ESTUDIOS CON FRACTALES, CAOS Y COMPLEJIDAD EN MÉXICO

My thesis provided data and insights about plastic pollution of a relatively small city, and how this contributes to the more global problem of plastic pollution. Although my data has been collected on a small sections of the Ross River, these collection sites were chosen because they were representative for other sections of the river, especially those adjacent to suburbs. Nonetheless, I cannot exclude that my data underestimates the overall debris loads entering the river and care must be taken when extrapolating my

139

results to other river systems. In addition, it was outside the scope of my thesis to collect samples or plastics from connecting creeks, lakes, or storm drain effluents that expel directly into the marina or onto the beaches. Therefore, additional empirical data is needed to make more robust estimations about the amount of debris items that enter the marine environment. In addition, future research would greatly benefit from freshwater models to determine the likelihood of plastic discharge from the river at various rainfall or water flow levels. This information would be important for managing organisations to understand the potential impact of large scale events, such as the recent flooding event that occurred in February of 2019, where the dam exceeded its capacity and consequently flooded large areas of Townsville’s riverside suburbs.

As shown in this thesis, littering on land is connected by many complex pathways before it ends up in aquatic systems. Therefore, it is important to continue research that investigates these connections and pathways. For example, Chapter 3 explored the connection between litter in parklands and debris collected in the adjacent river. To further investigate how litter arrives into the river system, additional surveys should be conducted along the conduits of the storm drains to identify the types of debris and quantify the accumulation of debris along the pathways. Such information can provide insights that could assist source reduction strategies. Future research should also continue quantifying the plastic loads into river and coastal systems year round, to have a better understanding of the seasonal effects and the impact of large weather events, such as cyclones and flooding, on plastic pollution in aquatic systems.

To reduce the input of plastic into the environment, further research into environmentally friendly use, reduction, and disposal of plastics is essential. This can involve experiments in which different infrastructures are tested in litter hotspots (e.g. cigarette bins near bus stops), or through social surveys to investigate the economic and social constraints around reducing overall plastic use. Furthermore, as mentioned in Chapter 6.4, additional information on the perceptions of marine debris and littering in younger age groups, such as teenagers and young adults could also provide information on an age group that is rarely surveyed in peer reviewed literature.

This thesis provided the first steps into testing possible indicator species to monitor plastic loads on the reef. To determine if my species or others can be used to detect plastic loads on the reef, further research is essential. This includes experimental

140

research focussed on testing different species exposed to various plastic sizes, shapes, and types in addition to field-based research. More specifically, field based research should include organisms collected from the reef, where the plastic loads found within the organism is compared with that found in the sediment and surface waters, similar to experiments performed in Bonanno and Orlando-Bonaca (2018). Identifying indicator species could greatly advance our ability to detect and estimate microplastic abundance in the environment, which would provide the evidence needed to understand the relative impact on the Great Barrier Reef. Hopefully this information could lead to more

efficient and targeted waste management strategies.

To improve future monitoring of microplastics in the environment and biota world-wide, refining the standardisation of the characterisation of plastic size classes, plastic type, and FTIR analysis in future research would help with reporting and comparing microplastic loads within the environment. Therefore, data could be more readily compared to studies that were unable to extract a wide range of microplastic sizes. In addition, there was very little research that provides information on how many particles are needed to scan, and how the data was corrected. Due to this lack of

information, it was difficult to determine the appropriate methods to use and if they can be accurately estimated against other research papers. I suggest that future research should include this information to provide results that can be more readily comparable.

Lastly, the overall implications of my thesis suggests that plastic management can vary greatly on a small, local scale, and is heavily influenced by local urban infrastructure, community attitudes, and local environmental factors. Therefore, the expansion of the research conducted in this thesis to other river systems could greatly contribute to the improvement of our understanding of the sources of microplastic pollution nation-wide. For example, it is likely that other river systems in Australia may have other factors that influence plastic abundances, such as sewage effluents, or occur in industrial areas that use or manufacture pellets. Therefore, further research on these areas could identify sources, and encourage policy and infrastructure, such as the improvement on the filtration systems on household washing machines, or more vigorous regulations on the transportation and production of resin pellets. The expansion of this research could improve our overall understanding on plastic inputs into aquatic and coastal systems.

141