## 3 Results and Discussion  
Chemical Properties of the Original Sediments and Lake Water and Electrochemical Performance from SMFCs  
Chemical properties of the original sediments from sites TH1 and TH2 were analyzed and are shown in Table S2: The TP amounts were 763.61 and 625.50 mg kg\({}^{-1}\) dry sediments; the TN amounts were 1250.28 and 1191.50 mg kg\({}^{-1}\) dry sediments; the cellulose amounts were 269.32 and 168.0 mg kg\({}^{-1}\) dry sediments; the TOC amounts were 15.70 and 9.70 mg kg\({}^{-1}\) dry sediments. The properties of the water samples from sites TH1 and TH2 were also measured (Table S2): pH were 8.0 and 7.8, respectively with a conductivity of 0.50 and 0.60 mS cm\({}^{-1}\), and a dissolved oxygen (DO) content of 11.79 and 12.47 mg L\({}^{-1}\). More nutrients were found in the macrophyte-dominated area. The cell voltages of SMFCs from the two sampling sites during the whole experimental period of 700 days showed the same changing tendencies (Figure 1). The voltage output in SMFCs showed a changing fluctuation throughout the experimental period. On the whole, the voltage from SMFCs increased quickly during the former 35 days. This was the startup stage of SMFC and an electrochemically active biofilm on the anode surfaces was formed during this period [26; 27]. After 80 days of operation, SMFCs for sediments from TH1 and TH2 reached the highest voltage of 123 mV and 145 mV respectively. The phenomenon indicated microbial population enrichment in this stage, which oxidized some easily biodegradable organic matters in sediments [28]. As the contents of easily biodegradable organic matters decreased, the voltages dropped drastically between Day 80 and Day 125. Then they maintained a relatively stable value between Day 125 and Day 282, and began dropping between Day 282 and Day 370. Voltages increased again on Day 370, followed by a gradual decrease to a minimum of 40 mV and 20 mV from TH1 and TH2 sediments, respectively on Day 700. The voltage drop might be due to the microorganisms in the sediment utilizing the stable, recalcitrant organic matter when the labile carbon pools were depleted. Although the overall trend of voltage change from the two sampling sites was the same, the maximum voltages were different. The voltage in sediments from site TH1 were lower in the early stage of the experiments but became higher after about 400 days of incubation compared to the voltages from site TH2. Current and power generation during the whole experiment were also obtained according to voltage output and the fixed external resistance (100 \(\Omega\)) (Figure S3). The maximum current and power were 1.4 mA and 210 mW from site TH1. Figure 2 shows the polarization curves for SMFC produced with sediments from sites TH1 and TH2 on Day 450. Notably, the SMFC from site TH1 had a significantly higher maximum power density (5.34 mW m\({}^{-2}\)) compared to that from site TH2 (1.82 mW m\({}^{-2}\)). Previous researches determined that the bioelectrochemical system of an SMFC was influenced by several operational characteristics, such as differently pretreated carbon felts, electrodes' resistance, microorganisms' growth and development, and electrode surface inhomogeneity [29; 30]. The same electrodes were designed in each reaction  
column, so the same electrodes' resistances were obtained (5.5 \(\Omega\)), which led to the speculation that the different electrical parameters from sites TH1 and TH2 might be mainly due to the microbial community composition. Polarization curves showed that the maximun power densities were produced using an 820 \(\Omega\) and a 2000 \(\Omega\) resistor, respectively, for sediments from the sites TH1 and TH2. _P. malaianus_ is a complex mixture of lignin, hemicellulose, and cellulose, which makes it much more difficult to break down or biodegrade than pure fibrous material.