Preliminary assessment of growth and survival of green alder (Alnus viridis),a potential biological stabilizer on fly ash disposal sites

Marcin Pietrzykowski?Wojciech Krzaklewski?Bart?omiej Wos′

Preliminary assessment of growth and survival of green alder (Alnus viridis),a potential biological stabilizer on fly ash disposal sites

Marcin Pietrzykowski?Wojciech Krzaklewski?Bart?omiej Wos′

This paper presents preliminary assessment of seedling survival and growth of green alder(Alnus viridis (Chaix)DC.in Lam.&DC.)planted on fly ash disposal sites.This kind of post-industrial site is extremely hard to biologically stabilize without top-soiling.The experiment started with surface preparation using NPK start-up mineral fertilizer at 60–36–36 kg ha-1followed by initial stabilization through hydro-seeding with biosolids(sewage sludge 4 Mg ha-1dry mass)and a mixture of grasses (Dactylis glomerata L.and Lolium multiflorum Lam.) (200 kg ha-1).Subsequently,three-years-old green alder seedlings were planted in plots on two substrate variants: the control(directly on combustion waste)and plots with 3 dm3lignite culm from a nearby mine introduced into the planting pit.Five years of preliminary monitoring show good survivalseedling rates and growth parameters(height (h),average increase in height(D h),number of shoots(Lo) and leaf nitrogen supply in the fly ash disposal habitat. Treatmentof the site with a combination of lignite culm in planting pits and preliminary surface preparation by hydroseeding and mineral fertilization had the most positive effect on green alder seedling parameters.The resultsindicate that it is possible and beneficial to use green alder for biological stabilization on fly ash disposal sites.

Fly ashGreen alderSeedlings survivalGrowthBiologicalstabilisation

Introduction

Electric power generation by combustion of lignite produces large amounts of waste in the form of ash and slag, most of which(about 70%)is deposited on the earth’s surface(Asokan et al.2005;Haynes 2009).Combustion waste exhibits a numberofunfavourable characteristics for biological stabilization and revegetation,including among others high susceptibility to cementation,strongly alkaline reaction,high salinity and high susceptibility to erosion (Junor 1978;Adriano et al.1980;Carlson and Adriano 1991;Pavlovic′et al.2004;Cˇerma′k 2008;Haynes 2009). Disposalsites composed of combustion fly ash are a source of air pollution and dust dispersal in surrounding areas (Junor 1978;Haynes 2009).To prevent erosion,various methods of surface stabilisation have been used including sealing layers of bituminous and asphalt emulsions(Carlson and Adriano 1991;Haynes 2009).These methods are, however,very expensive.Biological stabilisation of ash deposit sites consists mainly of planting turf or trees after an earlier application of an insulating layer in the form of a fertile sediment(Junor 1978;Carlson and Adriano 1991; Cheung et al.2000;Cˇerma′k 2008;Haynes 2009).However,the main problem with the use of this type of insulation is a shortage of suitable substrates and considerable cost of transportation and earthworks for large sites.

Combustion waste is characterised by a number of physical and chemical properties unfavourable for thegrowth oftrees,namely:high susceptibility to compaction, poor air and water ratios,excessively alkaline reaction, high EC variability,an almost complete absence of nitrogen and available phosphorus,and in some cases high content of heavy metals(Adriano et al.1980;Pillman and Jusaitis 1997;Cˇerma′k 2008;Haynes 2009;Krzaklewski et al.2012).Under such conditions it is important to develop methods for improving the properties of the substrate and to obtain biological stabilisation through permanent introduction of woody species.This is only possible with the use of a complex procedure taking into account appropriate selective disposal of waste already at the depositing stage,and subsequent improvement of the soilproperties by NPK mineralfertilising with the addition of a fertilising supplement(e.g.lignite),followed by the introduction of quickly adapting woody species with phytomelioration functions.In this process itis also necessary to apply initialsurface stabilization with biosolids(sewage sludge)(Krzaklewski et al.2012).Hence,to successfully afforest disposal sites,it is extremely important to test the adaptability of tree species to extreme habitat conditions (Carlson and Adriano 1991;Pavlovic′et al.2004;Cˇerma′k 2008;Haynes 2009;Pietrzykowski etal.2010;Krzaklewski etal.2012).

In forestland reclamation itispossible to promote natural succession by first planting pioneering species with phytomelioration and erosion prevention functions and only later planting species with more restricted habitat requirements.This is possible after pre-treatment of the substrate using reclamation treatments and pioneer vegetation to improve air–waterpropertiesofthe technosols,initiating the process ofaccumulation oforganic matter which is the key factor in the cycling of nutrients.Among the pioneering speciesyielding favourable habitatforming impacts,woody speciesofthe genus Alnus are essentialin forestrestoration. In the conditions surrounding the combustion fly ash disposal,green alderhasbeen used in addition to black and grey alder(i.e.species which have been utilised in other forest restoration)(Krzaklewski et al.2012).Alnus viridis(green alder)is distributed widely across the cooler parts of the Northern Hemisphere(Flora of North America;Flora Europaea,www.eFloras.org).In Europe,green alder is a subalpine species naturally occurring in the Alps(Ellenberg 1988).In Poland,green alder is naturally occurring only above the tree line in the Bieszczady Mountains.

This species has been introduced with good results on reclaimed mining areas composed of Quaternary sediments,including on waste dumps from lignite mining and on a former sand quarry(Krzaklewski et al.2003).This species,apart from its beneficial phytomelioration function,may also be particularly valuable for erosion prevention on disposal site slopes(Krzaklewskietal.2003).

Materials and methods

Study site

‘‘Lubien′’’combustion fly ash disposal site is located in central Poland(N 51 27,E 19 27).This region has precipitation ranging from 550 to 650 mm per year,average annual temperature from 7.6 to 8.0C and vegetation growing season from 210 to 218 days(Wos′1999).The disposal site has been in use since 1980 and currently occupies about 440 hectares of land.The study site is unique among local reclamation sites in that the entire facility is administratively zoned for afforestation.This presents a very difficult task due to the lack of sufficient quantities of mineral soil for use as insulation.

The disposalsite contains combustion waste with about 85%fly ash and 15%slag transported hydraulically and deposited on suitably constructed sedimentation tank polders.The main component of the fly ash is thermally processed silicates.The average contentof Al2O3and SiO2in the ash is about 60–70%and about 20%is calcium oxide CaO(Stolecki 2005).

Description of the experiment

The experiment was started in September 2005 on a wide shelfofthe combustion waste disposalsite.Eightplots were demarcated,each measuring 6 9 13 m and separated from one another by 2 m buffer strips.Initialstabilisation of the entire surface(both variants,see below)was accomplished by hydroseeding with biosolids(sewage sludge applied at 4 Mg ha-1)with a mixture of grass seeds(Dactylis glomerata L.i Lolium multiflorum Lam.)(200 kg ha-1)and NPK mineral fertilising at 60-36-36 kg ha-1.On this prepared soil,50 seedlings ofgreen alderperplotwere planted in pits measuring 40 9 40 9 40 cm with two substrate variants (with four replications each):(1)control(FA variant) (planted directly in fly ash after initial stabilization as described above),and(2)planting with 3 dm3of lignite culm(FA?L)amendmentperpit.

Saplings(three-years-old)of green alder were grown from seeds in the Bieszczady Mountains,an area in Poland where green alder occurs naturally.

Soil and litter sampling and laboratory tests

Before starting the experimentand to determine the initial properties ofthe substrate,a soilstick(Eijkelkamp set)was used to collect four collective samples from 16 points located along the diagonalof the surface from layers 0–20 and 20–40 cm.In addition,samples were collected fromseveral places in a stockpile of lignite culm used in the experiment.

Mixed samples of technosols were collected(1.0 kg mass of fresh sample)to determine basic soilproperties.In the lab,soil samples were dried and sieved through a 2.0 mm sieve.The basic soil parameters were determined using soil laboratory procedures:particle size distribution was determined by hydrometer analysis and sand fraction by sieving.SoilpH was determined in 1 M KClata 1:2.5 soil:solution ratio;electrical conductivity(EC)by conductometric methods at a 1:5 soil:solution ratio at a temperature of 21C;total nitrogen(Nt)using the Leco CNS 2000 analyser;available magnesium(Mg)by Schachtschabel’s method,potassium(K)and phosphorus(P)in a form available to plants was assayed in calcium lactate extract ((CH3CHOHCOO)2Ca)acidified with hydrochloric acid to pH 3.6 by the Egner-Riehm procedure and using the AAS method(Ostrowska etal.1991;Van Reeuwijk 2002).The contentoftrace elements(totalforms):Zn,Cu,Pb,Cd and Cr were determined after digestion in a mixture of HNO3(d=1.40)and 60%HClO4acid in 4:1 proportion,using the AAS method(Ostrowska et al.1991).

In autumn 2008,to determine the nitrogen content in plant material,leaves were collected from the top of the crowns of five trees on SW exposures regularly planted along the diagonal of each plot.The nitrogen content in alder leaves was determined using the‘Leco CNS 2000’device after they had been dried at65C and ground.

Assessment of survival and growth rates of trees and foliage sampling

Measurements and survival rate assessment of trees were conducted during autumn after the first year(2006)and afterfive years ofgrowth(2011).The following parameters were assessed on each plot:seedlings survival rate(%of live trees to the total number of trees planted),number of shoots(Lo)and height(h)of trees to 0.01 m accuracy. Average annual growth(D h)was calculated based on the results of measurements.

Statisticalprocedures

Data sets were statistically analysed using the Statistica 9.1 programme(StatSoft Inc.2009).Significant differences between mean values of survival rate and growth characteristics of green alder from differentgroups(e.g.substrate variants)were using the RIR-Tukey multiple comparison procedure(at p=0.05).Distribution conformity of the investigated features was compared to normal distribution using the Shapiro–Wilk test.The average analysis values characteristic for the substrate were compared using ANOVA preceded by Leven’s variance homogeneity test.

Results

Properties of the soil substrates

The initialcharacteristics of fly ash were unfavourable for the planted vegetation.They displayed a strongly alkaline reaction(pH in KCl:9.6),high EC(954.5 l S cm-1),low content of total nitrogen(Nt)at 272.25 mg kg-1and available forms of potassium(K2O)at 33.6 mg kg-1, magnesium(MgO)at 49.3 mg kg-1and phosphorus (P2O5)at 1.05 mg kg-1(Table 1).The content of selected heavy metals in fly ash was relatively low and did notpose any phytotoxic threat to the introduced vegetation:Zn 57.8 mg kg-1,Cu 22.3 mg kg-1,Pb 10.08 mg kg-1,Cd 0.75 mg kg-1and Cr 19.93 mg kg-1(Table 1).

Lignite culm used as enhancing substrate displayed the following properties:pH in KCl=5.5,PEW=162.0 l S cm-1, carbon content(C%)=57.26%,total nitrogen(Nt)= 4,800 mg kg-1,available forms of potassium(K2O)= 36.1,magnesium(MgO)=326.0 and phosphorus(P2O5)=4.6 mg kg-1of soil and trace amounts of the analysed heavy metals(Table 1).

Seedlings survivalrate,growth parameters and nitrogen supply

Green alder seedling survival in the first year of the experiment ranged from 83%(SD=17)in the control (FA)to 97%(SD=2)in the variant with lignite (FA?L)and after5 years itwas significantly lowerin the control(FA)at72%(SD=25),while in the variantusing lignite(FA?L)it declined slightly to 93%(SD=2) (Fig.1).Height(h)after 5 years ranged from 74 cm in control plots(FA)to 93 cm in the plots enhanced with lignite(FA?L),and the difference was statisticallysignificant(Fig.2).The average height gain over a 4-year period(autumn 2006–spring 2011)was 5.2 cm year-1for control plots(FA)and 7.8 cm year-1in the plots with lignite enhancement(FA?L).However,these differences were notstatistically significant.The number ofgreen alder tree shoots(Lo)after 5 years of growth ranged on average from 6 shoots/tree in control plots(FA)to 7 shoots/tree in the plots with lignite culm(FA?L)(Fig.3).

Table 1 Initial properties of technosol substrate used in the experiment:fly ash and lignite culm

Fig.1 Survival rate(%)of green alder trees in the experiment at Lubien′combustion fly ashes disposalsite

Fig.2 Average height(m)of green alder trees in the experiment at Lubien′combustion fly ashes disposal site

Fig.3 Number ofshoots(pc)ofgreen alderatLubien′combustion fly ashes disposal site

The nitrogen(N)contentin the foliage(leaves)of green alder was similar in both substrate variants.N content averaged 28.30 g kg-1in the control plots and 29.46 g kg-1in the plots with lignite enhancement.

Discussion

Under natural conditions in the Bieszczady Mountains, green alder occurs in permanently humid Eutric Gleysols (FAO-UNESCO ISSS-ISRIC 2006;Soil Atlas of Europe 2005)and in a montane climate.Average annual temperature varies from 4 to 6C and annual rainfall can be as high as 1,300 mm(Wos′1999).However,in the area of‘‘Lubien′’’disposalsite,the annualtemperature ranges from 7.6 to 8.0and annualrainfallis low(550–600 mm)(Wos′ 1999).The disposal site introduced a rainfall retention watermanagementscheme which means thatvegetation on the site uses only rainwater.Therefore,satisfactory seedling survivaland growth ofgreen aldersupports its putative potentialfor high adaptability to extreme conditions on the combustion waste disposal site.

In Poland,green alder has been planted experimentally to date on post-mining sites reclaimed for forestry such as:‘‘Szczakowa’’sand pit,‘‘Siersza’’Coal Mine Carboniferous waste dump and‘‘Be?chato′w’’Lignite Mine external dump(Krzaklewski et al.2003).Following 4 years of green aldergrowth,average heightranged from 51.5 cm in Szczakowa to 126.5 cm on carboniferous waste.Alders typically formed 4–6 shoots and survivalranged from 77% at Szczakowa sand pit to 79%at Be?chato′w Lignite Mine external dump(Krzaklewski et al.2003).Compared to these values,the green alder growth and survivalmeasured on both variants of substrates in this experiment may be regarded as good.

Combustion waste deposited on disposal sites typically has numerous physical and chemical properties unfavourable for plant growth(Junor 1978;Adriano et al.1980; Carlson and Adriano 1991;Pavlovic′et al.2004;Krzaklewski et al.2003;2008;Haynes 2009).To improve the properties of the substrate and the growth conditions for trees without top-soiling,apart from NPK mineral fertilization and initial stabilization using hydroseeding with biosolids(sewage sludge),the experiment tested the use of powdered lignite introduced into the planting pits.Available literature documented use oflignite as a fertiliser(Kwiatkowska et al.2008;Chassapis et al. 2009;Giannouli et al.2009;Krzaklewski et al.2012). Furthermore,powdered lignite culm was available in the immediate vicinity of the ash disposal site from lignite mines.After 5 years of growth,green alder in plots where lignite was applied(FA?L)displayed significantly higher seedling survival,lowervariability in seedling survivaland significantly greater seedling height(h)in comparison to seedlings planted on the controlplots(FA).This indicateshighervariability and instability ofconditions affecting the survival rate of seedlings on control plots(FA).For these reasons,the use of a combination of lignite culm,initial fertilising and stabilization by biosolids,and a mixture of appropriate grass seeds for substrate improvement,is recommended as reclamation treatment.

Apart from the growth rate,nutrient supply is an important aspect in the assessment of tree adaptability to extreme conditions(Heinsdorf 1999).Nitrogen is particularly scarce in post-industrial areas(Li and Daniels 1994; Heinsdorf 1999;Kuznetsova et al.2011).Uptake of nitrogen from combustion fly ash may be difficult due to limited development of root nodules on the roots of alder trees as a result of phosphorus deficiency(Ekblad and Huss-Danell 1995;Uliassi and Ruess 2002),water deficit (Sundstrom and Huss-Danell 1987)and the absence of symbiotic rhizosphere microorganisms(Chaia etal.2010). However,there is no estimate of the optimum range of nitrogen contentin the leaves ofgreen alder.Generally,for European conditions,nitrogen content in leaves of trees of Alnus species ranges from 20 to 40 g kg-1(Urietal.2002; Kuznetsova etal.2011).In view of this documented range, the nitrogen content in the leaves of green alder in this study(28.30–29.46 g kg-1)suggests green alderis a robust choice for planting on fly ash disposal sites.This also confirms green alder’s high seedling survivaland potential adaptability to the habitat conditions at combustion waste disposal sites,and good assimilation of nitrogen in an environment characterised by a paucity of this element.In addition to the adaptability of the species,it also indicates perspective for phytomelioration by increasing nitrogen cycling in the emerging ecosystem.

Conclusions

The applied biologicalstabilisation treatmentand enhancement of fly ash substrate properties by initial NPK mineral fertilization(60–36–36 kg ha-1)and stabilisation using hydroseeding with biosolids(sewage sludge 4 Mg ha-1)and a mixture of appropriate grass seeds(200 kg ha-1D. glomerata and L.multiflorum)permitted the survival and growth ofgreen alder.Within the first5 yearsafterplanting, alder exhibited good growth,high survival and adequate nitrogen supply on all experimental plots.The addition of 3 dm3lignite culm per planting pit to the combination of mineral fertilizer and initial stabilization by biosolids significantly improved the growth ofgreen alderand resulted in its higher(and less variable)survival as compared to trees planted on controlplots(fly ash with initialfertilising only). We conclude thatgreen alderis a usefulspecies forbiologicalstabilisation oflignite combustion fly ash disposalsites.

AcknowledgmentsThe authors appreciate the efforts of parties representing mining firms:Power Plant‘‘Be?chato′w’’,and The State Forests National Forest Holding PGL Lasy Pan′stwowe,Forest Districts:Be?chato′w,who provided site accesspermissionsand assistance. Thanks to Iwona Skowron′ska MSc.from Laboratory of Geochemistry and Reclamation,Dept.of Forest Ecology and Forest Soil Science for laboratory analyses.This study was financially supported by the Polish Ministry of Science and Higher Education in frame of DS 3420 KEkL, Dept.of For.Ecol.UA in Krakow.We thank for Natalie S.van Doorn of the Dept.of Environmental Science,Policy,and Management, University of California,Berkeley for her criticaltextcorrection.

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17 April 2013/Accepted:17 December 2013/Published online:22 January 2015

Project funding:This study was financially supported by the Polish Ministry of Science and Higher Education in frame of DS 3420 KEkL 2013,Department of Forest Ecology,Agricultural University of Krakow.

The online version is available athttp://www.springerlink.com

Corresponding editor:Chai Ruihai

M.Pietrzykowski(&)W.KrzaklewskiB.Wos′

Department of Forest Ecology,Forest Faculty,University of Agriculture in Krakow,Al.29 Listopada 46,31-425 Krako′w, Poland

e-mail:rlpietrz@cyf-kr.edu.pl