Anthropogenic and natural sources of acidity and metals and their influence on the structure of stream food webs

Soil contamination with permissible levels of lead negatively affects the community of plant-associated insects: A case of study with kale

This study investigated whether lead (Pb), at concentrations allowed for soil, affects the community of insects that live in the aerial part of plants. We evaluated the effect of Pb concentrations on accumulated species richness, composition, and abundance of different functional groups of insects. Kale plants were grown in soil experimentally contaminated with four concentrations of lead nitrate: 0 (control), 144 (T1), 360 (T2), and 600 (T3) mg/kg of soil. The experiment was conducted in an open greenhouse for the natural colonization of insects. Insects were collected twice using trap bags attached to the plant leaf and by direct removal. The concentration of Pb in the stem and leaf samples increased with the increased soil contamination, even showing values above the limit allowed by the legislation for this plant species. Control plants showed a higher richness of accumulated insect species. In addition, the treatments had an effect on the community composition, in which Diaeretiella rapae (primary parasitoid) was found as an indicator of the control + T1 treatments and the top species Pachyneuron sp. (parasitoid of predators) was associated with the control. The abundance of chewing and sucking herbivores, their respective parasitoids, predators, and parasitoids of predators were negatively affected. Hyperparasitoid abundance was not affected, but their accumulated species richness was. This study was innovative in demonstrating that soil contamination by different concentrations of a heavy metal (Pb) can negatively affect the community of plant-associated insects, even at concentrations allowed for soil, reflecting possible damage to the ecosystem.

Using Periphyton Assemblage and Water Quality Variables to Assess the Ecological Recovery of an Ecologically Engineered Wetland Affected by Acid Mine Drainage after a Dry Spell

The Grootspruit valley bottom wetland in South Africa, due to the impact of acid mine drainage (AMD) from an abandoned coal mine, was severely degraded before ecologically engineered interventions, as a passive treatment process, in 2014. The surface water flow of the wetland was redirected using concrete structures to enlarge the surface area of the wetland by 9.4 ha and to optimize passive treatment. Although the ecologically engineered interventions showed an improvement in water quality after the rewetting of the enlarged wetland areas, the 2016 drought had a devastating effect on the wetland’s water quality. Limited natural removal of metals and sulfate concentrations by the wetland occurred during the 2016 drought, when compared with the 2015 pre-drought conditions. This period showed higher concentrations of metals, sulfate (SO42−), and electrical conductivity (EC) associated with the acidic surface water. Of particular interest was an observation of a substantial shift in pollutant-tolerant algae species in the ecologically engineered wetland outflow between the years 2015 and 2016. During the dry spell period of 2016, the diatoms Gyrosigma rautenbachiae (Cholnoky), Craticula buderi (Brebisson), and Klebsormidium acidophilum (Noris) were observed at the outflow. The latter species were not observed during the wetland surveys of 2015, before the dry spell. From late 2017 onwards, after the drought, environmental conditions started improving. In 2018, periphyton indicator species and the surface water quality were comparable to the wetland’s recorded status pre-2016. The study revealed not only a regime shift, but also an ecological function loss during the drought period of 2016, followed by recovery after the dry spell. A distinct reduction in SO42−, sodium (Na), magnesium (Mg), EC, manganese (Mn), iron (Fe), silicon (Si), aluminum (Al), and pH, following the 2016 drought, highlights the utilization of water quality variables to not only assess the passive treatment responses of an ecologically engineered wetland, but also the progress relating to ecological recovery.

Interactive effects of freshwater acidification and selenium pollution on biochemical changes and neurotoxicity in Oreochromis mossambicus

Effect of selenium and acidification in freshwater environment was assessed solitary but no reports are available on the impacts of both factors act together. In the present study, effects of combined simultaneous exposure to selenium (Se) and low pH were assessed in Mozambique tilapia, Oreochromis mossambicus. Responses were measured based on antioxidant defenses (enzymatic SOD, CAT, GPx and non-enzymatic GSH), biotransformation enzyme (GST), metallothionein levels (MT), oxidative damage (LPO, CP), Na⁺/K⁺-ATPase (NKA) activity in gills and liver tissues and neurotoxicity (acetylcholinesterase, AChE) response in brain tissue. Fish were exposed to combined treatment at different pH levels (7.5, control (optimum pH for tilapia growth); 5.5, low pH) and Se concentrations (0, 10, and 100 μg L^-1). Toxicity levels of Se were not significantly different under control and low pH indicating that pH did not affect Se toxicity. Levels of GSH and MT were enhanced in Se-exposed fish at both pH. Combined effects of high Se concentration and low pH decreased SOD and CAT activities and increased those of GPx and GST. However, organisms were not able to prevent cellular damage (LPO and CP), indicating a condition of oxidative stress. Furthermore, inhibition of Na⁺/K⁺-ATPase activity was showed. Additionally, neurotoxicity effect was observed by inhibition of cholinesterase activity in organisms exposed to Se at both pH conditions. As a result, the combined stress of selenium and freshwater acidification has a slight impact on antioxidant defense mechanisms while significantly inhibiting cholinesterase and Na+/K + -ATPase activity in fish. The mechanisms of freshwater acidification mediating the toxic effects of trace non-metal element on freshwater fish need to investigate further.

Passive Treatment for Acid Mine Drainage Partially Restores Microbial Community Structure in Different Stream Habitats

The assessment of the degree to which biological communities in streams impaired by acid mine drainage (AMD) are restored by passive treatment has focused primarily on eukaryotic-cell organisms and microbial processes. The responses of microbial community structure to passive treatment have received much less attention, even though functional processes such as nutrient cycling and organic matter decomposition depend on taxonomic composition. Our objective was to determine the degree to which passive treatment restored microbial communities in three types of habitats: aqueous, leaf, and sediment. To assess their recovery, we compared the community composition in these habitats based on 16S rRNA gene sequencing at three different stream sites: an untreated AMD site (U), a remediated site below AMD passive treatment (T), and an unimpaired reference site (R). The acidity, conductivity, and soluble metal concentrations at T were found to be elevated compared to R, but generally 1–2 orders of magnitude less than at U. Microbial community composition was found to be synergistically affected by habitat type and AMD impact, with the similarity among communities in the three habitats increasing with the severity of the AMD. Sediment- and leaf-associated microbial communities at U were characterized by taxa that are tolerant to severe AMD. The absence of the nitrogen oxidizing bacterium Nitrospira in sediment communities at T and U was found to correspond to higher NH4+ concentrations compared to R, possibly because of the presence of iron oxyhydroxide precipitate. In contrast, the microbial composition was found to be similar between the T and R sites for both aqueous and leaf communities, indicating that passive treatment was more able to restore these communities to the reference condition than sediment communities. The remediation of AMD streams should consider the habitat-specific responses of microbial community composition and be guided by future studies that empirically couple changes in taxonomic composition to measured functional processes.

Ecotoxicity assessment of a molybdenum mining effluent using acute lethal, oxidative stress, and osmoregulatory endpoints in zebrafish (Danio rerio)

The present study investigated the ecotoxicity of raw mining effluent from the largest molybdenum (Mo) open-pit mine in the Qinling mountains, China, and the treated effluent with neutralization and coagulation/adsorption processes, using zebrafish (Danio rerio). The results showed the following: (1) the mining effluent is acid mine drainage (AMD) and is highly toxic to zebrafish with a 96-h median lethal concentration (LC₅₀) of 3.80% (volume percentage) of the raw effluent; (2) sublethal concentrations of the raw effluent (1/50, 1/10, and 1/2 96-h LC₅₀) induced oxidative stress and osmoregulatory impairment, as reflected by the alterations in activities of superoxide dismutase and catalase and contents of malondialdehyde, and inhibition of Na⁺, K⁺-ATPase activity in gills and muscle after 28 days of sub-chronic exposure when compared with the unexposed group; and (3) the treatment of the raw effluent with neutralizer (NaOH) and adsorbent activated carbon reduced the acute lethal effect of raw effluent. The used endpoints including acute lethal and biochemical parameters related to oxidative stress and osmoregulatory impairment in zebrafish are cost-effective for toxicity assessment of AMD like the studied Mo mining effluent. Mining effluent management strategies extended by these results, i.e., the restriction of discharging raw and diluted effluent to adjacent waterways and the introduction of bio-monitoring system across all mining drainages in this area, were also proposed and discussed.

Physiological responses of three mono-species phototrophic biofilms exposed to copper and zinc

In freshwater ecosystem, phototrophic biofilms play a crucial role through adsorption and sequestration of organic and inorganic pollutants. However, extracellular polymeric substance (EPS) secretion by phototrophic biofilms exposed to metals is poorly documented. This work evaluated the physiological responses of phototrophic biofilms by exposing three microorganisms (cyanobacterium Phormidium autumnale, diatom Nitzschia palea and green alga Uronema confervicolum) to 20 and 200 μg L^-1 of Cu or 60 and 600 μg L^-1 of Zn, both individually and in combination. Analysis of metal effects on algal biomass and photosynthetic efficiency showed that metals were toxic at higher concentrations for these two parameters together and that all the strains were more sensitive to Cu than to Zn. U. confervicolum was the most impacted in terms of growth, while P. autumnale was the most impacted in terms of photosynthetic efficiency. In consequence to metal exposure at higher concentrations (Cu200, Zn600 and Cu200Zn600), a higher EPS production was measured in diatom and cyanobacterium biofilms, essentially caused by an overproduction of protein-like polymers. On the other hand, the amount of secreted polysaccharides decreased during metal exposure of the diatom and green alga biofilms. Size exclusion chromatography revealed specific EPS molecular fingerprints in P. autumnale and N. palea biofilms that have secreted different protein-like polymers during their development in the presence of Zn600. These proteins were not detected in the presence of Cu200 despite an increase of proteins in the EPS extracts compared to the control. These results highlight interesting divergent responses between the three mono-species biofilms and suggest that increasing protein production in EPS biofilms may be a fingerprint of natural biofilm against metal pollutants in freshwater rivers.

Toward Sustainable Environmental Quality: Priority Research Questions for North America

Anticipating, identifying, and prioritizing strategic needs represent essential activities by research organizations. Decided benefits emerge when these pursuits engage globally important environment and health goals, including the United Nations Sustainable Development Goals. To this end, horizon scanning efforts can facilitate identification of specific research needs to address grand challenges. We report and discuss 40 priority research questions following engagement of scientists and engineers in North America. These timely questions identify the importance of stimulating innovation and developing new methods, tools, and concepts in environmental chemistry and toxicology to improve assessment and management of chemical contaminants and other diverse environmental stressors. Grand challenges to achieving sustainable management of the environment are becoming increasingly complex and structured by global megatrends, which collectively challenge existing sustainable environmental quality efforts. Transdisciplinary, systems-based approaches will be required to define and avoid adverse biological effects across temporal and spatial gradients. Similarly, coordinated research activities among organizations within and among countries are necessary to address the priority research needs reported here. Acquiring answers to these 40 research questions will not be trivial, but doing so promises to advance sustainable environmental quality in the 21st century. Environ Toxicol Chem 2019;38:1606-1624. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Effects of secondary salinisation on macroinvertebrate functional traits in surface mining-contaminated streams, and recovery potential

Secondary salinisation has become a hot spot internationally due to its adverse effects on freshwater ecosystems. Although its effects on ecosystem patterns has been broadly studied, its potential effect on ecosystem functions, in particular on the functional traits of freshwater organisms, and functional trait recovery are largely unknown. In this study, we conducted a field investigation at 405 sample sites from May 2009 to July 2016 in surface mining-contaminated streams, in order to evaluate the influence of secondary salinisation on macroinvertebrate functional traits and the recovery potential of dominant functional traits. Results of univariate models showed that sensitive, very tolerant, gill-breathers, cutaneous-breathers, shredders, predators and gatherers were the most responsive indicators to enhanced specific conductivity and sulfate loadings with sensitive, gill-breathers, shredders and predators demonstrating a reduction in abundance, whereas cutaneous-breathers and gatherers exhibiting an increase. Complicated relationships among different species indicated that co-exclusions would not occur because all macroinvertebrate taxa exhibited positive correlations. Results of relative recovery potential showed that omnivores and gatherers recovered quickly following improvements in water quality, whereas gill-breathers, pneumostome-breathers, filterers and scrapers would be expected to recover slowly due to their sensitivity to both specific conductivity and sulfate and low drift propensity. Overall, secondary salinisation has posed severely ecological risks to macroinvertebrate functional attributes in surface mining-contaminated streams, and their effects should be considered in future conservation plans.

Long-term effects and recovery of streams from acid mine drainage and evaluation of toxic metal threshold ranges for macroinvertebrate community reassembly

Monitoring of benthic invertebrates in streams receiving acidic metal-contaminated water over an 18-yr period revealed both degraded conditions and recovery along a network of downstream locations. Compared with reference streams, and over the course of clean-up remediation efforts below an abandoned open-pit sulfur mine in the central Sierra Nevada of California, improving water quality was accompanied by recovery of benthic communities at some sites. Years of high flow resulted in degraded biological status when acid mine drainage capture was incomplete and metal loading had increased with runoff. Seasonal patterns of recovery evident in the fall after the summer treatment season reverted in the next spring after overwinter periods when sources were not captured. As the metal load has been reduced, phased recovery of community structure, function, and similarity progressed toward that of reference assemblage taxonomic composition. From impacted communities dominated by relatively tolerant midges, reassembly involved an increase in density, return of long-lived taxa, an increased ratio of sensitive-to-tolerant forms, then overall diversity and community composition, and eventually large predators and grazers reappearing along with mayfly, stonefly, and caddisfly richness. Threshold effect levels defined using several analysis methods showed that the response range of biological indicators corresponds to US Environmental Protection Agency guidelines of predicted effects utilizing cumulative criterion units (CCUs) of metal toxicity (i.e., CCU ∼ 1). All sites have shown improved function with increased density of some or all trophic groups over time. Although recovery is progressing, year-around treatment may be necessary to fully restore biological integrity in streams nearest the mine. Environ Toxicol Chem 2018;37:2575-2592. © 2018 SETAC.

A freshwater diatom challenged by Zn: Biochemical, physiological and metabolomic responses of Tabellaria flocculosa(Roth) Kützing

Freshwater ecosystems are under threatening anthropogenic pressures worldwide, namely by metals. Diatoms are used as water quality indicators, but the influence of micronutrients such as Zn and its impacts are poorly understood. Thus, our study aimed to elucidate the tolerance level, the cellular targets and the responses to counteract Zn toxicity of freshwater diatoms by exposing Tabellaria flocculosa, isolated from a Zn contaminated stream. Biochemical, physiological and metabolomic approaches were used. It was demonstrated that Zn is toxic to T. flocculosa at concentrations occurring in contaminated environments. At low stress (30 μg Zn/L) few alterations in the metabolome were observed, but the enzymatic (SOD, CAT) and molecular (GSH, GSSG) antioxidant systems were induced, protecting cells from oxidative stress. At moderate stress (500 μg Zn/L) the main changes occurred in the metabolome (increases in fatty acids, amino acids, terpenoids, glycerol and phosphate, decreases in sucrose and lumichrome) with a moderate increase in cell damage (LPO and PC). The concerted action of all these mechanisms resulted in a non-significant decrease of growth, explaining the survival of this T. flocculosa strain in an environment with this Zn concentration. At the highest stress level (1000 μg Zn/L) the metabolome was identical to 500 μg Zn/L, and the induction of antioxidant systems and extracellular ion chelation (exopolysaccharides, frustulins) were the main responses to the increase of Zn toxicity. However, these mechanisms were unable to effectively abrogate cellular damage and growth reduction was observed. Moreover, the decrease in sucrose and especially in lumichrome should be tested as new specific markers of Zn toxicity. The information obtained in this study can assist in environmental risk assessment policies, support the prediction of diatom behaviour in highly impacted Zn environments, such as mining scenarios, and may help develop new indices, which include alterations induced by metals.

Assessing Cu impacts on freshwater diatoms: biochemical and metabolomic responses of Tabellaria flocculosa (Roth) Kützing

Metals are a recognised threat to aquatic organisms but the impact of metals such as copper (Cu) on benthic freshwater diatoms is poorly understood, even if diatoms are commonly used as water quality indicators. Our study aimed to elucidate the cellular targets of Cu toxicity and the mechanisms cells resort to counteract toxicity and to increase tolerance to Cu. A concerted approach analysing the biochemical, physiological and metabolome alterations in diatom cells was conducted by exposing the freshwater diatom Tabellaria flocculosa to 0, 0.3, 6 and 10μgCu/L. Cu was already toxic to T. flocculosa at concentrations common in environments and which are not usually considered to be contaminated (0.3μgCu/L). Under Cu impact, the metabolome of T. flocculosa changed significantly, especially at high concentrations (6 and 10μgCu/L). Cu toxicity was counteracted by increasing extracellular immobilization (EPS, frustulins), antioxidant (SOD, CAT) and detoxifying (GSTs) enzymes activity and low molecular weight antioxidants (GSH). These mechanisms were fuelled by higher energy production (increased ETS activity). At the highest Cu concentration (10μg/L), these processes were specially enhanced in an attempt to restrain the oxidative stress generated by high intracellular Cu concentrations. However, these mechanisms were not able to fully protect cells, and damage in membranes and proteins increased. Moreover, the decrease of hydroxylamine and unsaturated fatty acids and the increase of saturated fatty acids, 2-palmitoylglycerol, glycerol and diterpenoid compounds should be tested as new specific markers of Cu toxicity in future studies. This information can support the prediction of diatom behaviour in different Cu contamination levels, including highly impacted environments, such as mining scenarios, and may assist in environmental risk assessment policies and restoration programs.

Dry conditions disrupt terrestrial-aquatic linkages in northern catchments

Aquatic ecosystems depend on terrestrial organic matter (tOM) to regulate many functions, such as food web production and water quality, but an increasing frequency and intensity of drought across northern ecosystems is threatening to disrupt this important connection. Dry conditions reduce tOM export and can also oxidize wetland soils and release stored contaminants into stream flow after rainfall. Here, we test whether these disruptions to terrestrial-aquatic linkages occur during mild summer drought and whether this affects biota across 43 littoral zone sites in 11 lakes. We use copper (Cu) and nickel (Ni) as representative contaminants, and measure abundances of Hyalella azteca, a widespread indicator of ecosystem condition and food web production. We found that tOM concentrations were reduced but correlations with organic soils (wetlands and riparian forests) persisted during mild drought and were sufficient to suppress labile Cu concentrations. Wetlands, however, also became a source of labile Ni to littoral zones, which was linked to reduced abundances of the amphipod H. azteca, on average by up to 70 times across the range of observed Ni concentrations. This reveals a duality in the functional linkage of organic soils to aquatic ecosystems whereby they can help buffer the effects of hydrologic disconnection between catchments and lakes but at the cost of biogeochemical changes that release stored contaminants. As evidence of the toxicity of trace contaminant concentrations and their global dispersion grows, sustaining links among forests, organic soils and aquatic ecosystems in a changing climate will become increasingly important.

Identifying Catchment-Scale Predictors of Coal Mining Impacts on New Zealand Stream Communities

Coal mining activities can have severe and long-term impacts on freshwater ecosystems. At the individual stream scale, these impacts have been well studied; however, few attempts have been made to determine the predictors of mine impacts at a regional scale. We investigated whether catchment-scale measures of mining impacts could be used to predict biological responses. We collated data from multiple studies and analyzed algae, benthic invertebrate, and fish community data from 186 stream sites, including un-mined streams, and those associated with 620 mines on the West Coast of the South Island, New Zealand. Algal, invertebrate, and fish richness responded to mine impacts and were significantly higher in un-mined compared to mine-impacted streams. Changes in community composition toward more acid- and metal-tolerant species were evident for algae and invertebrates, whereas changes in fish communities were significant and driven by a loss of nonmigratory native species. Consistent catchment-scale predictors of mining activities affecting biota included the time post mining (years), mining density (the number of mines upstream per catchment area), and mining intensity (tons of coal production per catchment area). Mining was associated with a decline in stream biodiversity irrespective of catchment size, and recovery was not evident until at least 30 years after mining activities have ceased. These catchment-scale predictors can provide managers and regulators with practical metrics to focus on management and remediation decisions.

Long-term chemical and biological improvement in an acid mine drainage-impacted watershed

Acid mine drainage (AMD) is a common result of coal and metal mining worldwide caused by weathering of metal sulfides exposed during mining. AMD typically results in low-pH, high-metal, high-conductivity water that does not support aquatic life. Chemical water quality improvement does not necessarily lead to rapid biological recovery. Little Raccoon Creek, a major tributary to Raccoon Creek in the Western Allegheny Plateau of Ohio, drains 401 km(2), has a legacy of AMD that stems from mining activities over more than a century. Since 1999, seven major passive treatments systems have been installed in the watershed to a total of over $6.5 million. This study analyzes the hourly water quality data collected at a United States Geological Survey gage station alongside trends in fish and macroinvertebrate communities. Both fish and macroinvertebrate communities have shown a statistically significant improvement in the lower reaches of Little Raccoon Creek since treatment began. Long-term chemical monitoring shows a significant increase in pH, but no significant change in conductivity. The conductivity data is well correlated with sulfate concentrations and discharge, while the pH is well correlated with net  alkalinity data, but not with discharge. Significant investment in passive treatment systems and land reclamation has decreased the percent occurrence of pH measurements below the target of 6.5 and has led to recovery of both fish and macroinvertebrate communities in the downstream reaches of Little Raccoon Creek. Long-term monitoring has proven to be a valuable tool to assess success of a high-cost remediation program.

Use of leaf litter breakdown and macroinvertebrates to evaluate gradient of recovery in an acid mine impacted stream remediated with an active alkaline doser

The spatial congruence of chemical and biological recovery along an 18-km acid mine impaired stream was examined to evaluate the efficacy of treatment with an alkaline doser. Two methods were used to evaluate biological recovery: the biological structure of the benthic macroinvertebrate community and several ecosystem processing measures (leaf litter breakdown, microbial respiration rates) along the gradient of improved water chemistry. We found that the doser successfully reduced the acidity and lowered dissolved metals (Al, Fe, and Mn), but downstream improvements were not linear. Water chemistry was more variable, and precipitated metals were elevated in a 3-5-km "mixing zone" immediately downstream of the doser, then stabilized into a "recovery zone" 10-18 km below the doser. Macroinvertebrate communities exhibited a longitudinal pattern of recovery, but it did not exactly match the water chemistry gradient Taxonomic richness (number of families) recovered about 6.5 km downstream of the doser, while total abundance and % EPT taxa recovery were incomplete except at the most downstream site, 18 km away. The functional measures of ecosystem processes (leaf litter breakdown, microbial respiration of conditioned leaves, and shredder biomass) closely matched the measures of community structure and also showed a more modest longitudinal trend of biological recovery than expected based on pH and alkalinity. The measures of microbial respiration had added diagnostic value and indicated that biological recovery downstream of the doser is limited by factors other than habitat and acidity/alkalinity, perhaps episodes of AMD and/or impaired energy/nutrient inputs. A better understanding of the factors that govern spatial and temporal variations in acid mine contaminants, especially episodic events, will improve our ability to predict biological recovery after remediation.

Are biological communities in naturally unproductive streams resistant to additional anthropogenic stressors?

Studies on the interactive responses to multiple simultaneously acting stressors have focused on individual or population-level responses in laboratory microcosms, while field-based studies on community-level responses are rare. We examined the influence of a natural (non-anthropogenic acidity) vs. human-induced stress (land drainage) and their interaction on species richness and spatial turnover (β diversity) of stream diatom, bryophyte, and benthic invertebrate communities. Our four stream categories were: circumneutral reference, circumneutral impacted, naturally acidic, and naturally acidic impacted streams. We expected the most sensitive species to be present only in the circumneutral reference streams. Therefore, species richness should be highest in these streams and lowest in the naturally acidic streams additionally stressed by forest drainage. Alternatively, communities in acidic streams may consist of the most tolerant taxa that are unaffected by further stressors, species richness in these streams remaining unaffected by drainage. We also expected spatial turnover to be highest in the circumneutral near-pristine streams and lowest in the drainage-impacted acidic streams. In all three taxonomic groups, α diversity was lower in the naturally acidic than in circumneutral streams. The additional impact of the anthropogenic stress on species richness varied between groups, having no effect on diatoms, antagonistic effect on bryophytes, and additive effect on invertebrates. We also found differences in how each stressor modified β diversity of each taxonomic group. For diatoms, β diversity showed an overall tendency to decrease with increasing stress level, while bryophyte β diversity responded mainly to forest drainage. Benthic invertebrate β diversity did not differ between treatments. Our results suggest that non-additive effects among stressors need special attention to improve the understanding and management of multifactor responses in streams. Our results also argue for the primacy of a multi-taxon approach to environmental impact detection, and for the inclusion of a wide array of ecological responses, particularly community turnover, in bioassessment programs to detect responses that may go unnoticed by conventional richness-based measures.

Changes in macroinvertebrate community structure provide evidence of neutral mine drainage impacts

Contamination of aquatic environments as a consequence of metal mining is an international issue. Most historic studies have considered the impact of acid mine drainage (pH < 6) on instream communities and comparatively little attention has been given to sites where drainage is typically circum-neutral (6 > pH < 8). Here, the impacts of historic mining activities on the benthic macroinvertebrate community of a circum-neutral river in Central Wales are assessed. Biotic and diversity indices, widely used for biomonitoring purposes, indicate aquatic macroinvertebrate assemblages within the Afon Twymyn to be in a good condition, despite severe metal contamination of bed sediments and river water. However, Canonical Correspondence Analysis identifies differences in community structure between mining impacted and unimpacted reaches of the river associated with chalcophile (Zn, Pb, Cu, Cd) and common (Fe and Mn) metals. Stream pH was not a significant factor structuring the macroinvertebrate community. Widely utilised macroinvertebrate indices failed to identify impacts at the community level because they either seek to identify impacts of a specific contaminant or are dependent on a model community response to a given stress. The nature of metal mine discharges is temporally complex, having highly variable chemical signatures and as a result, care is advised when interpreting and modelling community impacts. The use of standard macroinvertebrate biotic and diversity indices in the context of the EU Water Framework Directive could lead to erroneous classifications of aquatic ecosystem health when used for bio-monitoring rivers affected by neutral mine drainage where other indicators are unavailable.

Epilithic community metabolism as an indicator of impact and recovery in streams affected by acid mine drainage

We measured biomass and metabolism of epilithic communities on five dates in different seasons at four sites in a watershed that has received extensive restoration for acid mine drainage (AMD) through the construction of passive treatment systems. Chlorophyll a biomass and productivity directly corresponded to AMD stress from coal mining. The site downstream of extensive passive treatment had significantly greater biomass and gross primary productivity rates than the site receiving only untreated AMD, but values were below those for two reference sites, indicating incomplete recovery. The degree of difference in these metrics among sites varied seasonally, primarily related to differences in canopy cover changes, but the ranking of sites in terms of stress generally was consistent. Reference sites had a significantly greater chlorophyll a/pheophytin ratio than untreated and treated sites, also indicating AMD stressed the communities. Community respiration was less affected by AMD stress than productivity or chlorophyll a. Productivity measures are not widely used to assess AMD impacts, and have been shown to both increase and decrease with AMD stress. The elimination of herbivores in AMD-impacted streams can increase productivity in the benthic algal community. Our study found productivity decreased with increasing AMD stress. Although sites with AMD stress had reduced herbivore populations, light, nutrients and metal precipitates appear to have limited growth of AMD-tolerant algal taxa. Therefore, it appears changes in food web structure due to AMD stress had less of an effect on epilithic productivity than environmental conditions within the stream.