Environmental Engineering Reference
In-Depth Information
Fig. 7.3
A sudden drop in
chlorophyll a (expressed in
mgm
−
3
) level during
March 2013
—
one month
after the volcanic episode
2
1.5
1
0.5
0
coincided with major volcanic eruption of
Mt. Pinatubo in June 1991 in Philippines and
Mt. Pinatubo
and smothering. However, little is known about
the effect of moderate amounts of small particu-
late ash deposits on reef communities. Volcanic
ash contains a diversity of chemical compounds
that can induce nutrient enrichments triggering
changes in benthic composition. Two indepen-
dently collected data sets on the marine benthos of
the pristine and remote reefs around Pagan Island,
Northern Mariana Islands, reveal a sudden critical
transition to cyanobacteria-dominated communi-
ties in 2009
s eruption was of very large mag-
nitude, it is very dif
'
cult to differentiate individual
contributions during 1991 episode, and hence, it
may be considered as a combined effect of both
the eruptions. However, such eruptions cause
considerable decrease of phytoplankton standing
stock. The chlorophyll concentration also reduces
drastically. However, very few studies re
fl
ect the
cause
effect relationship between volcanic erup-
tions and coastal vegetation.
The present authors observed a signi
2010, which coincides with a period
of continuous volcanic ash eruptions.
Pagan is the largest island of the northern
Mariana Arc (48 km
2
) and the
-
-
cant
decrease in chlorophyll
(Fig.
7.3
) and phyto-
plankton count (Fig.
7.4
) in the aquatic phase
around Barren Island after the volcanic episode
of 16 February 2013.
Volcanically active islands abound in the
tropical Paci
a
fth largest of all
Mariana Islands. The largest eruption of Pagan in
recent history occurred in 1981 and instigated the
evacuation of its
fty-some permanent residents.
Since then, few temporary residents have lived
on the island with lately just one or two of
c and harbour complex coral com-
munities. Researchers have observed severe
adverse effect of deep volcanic ash deposits that
often devastate coral communities through burial
cial
representatives of the mayor of the Northern
Mariana Islands. The strong volcanic activity
in 1981 was followed by intermittent
light
Fig. 7.4
A sudden drop in
phytoplankton population
(expressed in No./L) during
March 2013
100000
80000
one month
after the volcanic episode
—
60000
40000
20000
0
