Browsing by Author "Perera, K.A.R.S."

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Carbon retention capacity of two mangrove species, Bruguiera gymnorrhiza (L.) Lamk. and Lumnitzera racemosa Willd. in Negombo estuary, Sri Lanka
(Faculty of Graduate Studies, University of Kelaniya, 2012) Perera, K.A.R.S.; Sumanadasa, W.A.; Amarasinghe, M.D.
Carbon accumulation/sequestration by plants is a major function that contributes to removal of carbon dioxide from the atmosphere and capacity to perform it depends on the plant species and environmental conditions under which they live. Carbon retention by natural ecosystems such as mangroves therefore‚ is considered a crucial ecological service‚ and valued highly under the current global context of continued increase in greenhouse gas emission and associated climate change, on which marginal effort has hitherto been spared over its quantification. The Present study was conducted to characterize two true Sri Lankan mangrove species, i.e. Bruguiera gymnorrhiza (L.) and Lumnitzera racemosa Willd.,. with respect to their carbon retention capacity, and to develop allometric relationships between biomass of plant components and stem diameter at breast height (dbh) of the two species with a view to assisting quantification of carbon-sink function of mangrove ecosystems. Fourteen trees of B. gymnorrhiza, and ten trees of L. racemosa that represented the range of dbh distribution in the mangrove area at Kadolkele in Negombo estuary were selected, harvested and dry weights (biomass) were obtained of the components based on wet:dry weight. Organic carbon in samples taken from each plant component of the two species was determined using dichromate oxidation and colorimetry using spectrophotometer. Partitioning of biomass between above (A) and below (B) ground components is approximately 3:1, revealing that the pattern resembles more of that of terrestrial plants (A/B = 3.9-4.5) than mangrove species in higher latitudes (A/B = 2-3). A positive correlation (p<0.01) and non-linear relationship (linear log-log relationship) was revealed between dbh and biomass (component and total) of the two species and allometric equations were derived that could be used to quantify carbon-sink function of mangrove ecosystems comprised of these species and the potential of mangroves in carbon mitigation programmes with financial incentives for mangrove conservation. The average amount of carbon retained by an individual was 9.16 kg per tree and thus the total organic carbon retained by L. racemosa in the mangrove ecosystem in Kadolkele was 9.44 t/ha while that of B. gymnorrhiza, was 5.6 t/ha, despite its greater capacity of individual carbon retention (13.76 kg per tree) due to its relatively low density and basal area. L. racemosa contains higher percentage of carbon in the stems, branches and roots than B. gymnorrhiza revealing its superior contribution to carbon-sink function of mangrove ecosystems
Carbon sink function of Sri Lankan mangrove ecosystems with special reference to Negombo estuary
(2014) Perera, K.A.R.S.
Development of allometric equations to determine above and below ground biomass and organic carbon content in Bruguiera gymnorrhiza and Lumnitzera racemosa
(University of Kelaniya, 2011) Perera, K.A.R.S.; Saparamadu, M.D.J.S.; Amarasinghe, M.D.
Bruguiera gymnorrhiza and Lumnitzera racemosa are two species of true mangroves commonly found in Sri Lankan mangrove areas. Determination of amount of carbon assimilated by these two species therefore, is of considerable importance to estimate the carbon fixing capacity of Sri Lankan mangrove areas. Objective of the present study therefore, is to develop allometric relationships between biomass of stems, leaves, below and above ground roots with easily measured variables such as girth/ diameter at breast height (gbh/dbh) that can be used in estimating the carbon assimilation capacity of Sri Lankan mangrove ecosystems. The below ground biomass of trees of the two mangrove species accounted for 20 – 44 % of the total biomass of the plants. The ratio (A/B) between above (A) to below (B) ground biomass of Lumnitzera racemosa ranged 1.4 – 3.9 and that for Bruguiera gymnorhiza was 1.2 – 4.4, indicating relatively greater amount of biomass in the below ground root systems.Data on dry weight of plant components were analyzed with SPSS ver.16 and a strong positive correlation (p<0.01) and non-leaner relationship (r2 >0.80) were revealed for stems, roots, above ground and total biomass of plants with dbh of individuals of the two species. Four allometric equations were derived between biomass of different components with dbh of Bruguiera gymnorrhiza ; biomass of stem= 0.115 (dbh)2.386, biomass of root = 0.100 (dbh)2.364, above ground biomass =0.289 (dbh)2.327 and total biomass (above +below)= 0.405 (dbh)2.320 . Four other allometric equations were derived between biomass of different components with dbh of Lumnitzera racemosa; biomass of trunk= 0.098 (dbh)2.244, biomass of root = 0.118 (dbh)2.063, above ground biomass =0.114 (dbh)2.523 and total biomass (above +below)= 0.220 (dbh)2.376 . Using the organic carbon content embodied in biomass of the components of the plants of the two species, equations were altered to represent the relationship between organic carbon present and the dbh. Organic carbon content in Bruguiera gymnorhiza stem=0.0631 (dbh)2.386 and root = 0.0529 (dbh)2.364 and organic carbon content Lumnitzera racemosa trunk = 0.0546 (dbh)2.244 and root= 0.0624 (dbh)2.063 . These allometric relationships are required to estimate the amount of carbon accumulated in the plants of these mangrove species and thus the carbon assimilation capacity of the mangrove stands that comprise these mangrove species.
Effect of vegetation structure on carbon assimilation capacity of mangrove ecosystems in the east coast of Sri Lanka
(2014) Perera, K.A.R.S.; Amarasinghe, M.D.
Effect of vegetation structure on potential gross primary productivity of mangrove ecosystems in Negombo estuary, Sri Lanka
(Research Symposium 2010 - Faculty of Graduate Studies, University of Kelaniya, 2010) Perera, K.A.R.S.; Amarasinghe, M.D.; Pahalawathaarachchi, V.
Photosynthetically active radiation (PAR) absorbed by the plant canopies/ leaves gives a reliable measure of its gross primary production. The potential gross primary productivity of two mangrove stands, i.e. Kadolkele (70 11’42.18” - 7011’50.48” N; 790 50’32.08” – 790 50’47.50” E) a relatively undisturbed natural mangrove area and a cultivated and selectively harvested stand at Wedikanda (70 11’18.29” – 70 11’29.09” N; 790 49’56.37” – 790 50’04.96” E) located at northern part of the Negombo estuary were studied in relation to mangrove vegetation structure which was characterized with species richness, plant density, basal area and stand height. Amount of PAR absorbed by the canopies of two mangrove stands were estimated by calculating leaf area index (LAI) values obtained from the relationship between incident PAR and PAR under the canopy that were measured using LI-191SA line Quantum sensor during wet (raining) and dry seasons. Natural mangrove stands at Kadolkele were revealed to be structurally more complex/ superior with a complexity index value of 42.36, in comparison to that of Wedikanda which recorded a value of 22.48. LAI in both study areas recorded higher values for the zone near the estuarine shoreline and it decreased towards inland. LAI recorded higher values in wet season ( Kadolkele 7.336 and Wedikanda 6.157) than in the dry period (Kadolkele 6.693 and Wedikanda 5.896). Gross primary productivity too showed a similar trend as structural diversity, along the estuary-land gradient and it was manifested in both the mangrove stands. Kadolkele recorded relatively a high average potential gross primary productivity, i.e. 24.541 t/ha/yr than Wedikanda that recorded 21.011 t/ha/yr. Artificial selection of mangrove species for planting and periodic harvesting of mangrove branches to construct a traditional fishing device known as “brush parks” may contribute to the lower gross primary productivity value of the cultivated mangrove stands at Wedikanda.
Human influence on structure of mangrove vegetation in Negombo estuary
(Sri Lanka Association for Fisheries and Aquatic Resources, 1999) Perera, K.A.R.S.; Amarasinghe, M.D.
Mangrove soils are superior carbon sinks: Evidence from Sri Lankan mangrove ecosystems
(Sri Lanka Association for Fisheries and Aquatic Resources, 2015) Perera, K.A.R.S.; Amarasinghe, M.D.
Mangroves are among the most carbon rich ecosystems in the tropics. Inundation with tides and land-based surface runoff leads to anaerobic soil conditions that are conducive for accumulation of partially decomposed organic carbon. Present study was conducted to assess quantitatively the capacity of mangrove soils in retaining organic carbon. Distribution of total organic carbon (TOC) in soils of mangrove ecosystems in Negombo, Chilaw, Kala Oya, Malwathu Oya, Uppar, Batticaloa and Rekawa lagoons/estuaries, that represent western eastern and southern coasts as well as wet and dry climatic zones of Sri Lanka, was determined by using soil samples taken along the water-land gradient at 0-15 cm, 15-30 cm and 30-45 cm depths. Dichromate oxidation followed by colorimetric measurements were used to determine the percentage TOC and TOC densities were calculated using bulk density and % TOC values. Except for Batticaloa and Uppar lagoons in the dry zone, relatively a high soil TOC contents were observed in the surface soil layers (0-15 cm depth). By and large, the area between 10-30 m from the shoreline retained the highest average TOC in all mangrove areas. The highest percentage TOC in Sri Lankan mangrove soils is found not at the surface layer (4.92 - 15.1 % at the surface – 15 cm depth), but the layer below it down to a depth of 30 m (5.31 – 9.87 % at 16 – 30 cm depth). Soil beneath 30 cm contained the lowest amount (3.05 – 8.34 % at 31 -45 cm depth). Average TOC density of surface soil was 0.066 - 0.145 g cm-3 and in it was higher in mangroves of wet and intermediate climatic zones than those in the dry zone. The carbon retention capacity of Sri Lankan mangrove soils therefore was calculated to range between 313 – 492 t ha-1 and the highest was found to occur in the wet zone while it was 414 t ha-1in the intermediate zone. Soils of mangroves in the dry zone retained approximately 361 t ha-1 .of organic carbon up to a depth of 45 cm. The TOC retained by the soils of mangrove areas in Sri Lanka can be estimated as 5816 x 103 t. Inundation frequencies and durations as well as other bio-physical factors may affect the magnitude of TOC in mangrove soils.
Net photosynthetic production and potential carbon assimilation capacity of mangroves of Kadolkele in Negombo estuary, Sri Lanka
(University of Kelaniya, 2011) Perera, K.A.R.S.; Saparamadu, M.D.J.S.; Amarasinghe, M.D.
Mangroves are considered as highly productive ecosystems that have considerable potential to serve as efficient sinks of carbon, both on short and long time scales. Magnitude of mangrove primary productivity is highly variable in space and time and it depends on factors such as tidal flushing, latitude, temperature, salinity and nutrient regimes as well as substrate characteristics. Net primary production is represented by above and below ground biomass, litter production and the rate of grazing by herbivores. Since results of very few studies on primary productivity of Sri Lankan mangroves are available, the present study was conducted with the objective of understanding the net primary productivity and magnitude of net carbon assimilation capacity of mangrove ecosystem at Kadolkele. The study was conducted at Kadolkele (7011‟42.18”- 7011‟50.48” N; 790 50‟32.08”– 790 50‟47.50” E), a relatively undisturbed natural mangrove stand extending over 13.5ha, at the northern end of Negombo estuary. Data on biomass increment and litterfall during study period were gathered from twenty 10 m x10 m permanent study plots of three belt transect of 10 m wide laid perpendicular to the shoreline. Annual increment of above and below ground biomass was calculated by girth (gbh) increment, using allometric relationships developed between gbh and biomass of mangrove trees. Biomass loss through herbivory was assumed to be negligible due to high tannin content in mangrove plant parts and thus their low palatability. Organic carbon content of each component of mangrove trees was determined by Walkey and Black wet oxidation without external heating procedure followed by colorimetric method to determine absorbance at 600 nm, using a UV- visible spectrophotometer. Annual organic carbon accumulation was calculated from NPP and organic carbon content. Relatively high values of NPP were recorded from the water-front areas of the mangrove stand and it decreased towards inland. Annual total organic carbon increment was recorded to be 1232.17 + 9.23 g m-2y-1 of which 682.80 + 7.51 g m-2y-1 was found deposited in the above ground woody parts while 396.46 + 4.65 g m-2y-1 was in the plant litter and 152.91 + 1.94 g m-2y-1 in the roots. Potential capacity of Kadolkele mangroves in assimilating and accumulating carbon is 166.66 t y-1 and this amount is equivalent to the amount of carbon emitted as CO2 by combustion of 272,694 (nearly quarter of a million) liters of diesel in motor vehicles. Assuming a motor car consumes 1200 liters of diesel per year, this mangrove stand at Kadolkele with an extent of 13.5 ha can remove atmospheric carbon produced by 227 cars during one year.
Spatial distribution and dynamics of selected mangrove forests on the east and west coasts of Sri Lanka
(Sri Lanka Journal of Aquatic Sciences, 2022) De Silva, W.; Perera, K.A.R.S.; Amarasinghe, M. D.
The climate and edaphic characteristics primarily determine the spatial distribution and dynamics of mangrove forests. The present study was initiated to determine how species composition and structural characteristics vary along with climate and substrate salinity of six mangrove forests located on the west coast, i.e., Negombo estuary, Chilaw lagoon, and Malwathu oya estuary, and east coast, i.e., Batticaloa lagoon, Uppar lagoon, and Urani lagoon. The structural parameters in terms of tree height, basal area, biomass, and density were obtained to determine the vegetation structure of mangrove forests. The current study found that although the structure of mangrove communities of the two coasts does not differ significantly (P<0.05), plant diversity in mangrove areas on the west coast is significantly higher than that of the east coast mangroves. In contrast, the biomass accumulation in west coast mangroves is relatively lower than that of east coast. Tree height was found to influence the productivity in terms of biomass increment of mangrove forests under investigation. As such, our study suggests that regional variations in salinity, temperature, and rainfall primarily serve as drivers of variation in mangrove species composition and vegetation structure of mangrove forests along the coasts of Sri Lanka.