Plastic pollution in Moreton Bay sediments, Southeast Queensland, Australia.

The mounting issue of plastic waste in the aquatic ecosystem is a growing source of concern. Most plastic waste originates on land and a significant proportion of this eventually finds its way into the marine environment, which is widely regarded as a major repository for plastic debris. Currently, there exists a substantial gap in our understanding of how much plastic, the main polymer types, and the distribution of plastic in the marine environment. This study aimed to provide information on mass concentrations of a range of plastics in the surface sediments in the semi-enclosed Moreton Bay, just offshore the large city of Brisbane, Southeast Queensland, Australia. Surface sediment samples were quantitatively analysed for a suite of 7 common plastic polymer types (i.e., polystyrene (PS), polycarbonate (PC), poly-(methyl methacrylate) (PMMA), polypropylene (PP), polyethylene terephthalate (PET), polyethylene (PE) and polyvinyl chloride (PVC)) using a pressurized liquid extraction (PLE) followed by double-shot microfurnace pyrolysis coupled to gas chromatography mass spectrometry (Pyr-GC/MS). The advantage of this approach is that it can measure plastics below the limit of visual detection. The study revealed that Σ7plastics were consistently present in the samples, although the concentrations displayed a wide range of concentrations from 3.3 to 2194.2 µg/g across different sites. Among the polymers analysed, PE and PVC were found at the highest concentrations, ranging from 2.3 to 1885.9 µg/g and 3.0-979.5 µg/g, respectively. Based on the average concentrations of plastics measured, the dry bulk density and volume of sediments within the top 10 cm of the bay, it was estimated that there is a minimum of 7000 t of plastics stored in the surface sediments of the bay. This study is the first to report the mass concentrations of identified plastics and identify the main polymer types in Moreton Bay. This is important information to develop management plans to reduce the plastic waste entering the coastal marine environment.

Nitrogen loading resulting from major floods and sediment resuspension to a large coastal embayment.

Major floods pose a severe threat to coastal receiving environments, negatively impacting environmental health and ecosystem services through direct smothering with sediment and nutrient loading. This study examined the short and long-term impacts of the February 2022 major flood event on mud extent and sediment nitrogen flux in Moreton Bay (the Bay), a large, sub-tropical embayment in Southeast Queensland, Australia. Short-term impacts were assessed three days after the flood peak by sampling surface water at 47 sites in the direction of the predominant circulation pattern. Longer-term impacts were assessed by undertaking an intensive sediment survey of 223 sites and a nutrient flux experiment using sediment core incubations to simulate calm and resuspension conditions for the four key sediment classes. Short-term impacts revealed elevated turbidity levels extended across the Bay but were highest at the Brisbane River mouth, ammonium concentrations varied inversely with surface turbidity, whereas nitrate concentrates closely tracked surface turbidity. The sediment survey confirmed fine sediment deposition across 98 % of the Bay. Porewater within the upper 10 cm contained a standing pool of 280 t of ammonium, with concentrations more than three orders of magnitude higher than overlying surface waters. The nutrient flux experiment revealed an order of magnitude higher sediment ammonium flux rate in the sandy mud sediment class compared to the other sediment classes; and for simulated resuspension conditions compared to calm conditions for sand, muddy sand, and mud sediment classes. Scaling across the whole Bay, we estimated a mean annual sediment flux of 17,700 t/year ammonium, with a range of 13,500 to 21,900 t/year. Delivery of fine sediments by major floods over the last 50 years now impact >98 % of the benthic zone and provide a major loading pathway of available nitrogen to surface waters of Moreton Bay; representing a significant threat to ecosystem health.

Datasets for turbulence characterization collected with AD2CPs in potential tidal energy sites in Australia.

Sites with great potential for electricity generation from tidal stream energy are often characterized by high levels of turbulence and severe wave climates. These characteristics are known to substantially increase turbine blade loadings fluctuations, which may lead to premature device failure and blade fatigue. In order to be commercially competitive, tidal energy devices must function in turbulent environments for approximately 25 years without requiring major maintenance operations. Hence, knowledge of turbulence parameters prior to device deployment is crucial to avoid unnecessary costs with overengineering and maintenance. Aiming to support the development of tidal energy in Australia, the Tidal Energy in Australia (AUSTEn) Project identified two sites with potential for tidal energy: Banks Strait, Tasmania and Clarence Strait, Northern Territory. The datasets presented here reveal high-frequency current velocity measurements taken throughout the water column with Nortek Signature new generation Acoustic Doppler Current Profilers (AD2CPs) at one measurement station in Banks Strait and two in Clarence Strait. Measurement periods are between 2 and 3 months, which are significantly long deployment periods for turbulence characterization in tidal energy sites compared to other datasets available in the literature. Processing steps include the removal of bad quality data points using the manufacturer's software Ocean Contour, considering low correlation, side lobe interference and high amplitude spikes. These data have been used by Perez et al.(2021) to calculate turbulent kinetic energy (TKE), turbulence intensity (TI), Reynolds stresses, integral length scales, TKE dissipation and production rates as well as to discuss wave-turbulence interaction and the application of decomposition methods. In the dataset collected in Banks Strait, velocity fluctuation enhancements caused by wave orbital velocities were mitigated using the Synchrosqueezing Wavelet Transform (SWT) decomposition method. Turbulence estimates were organized by month and are revealed in the post-processed data files. Here we provide raw, processed and post-processed data files, which were made publicly available through the University of Queensland UQ eSpace repository. These datasets may be reused to further advance the understanding of turbulence and its impacts on tidal turbine performance as well as to help establish international guidelines for turbulence measurements in tidal energy site assessments.

Event loading drives distribution of the organochlorine pesticide metabolite DDE in a sub-tropical river system, Brisbane River, Australia.

Past catchment practices can contribute to environmental impacts for decades following their cessation. We examine the distribution of the prevalent organochlorine pesticide, dichlorodiphenyltrichloroethane (DDT) and its metabolites (DDE, DDD) in the sediments of a sub-tropical river system (Brisbane River, Australia). This study aimed to identify sources of DDT, DDE, DDD into the lower reaches of the Brisbane River. Annual sediment sampling of the lower Brisbane River over a period of 15 years (2001-2015) revealed a significant increase in sediment DDT, DDE and DDD content following major floods. A regional survey detected elevated sediment DDT, DDE and DDD content at 32 of 79 sites sampled; however, these were generally below guideline trigger values. DDE was the sole fraction at all but one site with creek systems dominated by intensive cropping practices identified as legacy sources and major flood events as a driver of elevated sediment DDE content in the lower reaches.

Water quality challenges associated with industrial logging of a karst landscape: Guadalcanal, Solomon Islands.

Human disturbance of karst landscapes in tropical volcanic islands present a unique challenge for understanding sediment transport to the coastal zone. Here we present the first evidence of urban drinking water quality impacts from industrial logging in the Solomon Islands. Despite only 6% of the Honiara's drinking water catchment being disturbed by logging, rhodamine dye tracers demonstrated complex karst sinkholes that led to high suspended sediment concentrations being transported from neighbouring Kovi catchment into the Kongulai water supply offtake point for Honiara. This has resulted in the exceedance of practical treatment thresholds of 20 NTU 9.5% of the time, leading to water supply for the majority of Honiara's residents being unavailable for 58 days in 2019. This work highlights the cost-benefit disparity between industrial logging yielding minimal short-term economic yields in comparison to on-going broader impacts of increased coastal sediment transport while restricting water supply to a developing nation's capital.

Assessing the potential of unmanned aerial vehicle spraying of aqueous ozone as an outdoor disinfectant for SARS-CoV-2.

The COVID-19 pandemic has revealed gaps in our understanding of safe, effective and efficient means of disinfecting high use public spaces. Whilst this creates an opportunity for development and application of innovative approaches such as unmanned aerial vehicle (UAV) based disinfection, unregulated outdoor disinfection using chlorine has led to environmental and public health risks. This study has quantified the efficiency, safety and efficacy of UAV-based spraying of aqueous ozone. Optimised UAV flight characteristics of 4.7 km/h at 1.7 m elevation spraying 2.4 L/min were able to provide >97% and >92% coverage of a 1 m and 2 m wide swath respectively. During spraying operations using 1 mg/L aqueous ozone, atmospheric concentrations of ozone remained within background levels (<0.04 ppm). Highly efficient inactivation of two different isolates of SARS-CoV-2 virus was achieved at aqueous ozone concentrations of 0.75 mg/L after an incubation period of only 5 min, with 0.375 mg/L achieving 82-91.5% inactivation in this time. Exposure of diamondback moth larvae and parasitic wasps to 1 mg/L aqueous ozone did not significantly affect their survivorship. These results indicate for the first time that aqueous ozone may provide the required balance between human and environmental safety and viral inactivation efficacy for targeted application in high risk outdoor settings.

Sediment arsenic hotspots in an abandoned tailings storage facility, Gold Ridge Mine, Solomon Islands.

Gold mining of arsenopyrite ore bodies result in waste tailings that contain elevated levels of arsenic. Disposal of these wastes in a Tailings Storage Facility (TSF) represents a substantial environmental risk if not properly managed. The Gold Ridge mine on Guadalcanal, in the Solomon Islands was abandoned from 2014 to 2018, leaving the TSF with little ongoing environmental management. Surface water quality monitoring observed a threefold increase in surface water arsenic concentrations over a 6-month period when no mining operations were occurring. This study aimed to investigate bottom sediments as the source of elevated concentrations of arsenic in the surface waters of the TSF during mine closure. This was achieved by analysing arsenic concentrations in the surface water, sediment porewaters and by quantifying sediment arsenic flux as dissolved oxygen availability declined. It was evident that bottom sediments of the TSF were the potential source of arsenic, having an average arsenic concentration of 437.9 mg kg-1. In addition, average sediment porewater arsenic concentrations across the TSF were 1.07 mg L-1, with a large central zone of highly elevated concentrations peaking at over 17 mg L-1. Long term sediment core incubations demonstrated arsenic effluxes from all sites monitored under both oxic and hypoxic conditions, ranging from 0.72 mg m-2 day-1 to 7.01 mg m-2 day-1 respectively. These results suggest that arsenic hotspots within the TSF have the capability to contribute to increased arsenic concentrations in surface waters. Management of mine TSF's should consider these geochemical interactions that can occur in abandoned sites.

Importance of sediment organic matter to methane ebullition in a sub-tropical freshwater reservoir.

This paper summarises the results of an extensive field campaign which demonstrates that high sediment organic matter is the primary driver of methane ebullition in a sub-tropical, freshwater reservoir. Methane emissions from freshwater reservoirs represent an important global methane source. Whilst diffusive methane fluxes are commonly used for predicting total emissions, recent studies show that the under-reported ebullitive fluxes can vary by over three orders of magnitude within an individual system and have a greater relative contribution compared to diffusion. Key to predicting this variability in emission rates is to better understand the primary drivers of different emission pathways, and in particular ebullition. Zones of catchment derived organic material as well as elevated water column chlorophyll a concentration have been associated with increased rates of ebullition. Little Nerang Dam (LND), a subtropical freshwater reservoir in Queensland Australia, consistently experiences high rates of ebullition adjacent to major inflow arms that are both deposition zones of catchment organic material as well as areas with elevated water column chlorophyll a concentration. A year-long study of emission rates was undertaken on LND during which water column chlorophyll a concentration, bottom water temperature and sediment organic matter content were assessed for methane ebullition potential. This included a transect with high-spatial sampling (259 sites) from the dam wall to the ebullition zones to explore the relationship between water column chlorophyll a concentration, sediment organic matter content and methane ebullition. These results showed that ebullition was associated with the large forest litter deposits adjacent to major inflow sites where sediment organic matter content was significantly higher compared with the main body of the reservoir.

Environmental change in a modified catchment downstream of a gold mine, Solomon Islands.

Solomon Islands is rapidly developing its natural resource exploitation sector, but data needed to assess consequent environmental impacts are scarce. We assessed catchments surrounding the Gold Ridge gold mine (Guadalcanal, Solomon Islands) and found that extensive changes in river course, and water and sediment quality have occurred downstream of the gold mine since its development. Sediment run-off from exposed areas associated with the mine pit has increased, elevating turbidity (up to 2450 NTU) and metal and arsenic levels, with levels of the latter being up to 0.141 mg/L in surface waters and 265 mg/kg in sediments. An overfull, inoperative tailings storage facility associated with the currently inactive gold mine with fluctuating arsenic levels (up to 0.087 mg/L in the water; 377 mg/kg in the sediment) presents an ongoing threat to the environment. Arsenic, due to its toxicity, appears to be the greatest threat, with sediment and water guideline levels in rivers exceeded 10-fold and exceeded nearly 20-fold in the tailings dam sediments. Despite elevated metal and arsenic content in the area, no toxic inorganic arsenic was found to have bioaccumulated in locally harvested food. In summary, the natural environment surrounding the Gold Ridge mine has been modified substantially and requires an ongoing monitoring program to ensure the ecosystem services of food and water for the local communities continue to be safe. This study informs not only the local area but also provides a microcosm of the broader global challenges facing the regulation of extractive industries in proximity to subsistence communities.

Dramatic increase in mud distribution across a large sub-tropical embayment, Moreton Bay, Australia.

Major flood events can dramatically alter the coastal sediment environment. This study established the current sediment distribution in a large sub-tropical embayment, Moreton Bay, Australia, and examined the effect of three recent floods on modifying this distribution. In 2015, surface sediment samples were collected from 223 sites across the study area and analysed for particle size distribution with the resultant sediment distribution mapped. In addition, sampling of flood waters during two major events in 2011 and 2013 was undertaken and particle size distribution of suspended sediment was determined. Data was compared to the result of an earlier large-scale survey completed in 1970, with three large flood events occurring between the two surveys. The sediment environment has undergone a dramatic change with muddy sediments now covering an estimated area of over 860km2, more the double the area found in 1970. Mud is now the dominant sediment type within Moreton Bay.

Insight into dissolved organic matter fractions in Lake Wivenhoe during and after a major flood.

Dissolved organic matter is an important component of biogeochemical processes in aquatic environments. Dissolved organic matter may consist of a myriad of different fractions and resultant processing pathways. In early January 2011, heavy rainfall occurred across South East Queensland, Australia causing significant catchment inflow into Lake Wivenhoe, which is the largest water supply reservoir for the city of Brisbane, Australia. The horizontal and vertical distributions of dissolved organic matter fractions in the lake during the flood period were investigated and then compared with stratified conditions with no catchment inflows. The results clearly demonstrate a large variation in dissolved organic matter fractions associated with inflow conditions compared with stratified conditions. During inflows, dissolved organic matter concentrations in the reservoir were fivefold lower than during stratified conditions. Within the dissolved organic matter fractions during inflow, the hydrophobic and humic acid fractions were almost half those recorded during the stratified period whilst low molecular weight neutrals were higher during the flood period compared to during the stratified period. Information on dissolved organic matter and the spatial and vertical variations in its constituents' concentrations across the lake can be very useful for catchment and lake management and for selecting appropriate water treatment processes.

Corals persisting in naturally turbid waters adjacent to a pristine catchment in Solomon Islands.

Few water quality measurements exist from pristine environments, with fewer reported studies of coastal water quality from Solomon Islands. Water quality benchmarks for the Solomons have relied on data from other geographic regions, often from quite different higher latitude developed nations, with large land masses. We present the first data of inshore turbidity and sedimentation rate for a pristine catchment on Isabel Island. Surveys recorded relatively high coral cover. The lowest cover was recorded at 22.7% (Jejevo) despite this site having a mean turbidity (continuous monitoring) of 32 NTU. However, a similar site (Jihro) was significantly less turbid (2.1 mean NTU) over the same period. This difference in turbidity is likely due to natural features of the Jihro River promoting sedimentation before reaching coastal sites. We provide an important baseline for Solomon Island inshore systems, whilst demonstrating the importance of continuous monitoring to capture episodic high turbidity events.

Methane and nitrous oxide emissions from a subtropical coastal embayment (Moreton Bay, Australia).

Surface water methane (CH4) and nitrous oxide (N2O) concentrations and fluxes were investigated in two subtropical coastal embayments (Bramble Bay and Deception Bay, which are part of the greater Moreton Bay, Australia). Measurements were done at 23 stations in seven campaigns covering different seasons during 2010-2012. Water-air fluxes were estimated using the Thin Boundary Layer approach with a combination of wind and currents-based models for the estimation of the gas transfer velocities. The two bays were strong sources of both CH4 and N2O with no significant differences in the degree of saturation of both gases between them during all measurement campaigns. Both CH4 and N2O concentrations had strong temporal but minimal spatial variability in both bays. During the seven seasons, CH4 varied between 500% and 4000% saturation while N2O varied between 128 and 255% in the two bays. Average seasonal CH4 fluxes for the two bays varied between 0.5±0.2 and 6.0±1.5 mg CH4/(m2·day) while N2O varied between 0.4±0.1 and 1.6±0.6 mg N2O/(m2·day). Weighted emissions (t CO2-e) were 63%-90% N2O dominated implying that a reduction in N2O inputs and/or nitrogen availability in the bays may significantly reduce the bays' greenhouse gas (GHG) budget. Emissions data for tropical and subtropical systems is still scarce. This work found subtropical bays to be significant aquatic sources of both CH4 and N2O and puts the estimated fluxes into the global context with measurements done from other climatic regions.

Rapid Reactivation of Cyanobacterial Photosynthesis and Migration upon Rehydration of Desiccated Marine Microbial Mats.

Desiccated cyanobacterial mats are the dominant biological feature in the Earth's arid zones. While the response of desiccated cyanobacteria to rehydration is well-documented for terrestrial systems, information about the response in marine systems is lacking. We used high temporal resolution hyperspectral imaging, liquid chromatography, pulse-amplitude fluorometry, oxygen microsensors, and confocal laser microscopy to study this response in a desiccated microbial mat from Exmouth Gulf, Australia. During the initial 15 min after rehydration chlorophyll a concentrations increased 2-5 fold and cyanobacterial photosynthesis was re-established. Although the mechanism behind this rapid increase of chlorophyll a remains unknown, we hypothesize that it involves resynthesis from a precursor stored in desiccated cyanobacteria. The subsequent phase (15 min-48 h) involved migration of the reactivated cyanobacteria toward the mat surface, which led, together with a gradual increase in chlorophyll a, to a further increase in photosynthesis. We conclude that the response involving an increase in chlorophyll a and recovery of photosynthetic activity within minutes after rehydration is common for cyanobacteria from desiccated mats of both terrestrial and marine origin. However, the response of upward migration and its triggering factor appear to be mat-specific and likely linked to other factors.

Assessing the spatial and temporal variability of diffusive methane and nitrous oxide emissions from subtropical freshwater reservoirs.

Surface water-methane (CH4) and nitrous oxide (N2O) concentrations were measured and diffusive fluxes were estimated in three subtropical freshwater reservoirs (Little Nerang Dam (LND), Lake Wivenhoe (LW) and Lake Baroon (LB)) in southeast Queensland, Australia, during four seasons in 2011-2012. All reservoirs were strong sources of CH4 in all seasons. Surface water CH4 varied between 1350 and 524,000% saturation, and was overall highest in spring and summer, and lowest in winter, however, with no clear patterns common to all reservoirs. In contrast, all reservoirs switched from weak N2O sinks in spring to strong N2O sources for the rest of the year. N2O saturation in all reservoirs varied between 70 and 1230%. There were significant differences for CH4 concentrations and fluxes between the reservoirs. Within each reservoir, there was strong spatial CH4 variability but minimal N2O saturation variability. CH4 saturation was higher in inflow zones than in the main body. Area-weighted average fluxes were estimated using six water-air gas transfer velocity estimation models and resulted in fluxes in the range 4.8-20.5, 2.3-5.4, and 2.3-7.5 mg CH4 m(-2) d(-1), while N2O was 0.07-0.41, 0.09-0.22, and 0.03-0.09 mg N2O m(-2) d(-1) for LND, LW, and LB, respectively. Total emissions, in carbon dioxide equivalents, from all measurement campaigns were CH4 dominated (67-86%). The measured degree of CH4 saturation and fluxes are among the highest reported thus far indicating that subtropical freshwater reservoirs could be significant aquatic greenhouse gas sources. This paper provides a comprehensive assessment of the interplay between biogeochemical processes and the physical forcing driving the water-air gaseous emissions. The high variability coupled with the lack of consensus among estimation models calls for concerted efforts to address uncertainty of measurements for reliable emissions accounting.

Baseline arsenic levels in marine and terrestrial resources from a pristine environment: Isabel Island, Solomon Islands.

Baseline records are crucial in understanding how chemicals of concern impact on the receiving environment. We analysed terrestrial and marine resources from a pristine site on Isabel Island, Solomon Islands, to provide environmental baseline levels for total arsenic and arsenic species composition for commonly consumed marine resources. Our data show that levels of the more toxic inorganic arsenic species were very low or below detectable limits, with the exception of the seaweed Sargassum sp. that contained pentavalent inorganic arsenic levels of 4.63 µg g(-1). Total arsenic concentrations in the majority of marine and terrestrial samples collected were below 2 µg g(-1). The less toxic arsenobetaine was the predominant arsenic species present in all marine fauna samples analysed. This work highlights the need for arsenic speciation analysis to accurately assess potential toxicity of marine resources and provides a crucial baseline to assess the impact of future development within this region.

Methane and nitrous oxide emissions from a subtropical estuary (the Brisbane River estuary, Australia).

Methane (CH4) and nitrous oxide (N2O) are two key greenhouse gases. Their global atmospheric budgeting is, however, flout with challenges partly due to lack of adequate field studies determining the source strengths. Knowledge and data limitations exist for subtropical and tropical regions especially in the southern latitudes. Surface water methane and nitrous oxide concentrations were measured in a subtropical estuarine system in the southern latitudes in an extensive field study from 2010 to 2012 and water-air fluxes estimated using models considering the effects of both wind and flow induced turbulence. The estuary was found to be a strong net source of both CH4 and N2O all-year-round. Dissolved N2O concentrations ranged between 9.1 ± 0.4 to 45.3 ± 1.3 nM or 135 to 435% of atmospheric saturation level, while CH4 concentrations varied between 31.1 ± 3.7 to 578.4 ± 58.8 nM or 1210 to 26,430% of atmospheric saturation level. These results compare well with measurements from tropical estuarine systems. There was strong spatial variability with both CH4 and N2O concentrations increasing upstream the estuary. Strong temporal variability was also observed but there were no clear seasonal patterns. The degree of N2O saturation significantly increased with NOx concentrations (r(2)=0.55). The estimated water-air fluxes varied between 0.1 and 3.4 mg N2O m(-2)d(-1) and 0.3 to 27.9 mg CH4 m(-2)d(-1). Total emissions (CO2-e) were N2O (64%) dominated, highlighting the need for reduced nitrogen inputs into the estuary. Choice of the model(s) for estimation of the gas transfer velocity had a big bearing on the estimated total emissions.