Impact Of Acid Mine Drainage Research Articles

Development of a diatom index of biotic integrity for acid mine drainage impacted streams

Abstract Acid mine drainage (AMD) resulting from extensive coal mining throughout Appalachia since the 1800s has caused a legacy of severe acid and dissolved metal loads to thousands of stream miles, which has critically impacted aquatic life and ecological attributes. Relationships of diatoms and macroinvertebrates with AMD have been established, but no index specifically designed to quantify AMD impacts using diatoms has been created, nor have the response of multiple organism groups been compared for their utility as indices assessing AMD severity. For the purpose of developing an effective assessment and management strategy for AMD impacted streams, this study created and tested a multi-metric AMD-diatom index of biotic integrity (AMD-DIBI) and compared its response to AMD severity with an already established multi-metric macroinvertebrate community index (ICI). In 2006, 41 sites in southeast Ohio were sampled that represented an AMD impact gradient and non-AMD impacted reference sites. Metrics comprising the AMD-DIBI were selected based on their responsiveness to AMD and nutrient impacts. In the following year, the AMD-DIBI and its metrics were tested on a validation dataset consisting of 18 sites in an AMD impacted watershed. Results indicated a significant correlation between AMD-DIBI and ICI scores, and both indices and all metrics were strongly correlated with water chemistry variables indicative of AMD pollution ( P r 2 = 0.70) and ICI scores (adjusted r 2 = 0.66). Narrative classes (e.g., Poor, Fair, Good, and Excellent) defined by index scores provided effective classifications of AMD severity. When tested on the watershed scale, AMD-DIBI and its metrics very successfully quantified AMD gradients and coal mining impacts as indicated by canonical correspondence analysis. This newly developed AMD-DIBI will be very useful for assessing impairment, sensitivity, and recovery of diatom communities in streams damaged or threatened by coal mining activities. In addition, because the AMD-DIBI was very responsive to a gradient of AMD pollution, it could be used in future studies measuring the long-term status of streams and effectiveness of various remediation methods. This study highlights the responsive power of diatom-based metrics.

Biofilm bacterial community structure in streams affected by acid mine drainage.

We examined the bacterial communities of epilithic biofilms in 17 streams which represented a gradient ranging from relatively pristine streams to streams highly impacted by acid mine drainage (AMD). A combination of automated ribosomal intergenic spacer analysis with multivariate analysis and ordination provided a sensitive, high-throughput method to monitor the impact of AMD on stream bacterial communities. Significant differences in community structure were detected among neutral to alkaline (pH 6.7 to 8.3), acidic (pH 3.9 to 5.7), and very acidic (pH 2.8 to 3.5) streams. DNA sequence analysis revealed that the acidic streams were generally dominated by bacteria related to the iron-oxidizing genus Gallionella, while the organisms in very acidic streams were less diverse and included a high proportion of acidophilic eukaryotes, including taxa related to the algal genera Navicula and Klebsormidium. Despite the presence of high concentrations of dissolved metals (e.g., Al and Zn) and deposits of iron hydroxide in some of the streams studied, pH was the most important determinant of the observed differences in bacterial community variability. These findings confirm that any restoration activities in such systems must focus on dealing with pH as the first priority.

Impact of Acid Mine Drainage (AMD) on Water Quality, Stream Sediments and Periphytic Diatom Communities in the Surrounding Streams of Aljustrel Mining Area (Portugal)

Aljustrel mining area is located in the Iberian Pyrite Belt, one of the greatest concentrations of massive sulphide deposits that extends from Lousal (Portugal) to Aznalcollar (Spain). The surrounding streams, Roxo, Agua Azeda and Agua Forte, are influenced by the erosion of the tailing deposits and the input of acid mine drainage (AMD) from the abandoned Aljustrel pyrite mines, recently reopened in 2007. The purpose of this study was to understand how these adverse conditions influenced the stream sediments, water quality and periphytic diatom communities and establish the pre-restoration local conditions to judge the success of rehabilitation program now under way. For stream sediments, the highest metal concentration samples were found at sites F, G and H. Arsenic, Cu, Fe, Pb and Sb detected concentrations, generally exceeded the probable effect concentration values reaching level 4: the highest toxicity level. In surficial water samples of AMD affected sites (F, G and H), low pH values (1.5 to 3.5) and high metal concentrations of As (6,837 μg L−1), Cd (455 μg L−1), Cu (68,795 μg L−1), Fe (1,262,000 μg L−1), Mn (19,451 μg L−1), Pb (136 μg L−1), and Zn (264,377 μg L−1) were found. In these sites, the diversity index (H′) for diatoms was low (0.6 to 2.8) and the dominant taxa were Eunotia exigua (site F, 33.5%) and Pinnularia acoricola (abundances in sites: F, 86.8%; G, 88.5%; and H, 91.1%). In opposition, in less AMD impacted, H′ was high (1.5 to 4.6) and low metal concentrations and high pH were found. Achnanthidium minutissimum was the dominant taxon in (abundances in sites: A, 76.1% and B, 24.39%). Canonical correspondence analysis showed that spatial variation due to mine influence was more important than seasonal variation, which did not show any pattern.

Environmental Impact on an Arctic Soil–Plant System Resulting from Metals Released from Coal Mine Waste in Svalbard (78° N)

Impact of acid mine drainage (AMD) from a coal mine waste rock pile deposited within a permafrost-affected Arctic ecosystem was investigated near Longyearbyen (Svalbard, 78° N). Analyses included metal concentrations (Al, Fe, Mn, Zn, Ni, Cr, As and Pb) in runoff, soil and plants. It was observed that impacts of AMD, such as plant degradation, were similar to impacts reported from non-arctic ecosystems. It was found that bio-available metal concentrations in soil samples were not useful in assessing potential plant toxicity, as metals were not accumulated in the most impacted area due to low soil pH (pH < 4). Native graminoid plants in the high impacted area showed accumulation of all the investigated elements. Al, Mn and As were found at phyto-toxic concentrations. Metal uptake in two native graminoid plants was studied in the laboratory. Positive correlations were noted between metal concentrations and plant uptake for all metals investigated, except Fe. High Fe concentrations found in plant samples in the impacted area are considered a result of Fe-oxide precipitation (plaque) on leaves during the spring flush when runoff covers the plants. We conclude that the weathering products Al, Mn and Fe induce the largest negative impact on vegetation in the area, and that a major fraction of the annual uptake of metals occurs during spring flushes. During these flushes, metals produced from weathering processes throughout the winter are released in high concentrations, coinciding with low pH values, low infiltration rates due to permafrost and the start of the plant growth season.

Biomonitoring acidic drainage impact in a complex setting using periphyton

Acid mine drainage (AMD) often exerts various environmental pressures on nearby water courses: chemical stress from low pH and dissolved metals; physical stress from metal oxide deposits. Affected streams can thus display a spatially variable combination of stress agents that may complicate its biomonitoring using native communities such as periphyton. Here, we have measured water and periphyton variables in four streams that surround an abandoned copper mine to determine which periphyton attributes consistently detected AMD impact in a complex environmental setting. Seventeen years after the end of commercial exploitation, the abandoned mine still decreases water quality in nearby streams: moderate acidification, very high metal load (Al, Ni, Cu, Zn), and a conspicuous presence of metal oxide deposits with diverse composition. Even under the resultant complex pattern of polluted conditions, periphyton was a reliable bioindicator of AMD. Epilithic diatom taxa tolerant of acidic conditions increased in AMD sites and, at severely impacted locations, species richness decreased. Also, algal biomass may have been negatively affected in some stream reaches affected by metal oxide deposits. Other periphyton attributes (total biomass, diatom diversity) seemed mostly unrelated to AMD. Diatom assemblage composition was the most sensitive and consistent bioindicator of mine drainage; besides, it rendered a biological assessment of AMD impact that largely coincided with the physicochemical evaluation. Still, including other taxonomic (proportion of acid-tolerant diatom species, diatom richness) and non-taxonomic (algal biomass) attributes in the biomonitoring procedure rendered a more comprehensive assessment of the negative consequences generated by AMD.

Comparison of benthic macroinvertebrate indices for the assessment of the impact of acid mine drainage on an Irish river below an abandoned Cu–S mine

A range of macroinvertebrate indices were compared to assess the most appropriate metric for the assessment of acid mine drainage (AMD) in a low alkalinity, highly erosional river in south-east Ireland. Differences were found in the ability of indices to discriminate AMD impact with the Brillouin, BMWP score, Margalef and Shannon Indices the most precise. Taxon richness was also strongly correlated with AMD indicator parameters (e.g. pH alkalinity, sulphate, Zn and Fe) at impacted sites being an equally reliable metric. The response of the community structure to AMD in this river does not fulfil the optimum criteria for either diversity or biological indices, which may explain the variation in the success of different indices seen in this and other studies. The development of indices that model the expected community response to AMD more accurately or are based on the response of indicator species to AMD pollutants are required.

Impact of acid mine drainage from Tinoca Mine on the Abrilongo dam (southeast Portugal)

AbstractThis work presents a geochemical study conducted on the abandoned Tinoca Copper mine (southeast Portugal) to evaluate the potential hazard in surrounding areas particularly the effect on the Abrilongo River Dam which receivesthe acid waters from the mine watershed. The characterization of the area was performed over a period of 3 y and involved the study of waters, sediments and mine wastes. A sequential extraction methodology was conducted on the sediments and mine wastes and five elements were selected (Cu, Fe, Zn, Cd and Pb). The statistical and spatial analysis allowed the inference of the affinities between the chemical elements and specific mineralogical phases and to characterize chemical behaviour such as mobility and bioavailability. The results show that the distance to the source (mine-waste deposit), the point of zero charge, and the dynamics of the system are factors that control the behaviour of the elementss tudied. The acid drainage is characterized by an average pH of 2.5 and concentrationsof copper 20 timesgreater than the legal limit for irrigation waters.

On the ecology of the filter-feeding Neureclipsis bimaculata (Trichoptera, Polycentropodidae) in an acid and iron rich post-mining stream

Open-pit mining of lignite in East Germany has created landscapes with extreme environmental conditions. Post-mining aquatic habitats are characterized by low biodiversity and simple food webs due to the impact of acid mine drainage. In this study, the ecology of the filter-feeding caddisfly Neureclipsis bimaculata (L.) was examined, which is abundant in the acidic Flosgraben stream (pH 2.5–3.6) in Lower Lusatia, Germany. From benthic samples, we measured larval size and biomass and estimated population dynamics. The seston drift was sampled and retention efficiency of the larvae’s nets was assessed in a field tracer experiment to evaluate diet availability. Mean annual abundance was 1,380 ind m−2 with a biomass of 1,010 mg m−2. Annual secondary production of N. bimaculata was 8,450 mg m−2. The larval microdistribution reflected the preference for in-stream wood and a limitation by low flow velocity. Morphometric factors of the larvae in the acidic stream were in the range of morphometric factors found in circumneutral streams that covered a range of trophic levels. Although coverage by iron particles reduced flow, the nets account for 63% of the mean particle retention. It is suggested that the retention efficiency and the availability of drifting organisms allowed the larvae to feed on 8.4 mg m−2 per day, which revealed a ratio of biomass production to ingested food of 60%.

Stable isotopes in aqueous sulphate as tracers of natural and contaminant sulphate sources: a reconnaissance study of the Xingwen karst aquifer, Sichuan, China

Abstract Isotopic compositions of sulphate (δ 18 O and δ 34 S) have been analysed in groundwaters from a karst aquifer in Xingwen, China to assess their use as indigenous tracers of different pollutant sulphate sources. Sulphate δ 18 O is highly effective at distinguishing sulphate from atmospheric ‘acid rain’ sources (higher δ 18 O values) from sulphate produced by aqueous pyrite oxidation (natural or acid mine drainage), which always has lower δ 18 O. The range of sulphate δ 34 S produced by aqueous oxidation of different pyrite sources is sufficiently wide to enable different natural and pollutant sulphate sources to be distinguished. Despite the fact that streams containing processing fines and pyrite mine drainage both derive sulphate from oxidation of ore materials, there is still a clear distinction in their sulphate δ 34 S. A combination of sulphur and oxygen isotopic measurements is thus highly effective at discriminating between all the sulphate sources to the karst aquifer and this indigenous tracer provides a powerful tool for assessing the impact of acid mine drainage on karst groundwater.

The Impact of Acid Mine Drainage on the Water Quality of the Odiel River (Huelva, Spain): Evolution of Precipitate Mineralogy and Aqueous Geochemistry Along the Concepción-Tintillo Segment

The Odiel river emerges in Sierra de Aracena (N Huelva, Spain) as a clean, circumneutral river which shows abundant fish and fluvial microfauna. At 20km from the riverhead and along a 7km-long reach, this river receives four small discharges of acid mine water emanating from several abandoned mines of the Iberian Pyrite Belt (namely, Concepcion, San Platon, Esperanza and La Poderosa-El Soldado). During two field studies performed in October 2003 and May 2004, it has been observed that these acidic waters (with flow rate of 0.2–8.5L/s and pH 2.3–2.8) transfer to the Odiel river significant amounts of acidity and dissolved metals (specially Fe, Al, Mn, Cu, Zn, Cd, Co and Ni) and sulphate. Despite this mine-related pollution, the pH of the river remains near-neutral (pH = 7–8, flow rate = 220–1,000L/s), as the alkalinity of the river (108–155mg/L CaCO3 eq.) neutralizes the acidity and causes the precipitation of dissolved Fe and Al in the form of ochreous to whitish minerals (ferrihydrite, Al-oxyhydroxides). These poorly crystallized minerals retain, by sorption, large amounts of trace metals (specially Cu and Zn). Subsequently, the Odiel river converges with the acidic Tintillo river (pH = 2.5–2.8, flow rate = 48–240L/s), which drains a vast mining area occupied by large waste-rock piles and tailings impoundments around Corta Atalaya (Riotinto mines). At this confluence, all the alkalinity is totally consumed and the pH drastically decreases to around 3. The mineral paragenesis of the ochreous precipitates is then dominated by schwertmannite, which shows a very limited sorption capacity under such acidic conditions. Consequently, metal concentrations are sharply increased from near-zero to tens of mg/L (e.g., 18mg/L Fe, 76mg/L Al, 14mg/L Mn, 10mg/L Cu, and 20mg/L Zn in May 2004). The buffering capacity of the Fe(III) hydrolysis stabilizes the pH of the Odiel river around 3± 0.5 along the rest of its course to the Huelva estuary, and the water quality of the river is thus irreversibly damaged.

Evaluation of the Impact of Acid Mine Drainage on the Chemistry and the Macrobenthos in the Carolina Stream (San Luis – Argentina)

The purpose of this study was to evaluate the impact of acid mine drainage on the chemistry and the macrobenthos of the Carolina stream (San Luis - Argentina). Samples were obtained in the years 1997-1998 at two sites: site C(1), located 200 m upstream of the drainage, and site C(2), located 800 m downstream. The system buffer capacity was evaluated in the non - contaminated site by means of the buffer index calculation. The physico - chemical changes observed as a consequence of the contribution of acid mine drainage (AMD) were: a decreasing of pH and an increase in the ionic concentration, especially sulfate and Fe coming from the oxidation produced by chemiolithotrophic bacteria. The values obtained indicated a low buffer capacity and a high intrinsic vulnerability of the system to resist the impact originated by the AMD, producing a remarkable decreasing of pH of the receiving stream. These changes caused modifications in the original benthic community that was replaced by organisms more tolerant to the acid stress. A reduction in the abundance and in the taxonomic richness of the benthic macroinvertebrates was observed when compared with the reference station. An increase in the proportion of Chironomidae and of Acari and a decrease in the proportion of the remaining taxa were observed. The most sensitive groups were Ephemeroptera, Trichoptera and Mollusca. The community was mostly affected by the following variables: pH, conductivity, sulfate and dissolved total Fe.

Impacts of acid mine drainage on a stream in subtropical China during a major flood event

Impacts of acid mine drainage on a stream in subtropical China during a major flood event

Estimating spatial distributions of hydraulic parameters for a two-scale structured heterogeneous lignitic mine soil

In lignitic mine soils, monitoring of water and solute fluxes is required to assess and mitigate the impact of acid mine drainage on groundwater quality and the success of revegetation. These soils exhibit an appreciable heterogeneity of hydraulic properties, which originates both from the spatial distribution of lignitic components and inclined sedimentary structures. Both types of heterogeneity may lead to preferential flow. Water and element balances are mostly calculated by using one-dimensional (1D) numerical models, which do not account for preferential flow effects. Application of more complex model approaches is hampered by the lack of information about the spatial distribution of hydraulic parameters. The objective of this study is to assess the spatial distribution of hydraulic parameters for a sandy lignitic mine soil site based on visible structures in a 2D-vertical excavated soil cross-section. The hydraulic properties are calculated from the measured bulk densities and texture data, using the Kozeny–Carman-equation for the saturated hydraulic conductivity, K s, and the Arya–Paris approach for the water retention characteristics, ψ( θ). The effective porosity for K s is reduced and the water retention increased in proportion to the lignite contents. Small-scale variability of hydraulic parameters is evaluated by using photographs of lignitic fragment distributions. For the discernable inclined layer structures, with a width of approximately 40 cm and a dip of 35°, K s values in the range between 2.5 and 250 cm/d are estimated. The variability of the water retention characteristics is less pronounced. The predicted ψ( θ) functions are more comparable with loamy than sandy soils. The small-scale intra-layer variability of hydraulic parameters is higher than for lignite-poor mine spoil sediments and for most natural soils. The results may help to improve the analyses of flow and transport in lignitic mine soils by providing 2D two-scale parameter distributions for numerical simulations.

Impact of acid mine drainage from the abandoned Halikoy mercury mine (western Turkey) on surface and groundwaters.

Impact of acid mine drainage from the abandoned Halikoy mercury mine (western Turkey) on surface and groundwaters.

Establishing the impact of acid mine drainage through metal bioaccumulation and taxa richness of benthic insects in a tropical Asian stream (The Philippines).

The Boac-Makulapnit River (The Philippines) is contaminated with heavy metals primarily due to acid mine drainage (AMD). Heavy-metal levels in river water, sediment, and algae suggest that Cu is the primary contaminant in this system. Copper concentrations decrease longitudinally, indicating a contamination gradient away from the mine. This is also reflected in the whole-body metal concentration of the caddisfly Hydropsyche, wherein higher Cu levels are observed in upstream stations (677-980 microg/g in 2001). In 2002, AMD formation was observed in a midstream station resulting from the oxidation of mine tailings in floodplains deposited during a 1996 tailings spill event. This consequently increased heavy-metal concentrations locally in environmental media and is likewise perceived to have caused the absence of aquatic insects in the midstream reach. Copper concentrations also increased in Hydropsyche found downstream of the new AMD site during this year. Furthermore, even the lower Cu concentrations in Hydropsyche observed in downstream stations are still at least six times higher than the established regional baseline value (29.9 microg/g), which is calculated from samples from clean tributary streams. These tributary streams also showed higher taxa richness for aquatic insect community in riffle zones. Both biomonitoring tools suggest that the whole length of the river is severely impacted. Rehabilitation projects will be underway next year; therefore, such monitoring programs will truly be beneficial when gauging river habitat recovery.

59 Utility of the periphyton index of biotic integrity (PIBI) as an indicator of acid mine drainage impacts in southeastern ohio

In the Appalachian region, numerous streams are polluted with acid mine drainage (AMD). These waters are sulfate‐rich with elevated amounts of total acidity, low pH, and high levels of dissolved metals. Biotic multimetric indices, such as the Periphyton Index of Biotic Integrity (PIBI) have been employed to determine water quality across a variety of environmental conditions and may prove useful for AMD impacts. This study was initiated (1) to evaluate the PIBI for distinguishing AMD impact in streams and (2) to examine whether PIBI scores are impacted by seasonal differences. Twelve AMD and three reference streams were sampled for periphyton in June, August, and October. Water chemistry was collected at least once during the sampling period. Preliminary results showed that PIBI scores were significantly different (p&lt;0.05) among the seasons. In addition, the seasonal trends in PIBI scores among streams were not consistent. The PIBI scores were correlated with six water chemistry variables in August and with at least one variable indicative of AMD in each season sampled. PCA and UPGMA analyses of water chemistry data grouped the streams into five categories: (1) moderately impacted AMD streams with lower total dissolved solids, sulfate, total aluminum, and alkalinity, and higher sulfate; (2) AMD streams with higher alkalinity and lower total aluminum; (3) AMD streams with lower alkalinity and higher total aluminum; (4) reference streams and (5) an outlier reference stream affected by nutrients. Relationships between the groups based on water chemistry and the groups derived from the PIBI will be discussed.

Impact of acid mine drainage on benthic communities in streams: the relative roles of substratum vs. aqueous effects

Restoration of streams impacted by acid mine drainage (AMD) focuses on improving water quality, however precipitates of metals on the substrata can remain and adversely affect the benthos. To examine the effects of AMD precipitates independently of aqueous effects, four substrata treatments, clean sandstone, clean limestone, AMD precipitate-coated sandstone and coated limestone, were placed in a circumneutral stream of high water quality for 4 weeks. Iron and Al were the most abundant metals on rocks with AMD precipitate, and significantly decreased after the exposure. Precipitate on the substrata did not significantly affect macroinvertebrate or periphyton density and species composition. In an additional experiment, percent survival of caged live caddisflies was significantly lower when exposed in situ for 5 days in an AMD affected stream than in a reference stream. Caddisfly whole-body concentrations of all combined metals and Fe alone were significantly higher in the AMD stream. Whole-body metal concentrations were higher in killed caddisflies than in live, indicating the importance of passive uptake. The results suggest the aqueous chemical environment of AMD had a greater affect on organisms than a coating of recent AMD precipitate on the substrata (ca. 0.5 mm thick), and treatment that improves water quality in AMD impacted streams has the potential to aid in recovery of the abiotic and biotic benthic environment.

A river runs through it: impact of acid mine drainage on the geochemistry of West Little Sugar Creek pre- and post-reclamation at the Green Valley coal mine, Indiana, USA

Acid mine drainage (AMD) associated with coal waste material at the abandoned Green Valley mine in Indiana discharges into West Little Sugar Creek, a nearby steam. The acidic effluent and mixed stream water carry elevated SO4, Fe3+, Al, Fe2+, Ca, Mg, Na, Cl, Mn, K, Si, Zn, Ni, Pb, Cd, V, Be, and Cr, with several of these contaminants exceeding local and/or national surface water quality standards. Iron- and aluminum-dominated precipitates form on site and in the mixing zone and contain high concentrations of major and trace elements, suggesting that many of these constituents partition into the solid phase. Phase stability relationships indicate ferrous iron sulfate aqueous species are in equilibrium with melanterite and goethite. Despite past reclamation efforts, as well as natural metal removal associated with formation of AMD-related precipitates, poor stream water quality persists and presents an ongoing threat to the aquatic ecosystem.

Macroalgal communities from an acid mine drainage impacted watershed

Twenty-eight streams were sampled seasonally and a subset of 10 streams was sampled monthly for one year throughout the Hocking River drainage basin, Ohio, USA. Streams ranged from those receiving acid mine drainage (AMD), to reclaimed sites, to those never receiving mine wastes. Physical and chemical parameters were measured and macroalgal taxa were collected with estimations of percent cover. Canonical correspondence analysis showed AMD and seasonal parameters to be influential in grouping streams and macroalgal communities. The macroalgal composition was only useful in distinguishing between heavily impacted AMD streams and all others. We were unable to utilize the macroalgal community to detect differences among reclaimed sites and clean streams. This result was most likely due to the spatially heterogeneous occurrence of many macroalgal taxa. Two taxa, Klebsormidium rivulare and Microspora tumidula, did appear to be useful assessors of intense AMD impact. A total of 40 infrageneric taxa were recorded with the greatest species richness occurring in the spring (27 taxa). Chlorophytes were the dominant group throughout the watershed with 19 species. Percent macroalgal cover of stream reaches varied throughout the year within a single stream and among lotic systems. Our results showed that numerous taxa were overlooked in the seasonal versus monthly sampling, but that sampling more streams on a less frequent basis compensated to provide a complete listing of taxa for the watershed.

Impacts of acid mine drainage on juvenile salmonids in an estuary near Britannia Beach in Howe Sound, British Columbia

The abandoned copper mine at Britannia Beach, British Columbia, has been releasing acid mine drainage (AMD) into Howe Sound for many years. To assess the impacts of AMD on juvenile salmonids in the Britannia Creek estuary, we compared fish abundance, distribution, and survival at contaminated sites near the creek with uncontaminated areas in Howe Sound. Water quality near Britannia Creek was poor, particularly in spring when dissolved Cu exceeded 1.0 mg·L-1 and pH was less than 6. Beach seine surveys conducted during April-August 1997 and March-May 1998 showed that chum salmon (Oncorhynchus keta) fry abundance was significantly lower near Britannia Creek mouth (0-1.2·100 m-2) than in reference areas (11.5-31.4·100 m-2). Laboratory bioassays confirmed that AMD from Britannia Mine was toxic to juvenile chinook (Oncorhynchus tshawytscha) and chum salmon (96-h LC50 = 0.7-29.7% in freshwater and 12.6-62.2% in 10 ppt water). Chinook salmon smolts transplanted to surface cages near Britannia Creek experienced 100% mortality within 2 days. These results demonstrated that juvenile salmonids are vulnerable to AMD from Britannia Creek: their abundance peaks during spring when Cu concentrations are highest and toxicity is greatest in surface freshwater, which matches their preferred vertical distribution.