## 3 Results
### Soil Carbon Profile  
Soil organic carbon (SOC) concentrations varied widely, with values ranging from 3.8 to 344 g-C kg\({}^{-1}\) in the mangrove settings along the tidal creeks (Table 2; Figure 3). Percent soil carbon among sites ranged from 0.003% to 34%, with a mean of 14.3%. Mean SOC concentration of our reference tidal creek site (SC) was 15.3%, while the mean of the disturbed creek (HA) was 13.1%. The mean SOC in the dwarf mangrove setting at the reference creek was 6.9%. Throughout the study locations, the majority of carbon was organic carbon (range: 89%-99%). Higher values of inorganic carbon were noted in reference basin and fringe mangroves and disturbed fringe mangroves, but only at a very limited number of depths. The highest SOC was in the disturbed riverine mangrove site (342 g-C kg\({}^{-1}\)) near the surface (4-cm depth), while the lowest SOC was found in the reference basin mangrove setting (5.4 g-C kg\({}^{-1}\)) at 30 cm depth (Table 2). SOC in the disturbed riverine mangroves remained consistently high throughout the soil profile, while SOC decreased with depth in all other locations, except for the reference riverine mangroves. The decreasing trend with depth was most pronounced in the reference basin sites where the uppermost 6 cm (0-6 cm depth) of substrate held an  
Figure 2: Average bulk density (g: cm\({}^{-3}\)) for the past 50 years within soils located in seven different mangrove sites in different hydrogeomorphic settings in the hydrologically disturbed Hamilton Avenue Creek (HA) and the reference Susan’s Creek (SC). average of 265 \(\pm\) 9.8 g-C kg\({}^{-1}\), while the lower layers (26-32 cm depth) held 6.0 \(\pm\) 1.2 g-C kg\({}^{-1}\). There was a less pronounced trend in the fringe mangroves; SOC values in the upper 6 cm of the soil profile contained 259 \(\pm\) 12 and 177 \(\pm\) 5.1 g-C kg\({}^{-1}\), while the lowermost soil layers contained 153 \(\pm\) 15 and 67.2 \(\pm\) 6.3 g-C kg\({}^{-1}\) for SC and HA creeks, respectively. The reference riverine setting is the only site where SOC increased with depth; average SOC in the uppermost 6 cm was 140 \(\pm\) 8.1 g-C kg\({}^{-1}\) while the SOC in the lowermost 6 cm (28-32 cm depth) was, on average, 199 \(\pm\) 3.3 g-C kg\({}^{-1}\). \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & \multicolumn{6}{c}{**Hydrogeomorphic Setting**} \\ \hline  & \multicolumn{2}{c}{**Basin**} & \multicolumn{2}{c}{**Fringe**} & \multicolumn{2}{c}{**Riverine**} & \multicolumn{2}{c}{**Dwarf**} \\ \hline
**Tidal Creek** & **SC** & **HA** & **SC** & **HA** & **SC** & **HA** & **SC** \\ \hline bulk density (g-cm\({}^{-3}\)) & 0.13 \(\pm\) 0.009 & 0.78 \(\pm\) 0.09 & 0.23 \(\pm\) 0.03 & 0.25 \(\pm\) 0.004 & 0.22 \(\pm\) 0.02 & 0.13 \(\pm\) 0.005 & 0.10 \(\pm\) 0.003 \\ \hline accretion rate (\({}^{201}\)Pb) (mm-year\({}^{-1}\)) & 1.68 & 1.58 & 2.28 & 2.23 & 5.43 & 3.04 & 1.41 \\ \hline accretion rate (\({}^{137}\)Cs) (mm-year\({}^{-1}\)) & - & 7.34 & 3.26 & 3.67 & 3.67 & 2.85 & - \\ \hline carbon concentration (g-C kg\({}^{-1}\)) & 238 \(\pm\) 3 & 40 \(\pm\) 7 & 232 \(\pm\) 38 & 131 \(\pm\) 18 & 143 \(\pm\) 21 & 324 \(\pm\) 4 & 91 \(\pm\) 5 \\ \hline carbon pool (g-C m\({}^{-2}\)) & 2.5 \(\pm\) 0.2 & 2.3 \(\pm\) 0.2 & 6.3 \(\pm\) 17 & 3.7 \(\pm\) 0.5 & 8.1 \(\pm\) 0.3 & 6.2 \(\pm\) 0.3 & 1.0 \(\pm\) 0.3 \\ \hline carbon sequestration rate (g-C m\({}^{-2}\)year\({}^{-1}\)) & 50 \(\pm\) 4 & 47 \(\pm\) 4 & 127 \(\pm\) 33 & 74 \(\pm\) 10 & 162 \(\pm\) 5 & 126 \(\pm\) 6 & 21 \(\pm\) 5 \\ \hline Carbon sequestration rates in the last row are estimated by using the \({}^{210}\)Pb accretion rates. Mean \(\pm\) standard errors are shown for bulk density, carbon concentration, carbon pool, and carbon sequestration. &  
\end{table} 
Table 2: Soil bulk density (past 50 years), sediment accretion rates (two methods), carbon concentration, carbon pool, and carbon sequestration rates at mangrove study sites at Susan’s Creek (SC; reference) and Hamilton Avenue Creek (HA; disturbed), adjacent to Naples Bay.