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Freshwater plastic pollution is critically understudied in Southeast Asia (SEA). Recent modelling studies indicate that SEA rivers contribute vast quantities of plastic to the world’s oceans, however, these fail to capture the complexity of individual systems. We determine the volume of mismanaged plastic waste (MPW) entering Tonle Sap Basin (TSB)—the largest freshwater lake–river system in SEA, between 2000 and 2030. Using economic, population and waste data at provincial and national levels, coupled with high resolution population and flood datasets, we estimate that ca . 221,700 tons of plastic entered between 2000 and 2020, and 282,300 ± 8700 tons will enter between 2021 and 2030. We demonstrate that policy interventions can reduce MPW up to 76% between 2021 and 2030. The most-stringent scenario would prevent 99% of annual MPW losses by 2030, despite substantially higher waste volumes and population. If successfully implemented, Cambodia will prevent significant losses in natural capital, material value and degradation in TSB worth at least US$4.8 billion, with additional benefits for the Mekong River and South China Sea.

Recent studies have reported on the widespread abundance of atmospheric microplastics (At-MPs) and atmospheric anthropogenic microfibres (At-AMFs) in urban and remote locations. This study sought to test whether there were differences in the quantity of deposited At-AMFs collected when comparing three different surface sampler areas (small: 0.0113 m 2 (Φ = 120 mm), medium: 0.0254 m 2 (Φ = 180 mm) and large: 0.0346 m 2 (Φ = 210 mm)). The analysis revealed no statistically significant variation in the number of At-AMFs recorded, when data was presented in At-AMFs per m 2 day −1 . However, our findings indicate that for any given individual sampling event, the amount of deposition can range by ∼ 150 to 200 At-AMFs m 2 d −1 even if samplers are kept relatively close together. To account for this, we would recommend that future studies collect data in duplicate or triplicate. Our results suggest that data can be compared across different sites and geographical regions—at least if comparing the overall mean and standard deviation of all samples collected. These findings are important because currently there is no standard sampler size for passive collection of At-AMFs and At-MPs.

Plastic pollution is a growing problem around the world, with Southeast Asia being an epicentre for plastic waste emissions into the environment, and for the associated local and regional repercussions that this brings. This thesis presents published research on the topic from Cambodia and Singapore. First, a modelling study estimated the plastic waste generation and inputs into Tonle Sap, Cambodia, between 2000 and 2020, and projected estimates for 2021 to 2030. This work also discusses various scenarios, showcasing potential outcomes on plastic waste inputs if reductions are implemented, and the impacts if no action is taken. Second, a technique was developed for the processing atmospheric microplastic samples that significantly improves the data generated by Fourier Transform Infrared (FT-IR) spectroscopy, which is commonly used in the analysis of atmospheric microplastics. Third, data were collected from samplers with varying surface areas, during the monitoring of deposited atmospheric microplastics in Singapore. This paper examined whether the data generated can be compared interchangeably when converted to particles per m2 day-1 . Fourth, based on the findings from atmospheric sampling in Singapore and Phnom Penh, a systematic literature review was carried out which examined the general proportion of anthropogenic cellulosic and synthetic (plastic) microfibres found in the atmosphere. Overall, my research improves scientific knowledge related to a modest part of the large, and multi-faceted plastic pollution challenge in Southeast Asia. My work mainly contributes to the field by improving methods for compositional analyses, and interpretation of atmospheric microplastics. Such techniques deliver more robust sampling and data analyses, which allow for comparable studies across different locations.

The challenge of consistent identification of internal structure in galaxies - in particular disc galaxy components like spiral arms, bars, and bulges - has hindered our ability to study the physical impact of such structure across large samples. In this paper we present Galaxy Zoo: 3D (GZ: 3D) a crowdsourcing project built on the Zooniverse platform which we used to create spatial pixel (spaxel) maps that identify galaxy centres, foreground stars, galactic bars and spiral arms for 29831 galaxies which were potential targets of the MaNGA survey (Mapping Nearby Galaxies at Apache Point Observatory, part of the fourth phase of the Sloan Digital Sky Surveys or SDSS-IV), including nearly all of the 10,010 galaxies ultimately observed. Our crowd-sourced visual identification of asymmetric, internal structures provides valuable insight on the evolutionary role of non-axisymmetric processes that is otherwise lost when MaNGA data cubes are azimuthally averaged. We present the publicly available GZ:3D catalog alongside validation tests and example use cases. These data may in the future provide a useful training set for automated identification of spiral arm features. As an illustration, we use the spiral masks in a sample of 825 galaxies to measure the enhancement of star formation spatially linked to spiral arms, which we measure to be a factor of three over the background disc, and how this enhancement increases with radius.