Carbon sequestration and sedimentation in mangrove swamps influenced by hydrogeomorphic conditions and urbanization in Southwest Florida

Abstract

This study compares carbon sequestration rates along two independent tidal mangrovecreeks near Naples Bay in Southwest Florida, USA. One tidal creek is hydrologically disturbeddue to upstream land use changes; the other is an undisturbed reference creek. Soil cores werecollected in basin, fringe, and riverine hydrogeomorphic settings along each of the two tidal creeksand analyzed for bulk density, total organic carbon profiles, and sediment accretion. Radionuclides 137Cs and 210Pb were used to estimate recent sediment accretion and carbon sequestration rates.Carbon sequestration rates (mean ± standard error) for seven sites in the two tidal creeks on theNaples Bay (98 ± 12 g-C m-2· year-1 (n = 18)) are lower than published global means for mangrovewetlands, but consistent with other estimates from the same region. Mean carbon sequestration ratesin the reference riverine setting were highest (162 ± 5 g-C m-2· year-1), followed by rates in thereference fringe and disturbed riverine settings (127 ± 6 and 125 ± 5 g-C m-2· year-1, respectively).The disturbed fringe sequestered 73 ± 10 g-C m-2· year-1, while rates within the basin settingswere 50 ± 4 g-C m-2· year-1 and 47 ± 4 g-C m-2· year-1 for the reference and disturbed creeks,respectively. These data support our hypothesis that mangroves along a hydrologically disturbedtidal creek sequestered less carbon than did mangroves along an adjacent undisturbed reference creek.