Claire Streten

Saltwater intrusion history shapes the response of bacterial communities upon rehydration

Saltwater intrusion (SWI) can result in the loss of dominant vegetation from freshwater habitats. In northern Australia, sea level is predicted to rise 17-50 cm by 2030-2070. This will exacerbate the impact of SWI, threatening Ramsar-listed habitats. Soil bacteria in these habitats play a significant role in biogeochemical cycling, regulating availability of essential nutrients such as nitrogen to vegetation. However, there is limited understanding as to how SWI will impact these soil bacteria. Floodplain soil samples were collected from the South Alligator River floodplain in Northern Australia from sites with contrasting histories of SWI. A SWI event was simulated over 7 days with treatments of saltwater and freshwater. Bacterial community composition before and after treatment were measured using next generation sequencing of bacterial DNA. Sites with no history of SWI showed no significant changes in community taxonomic composition following treatments, suggesting the community at these sites have broad functional capacity which may be due to their historic conditioning over many years. Sites with a history of SWI showed a significant response to both treatments. Following saltwater treatment, there was an increase in sulfate-reducing bacteria, which are known to have an impact on carbon and nitrogen cycling. We suggest that the impact of SWI causes a shift in the soil bacteria which alters the community to one which is more specialised, with implications for the cycling of essential elements and nutrients.

Aluminium, gallium, and molybdenum toxicity to the tropical marine microalga Isochrysis galbana

There is a shortage of established chronic toxicity test methods for assessing the toxicity of contaminants to tropical marine organisms. The authors tested the suitability of the tropical microalga Isochrysis galbana for use in routine ecotoxicology and assessed the effects of 72-h exposures to copper (Cu, a reference toxicant), aluminium (Al), gallium (Ga), and molybdenum (Mo), key metals of alumina refinery discharge, on the growth of I. galbana at 3 temperatures: 24u2009°C, 28 °C, and 31u2009°C. The sensitivity of both I. galbana and the test method was validated by the response to Cu exposure, with 10% and 50% effect concentrations (EC10 and EC50) of 2.5 μg/L and 18 μg/L, respectively. The EC10 and EC50 values for total Al at 28u2009°C were 640 μg/L and 3045 μg/L, respectively. The toxicity of both Cu and Al at 24u2009°C and 31u2009°C was similar to that at 28u2009°C. There was no measurable toxicity from dissolved Ga exposures of up to 6000 μg/L or exposures to dissolved Mo of up to 9500 μg/L. Solubility limits at 28 °C for the dissolved fractions (<10 kDa) of Al, Ga, and Mo were approximately 650 μg/L Al, >7000 μg/L Ga, and >6000 μg/L Mo. In test solutions containing >650 μg/L total Al, dissolved and precipitated forms of Al were present, with precipitated Al becoming more dominant as total Al increased. The test method proved suitable for routine ecotoxicology, with I. galbana showing sensitivity to Cu but Al, Ga, and Mo exhibiting little to no toxicity to this species.

A novel bioassay using the barnacle Amphibalanus amphitrite to evaluate chronic effects of aluminium, gallium and molybdenum in tropical marine receiving environments

A need exists for appropriate tools to evaluate risk and monitor potential effects of contaminants in tropical marine environments, as currently impact assessments are conducted by non-representative approaches. Here, a novel bioassay is presented that allows for the estimation of the chronic toxicity of contaminants in receiving tropical marine environments. The bioassay is conducted using planktonic larvae of the barnacle Amphibalanus amphitrite and is targeted at generating environmentally relevant, chronic toxicity data for water quality guideline derivation or compliance testing. The developmental endpoint demonstrated a consistently high control performance, validated through the use of copper as a reference toxicant. In addition, the biological effects of aluminium, gallium and molybdenum were assessed. The endpoint expressed high sensitivity to copper and moderate sensitivity to aluminium, whereas gallium and molybdenum exhibited no discernible effects, even at high concentrations, providing valuable information on the toxicity of these elements in tropical marine waters.

A chronic toxicity test for the tropical marine snail Nassarius dorsatus to assess the toxicity of copper, aluminium, gallium, and molybdenum

Chronic toxicity test methods for assessing the toxicity of contaminants to tropical marine organisms are generally lacking. A 96-h chronic growth rate toxicity test was developed for the larval stage of the tropical dogwhelk, Nassarius dorsatus. Growth rates of N. dorsatus larvae were assessed following exposures to copper (Cu), aluminium (Al), gallium (Ga), and molybdenum (Mo). Exposure to Cu at 28u2009°C validated the sensitivity of the test method, with 10% (EC10) and 50% (EC50) effect concentrations of 4.2u2009μg/L and 7.3u2009μg/L Cu, respectively. The EC10 and EC50 values for Al (<0.45-μm filtered fraction) at 28u2009°C were 115u2009μg/L and 185u2009μg/L, respectively. The toxicity of Cu and Al was also assessed at 24u2009°C and 31u2009°C, representing average year-round water temperatures for subtropical and tropical Australian coastal environments. At 24u2009°C, the growth rate of control larvae was reduced by 52% compared with the growth rate at 28u2009°C and there was an increase in sensitivity to Cu (EC50u2009=u20094.7u2009μg/L) but a similar sensitivity to Al (EC50u2009=u2009180u2009μg/L). At 31u2009°C the control growth rate increased by 35% from that measured at 28u2009°C and there was reduced sensitivity to both Cu and Al (EC50su2009=u20098.5u2009μg/L and 642u2009μg/L, respectively). There was minimal toxicity resulting from Ga (EC50u2009=u20094560u2009μg/L) and Mo (no effect at ≤7000u2009μg/L Mo). Environ Toxicol Chem 2016;35:1788-1795.

A protocol for identifying suitable biomarkers to assess fish health: A systematic review

Background Biomarkers have been used extensively to provide the connection between external levels of contaminant exposure, internal levels of tissue contamination, and early adverse effects in organisms. Objectives To present a three-step protocol for identifying suitable biomarkers to assess fish health in coastal and marine ecosystems, using Gladstone Harbour (Australia) as a case study. Methods Prior to applying our protocol, clear working definitions for biomarkers were developed to ensure consistency with the global literature on fish health assessment. First, contaminants of concern were identified based on the presence of point and diffuse sources of pollution and available monitoring data for the ecosystem of interest. Second, suitable fish species were identified using fisheries dependent and independent data, and prioritised based on potential pathways of exposure to the contaminants of concern. Finally, a systematic and critical literature review was conducted on the use of biomarkers to assess the health of fish exposed to the contaminants of concern. Results/Discussion We present clear working definitions for bioaccumulation markers, biomarkers of exposure, biomarkers of effect and biomarkers of susceptibility. Based on emission and concentration information, seven metals were identified as contaminants of concern for Gladstone Harbour. Twenty out of 232 fish species were abundant enough to be potentially suitable for biomarker studies; five of these were prioritised based on potential pathways of exposure and susceptibility to metals. The literature search on biomarkers yielded 5,035 articles, of which 151met the inclusion criteria. Based on our review, the most suitable biomarkers include bioaccumulation markers, biomarkers of exposure (CYP1A, EROD, SOD, LPOX, HSP, MT, DNA strand breaks, micronuclei, apoptosis), and biomarkers of effect (histopathology, TAG:ST). Conclusion Our protocol outlines a clear pathway to identify suitable biomarkers to assess fish health in coastal and marine ecosystems, which can be applied to biomarker studies in aquatic ecosystems around the world.

Assessing the chronic toxicity of copper and aluminium to the tropical sea anemone Exaiptasia pallida

The worlds most productive bauxite mines and alumina refineries are located in tropical or sub-tropical regions. The discharge water from alumina refineries can contain elevated aluminium (Al, <0.45µm fraction), from 30 to 1000μg/L. There is a need for additional information on the toxicity of Al to aquatic organisms to improve the environmental regulation and management of alumina refinery operations in tropical coastal regions. A 14-d chronic toxicity test was developed for the tropical sea anemone Exaiptasia pallida. Asexual reproduction and growth rates of E. pallida were assessed using the number of lacerates produced and oral disc diameter. The comparative sensitivity of E. pallida was assessed through exposure to a commonly-used reference toxicant, copper (Cu) at 28°C, with asexual reproduction toxicity estimates of 10% (EC10) and 50% (EC50) effect concentrations, calculated as 8.8µg/L (95% confidence limits (CL): 1-18µg/L) and 35µg/L Cu (95% CL: 30-39µg/L), respectively. Growth rate was a suitable additional endpoint (EC50=35µg/L Cu, 95% CL: 23-49µg/L). The EC10 and EC50 for Al (total fraction, based on reproduction) at 28°C were 817µg/L (95% CL: 440-1480µg/L) and 2270µg/L (95% CL: 1600-3900µg/L), respectively. The toxicity of Cu and Al was also assessed at 24°C and 31°C, representing average year-round water temperatures for sub-tropical and tropical Australian coastal environments. Changing the temperature from 28°C to 24°C or 31°C resulted in up to 45% less reproduction of anemones and increased their sensitivity to Cu (EC50s at 24°C=21µg/L, 95% CL: 17-26µg/L and at 31°C=23µg/L, 95% CL: 21-25µg/L). Sensitivity to Al was reduced at 24°C with an EC50 of 8870µg/L (95% CL: 6200-NC). An EC50 for Al at 31°C could not be calculated. This test is a reliable and sensitive addition to the suite of standardised tests currently developed for tropical marine species.

Bacteria in tropical floodplain soils are sensitive to changes in saltwater

Bacterial communities in floodplain and wetland soils cycle elements essential for flora and fauna. The coastal habitats of northern Australia are threatened with increasing saltwater intrusion (SWI) events that will destroy freshwater habitats. The effect of the impending SWI on bacterial communities is unknown. Here, we examined the bacterial communities of a tropical river floodplain located in World Heritage Kakadu National Park. Using 16S rRNA gene pyrosequencing, we measured the baseline bacterial communities from three morphologically distinct regions of the floodplain (lower, upper and backwater swamp), within three zones of the South Alligator River (upstream, cuspate and estuarine funnel or sinuous). Significant differences in the bacterial community were observed at each category of floodplain morphology and river zone. The greatest differences were due to pH and salinity. Large changes in bacterial compositions are predicted to occur with increases in salinity and pH. Saltwater intrusion is predicted to increase substantially in the next decades with sea-level rise, and is likely to cause large and significant changes to the bacterial community with unknown consequences for biogeochemical cycling. Kakadu National Park may benefit from incorporating bacteria into routine studies, because we have shown here that they are sensitive indicators of change, even across small ranges of abiotic variables.

Sea-level rise in northern Australia’s Kakadu National Park: a survey of floodplain eukaryotes

Forecasted climate-change models predict that much of northern Australia’s coastal habitats will be in retreat because of saltwater intrusion (SWI) from sea-level rise. A region of primary concern is the nutrient-rich and biodiverse floodplains of world heritage-listed Kakadu National Park (KNP). To understand the implications of SWI, we need fundamental baseline information for floodplain biota from the South Alligator River, KNP, northern Australia, and informative data on how increased and prolonged exposure to salt is likely to shape the eukaryotic community. To assist in addressing these key knowledge gaps, we used amplicon sequencing to examine the composition of eukaryotic soil communities from the South Alligator River floodplain, an ecologically important area at the ‘coalface’ of sea-level rise. Samples were obtained from three river zones and three floodplain morphologies, capturing a wide range of habitats and episodic exposures to both saltwater and freshwater. We found that both the floodplain morphology and positioning along the river significantly influenced eukaryotic composition. However, the influence of these variables varied greatly among the floodplain morphologies, with correlative evidence suggesting that both salinity and pH played a dominant role in shaping communities within lower parts of the floodplain, with this being particularly evident in those regions subjected to major tidal influence (estuarine funnel and sinuous, and cuspate).

Water quality guideline values for aluminium, gallium and molybdenum in marine environments

Revised water quality guideline values (WQGVs) are presented for the metals aluminium (Al), gallium (Ga) and molybdenum (Mo) in receiving marine environments. These elements are commonly found in elevated concentrations in alumina refinery waste streams, yet current WQGVs fail to accurately assess the environmental risk. Here, chronic biological effects data we have generated over the course of several years were combined with toxicity data from the open literature to construct species sensitivity distributions (SSDs) which enabled the computation of revised WQGVs for Al, Ga and Mo in marine environments. These procedures are in accordance with internationally recommended derivation procedures, and newly computed WQGVs may be incorporated in regulatory frameworks aimed at sustainable exploitation of environmental resources and ongoing protection of the marine estate. Where the available datasets allowed such distinction, separate SSDs were constructed for temperate and tropical environments and zone-specific WQGVs derived. Extrapolated from the SSDs, WQGVs of 56xa0μg Al L−1, 800xa0μgxa0Gaxa0L−1 and 3.88xa0mg Mo L−1 (in the 0.45-μm filtered fraction) for 95% species protection were recommended for implementation in both temperate and tropical receiving environments. Currently, there is insufficient validation to separate the tropical from the temperate data and in most cases, application of the generic WQGVs is recommended.

Assessing chronic toxicity of aluminium, gallium and molybdenum in tropical marine waters using a novel bioassay for larvae of the hermit crab Coenobita variabilis

A novel bioassay is presented that allows for the estimation of the chronic toxicity of contaminants in receiving tropical marine environments. Relevant procedures to identify contaminants of concern and evaluate hazards associated with contamination in these environments have long remained inadequate. The 6-day bioassay is conducted using freshly hatched planktonic larvae of the hermit crab Coenobita variabilis and is targeted at generating environmentally relevant, chronic toxicity data. The developmental endpoint demonstrated consistently high control performance and was validated through the use of copper as a reference toxicant. In addition, the biological effects of aluminium, gallium and molybdenum were assessed. The endpoint expressed high sensitivity to copper (EC10 =u202f24u202fµgu202fL-1) and moderate sensitivity to aluminium (EC10 =u202f312u202fµgu202fL-1), whereas gallium and molybdenum elicited no obvious effects, even at high concentrations (EC10 >u202f6000u202fµgu202fL-1), providing valuable information on the toxicity of these elements in tropical marine waters for derivation of water quality guidelines or testing of compliance limits.