0.45 μm gf f filter

The temperature, pH, electrical conductivity (EC), dissolved oxygen (DO) and oxidation-reduction potential (ORP) were measured in situ during sampling using a multiparameter water quality analyser (HQ40d, Hach, CO, USA). The turbidity was monitored by a turbidimeter (2100 P, Hach, CO, USA). The velocity of the water was measured with a handheld Acoustic Doppler Velocimeter (FlowTracker, SonTek, CA, USA). Water samples were filtered through pre-combusted 0.45 μm GF/F filters (Whatman, NJ, USA) and acidified with HCl to analyse the dissolved organic carbon (DOC). The DOC concentrations were determined by an Elementar Liquid-TOC analyser (Frankfurt, Germany). Dissolved silicate (DSi) was estimated with the molybdate blue spectrophotometric method^{34 (link)}. Total phosphorus (TP) and total nitrogen (TN) were measured colourimetrically after acid hydrolysis with persulfate digestion (30 min, 120 °C). Soluble reactive phosphorus (SRP), nitrite nitrogen ( ${\mathit{NO}}_2^{-}$ -N), nitrate nitrogen ( ${\mathit{NO}}_3^{-}$ -N) and ammonium nitrogen ( ${\mathit{NH}}_4^{+}$ -N) were measured colourimetrically by an AA3 Auto-Analyzer (Seal, Norderstedt, Germany). The detection limits of SRP, ${\mathit{NO}}_2^{-}$ , ${\mathit{NO}}_3^{-}$ and ${\mathit{NH}}_4^{+}$ were 0.004, 0.001, 0.003 and 0.003 mg L⁻¹, respectively.

During the growing season (May–August) from 2009 to 2019, we measured NH₄ and PO₄ concentrations as well as salinity, in marsh porewater monthly at each of the 51 permanent vegetation monitoring plots. Triplicate porewater samples were collected each month from each plot, with sample locations immediately adjacent to three corners of each permanent plot at a depth of 25 cm using modified porewater diffusion equilibrators [36 (link)]. Equilibrators contained 20mL glass scintillation vials filled with deionized water and covered with nitex mesh (20 μm) membranes which were secured with an open-topped screw cap. Vials were placed in porous PVC pipes driven into the marsh sediment where they were left to equilibrate for approximately one month. Upon retrieval, samples were capped and placed on ice in the field. Upon returning to the lab, sample salinities were measured using a Mettler-Toledo Seven2Go pro conductivity probe and samples were then filtered using Whatman 0.45 μm GF/F filters. Filtered samples were analyzed for nutrients within 24 hours using a Seal Analytical AA3 Segmented Flow AutoAnalyzer following standardized colorimetric methods [37 –40 ].

Samples (5 mL) are filtered through a 0.45 μm GF/F filter (Whatman, UK), and the filtrate is used for zeta potential determination (Li et al., 2015). The zeta potential is measured using a zeta potential analyzer (Zetasizer Nano ZS 90, Malvern, UK) [28 (link)].