CO₂ and CH₄ emissions from tidal channels play a central role in mangrove carbon cycling, although their spatial variability and environmental controls remain insufficiently resolved in macrotidal Amazonian systems. Measurements across large and small channels on the Ajuruteua Peninsula revealed pronounced differences in gas efflux associated with salinity regimes, water source, tidal forcing, and physicochemical conditions. Variation in temperature, dissolved oxygen, turbidity, pH, and oxidation–reduction potential shaped emission patterns, with temperature consistently driving both gases across multiple channels. Freshwater-influenced areas tended to exhibit enhanced efflux, whereas more marine sites showed reduced CH₄ release, reflecting the influence of sulfate-rich waters on methanogenesis. Comparisons among channel sizes indicated broadly similar emission magnitudes, suggesting that hydrodynamic processes may override geometric differences. The findings highlight the heterotrophic character of mangrove-connected waters and underscore the need to integrate tidal channels and creeks into carbon-budget assessments for tropical coastal wetlands.