Plastic litter is a part of the carbon cycle in an urban river: Microplastic and macroplastic accumulate with organic matter in floating debris rafts.

Watershed models of plastic export from rivers to oceans have large uncertainties, and improvements require direct measurements of riverine macroplastic (>5 mm) and microplastic (<5 mm). Also, plastic represents allochthonous carbon inputs to rivers but is rarely measured as carbon mass. We quantified plastic and organic matter within floating debris rafts and open water in an urban river. Macroplastics only occurred in debris rafts. Microplastics had higher concentrations in debris rafts relative to open water. Across sites, organic matter was positively correlated with microplastics and macroplastics. Last, carbon in plastic was 40% of the carbon mass in coarse particulate organic matter in debris rafts. Floating plastic litter accumulates with particulate organic matter in debris rafts. Plastic is an overlooked and ecological meaningful component of carbon standing stocks in urban rivers. Results will inform improved carbon budget calculation in rivers and watershed models of plastic export. PRACTITIONER POINTS: Plastic particles floating on the surface of an urban river accumulate in debris rafts compared to open water in terms of count and mass. Abundance and composition of plastic particles in debris rafts were distinct from those in open water areas. Plastic litter as units of carbon mass was in the same order of magnitude as carbon mass in course particulate organic matter. Plastic litter moves in similar ways to naturally occurring organic particles and should be measured as a part of the riverine carbon cycle.

A 22-Site Comparison of Land-Use Practices, E-coli and Enterococci Concentrations.

Land-use practices can greatly impact water quality. Escherichia (E.) coli and Enterococcus are accepted water quality indicators. However, surprisingly little research has been conducted comparing both organisms' population density relationships to land use practices and water quality. Stream water grab samples were collected monthly (n = 9 months) from 22 stream monitoring sites draining varying land use practice types in a representative mixed-land-use watershed of the northeastern United States. E. coli and enterococci colony forming units (CFU per 100 mL) were estimated (n = 396) and statistically analyzed relative to land use practices, hydroclimate, and pH, using a suite of methods, including correlation analysis, Principal Components Analysis (PCA), and Canonical Correspondence Analysis (CCA). Correlation analyses indicated significant (p < 0.05) relationships between fecal indicator bacteria concentrations, water quality metrics and land use practices but emphasized significant (p < 0.05) negative correlations between pH and instream enterococci concentrations. PCA and CCA results indicated consistent spatial differences between fecal indicator bacteria concentrations, pH, and land use/land cover characteristics. The study showed that pH could be considered an integrated proxy variable for past (legacy) and present land use practice influences. Results also bring to question the comparability of E-coli and enterococci relative to dominant land use practices and variations in pH and provide useful information that will help guide land use practice and water pollutant mitigation decision making.

The occurrence and transport of microplastics: The state of the science.

Microplastic (MP) particles have been observed in most environments and concentrations are expected to increase over the coming decades given continued and increased production of synthetic polymer products. The expected increase in plastic pollution (including MPs) may elevate the risk posed by these synthetic particles to both environmental and human health. The purpose of this review is to provide a review of the state of knowledge regarding the occurrence and transport of MPs in and across three of the Earths subsystems, specifically, the lithosphere, atmosphere, and hydrosphere. Evidence is presented that shows the lithosphere includes substantial MP accumulation (e.g. approximately 25 particles L-1 in landfill leachate), the impacts of which remain poorly understood. The atmosphere plays an important role in MP transport, with increased occurrence and higher transport concentrations noted in more densely populated areas (e.g. 175 to 313 particles m-2 d-1 in Dongguan China). In the hydrosphere, freshwater ecosystems alternate between MP transport (e.g. rivers) and deposition (e.g. lakes) with flow rate being identified as a key factor determining the movement and fate of MPs. Conversely, marine ecosystems act as a major sink for MP pollution (e.g. MP comprise 94%, approximately 1.69 trillion pieces, of plastic pieces in the Great Pacific Garbage Patch), driven by direct deposition or by transport via the atmosphere or freshwater conveyance systems (e.g. streams, rivers, or ice sheets). Once ingested by organisms, the trophic transfer and bioaccumulation of MPs has been confirmed with the polymer particles potentially accumulating in or impacting fauna, flora, microbes, and humans. Finally, 16 areas are identified in which future MP research efforts should be focused, with the goal of accurately identifying the scope and potential risks posed by synthetic polymer pollution. This review serves as a valuable steppingstone for future research and researchers wishing to address MP research gaps across various environmental settings in the coming decades.