Plant community and soil PAH pollution survey
Quadrat sampling of desert plant communities (4 m2quadrat unit size; n = 200 samples) was carried out in 2011 within the
seven sampling areas. The selected areas represent a range of
geographical locations and intensity of soil PAH pollution throughout
Kuwait.
The fieldwork was carried out from January to March 2011. This sampling
period was at the end of the rainy season in which the soil seedbank
generally germinated after rain events and provided an opportunity to
carry out ecological study of desert plant communities
(Springuel
et al. 1996, 1997; Bainbridge
2007).
The number of samples varied at different areas, but each sampling event
per area contained at least 10 quadrats. The Universal Transverse
Mercator (UTM) geo-coordinates were determined using GPS device (Garmin
Etrex: Basic), and minimum of 5 randomly positioned quadrats were
sampled around the established sampling site. The percentage frequency
of individual species, and mean vegetation height (cm) at each quadrat
were collected. The nomenclature of plant species followed the procedure
used by Boulos & Al-Dousari (1994). We further confirmed the naming of
the species using The Plant List (2013):www.theplantlist.org.
Species abundance was assessed using a quadrat-scale frequency method.
For each quadrat, the percent frequency of individual species (%F), and
the mean vegetation height (cm) were recorded to determine plant
distribution within the selected areas. Species abundance was assessed
using the percent frequency at two scales. The first scale was at the
sample area scale calculated as:
\begin{equation}
\%FA=100\times\frac{\text{number\ of\ quadrats\ with\ species}}{\text{total\ number\ of\ quadrats\ sampled\ per\ area}}\nonumber \\
\end{equation}The second scale was at the quadrat scale. for every species present in
the sampled quadrat, the %FQ was calculated using the
following equation:
\begin{equation}
\%F=\frac{number\ of\ hits\ within\ 400\ sub-units}{4}\nonumber \\
\end{equation}The calculation is based on the fact that each quadrat covers an area of
4 m2, and the plant species count was conducted by
dividing the quadrat into 400 sub-units with 10 x 10 cm in each unit.
Several vegetation parameters were also measured including the mean
vegetation height averaged across the quadrat (cm), species diversity as
number of species present per quadrat sample (SQm-2), and number of species per sampling area
(SA). Other variables determined for each sample unit
were latitude and longitude (°N; °E), semi-quantitative Oil Damage Score
(ODS: on a 1 – 3 scale, with 1 = no visible damage, to 3 = major
visible evidence of oil damage to soil), and concentrations of
polycyclic aromatic hydrocarbons (PAHs: μg kg-1 dry
weight of soil or plant tissue) in soil.
Plant leaves and soil samples were collected to assess the degree of
soil hydrocarbon pollution, and to determine the uptake of petroleum
hydrocarbons by the chosen dominant plant species. A total of 63 plant
tissue (leaf) samples, from three oil-polluted areas (Um Al-Aish,
Sabriya, and Um-Ghadair Oilfields) and one uncontaminated area (Sabah
Al-Ahmad Protected Area) were collected in sealed glass jars (frozen)
and subsequently analysed at the Central Environmental Laboratory (CEL)
(ISO 17025), Kuwait University. These samples included 32 H.
salicornicum samples, collected from the Um Al-Aish Oilfield, and 18
specimens of C. conglomeratus (16 from the Sabriya Oilfield, one
from Sabah Al-Ahmad Protected Area, and one from the Um-Ghadair
Oilfield). The other 13 specimens were R. epapposum , from the
Sabriya Oilfield.
In carrying out the soil sample analysis, 184 soil samples were analyzed
at CEL in March 2011, comprising 35 soils from Um Al-Aish, 30 from
Sabriya Oilfield, 26 from Bahra, 7 from Um Al-Rros, 45 from Sabah
Al-Ahmad Protected Area, 21 from Burgan Oilfield, and 20 from Um-Ghadair
Oilfield. The moisture contents of soil and plant tissue samples were
determined, and the samples were then analysed for 16 priority PAHs,
identified by the US Environmental Protection Agency (US-EPA) in oil
polluted soils. These 16 compounds were acenaphthylene (ANAY);
acenaphthene (ANA); anthracene (ANTH); benzo(a)anthracene
(B[a]ANTH); benzo(a)pyrene (B[a]P); (benzo(g,h,i)perylene
(B[ghi]PERY); benzo(b)fluoranthene (B[b]FLAN);
benzo(k)fluoranthene (B[k]FLAN); chrysene (CH);
dibenzo(a,h)anthracene (D[ah]ANTH); fluoranthene (FLAN); fluorene
(FL); indeno(1,2,3-cd) pyrene (I[123-cd]PY); naphthalene (NA);
phenanthrene (PH) and pyrene (PY). In this study, these hydrocarbons
fractions were used to assess the total Petroleum Hydrocarbon (TPH:
mV.sec) content of oil-polluted soils.
The concentrations of each
compound are reported as µg kg-1 of dry soil or dried
plant tissue. These compounds were quantified using semivolatiles gas
chromatography/mass spectrometry (GC/MS) method
(Smith
& Lynam 2014).