Dissolved Oxygen Chapter 6.2 of Section A, National Field Manual for the Collection of Water-Quality Data Book 9, Handbooks for Water-Resources Investigations Techniques and Methods 9–A6.2 Supersedes USGS Techniques of Water-Resources Investigations, Book 9, Chapter A6.2, Version 3.0 U.S. Department of the Interior U.S. Geological Survey Cover: Accurate measurement of dissolved oxygen is essential in studies of aquatic ecosystems. Photograph by Gerolamo C. Casile, U.S. Geological Survey. Dissolved Oxygen By U.S. Geological Survey Chapter 6.2 of Section A, National Field Manual for the Collection of Water-Quality Data Book 9, Handbooks for Water-Resources Investigations Techniques and Methods 9–A6.2 Supersedes USGS Techniques of Water-Resources Investigations, Book 9, Chapter A6.2, Version 3.0 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior DAVID BERNHARDT, Secretary U.S. Geological Survey James F. Reilly II, Director U.S. Geological Survey, Reston, Virginia First Release: April 1998, as Techniques of Water-Resources Investigations (TWRI), book 9, chapter A6.2, version 1.0 Revised: May 2006, online as TWRI 9–A6.2, version 2.0 Revised: June 2006, online as TWRI 9–A6.2, version 2.1 Revised: September 2013, online as TWRI 9–A6.2, version 3.0 Revised: October 2020, online as Techniques and Methods, book 9, chapter A6.2 For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment—visit https://www.usgs.gov or call 1–888–ASK–USGS. For an overview of USGS information products, including maps, imagery, and publications, visit https://store.usgs.gov. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner. Suggested citation: U.S. Geological Survey, 2020, Dissolved oxygen: U.S. Geological Survey Techniques and Methods, book 9, chap. A6.2, 33 p., https://doi.org/10.3133/tm9A6.2. [Supersedes USGS Techniques of Water-Resources Investigations, book 9, chap. A6.2, version 3.0.] ISSN 2328-7055 (online) iii Contents Abstract ...........................................................................................................................................................1 1.0 Introduction .............................................................................................................................................1 1.1 Overview of Dissolved Oxygen ....................................................................................................2 2.0 Optical (Luminescence) Sensor Method ............................................................................................3 2.1 Equipment and Field Preparations ..............................................................................................3 2.1.1 Equipment Description and Maintenance .....................................................................3 2.1.2 Field-Trip Preparations .....................................................................................................5 2.2 Calibration of Optical Sensors .....................................................................................................5 2.2.1 Correction for Atmospheric Pressure and Salinity ......................................................6 2.2.2 Selection of Calibration Method .....................................................................................7 2.2.3 Optical (Luminescence) DO Sensors—Calibration Procedures ...............................7 Procedure 1—Calibration in Air .......................................................................................8 Variation of Procedure 1—Air Calibration with a Wet Towel ......................................8 Procedure 2—Calibration with Air-Saturated Water ..................................................9 2.3 Measurement ...............................................................................................................................10 2.3.1 Surface Water ..................................................................................................................10 2.3.2 Groundwater.....................................................................................................................11 3.0 Spectrophotometric (Rhodazine D and Indigo Carmine) Methods ..............................................13 3.1 Equipment and Supplies .............................................................................................................14 3.2 Calibration and Interferences ...................................................................................................14 3.3 Measurement ...............................................................................................................................15 4.0 Reporting ................................................................................................................................................17 5.0 Correction Factors for Oxygen Solubility and Salinity ....................................................................17 Acknowledgments .......................................................................................................................................18 References Cited..........................................................................................................................................18 Appendix 1. Example comparison between spectrophotometric and optical dissolved-oxygen meter data........................................................................................................................................32 Tables 6.2–1. Equipment and supplies for the optical sensor method of determining dissolved-oxygen concentration ................................................................................................4 6.2–2. Solubility of oxygen in freshwater at various temperatures and pressures ....................20 6.2–3. Equipment and supplies for the spectrophotometric method of determining dissolved-oxygen concentration using Rhodazine D and Indigo Carmine reagents ......14 6.2–4. Salinity correction factors for dissolved oxygen in water ..................................................26 1–1A. Data for comparison between spectrophotometric and optical dissolved-oxygen meter methods ............................................................................................................................32 1–1B. Calibration data for readings in table 1–1A ...........................................................................33 iv Conversion Factors International System of Units to U.S. customary units Multiply By To obtain Length centimeter (cm) 0.3937 inch (in.) millimeter (mm) 0.03937 inch (in.) meter (m) 3.281 foot (ft) Mass gram (g) 0.03527 ounce, avoirdupois (oz) kilogram (kg) 2.205 pound avoirdupois (lb) Volume liter (L) 0.2642 gallon (gal) milliliter (mL) 0.03381 ounce, fluid (fl. oz) cubic centimeter (cm3) 0.06102 cubic inch (in3) Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows: °F=(1.8×°C)+32 Specific conductance is reported in microsiemens per centimeter at 25 degrees Celsius (µS/cm at 25 °C). Siemens per centimeter are the equivalent of mhos per centimeter. Molality of a solution is the number of moles (m) of a constituent per kilogram (kg) of solution. Units of molality are reported in moles per kilogram (m/kg). Abbreviations and Symbols DIW deionized water with resistance greater than or equal to 18 megaohms (MΩ), and that has been quality assured DO dissolved oxygen EDI equal-discharge increment, isokinetic sampling method EWI equal-width increment, isokinetic sampling method LED light emitting diode LDO luminescent dissolved oxygen µg/L micrograms per liter mg/L milligrams per liter M molar NFM “National Field Manual for the Collection of Water Quality Data” (USGS) NIST National Institute of Standards and Technology nm nanometer v NWIS National Water Information System (USGS) NWS National Weather Service RDO rugged dissolved oxygen USGS U.S. Geological Survey WMA Water Mission Area (USGS) WSC Water Science Center (USGS) YSI Yellow Springs Incorporated > greater than < less than Chemical Formulas H2O water H2S hydrogen sulfide Hg mercury vi Requirements and Recommendations As used in the U.S. Geological Survey (USGS) “National Field Manual for the Collection of Water-Quality Data” (NFM), the terms “required” and “recommended” have the USGS- specific meanings described below: • The terms “require,” “required,” and “requirements” in reference to USGS protocols indicate that USGS Water Mission Area (WMA) policy has been established on the basis of research or consensus of the technical staff, and has been reviewed by water- quality specialists and other professionals having the appropriate expertise. Technical memorandums and other documents that define USGS WMA policy are cited in the NFM. USGS field personnel are instructed to use required equipment and procedures as described in the NFM. Departure from or modifications to stipulated requirements, if necessary for accomplishing specific data-quality requirements or study objectives, must be independently quality assured and documented (Office of Water Quality Technical Memorandum 2002.13—U.S. Geological