The distribution of metal and petroleum-derived contaminants within sediments around oil and gas infrastructure in the Gippsland Basin, Australia.

As oil and gas infrastructure comes to the end of its working life, a decommissioning decision must be made: should the infrastructure be abandoned in situ, repurposed, partially removed, or fully removed? Environmental contaminants around oil and gas infrastructure could influence these decisions because contaminants in sediments could degrade the value of the infrastructure as habitat, enter the seafood supply if the area is re-opened for commercial and/or recreational fishing, or be made biologically available as sediment is resuspended when the structures are moved. An initial risk hypothesis, however, may postulate that these concerns are only relevant if contaminant concentrations are above screening values that predict the possibility of environmental harm or contaminant bioaccumulation. To determine whether a substantive contaminants-based risk assessment is needed for infrastructure in the Gippsland Basin (South-eastern Australia), we measured the concentration of metals and polycyclic aromatic hydrocarbons (PAHs) in benthic sediments collected around eight platforms earmarked for decommissioning. The measurements were compared to preset screening values and to background contaminant concentrations in reference sites. Lead (Pb), zinc (Zn), PAHs and other contaminants were occasionally measured at concentrations that exceeded reference values, most often within 150 m of the platforms. The exceedance of a few screening values by contaminants at some platforms indicates that these platforms require further analysis to determine the contaminant risks associated with any decommissioning option.

Transcriptomic and Histological Analysis of the Greentail Prawn (Metapenaeus bennettae) Following Light Crude Oil Exposure.

Oil spills pose a significant threat to marine biodiversity. Crude oil can partition into sediments where it may be persistent, placing benthic species such as decapods at particular risk of exposure. Transcriptomic and histological tools are often used to investigate the effects of hydrocarbon exposure on marine organisms following oil spill events, allowing for the identification of metabolic pathways impacted by oil exposure. However, there is limited information available for decapod crustaceans, many of which carry significant economic value. In the present study, we assess the sublethal impacts of crude oil exposure in the commercially important Australian greentail prawn (Metapenaeus bennettae) using transcriptomic and histological analyses. Prawns exposed to light, unweathered crude oil "spiked" sediments for 90 h were transferred to clean sediments for a further 72 h to assess recovery. Chemical analyses indicated that polycyclic aromatic hydrocarbons increased by approximately 65% and 91% in prawn muscle following 24 and 90 h of exposure, respectively, and significantly decreased during 24- and 72-h recovery periods. Transcriptomic responses followed an exposure and recovery pattern with innate immunity and nutrient metabolism transcripts significantly lowered in abundance after 24 h of exposure and were higher in abundance after 72 h of recovery. In addition, transcription/translation, cellular responses, and DNA repair pathways were significantly impacted after 24 h of exposure and recovered after 72 h of recovery. However, histological alterations such as tubule atrophy indicated an increase in severity after 24 and 72 h of recovery. The present study provides new insights into the sublethal impacts of crude oil exposure in greentail prawns and identifies molecular pathways altered by exposure. We expect these findings to inform future management associated with oil extraction activity and spills. Environ Toxicol Chem 2022;41:2162-2180. © 2022 John Wiley & Sons Ltd. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Stable mercury concentrations of tropical tuna in the south western Pacific ocean: An 18-year monitoring study.

Global anthropogenic mercury (Hg) emissions to the atmosphere since industrialization are widely considered to be responsible for a significant increase in surface ocean Hg concentrations. Still unclear is how those inputs are converted into toxic methylmercury (MeHg) then transferred and biomagnified in oceanic food webs. We used a unique long-term and continuous dataset to explore the temporal Hg trend and variability of three tropical tuna species (yellowfin, bigeye, and skipjack) from the southwestern Pacific Ocean between 2001 and 2018 (n = 590). Temporal trends of muscle nitrogen (δ15N) and carbon (δ13C) stable isotope ratios, amino acid (AA) δ15N values and oceanographic variables were also investigated to examine the potential influence of trophic, biogeochemical and physical processes on the temporal variability of tuna Hg concentrations. For the three species, we detected significant inter-annual variability but no significant long-term trend for Hg concentrations. Inter-annual variability was related to the variability in tuna sampled lengths among years and to tuna muscle δ15N and δ13C values. Complementary AA- and model-estimated phytoplankton δ15N values suggested the influence of baseline processes with enhanced tuna Hg concentrations observed when dinitrogen fixers prevail, possibly fuelling baseline Hg methylation and/or MeHg bioavailability at the base of the food web. Our results show that MeHg trends in top predators do not necessary capture the increasing Hg concentrations in surface waters suspected at the global oceanic scale due to the complex and variable processes governing Hg deposition, methylation, bioavailability and biomagnification. This illustrates the need for long-term standardized monitoring programs of marine biota worldwide.

Functional traits explain trophic allometries of cephalopods.

Individual body size strongly influences the trophic role of marine organisms and the structure and function of marine ecosystems. Quantifying trophic position-individual body size relationships (trophic allometries) underpins the development of size-structured ecosystem models to predict abundance and the transfer of energy through ecosystems. Trophic allometries are well studied for fishes but remain relatively unexplored for cephalopods. Cephalopods are important components of coastal, oceanic and deep-sea ecosystems, and they play a key role in the transfer of biomass from low trophic positions to higher predators. It is therefore important to resolve cephalopod trophic allometries to accurately represent them within size-structured ecosystem models. We assessed the trophic positions of cephalopods in an oceanic pelagic (0-500 m) community (sampled by trawling in a cold-core eddy in the western Tasman Sea), comprising 22 species from 12 families, using bulk tissue stable isotope analysis and amino acid compound-specific stable isotope analysis. We assessed whether ontogenetic trophic position shifts were evident at the species-level and tested for the best predictor of community-level trophic allometry among body size, taxonomy and functional grouping (informed by fin and mantle morphology). Individuals in this cephalopod community spanned two trophic positions and fell into three functional groups on an activity level gradient: low, medium and high. The relationship between trophic position and ontogeny varied among species, with the most marked differences evident between species from different functional groups. Activity-level-based functional group and individual body size are best explained by cephalopod trophic positions (marginal R2  = 0.43). Our results suggest that the morphological traits used to infer activity level, such as fin-to-mantle length ratio, fin musculature and mantle musculature are strong predictors of cephalopod trophic allometries. Contrary to established theory, not all cephalopods are voracious predators. Low activity level cephalopods have a distinct feeding mode, with low trophic positions and little-to-no ontogenetic increases. Given the important role of cephalopods in marine ecosystems, distinct feeding modes could have important consequences for energy pathways and ecosystem structure and function. These findings will facilitate trait-based and other model estimates of cephalopod abundance in the changing global ocean.

Nitrogen sufficiency enhances thermal tolerance in habitat-forming kelp: implications for acclimation under thermal stress.

Local and global changes associated with anthropogenic activities are impacting marine and terrestrial ecosystems. Macroalgae, especially habitat-forming species like kelp, play critical roles in temperate coastal ecosystems. However, their abundance and distribution patterns have been negatively affected by warming in many regions around the globe. Along with global change, coastal ecosystems are also impacted by local drivers such as eutrophication. The interaction between global and local drivers might modulate kelp responses to environmental change. This study examines the regulatory effect of NO3- on the thermal plasticity of the giant kelp Macrocystis pyrifera. To do this, thermal performance curves (TPCs) of key temperature-dependant traits-growth, photosynthesis, NO3- assimilation and chlorophyll a fluorescence-were examined under nitrate replete and deplete conditions in a short-term incubation. We found that thermal plasticity was modulated by NO3- but different thermal responses were observed among traits. Our study reveals that nitrogen, a local driver, modulates kelp responses to high seawater temperatures, ameliorating the negative impacts on physiological performance (i.e. growth and photosynthesis). However, this effect might be species-specific and vary among biogeographic regions - thus, further work is needed to determine the generality of our findings to other key temperate macroalgae that are experiencing temperatures close to their thermal tolerance due to climate change.

Adjustments in fatty acid composition is a mechanism that can explain resilience to marine heatwaves and future ocean conditions in the habitat-forming seaweed Phyllospora comosa (Labillardière) C.Agardh.

Marine heatwaves are extreme events that can have profound and lasting impacts on marine species. Field observations have shown seaweeds to be highly susceptible to marine heatwaves, but the physiological drivers of this susceptibility are poorly understood. Furthermore, the effects of marine heatwaves in conjunction with ocean warming and acidification are yet to be investigated. To address this knowledge gap, we conducted a laboratory culture experiment in which we tested the growth and physiological responses of Phyllospora comosa juveniles from the southern extent of its range (43-31°S) to marine heatwaves, ocean warming and acidification. We used a 'collapsed factorial design' in which marine heatwaves were superimposed on current (today's pH and temperature) and future (pH and temperature projected by 2100) ocean conditions. Responses were tested both during the heatwaves, and after a 7-day recovery period. Heatwaves reduced net photosynthetic rates in both current and future conditions, while respiration rates were elevated under heatwaves in the current conditions only. Following the recovery period, there was little evidence of heatwaves having lasting negative effects on growth, photosynthesis or respiration. Exposure to heatwaves, future ocean conditions or both caused an increase in the degree of saturation of fatty acids. This adjustment may have counteracted negative effects of elevated temperatures by decreasing membrane fluidity, which increases at higher temperatures. Furthermore, P. comosa appeared to down-regulate the energetically expensive carbon dioxide concentrating mechanism in the future conditions with a reduction in δ13 C values detected in these treatments. Any saved energy arising from this down-regulation was not invested in growth and was likely invested in the adjustment of fatty acid composition. This adjustment is a mechanism by which P. comosa and other seaweeds may tolerate the negative effects of ocean warming and marine heatwaves through benefits arising from ocean acidification.

Trends in tuna carbon isotopes suggest global changes in pelagic phytoplankton communities.

Considerable uncertainty remains over how increasing atmospheric CO2 and anthropogenic climate changes are affecting open-ocean marine ecosystems from phytoplankton to top predators. Biological time series data are thus urgently needed for the world's oceans. Here, we use the carbon stable isotope composition of tuna to provide a first insight into the existence of global trends in complex ecosystem dynamics and changes in the oceanic carbon cycle. From 2000 to 2015, considerable declines in δ13 C values of 0.8‰-2.5‰ were observed across three tuna species sampled globally, with more substantial changes in the Pacific Ocean compared to the Atlantic and Indian Oceans. Tuna recorded not only the Suess effect, that is, fossil fuel-derived and isotopically light carbon being incorporated into marine ecosystems, but also recorded profound changes at the base of marine food webs. We suggest a global shift in phytoplankton community structure, for example, a reduction in 13 C-rich phytoplankton such as diatoms, and/or a change in phytoplankton physiology during this period, although this does not rule out other concomitant changes at higher levels in the food webs. Our study establishes tuna δ13 C values as a candidate essential ocean variable to assess complex ecosystem responses to climate change at regional to global scales and over decadal timescales. Finally, this time series will be invaluable in calibrating and validating global earth system models to project changes in marine biota.

Responses of macroalgae to CO2 enrichment cannot be inferred solely from their inorganic carbon uptake strategy.

Increased plant biomass is observed in terrestrial systems due to rising levels of atmospheric CO2, but responses of marine macroalgae to CO2 enrichment are unclear. The 200% increase in CO2 by 2100 is predicted to enhance the productivity of fleshy macroalgae that acquire inorganic carbon solely as CO2 (non-carbon dioxide-concentrating mechanism [CCM] species-i.e., species without a carbon dioxide-concentrating mechanism), whereas those that additionally uptake bicarbonate (CCM species) are predicted to respond neutrally or positively depending on their affinity for bicarbonate. Previous studies, however, show that fleshy macroalgae exhibit a broad variety of responses to CO2 enrichment and the underlying mechanisms are largely unknown. This physiological study compared the responses of a CCM species (Lomentaria australis) with a non-CCM species (Craspedocarpus ramentaceus) to CO2 enrichment with regards to growth, net photosynthesis, and biochemistry. Contrary to expectations, there was no enrichment effect for the non-CCM species, whereas the CCM species had a twofold greater growth rate, likely driven by a downregulation of the energetically costly CCM(s). This saved energy was invested into new growth rather than storage lipids and fatty acids. In addition, we conducted a comprehensive literature synthesis to examine the extent to which the growth and photosynthetic responses of fleshy macroalgae to elevated CO2 are related to their carbon acquisition strategies. Findings highlight that the responses of macroalgae to CO2 enrichment cannot be inferred solely from their carbon uptake strategy, and targeted physiological experiments on a wider range of species are needed to better predict responses of macroalgae to future oceanic change.

Monitoring sublethal changes in fish physiology following exposure to a light, unweathered crude oil.

Biomarkers are frequently used to determine the exposure of fish to petroleum hydrocarbons following an oil spill. These biomarkers must be chosen carefully if they are to be used to determine sublethal toxic impacts as well as oil exposure. Many commonly used biomarkers relate to the metabolism of high molecular weight, typically pyrogenic, polycyclic aromatic hydrocarbons (PAHs), which are not abundant in unweathered crude oil. The goal of this study was to compare the efficacy of different biomarkers, including histological examination and transcriptomic profiling, in showing exposure to oil and the potential for sublethal toxic impacts. To achieve these goals, subadults/adults of the spotted dragonet (Repomucenus calcaratus) were exposed to a representative light, unweathered Australian oil for 96 h, so that the physiological changes that occur with exposure could be documented. Fish were then transferred to clean sediment for 90 h to quantify recovery. Biomarker changes, including PAH metabolites, 7-ethoxyresorufin O-deethylase (EROD), and histopathology, are presented in this work. In addition, a de novo transcriptome for the spotted dragonet was assembled, and differential transcript abundance was determined for the gill and liver of petroleum-exposed fish relative to a control. Increased levels of some biliary phenanthrene metabolites were seen throughout the exposure period. EROD levels showed modest, but not significant, increases. Transcriptomic differences were noted in the abundances of transcripts with a role in inflammation, primary metabolism and cardiac function. The patterns of transcript abundance in the gill and the liver changed in a manner that reflected exposure and recovery. The histology showed elevated prevalence of lesions, most notably vacuolization in liver and heart tissue, multi-organ necrosis, and lamellar epithelial lifting and telangiectasia in the gill. These findings suggest that short-term exposures to low molecular weight PAHs could elicit changes in the health of fish that are well predicted by the transcriptome. Furthermore, when light oil is released into the environment, exposure and subsequent risk would be better estimated using phenanthrene metabolite levels rather than EROD. This study also adds to the weight of evidence that exposure to low molecular weight PAHs may cause cardiac problems in fish. Further study is needed to determine the impact of these changes on reproductive capacity, long-term survival, and other population specific parameters.

Transcriptomic, lipid, and histological profiles suggest changes in health in fish from a pesticide hot spot.

Barramundi (Lates calcarifer) were collected at the beginning (1st sampling) and end (2nd sampling) of the wet season from Sandy Creek, an agriculturally impacted catchment in the Mackay Whitsundays region of the Great Barrier Reef catchment area, and from Repulse Creek, located approximately 100 km north in Conway National Park, to assess the impacts of pesticide exposure. Gill and liver histology, lipid class composition in muscle, and the hepatic transcriptome were examined. The first sample of Repulse Creek fish showed little tissue damage and low transcript levels of xenobiotic metabolism enzymes. Sandy Creek fish showed altered transcriptomic patterns, including those that regulate lipid metabolism, xenobiotic metabolism, and immune response; gross histological alterations including lipidosis; and differences in some lipid classes. The second sampling of Repulse Creek fish showed similar alterations in hepatic transcriptome and tissue structure as fish from Sandy Creek. These changes may indicate a decrease in health of pesticide exposed fish.

Photo-induced toxicity following exposure to crude oil and ultraviolet radiation in 2 Australian fishes.

Some polycyclic aromatic hydrocarbons (PAHs), components of crude oil, are known to cause increased toxicity when organisms are co-exposed with ultraviolet radiation, resulting in photo-induced toxicity. The photodynamic characteristics of some PAHs are of particular concern to places like Australia with high ultraviolet radiation levels. The objective of the present study was to characterize the photo-induced toxicity of an Australian North West Shelf oil to early life stage yellowtail kingfish (Seriola lalandi) and black bream (Acanthopagrus butcheri). The fish were exposed to high-energy water accommodated fractions for 24 to 36 h. During the exposure, the fish were either co-exposed to full-intensity or filtered natural sunlight and then transferred to clean water. At 48 h, survival, cardiac effects, and spinal deformities were assessed. Yellowtail kingfish embryos co-exposed to oil and full-spectrum sunlight exhibited decreased hatching success and a higher incidence of cardiac arrhythmias, compared with filtered sunlight. A significant increase in the incidence of pericardial edema occurred in black bream embryos co-exposed to full-spectrum sunlight. These results highlight the need for more studies investigating the effects of PAHs and photo-induced toxicity under environmental conditions relevant to Australia. Environ Toxicol Chem 2018;37:1359-1366. © 2018 SETAC.

Growth, ammonium metabolism, and photosynthetic properties of Ulva australis (Chlorophyta) under decreasing pH and ammonium enrichment.

The responses of macroalgae to ocean acidification could be altered by availability of macronutrients, such as ammonium (NH4+). This study determined how the opportunistic macroalga, Ulva australis responded to simultaneous changes in decreasing pH and NH4+ enrichment. This was investigated in a week-long growth experiment across a range of predicted future pHs with ambient and enriched NH4+ treatments followed by measurements of relative growth rates (RGR), NH4+ uptake rates and pools, total chlorophyll, and tissue carbon and nitrogen content. Rapid light curves (RLCs) were used to measure the maximum relative electron transport rate (rETRmax) and maximum quantum yield of photosystem II (PSII) photochemistry (Fv/Fm). Photosynthetic capacity was derived from the RLCs and included the efficiency of light harvesting (α), slope of photoinhibition (ß), and the light saturation point (Ek). The results showed that NH4+ enrichment did not modify the effects of pH on RGRs, NH4+ uptake rates and pools, total chlorophyll, rETRmax, α, ß, Fv/Fm, tissue C and N, and the C:N ratio. However, Ek was differentially affected by pH under different NH4+ treatments. Ek increased with decreasing pH in the ambient NH4+ treatment, but not in the enriched NH4+ treatment. NH4+ enrichment increased RGRs, NH4+ pools, total chlorophyll, rETRmax, α, ß, Fv/Fm, and tissue N, and decreased NH4+ uptake rates and the C:N ratio. Decreased pH increased total chlorophyll content, rETRmax, Fv/Fm, and tissue N content, and decreased the C:N ratio. Therefore, the results indicate that U. australis growth is increased with NH4+ enrichment and not with decreasing pH. While decreasing pH influenced the carbon and nitrogen metabolisms of U. australis, it did not result in changes in growth.

Inorganic carbon physiology underpins macroalgal responses to elevated CO2.

Beneficial effects of CO2 on photosynthetic organisms will be a key driver of ecosystem change under ocean acidification. Predicting the responses of macroalgal species to ocean acidification is complex, but we demonstrate that the response of assemblages to elevated CO2 are correlated with inorganic carbon physiology. We assessed abundance patterns and a proxy for CO2:HCO3- use (δ13C values) of macroalgae along a gradient of CO2 at a volcanic seep, and examined how shifts in species abundance at other Mediterranean seeps are related to macroalgal inorganic carbon physiology. Five macroalgal species capable of using both HCO3- and CO2 had greater CO2 use as concentrations increased. These species (and one unable to use HCO3-) increased in abundance with elevated CO2 whereas obligate calcifying species, and non-calcareous macroalgae whose CO2 use did not increase consistently with concentration, declined in abundance. Physiological groupings provide a mechanistic understanding that will aid us in determining which species will benefit from ocean acidification and why.

Ocean acidification reverses the positive effects of seawater pH fluctuations on growth and photosynthesis of the habitat-forming kelp, Ecklonia radiata.

Ocean acidification (OA) is the reduction in seawater pH due to the absorption of human-released CO2 by the world's oceans. The average surface oceanic pH is predicted to decline by 0.4 units by 2100. However, kelp metabolically modifies seawater pH via photosynthesis and respiration in some temperate coastal systems, resulting in daily pH fluctuations of up to ±0.45 units. It is unknown how these fluctuations in pH influence the growth and physiology of the kelp, or how this might change with OA. In laboratory experiments that mimicked the most extreme pH fluctuations measured within beds of the canopy-forming kelp Ecklonia radiata in Tasmania, the growth and photosynthetic rates of juvenile E. radiata were greater under fluctuating pH (8.4 in the day, 7.8 at night) than in static pH treatments (8.4, 8.1, 7.8). However, pH fluctuations had no effect on growth rates and a negative effect on photosynthesis when the mean pH of each treatment was reduced by 0.3 units. Currently, pH fluctuations have a positive effect on E. radiata but this effect could be reversed in the future under OA, which is likely to impact the future ecological dynamics and productivity of habitats dominated by E. radiata.

High prevalence of diffusive uptake of CO2 by macroalgae in a temperate subtidal ecosystem.

Productivity of most macroalgae is not currently considered limited by dissolved inorganic carbon (DIC), as the majority of species have CO2-concentrating mechanisms (CCM) allowing the active uptake of DIC. The alternative, diffusive uptake of CO2 (non-CCM), is considered rare (0-9% of all macroalgal cover in a given ecosystem), and identifying species without CCMs is important in understanding factors controlling inorganic carbon use by eukaryotic algae. CCM activity has higher energetic requirements than diffusive CO2 uptake, therefore when light is low, CCM activity is reduced in favour of diffusive CO2 uptake. We hypothesized that the proportional cover of macroalgae without CCMs (red and green macroalgae) would be low (<10%) across four sites in Tasmania, southern Australia at two depths (4-5 and 12-14 m); the proportion of species lacking CCMs would increase with decreasing depth; the δ(13)C values of macroalgae with CCMs would be more depleted with depth. We found the proportion of non-CCM species ranged from 0 to 90% and included species from all three macroalgal phyla: 81% of red (59 species), 14% of brown (three species) and 29% of green macroalgae (two species). The proportion of non-CCM species increased with depth at three of four sites. 35% of species tested had significantly depleted δ(13)C values at deeper depths. Non-CCM macroalgae are more abundant in some temperate reefs than previously thought. If ocean acidification benefits non-CCM species, the ramifications for subtidal macroalgal assemblages could be larger than previously considered.

Effects of estuarine sediment hypoxia on nitrogen fluxes and ammonia oxidizer gene transcription.

The effects of sediment hypoxia, resulting from increased carbon loads or decreased dissolved oxygen (DO), on nitrogen cycling in estuarine environments is poorly understood. The important role played by bacterial and archaeal ammonia oxidizers in the eventual removal of nitrogen from estuarine environments is likely to be strongly affected by hypoxic events. In this study, an analysis of the effects of different levels of sediment hypoxia (5%, 20% and 75% DO) was performed in a microcosm experiment. Changes in the nutrient fluxes related to nitrification at 5% DO were observed after 4 h. Quantification of the key nitrification gene ammonium monooxygenase (amoA) in both DNA and RNA extracts suggests that bacterial amoA transcription was reduced at both of the lower DO concentrations, while changes in DO had no significant effect on archaeal amoA transcription. There was no change in the diversity of expressed archaeal amoA, but significant change in bacterial amoA transcriptional diversity, indicative of low- and high-DO phylotypes. This study suggests that groups of ammonia oxidizers demonstrate differential responses to changes in sediment DO, which may be a significant factor in niche partitioning of different ammonia oxidizer groups.

Archaeal ammonia oxidizers and nirS-type denitrifiers dominate sediment nitrifying and denitrifying populations in a subtropical macrotidal estuary.

Nitrification and denitrification are key steps in nitrogen (N) cycling. The coupling of these processes, which affects the flow of N in ecosystems, requires close interaction of nitrifying and denitrifying microorganisms, both spatially and temporally. The diversity, temporal and spatial variations in the microbial communities affecting these processes was examined, in relation to N cycling, across 12 sites in the Fitzroy river estuary, which is a turbid subtropical estuary in central Queensland. The estuary is a major source of nutrients discharged to the Great Barrier Reef near-shore zone. Measurement of nitrogen fluxes showed an active denitrifying community during all sampling months. Archaeal ammonia monooxygenase (amoA of AOA, functional marker for nitrification) was significantly more abundant than Betaproteobacterial (beta-AOB) amoA. Nitrite reductase genes, functional markers for denitrification, were dominated by nirS and not nirK types at all sites during the year. AOA communities were dominated by the soil/sediment cluster of Crenarchaeota, with sequences found in estuarine sediment, marine and terrestrial environments, whereas nirS sequences were significantly more diverse (where operational taxonomic units were defined at both the threshold of 5% and 15% sequence similarity) and were closely related to sequences originating from estuarine sediments. Terminal-restriction fragment length polymorphism (T-RFLP) analysis revealed that AOA population compositions varied spatially along the estuary, whereas nirS populations changed temporally. Statistical analysis of individual T-RF dominance suggested that salinity and C:N were associated with the community succession of AOA, whereas the nirS-type denitrifier communities were related to salinity and chlorophyll-alpha in the Fitzroy river estuary.

Investigation of evaporation and biodegradation of fuel spills in Antarctica. I. A chemical approach using GC-FID.

Little effort has been devoted to differentiating between hydrocarbon losses through evaporation and biodegradation in treatability studies of fuel-contaminated Antarctic soils. When natural attenuation is being considered as a treatment option, it is important to be able to identify the mechanism of hydrocarbon loss and demonstrate that rates of degradation are sufficient to prevent off-site migration. Similarly, where complex thermally enhanced bioremediation schemes involve nutrient addition, water management, air stripping and active heating, it is important to appreciate the relative roles of these mechanisms for cost minimisation. Following the loss of hydrocarbons by documenting changes in total petroleum hydrocarbons offers little insight into the relative contribution of evaporation and biodegradation. We present a methodology here that allows identification and quantification of evaporative losses of diesel range organics at a range of temperatures using successively less volatile compounds as fractionation markers. We also present data that supports the general utility of so-called biodegradation indices for tracking biodegradation progress. We are also able to show that at 4 degrees C indigenous Antarctic soil bacteria degrade Special Antarctic Blend fuel components in the following order: naphthalene and methyl-napthalenes, light n-alkanes, then progressively heavier n-alkanes; whereas isoprenoids and the unresolved complex mixture are relatively recalcitrant.

Effects of temperature on mineralisation of petroleum in contaminated Antarctic terrestrial sediments.

Although petroleum contamination has been identified at many Antarctic research stations, and is recognized as posing a significant threat to the Antarctic environment, full-scale in situ remediation has not yet been used in Antarctica. This is partly because it has been assumed that temperatures are too low for effective biodegradation. To test this, the effects of temperature on the hydrocarbon mineralisation rate in Antarctic terrestrial sediments were quantified. 14C-labelled octadecane was added to nutrient amended microcosms that were incubated over a range of temperatures between -2 and 42 degrees C. We found a positive correlation between temperature and mineralisation rate, with the fastest rates occurring in samples incubated at the highest temperatures. At temperatures below or near the freezing point of water there was a virtual absence of mineralisation. High temperatures (37 and 42 degrees C) and the temperatures just above the freezing point of water (4 degrees C) showed an initial mineralisation lag period, then a sharp increase in the mineralisation rate before a protracted plateau phase. Mineralisation at temperatures between 10 and 28 degrees C had no initial lag phase. The high rate of mineralisation at 37 and 42 degrees C was surprising, as most continental Antarctic microorganisms described thus far have an optimal temperature for growth of between 20 and 30 degrees C and a maximal growth temperature <37 degrees C. The main implications for bioremediation in Antarctica from this study are that a high-temperature treatment would yield the most rapid biodegradation of the contaminant. However, in situ biodegradation using nutrients and other amendments is still possible at soil temperatures that occur naturally in summer at the Antarctic site we studies (Casey Station 66 degrees 17(') S, 110 degrees 32(') E), although treatment times could be excessively long.