نوع مقاله : مقاله پژوهشی
1 دانشکده کویر شناسی، دانشگاه سمنان
2 جنگلداری، کویرشناسی، دانشگاه سمنان، سمنان، ایران
3 سازمان تحقیقات، آموزش و ترویج کشاورزی، تهران، ایران
عنوان مقاله [English]
Caspian forest of Iran with an area of approximately 1.8 million hectares with more than 80 species of trees and 50 species of shrubs have been identified as the oldest forests in the world which belong to the third geological period. Increasing growth of human population and the development of industries to response of its demands, cause to production of various types of waste. Select landfill without regard to environmental issues poses many threats to the environment, choosing the right place and location for landfill is essential. Accumulation of waste in the forest increases heavy metals such as lead, cadmium, nickel and chromium. Some trees are very sensitive to leachate from sewage and dry out quickly.
Hyrcanian forests are one of important reserve habitat in our country. There are many various natural and human threats on it that cause many problems in its ecosystem. One of these threats is landfill forest. Also, the lack of effective studies to determine the negative effects of landfills on forest ecosystems, the purpose of the present study identifies the negative effects of landfills in forest areas in Zarandin region of Neka city.
The purpose of this study is to investigate the effect of landfills in forest lands on heavy metals (lead, cadmium, nickel and chromium) and tree species in Zarandin region. The study area is a forest ecosystem around Zarandin landfill with an area of about 26 hectares located 9 km southeast of Neka city. The important tree species and shrubs of the area can considered to Zelkova carpinifolia (Pall.) k.koch, Parrotia persica C.A.Mey , Quercus castaneifolia C.A.Mey, Carpinus betulus L., Acer velutinum Boiss, Alnus subcordata C.A.Mey ,(Acer cappadocicum Gled ,Diospyros lotus L., Mespilus germanica L, Crataegus microphylla k.koch , Prunus divaricate Ledeb.
Along the leachate channel, 10 sampling stations were selected up to a distance of 1000 meters from the landfill. Stations were chosen at intervals of 100 meters along the channel. each sampling station includes of two points; one point at the edge of the channel and the second point at a distance of 20 meters from the channel. Soil samples were taken with three replications. A forest area adjacent to the landfill with similar environmental and floristic characteristics but far from the direct impact of the landfill was selected as a control area. in the control section 10 samples were taken. At each station, soil samples were prepared for laboratory operations. Vegetation inventory were also performed in all plots. The selected plots were similar in terms of slope, general direction and height to minimize the impact of environmental conditions and topography on the comparisons. Plots 20 × 20 m were used to study tree and shrub species and plots 1 *1 m were used to analysis of tree species generation and grass coverage.
Determination of heavy metal concentrations
Soil samples were tested to determine the concentrations of the heavy metals lead, nickel, cadmium and chromium. For chemical analysis, the concentration of heavy metals in the soil is weighed 1 gram of each sample dried by a digital scale and poured into Erlenmeyer containers. Then 10 cc of concentrated nitric acid is added to it and placed on a digester (Hot block digester) and placed at a low temperature of 130 ° C for 1 hour and then 400 cc of hydrogen peroxide is added to it. Samples are filtered with S&S filter paper in 50cc c-balloons and the filtered solution is reduced to 50cc using deionized water and poured into plastic containers (Heinrichs et al., 1986).
In order to investigate and evaluate soil contamination in the study area, the results of heavy metal analysis with NFSI index (Utermann et al., 2019) were compared and the enrichment factor of all samples was calculated.The concentration of elements compared to the normal concentration was measured using the enrichment factor. The following equation was used to calculate this factor.
EF = Se / Re
EF is the enrichment factor, Se is the concentration of elements in the soil and Re is the concentration of elements in the reference material. The classification of enrichment factor values in determining the degree of contamination is given in the table below (enrichment factor value classification table) (Bhuiyana et al., 2010).
Table 1: Classification of enrichment factor values
Factor amount Pollution degree
No pollution 0
No pollution to moderate pollution 1
moderate pollution 2
Medium to strong pollution 3
strong pollution 4
strong pollution to Very strong pollution 5
Very strong pollution 6
The results showed that the pH and EC in the soil of the contaminated area increased and the concentration of all studied metals in the contaminated area compared to the control area showed a significant difference (P <0.05). The density of Parrotia persica, Carpinus betulus and Zelkova carpinifolia in the infected plot was lower than the control plot. Quecus castanifolia did not show a significant difference but the number of Acer sp in the infected area showed a significant increase. Also, reproduction of Carpinus betulus, Quecus castanifolia and Zelkova carpinifolia in the infected area, a significant decrease and Parrotia persica and Acer regeneration in the infected plot showed a significant increase.
Finally, the results of this study showed that the acidity, concentration of lead, nickel, chromium, cadmium in the soil of the landfill and its margin was significantly higher than the soil of the control area. Soil factors such as pH and EC was high in soil samples in infected area. Also, the results of density of tree and shrub showed that the difference in species density between infected and control plots was significant in all species except Quecus castanifolia. The number of Parrotia persica and Carpinus betulus and Zelkova carpinifolia tree stocks showed a significant decrease in the infected area.
Finally, the results of this study showed that municipal waste landfilling has significant effects on the chemical properties of forest soil, so providing the necessary facilities for waste management such as waste incinerators and compost factories in these areas is necessary. It is also necessary to conduct more extensive studies in order to obtain comprehensive information for optimal forest management and reduction of pollution and its spread in forest areas.