Environ Sci Pollut Res DOI 10.1007/s11356-015-4499-2
SHORT RESEARCH AND DISCUSSION ARTICLE
Foam production as a side effect of an offshore liquefied natural gas terminal: how do plankton deal with it? Annalisa Franzo 1 & Ana Karuza 1 & Mauro Celussi 1 & Daniela Fornasaro 1 & Alfred Beran 1 & Elena Di Poi 1 & Paola Del Negro 1
Received: 3 October 2014 / Accepted: 6 April 2015 # Springer-Verlag Berlin Heidelberg 2015
Abstract The future growing demand of fossil fuels likely will lead to an increased deployment of liquefied natural gas terminals. However, some concerns exist about their possible effects on the marine environment and biota. Such plants showed to cause the production of foam, as occurred at the still operative terminal of Porto Viro (northern Adriatic Sea). Here, we present results from two microcosm experiments focused on the effects of such foam on microbially mediated degradation processes and its consequent incorporation within the pelagic food web. Such material could be considered as a heterogeneous matrix of both living and non-living organic matter, which constitutes an important substrate for exoenzymes as suggested by the faster hydrolytic rates measured in the treatment microcosms. In the second experiment, a quite immediate and efficient carbon transfer to planktonic biomass through prokaryotic incorporation and consequent predation by heterotrophic flagellates was highlighted. Although no negative effect was evidenced on the overall microbes’ growth and foam-derived C seemed to be easily reworked and transferred to higher trophic levels, an important reduction in biodiversity was evidenced for microalgae. Among them, mixotrophic organisms seemed to be favoured suggesting that the addition of foam could cause a modification of the microbial community structure.
Responsible editor: Philippe Garrigues * Annalisa Franzo [email protected] 1
Sezione Oceanografia, OGS (Istituto Nazionale di Oceanografia e Geofisica Sperimentale), v. A. Piccard 54, 34151 Trieste, Italy
Keywords Liquefied natural gas . Foam . Microcosms . Prokaryotes . Exoenzymatic activities . Heterotrophic C production . Pelagic food web
Introduction In the last decades, the increasing growth of gas consumption in domestic households, industry and power plants has gradually turned natural gas into a major source of energy. Several countries have not enough fossil fuel reservoirs in their own territory for satisfying energy requirements; therefore, its importation is widely adopted. Before being transported in huge amounts by special ships, natural gas needs to be cooled at −162 °C, the temperature at which the liquid state is reached (i.e. the so-called liquefied natural gas, LNG). LNG requires therefore the use of terminals dedicated to the conversion of natural gas to LNG and vice versa. In Italy, the LNG alternative is still at its infancy since only two terminals are operative within the territory (Panigaglia and Porto Viro, an onshore and an offshore representative, respectively). Nevertheless, several projects aimed at the settlement of brand new terminals are under examination by the competent authority. Simultaneously, concerns related to the impacts associated to such plants are debated, particularly in terms of human health, safety and environment. Focusing on this latter aspect, the production of foams by the Adriatic liquefied natural gas (ALNG) of Porto Viro exhorts to caution, particularly when the settlement of specific kinds of LNG terminals is under discussion. This plant is in fact an example of Open Rack Vaporizer technology (ORV), i.e. it utilizes seawater as the major heat source for the evaporation of LNG leading to its subsequent introduction in the network. ORV terminals cause an ambient water temperature decrease, leading to possible modifications of the natural
Environ Sci Pollut Res
thermal and hydrological regimes in the near-field area. In a biological perspective, the water discharged is enriched by chlorine which is added to control biofouling in the heatexchange system of the LNG terminal. The chlorination could form toxic residual organic compounds, some of them carcinogenic and mutagenic such as chlorinated organic acids, phenols and chloroforms (Malačič et al. 2008). Focusing on the Porto Viro plant, the mechanical handling of significant volumes of marine waters is responsible for the formation of foams. Together with the thermal shock associated to the lower temperature of the water discharged, in fact, particles naturally present in the environment (e.g. organic matter, unicellular and multicellular organisms) are broken in the circuit and inserted in a complex matrix that appears as foam. Marine planktonic food web is controlled by the availability of resources and removal processes such as grazing and viral lysis (Azam and Malfatti 2007). The strength of the match between these two pathways determines carbon fluxes within aquatic food webs (Legendre and Rivkin 2002; Pugnetti et al. 2008). In most marine environments, major fluxes of organic matter move to heterotrophic bacteria and archaea (hereinafter collectively referred to as heterotrophic prokaryotes) that are able to use dissolved organic substrates incorporating them in new biomass (Amon and Benner 1996). Heterotrophic prokaryotes use several strategies to acquire organic matter. High molecular weight compounds are reduced in size by means of exoenzymes in order to be utilized as a C and energy source (Hollibaugh and Azam 1983). In turn, prokaryotic biomass may be removed from the aquatic system by several mechanisms among which the grazing by heterotrophic flagellates is one of the most important (Fenchel 1982; Sherr et al. 1989; Fonda Umani and Beran 2003). This step is essential for conveying an important amount of C from heterotrophic prokaryotes to the higher trophic levels through flagellates and ciliates biomass. Also, the C represented by primary producers is channeled to the higher trophic levels through the microbial loop (for Cyanobacteria) or the classic food chain (for phytoplankton >2 μm). In view of the paucity of existing data related to the potential ecological impacts associated to an ORV plant, two microcosm experiments have been performed. Microbes (from prokaryotes to microplankton) have been chosen as our target organisms because they occur in abundances favourable for enclosure experiments and because their fast regeneration times likely give quick responses to specific perturbations. Since to the best of our knowledge there is an overall lack of investigations focused on the effects of foam on the C flow through the pelagic system, our experiments have been addressed to answer the following questions: 1. As potential substrates for the main degradation processes, do foams alter the prokaryote-mediated organic matter degradation rates (experiment 1)?
2. Is the C derived from foams degradation channelled and to what extent into the pelagic trophic web (experiment 2)?
Material and methods Study area The studied ALNG terminal is situated 15 km offshore Porto Viro in the south of the Gulf of Venice (Italy). The area is heavily influenced by inputs of the Po river and described as mesotrophic. It is actually characterized by a high variability in nutrient inputs and trophic status at a relatively short temporal and spatial scales (Del Negro et al. 2008 and references therein; Pugnetti et al. 2008). Sampling procedures The study was carried out in October 2013, and water samples were collected at different stations according to their use, i.e. for the characterization of in situ conditions and for the setup of the two experiments (Fig. 1). In order to characterize the in situ conditions, water samples were collected for the determination of total organic carbon (TOC) at three stations located along a transect which followed the main drift of the foam: stations A (45° 05.400′ N; 12° 35.100′ E), B (45° 05.400′ N; 12° 35.200′ E) and C (45° 05.500′ N; 12° 35.400′ E) at 50, 100 and 300 m from the terminal, respectively. Furthermore, water samples were collected at the control site (station D; 45° 05.400′ N; 12° 34.400′ E) located at ~500 m upstream from the terminal in an area characterized by the absence of foams. At each station of the transect, 2×1 L seawater samples were collected at 15 cm underneath the foam using a Millipore Multiplex peristaltic pump. In parallel at the same sites, 2×1 L of surface water was manually sampled using sterile polycarbonate bottles (Nalgene) after the careful removal of the foam. At St. D, 2× 1 L of water samples for TOC analysis were collected only at 12 m depth by Millipore Multiplex peristaltic pump. At the control station, water temperature, dissolved oxygen and salinity were measured by CTD probe model Sea-Bird Electronics 19 plus SEACAT profiler (Sea-Bird Electronics, Inc. Bellevue, Washington, USA). For the setup of the two experiments, seawater (75 L) was collected at 12 m depth at St. D as previously described and transferred in three polycarbonate bottles of 25 L each. This depth was chosen because it corresponds to the water intake of the ALNG terminal. Foam (4×100 L) was collected manually just in proximity of the ALNG outfall (45° 05.446′ N; 12° 35.107′ E). Samples were immediately transferred into plastic (HDPP) containers and liquefied by manual stirring. The volume of the resulting residue was measured: Each 100 L of
Environ Sci Pollut Res
Fig. 1 Location of the ALNG terminal and of the sampling stations
foam yielded an amount comprised between 600 and 1200 mL of liquid residue. An aliquot of the foam residue was subsampled for dissolved and particulate organic carbon (DOC and POC) analyses. All samples were kept refrigerated until their arrival at the on-land laboratory, which occurred within 8 h.
taken initially (T0) at T3, T8, T24 and T48 (expressed in hours) for the determination of DOC concentration, prokaryotic abundance and exoenzymatic activities. All data are presented as mean values±the standard deviation (SD) of measurements obtained in the two experimental replicates.
Foam biodegradation experimental design
Foam-to-plankton C transfer experimental design
About 25 L of the seawater sample from station D was first filtered through a nylon sieve with a 200-μm mesh size to eliminate mesozooplanktonic organisms (hereinafter called SW) and transferred into 5 L polypropylene carboys. Part of this seawater was subsequently filtered through a 0.22-μm pore size Millipore filter (Ø 142 mm) using a peristaltic pump to obtain the diluent for the dilution of the samples for the microbiological analysis. In order to perform the biodegradation experiment, two types of microcosms were set up in two replicates (2.5 L polycarbonate Nalgene bottles previously sterilized by autoclaving). Two bottles were filled with 2 L of SW only and served as the control while two microcosms were set up with 1 %v/v of foam residue into SW (2 L final volume). Microcosms were incubated for 48 h on a shaker at 20 °C at a light:dark cycle of 12:12 h. From each microcosm, subsamples (50 mL) were
For the plankton experiment, four 5-L Pyrex flasks were autoclaved and filled with seawater collected at station D. Two of them were amended with 1 %v/v of foam residue (duplicate treatments) whereas the other two served as controls. During the experiment, the flasks were kept under mild shaking at 20 °C and subjected to a light:dark cycle 12:12. Sampling was performed at T0 (d0) and after 2 (d2), 5 (d5), 8 (d8) and 14 (d14) days. At each sampling, seawater aliquots were collected for total organic carbon (TOC), prokaryotic abundance and biomass, phytoplankton abundance and biomass and heterotrophic C production (HCP). The volume collected at each sampling was equal to 150 mL, leading to a total volume decrease of ~750 mL in the flasks after 14 days. All data are presented as mean values ± the standard deviation (SD) of measurements obtained in the two experimental replicates.
Environ Sci Pollut Res
Analytical procedures Total, dissolved and particulate organic matter Samples for total organic carbon (TOC) analyses were collected in 20-mL glass vials (previously treated with chromic acid for 24 h, washed with Milli-Q water and precombusted for 4 h at 480 °C) and stored at −20 °C. Before analysis, the samples were automatically acidified to pH
SHORT RESEARCH AND DISCUSSION ARTICLE
Foam production as a side effect of an offshore liquefied natural gas terminal: how do plankton deal with it? Annalisa Franzo 1 & Ana Karuza 1 & Mauro Celussi 1 & Daniela Fornasaro 1 & Alfred Beran 1 & Elena Di Poi 1 & Paola Del Negro 1
Received: 3 October 2014 / Accepted: 6 April 2015 # Springer-Verlag Berlin Heidelberg 2015
Abstract The future growing demand of fossil fuels likely will lead to an increased deployment of liquefied natural gas terminals. However, some concerns exist about their possible effects on the marine environment and biota. Such plants showed to cause the production of foam, as occurred at the still operative terminal of Porto Viro (northern Adriatic Sea). Here, we present results from two microcosm experiments focused on the effects of such foam on microbially mediated degradation processes and its consequent incorporation within the pelagic food web. Such material could be considered as a heterogeneous matrix of both living and non-living organic matter, which constitutes an important substrate for exoenzymes as suggested by the faster hydrolytic rates measured in the treatment microcosms. In the second experiment, a quite immediate and efficient carbon transfer to planktonic biomass through prokaryotic incorporation and consequent predation by heterotrophic flagellates was highlighted. Although no negative effect was evidenced on the overall microbes’ growth and foam-derived C seemed to be easily reworked and transferred to higher trophic levels, an important reduction in biodiversity was evidenced for microalgae. Among them, mixotrophic organisms seemed to be favoured suggesting that the addition of foam could cause a modification of the microbial community structure.
Responsible editor: Philippe Garrigues * Annalisa Franzo [email protected] 1
Sezione Oceanografia, OGS (Istituto Nazionale di Oceanografia e Geofisica Sperimentale), v. A. Piccard 54, 34151 Trieste, Italy
Keywords Liquefied natural gas . Foam . Microcosms . Prokaryotes . Exoenzymatic activities . Heterotrophic C production . Pelagic food web
Introduction In the last decades, the increasing growth of gas consumption in domestic households, industry and power plants has gradually turned natural gas into a major source of energy. Several countries have not enough fossil fuel reservoirs in their own territory for satisfying energy requirements; therefore, its importation is widely adopted. Before being transported in huge amounts by special ships, natural gas needs to be cooled at −162 °C, the temperature at which the liquid state is reached (i.e. the so-called liquefied natural gas, LNG). LNG requires therefore the use of terminals dedicated to the conversion of natural gas to LNG and vice versa. In Italy, the LNG alternative is still at its infancy since only two terminals are operative within the territory (Panigaglia and Porto Viro, an onshore and an offshore representative, respectively). Nevertheless, several projects aimed at the settlement of brand new terminals are under examination by the competent authority. Simultaneously, concerns related to the impacts associated to such plants are debated, particularly in terms of human health, safety and environment. Focusing on this latter aspect, the production of foams by the Adriatic liquefied natural gas (ALNG) of Porto Viro exhorts to caution, particularly when the settlement of specific kinds of LNG terminals is under discussion. This plant is in fact an example of Open Rack Vaporizer technology (ORV), i.e. it utilizes seawater as the major heat source for the evaporation of LNG leading to its subsequent introduction in the network. ORV terminals cause an ambient water temperature decrease, leading to possible modifications of the natural
Environ Sci Pollut Res
thermal and hydrological regimes in the near-field area. In a biological perspective, the water discharged is enriched by chlorine which is added to control biofouling in the heatexchange system of the LNG terminal. The chlorination could form toxic residual organic compounds, some of them carcinogenic and mutagenic such as chlorinated organic acids, phenols and chloroforms (Malačič et al. 2008). Focusing on the Porto Viro plant, the mechanical handling of significant volumes of marine waters is responsible for the formation of foams. Together with the thermal shock associated to the lower temperature of the water discharged, in fact, particles naturally present in the environment (e.g. organic matter, unicellular and multicellular organisms) are broken in the circuit and inserted in a complex matrix that appears as foam. Marine planktonic food web is controlled by the availability of resources and removal processes such as grazing and viral lysis (Azam and Malfatti 2007). The strength of the match between these two pathways determines carbon fluxes within aquatic food webs (Legendre and Rivkin 2002; Pugnetti et al. 2008). In most marine environments, major fluxes of organic matter move to heterotrophic bacteria and archaea (hereinafter collectively referred to as heterotrophic prokaryotes) that are able to use dissolved organic substrates incorporating them in new biomass (Amon and Benner 1996). Heterotrophic prokaryotes use several strategies to acquire organic matter. High molecular weight compounds are reduced in size by means of exoenzymes in order to be utilized as a C and energy source (Hollibaugh and Azam 1983). In turn, prokaryotic biomass may be removed from the aquatic system by several mechanisms among which the grazing by heterotrophic flagellates is one of the most important (Fenchel 1982; Sherr et al. 1989; Fonda Umani and Beran 2003). This step is essential for conveying an important amount of C from heterotrophic prokaryotes to the higher trophic levels through flagellates and ciliates biomass. Also, the C represented by primary producers is channeled to the higher trophic levels through the microbial loop (for Cyanobacteria) or the classic food chain (for phytoplankton >2 μm). In view of the paucity of existing data related to the potential ecological impacts associated to an ORV plant, two microcosm experiments have been performed. Microbes (from prokaryotes to microplankton) have been chosen as our target organisms because they occur in abundances favourable for enclosure experiments and because their fast regeneration times likely give quick responses to specific perturbations. Since to the best of our knowledge there is an overall lack of investigations focused on the effects of foam on the C flow through the pelagic system, our experiments have been addressed to answer the following questions: 1. As potential substrates for the main degradation processes, do foams alter the prokaryote-mediated organic matter degradation rates (experiment 1)?
2. Is the C derived from foams degradation channelled and to what extent into the pelagic trophic web (experiment 2)?
Material and methods Study area The studied ALNG terminal is situated 15 km offshore Porto Viro in the south of the Gulf of Venice (Italy). The area is heavily influenced by inputs of the Po river and described as mesotrophic. It is actually characterized by a high variability in nutrient inputs and trophic status at a relatively short temporal and spatial scales (Del Negro et al. 2008 and references therein; Pugnetti et al. 2008). Sampling procedures The study was carried out in October 2013, and water samples were collected at different stations according to their use, i.e. for the characterization of in situ conditions and for the setup of the two experiments (Fig. 1). In order to characterize the in situ conditions, water samples were collected for the determination of total organic carbon (TOC) at three stations located along a transect which followed the main drift of the foam: stations A (45° 05.400′ N; 12° 35.100′ E), B (45° 05.400′ N; 12° 35.200′ E) and C (45° 05.500′ N; 12° 35.400′ E) at 50, 100 and 300 m from the terminal, respectively. Furthermore, water samples were collected at the control site (station D; 45° 05.400′ N; 12° 34.400′ E) located at ~500 m upstream from the terminal in an area characterized by the absence of foams. At each station of the transect, 2×1 L seawater samples were collected at 15 cm underneath the foam using a Millipore Multiplex peristaltic pump. In parallel at the same sites, 2×1 L of surface water was manually sampled using sterile polycarbonate bottles (Nalgene) after the careful removal of the foam. At St. D, 2× 1 L of water samples for TOC analysis were collected only at 12 m depth by Millipore Multiplex peristaltic pump. At the control station, water temperature, dissolved oxygen and salinity were measured by CTD probe model Sea-Bird Electronics 19 plus SEACAT profiler (Sea-Bird Electronics, Inc. Bellevue, Washington, USA). For the setup of the two experiments, seawater (75 L) was collected at 12 m depth at St. D as previously described and transferred in three polycarbonate bottles of 25 L each. This depth was chosen because it corresponds to the water intake of the ALNG terminal. Foam (4×100 L) was collected manually just in proximity of the ALNG outfall (45° 05.446′ N; 12° 35.107′ E). Samples were immediately transferred into plastic (HDPP) containers and liquefied by manual stirring. The volume of the resulting residue was measured: Each 100 L of
Environ Sci Pollut Res
Fig. 1 Location of the ALNG terminal and of the sampling stations
foam yielded an amount comprised between 600 and 1200 mL of liquid residue. An aliquot of the foam residue was subsampled for dissolved and particulate organic carbon (DOC and POC) analyses. All samples were kept refrigerated until their arrival at the on-land laboratory, which occurred within 8 h.
taken initially (T0) at T3, T8, T24 and T48 (expressed in hours) for the determination of DOC concentration, prokaryotic abundance and exoenzymatic activities. All data are presented as mean values±the standard deviation (SD) of measurements obtained in the two experimental replicates.
Foam biodegradation experimental design
Foam-to-plankton C transfer experimental design
About 25 L of the seawater sample from station D was first filtered through a nylon sieve with a 200-μm mesh size to eliminate mesozooplanktonic organisms (hereinafter called SW) and transferred into 5 L polypropylene carboys. Part of this seawater was subsequently filtered through a 0.22-μm pore size Millipore filter (Ø 142 mm) using a peristaltic pump to obtain the diluent for the dilution of the samples for the microbiological analysis. In order to perform the biodegradation experiment, two types of microcosms were set up in two replicates (2.5 L polycarbonate Nalgene bottles previously sterilized by autoclaving). Two bottles were filled with 2 L of SW only and served as the control while two microcosms were set up with 1 %v/v of foam residue into SW (2 L final volume). Microcosms were incubated for 48 h on a shaker at 20 °C at a light:dark cycle of 12:12 h. From each microcosm, subsamples (50 mL) were
For the plankton experiment, four 5-L Pyrex flasks were autoclaved and filled with seawater collected at station D. Two of them were amended with 1 %v/v of foam residue (duplicate treatments) whereas the other two served as controls. During the experiment, the flasks were kept under mild shaking at 20 °C and subjected to a light:dark cycle 12:12. Sampling was performed at T0 (d0) and after 2 (d2), 5 (d5), 8 (d8) and 14 (d14) days. At each sampling, seawater aliquots were collected for total organic carbon (TOC), prokaryotic abundance and biomass, phytoplankton abundance and biomass and heterotrophic C production (HCP). The volume collected at each sampling was equal to 150 mL, leading to a total volume decrease of ~750 mL in the flasks after 14 days. All data are presented as mean values ± the standard deviation (SD) of measurements obtained in the two experimental replicates.
Environ Sci Pollut Res
Analytical procedures Total, dissolved and particulate organic matter Samples for total organic carbon (TOC) analyses were collected in 20-mL glass vials (previously treated with chromic acid for 24 h, washed with Milli-Q water and precombusted for 4 h at 480 °C) and stored at −20 °C. Before analysis, the samples were automatically acidified to pH
