Novel and legacy per- and polyfluoroalkyl substances (PFAS) in freshwater sporting fish from background and firefighting foam impacted ecosystems in Eastern Canada.

Emerging PFAS were recently reported at sites impacted by aqueous film-forming foams (AFFFs) and near major manufacturing centers; however, few studies have evaluated whether these can occur far from release sites. Here, newly identified PFAS were investigated in wild sporting fish from boreal freshwater ecosystems (background sites, 2013-2014 summer seasons), compared to fish impacted by a major AFFF release (summer 2013 and autumn 2014). Different freshwater wild sporting fish species (Esox lucius, Esox masquinongy, Micropterus dolomieu, Sander vitreus, Perca flavescens, and Semotilus corporalis, n = 74) were collected from 13 ecosystems (lakes, reservoirs, and rivers) across Eastern Canada. Of 29 quantitative PFAS, 15 compounds were detected in fish from background sites, including perfluorocarboxylates (C6,8-14), perfluoroalkane sulfonates (C6,8,10), perfluorooctane sulfonamide (FOSA), 6:2 fluorotelomer sulfonate (6:2 FTSA), 7:3 fluorotelomer carboxylic acid (7:3 FTCA), and a zwitterionic PFAS-perfluorooctane sulfonamidoalkyl betaine (PFOSB). To our knowledge, this is the first report of PFOSB in biota. It is also one of the first reports of anionic fluorotelomers (6:2 FTSA, 7:3 FTCA, 9:3 FTCA) in wildlife from background sites. Long-chain fluorotelomer sulfonamidoalkyl betaines (e.g., 8:2 and 10:2 FTAB), fluorotelomer betaines (e.g., 9:3 and 9:1:2 FTB), and fluorotelomer sulfone propanoic acids (e.g., 8:2 FT(SO2)-PA, 10:2 FT(SO2)-PA)) were solely prevalent (up to 97% of summed suspect PFAS) in Smallmouth Bass (M. dolomieu) from the AFFF-impacted site. Perfluorobutane sulfonamide (FBSA), perfluorohexane sulfonamide (FHxSA), 6:2 FTSA and 7:3 FTCA were detected in at least one Smallmouth Bass sample both at the AFFF-impacted and background sites. According to the estimated chronic daily intake and current tolerable daily intake suggested by national agencies, the observed PFOS levels would not pose a health risk to anglers who might consume these wild-caught fish.

Effects of changes in isotopic baselines on the evaluation of food web structure using isotopic functional indices.

BACKGROUND: This study aimed to assess whether ecological inferences from isotopic functional indices (IFIs) are impacted by changes in isotopic baselines in aquatic food webs. We used sudden CO2-outgassing and associated shifts in DIC-δ 13C brought by waterfalls as an excellent natural experimental set-up to quantify impacts of changes in algal isotopic baselines on ecological inferences from IFIs. METHODS: Carbon (δ 13C) and nitrogen (δ 15N) stable isotopic ratios of invertebrate communities sharing similar structure were measured at above- and below-waterfall sampling sites from five rivers and streams in Southern Quebec (Canada). For each sampled invertebrate community, the six Laymans IFIs were then calculated in the δ -space (δ 13C vs. δ 15N). RESULTS: As expected, isotopic functional richness indices, measuring the overall extent of community trophic space, were strongly sensitive to changes in isotopic baselines unlike other IFIs. Indeed, other IFIs were calculated based on the distribution of species within δ-space and were not strongly impacted by changes in the vertical or horizontal distribution of specimens in the δ-space. Our results highlighted that IFIs exhibited different sensitivities to changes in isotopic baselines, leading to potential misinterpretations of IFIs in river studies where isotopic baselines generally show high temporal and spatial variabilities. The identification of isotopic baselines and their associated variability, and the use of independent trophic tracers to identify the actual energy pathways through food webs must be a prerequisite to IFIs-based studies to strengthen the reliability of ecological inferences of food web structural properties.

Testing the influence of environmental heterogeneity on fish species richness in two biogeographic provinces.

Environmental homogenization in coastal ecosystems impacted by human activities may be an important factor explaining the observed decline in fish species richness. We used fish community data (>200 species) from extensive surveys conducted in two biogeographic provinces (extent >1,000 km) in North America to quantify the relationship between fish species richness and local (grain <10 km(2)) environmental heterogeneity. Our analyses are based on samples collected at nearly 800 stations over a period of five years. We demonstrate that fish species richness in coastal ecosystems is associated locally with the spatial heterogeneity of environmental variables but not with their magnitude. The observed effect of heterogeneity on species richness was substantially greater than that generated by simulations from a random placement model of community assembly, indicating that the observed relationship is unlikely to arise from veil or sampling effects. Our results suggest that restoring or actively protecting areas of high habitat heterogeneity may be of great importance for slowing current trends of decreasing biodiversity in coastal ecosystems.

Incorporating temporally dynamic baselines in isotopic mixing models.

Stable isotopes (particularly C and N) are widely used to make inferences regarding food web structure and the phenology of consumer diet shifts, applications that require accurate isotopic characterization of trophic resources to avoid biased inferences of feeding relationships. For example, most isotope mixing models require that endmembers be adequately represented by a single probability distribution; yet, there is mounting evidence that the isotopic composition of aquatic organisms often used as mixing model endmembers can change over periods of weeks to months. A review of the literature indicated that the delta13C values of five aquatic primary consumer taxa, commonly used as proxies of carbon production sources (i.e., trophic baselines), express seasonally dynamic cycles characterized by an oscillation between summer maxima and winter minima. Based on these results, we built a dynamic baseline mixing model that allows a growing consumer to track temporal gradients in the isotopic baselines of a food web. Simulations showed that the ability of a consumer to maintain or approach isotopic equilibrium with its diet over a realistic growth season was strongly affected by both the rate of change of the isotopic baseline and equilibration rate of the consumer. In an empirical application, mixing models of varying complexity were used to estimate the relative contribution of benthic vs. pelagic carbon sources to nine species of juvenile fish in a fluvial lake of the St. Lawrence River system (Québec, Canada). Estimates of p (proportion of carbon derived from benthic sources) derived from a static mixing model indicated broad interspecific variation in trophic niche, ranging from complete benthivory to > 95% reliance on pelagic food webs. Output from the more realistic dynamic baseline mixing model increased estimated benthivory by an average of 36% among species. Taken together, our results demonstrate that failing to identify dynamic baselines when present, and (or) matching consumers with baseline taxa that possess substantially different equilibration rates can seriously bias interpretation of stable isotope data. Additionally, by providing a formalized framework that allows both resources and consumers to shift their isotopic value through time, our model demonstrates a feasible approach for incorporating temporally dynamic isotope conditions in trophic studies of higher consumers.

Variability and directionality of temporal changes in δ(13)C and δ (15)N of aquatic invertebrate primary consumers.

Seasonal oscillations in the carbon (δ(13)C) and nitrogen (δ(15)N) isotope signatures of aquatic algae can cause seasonal enrichment-depletion cycles in the isotopic composition of planktonic invertebrates (e.g., copepods). Yet, there is growing evidence that seasonal enrichment-depletion cycles also occur in the isotope signatures of larger invertebrate consumers, taxa used to define reference points in isotope-based trophic models (e.g., trophic baselines). To evaluate the general assumption of temporal stability in non-zooplankton aquatic invertebrates, δ(13)C and δ(15)N time series data from the literature were analyzed for seasonality and the influence of biotic (feeding group) and abiotic (trophic state, climate regime) factors on isotope temporal patterns. The amplitude of δ(13)C and δ(15)N enrichment-depletion cycles was negatively related to body size, although all size-classes of invertebrates displayed a winter-to-summer enrichment in δ(13)C and depletion in δ(15)N. Among feeding groups, periphytic grazers were more variable and displayed larger temporal changes in δ(13)C than detritivores. For nitrogen, temporal variability and magnitude of directional change of δ(15)N was most strongly related to ecosystem trophic state (eutrophic > mesotrophic, oligotrophic). This study provides evidence of seasonality in the isotopic composition of aquatic invertebrates across very broad geographical and ecological gradients as well as identifying factors that are likely to modulate the strength and variability of seasonality. These results emphasize the need for researchers to recognize the likelihood of temporal changes in non-zooplankton aquatic invertebrate consumers at time scales relevant to seasonal studies and, if present, to account for temporal dynamics in isotope trophic models.

Estimating the feeding range of a mobile consumer in a river-flood plain system using δ(13)C gradients and parasites.

1. The feeding range of an individual is central to food web dynamics as it determines the spatial scale of predator-prey interactions. However, despite recognition of its importance as a driving force in population dynamics, establishing feeding range is seldom done as detailed information on trophic interactions is difficult to obtain. 2. Biological markers are useful to answer this challenge as long as spatial heterogeneity in signal is present within the area investigated. A spatially complex ecosystem, Lake St. Pierre (LSP), a fluvial lake of the St Lawrence River (Québec, Canada), offered a unique opportunity to determine the feeding range of a secondary consumer, yellow perch (Perca flavescens) using isotopic ratios of carbon (δ(13)C). However, because food chains based on phytoplankton have generally more negative δ(13) C than those depending on periphyton, it was essential to determine the contribution of zooplankton in fish diet to correctly interpret spatial patterns of δ(13)C. We used parasites in perch to examine whether their δ(13)C was reflecting local δ(13)C baseline conditions rather than a feeding specialization on zooplankton. 3. δ(13)C of primary consumers was highly variable and exhibited a striking gradient along the shore-channel axis, suggesting that δ(13)C should reflect an individual consumer's spatial position in LSP. 4. This strong isotopic gradient allowed us to estimate the spatial scale of the resources used by individual perch following an approach presented by Rasmussen, Trudeau & Morinville (Journal of Animal Ecology, 78, 2009, 674). By comparing the δ(13)C variability in perch to that of primary consumers, we estimated that the adults feeding range was around 2 km along the shore-channel axis. 5. The combined use of isotopic ratios and parasites allowed us to determine that the adult population uses a wide range of habitats between the flood plain and the main channel. However, individually, each perch depended on a limited foodshed.

Does delta15N in river food webs reflect the intensity and origin of N loads from the watershed?

Stable nitrogen isotope ratios (delta15N) were measured in invertebrates and fish collected from 82 river sites located in the Saint-Lawrence Lowlands in Québec, Canada, to examine the relationship between aquatic biota delta15N and anthropogenic nitrogen (N) loads. Mean delta15N values of all three trophic levels examined (primary consumers, predatory invertebrates and invertebrate-feeding fish) were highly correlated with total anthropogenic N loads on the watershed (kg N km-2 year-1; r2>0.61, p<0.0001) and with N loads originating from livestock manure (r2>0.62, p<0.0001), synthetic fertilizers (r2>0.45, p<0.0001), and human population (r2>0.29, p<0.0001), respectively. Significant relationships were also observed between primary consumer delta15N and N loads originating from each of the three livestock species examined (bovines, pigs and poultry; p<0.0001). Furthermore, all three animal species contributed significantly and independently in elevating primary consumer delta15N (multiple r2=0.67, p<0.0001). Curvilinear regressions were observed at all levels of analysis, delta15N values increasing slowly over a wide range of low levels of N loads, but increasing much faster as N loads grew larger. The three anthropogenic N sources examined were highly correlated with one another, preventing us from statistically isolating their respective effects on delta15N. When these loads were expressed as a proportion of total N load, delta15N of aquatic biota was still highly correlated with N from livestock and fertilizers, but not with N from human population. Overall, these results suggest that delta15N values of aquatic consumers could be used as indicators of the intensity of anthropogenic N loading on watersheds, but not as tracers of the relative importance of individual N sources.

An evaluation of the success of dredging as remediation at a DDT-contaminated site in San Francisco Bay, California, USA.

Lauritzen Canal, a portion of San Francisco Bay near Richmond, California, USA, was heavily contaminated with dichlorodiphenyltrichloroethane (DDT) and dieldrin as a result of releases from a pesticide-formulating firm. In 1996 and 1997, 82,000 m3 of contaminated sediment was removed from the canal by dredging. This study evaluated the success of the dredging based largely on body burdens of DDT and its metabolites (sigmaDDT) in resident biota, with some data on sediment- and water-contaminant levels and sediment toxicity testing. Sediment disturbance during dredging introduced a pulse of sigmaDDT into the Lauritzen Canal ecosystem, and body burdens of fish and invertebrates increased 2- to 76-fold, depending on the species. Approximately 1 1/2 years after remediation, 11 of 14 indicators showed contamination comparable with or worse than the contamination that existed prior to dredging. Monitoring of mussels up to four years postdredging suggests some modest improvement, although the sigmaDDT body burden of canal mussels remained far above the norm for San Francisco Bay. The elevated sigmaDDT body burdens in biota that persisted for years after remediation reflect recent exposure and are not merely a result of slow metabolic elimination of the sigmaDDT pulse associated with dredging. Sediment sigmaDDT concentrations were low immediately after dredging, but within months, the canal bottom became covered with a veneer of fine sediment as contaminated as that that had been removed. The source of this material has not been conclusively established, but we suspect it came from slumping and erosion from the flanks of the canal beneath docks and around pilings where dredging was not done. In retrospect, either capping in place or more thorough dredging may have been more successful in reducing pesticide exposure of the biota, although there were difficulties associated with both alternatives.