Functional Traits of Plant Species Suitable for Revegetation of Landfill Waste from Nickel Smelter
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applied sciences Article Functional Traits of Plant Species Suitable for Revegetation of Landfill Waste from Nickel Smelter Malvína Ciernikovˇ á 1,*, Ivana Vykouková 1 , Tomáš Orfánus 2 and Elena Masaroviˇcová 1 1 Department of Soil Science, Faculty of Natural Sciences, Comenius University, Mlynská dolina, Ilkoviˇcova6, 842 15 Bratislava, Slovakia; [email protected] (I.V.); [email protected] (E.M.) 2 Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovakia; [email protected] * Correspondence: [email protected] Abstract: The landfill waste of leached ore residue represents a serious environmental risk and may also negatively affect the appearance, growth and development of vegetation. Here we focused on the evaluation of functional traits of selected plant species Populus alba, Calamagrostis epigejos, and Diplotaxis muralis growing in an unfavourable environment. We determined different adaptive strategies of selected species to extreme conditions. For Diplotaxis muralis the highest values of the leaf dry matter content (LDMC) and the lowest values of the specific leaf area (SLA) were determined, while for Calamagrostis epigejos these two traits correlated in opposite directions. Populus alba reached the lowest value of the water saturation deficit (WSD), suggesting that this species was most affected by soil water deficiency. The leaf water content (LWC) correlated negatively with the LDMC and positively with the SLA (narrow leaf blade). Although each plant species belongs to a different strategic group (therophyte, hemicryptophyte and phanerophyte in the juvenile stage), they are all very plastic and therefore suitable for remediation. Despite the unfavourable conditions, selected plant species were able to adapt to poor conditions and form more or less vital populations, which indicate the revegetation as a key measure for remediation of landfill waste from nickel smelter. Citation: Cierniková,ˇ M.; Keywords: landfill waste; revegetation; functional traits; extreme conditions Vykouková, I.; Orfánus, T.; Masaroviˇcová,E. Functional Traits of Plant Species Suitable for Revegetation of Landfill Waste from 1. Introduction Nickel Smelter. Appl. Sci. 2021, 11, 658. https://doi.org/10.3390/ Industrial activities leave unwanted traces in the surrounding territory and have a app11020658 severe impact on the environment. As is well known, industrial and mining wastes with a high content of heavy metals pose a risk to the environment and have a demonstrable Received: 7 December 2020 toxic effect on vegetation and soil microorganisms and their life processes [1–3]. These Accepted: 8 January 2021 environmental burdens represent a very negative factor influencing the functional spatial Published: 12 January 2021 structure of the landscape. There is not only contaminated groundwater around the landfill but also a high level of air pollution with toxic dust. [4]. Recently, various methods have Publisher’s Note: MDPI stays neu- been used worldwide for the remediation of similarly contaminated sites: isolation and sta- tral with regard to jurisdictional clai- bilization of geochemically transformed elements [5–7], using natural alkaline material [8], ms in published maps and institutio- covering of mine tailings by using inert materials [9], soil washing [10], electrokinetic nal affiliations. remediation [11], microbiological methods [12] and many others. These technologies can be successful but generally require several specific processes, which take a long time. They are often expensive and can be practically used only in small areas [13]. Therefore, there is currently an increasing emphasis on the use of various phytotechnologies, including Copyright: © 2021 by the authors. Li- censee MDPI, Basel, Switzerland. phytoextraction, phytodegradation, rhizofiltration, phytostabilization, phytovolatilization This article is an open access article or phytocapping [1,13–15]. Revegetation is a low-cost measure based on the use of naturally distributed under the terms and con- occurring plants to cover mining sites to not allow a release of heavy metals from mining ditions of the Creative Commons At- waste into surrounding soil, groundwater and air by creating natural surface biomass layer tribution (CC BY) license (https:// as well as a branched root system. Thanks to this plant cover, water and wind erosion creativecommons.org/licenses/by/ are also prevented, rhizosphere properties can be improved and thus the landfill can be 4.0/). gradually revitalized [13]. Appl. Sci. 2021, 11, 658. https://doi.org/10.3390/app11020658 https://www.mdpi.com/journal/applsci Appl. Sci. 2021, 11, x FOR PEER REVIEW 2 of 14 Appl. Sci. 2021, 11, 658 2 of 14 and wind erosion are also prevented, rhizosphere properties can be improved and thus the landfill can be gradually revitalized [13]. The investigated site was the landfill waste of black mud near the town of Sereď (SW Slovakia),The investigated which is a sitesource was of the heavy landfill metal waste contamination. of black mud The near landfill the town environment of Sered’ (SW is Slovakia),unfavourable which for plant is a source growth. of Landfill heavy metal material contamination. is not soil in Thethe real landfill sense; environment it is industrial is unfavourable for plant growth. Landfill material is not soil in the real sense; it is industrial waste that has poor physical properties without developed soil structure. Due to its black waste that has poor physical properties without developed soil structure. Due to its black colour, the landfill surface heats up and dries out very quickly. The material is strongly colour, the landfill surface heats up and dries out very quickly. The material is strongly alkaline (pH 8.5) and the organic content is very low 0.05%. The C:N ratio is 0.74:0.05. alkaline (pH 8.5) and the organic content is very low 0.05%. The C:N ratio is 0.74:0.05. Total content of Fe2O3 is 78% and Al2O3 3.27%. Content of chromium is the highest 24,300 Total content of Fe O is 78% and Al O 3.27%. Content of chromium is the highest mg/kg, nickel 2920 2mg/kg,3 zinc 300 mg/kg2 3 and copper 79 mg/kg. [16]. It does not contain 24,300 mg/kg, nickel 2920 mg/kg, zinc 300 mg/kg and copper 79 mg/kg. [16]. It does not enough biogenic elements for the proper plant growth and nutrition. Greening of the land- contain enough biogenic elements for the proper plant growth and nutrition. Greening of fill waste can be considered as one of the most natural, and in this case, the most appro- the landfill waste can be considered as one of the most natural, and in this case, the most priate remediation methods. appropriate remediation methods. This work was aimed to characterise native plant species that have been able to adapt This work was aimed to characterise native plant species that have been able to adapt inin anan extremeextreme environmentenvironment unfavourableunfavourable forfor plantplant growth.growth. TheThe functionalfunctional traitstraits ofof threethree plantplant speciesspecies PopulusPopulus albaalba,, CalamagrostisCalamagrostis epigejos and DiplotaxisDiplotaxis muralis were evaluated,evaluated, whichwhich reflectreflect thethe plant’splant’s responseresponse toto thethe habitathabitat andand aa wayway ofof adaptingadapting toto environmentalenvironmental conditions. 1.1. Site Characterisation InIn the the second second half half of of the the last last century, century, nickel nickel ore orewas was processed processed near nearthe town the townof Sereď of Sered’(SW Slovakia, (SW Slovakia, Figure Figure1), where1), where the landfill the landfill waste wasteof black of blackmud (waste mud (waste from the from colour the colourmetallurgy metallurgy of nickel of and nickel cobalt) and cobalt)is a direct is a evidence direct evidence of this activity. of this activity. The tailin Theg is tailing 45 m ishigh, 45 m800 high, m long 800 mand long 550 and m wide 550 m(Figure wide (Figure2). In the2). south, In the west south, and west east, and it east,is in itcontact is in contactwith agricultural with agricultural land and land represents and represents a significant a significant anthropogenic anthropogenic barrier [16]. barrier It is [ 16a ].dis- It istinct a distinct anthropogenic anthropogenic form of form relief of with relief a withtypical a typicalconvex convexunit (Fi unitgure (Figure 2). The2 ).site The is non- site iscombustible noncombustible and has and a hasdistinctive a distinctive shape shape of a tabular of a tabular terrace, terrace, which which was wasformed formed by the by thegradual gradual deposition deposition of waste of waste layers layers—black—black nickel nickel mud. mud. It has Itsteep has steepslopes slopes of up to of 45 up de- to 45grees degrees (anthropogenic (anthropogenic table table mountain). mountain). According According to a to field a field survey survey by by Michaeli Michaeli et et al. al. [[4],4], thethe landfilllandfill wastewaste hashas high permeability;permeability; therefore,therefore, rainwaterrainwater quicklyquickly penetratespenetrates thethe lowerlower layers,layers, andand thethe remainingremaining waterwater evaporatesevaporates quicklyquickly sincesince thethe blackblack nickelnickel mudmud stronglystrongly absorbs sunlight andand thus rapidlyrapidly overheats.overheats. Figure 1. Map of Slovakia with the landfilllandfill wastewaste location.location. After the closure of the smelting factory in Sered’, the landfill waste was formed by After the closure of the smelting factory in Sereď, the landfill waste was