Understanding among-lake variability of mercury concentrations in Northern Pike (Esox lucius): A whole-ecosystem study in subarctic lakes.

Mercury concentrations ([Hg]) in fish reflect complex biogeochemical and ecological interactions that occur at a range of spatial and biological scales. Elucidating these interactions is crucial to understanding and predicting fish [Hg], particularly at northern latitudes, where environmental perturbations are having profound effects on land-water-animal interactions, and where fish are a critical subsistence food source. Using data from eleven subarctic lakes that span an area of ~60,000 km2 in the Dehcho Region of Northwest Territories (Canada), we investigated how trophic ecology and growth rates of fish, lake water chemistry, and catchment characteristics interact to affect [Hg] in Northern Pike (Esox lucius), a predatory fish of widespread subsistence and commercial importance. Results from linear regression and piecewise structural equation models showed that 83% of among-lake variability in Northern Pike [Hg] was explained by fish growth rates (negative) and concentrations of methyl Hg ([MeHg]) in benthic invertebrates (positive). These variables were in turn influenced by concentrations of dissolved organic carbon, MeHg (water), and total Hg (sediment) in lakes, which were ultimately driven by catchment characteristics. Lakes in relatively larger catchments and with more temperate/subpolar needleleaf and mixed forests had higher [Hg] in Northern Pike. Our results provide a plausible mechanistic understanding of how interacting processes at scales ranging from whole catchments to individual organisms influence fish [Hg], and give insight into factors that could be considered for prioritizing lakes for monitoring in subarctic regions.

Periphyton, bivalves and fish differentially accumulate select pharmaceuticals in effluent-dependent stream mesocosms.

Pharmaceuticals and other ionizable contaminants from municipal wastewater treatment plant effluent can bioaccumulate in fish, particularly in effluent dominated and dependent systems in semi-arid and arid regions. However, invertebrate bioaccumulation of these compounds has been less studied. Using municipal wastewater effluent as source water in outdoor stream mesocosms to simulate effluent-dependent lotic systems, we examined bioaccumulation of several widely-used pharmaceuticals including acetaminophen (nonsteroidal anti-inflamatory), caffeine (stimulant), carbamazepine (anti-epileptic), diltiazem (calcium channel blocker), diphenhydramine (anti-histamine), fluoxetine (anti-depressant), norfluoxetine (anti-depressant metabolite), and sertraline (anti-depressant) in freshwater clams (Corbicula fluminea), periphyton and stoneroller minnows (Campostoma anomalum), a commonly studied grazer in stream ecology, during a replicated outdoor stream mesocosm study at the Baylor Experimental Aquatic Research facility. Target analytes were determined in tissues, source effluent and stream water by isotope dilution LC-MS/MS. After an 8-day uptake period, clams accumulated a number of pharmaceuticals, including acetaminophen, carbamazepine, diltiazem, diphenhydramine, fluoxetine, norfluoxetine and sertraline with maximum concentrations reaching low µg/kg. We observed uptake rates in clams for acetaminophen at 2.8 µg/kg per day, followed by diphenhydramine (1.2 µg/kg per day) and carbamazepine (1.1 µg/kg per day). Caffeine, carbamazepine, diltiazem and diphenhydramine were measured in periphyton. Diphenhydramine was the only compound detected in all matrices, where bioaccumulation factors (BAFs) were elevated in bivalves (1631 ± 589 L/kg), compared to stoneroller minnows (247 ± 84 L/kg) and periphyton (315 ± 116 L/kg). Such BAF variability across multiple biological matrices highlight the need to understand bioaccumulation differences for ionizable contaminants among freshwater biota, including threatened and endangered species (e.g., unionids), commercially important bivalves (e.g., estuarine and marine bivalves), and fish.

Compensatory indirect effects of an herbicide on wetland communities.

The direct effects of large-scale disturbances are readily studied because their effects are often apparent and result in large changes to ecosystems. Direct effects can cascade through the ecosystem, leading to indirect effects that are often subtle and difficult to detect. Managing anthropogenic disturbances, such as chemical contamination, requires an understanding of both direct and indirect effects to predict, measure, and characterize the impact. Using a replicated whole-ecosystem experiment and path analyses (assesses the effects of a set of variables on a specified outcome, similar to multiple regression), we examined the direct and indirect effects of a glyphosate-based herbicide and nutrient enrichment on wetland communities. The latter did not impact any measured endpoints. The strongest drivers of macrophyte, benthic invertebrate, and amphibian assemblages were the ephemerality and the size of wetlands, factors which were not altered by herbicide applications. The herbicide had a direct negative effect on macrophyte cover, amphibian larval abundance, and the proportion of predatory benthic invertebrates. However, both amphibians and invertebrates were positively affected by the reduction in the macrophyte cover caused by the herbicide applications. The opposing directions of the direct and indirect effects lead to no net change in either group. The compensatory dynamics observed herein highlight the need for a better understanding of indirect effects pathways to determine whether common anthropogenic disturbances alter the ecological communities in small wetland ecosystems.

Dosing, Not the Dose: Comparing Chronic and Pulsed Silver Nanoparticle Exposures.

The environmental impacts of manufactured nanoparticles are often studied using high-concentration pulse-additions of freshly synthesized nanoparticles, while predicted releases are characterized by chronic low-concentration additions of weathered particles. To test the effects in wetlands of addition rate and nanoparticle speciation on water column silver concentrations, ecosystem impacts, and silver accumulation by biota, we conducted a year-long mesocosm experiment. We compared a pulse addition of Ag0-NPs to chronic weekly additions of either Ag0-NPs or sulfidized silver nanoparticles. The initially high water column silver concentrations in the pulse treatment declined such that after 4 weeks it was lower on average than in the two chronic treatments. While the pulse caused a marked increase in dissolved methane in the first week of the experiment, the chronic treatments had smaller increases in methane concentration that were more prolonged between weeks 28-45. Much like water column silver, most organisms in chronic treatments had comparable silver concentrations to the pulse treatment after only 4 weeks, and all but one organism had similar or higher concentrations than the pulse treatment after one year. Pulse exposures thus both overestimate the intensity of short-term exposures and effects and underestimate the more realistic long-term exposure, ecosystem effects, and accumulation seen in chronic exposures.

Titanium dioxide nanoparticle exposure reduces algal biomass and alters algal assemblage composition in wastewater effluent-dominated stream mesocosms.

A 5-week mesocosm experiment was conducted to investigate the toxicity of titanium dioxide nanoparticles (TiO2NPs) to periphytic algae in an environmentally-realistic scenario. We used outdoor experimental streams to simulate the characteristics of central Texas streams receiving large discharges of wastewater treatment plant effluent during prolonged periods of drought. The streams were continually dosed and maintained at two concentrations. The first represents an environmentally relevant concentration of 0.05 mg L-1 (low concentration). The second treatment of 5 mg L-1 (high concentration) was selected to represent a scenario where TiO2NPs are used for photocatalytic degradation of pharmaceuticals in wastewater. Algal cell density, chlorophyll-a, ash-free dry mass, algal assemblage composition, and Ti accumulation were determined for the periphyton in the riffle sections of each stream. The high concentration treatment of TiO2NPs significantly decreased algal cell density, ash-free dry mass, and chlorophyll-a, and altered algal assemblage composition. Decreased abundance of three typically pollution-sensitive taxa and increased abundance of two genera associated with heavy metal sorption and organic pollution significantly contributed to algal assemblage composition changes in response to TiO2NPs. Benefits of the use of TiO2NPs in wastewater treatment plants will need to be carefully weighed against the demonstrated ability of these NPs to cause large changes in periphyton that would likely propagate significant effects throughout the stream ecosystem, even in the absence of direct toxicity to higher trophic level organisms.

The combined influence of two agricultural contaminants on natural communities of phytoplankton and zooplankton.

Concentrations of glyphosate observed in the environment are generally lower than those found to exert toxicity on aquatic organisms in the laboratory. Toxicity is often tested in the absence of other expected co-occurring contaminants. By examining changes in the phytoplankton and zooplankton communities of shallow, partitioned wetlands over a 5 month period, we assessed the potential for direct and indirect effects of the glyphosate-based herbicide, Roundup WeatherMax(©) applied at the maximum label rate, both in isolation and in a mixture with nutrients (from fertilizers). The co-application of herbicide and nutrients resulted in an immediate but transient decline in dietary quality of phytoplankton (8.3 % decline in edible carbon content/L) and zooplankton community similarity (27 % decline in similarity and loss of three taxa), whereas these effects were not evident in wetlands treated only with the herbicide. Thus, even at a worst-case exposure, this herbicide in isolation, did not produce the acutely toxic effects on plankton communities suggested by laboratory or mesocosm studies. Indirect effects of the herbicide-nutrient mixture were evident in mid-summer, when glyphosate residues were no longer detectable in surface water. Zooplankton abundance tripled, and zooplankton taxa richness increased by an average of four taxa in the herbicide and nutrient treated wetlands. The lack of significant toxicity of Roundup WeatherMax alone, as well as the observation of delayed interactive or indirect effects of the mixture of herbicide and nutrients attest to the value of manipulative field experiments as part of a comprehensive, tiered approach to risk assessments in ecotoxicology.

Press or pulse exposures determine the environmental fate of cerium nanoparticles in stream mesocosms.

Risk-assessment models indicate that stream ecosystems receiving municipal wastewater effluent may have the greatest potential for exposure to manufactured nanoparticles. The authors determined the fate of cerium oxide (CeO2 ) nanoparticles in outdoor stream mesocosms using 1) 1-time pulse addition of CeO2 nanoparticles, representative of accidental release, and 2) continuous, low-level press addition of CeO2 nanoparticles, representative of exposure via wastewater effluent. The pulse addition led to rapid nanoparticle floc formation, which appeared to preferentially deposit on periphyton in low-energy areas downstream from the location of the input, likely as a result of gravitational sedimentation. Floc formation limited the concentration of suspended nanoparticles in stream water to <5% of target and subsequent downstream movement. In contrast, press addition of nanoparticles led to higher suspended nanoparticle concentrations (77% of target) in stream water, possibly as a result of stabilization of suspended nanoparticles through interaction with dissolved organic carbon. Smaller nanoparticle aggregates appeared to preferentially adsorb to stream surfaces in turbulent sections, where Ce concentrations were highest in the press, likely a result of stochastic encounter with the surface. Streams receiving wastewater effluent containing nanoparticles may lead to exposure of aquatic organisms over a greater spatial extent than a similar amount of nanoparticles from an accidental release. Exposure models must take into account these mechanisms controlling transport and depositional processes.

The direct and indirect effects of a glyphosate-based herbicide and nutrients on Chironomidae (Diptera) emerging from small wetlands.

Laboratory and mesocosm experiments have demonstrated that some glyphosate-based herbicides can have negative effects on benthic invertebrate species. Although these herbicides are among the most widely used in agriculture, there have been few multiple-stressor, natural system-based investigations of the impacts of glyphosate-based herbicides in combination with fertilizers on the emergence patterns of chironomids from wetlands. Using a replicated, split-wetland experiment, the authors examined the effects of 2 nominal concentrations (2.88 mg acid equivalents/L and 0.21 mg acid equivalents/L) of the glyphosate herbicide Roundup WeatherMax, alone or in combination with nutrient additions, on the emergence of Chironomidae (Diptera) before and after herbicide-induced damage to macrophytes. There were no direct effects of treatment on the structure of the Chironomidae community or on the overall emergence rates. However, after macrophyte cover declined as a result of herbicide application, there were statistically significant increases in emergence in all but the highest herbicide treatment, which had also received no nutrients. There was a negative relationship between chironomid abundance and macrophyte cover on the treated sides of wetlands. Fertilizer application did not appear to compound the effects of the herbicide treatments. Although direct toxicity of Roundup WeatherMax was not apparent, the authors observed longer-term impacts, suggesting that the indirect effects of this herbicide deserve more consideration when assessing the ecological risk of using herbicides in proximity to wetlands.

Setting an optimal α that minimizes errors in null hypothesis significance tests.

Null hypothesis significance testing has been under attack in recent years, partly owing to the arbitrary nature of setting α (the decision-making threshold and probability of Type I error) at a constant value, usually 0.05. If the goal of null hypothesis testing is to present conclusions in which we have the highest possible confidence, then the only logical decision-making threshold is the value that minimizes the probability (or occasionally, cost) of making errors. Setting α to minimize the combination of Type I and Type II error at a critical effect size can easily be accomplished for traditional statistical tests by calculating the α associated with the minimum average of α and ß at the critical effect size. This technique also has the flexibility to incorporate prior probabilities of null and alternate hypotheses and/or relative costs of Type I and Type II errors, if known. Using an optimal α results in stronger scientific inferences because it estimates and minimizes both Type I errors and relevant Type II errors for a test. It also results in greater transparency concerning assumptions about relevant effect size(s) and the relative costs of Type I and II errors. By contrast, the use of α = 0.05 results in arbitrary decisions about what effect sizes will likely be considered significant, if real, and results in arbitrary amounts of Type II error for meaningful potential effect sizes. We cannot identify a rationale for continuing to arbitrarily use α = 0.05 for null hypothesis significance tests in any field, when it is possible to determine an optimal α.

Petroleum coke and soft tailings sediment in constructed wetlands may contribute to the uptake of trace metals by algae and aquatic invertebrates.

The fate of trace metals in pore water collected from wetland sediments and organisms exposed to petroleum coke were evaluated within in situ aquatic microcosms. Oil sands operators of Fort McMurray, Alberta, Canada produced 60 million tonnes of petroleum coke by 2008, containing elevated concentrations of sulphur and several trace metals commonly seen in oil sands materials. This material may be included in the construction of reclaimed wetlands. Microcosms were filled with a surface layer of petroleum coke over mine-waste sediments and embedded in a constructed wetland for three years to determine how these materials would affect the metal concentrations in the sediment pore water, colonizing wetland plants and benthic invertebrates. Petroleum coke treatments produced significantly elevated levels of Ni. We also found unexpectedly higher concentrations of metals in "consolidated tailings" waste materials, potentially due to the use of oil sands-produced gypsum, and higher background concentration of elements in the sediment used in the controls. A trend of higher concentrations of V, Ni, La, and Y was present in the tissues of the colonizing macrophytic alga Chara spp. Aeshnid dragonflies may also be accumulating V. These results indicate that the trace metals present in some oil sands waste materials could be taken up by aquatic macro-algae and some wetland invertebrates if these materials are included in reclaimed wetlands.