Download An innovative approach for monitoring abiotic factors influencing

An innovative approach for monitoring abiotic factors influencing
mangrove forest biodiversity in an estuarine ecosystem
M. 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
1
Introduction
The UN’s Millennium Ecosystem Assessment (2005)
targeted coastal wetlands as environments that “are
experiencing some of the most rapid degradation and
loss worldwide”.
5
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).
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.
In Trinidad West Indies, land-use changes and sea
defenses impact water quality and alter mangrove forest
distribution and biodiversity.
Salinity and water quality parameters play a major role in
determining mangrove species diversity in a tropical
estuarine ecosystem.
This research therefore investigates the abiotic water
quality factors influencing mangrove zonation along the
South Oropouche River, Godineau Swamp.
2
Summary &
Conclusion
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.
Methodology
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
b
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).
4
•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.
Discussion
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).
*
1.
References
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.
(a)
(b)
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.
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.
20
1
0
0
Distance (m)
pH
Fig. 4: Percentage species abundance as a function of
0.00
500.00 1000.00 1500.00 2000.00 2500.00
pH (Side channel)
120
8.2
100
8.0
80
7.8
60
7.6
40
7.4
20
0
7.2
White
Black
0.00
500.00
1000.00
Black
Red
DO
1500.00
2000.00
120
100
80
60
40
20
0
Distance (m)
pH
2500.00
8
7
6
5
4
3
2
1
0
Distance (m)
White
Red
Fig. 6: Percentage species abundance as a function of Dissolved
Oxygen (DO) (Side channel)
pH
Distance (m)
White Black Red
40
DO (mg/l)
6.8
57
18
0
48
22
7.0
41
15
20
33
47
7.2
24
43
40
60
White
Black
Red
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.
DO
DO (mg/l)
7.4
5
4
3
2
49
4
11
57
17
27
23
50
26
76
33
47
38
13
43
33
48
22
54
94
60
39
60
80
16
7.6
pH
80
% Abundance of
dominant species
100
7.8
8
7
6
16
25
3
49
4
73
0
98
3
12
49
15
35
18
29
20
79
21
59
Fig.2: Aerial extent of mangrove boundary for the years 1962
(pink) and 2003 (pattern)
8.0
% Abundance of
dominant species
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).
100
17
27
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).
120
73
0
Results
8.2
16
3
Fig. 5: 1000.00
Percentage
species
abundance
as a function
2000.00
3000.00
4000.00 5000.00
6000.00of7000.00
0.00000 0000000
0000000
0000000
Dissolved
Oxygen
(DO)0000000
(Main 0000000
channel)0000000 0000000
000000
00
00
00
00
00
00
00
120
16
25
3
49
4
73
0
98
12 3
4
15 9
3
18 5
29
20
7
21 9
59
Plate 2. U-10 Water Quality Checker
% Abundance of
dominant species
Plate 1. Boat-mounted geophysical imaging
% Abundance of
dominant species
1000.00 2000.00 3000.00 4000.00 5000.00 6000.00 7000.00
Fig.3: Percentage
species
abundance
a function
of pH
0.00000
0000000 0000000
0000000
0000000as0000000
0000000
0000000
000000
00
00 (Main
00channel)
00
00
00
00