Abandoned mine lands continue to serve as non-point sources of acid and metal contamination to water bodies long after mining operations have ended. Although soils formed from abandoned mine spoil can support forest vegetation, as observed throughout the Appalachian coal basin, the effects of vegetation on metal cycling in these regions remain poorly characterized. Iron (Fe) and manganese (Mn) biogeochemistry were examined at a former coal mine where deciduous trees grow on mine spoil deposited nearly a century ago. Forest vegetation growing on mine spoil effectively removed dissolved Mn from pore water; however, mineral weathering at a reaction front below the rooting zone resulted in high quantities of leached Mn. Iron was taken up in relatively low quantities by vegetation but was more readily mobilized by dissolved organic carbon produced in the surface soil. Dissolved Fe was low below the reaction front, suggesting that iron oxyhydroxide precipitation retains Fe within the system. These results indicate that mine spoil continues to produce Mn contamination, but vegetation can accumulate Mn and mitigate its leaching from shallow soils, potentially also decreasing Mn leaching from deeper soils by reducing infiltration. Vegetation had less impact on Fe mobility, which was retained as Fe oxides following oxidative weathering.
Abstract Natural mineral coatings play an important role in controlling the transport of contaminants in soils and sediments. These materials contain complex mineral and organic components, and their formation, composition, and morphology are dependent on the mineralogical and chemical composition of the underlying grain and local (bio)geochemical conditions. Mineral coatings often have unique chemical and physical properties compared to primary minerals, which can affect their reactivity with respect to contaminant sequestration due to: (i) complex and variable porosity, which allows for limited flow potential within confined pore spaces; and (ii) a more chemically complex mineralogy and therefore type, abundance, and distribution of reactive surface sites. As the source material for mineral coatings can include both external components and material derived from the underlying surface, these materials therefore acts as a record of the recent environmental conditions to which they were exposed. Case studies are presented here highlighting the role that mineral coatings have in affecting the reactive transport of contaminants in near‐surface environments. Future work at the intersection of hydro(geo)logy, mineralogy, and (bio)geochemistry has the potential to yield a more unified understanding of contaminant transport through these complex material across a wide range of spatial regimes.
Abstract Abandoned mining operations continue to severely degrade many ecosystems worldwide by releasing acidic water and/or heavy metals into surface and groundwater. Contaminant concentrations in affected streams vary with discharge in patterns that reflect both geochemical reactions and variable mixing of contaminated and non‐contaminated waters. However, controls on concentration‐discharge (C‐Q) patterns remain unclear, particularly for constituents that experience changing solubility across redox and pH gradients. Understanding the C‐Q behaviour of contaminants aids in predicting both downstream transport and effects on aquatic life under variable flow. Here, we examined the C‐Q behaviours of non‐reactive (Na, K, Ca, Mg, Cl − ) and reactive (Fe, Mn, Al, H + , SO 4 2− ) solutes in a stream contaminated with acid mine drainage in northeastern Ohio, USA. Concentration‐discharge patterns at the watershed outlet primarily reflected mixing of contaminated baseflow with intermittent inputs of high pH water draining from a passive limestone treatment system into the stream. The treatment system acted as an ephemeral tributary that mitigated contamination in the stream by diluting solutes, raising pH, and driving metal precipitation, but only when flow was present during wet seasons. Consequently, AMD‐derived reactive solutes (H + , Fe, Mn, Al) decreased with increasing stream discharge while relatively conservative solutes (e.g., Ca, Mg, K, Na) decreased only slightly or were chemostatic. This study highlights both the unique C‐Q patterns of reactive solutes when compared to those of non‐reactive solutes and the potential for intermittent streams to control C‐Q behaviour in headwater catchments.
The Lens Opacities Classification Systems (LOCS III) was developed and standardized using photograding. The purpose of this study was to assess the validity of LOCS III at the slitlamp and to compare slitlamp with photograding. To do so, two independent observers graded cataract at the slitlamp and in photographs from two sets of patients; the first set consisted of 205 eyes (193 acceptable photographs) and the second set of 51 eyes (51 photographs). The 95% tolerance limits (TL) for grading at the slitlamp ranged from 0.9 to 1.8 for the first set and 0.6 to 1.2 for the second (intraclass correlation coefficients 0.79 to 0.91 vs. 0.70 to 0.97, respectively). Specifically, there was a significant decrease in 95% TL for cortical and nuclear color. For the first set of photograding, the 95% TL were 0.3 to 0.6 between the two observers and 0.6 to 0.8 for the same observer at two different sessions. Similar results were found for photograding the second set. The 95% TL for comparing slitlamp and photograding were generally < 1.0. The results suggest that (1) LOCS III at the slitlamp has 95% TL only slightly worse than those for LOCS III photogradings; (2) LOCS III slitlamp grading for cortical and nuclear color improves with practice; and (3) the slitlamp and photographic gradings cannot be used interchangeably.
Historical coal mining practices have caused various soil and water hazards, particularly through the dumping of mine waste. The primary environmental risk associated with this waste is the leaching of toxic metals from dumps of spoil or refuse into the subsurface soil or into nearby water resources. The extent of metal release is controlled via the oxidative dissolution of pyrite and potential re-sequestration through secondary Fe oxides. The characterization of the dominant Fe-bearing phase and the distribution of trace metals associated with these phases was determined via electron microscopy, synchrotron-based X-ray micro-fluorescence (μ-XRF) element and redox mapping from shallow mine soils from an impacted watershed in Appalachian Ohio. The dominant Fe-bearing phases were: (1) unweathered to partially weathered pyrite; (2) pseudomorphic replacement of pyrite with Fe(III) oxides; (3) fine-grained Fe oxide surface coatings; and (4) discrete Fe(III) oxide grains. Thicker secondary coatings and larger particles were sulfate rich, whereas smaller grains and thinner coatings were sulfate poor. The discrete Fe oxide grains exhibited the highest concentrations of Cr, Mn, Ni, and Cu, and sub-grain-scale concentration trends (Mn > Cr > Ni > Cu) were consistent with bulk soil properties. Predicting future metal transport requires an understanding of metal speciation and distribution from the sub-grain scale to the pedon scale.
Two sets of lens photogradings were used to investigate the effect of cataract type and severity on the intra- and interob-server agreement between two graders using the Lens Opacities Classification System III (LOCS III). The first set consisted of 193 eyes, largely of mild-to-moderate opacities for all cataract types. The second set consisted of a similar number of cataracts in each group subdivided into mild, moderate, and severe, a total of 159 lens photographs. Intraclass correlation coefficient (r1) was used to measure the intra- and interobserver reproducibility and 95% tolerance limit the intra- and interobserver variability. Results showed that more variability was seen in intra- and interobserver agreement when grading increasing posterior subcapsular opacities. Decreased reproducibility and increased variability in interobserver agreement were seen in increasing cortical gradings, and decreased reproducibility in interobserver agreement in more severe nuclear opacities. No difference was seen in nuclear color gradings. The results suggest that the effect of cataract severity on interobserver agreement should be taken into consideration in longitudinal studies requiring several photograders.
