Multi n c 2100

Dissolved organic carbon (DOC) concentrations in bulk WSOM solutions were measured using a total organic carbon analyzer (Multi N/C2100, Analytik Jena, Jena, Germany). The DOC concentration in biofilm WSOM were normalized to mg/g shown in Table S2. UV-vis absorption spectra were measured by a spectrophotometer (UV-1800, Shimadzu, Japan). The excitation–emission matrices (EEMs) of CDOM in WSOM were measured using a fluorescence spectrophotometer (F7000, Hitachi, Japan). Detailed information on spectral analysis is provided in SI. Parallel factor analysis (PARAFAC) was performed using the DOM Fluor toolbox in MATLAB (R2017a) software [33 (link)]. The relative contents of fluorescent components were obtained via F_max values analyzed by PARAFAC. Several UV-visible spectra-derived parameters were calculated to demonstrate the aromaticity (SUVA₂₅₄), hydrophobicity (E₂₅₄/E₂₀₄), and molecular weight (S_R) of biofilm WSOM. We also calculated parameters including biological index (BIX), humification index (HIX), and fluorescence index (FI) to describe the fluorescent characteristics of biofilm WSOM as described in the Table S3.

The aquatic environmental pH value was monitored with a pH meter (pH 30, Clean-Leau Instruments, China). DOM contents were measured using a total organic carbon (TOC) analyzer (Multi N/C 2100, Analytik Jena, Germany). In addition, DOM was quantitated with three-dimensional fluorescence excitation-emission matrix (3D-FEEM) spectrophotometry. Briefly, 3D-FEEM spectra were obtained using a fluorescence spectrophotometer (F-4500, Hitachi, Japan). The excitation (Ex) and emission (Em) slits were set to a bandpass of 5 nm. Ex wavelengths were scanned from 200 to 450 nm, and Em wavelengths were scanned from 220 to 550 nm. All of the 3D-FEEM spectral data were analyzed with Origin Pro 2018 software (www.originlab.com/origin). Fourier transformation infrared spectrometry (FTIR) (Nicolet 6700, Thermo Fisher Scientific, USA) was employed to collect spectra in the range of 400–4000 cm⁻¹ at 4 cm⁻¹ resolution and 64 scans of the DOM.

Soil samples in each plot were collected from 10 soil layers distributed evenly between the depths of 0 −200 cm using a soil auger (4 cm diameter). Three cores were collected randomly from each plot. The samples from the same depth in each plot were thoroughly mixed and the roots air-dried, and other visually identified organisms, such as residual roots, were removed. The air-dried samples were ground to fully pass through a 2-mm sieve. They were divided into two parts: one was used to measure the soil carbon after thoroughly passing through a 0.15 mm sieve, and the other was stored for validation. The soil carbon was measured using a multi N/C 2100 (Analytic JENA, AG-Germany) at the Institute of East China Sea Fisheries Research, Chinese Academy of Sciences. The soil total carbon (STC) was measured using the direct combustion of 10–20 mg of soil. The SOC was measured by pretreating 10−20 mg of the soil with 1 M HCl for 24 h to remove the carbonate and processing the sample using the same procedure as the STC. The SIC was calculated as the difference between the STC and SOC. The soil bulk density was determined using the oven-drying method to measure the soil mass and core volume (Soil Survey Staff, 2011 ).

Samples for chemical analysis were first filtered through a 0.45 μm filter membrane, and then the determination of NO₃⁻-N, NO₂⁻-N, and NH₄⁺-N followed the standard methods [26 ]. TOC and cell growth (OD₆₀₀) were determined by a TOC analyzer (Multi N/C 2100, Analytik Jena, Jena, Germany) and spectrophotometer at 600 nm, respectively. In addition, the inhibition rate of the net OD₆₀₀ value was also calculated by the following formula:

Methods to determine physicochemical
on-site parameters (temperature, pH, Eh, electrical conductivity,
and O₂ concentrations), alkalinity, sulfide (HS^–), and H₂ have been described elsewhere.^{18 (link)} The main inorganic anions as well as acetate (CH₃COO^–) and formate (HCOO^–) were
determined by ion chromatography (IC 881, Metrosep A Supp 5-150/4.0;
Deutsche Metrohm GmbH & Co. KG; Germany). The main inorganic cations
including dissolved iron and manganese were analyzed with an ICP-OES
(Vista AX; Varian Medical Systems, Inc.; CA). For determining the
concentrations of nonpurgeable organic carbon (NPOC), a TOC/TN analyzer
(multi N/C 2100; Analytik Jena AG; Germany) was used. Chlorinated
ethenes and C1–C5 hydrocarbons were measured by headspace gas
chromatography equipped with an ECD and FID detector (GC 6890plus,
HS7694; Agilent Technologies, Inc.; CA).
To gain the amount
of potential electron acceptors in the solid phase, the reactive Fe³⁺ content of 15 sediment samples from the injection horizon
of wells U03 and U05 was determined by extraction with 1 M HCl as
described in Leventhal and Taylor^{28 (link)} and
subsequent photometric analyses of the extracts using the ferrozine
method,^{29 (link)} whereby hydroxylammonium chloride
functions as a reductive agent.

Acid and alkaline phosphatases were determined following the methodology outlined by Tabatabai and Bremner^{32 (link)}, using 16 mM para (p)-nitrophenyl phosphate as substrate and reported as µg p-nitrophenol produced g⁻¹ dry soil hour⁻¹. Total organic carbon (TOC) was analyzed using a TOC analyzer (Multi N/C 2100, Analytikjena, Germany). To estimate TOC, the soil was first treated with HCl to eliminate soil inorganic carbon (calcium carbonates), and then, TOC was estimated following the dry combustion method³³ . The labile carbon pool was analyzed using modified Walkley and Black method^{34 (link)}. The chloroform-fumigation extraction method was used for the estimation of microbial biomass carbon (MBC)^{35 (link)}. Briefly, 20 g (dry weight equivalent) soil was fumigated with ethanol-free chloroform for 48 h. Both fumigated and non-fumigated soils were extracted with 50 ml of 0.5 M K₂SO₄, followed by shaking on an end-to-end shaker for 30 min. The organic carbon content of the extract was determined through oxidation with potassium dichromate^{36 (link)}. The difference in the carbon content of the fumigated and non-fumigated extracts was multiplied by a factor of 0.33 to calculate MBC and was expressed as µg g⁻¹ of dry soil^{37 (link)}.

Physicochemical properties and mixing ratio of the compounds investigated were given in Tables 1 and 3. The aerosol particles were generated from a constant output atomizer (1500, MSP) containing aqueous solutions with a mass concentration of 0.1%. The dilute solutions were prepared by dissolving each pure component or mixture in ultrapure water (EASY Pure^® II UF ultrapure water system, 18.2 MΩ cm). Due to its complex composition, humic acid could not be completely dissolved in the ultrapure water. The humic acid suspensions were filtered through the filter paper (Whatman, medium speed) to remove insoluble material. In order to accurately calibrate the concentration of humic acid, subsequent processing were performed with the clarified filtrate. The organic elemental analysis indicated that mass fraction of carbon, hydrogen, nitrogen in solid humic acid (Aldrich) samples were 41.32%, 3.29%, 1.21%, respectively. Carbon content (g ml⁻¹) in the humic acid solution was measured using a total organic carbon analyzer (TOC, Analytikjena multi N/C 2100). The concentration of HA is obtained as follows: Concentration of HA (g ml⁻¹) = carbon element concentration of the solution measured by TOC (g ml⁻¹)/mass fraction of carbon element in solid HA samples. The humic acid solution with specific concentration was used to prepare mixture solution containing KCl.