Portable dissolved oxygen meter

Environmental factors were analyzed according to the procedures described by Xiong et al. (2017) (link). Briefly, water temperature (T), pH, oxidation–reduction potential (ORP), electrical conductivity (EC) and total dissolved solid (TDS) were measured in situ with a multiparameter sensor (MYRON company, USA). The chlorophyll-a (Chl_a) and dissolved oxygen (DO) were determined in situ with a Handheld Fluorometer (Turner Designs, San Jose, CA, USA) and a portable dissolved oxygen meter (HACH company, Loveland, CO, USA), respectively. Total nitrogen (TN), nitrate nitrogen (NO₃-N) and ammonia nitrogen (NH₄-N) were measured using the alkaline potassium persulfate digestion UV spectrophotometric method, ultraviolet spectrophotometry and Nessler’s reagent spectrophotometry, respectively. Total phosphorus (TP) and soluble reactive phosphorus (SRP) were determined based on the ammonium molybdate spectrophotometric method. Chemical oxygen demand (COD) and metals (K, Ca, Na, Mg, Cd, Cr, Cu, Ni, Zn, Pb, and As) were measured with HACH COD digestion vials (HACH Company, Loveland, CO, USA) and inductively coupled plasma-mass spectrometry (ICP-MS, 7500A, Plasma Quad 3, USA), respectively. A total of 24 environmental factors were collected in this study.

To determine the water quality parameters, water temperature, dissolved oxygen (DO) and pH were determined in situ using the thermometer, portable dissolved oxygen meter and pH meter (Hach, Loveland, CO, USA) [18 ]. Meanwhile, the concentrations of total nitrogen (TN), ammonia nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃⁻-N) and total phosphorus (TP) were spectrophotometrically examined using a continuous flow analyzer (Seal Analytical AA3, Norderstedt, Germany) after the water samples were filtered by a polycarbonate membrane (0.22 μm) [22 (link)]. Permanganate index (COD_Mn) was measured using spectrophotometer with the DR6000 (Hach, Loveland, CO, USA). Fe concentration was determined by inductively coupled plasma-mass spectrometry (ICP-MS) (Perkin Elmer, Norwalk, CT, USA) [22 (link)].

For each site, we measured water temperature (T), electric conductivity (EC), pH, total dissolved solid (TDS), and oxidation–reduction potential (ORP) in the field using a multiparameter water quality sonde (MYRON L Company, CA, USA). A portable dissolved oxygen meter (HACH Company, CO, USA) and a Handheld Fluorometer (Turner Designs, CA, USA) were used to record dissolved oxygen (DO) and concentration of Chlorophyll a (Chl_a), respectively. Moreover, we measured the concentration of total nitrogen (TN), nitrate (NO₃‐N), ammonium (NH₄‐N), total phosphorous (TP), soluble reactive phosphorous (SRP), and chemical oxygen demand (COD) using the methods described by Xiong et al. (2017). We also measured the concentration of potassium (K), calcium (Ca), sodium (Na), and magnesium (Mg) using inductively coupled plasma optical emission spectrometry (PerkinElmer Inc., MA, USA).