Seasonal variation in leaf dust accumulation by vegetation of sub temperate region growing alongside the National Highway 5 in Himachal Pradesh
Abstract:
In order to develop the usefulness of plants as bio indicators, an appropriate selection of plant species is required which entails an utmost importance for a particular situation. Today’s growing population, rapid urbanization and industrialization has resulted in sudden increase in the number of vehicles. The air pollutants emitted out of motor vehicles are one of the major culprits for stress induced changes in plants. Air pollution may directly affect the plants via leaves or indirectly via soil acidification. Therefore, in the present study dust interception efficiency of some selected plant species alongside the National Highway 5 from Solan to Shimla in Himachal Pradesh was assessed. The plant species like Debregeasia hypoleuca, Rubus ellipticus and Quercus leucotrichophora which were common in occurrence along the highway were selected for the study. The dust accumulation pattern on leaves of selected plants was estimated during winter, spring, monsoon and summer seasons of the year. The highest amount of dust was accumulated by Rubus ellipticus, followed by Debregeasia hypoleuca which accumulated 0.057 g/m2 and Quercus leucotrichophora which accumulated 0.042 g/m2 of dust.
Keywords: Debregeasia hypoleuca, Rubus ellipticus, Quercus leucotrichophora
Introduction
Air pollution is one of the most severe problems, the world is facing today. The air pollutants transcend across boundaries and thus pose a threat to the vegetation, human health and even buildings and monuments. Since these are easily dispersed and not confined to a particular area, they affect not only the urban areas, but even spread to the rural area which is thus affecting agriculture, wildlife and forests. Today’s growing population, rapid urbanization and industrialization has resulted in sudden increase in the number of vehicles. Vehicular traffic is one of the major contributors of dust on plants growing alongside roads. Motor vehicles alone account for 60-70% of the pollution found in urban environment and thus the air pollutants emitted out of these are one of the major culprits for stress induced changes in plants (Dwivedi et al. 2008). Plants intercept tons of dust, absorb noise and serve as acoustic screens on busy highways and thus serve as sink by absorbing various air pollutants. The increasing number of industries and automobile vehicles are continuously adding toxic gases and other substances to the environment (Jahan and Iqbal, 1992). Industrialization and the automobiles are responsible for maximum amount of air pollutants and the crop plants are very sensitive to gaseous and particulate pollutants and these can be used as indicators of air pollution (Joshi et al., 2009). Plant leaves has been regarded as bio-filters as they absorb large quantities of particles from the environment CPCB (2007). The trees in urban environment improve air quality by enhancing the uptake of gases and particulate matter especially near roadways (Smith, 1971). Air pollutants damage plants, impair growth, and limit primary productivity according to their sensitiveness to pollutants (Ulrich, 1984).
Removal of pollutants by plants from air is done by three means, namely absorption by the leaves, deposition of particulates and aerosols over leaf surface, and fallout of particulates on the leeward side of vegetation which ultimately is decided by air movement (Tewari, 1994; Rawat and Banerjee, 1996). Vegetation naturally cleanses the atmosphere by absorbing gases and some particulate matter through leaves and consequently improves environment quality and human health. Trees remove pollution by intercepting airborne particles. Once inside the leaves the gas diffuses into intercellular spaces and may be absorbed by water films to form acids or react with inner leaf surfaces (Smith, 1990).
Urban trees particularly low volatile organic compounds (VOC) emitting species can be a viable strategy to help reduce urban ozone levels (Cardelino and Chameides, 1990; Tanah, 1996; Nowak et al., 2000) particularly through tree functions that reduce air temperature, remove air pollutants and reduce building energy and consequent power plant emissions. The foliage of plants filters several numerous solid particles due to roughness and large contact area and thus can reduce the damaging effect of particulate pollution. (Meusel et al., 1999).
Materials and Methods
Study area:
The study was conducted along the stretch of National Highway 5 from Solan, the Mushroom city of India to Shimla, which is an important tourist destination of North India; covering various small towns and villages in a total span of 45 Kilometres. The stretch of this highway is situated at an altitudinal range of 1450-2000 metres above mean sea level. The average annual rainfall of the region is in the range of 1150- 1600 mm and the temperature varies from around 100C in winters to 320C in summers. The terrain in the area is hilly with steep slopes having shallow, gravely and light textured soils with low water retentivity and is prone to soil erosion because of its fragility.
Figure 1. Solan-Shimla National highway
Sampling:
The section of study was Solan to Kandaghat which covers around 15 Kilometers. Three replications were considered for the study and four seasons (winter, spring, monsoon and summer) were selected. The study was conducted on mainly three species which are present throughout the National Highway. In order to study the horizontal distribution of the dust content, distances like 0-5 m., 5-10 m. and >100m. were considered. In total, there were 36 treatments.
Leaf dust accumulation
Fully matured leaves of the selected plant species were taken for the present study. The upper surfaces of the leaves were cleaned with a fine brush and identification marks were put on them. The leaves were kept undisturbed for 24 hours for dust accumulation which was collected in the pre weighed butter paper bags with the help of a fine brush. The amount of dust accumulated on leaves was weighed on top pan electronic balance and calculated by using the equation:
W = W1-W2/A
W is dust content (gm-2), W1 is initial weight of butter paper bag, W2 is final weight of butter paper bag with dust, a is total area of the leaf (m2)
Leaf area
Ten leaves from each plant were collected at random and leaf area was measured with Leaf area meter (Model-LI-COR-3100). The average leaf area was expressed as m2.
Results and Discussion:
The amount of dust accumulated by Rubus ellipticus was 0.058 g/m2 while that of Debregeasia hypoleuca and Quercus leucotrichophora was 0.057 g/m2 and 0.042 g/m2 respectively (table 2). There was significant difference in the dust content in all the seasons studied, with maximum accumulation in summer season followed by spring > winter > monsoon respectively (Table 3). As shown in Table 2, the amount of dust accumulated is significantly affected by distance, season and species (P < 0.05). However, the interaction among distance, species and season is non significant (P > 0.05). The study indicates that the amount of dust accumulated by the leaves of selected plant species varies with seasons as well as the distance from the National Highway. It was observed that in all the selected plant species, the amount of dust accumulated at the control site was least followed by the distance 5-10 metres and the distance 0-5 metres showed the highest amount of dust accumulated. The maximum dust accumulation, irrespective of the season and the distance from the National highway was noticed in case of Rubus ellipticus while minimum dust accumulation was noticed in case of Quercus leucotrichophora. In case of Rubus ellipticus, the leaves are thorny and this might facilitate the accumulation of dust particles. Dust accumulation in case of Debregeasia hypoleuca may be due to larger and rough leaf surface of. In case of Quercus leucotrichophora, the leaves are leathery and therefore this might lead to less accumulation of dust
The present findings are in line with Walker and Everett (1987), who studied road dust and its environment impact on Alaskan taiga and tundra and reported that there is decrease in dust load on leaves with increasing distance from Highways. Spatt and Miller (1981) also reported that the dust arising from vehicular traffic settled in greatest quantities near the road with the amount rapidly decreasing away from the road.
Table 1: Seasonal variation in leaf dust (g/m2) accumulation pattern of the selected plants growing alongside the National highway 5 in Himachal Pradesh
DISTANCE
PLANT SPECIES 0-5 m. 5-10 m. >100 m. D3 Mean
Winter Spring Summer Monsoon Winter Spring Summer Spring Winter Spring Summer Monsoon
Debregeasia hypoleuca 0.076 0.093 0.105 0.039 0.052 0.061 0.080 0.039 0.032 0.041 0.047 0.016
0.057
Quercus
leucotricophora 0.060 0.060 0.070 0.029 0.054 0.052 0.061 0.027 0.026 0.024 0.031 0.013
0.042
Rubus ellipticus 0.081 0.082 0.099 0.036 0.066 0.070 0.085 0.035 0.040 0.042 0.049 0.016
0.058
Mean 0.069 0.057 0.031
CD0.05 D= 0.003
S= 0.004
D x S= 0.006
Sp= 0.003
Table 2: Effect of horizontal distance and seasons on the leaf dust (g/m2) accumulation pattern of selected plants alongside the National Highway 5 in Himachal Pradesh
Season
Horizontal distance Winter Spring Summer Monsoon Mean
0-5 m. 0.072 0.078 0.091 0.035 0.069
5-10 m. 0.057 0.061 0.075 0.033 0.057
>100 m. 0.033 0.036 0.042 0.015 0.031
Mean 0.054 0.058 0.070 0.028
D x Sp= 0.005
S x Sp= 0.006
D x S x Sp= N/A
Source of Variation DF Sum of Squares Mean Squares F-Calculated Significance
Factor A 2 0.026 0.013 313.145 0.00000
Factor B 3 0.025 0.008 200.721 0.00000
Int A X B 6 0.002 0.000 8.942 0.00000
Factor C 2 0.006 0.003 65.946 0.00000
Int A X C 4 0.001 0.000 4.644 0.00216
Int B X C 6 0.001 0.000 5.466 0.00011
Int A X B X C 12 0.000 0.000 0.848 0.60171
Error 72 0.003 0.000
Total 107 0.065
Conclusion:
The study concluded that the interception of dust varied with species as well as with the distance from the National Highway. Among the selected plant species, Rubus ellipticus having the highest dust efficiency can be recommended for growing alongside the highway and for green belt development in order to reduce the atmospheric concentrations of dust, thereby making the environment healthy for human beings.
Acknowledgements
The authors are thankful to the Department of Science and Technology, Government of India for providing financial support for conducting the research.
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