Iron dynamics in a subtropical estuarine tidal marsh: effect of season and vegetation

摘要

To better understand how seasonal change and the presence of plants affect biogeochemical iron (Fe) cycling in tidal marsh sediments, we examined the seasonal dynamics of microbial Fe reduction (FeR) and related Fe speciation from 2012 to 2014 using in situ vegetated and unvegetated mesocosms created with macrobenthos-proof enclosures. The pools of Fe(III) oxides, Fe sulfides, porewater Fe2+, and rates of microbial sulfate reduction (SR) peaked in summer (hot and wet), whereas rates of FeR and non-sulfidic Fe(II) levels peaked in winter (mild and dry). Sedge presence greatly increased the FeR rate, organic matter pools, and Fe(III) oxide levels, but decreased carbon: nitrogen ratios and sulfide abundances. FeR rates were mainly affected by the SR level, and temperature and plant primary productivity had comparable effects on SR rates. The dominant organic carbon mineralization pathway changed from SR in summer to FeR in winter in both vegetated and unvegetated mesocosms. FeR was more important in the vegetated mesocosms than in the unvegetated mesocosms, and seasonal change contributed more to the total variability of each anaerobic pathway than the presence of sedge. Our study reveals that temperature and plants both mediate variations in the organic carbon mineralization pathways of a subtropical estuarine tidal marsh.