River diversions may cause microplastics to remain longer on land and in streams before reaching oceans

Date:
June 5, 2023
Source:
University of Birmingham
Summary:
Diverting streams and rivers to irrigate crops or provide drinking
water may significantly extend the time microplastics spend in river
catchments before they flow into our oceans, a new study reveals.


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FULL STORY ========================================================================== Diverting streams and rivers to irrigate crops or provide drinking water
may significantly extend the time microplastics spend in river catchments before they flow into our oceans, a new study reveals.

Publishing their findings in Water Research, an international group of scientists led by the University of Birmingham, highlight the impact of
water management in terms of river diversions for irrigation purposes
on microplastic transport.

These diversions can have significant impact on the estimates of the pollutant's flow towards our oceans, with the diverted water from rivers dispersing the tiny plastic particles across farmland from where they
may be flushed back into other watercourses or neighbouring catchments.

The research team studied two paired rivers in Colorado, United States --
the Boulder Creek and its less urbanised tributary South Boulder Creek
- - evaluating the effects of urbanisation and flow diversions on the
up-to- downstream profiles of local microplastic concentrations as well
as microplastic loads, indicating the flow-weighted downstream transport
of particles.

The researchers found that microplastic concentration patterns in both
rivers were related to the degree of catchment urbanisation: Data from
both streams suggests a link between microplastic concentration and urbanisation, as microplastic concentrations in Boulder Creek with a
more urbanised catchment were higher in both surface water and sediment
than in South Boulder Creek, and microplastic concentration increased
in downstream direction when passing more urbanised areas.

Lead author Anna Kukkola, from the University of Birmingham, commented:
"We discovered strong links between the degree of urbanisation in
the river catchment and observed river microplastic concentrations, highlighting how human activities resulted in immediate increase in microplastics in this mountainous catchment.

"A key novelty of this study is the application of the loading approach
which is used here for the first time for the quantification of
microplastics fluxes and enabled us to not only identify microplastic
sources but also determine the downstream evolution of microplastic
transport patterns and in this case also the diversion of microplastics
out of the river catchment." Co-author Rob Runkel, from the United
States Geological Survey, added: "These results for microplastics are consistent with our results for other urban- derived elements such as
chloride, where we are seeing 3 to 9 times more loading in the more
urbanized Boulder Creek watershed." The international team furthermore discovered that the magnitude of flow diversions from both streams
resulted in large quantities of microplastic being removed from each
stream and being transported out of their actual catchment.

They measured microplastic removal through flow diversions of over 500 microplastic particles per second (or 1,800,00 per hour) from the two
rivers studied.

To put this into perspective: In 2012, 241 km3 of water were diverted
for agricultural purposes in North America alone with 2,670 km3 having
been diverted globally. By using conservative estimates based on the >63
mym particle threshold of their study, the researchers estimated that
this could result in around 41 trillion microplastic particles being redistributed out of river networks into the terrestrial environment in
North America every year, with as many as 459 trillion particles being redistributed globally.

Co-author and Principal Investigator Professor Stefan Krause, from the University of Birmingham, commented: "How we manage our streams and rivers
can have a substantial impact on the transport of microplastics, yet
these effects have not been incorporated into global models that assume downstream convergence of microplastic fluxes along river networks. Our
current models may, therefore, underestimate the quantities and residence
times of plastics held in river catchments and overestimate the speed with which microplastics are transported into our oceans." While toxicity assessment was not a focus of the current study, co-author Professor
Iseult Lynch from the University of Birmingham noted: "The results of
this study are highly relevant for estimating ecotoxicological impacts
on aquatic and terrestrial environments and ecosystems, with enhanced terrestrial residence times resulting in extended (chronic) exposures."
* RELATED_TOPICS
o Earth_&_Climate
# Water # Floods # Geography # Atmosphere #
Ecosystems # Drought_Research # Environmental_Policy #
Environmental_Issues
* RELATED_TERMS
o River o Estuary o Levee o Rain o Ocean_current o
Water_pollution o Water_scarcity o Glacier

========================================================================== Story Source: Materials provided by University_of_Birmingham. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Anna Kukkola, Robert L. Runkel, Uwe Schneidewind, Sheila F. Murphy,
Liam
Kelleher, Gregory H. Sambrook Smith, Holly Astrid Nel, Iseult
Lynch, Stefan Krause. Prevailing impacts of river management
on microplastic transport in contrasting US streams: Rethinking
global microplastic flux estimations. Water Research, 2023; 240:
120112 DOI: 10.1016/ j.watres.2023.120112 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/06/230605181333.htm

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