51 research outputs found
Using hydrodynamic models to understand the impacts and risks of plastic pollution
No full textAnthropogenic marine debris, mainly of plastic origin, is accumulating in estuarine and coastal environments around the world, causing damage to multiple species of fauna and flora, as well as habitats. Plastics have the potential to accumulate in food webs, and cause economic losses to tourism and sea-going industries, like commercial fishing. The production and use of plastic products is growing, from 230 million tonnes produced globally in 2005 to 320 million tonnes in 2015, a 40% increase in production over 10 years. If we are to manage the increasing input and threat, we must understand where plastic pollution is accumulating in the environment and what the impacts to organisms in these areas are.
The goal of this thesis was to explore the dispersal and risks of plastic pollution in the coastal environment, at a scale that is useful to local management authorities. I used four research aims to achieve this goal. The aim of the first data chapter (Chapter 2) was to prioritise research that would improve modelling outputs in the future. In the second data chapter (Chapter 3), the aim was to locate the areas of highest exposure to plastic pollution for three vulnerable habitats. In the third data chapter (Chapter 4), I aimed to explore the dominant sources and processes of plastic accumulation. Lastly, in the final data chapter (Chapter 5), I aimed to understand the sublethal consequence of plastic exposure on a tropic reef fish.
The first data chapter of my thesis presents an advection-diffusion model that includes beaching, settling, resuspension/re-floating, degradation and topographic effects on the wind in nearshore waters to quantify the relative importance of these physical processes in governing plastic debris accumulation. I found that the source location has by far the largest effect on the accumulation location of the debris. The diffusivity, used to parameterise the sub-grid scale movements, and the relationship between debris resuspension/re-floating from beaches and the presence of a wind shadow created by high islands also has a dramatic impact on the modelled accumulation areas. The rate of degradation of macroplastics into microplastics also had a large influence in the prediction of debris dispersal and accumulation. These findings may help prioritise research on the physical processes that affect plastic accumulation, leading to more accurate modelling, and subsequently an improved empirical basis for management in the future.
In the second data chapter, I used the model described in Chapter 2 to predict the potential exposure of vulnerable habitats and species to plastic pollution using a spatial risk assessment approach. The effect of plastics on the marine environment is well documented, however the physical location of these interactions are largely unknown. I assessed the potential exposure of mangroves, coral reefs and marine turtles to plastics during the two main wind conditions of the region; the trade winds and monsoon wind seasons. By creating relative exposure categories based on the density of particles in modelling outputs of nil, low, medium and high exposure. I found that in the trade wind season (April to September, dominated by strong south-easterly winds) marine turtles, mangroves and reef habitats had lower exposure than during the monsoon wind season (October to March, dominated by lighter and more variable winds). A small proportion of coral reef habitat was in the high exposure categories, whereas the turtle home-range had a large area in high exposure categories (16% and 26% exposed to high microplastics during monsoon season, respectively). Unlike the other two case studies, the mangrove habitat had consistent hotspots of high exposure across both wind seasons. The outputs of this chapter can inform local scale management action, for example turtle management and recovery plans. The method presented here can also be transferred to other species and habitats and scaled up for larger jurisdictions.
In the third data chapter, I built on Chapter 2 (a sensitivity analysis of physical/modelled processes) by using field data for macro- and microplastics to interrogate the model. The aim was to find the likely sources of plastics to the Whitsunday region and understand the limitations for the model in a complex coastline and at a management-relevant scale. I found that, for microplastics, offshore sources are likely to be more important than onshore, and for macroplastics, local (onshore) sources are more important than they are for microplastics. Of the physical characteristics I examined, I found none that make a site more or less predictable in the modelling. Field data on sources at local scales is necessary, although, this is recognised as a difficult task.
In the last data chapter, I assessed the consequence of plastic exposure by quantifying the effect of microplastic exposure on juveniles of a widespread and abundant planktivorous fish (Acanthochromis polyacanthus). Under five different plastic concentrations, with plastics the same size as the natural food particles (mean 2 mm diameter), consumption of microplastic was low and there was no significant effect of plastic exposure on fish growth, body condition or behaviour. However, the number of plastics found in the gut of the fish vastly increased when plastic particle size was reduced to approximately one quarter the size of the normal food particles, with a maximum of 2102 small (< 300 μm diameter) particles present in the gut of individual fish after a 1-week plastic exposure period. Under conditions where food was replaced by plastic, there was a negative effect on the growth and body condition of the fish. These results suggest plastics could become more of a problem as they breakup into smaller size classes, and that environmental changes that lead to a decrease in plankton concentrations likely have a greater influence on fish populations than microplastic presence alone.
The risks of plastic pollution to environmental features remain largely unquantified. However, my thesis demonstrates significant gains in understanding of mechanisms that can be used to determine where plastics are likely to accumulate, and identifies priorities for future research to improve the statistical power of the models. For example, by understanding the resuspension of plastic in areas without wind driven waves. This thesis also highlights the need to understand different types of plastics separately, microplastics have different consequences to macroplastics, different areas of accumulation and different sources, therefore the risks and appropriate management actions are very different
Recollections of a fire insurance man, including his experience in U.S. Navy (Mississippi squadron) during the Civil War,
No full textMode of access: Internet
Effects of microplastic exposure on the body condition and behaviour of planktivorous reef fish (<i>Acanthochromis polyacanthus</i>)
No full textThe effect of a pollutant on the base of the food web can have knock-on effects for trophic structure and ecosystem functioning. In this study we assess the effect of microplastic exposure on juveniles of a planktivorous fish (Acanthochromis polyacanthus), a species that is widespread and abundant on Indo-Pacific coral reefs. Under five different plastic concentration treatments, with plastics the same size as the natural food particles (mean 2mm diameter), there was no significant effect of plastic exposure on fish growth, body condition or behaviour. The amount of plastics found in the gastro-intestinal (GI) tract was low, with a range of one to eight particles remaining in the gut of individual fish at the end of a 6-week plastic-exposure period, suggesting that these fish are able to detect and avoid ingesting microplastics in this size range. However, in a second experiment the number of plastics in the GI tract vastly increased when plastic particle size was reduced to approximately one quarter the size of the food particles, with a maximum of 2102 small (</div
Modelling accumulation of marine plastics in the coastal zone; what are the dominant physical processes?
No full textAnthropogenic marine debris, mainly of plastic origin, is accumulating in estuarine and coastal environments around the world causing damage to fauna, flora and habitats. Plastics also have the potential to accumulate in the food web, as well as causing economic losses to tourism and sea-going industries. If we are to manage this increasing threat, we must first understand where debris is accumulating and why these locations are different to others that do not accumulate large amounts of marine debris. This paper demonstrates an advection-diffusion model that includes beaching, settling, resuspension/re-floating, degradation and topographic effects on the wind in nearshore waters to quantify the relative importance of these physical processes governing plastic debris accumulation. The aim of this paper is to prioritise research that will improve modelling outputs in the future. We have found that the physical characteristic of the source location has by far the largest effect on the fate of the debris. The diffusivity, used to parameterise the sub-grid scale movements, and the relationship between debris resuspension/re-floating from beaches and the wind shadow created by high islands also has a dramatic impact on the modelling results. The rate of degradation of macroplastics into microplastics also have a large influence in the result of the modelling. The other processes presented (settling, wind drift velocity) also help determine the fate of debris, but to a lesser degree. These findings may help prioritise research on physical processes that affect plastic accumulation, leading to more accurate modelling, and subsequently management in the future
Effects of microplastic exposure on the body condition and behaviour of planktivorous reef fish (Acanthochromis polyacanthus)
No full textEffects of microplastic exposure on the body condition and behaviour of planktivorous reef fish (Acanthochromis polyacanthus
Fish growth and body condition during the acute phase of the plastic exposure experiment.
No full textTop panels (A-C) show the change in mass (g) relative to start mass during the acute exposure phase, for each clutch. The lower panels (D-F) show the change in length-weight relationship relative to the start of the acute exposure, for each clutch. The mid-line of the boxes represent means with the boxes showing the 25th and 75th percentile and the vertical lines representing the range.</p
Experimental design for acute and chronic plastic exposure experiment.
No full textConcentrations shown are the mean concentrations for each treatment, as treatment dosage was dependent on tank biomass.</p
Fish behaviour during exposure to different concentrations of microplastics.
No full textThe top panels (A-C) show the number of lines crossed per second for each treatment and clutch. The mid-line of the boxes represent means with the boxes showing the 25th and 75th percentile and the vertical lines representing the range. The lower panels (D-F) show the aggression index where the central horizontal line shows the mean and the vertical line indicates the range of values.</p
Particle and fish size dependence of plastic ingestion.
No full textA) Shows the proportion of fish that were found to have plastics in their digestive tract. B) Shows the range of plastic ingestion for fish per treatment, the mid-line of the boxes represent means with the boxes showing the 25th and 75th percentile and the vertical lines representing the range.</p
Correction: Effects of microplastic exposure on the body condition and behaviour of planktivorous reef fish (Acanthochromis polyacanthus)
No full textCorrection: Effects of microplastic exposure on the body condition and behaviour of planktivorous reef fish (Acanthochromis polyacanthus
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