Quantifying Sources, Sinks and Mitigation of Macroplastic and Other River Debris: A Trash Balance Model

Abstract Mismanaged consumer plastics and other waste that enters a river system, known as riverine debris, is a pervasive problem in urban rivers with consequences for ecosystem health and human livelihood. A better understanding of the loading pathways, fluxes, and fate of this debris is necessary...

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Main Authors: Todd Palmer, Trent Biggs, Ryoko Araki, Kian Bagheri, Hassan Davani, Rachel Downing, Sarah Hutmacher, Hilary K. McMillan
Format: Article
Language:English
Published: Wiley 2025-03-01
Series:Earth's Future
Subjects:
Online Access:https://doi.org/10.1029/2024EF005677
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author Todd Palmer
Trent Biggs
Ryoko Araki
Kian Bagheri
Hassan Davani
Rachel Downing
Sarah Hutmacher
Hilary K. McMillan
author_facet Todd Palmer
Trent Biggs
Ryoko Araki
Kian Bagheri
Hassan Davani
Rachel Downing
Sarah Hutmacher
Hilary K. McMillan
author_sort Todd Palmer
collection DOAJ
description Abstract Mismanaged consumer plastics and other waste that enters a river system, known as riverine debris, is a pervasive problem in urban rivers with consequences for ecosystem health and human livelihood. A better understanding of the loading pathways, fluxes, and fate of this debris is necessary for more effective mitigation efforts, and to reduce ocean emissions that become marine debris. This study presents a novel framework for quantifying riverine debris using a holistic mass balance modeling approach, applied in the San Diego River, California, a regionally important river with a large, urban watershed. This framework quantifies urban riverine debris sources, sinks and transport dynamics at the watershed scale. The model integrates a community science data set of floodplain debris with a simple stormwater runoff model to account for debris loading and applies probabilistic transport functions to estimate ocean emissions. Our key finding is that most riverine debris in the San Diego River is not washed in through storm drains but is directly deposited in the floodplain (79%–92% of total debris), with homeless encampments the largest contributing factor (62%–75% of total debris). Ongoing cleanup efforts substantially reduce the debris accumulation rate: without these efforts, debris stored on the floodplain increases by up to 48%. However, despite cleanups debris continues to accumulate over time with the potential for increased ocean emissions in subsequent years, especially during years with large flood events. Our approach is transferable to other urban rivers to understand the fate and flux of local debris, and therefore to inform effective mitigation initiatives.
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spelling doaj-art-3159d4cc9c74481e9c6ca0210e403a3b2025-08-20T03:17:57ZengWileyEarth's Future2328-42772025-03-01133n/an/a10.1029/2024EF005677Quantifying Sources, Sinks and Mitigation of Macroplastic and Other River Debris: A Trash Balance ModelTodd Palmer0Trent Biggs1Ryoko Araki2Kian Bagheri3Hassan Davani4Rachel Downing5Sarah Hutmacher6Hilary K. McMillan7San Diego State University Department of Geography San Diego CA USASan Diego State University Department of Geography San Diego CA USASan Diego State University Department of Geography San Diego CA USASan Diego State University Department of Civil, Construction, and Environmental Engineering San Diego CA USASan Diego State University Department of Civil, Construction, and Environmental Engineering San Diego CA USASan Diego River Park Foundation San Diego CA USASan Diego River Park Foundation San Diego CA USASan Diego State University Department of Geography San Diego CA USAAbstract Mismanaged consumer plastics and other waste that enters a river system, known as riverine debris, is a pervasive problem in urban rivers with consequences for ecosystem health and human livelihood. A better understanding of the loading pathways, fluxes, and fate of this debris is necessary for more effective mitigation efforts, and to reduce ocean emissions that become marine debris. This study presents a novel framework for quantifying riverine debris using a holistic mass balance modeling approach, applied in the San Diego River, California, a regionally important river with a large, urban watershed. This framework quantifies urban riverine debris sources, sinks and transport dynamics at the watershed scale. The model integrates a community science data set of floodplain debris with a simple stormwater runoff model to account for debris loading and applies probabilistic transport functions to estimate ocean emissions. Our key finding is that most riverine debris in the San Diego River is not washed in through storm drains but is directly deposited in the floodplain (79%–92% of total debris), with homeless encampments the largest contributing factor (62%–75% of total debris). Ongoing cleanup efforts substantially reduce the debris accumulation rate: without these efforts, debris stored on the floodplain increases by up to 48%. However, despite cleanups debris continues to accumulate over time with the potential for increased ocean emissions in subsequent years, especially during years with large flood events. Our approach is transferable to other urban rivers to understand the fate and flux of local debris, and therefore to inform effective mitigation initiatives.https://doi.org/10.1029/2024EF005677riverine debrismass balancecommunity sciencemacroplasticriverSan Diego
spellingShingle Todd Palmer
Trent Biggs
Ryoko Araki
Kian Bagheri
Hassan Davani
Rachel Downing
Sarah Hutmacher
Hilary K. McMillan
Quantifying Sources, Sinks and Mitigation of Macroplastic and Other River Debris: A Trash Balance Model
Earth's Future
riverine debris
mass balance
community science
macroplastic
river
San Diego
title Quantifying Sources, Sinks and Mitigation of Macroplastic and Other River Debris: A Trash Balance Model
title_full Quantifying Sources, Sinks and Mitigation of Macroplastic and Other River Debris: A Trash Balance Model
title_fullStr Quantifying Sources, Sinks and Mitigation of Macroplastic and Other River Debris: A Trash Balance Model
title_full_unstemmed Quantifying Sources, Sinks and Mitigation of Macroplastic and Other River Debris: A Trash Balance Model
title_short Quantifying Sources, Sinks and Mitigation of Macroplastic and Other River Debris: A Trash Balance Model
title_sort quantifying sources sinks and mitigation of macroplastic and other river debris a trash balance model
topic riverine debris
mass balance
community science
macroplastic
river
San Diego
url https://doi.org/10.1029/2024EF005677
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