Термоелектране у Србији–утицај летећег пепела на земљиште и биљке
Thermal power plants in Serbia – the impact of ash on soil and plants
Book part (Published version)
© Serbian Academy of Sciences and Arts
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Anthropogenically-caused disturbances, such as the formation of ash deposits as a result of the activities of thermal power plants, are processes which significantly alter the biodiversity of an area on varying temporal and spatial scales and all ecological levels. These processes lead to the loss of fertile soil; pollution of vegetation, soil and air; the uncontrolled introduction of allochthonous species; and erosion. The processes of anthropogenically-induced degradation reduce the quality of the habitat considerably, cause disturbances in the functioning of plants, as well as entire ecosystems, and set new demands in approaches to their restoration. Rarely in nature are plants exposed to the effects of just one stress factor; instead, exposure to multiple, complex effects is most common. In conditions at ash deposit sites, plants are continuously and simultaneously affected by the unfavourable physical and chemical properties of ash (increased salinity and alkalinity, B, As and Mo toxicity, and an N, P, K, Cu, Mn and Zn deficit) and extreme microclimatic conditions (drought and high temperatures). Such conditions limit the survival and development of vegetation at the ash deposits as they threaten the usual course of the physiological processes in plants (transpiration and photosynthesis) and with it, normal leafing, flowering and fruiting. It is frequently the case that the physiological activity of plants decreases prior to the appearance of visible damage symptoms. Despite the chronic and synergistic effects of stress factors, there are various plant species at the ash deposit sites which tolerate these unfavourable habitat conditions, and, with varying degrees of effort, manage to survive and spread across the ash. In this study, it is suggested favouring colonization by autochthonous plant species which take root easily and can populate the ash deposit site relatively quickly. The ecological potential of these species matches the potential of the ash deposits and hence the plants do not require any special management. Therefore, the best contenders for the recolonisation of the ash should be sought from among those species which have the following characteristics: plants which grow naturally in that area; perennials; plants which have an extensive root system and the ability for vegetative reproduction; plants which have nitrogen fixation ability (N-fixers); plants which can tolerate high pH, salinity and toxic elements; plants which are tolerant to extremely high temperatures and drought conditions. In the process of biologically restoring this type of degraded area, it is vital to bear in mind the existing ecological, vegetative and floristic potential of the area in question, which abounds in a wealth of life forms and ecological types of plants. Therefore, the spontaneous colonization of woody and herbaceous vegetation clearly points to one of the most important forms of activities aimed at stabilising the ash, with a minimum financial outlay. Aside from selecting the species, thought should also be given to when they are sown and planted, so as a cover that is functional all year round is formed. In addition, attention must be paid to the fact that different particle sizes of ash can be found at the ash ponds (from the coarsest particles on the embankments to the finest in the central areas), and this should be carefully considered when selecting the species which would be sown/planted on the embankments or in the central areas of the ash pond. The initial vegetative cover must also absorb nutrients effectively so as to prevent their being leached away into the deeper layers of ash and return them through decomposition, hence creating the conditions for the formation of the precursor to soil (humus). In this way, the conditions will be created for establishing stable plant communities. When the biological restoration of these sorts of areas is being considered, rather than talk about standards and regulations, it is far more worthwhile to reflect on experiences gained in recultivation, taking heed of the geographic and climatic circumstances, in order to allow for possible interpolation in concrete cases. Restoration strategies must be based on a sound knowledge of the characteristics of fly (mixture of boiler and fly ash) and bottom ash, of the deposition process and the characteristics of the ash deposit (technical specifications). In addition, it is important to know that the chemical characteristics of ash change over time, creating more favourable conditions for plant growth. Becoming acquainted with the conditions mentioned above and testing a large number of different plant species will allow vegetation cover to be quickly established, and the species selected for this purpose will bind the mobile substrate, as ash is, effectively, and reduce the unfavourable effects on the environment and human health. In addition, and no less importantly, this will result in a strategy for the long-term, sustainable management of ash deposits during the lifespan of thermal power plants. The permanent biological restoration of ash deposits is only possible once the thermal power plant has ceased operating as the periodic sluicing of ash into ash ponds which were inactive and which have already been colonised by plants destroys the long-term succession of vegetation. A biologically empty area forms once again and the process of revegetation restarts from the beginning.