Estimation of aboveground and belowground carbon stocks in urban freshwater wetlands of Sri Lanka

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Carbon Balance and Management Open Access

RESEARCH

Estimation of aboveground and belowground carbon stocks in urban freshwater wetlands of Sri Lanka Deekirikewage Dona Thamali Lushanya Dayathilake1*  , Erandathie Lokupitiya1 and Vithana Pathirannehelage Indika Sandamali Wijeratne2

Abstract  Background:  The occurrence of climate change at an unprecedented scale has resulted in alterations of ecosystems around the world. Numerous studies have reported on the potential to slow down climate change through the sequestration of carbon in soil and trees. Freshwater wetlands hold significant potential for climate change mitigation owing to their large capacity to sequester atmospheric carbon dioxide ­(CO2). Wetlands among all terrestrial ecosystems have the highest carbon density and are found to store up to three to five times more carbon than terrestrial forests. The current study was undertaken to quantify carbon stocks of two carbon pools: aboveground biomass (AGB) and belowground biomass (BGB). Chosen study sites; Kolonnawa wetland and Thalawathugoda wetland park are distributed within the Colombo wetland complex. Colombo was recognized as one of the 18 global Ramsar wetland cities in 2018. A combination of field measurements and allometric tree biomass regression models was used in the study. Stratification of the project area was performed using the normalized difference vegetation index (NDVI). Results:  The AGB carbon stock, across strata, is estimated to be in the range of 13.79 ± 3.65–66.49 ± 6.70 tC/ha and 8.13 ± 2.42–52.63 ± 10.00 tC/ha at Kolonnawa wetland and Thalawathugoda wetland park, respectively. The BGB carbon stock is estimated to be in the range of 2.47 ± 0.61–10.12 ± 0.89 tC/ha and 1.56 ± 0.41–8.17 ± 1.39 tC/ha at Kolonnawa wetland and Thalawathugoda wetland park, respectively. The total AGB carbon stock of Kolonnawa wetland was estimated at 19,803 ±  1566 ­tCO2eq and that of Thalawathugoda wetland park was estimated at 4180 ± 729 ­tCO2eq. Conclusions:  In conclusion, the study reveals that tropical freshwater wetlands contain considerable potential as carbon reservoirs. The study suggests the use of tropical freshwater wetlands in carbon sequestration enhancement plans in the tropics. The study also shows that Annona glabra, an invasive alien species (IAS), has the potential to enhance the net sink of AGB carbon in these non-mangrove wetlands. However, further studies are essential to confirm if enhanced carbon sequestration by Annona glabra is among the unexplored and unreported benefits of the species. Keywords:  Freshwater wetlands, Aboveground and belowground biomass, Tropical carbon stocks

*Correspondence: [email protected] 1 University of Colombo, PO Box 1490, Colombo 03, Sri Lanka Full list of author information is available at the end of the article

Background The occurrence of climate change at an unprecedented scale is indicated by many studies and global assessments. IPCC [1] indicates that global warming is likely to reach 1.5 °C above pre-industrial levels between 2030