Assessment of microplastic pollution hotspots in urban river systems and their effects on aquatic biota using citizen-science sampling and remote sensing.

Project Abstract

Microplastic pollution in urban river systems poses significant threats to aquatic biota and ecosystem services, yet spatially explicit understanding of hotspot locations and biotic impacts remains incomplete. This study integrates citizen-science sampling with remote sensing to map microplastic distribution, characterize pollution sources, and evaluate ecological responses across a gradient of urbanization. A mixed-methods framework was employed across three metropolitan river networks, combining in situ microplastic quantification, polymer identification, and size distribution analysis with high-resolution satellite imagery and GIS-based land-use metrics. Citizen-science participants were trained to collect surface and subsurface samples, record environmental conditions, and document potential pollution events, enabling dense spatial coverage that complements traditional sampling. Laboratory analyses used Fourier-transform infrared spectroscopy (FTIR) to identify polymer types and estimate degradation states, while microplastics were categorized by size (?1 mm, 1–5 mm) and morphology (fibers, fragments, beads). To link pollution patterns with ecological effects, we conducted biodiversity assessments on benthic invertebrate communities and applied standardized toxicity assays in situ for key taxa, complemented by metabolomic and physiological indicators in sentinel fish species. Remote sensing data (sentinel-2 and Landsat 8) were processed to extract land-use features, impervious surface area, proximity to wastewater infrastructure, and stormwater outfalls, enabling the development of a spatiotemporal hotspot model. Statistical analyses included generalized additive models to relate microplastic abundance to urban exposure metrics, geostatistical kriging for interpolation, and structural equation modeling to disentangle direct and indirect pathways of impact on biotic endpoints. Key findings reveal pronounced hotspot clusters downstream of wastewater treatment facilities, informal drainage channels, and densely paved corridors, with polymer composition indicating a predominance of polyethylene and polypropylene from consumer-waste streams. Temporal analyses show seasonal peaks corresponding to rainfall-runoff events, highlighting the role of hydrological regimes in mobilizing microplastics. Positive correlations emerged between microplastic load and reductions in macroinvertebrate diversity, shifts in functional feeding groups, and signs of energy allocation stress in sentinel fish, including altered hepatosomatic indices and differential expression of stress-related genes. The citizen-science component demonstrated high data quality and engagement, enabling robust spatial extrapolation of contamination patterns with strong agreement to laboratory results. The integrated approach provides actionable insights for urban watershed management, including targeted source control interventions, the design of green-blue infrastructure to intercept debris, and the calibration of wastewater-treatment and stormwater management strategies to mitigate downstream transport. Uncertainty analyses identified sampling bias associated with volunteer distribution and detection limits for smaller microplastics, which were mitigated through calibration exercises and method sensitivity testing. Overall, the study advances understanding of how urban structure and hydrology shape microplastic distributions and their cascading effects on aquatic biota, offering a scalable framework for monitoring and policy development in rapidly urbanizing river systems.

Project Overview

What This Project Is About

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A simple study that looks at tiny plastic pieces in city rivers and how they affect plants and animals living there. It uses easy citizen-science methods (non-scientists helping collect data) and basic remote sensing (satellite pictures) to map where microplastics are concentrated and what organisms are affected.

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The Problem It Addresses

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Urban rivers often carry plastic waste that breaks into microplastics. These tiny particles can be eaten by aquatic life and may travel through the food chain. There is a need for accessible ways to measure hotspots and link them to harm in wildlife and ecosystem health.

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Objectives of the Project

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1. Identify where microplastic hotspots occur in an urban river system.
2. Assess effects of microplastics on common aquatic species (e.g., invertebrates and small fish).
3. Use citizen-science methods to collect samples and observations.
4. Combine field data with satellite imagery to map pollution patterns.
5. Provide recommendations for reducing plastic inputs to the river.

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What You Will Do Step by Step

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1) Learn basic sampling techniques with guidance. 2) Collect water, sediment, and biota observations along the river. 3) Record sightings or signs of microplastics using simple protocols. 4) Use satellite images to identify land-use patterns near hotspots. 5) Analyze data to find correlations between plastic presence and wildlife impacts. 6) Prepare a clear report with maps and simple explanations for the public.

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Expected Outcome

A clear map of microplastic hotspots in an urban river, basic evidence of effects on local wildlife, and practical steps for reducing plastic inputs. The project should yield publishable class results and an accessible summary for non-experts.