Dario Tedesco

Volcanic carbon dioxide vents show ecosystem effects of ocean acidification

The atmospheric partial pressure of carbon dioxide (pCO2) will almost certainly be double that of pre-industrial levels by 2100 and will be considerably higher than at any time during the past few million years. The oceans are a principal sink for anthropogenic CO2 where it is estimated to have caused a 30% increase in the concentration of H+ in ocean surface waters since the early 1900s and may lead to a drop in seawater pH of up to 0.5 units by 2100 (refs 2, 3). Our understanding of how increased ocean acidity may affect marine ecosystems is at present very limited as almost all studies have been in vitro, short-term, rapid perturbation experiments on isolated elements of the ecosystem. Here we show the effects of acidification on benthic ecosystems at shallow coastal sites where volcanic CO2 vents lower the pH of the water column. Along gradients of normal pH (8.1–8.2) to lowered pH (mean 7.8–7.9, minimum 7.4–7.5), typical rocky shore communities with abundant calcareous organisms shifted to communities lacking scleractinian corals with significant reductions in sea urchin and coralline algal abundance. To our knowledge, this is the first ecosystem-scale validation of predictions that these important groups of organisms are susceptible to elevated amounts of pCO2. Sea-grass production was highest in an area at mean pH 7.6 (1,827 μatm pCO2) where coralline algal biomass was significantly reduced and gastropod shells were dissolving due to periods of carbonate sub-saturation. The species populating the vent sites comprise a suite of organisms that are resilient to naturally high concentrations of pCO2 and indicate that ocean acidification may benefit highly invasive non-native algal species. Our results provide the first in situ insights into how shallow water marine communities might change when susceptible organisms are removed owing to ocean acidification.

Methanotrophy below pH 1 by a new Verrucomicrobia species

Mud volcanoes, mudpots and fumaroles are remarkable geological features characterized by the emission of gas, water and/or semi-liquid mud matrices with significant methane fluxes to the atmosphere (10-1 to 103 t y-1). Environmental conditions in these areas vary from ambient temperature and neutral pH to high temperatures and low pH. Although there are strong indications for biological methane consumption in mud volcanoes, no methanotrophic bacteria are known that would thrive in the hostile conditions of fumaroles (temperatures up to 70 °C and pH down to 1.8). The first step in aerobic methane oxidation is performed by a soluble or membrane-bound methane mono-oxygenase. Here we report that pmoA (encoding the β-subunit of membrane-bound methane mono-oxygenase) clone libraries, made by using DNA extracted from the Solfatara volcano mudpot and surrounding bare soil near the fumaroles, showed clusters of novel and distant pmoA genes. After methanotrophic enrichment at 50 °C and pH 2.0 the most distant cluster, sharing less than 50% identity with any other described pmoA gene, was represented in the culture. Finally we isolated an acidiphilic methanotrophic bacterium Acidimethylosilex fumarolicum SolV belonging to the Planctomycetes/Verrucomicrobia/Chlamydiae superphylum, ‘outside’ the subphyla of the Alpha- and Gammaproteobacteria containing the established methanotrophs. This bacterium grows under oxygen limitation on methane as the sole source of energy, down to pH 0.8—far below the pH optimum of any previously described methanotroph. A. fumarolicum SolV has three different pmoA genes, with two that are very similar to sequences retrieved from the mudpot. Highly homologous environmental 16S rRNA gene sequences from Yellowstone Park show that this new type of methanotrophic bacteria may be a common inhabitant of extreme environments. This is the first time that a representative of the widely distributed Verrucomicrobia phylum, of which most members remain uncultivated, is coupled to a geochemically relevant reaction.

Continuous monitoring of distal gas emanations at Vulcano, southern Italy

The increasing activity of Vulcano Island (Italy) since 1985 led to the initiation of continuous geochemical monitoring of the lateral soil gas emissions. On the basis both of their relative geochemical characteristics and of local considerations, three gaseous components were selected for monitoring, namely CO2, He and 222Rn. Monitoring has been performed by means of specific analysers. Gases extracted from a water well located at the foot of the active cone were selected for monitoring, on the basis of their geochemical and isotopic characters that indicate their genetic link with central high temperature fumarolic gases emitted at the crater. Very strong variations of gas composition can be observed within one day (from 1 to about 94% for CO2). Some variations display a daily character and can be correlated with that of atmospheric pressure. The three monitored gases are highly correlated, suggesting very high kinetics of gas transfer in the system. Because of these considerable variations of chemical composition, bulk concentrations obviously are not suitable for monitoring at Vulcano. However, the evolution with time of ratios such as 222Rn/CO2 and He/CO2 (the latter being corrected for atmospheric contamination) supplies numerical parameters that the expected to characterize the intensity of the degassing process. A new input of magmatic gases, that would lead to an increase in the 222Rn/CO2 and He/CO2 ratios, should therefore be detected by such a monitoring station.

Impact of volcanic plume emissions on rain water chemistry during the January 2010 Nyamuragira eruptive event: implications for essential potable water resources.

On January 2, 2010 the Nyamuragira volcano erupted lava fountains extending up to 300 m vertically along an ~1.5 km segment of its southern flank cascading ash and gas on nearby villages and cities along the western side of the rift valley. Because rain water is the only available potable water resource within this region, volcanic impacts on drinking water constitutes a major potential hazard to public health within the region. During the 2010 eruption, concerns were expressed by local inhabitants about water quality and feelings of physical discomfort (e.g. nausea, bloating, indigestion, etc.) after consuming rain water collected after the eruption began. We present the elemental and ionic chemistry of drinking water samples collected within the region on the third day of the eruption (January 5, 2010). We identify a significant impact on water quality associated with the eruption including lower pH (i.e. acidification) and increases in acidic halogens (e.g. F(-) and Cl(-)), major ions (e.g. SO(4)(2-), NH(4)(+), Na(+), Ca(2+)), potentially toxic metals (e.g. Al(3+), Mn(2+), Cd(2+), Pb(2+), Hf(4+)), and particulate load. In many cases, the waters composition significantly exceeds World Health Organization (WHO) drinking water standards. The degree of pollution depends upon: (1) ash plume direction and (2) ash plume density. The potential negative health impacts are a function of the waters pH, which regulates the elements and their chemical form that are released into drinking water.

Chemical (He, H2, CH4, Ne, Ar, N2) and isotopic (He, Ne, Ar, C) variations at the solfatara crater (southern italy): mixing of different sources in relation to seismic activity

Here we describe temporal variations of noble gas (He, Ne and Ar), carbon isotopes and chemical data of fluids collected at the Bocca Grande fumarole (Solfatara crater) from 1990 to 1994, before the occurrence of a seismic swarm. After more than seven years of quiescence, a sudden vertical ground deformation and a seismic swarm of 100 quakes with an Mmax = 1.5 with epicenter located beneath the Solfatara crater, was recorded from August 23 to 25 1994. Isotopic composition of He, Ne, Ar and C (from CO2) and abundances of He, Ne, Ar, H2, CH4 and N2 have been analysed from fumarolic fluids collected at the Solfatara crater. To date these isotopic ratios have not been used as precursors of earthquakes, although several cases have been reported in which the helium isotopic ratio was used to interpret volcanic unrest. All the analyzed isotopic ratios, chemical species and a calculated equilibrium temperature show a significant change a few months before the occurrence of the seismic activity and ground deformation, followed by a sudden return to values recorded prior the swarm. Migration towards the surface of deep (and hotter) gas phase related to crustal and magmatic sources with the following decrease of the surficial atmospheric component is the cause of such wide variations.

Helium isotopic ratio in Vulcano island fumaroles: temporal variations in shallow level mixing and deep magmatic supply

Intensive gas emanations occur throughout the island of Vulcano, Italy. Sharp fluctuations recorded in the crater gas composition suggest the presence of two separate volcanic reservoirs and continuous mixing with another source, “crustal” waters. This mixing differs between the beach and crater fumaroles. Gas samples from three crater fumaroles with temperatures ranging from 200 to 550 ° C were sampled repeatedly over a one year period. During the same interval of time, six samples from submarine and subaerial beach fumaroles and water well gases were also sampled. Gases from one crater fumarole (F5) showed variations of (3He4He)fumarole to (3He4He)air between 5 and 6 correlated with variations of several chemical species. High 3He4He ratios for the beach fluids, similar to those of crater fluids, suggest the existence of a unique large magmatic reservoir at depth feeding both the crater and beach intermediate reservoirs. However, temporal changes clearly indicate variable degrees of fluids mixing, and the geographic distribution of the 3He4He ratios as well as the chemical composition of the fluids suggest the existence between the magma reservoir and the surface of two intermediate different reservoirs, independently related to crater and to beach fumaroles.

Intensive gas sampling of noble gases and carbon at Vulcano Island (southern Italy)

The helium isotopic ratio of crater, beach and submarine fumaroles, water wells, and soil gases at Vulcano Island has been, since 1987, repeatedly measured. The 3 He/ 4 He from crater fumaroles (F5 and FA) oscillates biennially between 4.9 and 6.0-6.2 R/R a . The periodicity of the 3 He/ 4 He oscillation may be linked to pressure variations in a deep gas reservoir. Chemical and carbon isotope variations during the same period closely reflect trends shown by helium. These simultaneous variations, chemical and isotopic, suggest a close relationship between these species and reflect one dominant process, which belong to the routine activity of the volcano. The 40 Ar/ 36 Ar ratio up to 1200 is not consistent with the presence of an air-rich source and suggests the addition of radiogenic argon. Neon data ( 20 Ne/ 22 Ne and 21 Ne/ 22 Ne) indicates that a crustal component is present beneath the volcano. Heavy carbon, 0‰ ∼ -2%o, also supports the existence of a crustal component. The isotopic data here obtained do not indicate that the recorded variations (chemical and isotopic) indicate a period of unrest at Vulcano Island. The present phase of activity is explained with a two-state model of the feeding sources of the volcano: (a) a gas release from intermediate and surficial sources and (b) a magmatic pulse, 3 He-rich, from a deep gas reservoir (not migration of magma) which continuously mixes with more surficial fluids. Additions of surficial (air saturated waters) or atmospheric fluids are minor and may occur during the ascent of the gas phase to the surface or, more likely, be added at the time of the gas collection.

Fluid geochemistry at Vulcano island: A change in the volcanic regime or continuous fluctuations in the mixing of different systems?

Increasing fumarolic activity and the rise of outlet fumarole temperatures has occurred at Vulcano island (southern Italy) since September 1987. Regular sampling and analysis have been conducted on the well-known F5 fumarolic and later on F5HT and FA f umaroles on the Fossa crater plus other gas emanations from different sites on the island. Significant chemical and isotopical oscillations have been recorded over the period 1987–1991. Variations of water vapor in the fumarolic fluid follow a seasonal pattern and can be related to both external (seasonal) and magmatic influences but they suggest a control by a source other than magmatic. Significant variations of H2O, and of some species in the anhydrous gas phase (H2, CO2, SO2, N2, and He), have been related in the past to chemical or dynamic changes in the feeding system at depth. Oscillations of the isotopic composition of helium and carbon suggest possible mixing with a nonsurficial source, possibly crustal in origin. Argon and neon isotopic data support this hypothesis. Several mechanisms are considered for explaining the chemical and isotopic data, in relation to the recent increase in activity. Not all of the chemical and isotopic variations recorded are related to geophysical parameters such as seismicity and deformation. The low CO content of the F5 fumarolic and the apparent constancy of the 3He/4He ratio do not suggest an increase in the input of deep magmatic fluids. The high CO content of the high temperature (650°C) FA fumarole, located at the interior of the crater, along with helium and carbon isotopic ratios similar to other fumarolics is probably due to an easier ascent of these fluids to the surface. Apparent equilibrium temperatures, close to the fumarolic outlet temperature, indicate isothermal expansion of the gas from a shallow equilibration zone for both high- and lower-temperature gases. In particular, the chemical and isotopic features of fluids belonging to both crater and beach fumarole fields are consistent with the existence of two intermediate system, independently feeding the two fields. High 3He/4He ratios for the beach fluids, similar to those of the crater fluids, suggest a large magmatic reservoir at depth, feeding both the crater and the beach intermediate reservoirs.

Chemistry and emission rate of volatiles from White Island Volcano (New Zealand)

Gases and a water condensate have been sampled at White Island volcano in two selected fumaroles (100 and 495°C). They have been analysed for major, minor and trace elements. Both the chemical composition of gases and thermodynamic calculations suggest that the fluids feeding high and low temperature fumaroles have the same origin, but that they follow different evolutions while ascending to the surface. Very low CO/CO2 ratios with respect to White Island previous results suggest that White Island is now in stage of reduced activity. According to the very low solubility of CO in silicate melts, an increase in activity due to a magmatic pulse should cause a significant increase of CO in the released gas phase. Long term fluxes of gases and metals have been estimated on the basis of COSPEC SO2 flux measurements performed during a medium activity stage. Our data concerning some heavy metals are similar to previous data, suggesting a constancy of the emissions during quiescent periods.

Radon hazard in shallow groundwaters: Amplification and long term variability induced by rainfall

(222)Rn concentrations have been determined with a RAD7 radon detector in shallow groundwaters of the Pietramelara Plain, north-western Campania, southern Italy, where pyroclastic deposits, along with recent stream alluvial sediments, come in contact with Mesozoic carbonate reservoirs. The aim of this study has been to study the annual variation of (222)Rn concentration in the shallow groundwaters, scarcely considered in the literature and of obvious relevance for radon hazard evaluation. Our results definitely show that (222)Rn levels are characterized by a clear annual periodicity, strictly related to rainfall and water table levels, with a pronounced difference between the dry and the wet season. In this last case with concentrations increasing up to two orders of magnitude (up to two times the lower threshold given in the Recommendation 2001/928/EURATOM for public waters). In relation to this, experimental field data will be presented to demonstrate that this variability is due to purely hydrological mechanisms, mainly rinse out and discharge that control leaching efficiency. The detected cycle (Radon Hydrological Amplification Cycle, RHAC) has been generalized for the Mediterranean Tyrrhenian climate. The marked and seasonally persistent amplification in (222)Rn levels poses the problem of evaluating the epidemiological risk brought up by this previously not yet reported mechanism. This mechanism, occurring in shallow groundwaters, very likely should strongly influence indoor radon levels via groundwater-soil-building exchange.