Structural and functional responses of periphyton and macroinvertebrate communities to ferric Fe, Cu, and Zn in stream mesocosms

Development of Multiple Linear Regression Models for Predicting Chronic Iron Toxicity to Aquatic Organisms

We developed multiple linear regression (MLR) models for predicting iron (Fe) toxicity to aquatic organisms for use in deriving site-specific water quality guidelines (WQGs). The effects of dissolved organic carbon (DOC), hardness, and pH on Fe toxicity to three representative taxa (Ceriodaphnia dubia, Pimephales promelas, and Raphidocelis subcapitata) were evaluated. Both DOC and pH were identified as toxicity-modifying factors (TMFs) for P. promelas and R. subcapitata, whereas only DOC was a TMF for C. dubia. The MLR models based on effective concentration 10% and 20% values were developed and performed reasonably well, with adjusted R² of 0.68-0.89 across all species and statistical endpoints. Differences among species in the MLR models precluded development of a pooled model. Instead, the species-specific models were assumed to be representative of invertebrates, fish, and algae and were applied accordingly to normalize toxicity data. The species sensitivity distribution (SSD) included standard laboratory toxicity data and effects data from mesocosm experiments on aquatic insects, with aquatic insects being the predominant taxa in the lowest quartile of the SSD. Using the European Union approach for deriving WQGs, application of MLR models to this SSD resulted in WQGs ranging from 114 to 765 μg l^-1 Fe across the TMF conditions evaluated (DOC: 0.5-10 mg l^-1 ; pH: 6.0-8.4), with slightly higher WQGs (199-910 μg l^-1 ) derived using the US Environmental Protection Agency (USEPA) methodology. An important uncertainty in these derivations is the applicability of the C. dubia MLR model (no pH parameter) to aquatic insects, and understanding the pH sensitivity of aquatic insects to Fe toxicity is a research priority. An Excel-based tool for calculating Fe WQGs using both European Union and USEPA approaches across a range of TMF conditions is provided. Environ Toxicol Chem 2023;00:1-15. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Drivers of aquatic macroinvertebrate communities in a Ramsar declared wetland system

Wetlands in the Global South are under increasing pressure due to multiple stressors associated with global change. Water and sediment quality assessments, as well as biomonitoring using macroinvertebrate communities, are fundamental tools for informing wetland condition and management strategies. Here, we examine water and sediment parameters affecting aquatic macroinvertebrates in Nlyslvey Wetland, Limpopo Province, South Africa. Water quality, sediments, fish and macroinvertebrate community data were collected across three seasons (hot-dry, hot-wet, cool-dry) from five sites. Baetidae, Corixidae, Coenogrionidae, Dytiscidae and Physidae were the most abundant and dominant families, with functional feeding group (FFG) ratios indicating that all sites were strongly autotrophic, had high predator-prey ratios, few shredders and had a stable substrate across seasons. Fish abundances increased significantly towards the cool-dry season. Based on redundancy analysis, P, Ca, pH, Cu and Na were strongly positively associated with macroinvertebrates, including Physidae, Corixidae, Planorbidae, Ostracoda, Potamonautidae and Hydropyschidae; turbidity and sulphur were associated with Dytiscidae, Oligochaetae, Libellulidae, Gerridae and Dixidae; and fish abundance, Fe, oxygen reduction potential and total dissolved solids were negatively associated with Baetidae, Belostomatidae, Hydrophilidae and Leptoceridae. Therefore, these variables accounted for high levels of variation in macroinvertebrate families, with the cool-dry season clearly distinguished from the hot-wet and hot-dry seasons according to functional feeding groups. Being a protected area, this information could provide a useful baseline for further studies into wetlands in the region subject to greater anthropogenic stresses, as well as future studies in this Ramsar site. Further studies are required to assess the importance of environmental factors influencing the richness and distribution of macroinvertebrate communities in wetlands under growing anthropogenic pressures.

Contaminant Subsidies to Riparian Food Webs in Appalachian Streams Impacted by Mountaintop Removal Coal Mining

Selenium is highly elevated in Appalachian streams and stream organisms that receive alkaline mine drainage from mountaintop removal coal mining compared to unimpacted streams in the region. Adult aquatic insects can be important vectors of waterborne contaminants to riparian food webs, yet pathways of Se transport and exposure of riparian organisms are poorly characterized. We investigated Se concentrations in stream and riparian organisms to determine whether mining extent increased Se uptake in stream biofilms and insects and if these insects were effective Se biovectors to riparian spiders. Biofilm Se concentration increased (p = 0.006) with mining extent, reaching a maximum value of 16.5 μg/g of dw. Insect and spider Se increased with biofilm Se (p = 0.004, p = 0.003), reaching 95 and 26 μg/g of dw, respectively, in mining-impacted streams. Adult insect biomass was not related to mining extent or Se concentrations in biofilm. Even though Se concentrations in aquatic insects were significantly and positively related to mining extent, aquatic insect Se flux was not associated with mining extent because the mass of emerging insects did not change appreciably over the mining gradient. Insect and spider Se concentrations were among the highest reported in the literature, regularly exceeding the bird Se dietary risk threshold of 5 μg/g of dw. Risks of Se exposure and toxicity related to mining are thus not constrained to aquatic systems but extend to terrestrial habitats and food webs.

Context-Dependent Responses of Aquatic Insects to Metals and Metal Mixtures: A Quantitative Analysis Summarizing 24 Yr of Stream Mesocosm Experiments

Modernizing water quality criteria to predict how contaminants affect natural aquatic communities requires that we utilize data obtained across multiple lines of evidence, including laboratory, mesocosm, and field studies. We report the results of 29 mesocosm experiments conducted from 1994 to 2017 at the Colorado State University Stream Research Laboratory (Fort Collins, CO, USA). The primary goal of the present study was to quantify responses of aquatic insect communities collected from 8 different locations to different combinations of cadmium (Cd), copper (Cu), iron (Fe), and zinc (Zn). Treatments that included Cu or Fe, either alone or in combination with other metals, were especially toxic to aquatic insects. The results showed that effects of metals were context dependent and varied significantly among the 8 sites where communities were collected. In particular, effects on communities from smaller streams were significantly greater than those from larger streams. Our analyses also showed that several morphological (body size, shape, gills, degree of sclerotization) and life history (voltinism) traits were significantly correlated with sensitivity to metals. Across all taxa and experiments, aquatic insects broadly classified as small (maximum body length <8 mm) were significantly more sensitive to metals than medium or large individuals. These findings demonstrate the advantages of integrating results of mesocosm experiments with species traits to develop a mechanistic understanding of biotic and abiotic factors that influence community responses to contaminants. Environ Toxicol Chem 2019;38:2486-2496. © 2019 SETAC.

Substratum-associated microbiota

This survey of 2018 literature on substratum-associated microbiota presents brief highlights on research findings from primarily freshwaters, but includes those from a variety of aquatic ecosystems. Coverage of topics associated with benthic algae and cyanobacteria, though not comprehensive, includes new methods, taxa new to science, nutrient dynamics, trophic interactions, herbicides and other pollutants, metal contaminants, nuisance, bloom-forming and harmful algae, bioassessment, and bioremediation. Coverage of bacteria, also not comprehensive, focused on methylation of mercury, metal contamination, toxins, and other environmental pollutants, including oil, as well as the use of benthic bacteria as bioindicators, in bioassessment tools and in biomonitoring. Additionally, we cover trends in recent and emerging topics on substratum-associated microbiota of relevance to the Water Environment Federation. PRACTITIONER POINTS: This review of literature from 2018 on substratum-associated microbiota presents highlights of findings on algae, cyanobacteria, and bacteria from primarily freshwaters. Topics covered that focus on algae and cyanobacteria include findings on new methods, taxa new to science, nutrient dynamics, trophic interactions, herbicides and other pollutants, metal contaminants, nuisance, bloomforming and harmful algae, bioassessment, and bioremediation. Topics covered that focus on bacteria include findings on methylation of mercury, metal contamination, toxins and other environmental pollutants, including oil, as well as the us e of benthic bacteria as bioindicators, in bioassessment tools and in biomonitoring. A brief presentation of new, noteworthy and emerging topics on substratum-associated microbiota, build on those from 2017, to highlight those of particular relevance to the Water Environment Federation.

Indirect Effects of Iron Oxide on Stream Benthic Communities: Capturing Ecological Complexity with Controlled Mesocosm Experiments

Ferric iron (Fe(III)) oxyhydroxides commonly precipitate at neutral pH and in highly oxygenated conditions in waterways receiving acid mine drainage, degrading stream benthic communities by smothering of habitat, primary producers, and aquatic invertebrates. Stream mesocosms were used to expose naturally colonized benthic communities to a gradient of ferric Fe (0-15 mg/L) for 14 days to estimate the effects of Fe precipitates on primary production, larval and emerging adult aquatic insects, and the macroinvertebrate community structure. Community composition was significantly altered at concentrations near or below the US Environmental Protection Agency chronic Fe criterion (1.0 mg/L). Iron exposure significantly decreased larval and emerging adult abundances of Baetidae (mayfly) and Chironomidae (Diptera); however, while Simuliidae (Diptera) larvae were not reduced by the Fe treatments, abundance of emerged adults significantly decreased. Iron substantially decreased the colonization biomass of green algae and diatoms, with estimated EC₂₀ values well below the Fe criterion. In contrast, cyanobacteria were stimulated with increasing Fe concentration. By integrating environmentally realistic exposure conditions to native benthic communities that have complex structural and functional responses, the ability to predict the effects of Fe in the field is improved. Traditional toxicity testing methodologies were not developed to evaluate indirect effects of contaminants, and modernized approaches such as community mesocosm experiments better characterize and predict responses in aquatic ecosystems outside the laboratory. Therefore, the development of water quality standards would benefit by including mesocosm testing results.

Host-parasite interaction as a toxicity test endpoint using asymmetrical exposures

Interspecific relationships frequently determine the effect a pollutant can have on an organism, and this is especially true in closely interacting species such as hosts and parasites. The high spatial and temporal variability of contaminant concentrations combined with the movement of aquatic biota can further influence the consequences that are associated with contamination. We used a full factorial design for the exposed and unexposed partners of the relationship between the parasitic larvae (glochidia) of the European freshwater mussel (Anodonta anatina) and its host fish (Squalius cephalus) to identify the sources of variation in the sublethal endpoints of species interaction (the intensity of parasite attachment, the spatial position of glochidia on the host body, and encapsulation success). We used the water-borne human pharmaceutical compounds methamphetamine (a central nervous system stimulant) and tramadol (an opioid) at environmentally relevant concentrations (˜ 6.7 and 3.8 nmol L^-1 of methamphetamine and tramadol, respectively) as a proxy for contaminant exposure because these compounds are emerging aquatic stressors that are known for high spatial and temporal variability in their detected concentration levels. The relationship between the bivalve and the fish species was influenced by the preceding contact with both methamphetamine and tramadol, but this effect was highly asymmetric. Our experimental design enabled us to identify the specific changes in the relationship outcome that are elicited by the exposure of individual partners, such as the significant increase in glochidia infection success rate from 59.6 ± 3.9% to 78.7 ± 2.8% (means ± s.e.) that was associated with host exposure to methamphetamine. Additionally, the significant interaction effect of the exposure was demonstrated by the lowered proportion of glochidia attached to gills after the coexposure of both partners to tramadol. The impact of pharmaceuticals on wild aquatic host-parasite relationships provides an example of the risks that are associated with the unintentional discharge of biologically active compounds into freshwater habitats. Given the increasing evidence showing the ecological impact of waste pharmaceuticals, the use of multitrophic interaction endpoints after joint and unilateral exposures provides an important step towards the realistic risk assessment of these compounds.

Chronic Toxicity of Ferric Iron for North American Aquatic Organisms: Derivation of a Chronic Water Quality Criterion Using Single Species and Mesocosm Data

Iron is a common pollutant in waters near coal and hard rock mine disturbances. The current 1000 µg/L total recoverable chronic criterion for iron (Fe) for protection of aquatic life in the United States was developed using very limited data in 1976 and has not been revised since. To develop a more scientifically based criterion, several chronic laboratory toxicity experiments (> 30 days) were conducted with ferric Fe at circumneutral pH on a taxonomically diverse group of organisms including brown trout (Salmo trutta), mountain whitefish (Prosopium williamsoni), boreal toad tadpoles (Bufo boreas), the oligochaete worm Lumbriculus variegatus, the mayfly Hexagenia limbata, and the planarian Dugesia dorotocephala. Results of these tests and those of previously published toxicity data were used to derive a Final Chronic Value (FCV) of 499 µg/L by using the US Environmental Protection Agency's recommended methods based on single species toxicity tests. In addition to single species toxicity tests, ferric Fe toxicity experiments (10 days) were performed on mesocosms containing naturally colonized communities of benthic macroinvertebrates. Fourteen genera in the mesocosms occurred at sufficient densities to estimate an iron concentration resulting in 20% reduction in abundance (EC₂₀). Three of these taxa had EC₂₀s less than the FCV of 499 µg/L derived from single species tests: the mayfly Epeorus sp. (335 µg/L), the caddisfly Micrasema sp. (356 µg/L), and midge Tanytarsini (234 µg/L). When mesocosm results were included, the FCV was lowered to 251 µg/L. These findings support the suggestion that modernization of water quality criteria should include data generated from mesocosm experiments and other lines of evidence.