Soil concentrations and atmospheric emissions of biogenic hydrogen sulphide (H2S) in a Rhizophora mangrove forest

Mangrove forests are potentially large biogenic sources of atmospheric hydrogen sulphide (H2S), featuring among the carbon-richest ecosystems in the world associated with strong soil anoxia and large quantities of sulphates brought by tides. H2S is highly toxic and acts as a precursor for atmospheric sulphur compounds and sulphate aerosols, which contribute to acid deposition and have implications for global climate change. Therefore, understanding H2S emissions in mangroves holds great importance. Yet, its range of emissions remains uncertain. In this exploratory study, soil H2S concentrations were measured during tide stall at both high and low tide in a semi-arid mangrove, which has never been done before. Then, potential H2S fluxes to the atmosphere were estimated at low tide. Soil concentrations were greater at high tide than low tide, probably due to larger soil anoxia (average of −377 vs −179 mV), with average values of 1.40 ± 0.55 and 0.73 ± 0.32 mmol L−1, respectively. Temperature was a key factor controlling soil concentrations, with higher values in the warm season than in the cold season. Average H2S emissions ranged from 5.81 ± 2.58 to 28.74 ± 6.98 μg S m−2 h−1 with a mean value of 14.90 ± 7.90 μg S m−2 h−1. This study contributes to reducing the uncertainty in the variation range of H2S fluxes from mangroves, which may be significant for the global sulphur cycle.