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Ceylon Journal of Science, Nov 23, 2017
The relatively low extent of mangroves in Sri Lanka supports 23 true mangrove plant species. In t... more The relatively low extent of mangroves in Sri Lanka supports 23 true mangrove plant species. In the last few decades, more plant species that naturally occur in terrestrial and freshwater habitats are observed in mangrove areas in Sri Lanka. Increasing freshwater input to estuaries and lagoons through upstream irrigation works and altered rainfall regimes appear to have changed their species composition and distribution. This will alter the vegetation structure, processes and functions of mangrove ecosystems in Sri Lanka. The geographical distribution of mangrove plant taxa in the micro-tidal coastal areas of Sri Lanka is investigated to have an insight into the climatic and anthropogenic factors that can potentially influence the ecological biogeography of mangroves and sustainability of these mangrove ecosystems.
Soil salinity in both coastal and inland, is known to affect vegetation structure and functions. ... more Soil salinity in both coastal and inland, is known to affect vegetation structure and functions. Mangrove vegetation at Kala Oya estuary on the north western coast of Sri Lanka was selected to study the effect of soil salinity on structure, potential gross primary productivity and plant biomass of the ecosystems. Five belt-transects were laid perpendicular to the shoreline, covering 3.5 km upstream and approximately at 750 m intervals to collect data for the purpose. Vegetation structure was determined using data collected on plant species diversity, density, basal area, leaf area index and tree height. Biomass (total of above and below ground) of mangrove trees was estimated by allometric methods and potential gross primary productivity was calculated using leaf area index measured with terrestrial radiation sensor. Total of eight (8) true mangrove species were encountered in the area and highest density was recorded for Rhizophora mucronata (528 trees/ha), followed by Excoecaria agallocha (447 trees/ha) and Lumnitzera racemosa (405 trees/ha). Vegetation complexity index (CI), basal area, total tree biomass leaf area index and potential gross primary productivity measurements revealed an inverse correlation with soil salinity. Mangrove species were observed to possess varying salinity tolerance levels and Avicennia marina was the most salinity tolerant species, followed by Rhizophora mucronata, Ceriops tagal and Lumnitzera racemosa. Excoecaria agallocha was the least salt tolerant species in the area. Mangrove areas located around 2 km from the estuary mouth, where the soil salinity ranged from 8-12 mg/l, was observed to be with the highest species richness and diversity, indicating its' ecological and conservation significance that may be considered in mangrove management decision-making for the area. Presence of a few species of terrestrial and freshwater plants among the mangroves indicates salinity changes that would have taken place due to trans-basin diversion of water to the area for irrigation purposes.
The capacity of plants to sequester carbon depends on net primary productivity and pattern of bio... more The capacity of plants to sequester carbon depends on net primary productivity and pattern of biomass/carbon partitioning within the plant which is not well understood for mangroves. Above (A) to below (B)-ground carbon ratio (A/B) of both Bruguiera gymnorrhiza (L.) Lamk. and Lumnitzera racemosa Willd. from where micro-tidal conditions prevail, Negombo estuary, Sri Lanka (7°11′42.18″N-79°50′47.50″E) was approximately 3, and more closely resembles that of terrestrial plants than mangroves in macro-tidal environments. Relatively low inundation frequency, duration and depth apparently promote aerial growth than root production. Wet oxidation without external heating, followed by colorimetric method was adopted to determine total organic carbon (TOC) of plant components. Except for leaves of L. racemosa, nearly half the biomass of all other components of the two species was composed of TOC. Statistically significant allometric relationships exist among TOC and dbh (diameter at breast height) of trees. It was found that 96.5% of TOC in L. racemosa was in sequestered form (in the wood) compared to B. gymnorrhiza which only accumulated 78.7% in sequestered form. Profuse branching of L. racemosa contributes to the higher carbon sequestration capacity.
Ceylon Journal of Science, Nov 23, 2017
The relatively low extent of mangroves in Sri Lanka supports 23 true mangrove plant species. In t... more The relatively low extent of mangroves in Sri Lanka supports 23 true mangrove plant species. In the last few decades, more plant species that naturally occur in terrestrial and freshwater habitats are observed in mangrove areas in Sri Lanka. Increasing freshwater input to estuaries and lagoons through upstream irrigation works and altered rainfall regimes appear to have changed their species composition and distribution. This will alter the vegetation structure, processes and functions of mangrove ecosystems in Sri Lanka. The geographical distribution of mangrove plant taxa in the micro-tidal coastal areas of Sri Lanka is investigated to have an insight into the climatic and anthropogenic factors that can potentially influence the ecological biogeography of mangroves and sustainability of these mangrove ecosystems.
Soil salinity in both coastal and inland, is known to affect vegetation structure and functions. ... more Soil salinity in both coastal and inland, is known to affect vegetation structure and functions. Mangrove vegetation at Kala Oya estuary on the north western coast of Sri Lanka was selected to study the effect of soil salinity on structure, potential gross primary productivity and plant biomass of the ecosystems. Five belt-transects were laid perpendicular to the shoreline, covering 3.5 km upstream and approximately at 750 m intervals to collect data for the purpose. Vegetation structure was determined using data collected on plant species diversity, density, basal area, leaf area index and tree height. Biomass (total of above and below ground) of mangrove trees was estimated by allometric methods and potential gross primary productivity was calculated using leaf area index measured with terrestrial radiation sensor. Total of eight (8) true mangrove species were encountered in the area and highest density was recorded for Rhizophora mucronata (528 trees/ha), followed by Excoecaria agallocha (447 trees/ha) and Lumnitzera racemosa (405 trees/ha). Vegetation complexity index (CI), basal area, total tree biomass leaf area index and potential gross primary productivity measurements revealed an inverse correlation with soil salinity. Mangrove species were observed to possess varying salinity tolerance levels and Avicennia marina was the most salinity tolerant species, followed by Rhizophora mucronata, Ceriops tagal and Lumnitzera racemosa. Excoecaria agallocha was the least salt tolerant species in the area. Mangrove areas located around 2 km from the estuary mouth, where the soil salinity ranged from 8-12 mg/l, was observed to be with the highest species richness and diversity, indicating its' ecological and conservation significance that may be considered in mangrove management decision-making for the area. Presence of a few species of terrestrial and freshwater plants among the mangroves indicates salinity changes that would have taken place due to trans-basin diversion of water to the area for irrigation purposes.
The capacity of plants to sequester carbon depends on net primary productivity and pattern of bio... more The capacity of plants to sequester carbon depends on net primary productivity and pattern of biomass/carbon partitioning within the plant which is not well understood for mangroves. Above (A) to below (B)-ground carbon ratio (A/B) of both Bruguiera gymnorrhiza (L.) Lamk. and Lumnitzera racemosa Willd. from where micro-tidal conditions prevail, Negombo estuary, Sri Lanka (7°11′42.18″N-79°50′47.50″E) was approximately 3, and more closely resembles that of terrestrial plants than mangroves in macro-tidal environments. Relatively low inundation frequency, duration and depth apparently promote aerial growth than root production. Wet oxidation without external heating, followed by colorimetric method was adopted to determine total organic carbon (TOC) of plant components. Except for leaves of L. racemosa, nearly half the biomass of all other components of the two species was composed of TOC. Statistically significant allometric relationships exist among TOC and dbh (diameter at breast height) of trees. It was found that 96.5% of TOC in L. racemosa was in sequestered form (in the wood) compared to B. gymnorrhiza which only accumulated 78.7% in sequestered form. Profuse branching of L. racemosa contributes to the higher carbon sequestration capacity.