Mining-impacted Site Research Articles

Hellgrammite as a Non-Conventional Biomonitor for Surface Water and Environmental Health Assessment.

The larvae of dobsonflies from the genus Corydalus, commonly known as Hellgrammites, are characterized by their notable size, extensive range of occurrence, and extended period of immaturity, which can last up to one year. Hellgrammites are clearly known to exhibit sensitivity to pollution and habitat structure impacts. Given these unique features, using Corydalus texanus larvae is highly suitable as reliable biomonitoring agents to assess the ecological integrity of aquatic ecosystems. This protocol aims to provide the necessary tools for C. texanus assessment and demonstrate their efficacy through a case study. Research findings have practical implications, indicating that C. texanus larvae exhibit early-warning responses to mining pollution, bioaccumulating high amounts of heavy metals such as Zn, Fe, and Al. The presence or absence of C. texanus populations may serve as a helpful indicator for identifying potential issues related to ecosystem health. The unconventional approach has shown early warnings of pollution in mining-impacted sites, highlighting the need for timely action to protect the environment. Given their unique traits, the use of C. texanus larvae is highly suggested as a reliable non-conventional bioindicator.

Microbially mediated sulfur oxidation coupled with arsenate reduction within oligotrophic mining-impacted habitats.

Arsenate [As(V)] reduction is a major cause of arsenic (As) release from soils, which threatens more than 200 million people worldwide. While heterotrophic As(V) reduction has been investigated extensively, the mechanism of chemolithotrophic As(V) reduction is less studied. Since As is frequently found as a sulfidic mineral in the environment, microbial mediated sulfur oxidation coupled to As(V) reduction (SOAsR), a chemolithotrophic process, may be more favorable in sites impacted by oligotrophic mining (e.g. As-contaminated mine tailings). While SOAsR is thermodynamically favorable, knowledge regarding this biogeochemical process is still limited. The current study suggested that SOAsR was a more prevalent process than heterotrophic As(V) reduction in oligotrophic sites, such as mine tailings. The water-soluble reduced sulfur concentration was predicted to be one of the major geochemical parameters that had a substantial impact on SOAsR potentials. A combination of DNA stable isotope probing and metagenome binning revealed members of the genera Sulfuricella, Ramlibacter, and Sulfuritalea as sulfur oxidizing As(V)-reducing bacteria (SOAsRB) in mine tailings. Genome mining further expanded the list of potential SOAsRB to diverse phylogenetic lineages such as members associated with Burkholderiaceae and Rhodocyclaceae. Metagenome analysis using multiple tailing samples across southern China confirmed that the putative SOAsRB were the dominant As(V) reducers in these sites. Together, the current findings expand our knowledge regarding the chemolithotrophic As(V) reduction process, which may be harnessed to facilitate future remediation practices in mine tailings.

Revegetation of mining-impacted sites with a tropical native grass: Constraints of climate seasonality and trace-element accumulation

The iron ore mining activity results in considerable waste production and impacts on surrounding ecosystems. Natural recovery of impacted areas is absent or occurs slowly, especially when associated with prolonged dry seasons in tropical regions. The objective of this work was to unveil the mechanisms of Paspalum densum (Poir.) grass to overcome the periods of seasonal drought and its metal accumulation in areas impacted by iron mining, a tailings storage facilities and surrounding ferruginous grassland in Brazil. Lower mortality was observed among individuals in the tailings storage facilities, with a 74.3% survival rate. In contrast, after the beginning of the dry season, all individuals died in the ferruginous grassland. The plants in the tailings deposits showed better nutrition, with a higher concentration of P, Cu, Fe, Zn, Mn and greater capacity to accumulate Pb and Cd over time. Pb was the element with highest bioconcetration factor (BCF) and bioaccumulation coefficient (BAC), while Mn was the one with the highest translocation factor (TF). The dry season resulted in reduced chlorophyll a, b and total and effective quantum yield of photosystem II (PSII) of P. densum individuals. However, the plants in the tailings storage facilities showed adjustments to overcome the effects of drought, with an increase in the concentration of proline in leaves and reduction of oxidative damage (MDA and H2O2) at the end of the dry season. The grass P. densum showed rapid acclimatization in the tailings storage facilities and resistance to drought through antioxidant and photosynthetic adjustments and was still able to bioaccumulate and translocate in plant tissues some metals present in the iron ore impacted sites.

Evaluation of the Impacts of Abandoned Mining Areas: A Case Study with Benthic Macroinvertebrate Assemblages.

Mining activities are among the most long-lasting anthropogenic pressures on streams and rivers. Therefore, detecting different benthic macroinvertebrate assemblages in the areas recovered from mining activities is essential to establish conservation and management plans for improving the freshwater biodiversity in streams located near mining areas. We compared the stability of benthic macroinvertebrate communities between streams affected by mining activities (Hwangjicheon: NHJ and Cheolamcheon: NCA) and the least disturbed stream (Songjeonricheon: NSJ) using network analysis, self-organizing map, and indicator species analysis. Species richness was lowest at sites where stream sediments were reddened or whitened due to mining impacts in NHJ and NCA. Among functional feeding groups, the ratio of scrapers was lower (i.e., NHJ) or not observed (i.e., NCA) in the affected sites by mining. The networks (species interactions) were less connected in NHJ and NCA than in NSJ, indicating that community stability decreased in the area affected by mining activity. We identified five groups based on the similarity of benthic macroinvertebrate communities according to the gradients of mining impacts using a self-organizing map. the samples from the reference stream (clusters 1 and 5), sites located near the mining water inflow area (cluster 4), sites where stream sediments acid-sulfated (cluster 2), and sites that had recovered from mining impacts (cluster 3). Among the 40 taxa selected as indicators defined from the five clusters in self-organizing map, only few (Physa acuta, Tipula KUa, and Nemoura KUb) indicator species were selected in each cluster representing the mining-impacted sites. Our results highlighted that the benthic macroinvertebrate community complexity was lower in streams affected by mining activity. Furthermore, the range of disturbed areas in the streams, where conservation and management plans should be prioritized, can be quantified by examining alterations in the benthic macroinvertebrate community.

A diversity and functional approach to evaluate the macroinvertebrate responses to multiple stressors in a small subtropical austral river

Aquatic macroinvertebrates are considered effective bioindicators of ecosystem health due to their different sensitivities to habitat alteration and pollution. Macroinvertebrate community structures can be assessed using commonly used diversity-based approaches, however, functional trait-based approaches are increasingly introduced into bioassessments. The Hex River is subjected to intensive mining activities, while urban and industrial effluents, as well as treated and untreated sewage also contributes to pollution in the river. The present study aimed to assess macroinvertebrate responses to different stressors (nutrient and chemical, especially metal pollutants), determine whether diversity-based or trait-based approaches provide a better indication of responses and, to evaluate the relationship between metal bioaccumulation and macroinvertebrate responses to this multi-stressor environment. The mining impacts, in combination with urban, industrial and sewage effluent, altered the macroinvertebrate community structure of the Hex River. The species richness significantly decreased from reference conditions (39 species) to impacted conditions (24 species), while the total number of individuals in tolerant species gradually increased. The diversity-based approach indicated a clear difference between reference and impacted conditions but did not clearly differentiate between different stressors, while the trait-based approach distinguished the urban, industrial and sewage effluent sites from mining impacted sites. The use of both approaches is, therefore, recommended as both complement each other. From the present study, it is evident that macroinvertebrates can be considered as both reliable accumulation-, and response bioindicators to pollution from mining, as well as urban and industrial activities.

High throughput screening of native species for tailings eco-restoration using novel computer visualization for plant phenotyping.

Historical hard-rock mine activities have resulted in nearly half a million mining-impacted sites scattered around the US. Compared to conventional remediation, (aided) phytostabilization is generally cost-effective and ecologically productive approach, particularly for large-scale sites. Native species act to maintain higher local biodiversity, providing a foundation for natural ecological succession. Due to heterogeneity of mine waste, revegetation strategies are inconsistent in approach, and to avoid failure scenarios, greenhouse screening studies can identify candidate plants and amendment strategies before scaling up. This greenhouse study aimed to concurrently screen a variety of native species for their potential to revegetate Cu/Pb/Zn mine tailings and develop a high throughput and non-destructive approach utilizing computer vision and image-based phenotyping technologies to quantify plant responses. A total number of 34 species were screened in this study, which included: 5 trees, 8 grasses, and 21 forbs and legumes. Most of the species tested were Missouri native and prairie species. Plants were non-destructively imaged, and 15 shape and color phenotypic attributes were extracted utilizing computer vision techniques of PlantCV. Compared to reference soil, all species tested were negatively impacted by the tailings' characteristics, with lowest tolerance generally observed in tree species. However, significant improvement in plant growth and tolerance generally observed with biosolids addition with biomass surpassing reference soil for most legumes. Accumulation of Cu, Pb, and Zn was below Domestic Animal Toxicity Limits in most species. Statistically robust differences in species responses were observed using phenotypic data, such as area, height, width, color, and 9 other morphological attributes. Correlations with destructive data indicated that area displayed the greatest positive correlation with biomass and color the greatest negative correlation with shoot metals. Computer visualization greatly increased the phenotypic data and offers a breakthrough in rapid, high throughput data collection to project site-specific phytostabilization strategies to efficiently restore mine-impacted sites.

Environmental risk of severely Pb-contaminated riverbank sediment as a consequence of hydrometeorological perturbation

Metal mining activities have resulted in the widespread metal pollution of soils and sediments and are a worldwide health concern. Pb is often prolific in metal-mining impacted systems and has acute and chronic toxic effects. Environmental factors controlling diffuse pollution from contaminated riverbank sediment are currently seen as a “black box” from a process perspective. This limits our ability to accurately predict and model releases of dissolved Pb. Previous work by the authors uncovered key mechanisms responsible for the mobilisation of dissolved Zn. The current study identifies key mechanisms controlling the mobilisation of dissolved Pb, and the environmental risk these releases pose, in response to various sequences of “riverbank” inundation/drainage. Mesocosm experiments designed to mimic the riverbank environment were run using sediment severely contaminated with Pb, from a mining-impacted site. Results indicated that, although Pb is generally reported as less mobile than Zn, high concentrations of dissolved Pb are released in response to longer or more frequent flood events. Furthermore, the geochemical mechanisms of release for Zn and Pb were different. For Zn, mechanisms were related to reductive dissolution of Mn (hydr)oxides with higher concentrations released, at depth, over prolonged flood periods. For Pb, key mechanisms of release were related to the solubility of anglesite and the oxidation of primary mineral galena, where periodic drainage events serve to keep sediments oxic, particularly at the surface. The results are concerning because climate projections for the UK indicate a rise in the occurrence of localized heavy rainfall events that could increase flood frequency and/or duration. This study is unique in that it is the first to uncover key mechanisms responsible for dissolved Pb mobilisation from riverbank sediments. The mineralogy at the mining-impacted site is common to many sites worldwide and it is likely the mechanisms identified in this study are widespread.

Diffusive Gradients in Thin Films Reveals Differences in Antimony and Arsenic Mobility in a Contaminated Wetland Sediment during an Oxic-Anoxic Transition.

Antimony (Sb) and arsenic (As) are priority environmental contaminants that often co-occur at mining-impacted sites. Despite their chemical similarities, Sb mobility in waterlogged sediments is poorly understood in comparison to As, particularly across the sediment-water interface (SWI) where changes can occur at the millimeter scale. Combined diffusive gradients in thin films (DGT) and diffusive equilibration in thin films (DET) techniques provided a high resolution, in situ comparison between Sb, As, and iron (Fe) speciation and mobility across the SWI in contaminated freshwater wetland sediment mesocosms under an oxic-anoxic-oxic transition. The shift to anoxic conditions released Fe(II), As(III), and As(V) from the sediment to the water column, consistent with As release being coupled to the reductive dissolution of iron(III) (hydr)oxides. Conversely, Sb(III) and Sb(V) effluxed to the water column under oxic conditions and fluxed into the sediment under anoxic conditions. Porewater DGT-DET depth profiles showed apparent decoupling between Fe(II) and Sb release, as Sb was primarily mobilized across the SWI under oxic conditions. Solid-phase X-ray absorption spectroscopy (XAS) revealed the presence of an Sb(III)-S phase in the sediment that increased in proportion with depth and the transition from oxic to anoxic conditions. The results of this study showed that Sb mobilization was decoupled from the Fe cycle and was, therefore, more likely linked to sulfur and/or organic carbon (e.g., most likely authigenic antimony sulfide formation or Sb(III) complexation by reduced organic sulfur functional groups).

Occurrence of arbuscular mycorrhizal fungi in mining-impacted sites and their contribution to ecological restoration: Mechanisms and applications

ABSTRACTMining activities generally decrease topsoil and vegetation, reduce soil biodiversity, and yield extremely harsh environmental conditions, which in turn limit natural revegetation and soil restoration. Ecological restoration of mining sites using beneficial microorganisms such as arbuscular mycorrhizal (AM) fungi (AMF) is considered necessary and useful. In this article, several aspects of AMF-assisted ecological restoration of mining-impacted sites were reviewed. First, the data collected from 98 previous studies show that more than 80% of surveyed plants growing on mining sites are colonized by AMF, and a great number of AMF species and a large AMF diversity exist in various mining-impacted sites. Second, AMF can promote ecological restoration of mining-impacted sites through various possible mechanisms at different scales, such as improving mineral acquisition and tolerance of host plants, contributing to soil structure and quality, and helping maintain ecosystem stability and functioning. Third, a total of 101 studies on AMF and mine restoration, including 22 field and 79 laboratory experiments, were summarized, most of which (95%) confirm that AMF exhibit significant positive effects, such as increased plant survival, enhanced growth and nutrition, improved soil structure and quality, and greater plant re-establishment. Finally, the future prospects regarding enhancing AMF-assisted restoration were discussed.

Metal-contaminated potato crops and potential human health risk in Bolivian mining highlands.

This study assessed metals in irrigation water, soil and potato crops impacted by mining discharges, as well as potential human health risk in the high desert near the historic mining center of Potosí, Bolivia. Metal concentrations were compared with international concentration limit guidelines. In addition, an ingested average daily dose and minimum risk level were used to determine the hazard quotient from potato consumption for adults and children. Irrigation water maximum concentrations of Cd, Pb and Zn in mining-impacted sites were elevated 20- to 1100-fold above international concentration limit guidelines. Agricultural soils contained total metal concentrations of As, Cd, Pb and Zn that exceeded concentration limits in agricultural soil guidelines by 22-, 9-, 3- and 12-fold, respectively. Potato tubers in mining-impacted sites had maximum concentrations of As, Cd, Pb and Zn that exceeded concentration limits in commercially sold vegetables by 9-, 10-, 16- and fourfold, respectively. Using conservative assumptions, hazard quotients (HQ) for potatoes alone were elevated for As, Cd and Pb among children (range 1.1-71.8), in nearly all of the mining-impacted areas; and for As and Cd among adults (range 1.2-34.2) in nearly all of the mining-impacted areas. Only one mining-impacted area had a Pb adult HQ for potatoes above 1 for adults. Toxic trace elements in a major regional dietary staple may be a greater concern than previously appreciated. Considering the multitude of other metal exposure routes in this region, it is likely that total HQ values for these metals may be substantially higher than our estimates.

Potentially Toxic Metals and Biological Contamination in Drinking Water Sources in Chromite Mining-Impacted Areas of Pakistan: A Comparative Study

Water quality and quantity are the major environmental concerns of developing countries like Pakistan. Safe drinking water is one of the major prerequisites for a healthy life. The current study assessed the contamination of drinking water including physicochemical parameters (pH, TDS, EC, TH, Cl1−, NO3 1−, PO4 3−, SO4 2−, Mn, Cd, Pb, Ni, Cr) and bacteriological contamination (Fecal coliform) in chromite mining-impacted areas of Pakistan. However, the main focus of the study was to identify the potential health risk of these parameters to the local people of the study area. Atomic Absorption Spectrometer (Perkin Elmer, AAS-PEA-700) was used to analyze the concentrations of potentially toxic metals. The concentrations of Cd, Pb, Ni, and Cr ranged from below detection limit (BDL)-7.20, BDL-14.4, BDL-78.3 and 0.20–69.0 and exceeded their respective limits in 31, 11, 17, and 36% samples of drinking water set by World Health Organization, while the concentration of Ni (63% samples) also exceeded the safe limit set by Pakistan Environmental Protection Agency. Furthermore, the chronic daily intake (CDI) and health risk index (HRI) of potentially toxic metals through consumption of drinking water were found in the order of Mn > Ni > Cr > Cd > Pb and Cd > Ni > Mn > Pb > Cr, respectively. The HRI values of selected toxic metals in mining-impacted sites were found within the safe limit (HRI <1). The results showed that both geogenic and anthropogenic activities were the main sources of drinking water contamination in the study area.

Use of Amendments to Restore Ecosystem Function to Metal Mining-Impacted Sites: Tools to Evaluate Efficacy

As in situ use of amendments for restoration of metal-contaminated mining sites becomes increasingly accepted, the expected level of ecosystem function at these sites will increase. Use of appropriate tools to measure both the level and value of that function is critical to expand use of this approach. For these sites, amendment mixtures must reduce metal availability in situ and restore ecosystem function. Combinations of mixtures, typically consisting of a material with high metal binding capacity (cyclonic ashes, municipal biosolids, or other materials rich in Fe, Al, or Mn oxides), material to adjust soil pH (sugar beet lime, cement kiln dust, dolomitic limestone), and an organic residual to provide soil structure and nutrients (composts, animal manures, municipal biosolids) have been tested in multiple lab and field trials on metal-contaminated sites. This review focuses on field tests of this approach with the goal of providing methods to quantify reduction of hazard and restoration of functional systems. Methods to evaluate success of amendments including extractions to measure changes in metal availability, microbial function and diversity, phytoavailability of metals, and earthworm and small mammal assays are discussed. In most cases, measures of metal availability and ecosystem function are related. For example, surveys of small mammals on restored sites provide information on metal availability as well as suitability of restored habitat. Additional measures of ecosystem function including soil fertility, physical properties, and diversity of habitat are described. Finally, measures of the value of this approach for restoring ecosystems are detailed.

Associations between metals in residential environmental media and exposure biomarkers over time in infants living near a mining-impacted site.

Infant exposures to metals are a concern for mining-impacted communities, although limited information is available to assess residential exposures over the first year of life. We measured lead (Pb), manganese, arsenic, and cadmium in indoor air, house dust, yard soil, and tap water from 53 infants' homes near the Tar Creek Superfund Site (Oklahoma, USA) at two time points representing developmental stages before and during initial ambulation (age 0-6 and 6-12 months). We measured infant metal biomarkers in: umbilical cord blood (n=53); 12- (n=43) and 24- (n=22) month blood; and hair at age 12 months (n=39). We evaluated cross-sectional and longitudinal associations between infant residential and biomarker concentrations. A doubling of mean dust Pb concentration was consistently associated with 36-49% higher 12-month blood Pb adjusting for cord blood Pb (P⩽0.05). Adjusted dust concentration explained 29-35% of blood Pb variance, and consistent associations with other media were not observed. Although concentrations in dust and blood were generally low, strong and consistent associations between dust and body burden suggest that house dust in mining-impacted communities may impact children's health. These relationships were observed at a young age, typically before blood Pb levels peak and when children's development may be particularly vulnerable to toxic insult.

The molecular diversity of arbuscular mycorrhizal fungi in the arsenic mining impacted sites in Hunan Province of China

Arbuscular mycorrhizal fungi (AMF) can establish a mutualistic association with most terrestrial plants even in heavy metal contaminated environments. It has been documented that high concentrations of toxic metals, such as arsenic (As) in soil could adversely affect the diversity and function of AMF. However, there are still gaps in understanding the community composition of AMF under long-term As contaminations. In the present study, six sampling sites with different As concentrations were selected in the Realgar mining area in Hunan Province of China. The AMF biodiversity in the rhizosphere soils of the dominant plant species was investigated by sequencing the nuclear small subunit ribosomal RNA (SSU rRNA) gene fragments using 454-pyrosequencing technique. A total of 11 AMF genera were identified, namely Rhizophagus, Glomus, Funneliformis, Acaulospora, Diversispora, Claroideoglomus, Scutellopora, Gigaspora, Ambispora, Praglomus, and Archaeospora, among which Glomus, Rhizophagus, and Claroideoglomus clarodeum were detected in all sampling sites, and Glomus was the dominant AMF genus in the Realgar mining area. Redundancy analysis indicated that soil pH, total As and Cd concentrations were the main factors influencing AMF community structure. There was a negative correlation between the AMF species richness and the total As concentration in the soil, but no significant correlation between the Shannon–Wiener index of the AMF and plants. Our study showed that high As concentrations can exert a selective effect on the AMF populations.

Origin of middle rare earth element enrichment in acid mine drainage-impacted areas

The commonly observed enrichment of middle rare earth elements (MREE) in water sampled in acid mine drainage (AMD)-impacted areas was found to be the result of preferential release from the widespread mineral pyrite (FeS2). Three different mining-impacted sites in Europe were sampled for water, and various pyrite samples were used in batch experiments with diluted sulphuric acid simulating AMD-impacted water with high sulphate concentration and high acidity. All water samples independent on their origin from groundwater, creek water or lake water as well as on the surrounding rock types showed MREE enrichment. Also the pyrite samples showed MREE enrichment in the respective acidic leachate but not always in their total contents indicating a process-controlled release. It is discussed that most probably complexation to sulphite (SO3 (2-)) or another intermediate S-species during pyrite oxidation is the reason for the MREE enrichment in the normalized REE patterns.

Community level physiological profiles of bacterial communities inhabiting uranium mining impacted sites

Bacterial activity and physiological diversity were characterized in mining and milling impacted soils collected from three abandoned uranium mine sites, Senokos, Buhovo and Sliven, using bacterial dehydrogenase activity and Biolog (EcoPlate) tests. The elemental composition of soils revealed high levels of uranium and heavy metals (sum of technogenic coefficients of contamination; TCCsum) pollution as follows: Sliven (uranium – 374mg/kg; TCCsum – 23.40) >Buhovo (uranium – 139.20mg/kg; TCCsum – 3.93) >Senokos (uranium – 23.01mg/kg; TCCsum – 0.86). The physiological profiles of the bacterial community level were site specific, and indicated intensive utilization of polyols, carbohydrates and carboxylic acids in low and medium polluted environments, and i-erithrytol and 2-hydroxy-benzoic acid in the highly polluted environment of Sliven waste pile. Enzymes which take part in the biodegradation of recalcitrant substances were more resistant to pollution than these from the pathways of the easily degradable carbon sources. The Shannon index indicated that the physiological diversity of bacteria was site specific but not in line with the levels of pollution. A general tendency of increasing the importance of the number of utilizable substrates to bacterial physiological diversity was observed at less polluted sites, whereas in highly polluted sites the evenness of substrate utilization rate was more significant. Dehydrogenase activity was highest in Senokos upper soil layer and positively correlated (p<0.01) with the soil organic matter content. The bacterial activity (EcoPlate) and physiological diversity (Shannon index) correlated significantly and negatively with As, Cu, Zn, Pb and U, and Co, Cr, Ni and Mn, respectively. We concluded that the observed site specific shifts in bacterial communities were complex due to both the environmental peculiarities and the bacterial tolerance to the relevant level of pollution, rather than a strong indication of uranium and heavy metals toxicity.

Vegetation structure and heavy metal uptake by plants in the mining-impacted and non mining-impacted sites of Southern Lake Victoria Wetlands

This study assessed the plant species composition and the heavy metal uptake by plants in the mining-impacted and non mining-impacted areas of the southern Lake Victoria basin. The vegetation of the wetlands was stratified into riverine forest, riverine thickets, swampy grassland, open woodland and floodplain grassland. Plant diversity at Nyamtukuza ranged between 2.34 to 2.70; at Geita was 2.29 to 2.57 and Mwakitolyo was between 1.08 to 1.70, which was significantly lower than the other two sites; whereas variation in plant species richness was not significant. TWINSPAN classification resulted into four clusters of the vegetation communities. Cluster A, a shrubby community with Combretum molle, Bersama abyssinica, Acalypha ornata and Acacia brevispica indicated previous cutting of woody species from the area. Cluster B was a severely disturbed community with Bidens pilosa and Anthocleista grandiflora as early successors. Cluster C was a community with moderate disturbance levels and cluster D was of wetland vegetation community types with indicator species such as Pistia stratiotes and Corchorus aestuans that are characteristic permanent wetland species. CCA ordination showed a significant positive correlation of the soil mineral elements to those in plants at axis 1. The influence of soil minerals on plant species distribution pattern was not significant at axis 1. Tanzania Journal of Science Vol. 32 (2) 2006: pp. 39-50

Element mobility during pyrite weathering: implications for acid and heavy metal pollution at mining-impacted sites

Based on back scattered electron images and electron micro-probe analysis results, four alteration layers, including a transition layer, a reticulated ferric oxide layer, a nubby ferric oxide layer and a cellular ferric oxide layer, were identified in the naturally weathering products of pyrite. These layers represent a progressive alteration sequence of pyrite under weathering conditions. The cellular ferric oxide layer correlates with the strongest weathering phase and results from the dissolution of nubby ferric oxide by acidic porewater. Leaching coefficient was introduced to better express the response of element mobility to the degree of pyrite weathering. Its variation shows that the mobility of S, Co and Bi is stronger than As, Cu and Zn. Sulfur in pyrite is oxidized to sulfuric acid and sulfate that are basically released into to porewater, and heavy metals Co and Bi are evidently released by acid dissolution. As, Cu and Zn are enriched in ferric oxide by adsorption and by co-precipitation, but they would re-release to the environment via desorption or dissolution when porewater pH becomes low enough. Consequently, Co, Bi, As, Cu and Zn may pose a substantial impact on water quality. Considering that metal mobility and its concentration in mine waste are two important factors influencing heavy metal pollution at mining-impacted sites, Bi and Co are more important pollutants in this case.

Effects of multiple stressors on hyporheic invertebrates in a lotic system

The impacts of co-occurring stressors (river regulation by a dam and mine drainage) on hyporheic macroinvertebrate assemblages and environmental variables were investigated in a mountainous area of central Colorado at seven sampling sites in Lake Fork during two different seasons. Specific aquatic macroinvertebrate assemblages were associated with river regulation and trace element impacts. Paraleuctra was primarily associated with mining impacted sites, while Polycelis , Hydra , and Simulium were most abundant at sites nearest the dam. There were sometimes large differences in toxicity between hyporheic and surface water samples. Occasionally toxicity was present in the surface water, but absent in hyporheic water from the same site, while on one date, toxicity was detected in the hyporheic but undetected in surface water. The distinct taxa found in the hyporheic, and differences between hyporheic and surface water quality suggest that understanding the hyporheic zone is important in the study of impacted aquatic systems.

Geochemical response to variable streamflow conditions in contaminated and uncontaminated streams

Seasonal variations in stream inorganic geochemistry are not well documented or understood. We sampled two mining‐impacted and two relatively pristine streams in western Montana over a 12‐month period, collecting samples every 4 weeks, with supplemental sampling (at least weekly) during spring runoff. We analyzed all samples for dissolved (operationally defined as &lt;0.2 μm) and total recoverable concentrations. Generally, the trace elements (Al, As, Cu, Fe, Mn, and Zn) did not correlate linearly with streamflow, while the major elements (e.g., Ca, K, and Mg) did. Suspended sediment, total recoverable metals, and H+ followed clockwise hysteresis rotations, driven by short‐term flushing events during the very early stages of spring runoff. Mining‐impacted sites had higher concentrations of many trace elements than did relatively pristine sites. One of the mining impacted sites exhibited strong geochemical responses to spring rain events in the basin. The results underscore the need to sample streams frequently during changing hydrologic and climatic conditions in order to accurately monitor surface water quality and to determine solute and particulate loads (both contaminant and noncontaminant).