*2.3. Sample Analysis*

TN content in each sediment sample was determined using a continuous flow analyzer (QuAAtro 39, Manufacturer: SEAL Co. Ltd., Norderstedt, Germany), while TC content was determined using a total organic carbon analyzer (TOC-VCPN, Manufacturer: Shimadzu Co. Ltd., Kyoto, Japan). Particle size was analyzed using a laser particle size meter (Mastersizer 3000, Manufacturer: Malvern Instrument Co. Ltd., Malvern, UK) with the measurement range of 0.01–3500 μm, after larger grains were removed through sieving. On the basis of the data from particle size analysis, the sediment type was determined. The sediment density (ρ) was quantified by the cutting ring method, and the permeability coefficient (K) was determined through the consolidation test.

For any water sample, NH<sup>+</sup> <sup>4</sup> concentration was determined using a continuous flow analyzer (QuAAtro 39, Manufacturer: SEAL Co. Ltd., Norderstedt, Germany) with a quantification limit of 0.02 mg/L, NO− <sup>3</sup> concentration was determined using an ion chromatograph (ICS-90, Manufacturer: DIONEX Co. Ltd., Sunnyvale, CA, USA) with a quantification limit of 0.02 mg/L, NO− <sup>2</sup> concentration was determined using a spectrophotometer (U-3010, Manufacturer: HITACHI Co. Ltd., Tokyo, Japan) with a quantification limit of 0.002 mg/L, and DOC concentration was determined using a total organic carbon analyzer (TOC-VCPN, Manufacturer: Shimadzu Co. Ltd., Kyoto, Japan).
