Litter addition potentially enhances volatile organic compound emission from a freshwater wetland

Plant litter could be a potential source of atmospheric volatile organic compounds (VOCs). Previous studies are mostly restricted to forest litter, but VOC budget of wetlands resulting from litter decomposition remains largely unexplored. Here we performed in-situ VOC flux measurements in a freshwater wetland and three treatments including A (no litter addition), B (1.15 kg litter m⁻²) and C (2.30 kg litter m⁻²) were designed to investigate impacts of litter decomposition on wetland-atmosphere exchange of VOCs. During year-round observation, average fluxes of net VOCs for B and C were 5.14 ± 2.75 μg m⁻² h⁻¹ and 7.85 ± 3.80 μg m⁻² h⁻¹, respectively, significantly higher than that of A (2.13 ± 2.41 μg m⁻² h⁻¹). These results suggested that freshwater wetlands were potential sources of atmospheric VOCs and that litter decomposition could enhance VOC release. The net VOC flux exhibited distinct seasonal patterns and was correlated with ambient temperature (p < 0.05). Moreover, the release or uptake of VOCs varied among different chemical groups. Specifically, non-methane hydrocarbons including alkanes, alkenes and aromatics showed positive net fluxes that increased with added litter. Halocarbons exhibited a negative net flux in A, but positive net fluxes in B and C. Oxygenated VOCs demonstrated negative net fluxes in both A and B, but switched to a positive flux in C. Positive net fluxes of volatile organic sulfide compounds were observed in three treatments. Based on the flux variations of specific VOC groups, our findings suggest that both temperature-dependent biotic and abiotic processes regulated the exchange of VOCs between freshwater wetland and atmosphere.