Pollen Concentration in the Atmosphere of Abha City, Saudi Arabia and its Relationship with Meteorological Parameters
Hussein M. Alwadie
A qualitative and quantitative evaluation of pollen
concentration in the atmosphere of Abha city, Saudi Arabia with the relation
to meteorological parameters is presented. Investigations were undertaken
from January to December 2006 using a Burkard 7 day volumetric spore trap.
A total of 6,492 pollen grains m-3 belonging to 50 pollen taxa
was detected. Poaceae represented 55.1% of total pollen, Leguminosae (11.7%),
Compositae (6.1%), Solanaceae (4.6%) and Cupressaceae (4.2%). Pollen grains
were found throughout the year. July represented the highest peak of pollen
number and also the highest pollen taxa. The monthly variation of pollen
taxa and their relationship to meteorological parameters were investigated.
It was found that the pollen concentration is positively correlated with
temperature and negatively correlated with rainfall, relative humidity
and wind velocity. May-September represented the months of highest pollen
number (95% of total pollen).
Pollen grains are male reproductive units and are released into the air
in huge amounts for the purpose of pollination. The concentration of different
pollen types in the atmosphere varies enormously from one country to another,
in regions of the same country and even among different cities, because
pollen emissions depend on the vegetational structure and meteorological
conditions (Kaplan, 2004). A positive correlation of pollen concentration
and surrounding vegetation density has been described (Romano et al.,
1988) indicating that changes in the floral composition of a given area
have a direct influence on its aeropalynological spectrum. Ninety-eight
percent of the total pollen grains in the atmosphere are from anemophile
plants, whereas 2% are from entemophile plants (Mullins and Emberlin,
1997; Molina et al., 2001).
Generally, meteorological parameters have an important influence on pollen
concentration in the air. Aerial transport of pollen may have an important
impact on earth life, which increases with economic expansion around the
world (Ribeiro et al., 2003).
In other countries, many of aeropalynological studies have been conducted
for several years using different types of samplers (Giorato et al.,
2000; Villegas and Nolla, 2001; Mishra et al., 2002; Murray et
al., 2002; Ballero and Maxia, 2003; Porsbjerg et al., 2003;
Rodrfguez-Rajo et al., 2003; Paloma et al., 2004; Hasnain
et al., 2005; Tejera and Beri, 2005; Ture and Salkurf, 2005).
In Saudi Arabia, aeropalynological studies are scarce but gaining importance
(Hasnain et al., 2005). However, the purpose of this study was
to identify pollen grains in the air of Abha city, Saudi Arabia and their
relation to meteorological parameters.
MATERIALS AND METHODS
Abha city (18°14` N and longitude 42°39` E, altitude of about
2093 m) lies in the Southwestern part of the Arabian Peninsula about 1100
km from Riyadh, the capital of Saudi Arabia. The city is characterized
by moderate climate, heavy rainfall, green pasture and agricultural plateaus.
The region abounds in mountains, valleys and fertile plains and surrounded
by dense forests.
Pollen sampling was carried out from January to December, 2005 using
a Burkard volumetric 7 day spore trap (Burkard Manufacturing Co. Ltd.,
England). The trap was placed on the roof of the laboratories building
at the College of Science, King Khalid University, approximately 15 m
above ground level. The Sampler was set for seven day sampling onto Melinex
tape which was coated with a thin film of Lubriseal (Levetin, 1991). Tapes
were changed weekly, cut into seven daily segments and mounted on microscope
slides. Slides were stained with glycerin jelly containing basic fuchsin
and examined microscopically at 400X using a single longitudinal traverse.
Microscope counts were converted into atmospheric concentrations and expressed
as pollen grains m-3. Daily concentrations were summed for
cumulative monthly totals. Pollen identification was followed using the
books on palynology (Erdman, 1966, 1969; McDonald and O`Driscoll, 1980;
Moore et al., 1991).
Meteorological data were kindly obtained from Abha Meteorological Station
With the help of MINITAB computer programme, non-parametric statistical
analysis by Spearman`s rank test was applied to determine whether monthly
pollen concentration and meteorological parameters were positively or
negatively correlated (MINITAB, 1985). The statistical significance of
correlation was studied by student`s-test for paired samples following
the methods of Subiza et al. (1992) and Vega-Maray et al.
During the year of observation, 6,492 pollen grains cm-3 belonging
to 50 pollen taxa were found. The highest concentration of pollen was
that of Poaceae (55.1%), Leguminosae (11.7%), Compositae (6.1%), Solanaceae
(4.6%) and Cupressaceae (4.2%) (Table 1). The total
pollen count varied throughout the year with the peak period in July (Fig.
1a). Brassicaceae is the only pollen taxon was found all year round
with maximum concentration during October, followed by Compositae (9 months,
from January-November) with maximum concentration during July, Poaceae
(8 months, from March-December) with maximum concentration during July.
Palmae and Crassulaceae were found all year round, except February and
March with maximum concentration during June and August, respectively.
The highest number of taxa was recorded in June (29 taxa), July (31 taxa)
and August (24 taxa), whereas, the lowest number of taxa was recorded
in February (5 taxa) (Table 2) which represented also
the lowest number of pollen.
In the present investigation, most of pollen number was recorded during
five months of the year (May-September) (95% of total pollen). During
this period, Poaceae, Leguminosae, Compositae, Solanaceae and Cupressaceae
In the present investigation, the influence of meteorological factors
on the pollen concentration was studied (Fig. 1a-c and
2a-c). Here, a positive and statistically significant
correlation was found between the air temperature and pollen concentration.
Conversely, a negative correlation was observed between rainfall, relative
humidity and wind velocity and pollen concentration (Table
Maximum concentration of pollen grains was found mostly between June-September
(Fig. 1a), probably due to moderately high temperature,
low relative humidity, moderately low wind velocity and low rainfall.
The count became very low during January-April and October-December may
be due to high wind velocity. Thus the pollen concentration depends upon
the climatic factors and this has been statistically supplemented. A correlation
was made between the monthly total pollen count (Table 3)
and meteorological parameters through statistical analysis. From the value
of the correlation coefficient (r), it was found that pollen concentration
was positively correlated with temperature and negatively correlated with
rainfall, relative humidity and wind velocity during the year (Table
3). The level of significance was also determined from the statistical
table. In case of temperature, the level of significance was below 0.1,
while it was between 0.1-0.05 for rainfall and between 0.01-0.001 for
relative humidity and below 0.1 for wind velocity.
||Relationship between pollen number (a) rainfall (b)
and wind velocity (c) during the year of study
||Monthly pollen taxa found in the air of Abha city from
January (1) December (12), 2006
||Monthly number of pollen taxa recorded during the period
Correlation between meteorological parameters and monthly
total pollen count (coefficient of correlation (r) values)
|Degree of Freedom (DF) (12-2 = 10)
Relationship between pollen number (a), temperature
(b) and relative humidity (c) during the year of study
The frequency of pollen differs from place to another due to the difference
in geographical position, local vegetation and other environmental conditions
(Subiza et al., 1992; Frenze, 2000; Vega-Maray et al., 2003).
Frenze (2000) demonstrated that airborne pollen concentrations exhibit
spatial variability, as pollens from nearby vegetation exert a profound
local influence. Moreover, the size of source area represented by a pollen
sampler depends on the distance between the sampler and the nearest vegetation.
The present results support the view of Frenze (2000), because of high
incidence of Poaceae, Leguminosae, Compositae, Solanaceae and Cupressaceae
pollens was probably due to the presence of a large area of such vegetation
and grass loan, in and around the sampling site.
Magnitude and quality of annual pollen load in the atmosphere varies
significantly. Meteorological parameters like temperature, rainfall, relative
humidity, wind velocity are responsible for fluctuations in pollen concentration
(Anderson, 1980; Bricchi et al., 1992).
In the present investigation, the influence of meteorological factors
on the pollen concentration was studied. Here, a positive and statistically
significant correlation was found between the air temperature and the
pollen concentration. Conversely, a negative correlation was observed
between rainfall, relative humidity and wind velocity and pollen concentration.
The present results are consistent with previous observations in different
countries (Puc and Wolski, 2002; Vega-Maray et al., 2003; Boral
et al., 2004).
Apart from rhythm of plant pollination, meteorological conditions are
considered the most important factors determining the dispersion and content
of pollen in the air (Subiza et al., 1992; Puc and Wolski, 2002).
Subiza et al. (1992) have shown that humidity and rainfall appear
to be the predominant factors in determining the grass pollen potential
for the season. It is evidenced that temperature is the factor that exerts
the greatest influence on the release of pollen grains in the atmosphere
(Puc, 2003; Vega-Maray et al., 2003). Rainfall and relative humidity
yielded negative correlations since water droplets wash away pollen particles
(Vega-Maray et al., 2003). Puc and Wolski (2002) showed a positive
and statistically significant correlation between the air temperature
and the Betula pollen concentration, while a similar but negative
correlation was found for Populus pollen. A relationship was established
between the airborne ragweed pollen concentration and the macrosynoptic
weather situation (Feher and Jarai-Komlodi, 1996).
Therefore, the aerobiological survey in relation to meteorological parameters
has proved that weather factors have great influence on the occurrence
and distribution of pollen grains in the atmosphere.
Fifty airborne pollen taxa have been identified from Abha city. Poaceae,
Leguminosae, Compositae, Solanaceae and Cupressaceae recorded the highest
pollen number throughout the year of investigation. July represented the
highest peak of pollen number and also the highest pollen taxa. A positive
correlation was found between pollen concentration and air temperature,
while a negative correlation of pollen concentration was observed with
rainfall, relative humidity and wind velocity.
| Fig. 3:
||One-year (2006) pollen calendar of Abha city
This study gives an idea about the airborne pollen types present in the Abha
atmosphere and gives also an indication of their main flowering seasons (Fig.
3). It can be concluded that Abha receives a large pollen concentration
from grasses, weeds, ornamental trees and shrubs found around the city. However,
an aeropalynological study of 1 year is not sufficient to analyze seasonal variations
of airborne pollen. It would be necessary to extend these studies to more years
and to other strategically placed areas to achieve a global pollen calendar
for the city and to improve the knowledge of flowering and pollen dynamics and
its relation to the meteorological parameters.
This study was financially supported by SABEC Company, Saudi Arabia.
The author is grateful to the Department of Biology, College of Science,
King Khalid University for providing the facilities of this study.
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