Assessment of the impact of railway traffic on the state of plant communities

The article reflects the results of studies on the impact of railway traffic on plant communities. The anthropogenic impact on the environment is complex. Many factors affect the species diversity of the flora near railways in different ways. The accumulation of Cd, Zn, Pb, Cr in plants ofPimpinella saxifragaL.,Hypericum perforatumL.,Trifolium mediumL was revealed. The anthropogenic stress leads to disruption of naturally formed ecosystems, which manifests in a decrease in species diversity, density and biological productivity. As a result of the anthropogenic impact adventitious plants appear, the share of which is 11% of the flora. Research in this area contributes to a deeper understanding of the processes of anthropogenic transformation of floristic complexes and should become the basis for environmental monitoring of disturbed habitats.


Introduction
Most of the technologies used by humanity today have anthropogenic impact to one degree or another and lead to ecosystem degradation. Railways are no exception.
A railway is a land corridor alienated from the natural environment, artificially adapted to the movement of trains with specified technical indicators. For the ecological system, it is an alien, aggressive element [1,2].
Railway traffic has an impact on the environment. The railroad system is seriously facing the challenges of reducing and preventing environmental pollution [3].
The main source of pollution is the exhaust gases of diesel locomotives. They contain carbon monoxide, nitric oxide and dioxide, various hydrocarbons, sulfur dioxide, and soot. Studies have shown that the content of carbon monoxide, nitrogen oxides, sulfur dioxide in the air exceeds the one-time maximum permissible concentration values. This indicates a significant air pollution by exhaust gases of diesel locomotives [4,5].
In the course of operation of railway transport, synthetic surfactants, oil products, phenols, hexavalent chromium, acids, alkalis, heavy metals, organic and inorganic suspended solids penetrate into the soil. The content of petroleum products in wastewater exceeds the maximum permissible concentration. The soil pollution is much higher in or near the areas where rolling stock is washed and flushed [6].
The anthropogenic impact on the environment can be local (from a single factor) or complex (from a group of different factors). These impacts, as a rule, are characterized by different environmental hazard coefficients depending on the type of impact and its nature, as well as the object of impact.
Operation of a railway greatly affects the habitat of plants. A railway changes the nearby landscape -it is becoming more open. Maintenance and repair activities affect the nature of the vegetation cover in all functional areas. In the first zone treatment by pesticides is performed, in the second zone burning is used along with pesticides, in the third zone -burning, mowing of the grass stands, cutting down of undergrowth of treeshrub species. These are just the main activities of the railroad services.
In addition, the impact of many factors affects the species diversity of the flora near railways in different ways: the sources of the formation of the indigenous component are, first of all, roadside biotopes, vegetation of adjacent territories. In case of a very severe pollution of the habitat, the plants stop developing and die [7,8].
The trends in the railway flora are most clearly "manifested only with the appearance of species alien to the local flora", while other aspects of the interaction of railways and adjacent natural complexes are ignored [9,10].
This project is aimed at studying the anthropogenic impact of railway traffic on plant phytocenoses that are located along the railway running through the territory of the Tobolsk industrial site (Tobolsk, Tyumen region, Russia). In this territory, there are railway tracks characterized by a high intensity of railway traffic.

Material and methods
The plots for study are located 10 meters along the railway track, at a considerable distance from each other. Plots 1, 2, 3 were located near the SIBUR Tobolsk LLC site, and plots 4, 5, 6 were located near the ZapSibNeftekhim LLC site. These enterprises are part of the Tobolsk Industrial Site (Tobolsk, Tyumen region, Russia). It is noted that the second line of the railway track (LLC ZapSibNeftekhim) is characterized by a heavy traffic.
The selection of geobotanical sites and the description of vegetation were carried out according to the methodological techniques adopted in phytocenology and widely used in geobotanical studies. The main method used in the field part of the research was the method for describing communities of terrestrial vegetation. At the geobotanical sites, the species composition of vascular plants at the time of survey and description was identified.
Dimensions and configuration of the area: 10m × 10m = 20 m 2 . In total, 6 geobotanical descriptions were drawn up during the field studies [11,12,13]. Vegetation samples were taken at the studied sites for a chemical analysis. For the purpose of decomposition, the most common (dominant) types of plants were selected for all plots. The sample (m = 0.3 g) was placed in a plastic tube. Then H2SO4:H2O2=1:3 was added. The samples were prepared using the speedwave MWS-2 microwave digestion system manufactured by PerkinElmer (USA).
The tube was placed in a microwave oven to decompose the sample using the program recommended by the manufacturer of the oven. The following heating conditions were used: temperature increased to 200 °C within 5 min, keeping for 5 minutes at 200 °C, cooling to 45 °C. The dissolved sample was transferred to a 15 mL test tube. The volume was brought up to 10 mL with distilled water. Then the sample was analyzed.
The quantitative chemical analysis of accumulated heavy metals and trace elements (Cd, Zn, Pb, Cr) in the soil samples and the total plant mass was conducted by the inductively coupled plasma method using the Optima 7000 DV atomic emission spectrometer manufactured by PerkinElmer (USA). Standard solutions of PerkinElmer (USA) were used for calibration. Before measuring the samples, the required parameters for the measurement were set (the background was measured, the necessary calibration was performed (the minimum and maximum concentration of 0.05-10 mg / dm 3 ).
Statistical processing of experimental data was performed using the Statistica 10.0 software. The arithmetic mean values (X), the standard errors of the arithmetic mean (SD), and the significance of differences in the arithmetic mean by Student's t criterion were calculated. The density of the plant community was determined by counting all individual vascular plants on the test sites. For this purpose, three squares (record plots) of 1 m 2 were set out within the sites. All grasses on the record plots were cut up to the soil level. In laboratory conditions, the phytomass was sorted by species. Then, the number of shoots was counted [14].
The biological productivity is the ability of living organisms to create, preserve and transform the organic matter. The productivity of a biological community is the amount of organic matter synthesized per unit time and unit area. The biological productivity of a plant community is composed of products of individual plant species making up this community or, more precisely, their coenopopulations. Thus, the biological productivity of individual plant species making up the plant community is the rate of phytomass accumulation over a certain time interval [14,15].
The grasses cut from three record plots were packaged in separate labeled bags. The bags were hermetically sealed to prevent evaporation of water. In laboratory conditions, the phytomass was weighed. It was dried in the open air, and the air-dried phytomass was weighed again. The collected material also served as the basis for calculating the oxygen productivity.

Results
Plant communities near the railway are characterized by diversity in species composition and structure. As a result of the analysis of the examined plots, forty-five species of vascular plants were identified.
The areas with a wide embankment (1,2,3) differ in the greatest variety of species; the nature of the vegetation cover of the surrounding area, near the railway track, also has an effect. Plants growing on railway embankments are evenly distributed by ecologicalcoenotic groups. Many eco-coenotic groups include a small number of species; therefore, it is convenient to combine them into ecological groups.
Fifteen species of adventive plants were noted, which makes up 11% of the flora. Adventive plants appear as a result of anthropogenic impact on phytocenoses, i.e. the number of adventitious plants in the flora is affected by the intensity of the anthropogenic impact. Therefore, they can be a sensitive indicator of anthropogenic stress. Thus, alien plants take an active part in the formation of the flora of railway embankments.
Most plant species present at the studied plots belong to the meadow type of vegetation. These species are dominant in the meadow phytocenosis. By the number of species, the group of weeds is also numerous, the presence of which indicates anthropogenic impact on the natural meadows.
It has been demonstrated that the ecosystem located at plots 3-5 is experiencing the most severe oppression. The territory of plots 1-3 is in more favorable conditions. The density of phytocenoses at the plots includes: the total average number of individuals per three meter test square -523 (1), 423 (2), 598 (3), 135 (4), 301 (5), 299 (6) specimens of shoots per 1 m 2 .
As a result of the study, it was revealed that the plant communities of plots 4,5,6 experience an anthropogenic impact, which affects the species composition of the vegetation cover, as well as density, biological productivity and oxygen productivity ( Table  1). It is known that the chemical composition of plants reflects the elemental composition of soils. Therefore, the excessive accumulation of anthropogenic compounds by plants is due primarily to their high concentrations in soils.
The results obtained revealed the accumulation of heavy metals in plants. For analysis, the most common plant species that were found in all areas were selected: Pimpinella saxifraga L., Hypericum perforatum L., Trifolium medium L.
The concentration of cadmium, zinc, lead, and chromium was determined. Cd, Crelements of intense absorption, Zn, Pb, -medium degree of absorption.  Table 2. Heavy metal content in Pimpinella saxifraga L., Hypericum perforatum L., Trifolium medium L., mg/kg To this end, we attempted to identify the main factors affecting both the formation of railroad flora and the functioning of floristic complexes.

Conclusion
Based on the studies conducted, it can be noted that the intense accumulation of heavy metals leads to disruption of naturally formed ecosystems, which is reflected in a decrease in species diversity, density and biological productivity. This is due to the complex environmental conditions prevailing in each of the plots. These indicators are decreasing in areas with intensive operation of railway transport. Fifteen species of adventive plants were identified, which makes up 11% of the flora. Adventive plants appear as a result of an anthropogenic impact on phytocenoses. Therefore, they can be a sensitive indicator of the anthropogenic stress. Thus, alien plants take an active part in the flora formation at railway embankments. Research in this area contributes to a deeper understanding of the processes of anthropogenic transformation of floristic complexes and should be the basis for environmental monitoring of disturbed habitats.