an innovative approach for monitoring abiotic factors ... · b an innovative approach for...
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An innovative approach for monitoring abiotic factors influencing
mangrove forest biodiversity in an estuarine ecosystemM. Atwell1; M.N. Wuddivira1; J. Gobin2; D.A. Robinson3
1Department of Food Production, University of the West Indies,2Department of Life Sciences, University of the West Indies,
3Centre for Ecology and Hydrology, Environment Centre, Wales, UK
*
The UN’s Millennium Ecosystem Assessment (2005)
targeted coastal wetlands as environments that “are
experiencing some of the most rapid degradation and
loss worldwide”.
Mangrove wetlands are important because they provide
a buffer, protecting vulnerable coastal and marine
ecosystems from rising sea levels and storm tides (Ewel
et al., 1998).
In Trinidad West Indies, land-use changes and sea
defenses impact water quality and alter mangrove forest
distribution and biodiversity.
This research therefore investigates the abiotic water
quality factors influencing mangrove zonation along the
South Oropouche River, Godineau Swamp.
An innovative measurement campaign using conventional sensors and
high spatial resolution geophysical imaging was adopted to monitor the
river water quality and salinity patterns. Seasonally at high tide,
measurements were obtained from two river channels, a 6km larger main
channel and a 2km shorter side channel (Fig. 1).
•Electromagnetic Induction (boat-mounted geophysical imaging) was used
to spatially map the salinity of the water non-invasively (Plate 1). River
water was spatially tested in situ for pH, dissolve oxygen (DO),
conductivity, temperature and turbidity using a U-10 multi parameter water
quality checker (Plate 2).
•Aerial photos were analyzed using GIS for the years 1962 and 2003 to
determine mangrove boundary change (Fig. 2). Species abundance was
identified using transects at 5m intervals along both sides of the river
banks. Data analysis included geostatistics with SGEMS, graphs and GIS.
Introduction1
Methodology2
Results3
Aerial photos (Fig.2) showed an overall decrease of
more than 10% in mangrove extent from 1962- 2003.
The apparent electrical conductivity (ECa) levels were
much lower in the main channel than in the side channel
both in the wet and dry season (Fig. 1). In the dry
season, however, saline water intrusion was very evident
as salt water moved further inland (Fig. 1b).
The pH and DO levels showed a marked decrease in the
side channel than in the main channel of the river (Figs.
3-6). Rhizophora mangle L. (red) as opposed to
Avicennia germinans (black) and Laguncularia
racemosa (white) was found under adverse water quality
conditions of low DO, pH levels and high levels of
salinity (Figs. 3-6).
Summary &
Conclusion
Rhizophora mangle (red), Avicennia germinans (black)
and Laguncularia racemosa (white) species of mangroves
were identified along the river banks. The red mangroves
thrived in areas of adverse water quality conditions and
indeed are the hardiest of the three species.
Salinity and water quality parameters play a major role in
determining mangrove species diversity in a tropical
estuarine ecosystem.
The novel use of boat-mounted geophysical imaging has
therefore proven to be a useful tool in determining saline
water intrusion and in the characterization of spatial and
temporal patterns of the abiotic factors affecting mangrove
zonation pattern.
5
4
Our results showed a significant decrease in
mangrove species diversity as adverse water
quality conditions prevailed. This is partly due
to saline water intrusion particularly in the dry
season, which takes place with increased tidal
inundation extending as far as 6km upstream
(Fig. 1).
Plate 1. Boat-mounted geophysical imaging Plate 2. U-10 Water Quality Checker
Fig.3: Percentage species abundance as a function of pH
(Main channel)
0
20
40
60
80
100
120
16 730
1727
2443
3347
4115
4822
5718
Distance (m)
% A
bu
nd
an
ce o
f
do
min
an
t sp
eci
es
6.8
7.0
7.2
7.4
7.6
7.8
8.0
8.2
0.00000
000000
1000.00
0000000
00
2000.00
0000000
00
3000.00
0000000
00
4000.00
0000000
00
5000.00
0000000
00
6000.00
0000000
00
7000.00
0000000
00
pH
White Black Red pH
Fig. 5: Percentage species abundance as a function of
Dissolved Oxygen (DO) (Main channel)
0
20
40
60
80
100
120
16 4941157
1727
2350
2676
3347
3813
4333
4822
5494
6039
Distance (m)
% A
bu
nd
ance
of
do
min
ant
spec
ies
0
1
2
3
4
5
6
7
8
0.00000
000000
1000.00
0000000
00
2000.00
0000000
00
3000.00
0000000
00
4000.00
0000000
00
5000.00
0000000
00
6000.00
0000000
00
7000.00
0000000
00
DO
(m
g/l)
White Black Red DO
Fig.2: Aerial extent of mangrove boundary for the years 1962
(pink) and 2003 (pattern)
References1. Ewel, K.C., Twilley, L.L. and Ong, J.E. 1998.
Different kinds of mangrove forests provide different
goods and services. Global Ecology and Biogeography
letters. 7:83-94.
2. “South Oropouche, Trinidad.” 2009. 61o29’56”N
and 10o13’13”E. Google Earth. August 29,
2009. Accessed August 29 2009.
3. “South Oropouche, Trinidad.” 2010. 61o29’56”N
and 10o13’13” E. Google Earth. February 19,
2010. Accessed February 19 2010.
4. Millennium Ecosystem Assessment "Synthesis
Report" (2005) 16.
Discussion
Fig. 4: Percentage species abundance as a function of
pH (Side channel)
0
20
40
60
80
100
120
16 253
494
730
983
1249
1535
1829
2079
2159
Distance (m)
% A
bu
nd
an
ce o
f
do
min
an
t sp
eci
es
7.2
7.4
7.6
7.8
8.0
8.2
0.00 500.00 1000.00 1500.00 2000.00 2500.00
pH
White Black Red pH
Fig. 6: Percentage species abundance as a function of Dissolved
Oxygen (DO) (Side channel)
0
20
40
60
80
100
120
16 253
494
730
983
1249
1535
1829
2079
2159
Distance (m)
% A
bu
nd
an
ce
of
do
min
an
t s
pe
cie
s
012345678
0.00 500.00 1000.00 1500.00 2000.00 2500.00
DO
(m
g/l)
White Black Red DO
(a) (b)
This adverse water quality may also be due to
low levels of pH and DO in the stagnant side
channel as a result of decomposition of organic
matter and run-off from acidified mangrove
soils (Figs. 4 and 6). In the side channel where
adverse water quality conditions were prevalent,
only the red mangrove predominates, indicating
a loss of mangrove species diversity.
Fig. 1: Spatial map of ECa along the main and side channels of the river in (a) wet season and (b) dry season. Blue represents low
salinity while red represents high salinity.