Root penetration of sealing layers made of fly ash and sewage sludge

Functional response of Betula species to edaphic and nutrient stress during restoration of fly ash deposits in the Middle Urals (Russia)

We studied the impact of fly ash produced by the thermal power station in the Middle Urals (Russia) on functional traits of two Betula species naturally colonizing ash dump lagoons. The main limiting factors for tree growth on fly ash deposits were nitrogen deficiency, high alkalinity, and unfavorable mechanical composition of substrate. Leaf area ratio (LAR) and leaf mass ratio (LMR) per tree, leaf area (LA), leaf shape coefficient (LSh), leaf thickness (LT), leaf mass per area (LMA), photosynthesis (A_max) and transpiration rates, chlorophyll (Chl), carotenoid (Car), and nitrogen (N) content were measured in Betula pendula Roth and Betula pubescens Ehrh. growing on the ash dump and in the forest near the dump. Both Betula species showed similar functional response to adverse conditions of the fly ash. We found a 1.5-2-fold increase in LAR and LMR in trees growing on fly ash deposits compared with trees in the forest. In both species, the most significant differences across leaf morphological traits were shown for LT. Higher LT provided an increase in Chl and N content per leaf area that caused the rise in A_max and photosynthetic water use efficiency in the trees on the ash deposit. At the same time, Betula species preserved interspecific differences in values of LA and LT which were larger in B. pubescens whiles B. pendula differed by higher LSh. We concluded that the increase in assimilation activity at both whole-plant and leaf levels provides plant adjustment to edaphic and nutrient stress that allow Betula species to colonize technogenic substrates as fly ash deposits.

Ecological restoration of coal fly ash-dumped area through bamboo plantation

The present study entails the phytoremediation potential of different bamboo species on 5-year-old FA-dumped site near Koradi thermal power plant of Nagpur, Maharashtra, India. The selected FA-dumped site was treated with farmyard manure, press mud, and bio fertilizer followed by plantation of six promising species of bamboo namely Bambusa balcooa Roxb., Dendrocalamus stocksii (Munro.) M. Kumar, Remesh and Unnikrishnan, Bambusa bambos (L.) Voss, Bambusa wamin E.G. Camus, Bambusa vulgaris var. striata (Lodd. ex Lindl.) Gamble, and Bambusa vulgaris var. vittata Riviere and Riviere. The experimental results indicated that the organic input in the FA-dumped site nourished the soil by improving its physico-chemical, and biological characteristics. The results revealed the contamination of the site with different trace elements in varied quantity including Cr (89.29 mg kg-1), Zn (84.77 mg kg-1), Ni (28.84 mg kg-1), Cu (22.91 mg kg-1), Li (19.65 mg kg-1), Pb (13.47 mg kg-1), and Cd (2.35 mg kg-1). A drastic reduction in concentration of heavy metals in FA was observed after 1 year of bamboo plantation as compared to the initial condition. The results showed that bamboo species are good excluders of Ba, Co, Cr, Li, Ni, Mn, and Zn, whereas they are good accumulators of Cd, Pb, and Cu. The values of biochemical parameters, such as pH, total chlorophyll, ascorbic acid (AA), and relative water content of all the bamboo leaves ranged from 5.11-5.70, 1.56-6.33 mg g-1, 0.16-0.19 mg g-1, and 60.23-76.68%, respectively. It is thereby concluded that the bamboo plantation with biofertilizers and organic amendments may indicate adaptive response to environmental pollution on FA-dumped site.

Aboveground and Belowground Colonization of Vegetation on a 17-Year-Old Cover with Capillary Barrier Effect Built on a Boreal Mine Tailings Storage Facility

Acid mine drainage is an important environmental risk linked to the surface storage of reactive mine tailings. To manage this problem, a cover with a capillary barrier effect (CCBE) can be used. This oxygen barrier cover relies on maintaining a fine-grained material layer (moisture-retaining layer, MRL) with a high degree of saturation. CCBEs can be colonized by surrounding plants. Plant roots pump water and could impact CCBE’s performance. This performance is predicted with unsaturated water flow numerical models in which vegetation parameters can be included. Vegetation parameters may be specific in a CCBE environment. Therefore, analyzing and quantifying the vegetation that colonizes this type of cover is necessary. Plant colonization was investigated through cover and density surveys on 12 transects on a 17-year-old CCBE in the mixed forest of Quebec, Canada. Then, aboveground vegetation and root colonization intensity at three depths in the MRL were characterized on 25 plots of five dominant vegetation types (Salix, Populus, Alnus, Picea sp., and herbaceous species). The mean root length density under plots dominated by Salix sp. was higher than in the other plots. Root colonization of the MRL was concentrated in the first 10 cm and occurred under all woody and herbaceous species as well. This work quantitatively describes, for the first time, the vegetation colonizing a CCBE both at the above- and belowground levels. These data will be useful to better predict the long-term performance of this engineered reclamation cover.

Alternative waste residue materials for passive in situ prevention of sulfide-mine tailings oxidation: a field evaluation

Novel solutions for sulfide-mine tailings remediation were evaluated in field-scale experiments on a former tailings repository in northern Sweden. Uncovered sulfide-tailings were compared to sewage-sludge biosolid amended tailings over 2 years. An application of a 0.2m single-layer sewage-sludge amendment was unsuccessful at preventing oxygen ingress to underlying tailings. It merely slowed the sulfide-oxidation rate by 20%. In addition, sludge-derived metals (Cu, Ni, Fe, and Zn) migrated and precipitated at the tailings-to-sludge interface. By using an additional 0.6m thick fly-ash sealing layer underlying the sewage sludge layer, a solution to mitigate oxygen transport to the underlying tailings and minimize sulfide-oxidation was found. The fly-ash acted as a hardened physical barrier that prevented oxygen diffusion and provided a trap for sludge-borne metals. Nevertheless, the biosolid application hampered the application, despite the advances in the effectiveness of the fly-ash layer, as sludge-borne nitrate leached through the cover system into the underlying tailings, oxidizing pyrite. This created a 0.3m deep oxidized zone in 6-years. This study highlights that using sewage sludge in unconventional cover systems is not always a practical solution for the remediation of sulfide-bearing mine tailings to mitigate against sulfide weathering and acid rock drainage formation.

Effect of residue combinations on plant uptake of nutrients and potentially toxic elements

The aim of the plant pot experiment was to evaluate potential environmental impacts of combined industrial residues to be used as soil fertilisers by analysing i) element availability in fly ash and biosolids mixed with soil both individual and in combination, ii) changes in element phytoavailability in soil fertilised with these materials and iii) impact of the fertilisers on plant growth and element uptake. Plant pot experiments were carried out, using soil to which fresh residue mixtures had been added. The results showed that element availability did not correlate with plant growth in the fertilised soil with. The largest concentrations of K (3534 mg/l), Mg (184 mg/l), P (1.8 mg/l), S (760 mg/l), Cu (0.39 mg/l) and Zn (0.58 mg/l) in soil pore water were found in the soil mixture with biosolids and MSWI fly ashes; however plants did not grow at all in mixtures containing the latter, most likely due to the high concentration of chlorides (82 g/kg in the leachate) in this ash. It is known that high salinity of soil can reduce germination by e.g. limiting water absorption by the seeds. The concentrations of As, Cd and Pb in grown plants were negligible in most of the soils and were below the instrument detection limit values. The proportions of biofuel fly ash and biosolids can be adjusted in order to balance the amount and availability of macronutrients, while the possible increase of potentially toxic elements in biomass is negligible seeing as the plant uptake of such elements was low.

Root penetration through sealing layers at mine deposit sites

To prevent acid mine drainage arising from oxygen and water penetration of sulphide-rich mine tailings, the tailings are covered with layers of dry sealing material. Plant roots have a great ability to penetrate dense materials, and if the roots are able to penetrate the sealing layer of a tailings deposit, its oxygen-shielding properties could be reduced. The objective of this study was to evaluate whether plant roots are able to penetrate sealing layers covering mine tailings deposits. Root penetration into layers of various sealing materials, such as clayey moraine (clay, 8-10%; silt, 22-37%; sand, 37-55%; gravel, 15-18%), moraine (unspecified), 6-mm bentonite (kaolin clay) fabric, lime and clay, Cefyll (mixture of pulverized coal fly ash, cement and water) and a mixture containing biosludge (30-35%) and bioashes (65-70%), was investigated. In the field, roots were studied by digging trenches alongside vegetation growing in 3- and 10-year-old mine sites. In the greenhouse root growth of Betula pendula, Pinus sylvestris, Poa pratensis and Salix viminalis were studied in compartments where the plants had been growing for 22 months. The results from the field experiment indicated that roots are able to penetrate both deep down in the cover layer (1.7 m) and also into the sealing layers of various materials, and even to penetrate hard Cefyll. The addition of nutrients in the top cover reduced deep root growth and thereby also penetration through the sealing layer. Low hydraulic conductivity of the sealing layer or a thick cover layer had less effect on root penetration. In the greenhouse experiment roots did not penetrate the thin bentonite fabric, due to low pH (2.1-2.7) that was created from the underlying weathered mine tailings. The clayey moraine was penetrated by all species used in the greenhouse experiment; Pinus sylvestris had the greatest ability to penetrate. To prevent root penetration of the other sealing layer, a suitable condition for the plants should be created in the upper part of the cover layer, namely a sufficient amount of plant nutrients. However, to define such a condition is difficult since different plant species have different requirements.