Despite growing concern about the occurrence of microplastics in aquatic ecosystems there is only rudimentary understanding of the pathways through which any adverse effects might occur. Here, we ...assess the effects of polystyrene microplastics (PS-MPs; <70 μm) on a common and widespread algal species, Chlorella sorokiniana. We used laboratory exposure to test the hypothesis that the lipids and fatty acids (FAs) are important molecules in the response reactions of algae to this pollutant. Cultivation with PS-MPs systematically reduced the concentration of essential linoleic acid (ALA, C18:3n-3) in C. sorokiniana, concomitantly increasing oleic acid (C18:1n-9). Among the storage triacylglycerols, palmitoleic and oleic acids increased at the expenses of two essential fatty acids, linoleic (LIN, C18:2n-6) and ALA, while PS-MPs had even more pronounced effects on the fatty acid and hydrocarbon composition of waxes and steryl esters. The FA composition of two major chloroplast galactolipids, monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG), were affected implying changes in the conformational structure of photosynthetic complexes in ways that can impair the photosynthesis. These data reveal how exposure to polystyrene microplastics can modify the concentrations of lipid molecules that are important intrinsically in cell membranes, and hence the lipid bilayers that could form an important barrier between algal cellular compartments and plastics in the aquatic environment. Changes in lipid synthesis and fatty acid composition in algae could also have repercussions for food quality, growth and stressor resistance in primary consumers. We advocate further studies of microplastics effects on the lipid composition of primary producers, and of their potential propagation through aquatic food webs.
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•Polystyrene microplastic disrupted lipid composition in widespread algae.•Exposure reduced two essential fatty acids, linoleic and linolinic.•Plastic affected fatty acids in galactolipids which are chloroplastic lipids involved in photosynthesis.•Potential mechanism of microplastic effects at the base of aquatic food webs.
Polystyrene causes fundamental changes in lipid composition of widespread algae opening a new front in understanding microplastic effects on food webs.
As a rapidly accelerating expression of global change, plastics now occur extensively in freshwater ecosystems, yet there is barely any evidence of their transfer through food webs. Following ...previous observations that plastics occur widely in their prey, we used a field study of free‐living Eurasian dippers (Cinclus cinclus), to test the hypotheses that (1) plastics are transferred from prey to predators in rivers, (2) plastics contained in prey are transferred by adults to altricial offspring during provisioning and (3) plastic concentrations in faecal and regurgitated pellets from dippers increase with urbanization. Plastic occurred in 50% of regurgitates (n = 74) and 45% of faecal samples (n = 92) collected non‐invasively from adult and nestling dippers at 15 sites across South Wales (UK). Over 95% of particles were fibres, and concentrations in samples increased with urban land cover. Fourier transform infrared spectroscopy identified multiple polymers, including polyester, polypropylene, polyvinyl chloride and vinyl chloride copolymers. Although characterized by uncertainty, steady‐state models using energetic data along with plastic concentration in prey and excreta suggest that around 200 plastic particles are ingested daily by dippers, but also excreted at rates that suggest transitory throughput. As some of the first evidence revealing that plastic is now being transferred through freshwater food webs, and between adult passerines and their offspring, these data emphasize the need to appraise the potential ecotoxicological consequences of increasing plastic pollution.
Using free‐living river birds (Eurasian dippers, Cinclus cinclus), we provide some of the first evidence of microplastic transfer through freshwater food webs, and from adult songbirds to their offspring. Plastic fibres of several polymers occurred in 50% of regurgitated pellets and 45% of faecal samples collected at 15 sites in South Wales (UK) at concentrations that increased with urbanization. Models using energetic data alongside plastic concentration in prey and excreta suggest that around 200 plastic particles are ingested daily by dippers, but also excreted at similar rates. These data reinforce the need to appraise the potential ecotoxicological consequences of increasing plastic pollution.
Understanding metal and proton toxicity under field conditions requires consideration of the complex nature of chemicals in mixtures. Here, we demonstrate a novel method that relates streamwater ...concentrations of cationic metallic species and protons to a field ecological index of biodiversity. The model WHAM-
F
TOX postulates that cation binding sites of aquatic macroinvertebrates can be represented by the functional groups of natural organic matter (humic acid), as described by the Windermere Humic Aqueous Model (WHAM6), and supporting field evidence is presented. We define a toxicity function (
F
TOX) by summing the products: (amount of invertebrate-bound cation)
×
(cation-specific toxicity coefficient,
α
i
). Species richness data for Ephemeroptera, Plecoptera and Trichoptera (EPT), are then described with a lower threshold of
F
TOX, below which all organisms are present and toxic effects are absent, and an upper threshold above which organisms are absent. Between the thresholds the number of species declines linearly with
F
TOX. We parameterised the model with chemistry and EPT data for low-order streamwaters affected by acid deposition and/or abandoned mines, representing a total of 412 sites across three continents. The fitting made use of quantile regression, to take into account reduced species richness caused by (unknown) factors other than cation toxicity. Parameters were derived for the four most common or abundant cations, with values of
α
i
following the sequence (increasing toxicity) H
+
<
Al
<
Zn
<
Cu. For waters affected mainly by H
+ and Al,
F
TOX shows a steady decline with increasing pH, crossing the lower threshold near to pH 7. Competition effects among cations mean that toxicity due to Cu and Zn is rare at lower pH values, and occurs mostly between pH 6 and 8.
Freshwater organisms remain at risk from bioaccumulation and biomagnification of persistent organic pollutants (POPs), but factors affecting their transfer through food webs are poorly understood. ...Here, we investigate transfer pathways of polychlorinated biphenyls, polybrominated diphenyl ethers, and organochlorine through a river food web, assessing the distribution and flux between basal resources (n = 3), macroinvertebrates (n = 22), and fish (n = 1). We investigate the effects of biological traits on the observed patterns and use trait-based models to predict POP bioaccumulation. Transfer pathways differed among POPs and traits such as habitat affinity, feeding behavior, and body size explained some variation in POP burdens between organisms. Trait-based models indicated that relationships between POPs, trophic transfers, and traits were relatively well conserved across a wider array of river food webs. Although providing more consistent predictions of POP bioaccumulation than steady-state models, variability in bioaccumulation across food webs limited the accuracy of trait-model predictions. As some of the first data to illustrate how ecological processes alter the flux of pollutants through river food webs, these results reveal important links between POPs and contrasting energetic pathways. These data also show the utility of trait-based methods in the assessment of persistent contaminants, but further field validations are required.
Water-body size and location influence zooplankton diversity in freshwaters, but less is known about systematic variations in zooplankton community composition between natural and artificial waters ...on different continents. We used meta-analysis to assess how zooplankton in artificial water bodies across different biomes might differ from natural water bodies of similar size. Among 79 lakes, ponds and reservoirs (11 artificial and 68 natural), proximity to other water bodies apparently increased species richness in all lake types, probably reflecting dispersal. However, richness did not differ systematically between natural and artificial water bodies of comparable size. In contrast, community composition differed between artificial and natural waters after accounting for depth, productivity, longitude and conductivity, with models explaining up to 50% of the overall variance at genus level. Leptodiaptomus, Chydorus, Cyclops, Acanthocyclops, Skistodiaptomus, Epischura, Limnocalanus, Senecella, Heterocope, Arctodiaptomus and Aglaodiaptomus all occurred more frequently in natural waters, whilst Thermocyclops, Moina and Epischura occurred more frequently in artificial lakes. Rank-occurrence data revealed that Ceriodaphnia, Orthocyclops, Holopedium and Eucyclops were equitably distributed across water bodies of contrasting sizes, depths and climates. Other genera occurred under more specific conditions, typically where they had strong associations with natural lakes (e.g. Limnocalanus, Senecella, Heterocope, Arctodiaptomus and Aglaodiaptomus). These results are among the first to illustrate systematic differences in zooplankton composition between natural and artificial lakes at a global scale. Potential explanations require further evidence, but might include provision for niche specialists in natural lakes versus reduced heterogeneity, management or disturbance effects in artificial lakes; and effects of lake age, stability and habitat naturalness in natural lakes. While zooplankton communities in natural lakes are well studied globally, more extensive data are required from artificial lakes.
We combined stable isotope tracers of blood plasma, blood cells and egg contents with faecal analysis during pre-breeding and egg laying phases in two dipper species
Cinclus cinclus and
Cinclus ...mexicanus to determine the occurrence of dietary shifts during egg production and to assess consequences for egg contaminant loads. In both species, changes in δ
13C (
C. cinclus) or δ
15N (
C. mexicanus) in female plasma relative to red blood cells indicated a dietary shift during laying that was not observed in males. Eurasian dippers increased prey consumption as breeding approached, shifting from primarily trichopteran insect larvae to ephemeropterans and plecopterans. In American dippers, egg-laying females switched to feeding at a higher trophic level by consuming more fish. Eggs derived from higher trophic level diets contained more mercury (American dipper), polychlorinated biphenyls and some organochlorines, especially DDT metabolites. The results demonstrate how dietary changes during egg laying accompany the demands for egg production with consequences for contaminant deposition in avian eggs.
Changes in laying diet influences contaminant deposition in bird eggs.
Stable isotope and contaminant analyses revealed differences in nutrient sources and contaminant pathways in two species of dipper, Cinclus mexicanus and Cinclus cinclus in western Canada and western ...Britain. We collected dipper prey and eggs from relatively pristine British Columbian rivers contrasting in the presence of salmon-derived nutrients, and rural Welsh rivers with varying food-web complexity associated with stream acidity. Enriched δ13C and to a lesser extent δ15N in American dipper eggs and prey confirmed that streams with migrating Pacific salmon were enriched with marine-derived nutrients, but overall contaminant concentrations did not differ strongly in dipper eggs between rivers with and without salmon. However dipper contaminant profiles, particularly PBDEs, mercury and ΣDDTs, were related to δ13C, reflecting the marine influence and greater fish consumption at salmon sites. Irrespective of catchment influences and despite feeding at a higher trophic level, American dipper eggs (n = 17) contained lower levels of organohalogens than Eurasian dippers (n = 37), but with similar PCB (153 and 138) and PBDE (47 and 99) congeners dominanating. Eurasian dipper eggs from circumneutral streams contained more dieldrin, ΣDDT and Σhexachlorocyclohexanes while Σchlordanes, mirex, ΣPBDEs and ΣPCBs predominated at acid sites. Our data reveal how dippers indicate contaminant levels and sources under contrasting conditions at scales ranging from local to intercontinental, but local environmental conditions apparently alter feeding ecology and exposure pathways even in these closely related species.
Periphytic diatoms were studied to evaluate the water quality of a newly created lake, formed by the enclosure of the formerly tidal Cardiff Bay (Wales, UK), and the effects of two inflowing rivers ...which drain densely populated and industrialised catchments. Seven sites in Cardiff Bay and two locations on the inflowing rivers were monitored for diatoms and water chemistry over 2 years. Water quality was assessed using a revised UK trophic diatom index (TDI) and new methods to determine ecological quality ratios and ecological status classes as required by the EU Water Framework Directive. Diatom assemblages reflected spatiotemporal variations in environmental conditions between the rivers and Cardiff Bay and within the bay. In the bay, diatoms reflected differences in river quality and possibly local pollution in certain areas of the lake. High values of the TDI indicated eutrophic to hypertrophic conditions in both rivers and in the bay and diatoms indicated poor ecological status.
The WHAM-FTOX model uses chemical speciation to describe the bioavailability and toxicity of proton and metal mixtures (including Al) to aquatic organisms. Here, we apply the previously parameterised ...model to 45 UK and Norwegian upland surface waters recovering from acidification, to compare its predictions of the maximum species richness of the macroinvertebrate Orders Ephemeroptera, Plecoptera and Trichoptera (SR-EPT) with time-series observations. This work uses data from two national scale survey programmes, the Acid Waters Monitoring Network in the UK and a lakes survey in Norway. We also investigate data from a long-studied catchment, Llyn Brianne in Wales. For the national surveys, model results relate well with actual trends, with Regional Kendall analysis indicating biological recovery rates for both actual and predicted species richness that are generally consistent (1.2–2.0 species per decade). However, actual recovery rates in AWMN lakes were less than in the rivers (0.6 vs. 2.0 species per decade), whilst predicted rates were similar (1.7 vs. 2.0). Several sites give a very good fit between model predictions and observations; at these sites chemistry is apparently the principal factor controlling limits of species richness. At other sites where there is poorer agreement between model predictions and observations, chemistry can still explain some of the reduction in species richness. However, for these sites, additional (un-modelled) factors further suppress species richness. The model gives a good indication of the extent of these un-modelled factors and the degree to which chemistry may suppress species richness at a given site.
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