine sample of the spring by ICP-OES. The concentrations of DIC water, SCUBA divers inserted a polyethyl- were determined on a UIC Coulometrics CO 2 ene tube (6 mm i.d.) into the well and samples Coulometer. The precisions, based on repli- were collected by syringe. Water samples cate analyses, were ±0.01 for pH, ±1 % for were filtered through 0.45 mm Millipore HA TA, and ±2 % for DIC and metals, and ±5 % membrane filters in a N -filled glove bag for nutrients, chloride and sulphide, respec- 2 under N pressure of 0.4 MPa. In spring wa- tively. The stable isotopic composition of 2 ter pH, total alkalinity (TA), dissolved inor- DIC was determined with the modified ganic carbon (DIC), 13C composition of DIC method of extraction (CAPASSO ET AL., 2003). (δ13C ), sulphide, and N and P nutrients The isotope ratios of extracted CO was then DIC 2 were analyzed immediately. Water samples determined directly from the headspace by for cation determinations were acidified us- Isotope Ratio Mass Spectrometer - IRMS ing “ultrapure” HNO . (Europa Scientific 20-20) with preparation 3 module for trace gas samples ANCA-TG Analyses - The pH of spring waters was equipped with a Gilson autosampler. The measured using a UniFET microelectrode. results are reported using conventional delta TA was determined by Gran titration. Am- (d) notation relative to PDB in per mil (‰). monia, phosphate and sulphide were ana- Overall analytical error was ±0.2 ‰. All lyzed colorimetrically and Cl- titrimetrically measuring data are collected in Table 1.

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Table 1. Chemical composition of the Izola spring water, “average” seawater and karst groundwater form SW Slovenia (KUKAR, 1998)

RESULTS AND DISCUSSION

The solute composition of Izola spring wa- of DIC in the Izola spring relative to the sea- ter was compared to typical groundwater water can be explained by oxidation of or- from SW Slovenia and to the composition ganic matter within the spring which could of the average seawater (Table 1). The salin- be also seen in the lower δ13C value. Ad- DIC ity of submarine spring water was 5 consis- ditionally, the realised of CO can also pro- 2 tent with dilution in ambient seawater by mote calcite dissolution in the spring. advection and mixing. The reducing subma- rine spring water is evidenced by the pres- Therefore, mixing of seawater supersaturated ence of sulphide (0.22 mM). The spring wa- with respect to calcite with fresh groundwa- ter is rich in Ca-DIC. The concentrations of ter saturated with respect to calcite results in Na, K, Mg and Sr are much higher in spring the solution where calcite dissolution occurs. water compared to the groundwater and, ex- This mechanism can be explained by non- cept for Ca, about 10-fold lower than in sea- linear dependence of activity coefficient on water. The calcite saturation index indicates ionic strength and by the non-linear depen- that calcite dissolution is thermodynamically dence of calcite solubility on pCO 2 favored in the spring water. The enrichment (PLUMMER, 1975; MOORE, 1999).

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Selected elements (Fe, Mn and Ba) suggest These results suggest that meteoric waters some interesting deviations from seawater discharged off Izola are geochemically simi- values as well. Mn and Fe concentrations lar to karst groundwater, characteristic of those were up to 10 to 100-times higher than in in SW Slovenia, mixed with about 15 % of the average seawater and groundwater. The the seawater based on the comparison with behavior of these two redox couples con- conservative tracers (e.g. Cl, Mg). Hence, the forms to a predictable oxidation state trans- onshore flow regime appears to extend onto formation in the reducing groundwaters from the Gulf of Trieste. The concentrations of more particles reactive to more soluble +2 major solutes in the spring water are similar states. Ba was also enriched in spring water to those found in the study of SWARZENSKI ET relative to seawater probably due to biologi- AL. (2001) of the submarine spring off Cres- cally mediated precipitation of barite cent Beach in Florida. As is the case in Izola, (BaSO ) in seawater. Concentration of Al and the source aquifer for the spring water is not a 4 Zn in spring water were close to onshore single geological formation, but a more dif- groundwater and higher than the average fuse and complicated karst-influenced mix- seawater. Nutrient data from the submarine ing regime. Considering the spring discharges spring water show that N is mostly (75 %) in the Gulf of Trieste of 1 m 3/min it seems and P almost totally present as NH + and that the flux of metals and nutrients to the 4 PO 3-, respectively, which could also be the southern part of the Gulf of Trieste is of lesser 4 consequence of organic matter degradation importance compared to other fresh water dis- present in the spring. Concentration level of charges (TURK & POTOÈNIK, 2001) represent- Si was, on the other hand, very similar to ing <0.2 % and <4 %, respectively, of the pore waters concentrations (ÈERMELJ ET AL., freshwater input. 1997), and B very similar to seawater con- centrations. On the other hand, the seawater Acknowledgement concentrations of nutrients were an order of magnitude lower than the spring water This research was financially supported by concentrations. IAEA under Contract No. 12156/R0.

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