Accumulation of plastic litter is accelerating worldwide. Rivers are a source of microplastic (i.e., particles <5 mm) to oceans, but few measurements of microplastic retention in rivers exist. We ...adapted spiraling metrics used to measure particulate organic matter transport to quantify microplastic deposition using an outdoor experimental stream. We conducted replicated pulse releases of three common microplastics: polypropylene pellets, polystyrene fragments, and acrylic fibers, repeating measurements using particles with and without biofilms. Depositional velocity (v
; mm/s) patterns followed expectations based on density and biofilm 'stickiness', where v
was highest for fragments, intermediate for fibers, and lowest for pellets, with biofilm colonization generally increasing v
. Comparing microplastic v
to values for natural particles (e.g., fine and coarse particulate organic matter) showed that particle diameter was positively related to v
and negatively related to the ratio of v
to settling velocity (i.e., sinking rate in standing water). Thus, microplastic v
in rivers can be quantified with the same methods and follows the same patterns as natural particles. These data are the first measurements of microplastic deposition in rivers, and directly inform models of microplastic transport at the landscape scale, making a key contribution to research on the global ecology of plastic waste.
To understand biological interactions of plastic litter in freshwater ecosystems, as well the potential effects of plastics on ecosystem processes, studies of the activity and composition of ...plastic-associated microbial communities are needed. The physical properties and chemical composition of plastic polymers are key components of plastic product design, and may also select for distinct microbial biofilms colonizing plastic litter. We monitored growth and succession of biofilm communities on plastic substrates of common morphotypes (i.e., hard, soft, foam, and film) and a natural surface (i.e., an unglazed ceramic tile) incubated in an urban stream. We measured biofilm biomass, metabolism, extracellular enzyme activity, and bacterial, fungal and algal community composition over four weeks during primary succession. Results demonstrated a general increase in biofilm biomass and enzymatic activity corresponding to carbon, nitrogen and phosphorus metabolism during biofilm development for all substrate types. We observed higher respiration rates and negative net ecosystem productivity on foam and tile surfaces in comparison to hard, soft and film plastic surfaces. Biofilm bacterial, fungal and algal assemblages showed few significant differences in composition among substrates. However, all microbial communities changed significantly in composition over time. While substrate type was not the major factor driving biofilm composition and activity, these data show plastic litter in streams is well colonized by an active and dynamic biofilm community. As plastic litter is increasing across all types of aquatic ecosystems, it should be considered a medium for biologically active organisms that contribute to key ecosystem processes.
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•Microbial colonization of plastic litter impacts its fate in urban streams.•We assessed succession in microbial activity and diversity on 4 plastic substrates.•Time, not substrate type, was major factor in driving microbial community trends.•Plastic biofilms active and dynamic, and can contribute to key ecosystem processes.
Anthropogenic litter (AL; trash) in the environment is increasing and persistent. Rivers are considered a major source of AL to oceans, but AL ecology within rivers is rarely examined. Also, the ...rapidly developing field of AL research will benefit from fundamental approaches in community and ecosystem ecology. We adapted methods for communities of organisms and movement of organic matter to measure density, mass, assemblages, sources, and flux of AL in riparian and benthic zones at 15 sites in five rivers. We compared riverine AL density, mass, and assemblages to marine habitats worldwide. Benthic zones had greater AL mass and a different assemblage than riparian zones. Reach-scale metrics of human activity (e.g., parking spaces) explained more variation in AL assemblages than total urban land use. AL export was driven by material type and hydrology, and turnover time was ≤ 1 yr. Riparian AL density was similar to beaches, but benthic AL density was higher than marine benthic habitats. Finally, AL assemblages in river benthic and riparian zones were similar to assemblages at beaches rather than marine benthic habitats. AL is abundant and mobile in rivers, which show dynamic periods of AL retention and export. Rivers are likely sites of AL breakdown and burial, with significant biotic interactions which have not yet been studied. Comprehensive assessments of AL across ecosystems require continued adaptation of fundamental ecosystem and community ecology tools. Results will integrate riverine AL dynamics with the growing field of marine AL ecology, and inform management of global AL accumulations.
Consumers contribute to nutrient cycling in aquatic ecosystems by nutrient retention in tissues, metabolic transformations and excretion, and promoting microbial processes that remove nutrients ...(i.e., nitrogen (N) loss via denitrification). Freshwater mussels (Unionidae) form dense assemblages in rivers, and affect nutrient transformations through feeding, biodeposition, and bioturbation. However, the effects of Unionid mussels on N and phosphorus (P) retention are not commonly measured. We quantified rates of filtration, retention, and biodeposition of carbon (C), N, and P for two Unionid species: Lasmigona complanata and Pyganodon grandis. We used continuous-flow cores with ¹⁵N tracers to measure denitrification in sediments alone and with a single individual of each species. We conducted measurements in an urban river near Chicago, IL, USA that is a target for Unionid restoration. Both Unionid species showed high rates of P-specific feeding and retention, but low N-specific rates. This was in agreement with high N:P ratio in the water column. Each species significantly increased denitrification relative to sediment alone. ¹⁵N tracers suggested direct denitrification of nitrate increased denitrification, although enhanced coupled nitrification–denitrification likely also contributed to denitrification. Finally, denitrification rates with and without mussels were used to estimate the value of N loss under different scenarios for mussel restoration at the river scale. Overall, restored Unionid populations may enhance P retention in soft tissues and shells and N loss via denitrification. Ecosystem managers may find greater support for restoration of Unionid populations with careful calculations of their ecosystem role in nutrient retention and removal.
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.
A fish tale Hou, Loren; McMahan, Caleb D.; McNeish, Rae E. ...
Ecological applications,
July 2021, Letnik:
31, Številka:
5
Journal Article
Recenzirano
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), and Neogobius 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.
In rivers, small and lightweight microplastics are transported downstream, but they are also found frequently in riverbed sediment, demonstrating long-term retention. To better understand ...microplastic dynamics in global rivers from headwaters to mainstems, we developed a model that includes hyporheic exchange processes, i.e., transport between surface water and riverbed sediment, where microplastic retention is facilitated. Our simulations indicate that the longest microplastic residence times occur in headwaters, the most abundant stream classification. In headwaters, residence times averaged 5 hours/km but increased to 7 years/km during low-flow conditions. Long-term accumulation for all stream classifications averaged ~5% of microplastic inputs per river kilometer. Our estimates isolated the impact of hyporheic exchange processes, which are known to influence dynamics of naturally occurring particles in streams, but rarely applied to microplastics. The identified mechanisms and time scales for small and lightweight microplastic accumulation in riverbed sediment reveal that these often-unaccounted components are likely a pollution legacy that is crucial to include in global assessments.
Research on plastics in global ecosystems is rapidly evolving. Oceans have been the primary focus of studies to date, whereas rivers are generally considered little more than conduits of plastics to ...marine ecosystems. Within a watershed, however, plastics of all sizes are retained, transformed, and even extracted via freshwater use or litter cleanup. As such, plastic litter in terrestrial and freshwater ecosystems is an important but underappreciated component of global plastic pollution. To gain a holistic perspective, we developed a conceptual model that synthesizes all sources, fluxes, and fates for plastics in a watershed, including containment (ie disposed in landfill), non‐containment (ie persists as environmental pollution), mineralization, export to oceans, atmospheric interactions, and freshwater extraction. We used this model of the “plastic cycle” to illustrate which components have received the most scientific attention and to reveal overlooked pathways. Our main objective is for this framework to inform future research, offer a new perspective to adapt management across diverse waste governance scenarios, and improve global models of plastic litter.
Oyster reefs have declined globally. Interest in their restoration has motivated research into oyster-mediated ecosystem services including effects on biodiversity, filtration, and nitrogen (N) ...cycling. Recent evidence suggests oysters may promote denitrification, or anaerobic respiration of nitrate (NO
3
−
) into di-nitrogen gas, via benthic deposition of carbon (C) and N-rich biodeposits. However, the mechanisms whereby biodeposits promote N transformations prerequisite to denitrification (e.g., mineralization and nitrification) are unclear. Previous research has also not measured oysters' influence on N cycling in urbanized areas. In May 2010 we deployed eastern oysters (
Crassostrea virginica
) in mesh cages above sand-filled boxes at four sites across a nutrient gradient in Jamaica Bay, New York City (New York, USA). Oysters were arranged at four densities: 0, 40, 85, and 150 oysters/m
2
. For 17 months we measured water-column nutrients and chlorophyll
a
, every two weeks to monthly. Every two months we measured sediment ash-free dry mass (AFDM), exchangeable ammonium (NH
4
+
), ammonification, nitrification, denitrification potential (DNP), and NO
3
−
and C limitation of DNP. Oysters increased sediment AFDM at three of four sites, with the greatest increase at high density. Oysters did not affect any N pools or transformations. However, variation among sites and dates illustrated environmental drivers of C and N biogeochemistry in this urban estuary. Overall, nitrification was positively related to net ammonification, water column NH
4
+
, and sediment NH
4
+
, but was not correlated with DNP. Denitrification was consistently and strongly NO
3
−
limited, while C was not limiting or secondarily limiting. Therefore, the oyster-mediated increase in AFDM did not affect DNP because C was not its primary driver. Also, because DNP was unrelated to nitrification, it is unlikely that biodeposit N was converted to NO
3
−
for use as a denitrification substrate. Predicting times or sites where denitrification is driven by the C and N species originating from oyster biodeposits remains a challenge under eutrophic conditions. Towards this goal, we synthesized our conclusions with literature predictions in a conceptual model for pathways whereby oysters might influence C and N dynamics differently in oligotrophic relative to eutrophic ecosystems.
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