Toc tn analyzer

Soil pH was measured using a pH Meter after shaking a soil water suspension (1:5 wt/vol) for 30 minutes. Soil moisture was measured gravimetrically. Total carbon (TC) and total nitrogen (TN) were determined by dichromate oxidation and titration with ferrous ammonium sulfate34 . Soil dissolved organic C (DOC) and dissolved total N (DTN) and mineral nitrogen were extracted by adding 50 ml of 0.5 M K₂SO₄ to 10 g fresh soil, shaking for 1 h and then vacuum filtering through glass fiber filters (Fisher G4, 1.2 μm pore space). Ammonium (NH₄⁺) and nitrate (NO₃⁻) contents in the extracts were determined colourimetrically by automated segmented flow analysis (Bran + Luebbe AAIII, Germany) using the salicylate/dichloroisocyanuric acid and cadmium column/sulphanilamide reduction methods, respectively. DOC and DTN were determined using a TOC-TN analyzer (Shimadzu, Kyoto, Japan). Dissolved organic N (DON) was calculated as follows: DON = DTN − (NH₄⁺ − N) − (NO₃⁻ − N). Microbial biomass C (MBC) and biomass N (MBN) were analyzed by the chloroform fumigation and extraction method35 , and the final values were calculated using 0.35 (k_C) and 0.4 (k_N) correction factors36 .

Soil bulk density was determined by cutting ring method. SOC concentrations of soil and sediment were determined with the dichromate oxidation method of Walkley and Black [28] . Soil particle sizes were analyzed using the pipette method [29] . Total organic carbon concentrations for the runoff samples were measured with a Shimadzu TOC-TN analyzer.
The ERoc of sediment was calculated by dividing the SOC content of the sediment by its content in the original soil material. In this study, the ERoc of sediment was the ratio between the SOC concentration of sediment and the value of the source soil for each plot.

Subsamples of fresh soil were extracted with 0.5 M K₂SO₄ (1:10, w/w) and filtered through ash free paper filters (Whatman nr. 42). Concentrations of dissolved organic C and total dissolved N were measured with a TOC/TN analyzer (Shimadzu). Dissolved organic N concentration was calculated from the difference of total dissolved N and inorganic N.
Concentrations of NH₄⁺, NO₃⁻ and PO₄⁻ were determined by flow-injection analysis (Fiastar 5000, FOSS analytical, Höganäs, Sweden), using applications AN 5220 for NH₄⁺, AN5201 for NO₃⁻ and AN5240 for PO₄⁻, respectively. Three data points were excluded (one for NH₄⁺, two for PO₄⁻) because of problems with analysis resulting from precipitation in the extracts.
Microbial biomass was determined by the fumigation-extraction method (Brookes et al. 1985 (link)). Microbial biomass C, N and P was calculated from the difference in concentrations of dissolved organic C, total dissolved N and PO₄⁻, respectively, in extracts of fumigated and non-fumigated soil samples. An extraction coefficient of 0.45 for C (Wu et al. 1990 (link)) and 0.4 for N and P (Jonasson et al. 1996 (link)) was used to account for incomplete extraction of microbial biomass C and N.

DOC and total dissolved nitrogen (TDN) concentrations were analyzed in Soxhlet extracts and SPE extracts. First, methanol was removed from aliquots of SPE extracts under a stream of nitrogen and afterwards DOM was re-dissolved in 6 ml ultrapure water. Measurements were performed by high-temperature catalytic oxidation (at 680°C) using a Shimadzu TOC/TN analyzer equipped with infrared and chemiluminescence detector (oxygen flow: 0.6 l min⁻¹). Prior to direct injection onto the catalyst samples were acidified with 0.12 ml HCl (2 M) in the autosampler and purged with oxygen to remove inorganic carbon. Final DOC and TDN concentrations were average values of triplicate measurements.

DOC concentration was measured using a Shimadzu TOC/TN analyzer, and the detection limit was 0.1 mgC/L. The permanganate index (PI) was measured by titration with sodium oxalate under acidic conditions. UV₂₅₄ was measured using a spectrophotometer (Beijing Purkinje General T6, Beijing, China) set to 254 nm. The chromaticity was measured by Platinum Cobalt Standard Colorimetry. The NaClO concentration (free Cl₂) was measured by DPD/FAS titration [23 (link)].
MTBE was used to extract the DBPs from the water sample. Following this, the volatile DBPs, including TCM and CH, were measured by gas chromatography (GC) with an electron capture detector (ECD) and an HP-5 capillary column (30 m × 0.25 mm i.d., 0.25 μm film thickness, J&W, New Brighton, MN, USA). Standard solutions of TCM and CH were diluted into a series of solutions with a gradient concentration. The concentration of TCM and CH in the samples was calculated through the standard curve. The methods for determining the carboxyl and carbonyl groups are shown in Text S1 (SI).