Ocean Acidification studies in the Baia di Levante (Vulcano island, Italy). Advantages and disadvantages of the “in situ” approach.

Years of scientific research have shown that acidification of oceans (OA) is an undisputed fact. Why is it so important to increase knowledge about OA? Because many animals and plants in the ocean have calcium carbonate skeletons or shells, and a decreasing in pH can affect their population health state and the marine-ecosystem structure. Another point of view about OA which must to be considered is that it may alter the behavior of sediment-bound metals, modifying their bioavailability and thus toxicity. The toxic free-ion concentration of metals such as copper may increase by as much as 115% in coastal waters in the next 100 years due to reduced pH. Since increasing atmospheric CO2 over the next 200 years will cause a pH decrease in ocean water, and consequently change the organic and inorganic speciation of metals in surface ocean waters, and it will effect on their interaction with marine species. Most of the intense submersed hydrothermal seeps are located near the isthmus of the Baia di Levante along the beach (38°25’01.44”N, 14°57’36.29”E), where dispersed underwater leaks cover a 130 × 35m shallow water area (<1m depth). Here we aim at studying the geochemical characteristics of seawater in the Baia di Levante area. We studied the most prominent geochemical parameters across the whole bay and focused on the spatio-temporal variability of pH/CO2 along a stretch of coast in the northeastern part of the bay in the Vulcanello area. Eh and pH were greatly affected by the main vents. Eh values range from -152 to 170 mV in April and from -23 to 171 mV in September 2011 and from -39.7 to 181.3 in May 2012, while pH values range between 5.70 and 8.05 in April and from 6.05 to 8.03 in September 2011 and from 5.85 to 8.03 in May 2012. These is the reason why a pH and Eh gradient (from bubbles to offshore) affect seawater chemistry and biota in the Bay. About 3.6 tonnes of CO2 bubble into Baia di Levante per day which strongly influences the seawater chemistry of the area. The pH displayed a clear gradient from 5.65 at the main gas vents increasing to 8.1 and may represent suitable sites for ocean acidification studies. The ternary diagram of CH4-(N2+O2)-CO2 confirms the atmospheric contribution to dissolved gases and shows variable ratios between CH4 and CO2. Dissolved gases samples were analysed with gas chromatography. Calcite and aragonite saturation in the bay is achieved only in the northern part where pH values exceed respectively 7.5 and 7.6. According to projections, 7.8 is the predicted average global sea surface pH value for the year 2100, and it is considered an ecological tipping point at which most subtidal calcifiers disappear in the Mediterranean. Vulcano’s seawater composition in terms of the major elements is close to that of Mediterranean surface waters even if salinity is few higher than oceans and greater variability is recorded for dissolved Fe concentrations and trace metals distribution along the bay. Major elements were analyzed with IC (Ionic Chromatography). Calculated enrichment factors (EF) for trace metals in general show that in general we can considered V as not so enriched, Ni, Al, Cu, Fe and Zn as medium enriched and Mn as very enriched, furthermore, EF show that, except for Cu, trace metals are enriched in Baia di Levante probably because of the hydrothermal input. Average seawater concentration for each metals are; 5.1 μg/l for Al, 0.8 μg/l for V, 11.4 μg/l for Mn, 3.7 μg/l for Fe, 0.3 μg/l for Ni, 0.5 μg/l for Cu, 2.3 μg/l for Zn and 5.2-3 μg/l for La. Seawater samples were pre-concentrated with chelex-100 resin and analyzed with ICP-MS. A transplant mussel experiment in acidic condition (natural seawater respectivly) was conducted and, after one month exposure mussel (Mytilus gallorpovincialis) had accumulated Fe, Zn, Cu and V. Soft body mussel metals concentration are 0.7 μg/g for Ni, 2.7 μg/g for V, 4.5 μg/g for Cu, 7.2 μg/g for Mn, 23 μg/g for Al, 78.6 μg/g for Zn and 336.4 μg/g for Fe. Mussels are confirmed to be good bioaccumulator of heavy metals, although, their study in situ in the context larger of OA studies is complicated despite the fact have a lot of vantages. Geochemical approach is fundamental in this field, and biota accumulation should always be matched with geochemical survey in their habitat in order to better understand the bio-accumulation dynamics

Plants as biomonitors for volcanic emissions

Biomonitoring techniques have been widely used in environmental studies to monitor anthropogenic pollutant. Recently such techniques have been applied also to ascertain the impact of contaminants naturally released by volcanic activity. In the present study a biomonitoring surveys has been performed in many different active volcanic systems: Mt. Etna and Vulcano (Italy), Nisyros (Greece), Nyiragongo (DRC), Masaya (Nicaragua), Gorely (Kamchatka, Russia). We sampled leaves of different species Betulla aethnensis, Pinus nigra, Populus tremula, Senecio aethnensis and Rumex aethnensis on Etna, Cistus creticus and salvifolius on Vulcano and Nisyros, Senecio ssp. on Nyiragongo, a Fern on Masaya and Salix arctica at Gorely. All samples were analyzed by ICP-MS and ICP-OES for 49 elements after acid digestion with a microwave oven (HNO3 + H2O2). Major constituents in leaves are K, Ca, Mg, Na, Si, Al and Fe ranging from about 10 3 to 105 ppm. Manganesium, Sr, Rb, Ba, Zn, B, Cu show also relatively high concentrations (100-103 ppm) while the remaining elements (As, Bi, Cd, Ce, Co, Cr, Cs, Ga, Li, Mo, Ni, Pb, Sb, Sc, Se, Th, Tl, U, V, Y and lanthanide series) display much lower values (10-4-101 ppm). Nearly all investigated elements show their highest concentrations in the samples collected closest to the main degassing vents (open craters, fumarolic fields). Increased concentrations are also found in the samples collected in the downwind direction where volcanic emissions are prevailingly dispersed. Leaves collected along radial transects from the active vents, highlight that the levels of metals decrease from one to two orders of magnitude with increasing distance from the source. The decrease is stronger for volatile elements, which are highly enriched in volcanic emissions, (As, Bi, Cd, Cs, Pb, Sb, Tl) than for more refractory elements (Al, Ba, Sc, Si, Sr, Th, U). The different species of plants show significant differences in the bioaccumulation processes for most of the analyzed elements, in particular lanthanides, which are systematically enriched in Rumex leaves. Needles of pine (non-deciduous tree) represent a good tool for biomonitoring investigation because they are important tracers of accumulation with time. The high concentrations of many toxic elements in the leaves allow us to consider some of these plants as highly tolerant species to the volcanic emissions, and suitable for biomonitoring researches further confirming their strong potential in tracing the impact and geographic distribution of these natural contaminants

Another kind of “volcanic risk”: the acidification of sea-water. Vulcano Island (Italy) a natural laboratory for ocean acidification studies

Acidification of seawater is one of the aspect tightly linked to volcanic risk, due to the presence of submarine vents releasing abundant volcanic fluids. In aquatic system CO2 gas dissolves, hydrates and dissociates to form weak carbonic acid, which is the main driver of natural weathering reactions [Drever, 1997]. The result of the CO2 increase is seawater acidification. Vulcano Island, the southernmost of Aeolian Islands, is located in the Southern Tyrrhenian Sea (Italy), approximately 18 miles off the NE coast of Sicily. The Baia di Levante can be considered a natural laboratory where almost all of the biogeochemical processes related to the ocean acidification can be studied. In this area many submarine vents release CO2. Four geochemical surveys of the Bay were carried out in April - September 2011 and May - June 2012. The main physic-chemical parameters (T, pH, Eh, electric conductivity) were measured at more than 70 sites and more than 40 samples for chemical analyses were collected at representative points. Major (Na, K, Mg, Ca, Cl, SO4) and some minor components (B, Sr, Fe) and trace elements (Mn, Mo, Al, U, Ce, Pb, Tm, Tb, Nd, Th) dissolved in water, the chemical composition of dissolved gases (He, H2, O2, N2, CH4 and CO2) and the isotopic composition of total dissolved inorganic carbon were determined in the laboratory. The bubbling CO2 produces a strong decrease in pH from the normal seawater value of 8.2 down to 5.5 (Figure 1). In the area close to the main degassing vents, characterized by very low pH, macroorganisms were absent. Acidification of sea water is one of the aspect tightly linked to volcanic risk, due to the presence of submarine vents releasing abundant volcanic fluids. At Baia di Levante, about 300 m from the main vents the seawater is only slightly acidic (pH 6.5 - 7.0) resembling the ocean water conditions in equilibrium with the high atmospheric CO2 concentrations expected in the near future. Therefore environments like this, naturally enriched in CO2, are good laboratories to study the consequences of ocean acidification on aquatic biota [Doney et al., 2009]. Furthermore acidification is tightly linked with the mobility and bio-availability of heavy metals [Millero et al., 2009] in sea water and volcanoes were always the favourite choice for human settlements; as a consequence economic anthropological activity, such as fishing, could be dangerous for human health, because of the presence toxic level of trace metals in the food chain due to the presence of the volcano’s. The present study could provide important information about the best environmental management of volcanic areas such as Vulcano IslandPublishedNicolosi (Catania)1.2. TTC - Sorveglianza geochimica delle aree vulcaniche attiveope