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1. Microplastic in riverine fish is connected to species traits

   https://doi.org/10.1038/s41598-018-29980-9  

   McNeish, R_E; Kim, L_H; Barrett, H_A; Mason, S_A; Kelly, J_J; Hoellein, T_J (August 2018, Scientific Reports)

   Abstract Microplastic is a contaminant of concern worldwide. Rivers are implicated as major pathways of microplastic transport to marine and lake ecosystems, and microplastic ingestion by freshwater biota is a risk associated with microplastic contamination, but there is little research on microplastic ecology within freshwater ecosystems. Microplastic uptake by fish is likely affected by environmental microplastic abundance and aspects of fish ecology, but these relationships have rarely been addressed. We measured the abundance and composition of microplastic in fish and surface waters from 3 major tributaries of Lake Michigan, USA. Microplastic was detected in fish and surface waters from all 3 sites, but there was no correlation between microplastic concentrations in fish and surface waters. Rather, there was a significant effect of functional feeding group on microplastic concentration in fish.Neogobius melanostomus(round goby, a zoobenthivore) had the highest concentration of gut microplastic (19 particles fish⁻¹) compared to 10 other fish taxa measured, and had a positive linear relationship between body size and number of microplastic particles. Surface water microplastic concentrations were lowest in the most northern, forested watershed, and highest in the most southern, agriculturally dominated watershed. Results suggest microplastic pollution is common in river food webs and is connected to species feeding characteristics. Future research should focus on understanding the movement of microplastic from point-source and diffuse sources and into aquatic ecosystems, which will support pollution management efforts on inland waters. 

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2. Distribution and transport of microplastic and fine particulate organic matter in urban streams

   https://doi.org/10.1002/eap.2429  

   Vincent, Anna E. S.; Hoellein, Timothy J. (August 2021, Ecological Applications)

   Abstract Plastic litter is accumulating in ecosystems worldwide. Rivers are a major source of plastic litter to oceans. However, rivers also retain and transform plastic pollution. While methods for calculating particle transport dynamics in rivers are well established, they are infrequently used to quantify the transport and retention of microplastics (i.e., particles < 5 mm) in flowing waters. Measurements of microplastic movement in rivers are needed for a greater understanding of the fate of plastic litter at watershed and global scales, and to inform pollution prevention strategies. Our objectives were to (1) quantify the abundance of microplastics within different river habitats and (2) adapt organic matter “spiraling” metrics to measure microplastic transport concurrent with fine particulate organic matter (FPOM). We quantified microplastic and FPOM abundance across urban river habitats (i.e., surface water, water column, benthos), and calculated downstream particle velocity, index of retention, turnover rate, and spiraling length for both particle types. Microplastic standing stock was assessed using a habitat‐specific approach, and estimates were scaled up to encompass the study reach. Spatial distribution of particles demonstrated that microplastics and FPOM were retained together, likely by hydrodynamic forces that facilitate particle sinking or resuspension. Microplastic particles had a higher downstream particle velocity and lower index of retention relative to FPOM, suggesting that microplastics were retained to a lesser degree than FPOM in the study reaches. Microplastics also showed lower turnover rates and longer spiraling lengths relative to FPOM, attributed to the slow rates of plastic degradation. Thus, rivers are less retentive of microplastics than FPOM, although both particles are retained in similar locations. Because microplastics are resistant to degradation, individual particles can be transported longer distances prior to mineralization than FPOM, making it likely that microplastic particles will encounter larger bodies of water and interact with various aquatic biota in the process. These empirical assessments of particle transport will be valuable for understanding the fate and transformation of microplastic particles in freshwater resources and ultimately contribute to the refinement of global plastic budgets. 

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3. A fish tale: a century of museum specimens reveal increasing microplastic concentrations in freshwater fish

   https://doi.org/10.1002/eap.2320  

   Hou, Loren; McMahan, Caleb D.; McNeish, Rae E.; Munno, Keenan; Rochman, Chelsea M.; Hoellein, Timothy J. (April 2021, Ecological Applications)

   Abstract Plastic is pervasive in modern economies and ecosystems. Freshwater fish ingest microplastics (i.e., particles <5 mm), but no studies have examined historical patterns of their microplastic consumption. Measuring the patterns of microplastic pollution in the past is critical for predicting future trends and for understanding the relationship between plastics in fish and the environment. We measured microplastics in digestive tissues of specimens collected from the years 1900–2017 and preserved in museum collections. We collected new fish specimens in 2018, along with water and sediment samples. We selected four species:Micropterus salmoides(largemouth bass),Notropis stramineus(sand shiner),Ictalurus punctatus(channel catfish), andNeogobius melanostomus(round goby) because each was well represented in museum collections, are locally abundant, and collected from urban habitats. For each individual, we dissected the digestive tissue from esophagus to anus, subjected tissue to peroxide oxidation, examined particles under a dissecting microscope, and used Raman spectroscopy to characterize the particles' chemical composition. No microplastics were detected in any fish prior to 1950. From mid‐century to 2018, microplastic concentrations showed a significant increase when data from all fish were considered together. All detected particles were fibers, and represented plastic polymers (e.g., polyester) along with mixtures of natural and synthetic textiles. For the specimens collected in 2018, microplastics in fish and sediment showed similar patterns across study sites, while water column microplastics showed no differences among locations. Overall, plastic pollution in common freshwater fish species is increasing and pervasive across individuals and species, and is likely related to changes in environmental concentrations. Museum specimens are an overlooked source for assessing historical patterns of microplastic pollution, and for predicting future trends in freshwater fish, thereby helping to sustain the health of commercial and recreational fisheries worldwide. 

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4. Population Status of the Tropical Freshwater Shrimp Xiphocaris elongata in Urban and Forest Streams in Puerto Rico

   https://doi.org/10.3390/hydrobiology2010018  

   Torres-Perez, Wesley X.; Perez-Reyes, Omar (March 2023, Hydrobiology)

   Most of the human population lives in cities, and understanding their impact on freshwater environments is essential. Streams in cities face many environmental challenges that have been described in the concept of Urban Stream Syndrome. This concept illustrates urban streams’ biological, hydrological, chemical, and physical stressors. In tropical streams, these stressors impact shrimp, fish, insects, and other macroinvertebrates that inhabit the freshwater ecosystems. Freshwater shrimp are vulnerable to urban activities, physical, chemical, and ecological impacts. For this reason, these organisms have been used as biological indicators of stream health in the tropics. The shredder shrimp Xiphocaris elongata plays a fundamental role in the organic matter process and decomposition. The objectives of this study were to characterize the population of X. elongata and to identify differences in the abundance of X. elongata between urban and forest streams. Our results showed that highly urbanized areas have a significantly lower abundance of the shredder shrimp X. elongata than medium or low urban reach in the urban and forested watersheds. This study also showed that physicochemical and geomorphological variables are important environmental factors that influence the abundance of X. elongata in Puerto Rican streams. 

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5. An ecological and social approach to the distribution of vector and nuisance mosquito species across residential land use types

   https://doi.org/10.1093/jme/tjaf056  

   Schierer, Megan; De_Urioste-Stone, Sandra; Gardner, Allison_M; Healy, ed., Kristen (June 2025, Journal of Medical Entomology)

   Abstract Mosquito abundance and distribution are related to environmental variables like rainfall and land cover which shape available aquatic habitat for oviposition and juvenile development. Many mosquito species rely on natural water sources for oviposition and juvenile development. However, others have evolved to occupy urban niches and artificial habitats associated with urbanization and human-dominated environments, like tires or storm drains. Additionally, as land cover changes over rural–urban gradients, mosquito species richness decreases via reduced habitat heterogeneity. Human exposure to mosquitoes is a product of environmental processes, and human behaviors related to mosquito control and personal protection. To understand mosquito distribution from both perspectives, we conducted a study with paired entomological and behavioral science data collection. We collected mosquitoes at 40 sites across a rural–urban gradient of 30 residential properties and 10 recreational forest sites in Bangor, Maine, and conducted a juvenile habitat assessment on the residential properties. Additionally, a Knowledge, Attitudes and Practice survey was administered among property owners to understand factors that affect engagement in mosquito control and protective behaviors. Mosquito abundance was highest in forested and rural residential sites. Nuisance species abundance was highest at rural residential sites, while vector species abundance was highest in urban residential sites. Despite 54% respondents reporting mosquitoes as a nuisance, only 10.5% and 5.3% reported frequent engagement in preventative behaviors such as wearing mosquito repellent or protective clothing, respectively. This study builds on literature demonstrating patterns of vector mosquito abundance in residential areas and exploration of resident mosquito control practices. 

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