## 3 Results and Discussion  
### DOC Concentrations and Carbon Mass Fractions of the Size-Fractioned SHS  
The basic properties of the AD- and FD-treated sediments are listed in Table 1. The AD and FD pH values were within neutral values, ranging from 6.63 to 7.25. The average FD pH value was significantly higher than the AD value (\(p\) = 0.017). The FD organic matter (OM) and TOC concentrations were higher than the AD but insignificantly different (\(p\) = 0.62 and 0.51, respectively).  
The DOC concentration is a standard parameter of natural organic matter and SHS [1; 40]. The DOC concentrations of the bulk SHS (BHS) sample and the three size-fractionated SHS samples are listed in Table 2. The BHS DOC concentrations (323-440 mg-C/L, average 7.36 g-C/kg based on sediment mass) of the FD sample were significantly higher than the AD sample (190-213 mg-C/L, average 4.02 g-C/kg based on sediment mass) (\(p\) = 0.011). The readily biodegradable and labile organic matter experienced oxidation cleavage that mineralized to carbon dioxide and generated organic acid via biodegradation in the AD process [4; 41]; hence, the AD sediment had a lower pH value, OM, and TOC concentrations, and BHS had lower DOC concentrations than the FD samples.  
The FD DOC concentrations were significantly higher in each size-fractionated SHS sample than the AD samples (\(p<0.02\)). The overall organic carbon recoveries between the size-fractionated SHS and BHS samples were 91.3 \(\pm\) 1.9% (AD) and 101.3 \(\pm\) 6.1% (FD), which were within a reasonable range (100 \(\pm\) 25%) [42]. The percent contribution of each size-fractionated solution to the total DOC concentration of the overall BHS solutions was 65.7 \(\pm\) 4.3%, 21.9 \(\pm\) 4.1%, and 12.4 \(\pm\) 1.1% for HHS, MHS, and LHS, respectively, for the AD samples and was 65.4 \(\pm\) 2.4%, 22.2 \(\pm\) 1.2%, and 12.6 \(\pm\) 3.5% for HHS, MHS, and LHS, respectively, for the FD samples. The two pre-treatment drying methods had no carbon mass fraction difference (\(p\) = 0.93-0.97). The organic carbon mass fractions of each size-fractionated SHS sample were not significantly different, which suggested that the  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample** & **pH** & **TOC (g/kg)** & **OM (\%)** & **TOC/OM (\%)** \\ \hline AD & 6.78 \(\pm\) 0.17 * & 44.1 \(\pm\) 11.0 & 7.45 \(\pm\) 1.1 & 58.8 \(\pm\) 12.1 \\ FD & 7.19 \(\pm\) 0.05 & 50.4 \(\pm\) 11.0 & 7.92 \(\pm\) 0.9 & 64.2 \(\pm\) 15.0 \\ \hline \hline \end{tabular}
* indicated \(p<0.05\).  
\end{table}
Table 1: Basic sediment properties in AD and FD samples.  
sediment OM was diagenetically uniform within the AD and FD treatments. The SHS carbon mass for the high molecular weight fraction (>1 kDa) averaged 87%, which was higher than the surface water systems' carbon mass fraction, which ranged from 20% to 67% [2, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45]. It was also higher than the water extracted organic matter (WEOM) from the sediment's carbon mass fractions, ranging from 52% to 53% [3]. The organic carbon mass fraction of the high molecular weight fraction was comparable to the alkaline-extracted SHS solutions from sediments and ranged from 78% to 85% [9, 10, 17]. The sediment particular organic matter experienced hydrolysis and/or oxidative cleavage, starting with the low molecular weight and labile organic matter [4]. The exchange process of particulate and dissolved organic matter left high molecular weight organic matter in the sediment; hence, the alkaline-extracted SHS had a higher percentage of the high molecular weight carbon mass fraction.