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1. Watershed land cover predicts the abundance of macroplastic and other anthropogenic litter in streams

   https://doi.org/10.1002/lno.70413  

   Schwenk, Bailey A; Kazmierczak, Elizabeth M; Petersen, Fritz; Haney, Jacob; Zhu, Xia; Zuidema, Shan; Lever, Emily K; Lammers, Richard B; Wollheim, Wilfred M; Rochman, Chelsea M; et al (June 2026, Limnology and Oceanography)

   Macroplastic and other types of macroscopic anthropogenic litter (AL; trash, particles > 5 mm) are pervasive across ecosystems, persistent in the environment, increasing in abundance, and can degrade into microplastics (particles < 5 mm). Rivers retain and transform AL prior to export downstream, but improved predictions of AL distribution and movement within rivers are needed. In particular, equations linking watershed land use with the abundance and assemblage of AL in rivers are lacking. We measured macroscopic AL abundance in three North American watersheds spanning a gradient of land‐cover types, with four sites per watershed, distributed from small streams to larger rivers. We quantified relationships between watershed land cover and AL abundance, measured as number and mass of particles per stream area. Across sites, AL abundance was 0.014–1.051 items/m²and 0.011–87.482 g/m². Watershed impervious surface area and urban cover were significant predictors of AL by count (pseudoR² = 0.418), likely due to greater numbers of AL sources and enhanced connectivity between terrestrial landscapes and urban streams. However, relationships between land cover and AL mass were weaker (pseudoR² = 0.19–0.29), suggesting strong reach‐scale influences on AL mass. Habitat type influenced AL assemblages: floating and overhanging zones showed higher proportions of lightweight materials, while benthic zones contained more dense materials. Our results show watershed urbanization and habitat‐specific retention processes structure AL abundance and assemblage in rivers, improving predictions of AL distribution at larger spatial scales and informing AL prevention and mitigation strategies. 

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2. 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. (December 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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3. Distribution and transport of microplastic and fine particulate organic matter in urban streams

   https://doi.org/10.1002/eap.2429  

   Vincent, Anna E.; Hoellein, Timothy J. (December 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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4. Evaluating the influence of marine protected areas on surf zone fish

   https://doi.org/10.1111/cobi.14296  

   Marraffini, M L; Hamilton, S L; Marin_Jarrin, J R; Ladd, M; Koval, G; Madden, J R; Mangino, I; Parker, L M; Emery, K A; Terhaar, K; et al (May 2024, Conservation Biology)

   Abstract Marine protected areas (MPAs) globally serve conservation and fisheries management goals, generating positive effects in some marine ecosystems. Surf zones and sandy beaches, critical ecotones bridging land and sea, play a pivotal role in the life cycles of numerous fish species and serve as prime areas for subsistence and recreational fishing. Despite their significance, these areas remain understudied when evaluating the effects of MPAs. We compared surf zone fish assemblages inside and outside MPAs across 3 bioregions in California (USA). Using seines and baited remote underwater videos (BRUVs), we found differences in surf zone fish inside and outside MPAs in one region. Inside south region MPAs, we observed higher abundance (Tukey's honest significant difference [HSD] = 0.83,p = 0.0001) and richness (HSD = 0.22,p = 0.0001) in BRUVs and greater biomass (HSD = 0.32,p = 0.0002) in seine surveys compared with reference sites. Selected live‐bearing, fished taxa were positively affected by MPAs. Elasmobranchs displayed greater abundance in BRUV surveys and higher biomass in seine surveys inside south region MPAs (HSD = 0.35,p = 0.0003 and HSD = 0.23,p = 0.008, respectively). Although we observed no overall MPA signal for Embiotocidae, abundances of juvenile and large adult barred surfperch (Amphistichus argenteus), the most abundant fished species, were higher inside MPAs (K–S testD = 0.19,p < 0.0001). Influence of habitat characteristics on MPA performance indicated surf zone width was positively associated with fish abundance and biomass but negatively associated with richness. The south region had the largest positive effect size on all MPA performance metrics. Our findings underscored the variability in species richness and composition across regions and survey methods that significantly affected differences observed inside and outside MPAs. A comprehensive assessment of MPA performance should consider specific taxa, their distribution, and the effects of habitat factors and geography. 

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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 (June 2025, Journal of Medical Entomology)

   Healy, Kristen (Ed.)

   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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