The role of natural biogeochemical barriers in limiting metal loading to a stream affected by mine drainage

Abstract

Rio San Giorgio (Iglesiente, Sardinia, Italy), a stream affected by abandoned mine wastes, is characterized by dense vegetation in the streambed, mainly comprised of Phragmites australis and Juncus acutus. This vegetation creates natural biogeochemical barriers that drive mineralization processes and attenuate metals load in the stream. Several techniques, covering scales from micrometres to kilometres, were applied to investigate the biogeochemical processes: water chemistry, injected hydrologic tracer, mineralogy, microscopic investigation and X-ray spectroscopy. From this multiscale and multimethod approach, we recognized two predominant sets of biogeochemical processes: microbially driven metal sulphide precipitation, mainly resulting in pyrite formation; and plant uptake of metals that leads to formation of iron oxide-hydroxide and incorporation of Zn within the roots and aerial part (stem and leaves). The dense vegetation in the Rio San Giorgio streambed controls its morphology, velocity of streamflow, and, as reflected by observed bromide-tracer loss, enhanced water exchange between the streambed and the hyporheic zone. The combined effect of these vegetative controls is to establish biogeochemical barriers that greatly retard trace-metal mobility in the hyporheic zone. We estimated this effect can lead to an apparent decrease in Zn load up to 60%

The Biogeophysical Effects of Revegetation around Mining Areas: A Case Study of Dongsheng Mining Areas in Inner Mongolia

“…Satellite-based LE in this study showed a closer correspondence than the MOD16 ET product (r = 0.71, bias = −3.5 W/m 2 , and RMSE = 14.2 W/m 2 ) [32]. These results suggested the reliability of estimated LE derived from Equation (5).…”

“…In recent years, revegetation around mines has attracted the scientific community's attention. Most studies have focused on some abilities of revegetation, mainly including vegetation cover changes [5][6][7], carbon sequestration [8,9], soil conservation and soil remediation [10,11]. For example, using Landsat satellite images with four different image processing methods, Karan et al [6] evaluated the effectiveness of ecological restoration in the Block II area of the Jharia coal field, in India.…”

Mineralogy and Zn Chemical Speciation in a Soil-Plant System from a Metal-Extreme Environment: A Study on Helichrysum microphyllum subsp. tyrrhenicum (Campo Pisano Mine, SW Sardinia, Italy)

“…In this study, SEM and EDS analysis showed the presence of a mineral rim made up of Al-silicates coating the epidermis of H. tyrrhenicum roots (Figure 2), as previously observed in other autochthonous plant species growing in similar environments, like E. pithyusa subsp. cupanii, P. lentiscus, P. australis, and J. acutus [23,[76][77][78]109]. This structure was also detected by STXM ( Figure 6), also showing that Zn is mainly stored in the root epidermis.…”

“…XAS spectra for each sample were collected at least in triplicate for averaging and statistics. According to literature data [23,26,50,52,[74][75][76][77][78], in the soil-plant system, Zn can occur in different coordination environments, both bound to organic compounds (e.g., organic acids, phytochelatins, metallothioneins, etc.) and to inorganic molecules (e.g., sulfur, sulfate, carbonate, etc.)…”

Plant Tissues and Embryos Biominerals in Sarcocornia pruinosa, a Halophyte from the Río Tinto Salt Marshes

“…Other minerals known to be formed by plants are amorphous silica or magnesium oxalate [2][3][4][5][6]. Also, Fe biomineralization such as jarosite and Fe-oxides (ferrihydrite, hematite and spinel phases) were thoroughly studied in the grass Imperata cylindrica growing on the Río Tinto and also under controlled hydroponic cultures [7,8]. Other authors also highlight the impact of biomineralization processes in plants that grow in environments with a high presence of metals resulting from biogeochemical cycles [9,10].…”