Survival and growth of alders (Alnus glutinosa (L.) Gaertn. and Alnus incana (L.) Moench) on fly ash technosols at different substrate improvement

Abstract

Difficulties in disposal of fly ash resulting from coal combustion at electric power plants are of increasing concern. Establishment of vegetation is often an effective means of stabilizing solid wastes. This paper presents an evaluation of adaptation based on survival, growth and nitrogen supply of black alder and grey alder introduced on the landfill fly ash resulting from lignite combustion in ‘Bełchatów’ Power Plant (Central Poland). The research was conducted at 3 substrate variants: control with pure fly ash (CFA), with addition (3 dm³ in planting hole) lignite culm (CFA + L) and Miocene, acidic and carboniferous sands from overburden of ‘Bełchatów’ Lignite Mine (CFA + MS). Before putting the experience uniformly on the whole surface sewage sludge (4 Mg ha⁻¹) mixed with grass seedling (200 kg ha⁻¹) and mineral fertilization (N – 60, P – 36 and K – 36 kg ha⁻¹) were applied by hydroseeding. The results show the high adaptability of alders for extremely hard site conditions on the landfill ash. After 5 years of investigation the survival of black alder was from 61% (at CFA + MS) to 88% (at CFA + L), and grey alder from 81% (at CFA + MS) to 87% (at CFA). Black alder was characterized by higher growth parameters (diameter growth d₀ and height h) compare to grey alder. The best substrate for fly ash enhancement was lignite culm. Therefore, if the goal of biological stabilization of fly ash landfill would be the greatest increase of tree biomass for example for energy plantations, the recommend solution for substrate improvement is using of lignite culm and Black alder. However, the introduction of alders directly on the fly ash using start up NPK fertilising and hydroseeding with seed sludge may be recommend mainly for economic reasons, especially when the introduced alders are to have primarily protective and phytomelioration functions and thus prepare the substrate for the afforestation and next generation of target species.

Introduction

Generation of electric power through the combustion of coal produces large amounts of waste, of which 70–75% is fly ash (Haynes, 2009). Its use amounts to little more than 30% worldwide, it is mainly utilised in the production of building materials, the rest is transported to various landfills (Asokan et al., 2005, Haynes, 2009). The impact of fly ash landfills results in a number of changes in the adjacent ecosystems as toxic substances are leached out and transported to the soil and groundwater (Juwarkar and Jambhulkar, 2008, Dellantonio et al., 2009, Haynes, 2009). Among the characteristics of having an adverse impact on the environment, increased content of heavy metals and radioactivity of ash are listed, as well (Tripathi et al., 2004, Haynes, 2009). These properties are characterized by high variability, however, depending on the type and origin of coal burned in power plants (Haynes, 2009). Furthermore, ash from landfills is susceptible to wind erosion as it remains suspended in the air for a long time and thus becomes a major source of pollution. This negatively affects the health of the local population, causing irritation of the upper respiratory tract and a number of adverse health effects, including even lung cancer (Dellantonio et al., 2009, Pandey et al., 2009).

The primary method of preventing erosion of ash landfills is technical and biological surface stabilization. Sealing lids made of bitumen emulsion, asphalt and other substances are used for technical stabilisation. These methods are, however, very expensive. Biological stabilization of ash landfills consists mainly of planting turf or trees after an earlier application of an insulating layer in the form of fertile sediment (Junor, 1978, Carlson and Adriano, 1991, Jusaitis and Pillman, 1997, Cheung et al., 2000, Čermák, 2008, Haynes, 2009). The introduction of vegetation directly on the ash, without the insulating layer, is however most advantageous due to low cost and labour input; it is also beneficial for the landscape and effective as anti-erosion protection (Gupta et al., 2002). The accumulation of heavy metals from fly ash in trees can be important to limit the migration of xenobiotics into the waters and adjacent ecosystems (Tripathi et al., 2004, Gupta et al., 2007, Malá et al., 2010). The introduced vegetation is also an important element which initiates the processes of soil formation and the process of ecological succession on completely anthropogenic post-industrial sites. Combustion waste deposited in landfills displays numerous properties which are unfavourable for plant growth, including mainly: high susceptibility to compaction, poor air and water ratio, excessively alkaline reaction, high EC variability, an almost complete absence of nitrogen and available phosphorus, and in some cases high content of heavy metals (Hodgson and Townsend, 1973, Adriano et al., 1980, Gray and Schwab, 1993, Pillman and Jusaitis, 1997, Čermák, 2008, Haynes, 2009). In some cases such as ‘Lubień’ landfill belonging to ‘Bełchatów’ lignite power station (Central Poland), afforestation is planned in the future. This is a very challenging project due to the considerable size of the site (about 440 ha) and the necessity to recreate soil directly on an artificial substrate (fly ash), without the use of a mineral soil horizon. For these reasons it is necessary to develop effective methods of biological stabilization and reforestation allowing to recreate soils in situ on substrate and then to introduce the target tree species. This is possible primarily by improving physical and chemical properties of the deposited ash. In case of afforestation it is also necessary to test the adaptability of trees and shrubs to the conditions on fly ash landfills. In Europe in the course of experiments concerning tree planting of fly ash landfills the following species were introduced: Scots pine (Pinus sylvestris L.), Silver Birch (Betula pendula Roth), black locust (Robinia pseudoaccacia L.), red oak (Quercus rubra L.), common oak (Quercus robur L.), black alder (Alnus glutinosa (L.) Gaertn.) and willow (Salix sp.) (Pietrzykowski et al., 2010, Čermák, 2008). In addition, attention was drawn to Nitrogen-fixing tree species: silverberry (Elaeagnus angustifolia L.), bladder senna (Colutea arborescens L.), common sea-buckthorn (Hippophae rhamnoides L.) and honey locust (Gleditsia triacanthos L.) which have fairly high tolerance to the conditions of fly ash landfill (Hodgson and Townsend, 1973). In the North America some investigation on pulverized coal ash was tested as a substrate for woody plant species, included Nitrogen-fixing species like alders and other like maples (Scanlon and Duggan, 1979). As reported in literature sweetgum (Liquidambar styraciflua L.) and American sycamore (Platanus occidentalis L.) grew acceptably on fly ash after coal burning, as well (McMinn et al., 1982, Carlson and Adriano, 1991). Previous experiments show a satisfactory growth of the introduced woody plants species, but it should be noted that they were conducted mostly after the ash was topped with mineral soil (Hodgson and Townsend, 1973, Junor, 1978, Scanlon and Duggan, 1979, Carlson and Adriano, 1991, Cheung et al., 2000, Čermák, 2008, Haynes, 2009, Pietrzykowski et al., 2010). Such a practice in addition to substantial costs also entails the risk of root system deformation due to the fact that it develops primarily in the surface horizons containing mineral soil (Čermák, 2008). This is very important for the stability of the introduced afforestation in later phases of development. As mentioned above this technology is very expensive, and stocks of more fertile soil are limited. Therefore, at present, research is needed on the introduction of trees directly on to the ash.

The optimum method of afforesting post-industrial sites, which are highly difficult from the point of view of biological reclamation should be to stimulate natural succession by introducing first pioneering species which also have phytomelioration functions. Only after habitats are prepared and the initial soil formation process is dynamized by the pioneering species (improvement of air–water properties, accumulation of organic matter and nutrients) should species with higher habitat requirements (such as oaks) be introduced. In Central Europe different species of alders (Alnus sp.) have potential significance as, owing to their capability of atmospheric nitrogen fixing by symbiotic bacteria of genus Frankia sp., they play an important phytomelioration role (Kuznetsova et al., 2010).

This paper presents the results of experiments on the introduction of alders (A. glutinosa (L.) GAERTN. and Alnus incana (L.) MOENCH) to a landfill containing fly ash generated by lignite combustion. In the experiment, enhancing substrates were applied (lignite culm and Miocene acidic sands) available in the immediate vicinity of the site and a variant in which trees were introduced on to the ash with no insulating layer was also included. The survival and growth rate of trees within 5 years of staring the experiment were assessed. This period is crucial for survival of introduced tree species and first phase of biological stabilization.