605
aerial root architecture in determining tolerance thresholds of mangrove species to
sediment burial has been studied and discussed in detail by Ellison (1998). As per
his study, the impact of sedimentation ranged from reduced vigour to death of mangrove trees, depending on the amount and type of sediments and the species of
mangroves involved.
When pneumatophores of Avecinnia or the knee roots of Bruguiera are completely buried, the mangrove trees usually die. When the sediment deposition is less
than the height of the aerial roots of these mangrove species, the tress can still be
adversely affected or die (Allingham and Neil 1995; Lee et al. 1996; Ellison 1998).
The ability of mangrove species to cope with the root burial (due to sediment
deposit) varies between species as a function of their root architectures. The pneumatophores of Avecinnia and Sonneratia and knee roots of Bruguiera and Xylocarpus
mekongensis may be able to extend upward (Hutchings and Saenger 1987). However,
these responses take time, but mangrove tree can adjust to gradual burial.
Response of mangrove species to root burial is not uniform. It depends on various factors such as, sediment texture, the presence of soil fauna and the tidal range.
Burial by sand does not appear to cause death of trees as readily as by silt or clay.
This could be because soil aeration is better through sand (Ellison 1998).
IRS LISS-III images of October 1998, February 1999, February 2001 and March
2007 pertaining to Kori creek are given in Fig. 19.14. Excess deposition of sand
over the mangrove area (due to some very specific coastal process) started sometime
in the beginning of November 1998. IRS LISS-III image of October 1998 (prior to
sand deposition) shows patches of dense mangroves (indicated as 1, on the image)
and sparse mangroves (indicated as- 2). LIS-III image of February 1999 (post event)
clearly shows the sand deposition (seen as white patches on the image, also marked
as ‘S’) and mangrove degradation has also taken place: dense mangrove patches
(marked as 1 in Oct 1998 image) has changed to sparse mangrove class (‘2’, in Feb
1999 image). Degradation of mangroves continued beyond Feb. 1999 due to sand
deposition. It is clearly seen on the LISS-III image of February 2001 (Fig. 19.14)
that the mangroves have further degraded. The patches of sparse mangroves (‘2’ on
Feb. 1999 image) has changed to the degraded mangrove category (‘3’) and sand
cover has further increased in Feb 2001 image (indicated as ‘IS’ – increased sand).
Mangrove-1 in Feb 1999 image has changed to mangrove-2 category in Feb 2001
image. IRS KLISS-III image acquired after another 6 years (March 2007) indicates
improvement in the mangrove cover density (indicated as ‘1*’) at few places, as
compared to Feb 2001. Change in mangrove-3 to mangrove-2 class has also been
observed in the March 2007 image.
19.7 Mangrove Health Assessment
We need to understand the meaning and concept of the “Ecosystem Health”, before
getting in to the real issues related to the health assessment of mangrove ecosystem.
Several definitions of ‘ecosystem health’ exist as of today. Among these, one of the
19 Mangrove Inventory, Monitoring, and Health Assessment
aerial root architecture in determining tolerance thresholds of mangrove species to
sediment burial has been studied and discussed in detail by Ellison (1998). As per
his study, the impact of sedimentation ranged from reduced vigour to death of mangrove trees, depending on the amount and type of sediments and the species of
mangroves involved.
When pneumatophores of Avecinnia or the knee roots of Bruguiera are completely buried, the mangrove trees usually die. When the sediment deposition is less
than the height of the aerial roots of these mangrove species, the tress can still be
adversely affected or die (Allingham and Neil 1995; Lee et al. 1996; Ellison 1998).
The ability of mangrove species to cope with the root burial (due to sediment
deposit) varies between species as a function of their root architectures. The pneumatophores of Avecinnia and Sonneratia and knee roots of Bruguiera and Xylocarpus
mekongensis may be able to extend upward (Hutchings and Saenger 1987). However,
these responses take time, but mangrove tree can adjust to gradual burial.
Response of mangrove species to root burial is not uniform. It depends on various factors such as, sediment texture, the presence of soil fauna and the tidal range.
Burial by sand does not appear to cause death of trees as readily as by silt or clay.
This could be because soil aeration is better through sand (Ellison 1998).
IRS LISS-III images of October 1998, February 1999, February 2001 and March
2007 pertaining to Kori creek are given in Fig. 19.14. Excess deposition of sand
over the mangrove area (due to some very specific coastal process) started sometime
in the beginning of November 1998. IRS LISS-III image of October 1998 (prior to
sand deposition) shows patches of dense mangroves (indicated as 1, on the image)
and sparse mangroves (indicated as- 2). LIS-III image of February 1999 (post event)
clearly shows the sand deposition (seen as white patches on the image, also marked
as ‘S’) and mangrove degradation has also taken place: dense mangrove patches
(marked as 1 in Oct 1998 image) has changed to sparse mangrove class (‘2’, in Feb
1999 image). Degradation of mangroves continued beyond Feb. 1999 due to sand
deposition. It is clearly seen on the LISS-III image of February 2001 (Fig. 19.14)
that the mangroves have further degraded. The patches of sparse mangroves (‘2’ on
Feb. 1999 image) has changed to the degraded mangrove category (‘3’) and sand
cover has further increased in Feb 2001 image (indicated as ‘IS’ – increased sand).
Mangrove-1 in Feb 1999 image has changed to mangrove-2 category in Feb 2001
image. IRS KLISS-III image acquired after another 6 years (March 2007) indicates
improvement in the mangrove cover density (indicated as ‘1*’) at few places, as
compared to Feb 2001. Change in mangrove-3 to mangrove-2 class has also been
observed in the March 2007 image.
19.7 Mangrove Health Assessment
We need to understand the meaning and concept of the “Ecosystem Health”, before
getting in to the real issues related to the health assessment of mangrove ecosystem.
Several definitions of ‘ecosystem health’ exist as of today. Among these, one of the
19 Mangrove Inventory, Monitoring, and Health Assessment