Seasonal and temporal CO2 dynamics in three tropical mangrove creeks - A revision of global mangrove CO2 emissions

Continuous high-resolution surface water pCO(2) and delta C-13-CO2 and Rn-222 (dry season only) were measured over two tidal cycles in the wet and dry season in three tropical tidal mangrove creeks on the north-eastern coast of Queensland, Australia. Mangrove surface water pCO(2) followed a clear tidal pattern (ranging from 387 to 13,031 mu atm) with higher pCO(2)-values in the wet season than in the dry season. The delta C-13-CO2 in the mangrove waters ranged from -21.7 to -8.8% and was rather indicative of a mixed source than a distinct mangrove signature. Surface water CO2 was likely driven by a combination of mangrove and external carbon sources, e.g. exchange with groundwater/pore water enriched in 13 C, or terrestrial carbon inputs with a significant contribution of C-4-vegetation (sugar cane) source. The kinetic and equilibrium fractionation during the gas exchange at the water-atmosphere interface may have further caused a C-13-enrichment of the CO2 pool in the mangrove surface waters. Average CO2 evasion rates (58.7-277.6 mmol m(-2) d(-1)) were calculated using different empirical gas transfer velocity models. Using our high-resolution time series data and previously published data, the average CO2 flux rate in mangrove ecosystems was estimated to be 56.5 +/- 8.9 mmol m(-2) d(-1), which corresponds to a revised global mangrove CO2 emission of 34.1 +/- 5.4 Tg C per year. (C) 2017 Elsevier Ltd. All rights reserved.