Patrick Byrne

The Impairment of River Systems by Metal Mine Contamination: A Review Including Remediation Options

Contamination of aquatic environments as a consequence of deep metal mining for Pb, Zn, Cu, Cd, and Fe is of widespread international concern. Pollution resulting from metal mining activities can result in significant environmental and ecological degradation and can pose serious risks to human health through contamination of food and drinking water. This paper provides a review of the impacts of deep metal mine water discharges on riverine sedimentology, hydrology, and ecology and explores strategies for the restoration of rivers draining historically abandoned metal mines. The review is concluded by identifying key recommendations for future research. An interdisciplinary approach, incorporating collaborative expertise and knowledge regarding sedimentological, hydrological, chemical, and ecological consequences of active and historic deep metal mining, is advocated and should be utilized for effective river basin management and the remediation and restoration of mining-impacted river systems.

Stormflow hydrochemistry of a river draining an abandoned metal mine: the Afon Twymyn, central Wales

Contaminated drainage from metal mines is a serious water-quality problem facing nations that exploit metal mineral resources. Measurements of river hydrochemistry during baseflow are common at mine sites, whilst detailed hydrochemical information regarding stormflow is limited and often confined to a single event. This study investigates the seasonal evolution of stormflow hydrochemistry at an abandoned metal mine in central Wales, UK, and the possible sources and mechanisms of metal release. Significant flushing of metals was observed during stormflow events, resulting in concentrations that severely exceeded water-quality guidelines. The relationship between metal concentrations and river discharge suggests dissolution of efflorescent metal sulphates on the surface of the mine spoil as the principal source of the contamination. High fluxes of Pb during stormflows are linked to extended periods of dry weather prior to storm events that produced water table drawdown and encouraged oxidation of Pb sulphide in the mine spoil. However, some Pb flushing also occurred following wet antecedent conditions. It is suggested that Fe oxide reduction in mine spoil and translatory flows involving metal-rich pore waters results in flushing during wetter periods. Detailed measurements of stormflow hydrochemistry at mine sites are essential for accurate forecasting of long-term trends in metals flux to understand metal sources and mechanisms of release, to assess potential risks to water quality and instream ecology, and to gauge the potential effectiveness of remediation. In order to protect riverine and riparian ecosystems, it is suggested that routine monitoring of stormflows becomes part of catchment management in mining-impacted regions.

The interplay between transport and reaction rates as controls on nitrate attenuation in permeable, streambed sediments

Anthropogenic nitrogen fixation and subsequent use of this nitrogen as fertilizer has greatly disturbed the global nitrogen cycle. Rivers are recognized hotspots of nitrogen removal in the landscape as interaction between surface water and sediments creates heterogeneous redox environments conducive for nitrogen transformations. Our understanding of riverbed nitrogen dynamics to date comes mainly from shallow sediments or hyporheic exchange flow pathways with comparatively little attention paid to groundwater-fed, gaining reaches. We have used 15N techniques to quantify in situ rates of nitrate removal to 1m depth within a groundwater-fed riverbed where subsurface hydrology ranged from strong upwelling to predominantly horizontal water fluxes. We combine these rates with detailed hydrologic measurements to investigate the interplay between biogeochemical activity and water transport in controlling nitrogen attenuation along upwelling flow pathways. Nitrate attenuation occurred via denitrification rather than dissimilatory nitrate reduction to ammonium or anammox (range = 12 to >17000 nmol 15N L-1 h-1). Overall, nitrate removal within the upwelling groundwater was controlled by water flux rather than reaction rate (i.e. Damkohler numbers 80% of nitrate removal occurs within sediments not exposed to hyporheic exchange flows under baseflow conditions, illustrating the importance of deep sediments as nitrate sinks in upwelling systems.

Synoptic sampling and principal components analysis to identify sources of water and metals to an acid mine drainage stream

Combining the synoptic mass balance approach with principal components analysis (PCA) can be an effective method for discretising the chemistry of inflows and source areas in watersheds where contamination is diffuse in nature and/or complicated by groundwater interactions. This paper presents a field-scale study in which synoptic sampling and PCA are employed in a mineralized watershed (Lion Creek, Colorado, USA) under low flow conditions to (i) quantify the impacts of mining activity on stream water quality; (ii) quantify the spatial pattern of constituent loading; and (iii) identify inflow sources most responsible for observed changes in stream chemistry and constituent loading. Several of the constituents investigated (Al, Cd, Cu, Fe, Mn, Zn) fail to meet chronic aquatic life standards along most of the study reach. The spatial pattern of constituent loading suggests four primary sources of contamination under low flow conditions. Three of these sources are associated with acidic (pH <3.1) seeps that enter along the left bank of Lion Creek. Investigation of inflow water (trace metal and major ion) chemistry using PCA suggests a hydraulic connection between many of the left bank inflows and mine water in the Minnesota Mine shaft located to the north-east of the river channel. In addition, water chemistry data during a rainfall-runoff event suggests the spatial pattern of constituent loading may be modified during rainfall due to dissolution of efflorescent salts or erosion of streamside tailings. These data point to the complexity of contaminant mobilisation processes and constituent loading in mining-affected watersheds but the combined synoptic sampling and PCA approach enables a conceptual model of contaminant dynamics to be developed to inform remediation.

Microwaves and Functional Materials: A Novel Method to Continuously Detect Metal Ions in Water

Protecting water from chemical pollutants is a major societal goal. Metal ion dispersion from abandoned mines is a global concern and one of the principal causes of metal pollution in water. Toxic metals are a particular concern because they are not degraded by normal biogeochemical cycles and cause adverse environmental and human health effects even with low concentrations if there is long-term exposure. Current laboratory-based methods are not suitable for monitoring adequately water pollution in the environment. Consequently, it is necessary to develop and deploy new sensing systems to investigate water quality continuously. Microwave spectroscopy has been demonstrated as an effective method for offering continuous measurement of material properties, nevertheless, this method suffers from a lack of selectivity and sensitivity (Zarifi et al. Sens Actuators B Chem 255:1561–1568 (2018), [1]). This chapter presents a feasibility study using unique functionalised electromagnetic (EM) sensors for continuous monitoring of zinc in water. The reaction between Zn and a Bi2O3 based thick film that is screen-printed onto a planar interdigitated electrode (IDE) sensors starts within 30 s, and the adsorption equilibrium was attained within 10 min. The response is faster during the initial stage and slows as equilibrium is reached. Results show good linear correlations between C (capacitance), S11 (reflection coefficient) and Zn concentration. Also, the recovery time of sensors is evaluated to be 100–150 s demonstrating the sensors reusability and potential for continuous monitoring.

Feasibility of in-situ quality assessment of zinc contamination in water

Metal pollution is a global problem, especially due to the dispersion of trace metals in freshwater surrounding abandoned mining areas. This paper reports the experimental procedure used for continuously detecting changes in the concentration of zinc in water using a combination of three methodologies based on electromagnetic (EM) waves: UV-Vis spectrophotometer; impedance analyser; and a novel microwave sensor method. With this last methodology, two planar sensors were used: interdigitated electrode (IDE) pattern on polytetrafluoroethylene (PFTE) substrate, and the same kind of sensor functionalised with bismuth III oxide coating. Reflected power as spectra signals were analysed in the 10 MHz–15 GHz frequency range. Results show signals were linearly dependent on the type of metal measured and on its concentration with R2 = 0.9942, R2 = 0.999 and R2 = 0.9899 respectively for absorbance, capacitance and reflected power measured with a coated IDE sensor. In conclusion, this novel sensing system could be a cost-effective alternative for detecting metal pollution in-situ, and in real-time.