Table 2. Global CH4 emissions, carbon burial rates, and offsets in mangroves.
Global emission and carbon burial rates are upscaled to the global mangrove forest area of 137,760 km2 (25). n refers to the number of study site locations (see tables S2, S3, and S5).
|
CH4 flux rate (μmol m−2 day−1) |
Global CH4 emission (Tg CH4 year−1) |
Global CH4 emission (Tg C year−1) |
CH4 (CO2 eq.) emission, GWP20 (Tg C year−1) |
CH4 (CO2 eq.) emission, GWP100 (Tg C year−1) |
Sequestration rate (g C m−2 year−1) |
Global carbon burial (Tg C year−1) |
Offset (%)* |
Sensitivity analysis offset range (%)† |
|
| Water-air CH4 flux |
(n = 9) | (n = 9) | (n = 9) | (n = 9) | (n = 9) | (n = 27) | (n = 27) | ||
| Min | 35.10 | 0.028 | 0.021 | 0.66 | 0.26 | 56.60 | 7.80 | ||
| Max | 659.8 | 0.531 | 0.398 | 12.45 | 4.92 | 651.0 | 89.68 | ||
| Average ± SE | 288.0 ± 73.2 | 0.232 ± 0.059 | 0.174 ± 0.044 | 5.43 ± 1.38 | 2.15 ± 0.55 | 227.2 ± 30.67 | 31.30 ± 4.22 | 17.3 | (15.7–18.5) |
| Sediment-air CH4 flux |
(n = 14) | (n = 14) | (n = 14) | (n = 14) | (n = 14) | (n = 27) | (n = 27) | ||
| Min | 0 | 0 | 0 | 0 | 0 | 56.60 | 7.80 | ||
| Max | 2,127.2 | 1.71 | 1.28 | 40.14 | 15.87 | 651.0 | 89.68 | ||
| Average ± SE | 391.2 ± 153.4 | 0.315 ± 0.123 | 0.236 ± 0.093 | 7.38 ± 2.90 | 2.92 ± 1.14 | 227.2 ± 30.67 | 31.30 ± 4.22 | 23.6 | (22.0–25.8) |
| Global total | (n = 23) | (n = 23) | (n = 23) | (n = 23) | (n = 23) | (n = 27) | (n = 27) | ||
| Average ± scaled error |
339.6 ± 106.2‡ | 0.273 ± 0.053‡ | 0.205 ± 0.040‡ | 6.41 ± 1.24‡ | 2.53 ± 0.49‡ | 227.2 ± 30.67 | 31.30 ± 4.22 | 20.5 | (19.8–21.0) |
*Offset is calculated from carbon burial (Tg C year−1) and the CH4 flux using the GWP20 (Tg C year−1).
†Carbon burial (Tg C year−1) and CH4 emissions (GWP20; Tg C year−1) are adjusted up and down by their errors.
‡Accounting for mangrove ecosystems being inundated 50% of the time (water-atmosphere flux) and exposed 50% of the time (sediment-atmosphere flux).