Nitrous Oxide Emission from a Flooded Tropical Wetland across a Vegetation and Land Use Gradient

Abstract

Whereas wetland ecosystems are among the most vital natural carbon sinks, they are also important sources of nitrous oxide (N2O), a highly potent greenhouse gas. However, due to differences in wetland characteristics, N2O emission is likely to vary across wetland types. We investigated the: 1) influence of vegetation community (Typha latifolia; Typha, Phragmites mauritianus; Phragmites and Cyperus papyrus; Papyrus) in a natural tropical freshwater wetland, and 2) impact of converting a natural tropical freshwater wetland into a rice paddy wetland on N2O emission. Results showed that N2O emission (µg m− 2 h− 1) from the natural wetland did not vary significantly (p > 0.05) among the vegetation communities during both the dry and wet seasons (Typha = 0.6 ± 1.6 [SE] and 0.5 ± 1.4, Phragmites = 0.5 ± 1.7 and 0.4 ± 1.5, Papyrus = 0.5 ± 1.3 and 0.5 ± 1.5, respectively). These emission rates insignificantly differed (p > 0.05) from those recorded in the rice paddy wetland (dry season = 0.7 ± 2.8 and wet season = 0.6 ± 2.7). There was no significant correlation (p > 0.05) between soil physico-chemical characteristics and N2O emission. We concluded that vegetation community does not affect N2O emission from a natural tropical freshwater wetland under continuous flooding. Similarly, under continuous flooding and no fertilization conditions, converting a natural tropical freshwater wetland into a rice paddy wetland does not influence N2O emission. We roughly estimated total annual N2O emissions (T yr− 1) and their carbon dioxide equivalents (CO2e; T yr− 1) from all Uganda’s natural and rice paddy wetlands as: natural wetlands = 115.1 ± 342.8 (CO2e = 30,501.5 ± 90,842) and rice paddy wetlands = 0.9 ± 2.7 (CO2e = 242.5 ± 707.6).

Plant controls over tropical wetland nitrous oxide dynamics: a review

“…degree of flooding, management, and soil properties), and studies that have assessed such processes often have small sample sizes. Were and Hein (2021) reported no significant differences in N2O emissions in the wet or dry season within a single Ugandan wetland site featuring Typha latifolia, Phragmites mauritianus, and Cyperus papyrus, with similar results reported elsewhere (Marín-Muñiz et al, 2015;Hernández and Junca-Gómez, 2020). However, such results may be because the studied species exhibit relatively similar adaptations to their environment, and therefore the relative differences in species-specific controls are small.…”