## 2 Materials and Methods  
### Sediment Collection and Treatment  
The studied sediment was collected from a sampling site (22\({}^{\circ}\)46\({}^{\prime}\)04.2\({}^{\prime\prime}\) N, 120\({}^{\circ}\)32\({}^{\prime}\)32.7\({}^{\prime\prime}\) E) in southern Taiwan, 50 m downstream of an animal wastewater discharge outlet. Water containing high concentrations of organic matter has been reported [9]. Livestock wastewater often contains high concentrations of particulate and dissolved organic matter which, when deposited on sediment, may cause a high level of organic matter in the sediment.  
The sampling time for this study was from July to August 2011. Samples were taken once a week and a total of three samples were taken as triple samples for each drying method. The sediment sample collection used a stainless-steel sampling long dipper to take the surface sediment (0-15 cm). Each sampling used a simple, random sampling method to take the three sediment samples; the samples were mixed evenly into one sample. Each sample was about 2 kg and packed into a wide-mouth brown bottle for individual drying.  
After the sediment was sent back to the laboratory, the sediments, which were to be air-dried, were spread on a plastic tray and placed in an area away from direct sunlight. The average outdoor temperature was 27 \(\pm\) 2 \({}^{\circ}\)C. During the drying period, the sediments were flipped from time to time to evenly expose the sediments to the air. Due to the high temperature, we estimated that the sediment was dry within a month. The other sediment samples were freeze-dried (FD) immediately and the FD samples were then stored in a 4 \({}^{\circ}\)C refrigerator for one month.  
The freeze- and air-dried samples were sieved with stainless-steel mesh (<2 mm). The sieved samples were then analyzed for basic properties, such as pH, total organic carbon (TOC), and organic matter, and stored in sealed plastic cans for subsequent tests. The dried sediments were passed through a 100-mesh (0.149 mm) sieve and one gram of the sieved sediment was analyzed with a solid TOC analyzer (1030S TOC Solids Module, O.I. Analytical) to quantify the TOC content in the sediment. To quantify the organic matter, one gram of sieved sediment was placed into a crucible, which was placed in the furnace (500 \({}^{\circ}\)C for 3 h). After cooling, the crucible was weighed. The organic matter content (%) = (weight lost by burning)/(weight of dried sediment) \(\times\) 100%.  
The extraction and purification of the SHS samples followed the procedure recommended by the International Humic Substances Society (IHSS) [6; 35]. A 0.1 N HCl solution was added to remove the alkaline earth metals and carbonate. The residual sediment was mixed with a 0.1 N NaOH solution at a ratio of 1/20 (\(w\)/\(v\)). The extracted NaOH solution was centrifuged (4500 rpm, 20 min) to separate the SHS, and then passed through a 0.45 \(\upmu\)m filter (Pall) to collect the bulk SHS (BHS) solution, which was at an alkaline pH. Sodium azide (0.5%) was added to the BHS solution to prevent bacterial growth and then stored in a 4 \({}^{\circ}\)C refrigerator. To avoid contamination of the container, it was previously washed with ultrapure water.