Dx 600

The concentration of ONZ was measured in a Waters e2695 HPLC system equipped with an Agilent C18 column (4.6 × 250 mm, 5 μm). The mobile phase was composed of methanol and water (20:80, v/v) with a flow rate of 1.0 mL/min. The ONZ was measured at a wavelength of 318 nm, and the column temperature was 30 °C. An ultraviolet–visible light (UV–Vis) spectrophotometer (D6000, Hach, USA) was used to obtain the UV spectra of the ONZ solution. The chemical oxygen demand (COD) and total organic carbon (TOC) were measured using a COD tester (DRB200, Hach, USA) and a TOC analyzer (TOC-VCPH, Shimadzu Corporation, Japan), respectively. The pH of the solution was measured using a Mettler-Toledo pH meter. An ion chromatograph (DX600, Dionex, USA) was used to detect the inorganic ions. The carbon content was determined by element analysis (Vario EL Ⅲ, Elementar, Germany). The iron content was determined with inductively coupled plasma atomic emission spectrometry (ICP-OES, ICPOES730, Agilent, USA) after HNO₃ digestion.

MFT samples removed from the columns were centrifuged (3075 g for 1 h) in a Sorvall RC 5B Superspeed centrifuge to collect the porewater. The solids fraction was analyzed as described below. For the soluble cations calcium (Ca²⁺), magnesium (Mg²⁺), sodium (Na⁺) and potassium (K⁺), porewater was filtered and diluted with 1% HNO₃ (trace metal grade) and analyzed using Inductively Coupled Plasma Mass Spectrometry (ICP-MS; Perkin Elmer SCIEX ELAN 9000) with appropriate internal and external standards. Chloride (Cl⁻), nitrate (NO⁻₃) and sulfate (SO²⁻₄) soluble anion concentrations were determined using an ion chromatograph (Dionex DX 600) equipped with a 4 mm analytical column (AS9-HC). Dissolved bicarbonates (HCO⁻₃) were determined using the methyl orange indicator method (US EPA, 1974 ) and Smartchem Discrete Wet Chemistry Analyzer 200 (Westco Scientific) at 550 nm. The PO³⁻₄ concentration was determined using the colorimetric Molybdenum Blue method (US EPA, 1993 ) using the SmartChem at λ 880 nm.

Geochemical data for the January and June samples have been reported in other publications9 (link)19 (link). For the August samples, the same analytical procedures were used for water and sediment geochemical analyses. Cation and anion concentrations were measured by using ion chromatography (Dionex DX-600, USA), and DOC and TN concentrations were measured on a multi N/C 2100S analyzer (Analytik Jena, Germany). Sediment samples for TOC and mineralogy measurements were dried and ground. TOC samples were treated with 1 N HCl overnight to remove carbonates and then washed to a neutral pH followed by analysis with the multi N/C 2100S analyzer. Samples for quantitative mineralogy were X-ray scanned from 2 to 70 degree two theta with Cu K-alpha radiation (40 kV, 35 mA).

Tissue samples harvested from ~5cm of the base of 6-month-old greenhouse-grown hybrid poplar trees were ground in a Wiley mill to pass a 0.4mm screen (40 mesh) and Soxhlet extracted overnight in hot acetone to remove extractives. The extractive-free material was used for all further analyses.
The lignin and carbohydrate content was determined with a modified Klason (Coleman et al., 2008 ), in which extracted ground stem tissue (0.2g) was treated with 3ml of 72% H₂SO₄ and stirred every 10min for 2h. Samples were then diluted with 112ml of deionized water and autoclaved for 1h at 121 °C. The acid-insoluble lignin fraction was determined gravimetrically by filtration through a pre-weighed medium coarseness sintered-glass crucible, while the acid-soluble lignin component was determined spectrophotometrically by absorbance at 205nm. Carbohydrate content was determined by using anion-exchange HPLC (Dx-600; Dionex) equipped with an ion-exchange PA1 (Dionex) column, a pulsed amperometric detector with a gold electrode, and a Dionex AS100 autosampler (Dionex).

HPLC measurements were performed with a Dionex liquid chromatograph DX600 (Dionex Corp., Sunnyvale, CA, USA) described in detail in [5 (link),9 (link)]. The identification of the quercetin peak was made by comparing the retention time of the peak and its UV–Vis spectra with those of the quercetin standard. The retention time of quercetin was 10.7 min. The quercetin concentrations in the resulting extracts were calculated from the calibration curve, which was constructed using six standard solutions of quercetin in the concentration range 1.44–144 µg/mL.

In summer 2010, nearshore sediments were collected from nine lakes on the northern Tibetan Plateau with a grab-bucket collection sampler (Table 1). The water depth of sampling sites was approximately 1.5 meter (Table 1). Specifically, surface lake sediments (0–5 cm) for DNA extraction were firstly collected into five 2.5-mL sterile centrifuge tubes (approximately 3g each tubes) using a sterile spatula. Subsequently, the collected sediment samples for DNA extraction were stored on dry ice in the field as well as during transportation. Upon arrival in the laboratory, sediment samples for DNA extraction were immediately stored at −80 ^oC until further analysis. In addition, pH values of these lakes were measured with a portable pH meter (PT-10, Sartorius, Germany) in the flied. Surface (0–5cm) lake water was first filtered through 0.2 μm Isopore filters (Whatman, UK) and then analyzed for major ions (K⁺, Na⁺, Ca²⁺, Mg²⁺, SO₄²⁻, Cl⁻, NO₃⁻ and NH₄⁺) in the laboratory by using ion chromatography (Dionex DX-600, USA). Salinity was calculated by summarizing the concentrations of major ions. Total organic carbon (TOC) was measured on a multi N/C 2100S analyzer (Analytik Jena, Germany). Before analyzing sediment TOC, samples were firstly acidified with 1 N HCl overnight to remove carbonates, subsequently washed to neutral pH, dried in oven and ground with mortar.