U.S. Department of the Interior

U.S. Geological Survey

Techniques and Methods 9–A6.2

Supersedes USGS Techniques of Water-Resources Investigations,

Book 9, Chapter A6.2, Version 3.0

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 
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

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

Chapter 6.2 of

Section A, National Field Manual for the Collection of Water-Quality Data

Book 9, Handbooks for Water-Resources Investigations
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

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Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

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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 USGSspecific 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 waterquality 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 Survey, 2002). 

• The terms “recommend,” “recommended,” and “recommendation” indicate that, on 

the basis of research or consensus, there are several acceptable alternatives to a given 

procedure or equipment selection in the NFM. Relevant technical memorandums and 

publications pertinent to such recommendations are cited in the NFM to the extent 

that such documents are available. Specific requirements, data-quality objectives, or 

other constraints of a project may affect the choice of recommended equipment or 

procedures. Selection from among the recommended alternatives should be based on 

referenced research and sound field judgment, and reasons for the selection must be 

documented. Departures from or modifications to the recommended procedures must 

be independently quality assured and documented (Office of Water Quality Technical 

Memorandum 2002.13—U.S. Geological Survey, 2002).
Chapter 6.2. Dissolved Oxygen

By U.S. Geological Survey

Abstract

The “National Field Manual for the Collection of WaterQuality Data” (NFM) provides guidelines and procedures for 

U.S. Geological Survey (USGS) personnel who collect data 

used to assess the quality of the Nation’s surface water and 

groundwater resources. This chapter, NFM A6.2, provides 

guidance and protocols for the measurement of dissolved 

oxygen, which include the scientific basis of the measurement, 

selection and maintenance of equipment, calibration, troubleshooting, and procedures for measurement and reporting. It 

updates and supersedes USGS Techniques of Water-Resources 

Investigations, book 9, chapter A6.2, version 3.0, by Stewart 

A, Rounds, Franceska D. Wilde, and George F. Ritz. Dissolved 

oxygen is routinely measured when water samples are collected, is often continually measured at USGS streamgages, 

and is a parameter regularly measured during laboratory 

and field experiments. The field method for measuring dissolved oxygen described in this chapter is applicable to most 

natural waters.

Before 2017, the USGS NFM chapters were released 

in the USGS Techniques of Water-Resources Investigations 

series. Effective in 2018, new and revised NFM chapters are 

being released in the USGS Techniques and Methods series; 

this series change does not affect the content and format of 

the NFM. More information is in the general introduction to 

the NFM (USGS Techniques and Methods, book 9, chapter 

A0—U.S. Geological Survey, 2018) at https://doi.org/10.3133/

tm9A0. The authoritative current versions of NFM chapters are available in the USGS Publications Warehouse at 

https://pubs.er.usgs.gov. Comments, questions, and suggestions related to the NFM can be addressed to nfm@usgs.gov.

1.0 Introduction

The “National Field Manual for the Collection of WaterQuality Data” (NFM) is the official and citable protocol for 

the collection of water-quality data by the Water Mission Area 

(WMA) of the U.S. Geological Survey (USGS). The NFM 

provides guidelines and procedures for USGS personnel who 

collect data for water quality in surface water and groundwater, with detailed, comprehensive, and citable procedures. It 

updates and supersedes USGS Techniques of Water-Resources 

Investigations, book 9, chapter A6.2, version 3.0, by Rounds 

and others (2013).

National USGS program and project personnel who 

collect water-quality data, as well as those in USGS Water 

Science Centers (WSCs), and including those conducting 

projects supported by the USGS Cooperative program, 

are mandated to use protocols provided in the NFM 

(USGS Office of Water-Quality Technical Memorandum 

2002.13—U.S. Geological Survey, 2002). Formal training, as 

provided in the USGS class “Field Water-Quality Methods for 

Groundwater and Surface Water,” and field apprenticeships 

supplement the information provided in the NFM and are 

needed to collect unbiased, high-quality data.

The USGS National Field Manual provides detailed, 

comprehensive, and citable procedures for monitoring the 

quality of surface water and groundwater. Formal training and field apprenticeships supplement the information 

provided in the NFM.

Chapter A6.2 of the NFM provides guidance and protocols for the measurement of dissolved oxygen (DO), which 

is best measured in the field. DO concentration can change 

rapidly as a result of several factors that can affect a sample 

after removal from a water body or aquifer. The measurement is straightforward and precise with many environmental applications. DO is routinely measured when water 

samples are collected, is often measured continually at USGS 

streamgages, and is regularly measured during laboratory and 

field experiments.

The field methods described in this chapter are applicable to most natural waters. This chapter covers the physical 

basis for measurement of DO in aqueous solutions, as well 

as factors that affect the measurement, terminology, method 

protocols, and applications.

Before 2017, the USGS NFM chapters were released 

in the USGS Techniques of Water-Resources Investigations 

series. Effective in 2018, new and revised NFM chapters 

are being released in the USGS Techniques and Methods 

series; this series change does not affect the content and 

format of the NFM. More information is in the general 

introduction to the NFM (USGS Techniques and Methods, 
2 Chapter A6.2. Dissolved Oxygen

measurement methods described are used by the USGS onsite 

for routine determination of DO concentrations in fresh to 

saline surface water and groundwater. 

The primary USGS field procedure for determination of 

DO is the use of luminescence-based (optical) sensors. Optical DO sensors are considered a major technological advance 

over previously used amperometric sensors because optical 

DO sensors are more robust in the field environment, are not 

flow dependent, and are generally easier to use while providing higher quality data, especially at low DO concentrations 

(<2 milligrams per liter [mg/L]).

Optical sensor methods (section 2.0) are applicable to 

nearly all aqueous environmental conditions. Optical sensor 

technology is available in single-parameter DO meters or in 

multiparameter sondes and can be either handheld for discrete 

measurements or deployed for longer term, unattended continuous and real-time measurements.

Spectrophotometric (colorimetric) instrumental methods 

(section 3.0) yield consistent results when applied to the determination of DO concentrations in oxygen-depleted waters (for 

example, in certain aquifers and deep-lake horizons) and can 

be used to report DO concentrations from about 2.0 mg/L to 

as little as 0.025 mg/L. Noninstrumental colorimetric methods 

that are available for visually determining DO concentrations 

to 0 mg/L can be useful for a quick reconnaissance of DO 

conditions and an accuracy check of DO-sensor performance. 

Noninstrumental colorimetric methods that are available for 

visually determining DO concentrations should not be used to 

report DO concentrations.

The iodometric (Winkler) method is regarded as an 

accurate and precise method for the calibration of DO sensors 

and the determination of DO concentration in water when 

performed under controlled laboratory conditions. Before 

sensors that could be immersed directly in the water column 

became commonly available, USGS personnel were trained 

to perform Winkler titrations onsite. Standard USGS practice 

no longer sanctions onsite Winkler titrations or the transport 

of field samples offsite for DO determination by the Winkler 

method. Step-by-step instructions for conducting a Winkler titration that were included in previous versions of this 

NFM chapter have been removed and are not included in 

this chapter.

• Some procedures for equipment operation recommended in this guidance document may not apply to 

your equipment because of technological advances 

or other changes. 

• Be sure to record any modifications made to 

the standard USGS procedures given in this 

field manual.

book 9, chapter A0—U.S. Geological Survey, 2018) at 

https://doi.org/10.3133/tm9A0. The authoritative current versions of NFM chapters are available in the USGS Publications 

Warehouse at https://pubs.er.usgs.gov. Comments, questions, 

and suggestions related to the NFM can be addressed to 

nfm@usgs.gov.

1.1 Overview of Dissolved Oxygen

The concentration of DO in water is affected by many 

factors, including ambient temperature, atmospheric pressure, 

and ion activity (ionic strength of the water body). Accurate 

dissolved-oxygen data are essential for understanding and 

documenting effects on environmental water resources that 

result from natural phenomena and human activities. Sources 

of DO in water include atmospheric aeration and photosynthetic activities of aquatic plants. Sinks of DO in water 

include respiration, aerobic decomposition processes, ammonia nitrification, and other chemical and biological reactions. 

Many chemical and biological reactions in groundwater and 

surface water depend on the amount of available oxygen. 

The presence of DO in aquatic systems is necessary for the 

survival and growth of many aquatic organisms and is used as 

an indicator of the health and geochemical quality of surface 

water and groundwater systems.

DISSOLVED OXYGEN:Molecular oxygen (oxygen gas) 

dissolved in water.

Standard procedures used by the USGS to determine 

concentrations of DO in surface water and groundwater involve 

the use of luminescence-based optical sensors, or spectrophoometric methods of analysis. Before the advent in the 2000s 

of optical sensors for DO measurement, the amperometric 

(Clark cell) sensor was used. Optical sensors have replaced 

the amperometric type of sensor. The amperometric sensor 

is an acceptable method for use in the measurement of DO; 

however, barring any project-specific requirements, optical 

sensors should be considered the standard field method. The 

iodometric (Winkler) method is no longer used by the USGS 

for routine measurement of DO at field sites, but remains an 

acceptable method for verifying the results of DO measurements made with other methods.

The selection of field equipment and measurement 

methods takes into consideration (1) whether equipment 

will be used at multiple and discrete locations and times or 

be deployed at a single location over a period during which 

it will be unattended, (2) anticipated environmental conditions, (3) the specific data-quality objectives of the datacollection program, and (4) specific program objectives. The 
2.0 Optical (Luminescence) Sensor Method 3

2.0 Optical (Luminescence) Sensor

Method

The optical sensor method can yield accurate results for 

measurement of DO concentrations under most field conditions encountered in routine USGS data-collection activities. 

The method is relatively simple to use, whether deployed for 

discrete (single) or continuous (unattended) DO measurements 

in surface water or groundwater. Because of the advantages 

introduced by advances in applying luminescence technology to DO measurement, optical sensors are favored for most 

standard USGS field operations.

Optical sensors—The technology used in optical DO 

sensors involves the measurement of light-emission characteristics of a luminescence-based reaction at the sensor-water 

interface (see Technical Note 1). Some characteristics of the 

optical DO method are—

• Oxygen is not consumed by the sensor at the sensorwater interface.

• The optical sensor is not dependent on water flow; 

consequently, no stirring mechanism is required at sites 

with slowly flowing or still waters.

• Optical sensors are relatively stable. They are able to 

maintain calibration over long-term deployment and 

over a wide range of environmental conditions, and 

sensor drift over time is minimal when the sensor is 

kept clean.

• There are no known sources of interference to the 

luminescence method in natural aquatic systems. 

Optical sensors will measure accurately in the presence of hydrogen sulfide (H2

S) and also when deployed 

in fresh, brackish, and mildly contaminated waters. 

Contact with organic solvents can compromise sensor 

integrity or performance, however.

• Cleaning and maintenance are relatively simple. 

The optical sensor contains no anode or cathode to 

service, and uses no electrolyte solution, membranes, 

or O-rings.

• Optical-sensor maintenance is dictated by manufacturer guidelines that are specific to the type of sensor in use and the conditions to which the sensor has 

been subjected.

• Manufacturers generally recommend annual to biannual replacement of the luminophore-containing 

module (also called “lumiphore”). Some sensors may 

have a prescribed lifetime of the module, after which 

the sensor becomes inoperative. The modules are easily 

replaced. Sensors should be calibrated or undergo a 

calibration check after module replacement.

TECHNICAL NOTE 1. 

The luminescence sensor employs a light-emitting diode 

(LED) to provide light of a specific wavelength that excites 

a luminescent-dye molecule substrate (luminophore) of the 

sensor. After some dissipation of the excitation energy, longer 

wavelength light is emitted. The intensity of the fluorescence 

is proportional to the DO concentration because the presence 

of oxygen can quench, or suppress, the fluorescence response 

of the dye. Higher DO concentrations result in greater quenching and a decreased fluorescence response. The signal to the 

fluorescence detector is greatest at lowest DO concentrations. 

More importantly, the timescale, or lifetime, of the fluorescence reaction is also dependent on the DO concentration and 

is not dependent on the light intensity of excitation or fluorescence, thereby allowing more reliable determination of the DO 

concentration. Temperature stability during calibration and 

measurement is extremely important, as temperature controls 

the solubility of oxygen in water.

2.1 Equipment and Field Preparations

DO instruments (meters and sensors) are available from a 

number of commercial vendors. Because of differences among 

manufacturers in the instrument design and instructions for 

use, calibration, and maintenance, it is important that the user 

be thoroughly familiar with the instructional manual for the 

specific instrument system to be used in addition to the guidance given here.

2.1.1 Equipment Description and Maintenance

Meters, sondes, and the DO sensors used in these instruments are sophisticated electronic equipment that require care 

in handling and operation. Information about the equipment 

and supplies required for the optical method of determining 

aqueous DO concentrations is summarized in table 6.2–1.

Guidance on when to replace the luminophore-containing 

cap or module varies among manufacturers and can be based 

on the specific design and materials used, the environmental 

conditions to which the sensor is exposed, the age of the sensor, and (or) the amount of time it is deployed. For example— 

• Hach specifies a 2-year life of the sensor cap of its 

LDO (Luminescent Dissolved Oxygen) sensor.

• YSI Environmental (EXO) specifies annual replacement of the sensor cap for its optical DO sensor.

• In-Situ, Inc., advises that the RDO (Rugged Dissolved 

Oxygen) sensor cap has a 2-year life.

• Thermo Scientific specifies a 365-day lifespan for the 

RDO cap once it is installed on the RDO sensor.
4 Chapter A6.2. Dissolved Oxygen

Table 6.2–1. Equipment and supplies for the optical sensor method of determining dissolved-oxygen concentration (modify this list to 

meet specific needs of the field effort).

[[DO, dissolved oxygen; mg/L, milligrams per liter; NFM, National Field Manual for the Collection of Water-Quality Data; –, minus; +, plus; °C, degrees 

Celsius; ±, plus or minus; NIST, National Institute of Standards and Technology; M, molar]

DO instrument should have a digital temperature and DO readout display and have:

• Automatic temperature compensation

• An operating range in water with a temperature range of at least –5 to 45 °C

• Capability to measure DO concentrations from 0.01 to 20 mg/L (instrument capability can range to 50 mg/L)

• Minimum display resolution of 0.01 mg/L DO

• Calibrated accuracy within ±0.1 mg/L DO

Calibration equipment, per manufacturer’s recommendation

Pocket altimeter-barometer or DO instrument with built-in barometer; barometer measures to nearest 1 millimeter of mercury and its 

calibration has been checked before use or at least annually against a NIST-traceable barometer or the uncorrected barometric pressure 

obtained from a National Weather Service location at the same altitude as calibration or calibration check

Thermometer (see NFM chapters A6.1 and A6.8 for calibration-check criteria)

Zero-DO solution. Dissolve approximately 2 grams sodium sulfite in 1 liter of deionized water (0.016–M solution, prepared fresh just 

before the field trip or during week of use)1

Flow-through chamber for determining groundwater DO concentration, if downhole sensor deployment is impractical

Oxygen-solubility table (table 6.2–2, at end of chapter), or access to table at https://water.usgs.gov/software/DOTABLES/

Waste-disposal containers

Spare batteries

Calibrated specific-conductance sensor, if measurement is being made in a saline or brackish system

Calibration and maintenance log books for DO instrument and barometer

1

Take special note of the manufacturer’s guidance for your sensor. Some manufacturers supply the zero-DO solution required or document the specific 

instructions for preparing the zero-DO solution recommended for their sensors, including an alternative by which nitrogen gas is forced into tap or deionized 

water to produce a zero-DO solution. (Consult with the manufacturer’s division of technical support.)
2.0 Optical (Luminescence) Sensor Method 5

• If the instrument reading is negative, consult the 

manufacturer's manual; a zero-DO calibration may 

be necessary.

• Rinse the sensor and wiper thoroughly and then 

reinstall the wiper elements. Multiple, thorough 

rinses with deionized water are necessary to remove 

the sodium sulfite and restore the sensor to proper 

operating condition and prevent subsequent measurements from being biased.

5. Review the care and maintenance guidance provided 

by the manufacturer for the specific sensor being used; 

instructions can differ appreciably depending on the 

make and model of the instrument.

• Check the condition and (or) deployment history of 

the luminophore-containing sensor module, referring 

to the manufacturer’s guidance for replacement of 

the luminophore module.

• Depending on the instrument, sensor modules are 

replaced annually or at least every 2 years, even if 

the sensor is idle.

6. Remember to document field preparations and all instrument tests and adjustments in the meter log book. Do not 

use an instrument that fails calibration checks.

CAUTION: 

Before handling sodium sulfite (or any other chemicals) 

refer to safety precautions for that chemical on the 

Safety Data Sheet (SDS).

2.2 Calibration of Optical Sensors

Sensor-based instrument systems used to determine DO 

in water must be calibrated properly before being used. Proper 

calibration procedures are necessary to ensure the overall 

accuracy and precision of DO measurements. It is recommended to calibrate instruments in the controlled atmosphere 

of the laboratory before going to the field. A calibration 

check is required at each field site, followed by recalibration 

as needed to meet the specific data-quality requirements of 

the project.

The accuracy required by the project for sites at which 

DO will be determined and the capabilities of the selected 

instrument will govern whether a one-point calibration will be 

sufficient or whether a two-point calibration should be used. 

In addition, some manufacturers of the DO instruments commonly used for USGS data-collection activities recommend 

testing in a laboratory setting to determine the accuracy of 

room-temperature calibrations compared with measurements 

made under the anticipated warmer or cooler field conditions. 

Project personnel are advised to be familiar with recommendations made by the manufacturer of their equipment.

Become familiar with the specific manufacturer’s recommendations for short-term (field) and long-term (office or laboratory) storage. Storage guidance for optical sensors (some 

specify the need for storage in a humid environment) and 

procedures for removing sensors from storage differ among 

manufacturers; consult the manual provided for the sensor.

2.1.2 Field-Trip Preparations

The service performed on all equipment, whether a full 

calibration, calibration check, or replacement or repair of 

parts for the instrument, and whether performed in the office, 

laboratory, or field, must be accurately recorded and dated in 

the instrument or sensor log book.

Field-measurement instruments are required to be maintained on a regular schedule and performance tested before 

field use, as described below:

1. Check all electrical connections and the charge on 

the batteries, as applicable for the instrument in 

use. Batteries should be in good condition with as 

high a state of charge as possible. Replace or charge 

questionable batteries.

2. Thermistors/thermometers must be calibrated 

and field checked before use, as described in 

NFM 6.1, Temperature.

3. Perform a 100-percent oxygen-saturation calibration 

check (see section 2.2). This performance check does not 

negate the need for an onsite sensor-calibration check 

at oxygen saturation. The result of the check should be 

within +/- 0.2 mg/L of the 100-percent saturated concentration determined from the DO solubility tables found at 

https://water.usgs.gov/software/DOTABLES.

4. Perform a zero-DO sensor-performance check.

• Prepare the zero-DO sodium sulfite 

solution (see table 6.2–1).

• Before immersing the sensor in the zero-DO solution, remove the wiper (or sponge) from the unit to 

avoid saturating it with the sodium sulfite solution. 

(Not all instruments have a wiper.)

• Immerse the sensor into the zero-DO solution, 

wait for reading to stabilize (usually within 

5–10 minutes), record reading.

• If the instrument reading exceeds 0.2 mg/L in the 

zero-DO solution, check DO again with a freshly 

prepared zero-DO solution; if a reading greater than 

0.2 mg/L persists, contact the instrument manufacturer and inquire whether the luminophore module 

should be replaced.
6 Chapter A6.2. Dissolved Oxygen

One-point calibration: The main goal of the one-point 

DO calibration procedure is to create a 100-percent saturated 

oxygen environment in which the DO sensor and its thermistor 

are at the same temperature. There are two procedures that can 

be used for a one-point calibration:

• Procedure 1—Calibration in air (can be accomplished with air-calibration chamber or wet-towel 

method)

• Procedure 2—Calibration in air-saturated water 

(water bubbled with air)

Two-point calibration: The two-point calibration typically 

involves calibration of the sensor at 100-percent saturation, 

and at zero DO. The two-point calibration adds complexity to 

the calibration process and is not recommended by all manufacturers of optical sensors. Conduct a zero-DO check before 

committing to a two-point calibration. Be sure to understand 

the instrument capabilities and then determine the best course 

of action. For routine applications, it is advisable to rely on a 

zero-DO performance check rather than a zero-DO calibration, 

which would risk corrupting the manufacturer’s zero-DO 

calibration.

• Use of a two-point calibration should be considered if 

(1) the calibration is needed to satisfy the data-quality 

objectives of the project, (2) oxygen concentrations 

less than 2 mg/L are likely to be encountered and 

zero-DO performance checks fail, or (3) the calibration 

is deemed necessary by experienced field personnel 

familiar with site conditions.

• Before starting or planning for a two-point calibration, 

consult the manufacturer’s instructions or technical 

support for the specific optical DO sensor being used.

• If a two-point DO calibration is used, calibrate the 

DO sensor only after calibrating other field-measurement sensors to prevent possible interference of the 

sodium sulfite (zero-DO) solution with the calibration 

of the other sensors. Unless the equipment manufacturer’s manual specifies otherwise, complete the 

DO calibration at 100-percent saturation before the 

zero calibration.

Sensor-performance checks—Verifying sensor performance before field use (calibration check) is a required 

standard procedure in USGS field operations (see section 2.1). 

• All DO sensors have the capability to undergo a performance check at zero DO. Most DO sensors have the 

capability to undergo a zero-DO calibration.1

• Verifying instrument performance at zero DO and 

using the two-point calibration can be particularly 

important for data accuracy when the instrument 

1

Manufacturers caution against routine zero recalibration of sensors but 

allow for zero-DO checks, stipulating the need to thoroughly rinse the zero 

solution from the sensor after the check procedure.

will be used to measure low DO concentrations (less 

than 2 mg/L).

• The result of a DO instrument performance check 

should be within +/- 0.2 mg/L of the 100-percent 

saturated concentration determined from the DO 

solubility tables found at https://water.usgs.gov/

software/DOTABLES or, if checking at the zero 

point, the sensor should read within 0.2 mg/L of zero. 

Project objectives may dictate a deviation of less than 

0.2 mg/L from the calculated 100-percent saturation 

value or zero. Recalibration and additional troubleshooting are warranted if instruments fail the DO 

performance checks.

Do not use an instrument that fails to calibrate properly 

or fails performance checks.

2.2.1 Correction for Atmospheric Pressure and 

Salinity

DO calibration procedures include corrections for 

atmospheric pressure and ionic strength. (Ionic strength is 

estimated from the conductivity measurement for routine field 

applications.) Atmospheric pressure, the temperature of the 

water or water vapor, and the ionic strength of the water must 

be known to determine the theoretical amount of oxygen that 

will be dissolved in water.

Record all calibration information in instrument log 

books and copy calibration data onto field forms at the time of 

calibration.

TECHNICAL NOTE 2. 

DO sensors do not directly measure oxygen in milligrams 

per liter or parts per million. Expressed concentrations are 

based on calculations that relate instrument sensor data with 

the temperature and ionic strength of the sample water. The 

sensor signal is proportional to the ambient partial pressure of 

oxygen, which can be displayed either as percent saturation or 

in milligrams per liter, depending on user specification.

Ambient atmospheric pressure is true atmospheric 

pressure at the measurement site, not the pressure that has 

been adjusted to sea level. Atmospheric pressure (also known 

as barometric pressure) reported by the National Weather 

Service (NWS) generally is not the absolute (ambient) value. 

NWS atmospheric pressure readings typically are adjusted to 

sea level for comparison among weather stations and must be 

adjusted back to the altitude of the weather station in order to 

obtain ambient barometric pressure values. Previous versions 

of this chapter described a procedure for correcting NWS 

barometric pressure readings for use during DO calibrations. 

With the advent of inexpensive, National Institute of Standards 

and Technology- (NIST) traceable barometers, correction of a 
2.0 Optical (Luminescence) Sensor Method 7

barometric pressure reading not measured at the DO calibration altitude for use during a DO calibration is no longer 

recommended. It is required that the barometric pressure be 

measured at the altitude of the DO calibration or check.

For DO calibrations, the ambient atmospheric pressure 

must be determined to the nearest 1 millimeter (mm) of 

mercury. A calibrated pocket altimeter-barometer typically has 

been used to determine atmospheric pressure; however, many 

multiparameter water-quality instruments and DO meters in 

common use include an internal barometer.

Check the accuracy of all field barometers (including 

barometers built into instrument systems) before each field trip 

or at least annually, and record readings and adjustments in the 

instrument log book. Check field barometers against a NISTtraceable barometer kept at the USGS Water Science Center, 

office, or laboratory, or check barometer accuracy while at an 

official weather station where ambient atmospheric pressure 

can be obtained.

Most modern multiparameter instruments (see NFM 6.8) 

incorporate a pressure-temperature and salinity compensation algorithm in their firmware for DO measurements; the 

instruments have a built-in conductivity sensor that is used 

to correct the DO-concentration data for salinity automatically. 

For instruments that are not equipped with a conductivity 

sensor, manual correction of the DO data for salinity 

is required.

If a user-specified salinity correction is needed, the 

preferred USGS method is to apply salinity-correction factors 

after calibrating and measuring the DO concentration of the 

environmental water body (see section 5.0). Interactive tables 

for user-specified temperature, pressure, and salinity are available at https://water.usgs.gov/software/DOTABLES/.

When a manual salinity correction is made by the user 

during calibration, the instrument requires recalibration for 

each measured field variation in salinity (see section 5.0).

If a multiparameter instrument that includes 

a calibrated conductivity sensor is used, salinity correction to the DO concentration reading is 

performed automatically.

2.2.2 Selection of Calibration Method

Manufacturers uniformly recommend a 100-percent saturated oxygen calibration of DO sensors regardless of whether 

calibration in air (Procedure 1) or calibration in air-saturated 

water (Procedure 2) is used. It is important to refer to the 

manufacturer-provided guidance, as each of the procedures 

has inherent advantages and disadvantages and may include 

instrument-specific sources of error.

Calibration or checking of an instrument in air 

(Procedure 1) is the preferred method specified by some 

manufacturers. The process is easily accomplished in the 

laboratory or field setting so long as the temperature of the air 

calibration chamber is stable.

The air calibration or check with a wet-towel method 

(variation of Procedure 1) is the recommended method to 

be performed at the field site. This method is well suited to 

checking an instrument after transportation to a field site followed by calibration if the instrument fails the check with a 

wet-towel procedure.

The air-saturated water method (Procedure 2) is the preferred method specified by some manufacturers. Temperature 

stability of the bubbled solution and equilibration of the DOsensor temperature with the solution is important and easily 

accomplished. This procedure is generally favored for laboratory calibrations because of the equipment required.

The DO-meter calibration check is required at each 

field site. 

2.2.3 Optical (Luminescence) DO Sensors—

Calibration Procedures

The luminescence technology used in optical DO field 

instruments has improved and simplified the data-collection 

process for field determination of DO concentration. Optical 

DO sensors generally have accuracy specifications of ±0.1 

mg/L or 1 percent after calibration. This level of accuracy is 

best achieved by calibrating under controlled conditions in a 

laboratory or simulated laboratory environment.

TECHNICAL NOTE 3.

Optical DO sensors contain internal calibration information 

from the manufacturer. Although some manufacturers advise 

that no further calibration is needed, the accuracy of factory 

calibrations does not necessarily satisfy the data-quality objectives required for USGS applications. Because the validity of 

a calibration can substantially affect the overall accuracy and 

precision of DO measurements, users are required to check the 

calibration at every field site or as often as is necessary to meet 

specific data-quality objectives.

Optical DO sensors are subject to very little drift after a 

successful calibration. A laboratory-performed calibration is 

likely to remain stable after transport to the field. Nevertheless, calibrations are required to be verified at the field site. 

Laboratory calibrations are generally preferred because of the 

stability of the laboratory environment compared to a typical 

field site.

The Rhodazine DTM 2 spectrophotometric method for 

DO measurement described in section 3.0 has been used to 

check the calibration of these instruments. USGS field scientists have corroborated the accuracy of the optical sensor to 

0.03 mg/L DO by using repeated comparisons of results with 

the Rhodazine D spectrophotometric method described in 

2

Rhodazine D is a proprietary product of CHEMetrics, Inc. (White and 

others, 1990).
8 Chapter A6.2. Dissolved Oxygen

section 3.0 of this field manual chapter. Results from optical 

sensor and spectrophotometric methods can be entered into the 

USGS National Water Information System (NWIS) database.

Procedure 1—Calibration in Air

This procedure is commonly used to calibrate optical 

DO instruments. The calibration chamber used is typically the 

calibration cup supplied with the instrument or is built into the 

instrument case. Use the calibration chamber that is provided 

or recommended by the manufacturer. For field check and 

calibration, the wet-towel variation of Procedure 1 described 

in the next section is recommended. 

1. Wet the inside of the calibration chamber with water 

and then pour out the water, leaving a few drops or a 

layer of water in the bottom of the calibration cup. Some 

manufacturers may provide a sponge to wet and place 

in the calibration chamber. Consult and follow specific 

manufacturer instructions. Remove any water droplets 

that remain on the temperature and optical DO sensors. 

Insert the sensor into the chamber per manufacturer’s 

instructions to ensure 100-percent humidity.

• If using a screw-on calibration chamber, make sure 

it is loose and does not make an airtight seal in order 

to maintain ambient barometric pressure. Do not 

tighten the chamber to cause a seal that isolates the 

DO sensor from the ambient barometric pressure.

• Keep the calibration assembly in a stable temperature environment and out of direct sunlight.

2. Allow 5 to 10 minutes for the air to saturate with water 

vapor and for the DO sensor and the air inside the 

calibration chamber to equilibrate. If appropriate for 

the instrument being used, run the instrument during 

the equilibration period to monitor stability. Achieving 

stability in temperature and DO concentration before the 

calibration begins is essential.

3. Using a calibration-checked barometer, read the ambient 

atmospheric pressure to the nearest 1 mm of mercury. 

4. Monitor the temperature and DO readings in the 

calibration chamber, observing readings until 

they stabilize. Read the temperature to the nearest 

0.1 degree Celsius (°C).

5. If calibrating to a given DO concentration rather than 

to a condition of 100-percent saturation, use table 6.2–2 

(at end of chapter) or the online software DOTABLES 

(https://water.usgs.gov/software/DOTABLES/) to determine DO saturation at the calibration temperature and 

atmospheric pressure.

6. Follow the manufacturer’s instructions for the calibration. When the instrument readings are stable, adjust the 

instrument to the DO-saturation value determined from 

the oxygen-solubility table.

• If an instrument that allows calibration simply to a 

100-percent saturation condition is used, all that may 

be needed is to provide the ambient atmospheric 

pressure for the instrument to determine (with 

internal software) the resulting DO concentration. If 

the instrument has an internal barometer, it may only 

be necessary to put the instrument into calibration 

mode and check the calibration once it has been 

completed.

7. Verify that the instrument reading is within ±0.2 mg/L or 

2 percent of the computed saturation value, or use more 

stringent accuracy criteria that reflect the data-quality 

requirements of the project.

8. Remove the sensor from the calibration chamber to 

check whether water droplets were on the optical 

module during calibration; water droplets on the 

sensor module or on the temperature sensor can cause 

improper calibration.

• Recalibrate the instrument if water droplets 

were present.

• After all the steps above have been followed, the DO 

sensor is calibrated and ready for use.

9. Record calibration information in instrument log books 

and transfer calibration data into electronic records or 

onto paper field forms at the time of calibration.

During saturated-air calibration, water droplets must 

be kept off the optical module and temperature sensor.

Variation of Procedure 1—Air Calibration with a Wet 

Towel

For many multiparameter instruments, a 100-percent 

humidity environment can be created by wrapping a wet 

towel around the sensor guard and inserting it into a plastic 

bag. The “wet-towel method” is almost identical to Procedure 

1, but the sensor (or sonde) guard will be wrapped in a wet 

towel instead of using a calibration cup or chamber. For field 

calibration verification of a DO sensor, the wet-towel method 

is recommended.

Equipment: Check or calibration with a wet towel

1 Towel, sized so that it will wrap around the sensor at least 

two full wraps

1 Trash bag, clear or white plastic 

1. Soak the towel either (1) in the water for DO measurement, or (2) with tap or deionized water. Wring it out, 

and then wrap the wet towel completely around the 

sensor guard or chamber two full wraps or more. As you 
2.0 Optical (Luminescence) Sensor Method 9

wrap the sensor, ensure that no water droplets are on 

either the temperature sensor or the optical DO sensor.

2. Place the wrapped sensor into the plastic bag and 

keep it out of direct sunlight to keep the temperature 

from changing. The plastic bag holding the sonde and 

towel can be placed into a cooler if necessary to attain 

temperature stability.

3. Allow 5 to 10 minutes for the air to saturate with water 

vapor and for the DO sensor and the air inside the towel 

(calibration chamber) to equilibrate. If appropriate for 

the instrument being used, run the instrument during the 

equilibration period to monitor for stability of DO and 

temperature.

4. Using a calibration-checked barometer, read the ambient 

atmospheric pressure to the nearest 1 mm of mercury.

5. If calibrating to a given DO concentration rather than 

to a condition of 100-percent saturation, use table 6.2–2 

(at end of chapter) or the online software DOTABLES 

(https://water.usgs.gov/software/DOTABLES/) to determine DO saturation at the calibration temperature and 

atmospheric pressure.

6. Follow the manufacturer’s instructions for the 

calibration. When the instrument readings are stable, 

adjust the instrument to the DO-saturation value determined from the oxygen-solubility table.

• If an instrument that allows calibration simply to a 

100-percent saturation condition is used, all that may 

be needed is to provide the ambient atmospheric 

pressure for the instrument to determine (with 

internal software) the resulting DO concentration. 

If the instrument has an internal barometer, it may 

only be necessary to put the instrument into calibration mode and check the calibration once it has 

been completed.

7. Verify that the instrument reading is within ±0.2 mg/L or 

2 percent of the computed saturation value, or use more 

stringent accuracy criteria that reflect the data-quality 

requirements of the project.

8. Remove the sensor from the wet towel to check whether 

water droplets were on the optical module during calibration; water droplets on the sensor module or on the 

temperature sensor can cause improper calibration.

• Recalibrate the instrument if water droplets 

were present.

• After all the steps above have been followed, the DO 

sensor is calibrated and ready for use.

9. Record calibration information in instrument log books 

and transfer calibration data into electronic records or 

onto paper field forms at the time of calibration.

Procedure 2—Calibration with Air-Saturated Water 

This procedure, in which the DO sensor or instrument 

system is calibrated in water that is saturated with oxygen at a 

known temperature and ambient atmospheric pressure, is preferred by some manufacturers for optical-sensor calibration. 

Some manufacturers provide the necessary aeration equipment with their instruments. Procedure 2 has the advantage 

of ensuring that all equipment parts equilibrate with water 

temperature simultaneously, and eliminates the need to check 

for water droplets on the optical module or temperature sensor. 

Care is required, however, to ensure that the water is indeed 

saturated with oxygen

Equipment—Calibration with air-saturated water

1 5-gallon bucket or manufacturer-provided aeration chamber

1 10-gallon aquarium air pump with two outlets

1 10-foot length of aquarium-pump tubing

2 Gas-diffusion (air) stones 

For this procedure, producing aerated water under 

controlled laboratory conditions is preferred; calibrate the 

DO sensor in the laboratory before departing for the field site 

(step 4a below). The variation of Procedure 1 using a wet 

towel is the recommended method to be performed at a field 

site.

1. In the laboratory, fill a 5-gallon bucket to three-quarters 

full with tap water.

2. Attach the pump tubing to the air pump and then the two 

air stones to the ends of the tubing. Place the tubing with 

air stones at the bottom of the filled bucket. 

3. Turn on the pump and aerate the water for a minimum 

of 30 minutes. Tip: The pump can be left to operate 

continuously (24/7) in order to have a ready supply of 

air-saturated water on hand for calibration in the laboratory. However, water will continuously evaporate from 

the bucket over time, raising the specific conductance 

of the aerated water. Be sure to replace the water in the 

bucket periodically.

4. Calibration—Take care to keep the optical sensor free of 

air bubbles.

a. For laboratory calibration, place the DO sensor (or 

multiparameter sonde) in the bucket and allow 5 to 

10 minutes for the sensor to come to thermal equilibrium with the aerated water. Take care not to place 

the sensor over or in the bubbles from the air stone.

b. For field calibration verification of a DO sensor, use 

the wet-towel method.

5. Read and record the temperature of the calibration water 

to the nearest 0.1 °C.
10 Chapter A6.2. Dissolved Oxygen

6. Using a calibration-checked barometer, determine the 

ambient atmospheric pressure to the nearest 1 mm 

of mercury.

7. Using oxygen-solubility table 6.2–2 (at end of chapter) 

or the online software DOTABLES (https://water.usgs.

gov/software/DOTABLES/), determine the DO-saturation value at the measured temperature and atmospheric 

pressure of the calibration water. (Refer to section 5.0 

and table 6.2–4 (at end of chapter) for salinity corrections; salinity corrections should not be necessary for 

tap water.) 

8. When the instrument readings are stable, adjust the 

instrument to the DO-saturation value determined from 

the oxygen-solubility table.

• If an instrument that allows calibration simply to a 

100-percent saturation condition is used, all that may 

be needed is to provide the ambient atmospheric 

pressure for the instrument to determine (with 

internal software) the resulting DO concentration. 

If the instrument has an internal barometer, it 

may only be necessary to put the instrument into 

calibration mode and check the calibration once it 

has been completed.

9. Verify that the instrument reading is within ±0.2 mg/L or 

2 percent of the computed saturation value, or use more 

stringent accuracy criteria that reflect the data-quality 

requirements of the project.

10. After all the steps above have been followed, the DO 

sensor is calibrated and ready for use. 

11. Record the calibration information in instrument 

log books and transfer calibration data into electronic records or onto paper field forms at the time 

of calibration.

For accurate calibration, ensure that the water is 

100-percent saturated with oxygen.

2.3 Measurement

The solubility of oxygen in water depends on the 

temperature and ionic strength of the water. The higher the 

atmospheric pressure on the water’s surface and the lower the 

temperature and conductivity of the water, the more oxygen 

will be dissolved in the water.

Degassing, mineral precipitation, and other chemical, 

physical, and biological reactions can cause the DO concentration of a water sample to change substantially within minutes 

after sample collection, especially if the water sampled was 

originally isolated from the atmosphere as in the case of 

groundwater or water in a deep lake or reservoir.

The solubility of oxygen in water decreases as salinity 

increases. Correction factors for salinity typically are applied 

after measuring DO for single-point samples; however, for 

DO measurements made with multiparameter instruments 

that include calibrated specific-conductance sensors, it is 

wise to activate the instrument’s internal salinity correction 

algorithms. Information that pertains to oxygen solubility and 

salinity is given in section 5.0, including the link to an online 

program that generates tables of DO solubility values and 

(or) salinity correction factors over a range of user-specified 

temperature, atmospheric pressure, and salinity or specific 

conductance (https://water.usgs.gov/software/DOTABLES/).

2.3.1 Surface Water

Standard determinations of DO in riverine surface water 

represent the cross-sectional median or mean DO concentration at the time of observation.

Multiparameter instruments (sondes) are in common use 

by the USGS for measurement of DO and other field parameters, both for in situ discrete measurements in surface water 

and for short- or long-term deployment in streams, lakes and 

reservoirs, and other surface-water bodies. Refer to NFM 

6.8, Wagner and others (2006), and manufacturer guidance 

for additional information regarding the siting and use of 

multiparameter instruments.

Measuring the DO concentration at one distinct point in 

a cross section is valid only for flowing water with a crosssectional DO variation less than 0.5 mg/L. Discerning such 

variation requires a reconnaissance cross-section measurement. Measurements made at multiple locations in the cross 

section are recommended when possible. Determining DO 

concentration for a single channel at the centroid of flow at the 

midpoint of the vertical represents the cross section only under 

ideal mixing conditions.

Do not measure DO in or directly below sections with 

turbulent flow, in still water, or from the bank unless these 

conditions represent most of the stream reach or are required 

to fulfill project objectives.

Verify whether or not the instrument in use applies salinity corrections automatically. If not, apply a salinity correction 

to the saturation values after making the DO measurement, 

referring to section 5.0 and table 6.2–4 (at end of chapter).

If the anticipated DO concentration is less than 1.0 mg/L, 

use of spectrophotometric methods (section 3.0) is required 

to develop an instrument-specific rating before measurements made with a field instrument can be reported. Optical 

DO instrument readings are required to be verified through 

the development of an instrument-specific comparison with 

spectrophotometric methods. The instrument-specific rating 

should consist of at least five measurements made as nearly 

simultaneously as possible with the optical instrument and 

the spectrophotometric method. When compared, the median 

of these measurements should agree within 0.03 mg/L. If the 

measurements do not agree within 0.03 mg/L, the optical 

instrument should be checked and, if necessary, calibrated to 
2.0 Optical (Luminescence) Sensor Method 11

the zero-DO point. The directions for the spectrophotometric 

method should also be checked and followed very closely. 

Once an instrument-specific rating has been developed, an 

optical DO instrument may be used to report DO concentrations greater than 0.03 mg/L. Example data for such a comparison are in appendix 1.3

DO must be measured in situ. Never measure DO in 

subsamples from a sample splitter or other vessel; DO 

measurements will not be representative because the 

chemistry of derived samples changes quickly.

Follow the steps below to measure DO in surface water:

1. Calibration checks:

• Check that the thermistor is accurate and that 

its calibration has been certified according to 

NFM 6.1 (Temperature).

• Check the performance of the DO sensor at saturation and zero DO (see sections 2.1 and 2.2).

• If a calibration adjustment is necessary or if it is 

required to address program protocols, data-quality 

requirements, or site-specific conditions, calibrate 

the DO sensor onsite in accordance with the procedures described in section 2.2.

2. Examine the variation in DO measured at multiple locations along the stream cross section (if this reconnaissance step was performed) to help select the sampling 

method.

• Flowing, shallow stream—Wade to the location(s) 

where DO is to be measured.

• Flowing stream too deep or swift to wade—Lower 

a weighted DO sensor from a bridge, cableway, or 

boat. Do not attach the weight directly to the sensors 

or sensor cables to avoid damaging the sensors or 

sensor cables. Contact the instrument manufacturer 

or vendor for information regarding the weights 

approved for use with the instrument and how to 

attach them.

• Still-water conditions—Measure DO at multiple 

depths at several points in the cross section.

• Lakes and reservoirs—Measure DO at a series of 

specific depths to determine a vertical profile at each 

location of interest.

3

Note that spectrophotometric methods for determining DO concentration 

generally are not approved by the U.S. Environmental Protection Agency for 

regulatory assessments.

3. Immerse the DO and temperature sensors directly into 

the water body and allow the sensors to equilibrate to the 

water temperature (no less than 60 seconds).

4. Record the temperature without removing the sensor 

from the water.

5. After the instrument reading has stabilized, record the 

median DO concentration (see NFM A6.0, Field Measurements). The reading should stabilize to within ±0.2 

mg/L.

• In still water, record the median of three or more 

sequential values.

• Equal Discharge Increment (EDI)—Record the mean 

value of all subsections measured. If there is only 

one vertical section, use the median at the centroid 

of flow.

• Equal Width Increment (EWI)—Record the mean 

(or median) of all subsections measured.

6. For EWI, EDI, or multiple vertical measurements, 

proceed to the next station in the cross section and repeat 

steps 3–5. 

7. When measurements for the stream have been completed, remove the sensor from the water, rinse it with 

deionized water or tap water, and store it according to 

the manufacturer’s instructions.

8. Record DO concentrations on the field forms.

2.3.2 Groundwater

Before the concentration of DO in groundwater can be 

determined, standing water must be evacuated from the well 

to ensure that measurements of DO concentration in the well 

will be representative of formation-water concentration. An 

adequate well purge ensures the flow of freshwater from the 

aquifer formation into the well (refer to NFM A4, Sample 

Collection, and NFM A6, Field Measurements, for detailed 

information). Measurement of ambient DO concentrations in 

groundwater additionally requires use of equipment and procedures that avoid aeration and mitigate losses or gains of dissolved gases in the water being sampled. A bailed sample, for 

example, is not recommended for DO measurement because 

the field sample-decanting process exposes the sample to the 

atmosphere; this provision likewise applies to any type of 

sampling device from which the sample is brought into contact 

with air when transferred to a measurement or analysis vessel. 

Project data-quality requirements and objectives, site 

characteristics, and equipment availability will dictate whether 

(1) measurements will be made in situ (DO measured downhole) or ex situ (DO measured above land surface, the inlineflow procedure), and whether (2) optical or spectrophotometric 

methods will be used for DO measurement.
12 Chapter A6.2. Dissolved Oxygen

The accuracy of DO measurements to 0.03 mg/L with an 

optical sensor has been field verified against Rhodazine D and 

Indigo Carmine spectrophotometric measurements on many 

occasions by USGS field-methods training class instructors. 

Therefore, applying optical sensor methods for groundwater DO 

measurements in the concentration range less than 2 mg/L is 

reliable. Data for some of these comparisons are in appendix 1.

If the anticipated DO concentration is less than 1.0 mg/L, 

use of spectrophotometric methods (section 3.0) is required 

to develop an instrument-specific rating before measurements made with a field instrument can be reported. Optical 

DO instrument readings are required to be verified through 

the development of an instrument-specific comparison with 

spectrophotometric methods. The instrument-specific rating 

should consist of at least five measurements made as nearly 

simultaneously as possible with the optical instrument and 

the spectrophotometric method. When compared, the median 

of these measurements should agree within 0.03 mg/L. If the 

measurements do not agree within 0.03 mg/L, the optical 

instrument should be checked and, if necessary, calibrated to 

the zero-DO point. The directions for the spectrophotometric 

method should also be checked and followed very closely. 

Once an instrument-specific rating has been developed, an 

optical DO instrument may be used to report DO concentrations greater than 0.03 mg/L. Example data for such a comparison are in appendix 1.

For DO concentration less than 2 mg/L, a zero-DO calibration check or calibration of the DO instrument is required. 

Instruments are required to be performance tested before field 

use as described in section 2.1.2, Field-Trip Preparations.

Refer to NFM A6, Field Measurements, for guidance 

related to the selection, preparation, and procedures for in 

situ and ex situ measurement of field-determined properties. 

Project objectives and site characteristics will dictate the 

specific method selected. Select the field-measurement system 

that best fits the requirements of the data-collection effort. 

Downhole (in situ) measurement: Submersible multiparameter sondes and single-parameter sensors are deployed 

downhole to the targeted depth interval. Deployment typically 

includes data collection for a single field trip. The sonde or 

sensor sometimes is deployed for unattended monitoring, but 

the appropriate conditions and protocols must be followed 

(see NFM A6.8, Multiparameter Instruments).

Inline flow-through cell/chamber (ex situ) measurement: 

Sample is pumped directly (inline) to an airtight, transparent 

chamber or manufacturer-provided cell having either (1) leakproof ports (compression fittings) that accommodate a DO 

single-parameter sensor (and other single-parameter sensors), 

or (2) a multiparameter sonde instrumented with an optical 

DO sensor.

The sample is transferred by using a positive-displacement 

submersible pump fitted with high-density plastic or fluorocarbon-polymer tubing that is relatively gas impermeable.

• Use of transparent materials for the tubing and 

chamber is recommended to permit checking for air 

bubbles in the water stream or adhering to the sides 

of the tubing and flow-through cell or chamber (that 

have been introduced as an artifact of the sampling 

procedure, as distinguished from gas bubbles that are 

native to the formation water). Air bubbles introduced through leaking fittings can add substantial 

error to low-level DO measurements and should be 

excluded.

• Protect exposed sample tubing and the flow-through 

cell or chamber from direct sunlight.

Do not measure groundwater DO concentration 

in a sample extracted from a bailer or other 

sampling device that results in sample exposure to 

the atmosphere.

Follow the steps below to measure DO in groundwater:

1. Calibration checks: 

• Check that the thermistor is accurate and that 

its calibration has been certified according to 

NFM 6.1, Temperature.

• Check the performance of the DO sensor at saturation and zero DO (refer to sections 2.1 and 2.2). 

• If a calibration adjustment is necessary or if it is 

required to address program protocols, data-quality 

requirements, or site-specific conditions, calibrate 

the DO sensor onsite, in accordance with the procedures described in section 2.2.

2. Install the DO equipment:

• Downhole system—Lower the DO and temperature 

sensors to the measuring point, followed by the 

pump, to monitor DO variation during purging.

• Inline flow-through system—Refer to NFM 6.0, 

Field Measurements, for installation guidelines. 

For a system that includes a multiparameter instrument sonde, install the sonde in the flow-through 

cell provided by the manufacturer and in accordance 

with manufacturer instructions. Be sure to:

• Install the DO sensor through an air-tight grommet if the chamber is instrumented with singleparameter sensors. Check that the seal around 

the DO sensor is intact and that the sensors are 

properly immersed.
3.0 Spectrophotometric (Rhodazine D and Indigo Carmine) Methods 13

• Shield the sample tubing and flow-through cell/

chamber from direct sunlight to minimize changes 

to sample temperature.

• Dislodge and flush entrained gas bubbles from 

the tubing walls and flow-through chamber by 

tapping the tubing with a blunt tool (see Technical 

Note 4). Note that air bubbles are an indication of 

air leakage into the sampling system and should 

be distinguished from gas bubbles that could be 

native to formation water.

• Check for and eliminate back pressure in the 

flow-through chamber. The outlet of the chamber 

should be free flowing.

3. Measure and record the DO concentration at regular 

intervals throughout purging. Allow the sensors to equilibrate with groundwater for a minimum of 5 minutes 

before making the first measurement.

4. Check the stability (measurement variability) of the DO 

concentration toward the end of purging. The stability 

criterion is met when five consecutive measurements 

made at regularly spaced intervals of 3 to 5 minutes or 

more are within ±0.2 mg/L. (For each reading, monitor 

fluctuations for 30 to 60 seconds and record the median 

value, if necessary.) If the ±0.2-mg/L criterion is not met, 

increase the purging period in accordance with project 

objectives and continue to record measurements at regularly spaced time intervals.

5. Report DO concentration as the median of the final 

five DO readings recorded. Record on field forms any 

difficulty that may have been encountered with reading 

stabilization.

6. Remove the sensor from the water and rinse it with 

deionized or tap water. Store the sensor according to the 

manufacturer’s instructions.

Air bubbles in the tubing lines and flow-through 

chamber can add substantial error to measurements of 

DO in low-DO or oxygen-depleted groundwater.

TECHNICAL NOTE 4.

Anomalously high DO measurements commonly are caused 

by aeration of groundwater during pumping. This situation can 

result from air leakage through loose fittings on productionwell pumping systems, or if drawdown in the aquifer introduces air into the well-screen perforations. To understand 

these problems, review information about the pump and its 

depth within the well, data on well construction and water 

levels during pumping, and previous data records. Corrective 

actions may or may not be possible.

3.0 Spectrophotometric (Rhodazine D

and Indigo Carmine) Methods

Various spectrophotometric methods (see Technical Note 

5) are available for determining DO over a broad range of 

concentrations. The information in this section, however, is 

limited to the application of spectrophotometric analysis of 

Rhodazine D and Indigo Carmine reagents for determining 

DO concentrations in relatively oxygen-deficient waters—that 

is, DO concentration from about 2 to 0 mg/L. Indigo carmine 

is an organic salt formulated by sulfonating indigo dye. The 

reduced form of indigo carmine reacts with DO to form a 

blue product. The Rhodazine D (phenzone dye) compound, in 

reduced form, reacts with DO to form a bright pink reaction 

product. (CHEMetrics, Inc., 2012). The option to measure 

DO in the higher concentration ranges by spectrophotometry 

generally is selected when field conditions limit use of optical 

sensor methods. (Noninstrumental analyses of Rhodazine D 

and Indigo Carmine reagent indicators also are available for 

measuring aqueous DO concentrations, but the analysis can be 

subject to considerable operator variability and is not applicable to standard USGS field protocols, and is therefore beyond 

the scope of this guidance.)

TECHNICAL NOTE 5.

Photometry measures only in the visible spectral region from 

360 nanometers (nm) to 830 nm, the range in which human 

eyes are sensitive. Spectrophotometry is the quantitative 

measurement of the reflection or transmission properties of 

a material as a function of light wavelength. The National 

Institute of Standards and Technology (NIST) maintains 

the national scales for reflectance and transmittance in the 

ultraviolet, visible, and near-infrared spectral regions—that is, 

250 to 2,500 nm (see http://www.nist.gov/pml/div685/grp03/

photometry.cfm and http://www.nist.gov/pml/div685/grp03/

spectrophotometry.cfm).

Spectrophotometric methods for DO measurement have 

been used in USGS fieldwork for measuring DO in oxygendepleted groundwater and can be adapted for work in oxygendepleted zones of lakes and reservoirs, but are not approved 

by the U.S. Environmental Protection Agency for application 

to regulatory assessments. The Rhodazine D spectrophotometric method for determining DO concentrations in groundwater 

was introduced by White and others (1990) as a means for 

obtaining accurate DO-concentration data for groundwater at a time when sensor methods were not capable of in 

situ measurement.

As mentioned previously, USGS technical staff have documented optical sensor measurements at DO concentrations 

of 0.03 mg/L and spectrophotometric readings by using either 

Rhodazine D or Indigo Carmine to be of comparable accuracy. 

Data are shown in appendix 1. Comparisons between optical 
14 Chapter A6.2. Dissolved Oxygen

Table 6.2–3. Equipment and supplies for the spectrophotometric 

method of determining dissolved-oxygen concentration using 

Rhodazine D and Indigo Carmine reagents.

[DO, dissolved-oxygen concentration; μS/cm, microsiemens per centimeter at 

25 degrees Celsius]

Portable spectrophotometer (or photometer)

Appropriate reagent kits for the expected DO range of the environmental condition

Blank ampule (zero DO), included in each Rhodazine D kit

Submersible sampling tool, used in situ, to meet criteria described 

in White and others (1990)

Sampler device (overflow cell), length of C-flex tubing, and sample 

pump

Safety gloves, glasses, and apron 

Waste-disposal container

Deionized water (maximum conductivity 1 μS/cm)

Bottle, squeeze dispenser, for deionized water

Lint-free wipes to remove moisture from the surface of the ampule

sensors and spectrophotometric methods were made by using 

an In-Situ, Inc., multiparameter sonde (various models) with 

a rugged dissolved oxygen (RDO) optical sensor. Before 

measuring and reporting hypoxic to anoxic (concentration 

less than 1.0 mg/L) DO-concentration data from optical sensors, the capability and accuracy of the optical sensor in this 

low-DO concentration range is required to be documented by 

making side-by-side measurements onsite to compare results 

with values obtained by using a spectrophotometric method. 

(See section 2.3, Measurement, above.)

The Rhodazine D spectrophotometric method is applicable to a range of DO concentrations from 0.025 to 1.0 

mg/L in aqueous environments. The low-level Indigo Carmine spectrophotometric methods are applicable to a range 

of DO concentrations from either 0.006 to 0.8 mg/L or 0.2 to 

2.0 mg/L, depending on the specific method being used for the 

concentration range of interest.

3.1 Equipment and Supplies

The Rhodazine D and Indigo Carmine spectrophotometric methods were designed to minimize atmospheric interaction with the water sampled. Two sampling systems commonly 

are used—(1) an in situ (submersible or downhole) sampler, 

such as the assemblies discussed in White and others (1990); 

and (2) a plastic overflow cell through which sample water is 

pumped (see table 6.2–3).

The sampling system is configured to use a self-filling 

ampule with the Rhodazine D or Indigo Carmine reagent vacuum sealed inside. DO concentration is determined instrumentally on the resultant solution by using a spectrophotometer or 

photometer. The spectrophotometer (or photometer) selected 

must be adjustable to the appropriate wavelength of incident 

light needed for the determination of DO concentration in the 

resultant colored sample, based on the reagent used. Applicable spectrophotometers, photometers, and ampule kits are 

available commercially from various companies for a variety 

of concentration ranges.

Information about the accuracy of commercially available reagent kits may not be included with the equipment 

or supplies purchased. Always check with the manufacturer 

regarding the accuracy of the specific test kit(s) of interest. 

The accuracy of the test kits will typically be a function of the 

range of DO concentration in the sample.

3.2 Calibration and Interferences

For the Rhodazine D and Indigo Carmine methods, DO 

is measured by the spectrophotometer as percent absorbance. 

A calibration chart typically is provided with each chemical reagent kit, along with a regression formula to convert 

absorbance to micrograms per liter of DO for use with a 

spectrophotometer that does not perform the conversion automatically. Most current spectrophotometers and photometers 

available for measurement of DO are precalibrated for direct 

readout of DO concentration in milligrams per liter. 

Ensure that an appropriate blank ampule is used to zero 

the spectrophotometer (or photometer).

Additional calibration is needed if the method will be 

used to determine DO in heavily contaminated or acidic 

waters. Advanced calibration can be done by equilibrating a water sample with known partial pressures of atmospheric oxygen (White and others, 1990). Atmospheric 

oxygen standards are available from suppliers of gaschromatography equipment.

Rhodazine D and Indigo Carmine chemical reagent-based 

methods are not subject to salinity or dissolved-gas interferences (ASTM International, 2009; ASTM International, 2018; 

White and others, 1990; Gilbert and others, 1982). Interferences from total salinity, major dissolved inorganic species, 

dissolved gases, or temperature are typically negligible with 

these methods. However, turbidity may affect the Indigo 

Carmine method, and color and turbidity may affect the 

Rhodazine D method. If these methods are used in colored or 

turbid water, first conduct an assessment of the amount of bias 

attributable to such effects.

The spectrophotometric method using Rhodazine D 

reagent is affected by the presence of oxidizing agents, including chlorine, ferric and cupric ions, and hexavalent chromium, 

resulting in high-biased DO readings (White and others, 

1990).4

• The presence of cupric copper and ferric iron at a 

concentration less than 50 micrograms per liter (μg/L) 

may cause a bias of less than 1 μg/L; at a concentration 

4

See also CHEMetrics, Inc., Simplicity in water analysis, accessed September 4, 2019, at https://www.chemetrics.com/product-category/test-kits/

oxygen-dissolved/.
3.0 Spectrophotometric (Rhodazine D and Indigo Carmine) Methods 15

of 100 μg/L, cupric copper may cause a bias of 5 μg/L, 

and ferric iron may cause a bias of 7 μg/L.

• A sample pH of 2 or less may cause erroneous results.

• A hydroquinone concentration greater than 200 μg/L 

is a positive interferent and its oxidation byproduct, 

benzoquinone, causes a false positive result. The effect 

from oxidizing agents can be corrected if the concentrations of the interfering species are known (White 

and others, 1990).

The spectrophotometric method using Indigo Carmine 

reagent is affected by ferric iron, hypochlorite (chlorine), and 

chromate, which can cause a false positive at concentrations 

equal to or greater than 10 mg/L each. 

• Cupric copper interferes positively at a concentration 

equal to or greater than 100 mg/L. 

• Seawater may cause the reagent to precipitate.

3.3 Measurement

USGS spectrophotometric measurement procedures for 

the determination of DO concentration using the Rhodazine 

D and Indigo Carmine reagents provided in commercially 

available kits supplied by CHEMetrics, Inc., and Hach, 

respectively, have been tested and quality assured.5 Although 

the instructions provided by the manufacturers generally 

should be followed, augmented instructions and information 

are provided below and advised for USGS personnel to follow 

to ensure that DO measurements meet USGS standards for 

accuracy and reproducibility.

Rhodazine D and Indigo Carmine reagents react with 

DO to produce an oxidized complex characterized by bright 

pink- or bright blue-colored reaction products, respectively. 

The color intensity is proportional to the concentration of the 

initial DO present. Timing is critically important for colorimetric analyses made with a spectrophotometer. Follow 

the explicit instructions for the waiting time after the sample 

mixes with the reagent. The reaction with the reagents occurs 

almost instantaneously for both the Rhodazine D and Indigo 

Carmine methods. Color development continues after the time 

interval specified for these methods because oxygen from the 

atmosphere continuously diffuses into the sample through the 

broken ampule tip.

Do not extend the waiting times specified in the Rhodazine D and Indigo Carmine methods. Adhere to them 

strictly.

Excessive mixing of the ampule before placing it into the 

spectrophotometer also may introduce atmospheric oxygen, 

which can bias the results.

5

Instructions from Hach and CHEMetrics, Inc., for selected colorimetrybased methods at DO concentration ranges relevant to routine USGS sampling 

were selected for testing because USGS field personnel currently use the 

equipment and reagent kits from these companies.

Use a pumping flow rate of about 500 milliliters per 

minute for sample collection. Allow the sampling device to 

overflow during sample collection.

Follow the steps below to measure DO using the spectrophotometric method:

1. Familiarize yourself with the manufacturer’s instructions 

regarding use of the kit and adjust the instructions to 

incorporate the procedures that follow, as applicable. 

2. Accounting for site characteristics and project objectives, if measuring DO in groundwater, purge the well 

following guidelines in NFM 4.

3. Set the spectrophotometer to an appropriate wavelength 

for the kit being used. When using a manufacturer-designated DO photometer (or spectrophotometer), verify 

whether or not introduction of the ampule provided in 

the kit will automatically trigger the correct wavelength 

setting. 

4. “Zero” the spectrophotometer by using the blank provided in the kit or native water according to the manufacturer’s instructions.

5. When collecting the sample: 

• Prevent sample aeration. Use a positive-displacement submersible pump and high-density plastic or 

fluorocarbon polymer sample tubing that is relatively 

gas impermeable, if possible, throughout the measurement system.

• Operate equipment to mitigate losses or gains of 

dissolved gases. (Consult NFM 6.0 for proper 

downhole and inline flow-through chamber sampling 

procedures.)

6. Select your sample-collection method. Use either a 

downhole or an overflow-sampler device.

• Go to step 7 for the downhole sampling tool 

method6, or 

• Go to step 8 for the plastic overflow-sampler device 

with a suitable pump method.

7. Downhole system: After purging the well (according to 

guidelines in NFM 4), follow steps 7a through 7d.

a. Carefully immerse a reagent-containing ampule on 

the sampling tool that is attached to a wire line.

b. At the desired depth of sample collection (in a well 

or surface-water body), break the scored tip of the 

ampule by using a sharp upward tugging motion on 

the sampling tool. This action permits sample water 

6

A downhole sampling tool is described by White and others (1990).
16 Chapter A6.2. Dissolved Oxygen

to be drawn into the ampule. During the sample’s 

transit to the surface, the progressively decreasing 

pressure surrounding the ampule prevents cross 

contamination from overlying water through the 

ampule tip.

c. Withdraw the ampule from the sampling device 

and invert once to mix the contents of the ampule, 

allowing the bubble to travel from end to end; follow 

the kit-specific instructions regarding the number of 

ampule inversions keeping in mind that USGS field 

observations indicate that vigorous or repeated mixing of the filled ampule can introduce atmospheric 

oxygen and bias the measurement. Take care not 

to introduce atmospheric oxygen into the ampule. 

Ensure that the time required to bring the ampule 

to the surface does not exceed the waiting times 

specified by the method. The downhole sampling 

system may work best for shallow wells and surfacewater bodies.

d. Wipe all liquid from the exterior of the ampule by 

using a lint-free tissue. To make the DO measurement, skip to step 9.

8. Overflow device: After purging the well (according to 

guidelines in NFM 4), follow steps 8a through 8d.

a. Connect the plastic overflow-sampling device to 

the outlet of the pump tubing with gas-impermeable 

tubing 1 meter or less in length. The overflow device 

is used to break the ampule in the stream of flowing 

water. If the Rhodazine D method is used, the kit is 

equipped with the appropriate overflow-sampling 

device needed to crack the ampule. If the Indigo 

Carmine method is used, adapt the instructions as 

follows to supplement those provided7:

• Obtain a plastic funnel with a funnel size of 

approximately 250 milliliters.

• Adapt the funnel to the end of a length of gasimpermeable tubing. This funnel, while overflowing, will allow the tip of the Indigo Carmine 

ampule to be broken very close to the location 

where the newest, unmixed sample water flows 

into the funnel.

• The flexible rubber-like cap supplied with the 

Hach Indigo Carmine ampules can be filled with 

sample water and inverted to cover the broken 

tip of the ampule if the ampule is also inverted 

with the broken tip facing down. This action 

7

The Hach Indigo Carmine kit instructs the user to collect the sample from a 

stream of water that is hard plumbed to the sample source and mentions using 

a funnel. Tests conducted by USGS personnel indicated that further supplementing the directions in step 8 substantially improves measurement accuracy 

and reproducibility.

provides protection from oxygen diffusion from 

the atmosphere into the broken tip of the ampule 

during transport and drying for measurement in 

the spectrophotometer.

b. Check for air bubbles in or adhering to the tubing 

and flow-through chamber.

c. Tap the tubing with a blunt tool to dislodge entrained 

air bubbles.

• Insert the glass ampule, tip first, into the overflowing sampling device so that the tip is at the bottom 

of the device, near the point of water inflow.

• Snap the tip by gently pressing the upper end 

of the ampule toward the wall of the sampling 

device. The vacuum ampule will draw the sample 

water in, leaving a small bubble at one end.

d. Ensure that the ampule is full before proceeding to 

prevent entraining excess atmospheric oxygen and 

thereby producing erroneous readings.

• Withdraw the ampule from the sampling device 

and invert it to mix the contents of the ampule, 

allowing the bubble to travel from end to end; 

follow the kit-specific instructions regarding the 

number of ampule inversions, keeping in mind 

that USGS field observations indicate that vigorous or repeated mixing of the filled ampule can 

introduce atmospheric oxygen and bias the measurement. Take care to not introduce atmospheric 

oxygen into the ampule.

• Wipe all liquid from the exterior of the ampule by 

using a lint-free tissue.

9. Insert the ampule directly into the spectrophotometer cell 

holder, either immediately after retrieval or as specified 

in the kit-specific instructions.

10. Read the concentration or absorbance:

• Rhodazine D—Record the measurement within the 

time interval directed by the kit manufacturer (for 

example, within 30 seconds when using the CHEMetrics ampule kit).

• Indigo Carmine—Record the measurement within 

the time interval directed by the kit manufacturer.

• If using a spectrophotometer that does not convert 

absorbance values of DO measurements to units 

of milligrams per liter for the kit being used, use 

regression equations (or the chart provided in the kit) 

to convert the units (see White and others, 1990). 

11. Quality control: It is recommended to make multiple 

measurements to document the precision and (or) 
5.0 Correction Factors for Oxygen Solubility and Salinity 17

accuracy of the DO concentration to be reported. Repeat 

steps 9 and 10 twice in rapid succession to document 

measurement precision. Make a total of three measurements to document the precision of the method.

12. To document the variability of DO concentrations within 

the water system being measured, repeat the measurement on three sequentially collected samples.

Do not exceed time interval specified by manufacturer 

for completion of DO measurement when using Rhodazine D or Indigo Carmine reagents.

4.0 Reporting

USGS personnel are instructed to enter the DO value on 

field forms or into electronic records indicating the method 

code (optical, spectrophotometric, other) appropriate for the 

method used for DO measurement.

DO concentrations for the optical-sensor method are 

reported to the nearest 0.1 mg/L and stored to the nearest 

0.01 mg/L.

DO concentrations for the spectrophotometric/Rhodazine 

D and Indigo Carmine methods are reported and stored to the 

nearest 0.01 mg/L.

Note that the percentage of DO saturation in water can 

be greater than 100 as a result of nonequilibrium conditions 

induced by photosynthesis and oxygen exchange with the 

atmosphere. When the concentration exceeds 20 mg/L, check 

the sensor manufacturer’s specifications and:

• Report “> the listed numerical limit” if the concentration exceeds the manufacturer’s specified sensor range.

5.0 Correction Factors for Oxygen 

Solubility and Salinity

Solubility concentrations of oxygen in freshwater at 

various temperatures and pressures (table 6.2–2, at end of 

chapter) and correction factors for salinity based on specific 

conductance (table 6.2–4, at end of chapter) were generated 

from the equations of Benson and Krause (1980, 1984) and 

can be customized to cover the range and number of decimal 

places needed; see U.S. Geological Survey Office of Water 

Quality Technical Memorandum 2011.03 (U.S. Geological 

Survey, 2011). By accessing “DOTABLES” at https://water.

usgs.gov/software/DOTABLES/, the interactive software that 

generated tables 6.2–2 and 6.2–4 (at end of chapter) the user 

can self-generate individual values or tables of a specific range 

of oxygen-solubility and salinity correction factors.

To adjust freshwater oxygen-solubility values for the 

effects of salinity, use correction factors based on specific 

conductance. Report the corrected values. Refer to the manufacturer’s instructions for the DO instrument before applying 

a salinity correction. Most multiparameter instruments that 

include DO and specific-conductance sensors automatically 

correct the DO reading for salinity if needed, unless the feature is turned off by the user.

Correcting DO solubility for saline waters (specific 

conductance greater than 2,000 μS/cm) varies with instrument type, calibration method, and the salts in solution. The 

correction based on specific conductance (table 6.2–4, at end 

of chapter) is useful because accurate conductivity can be 

determined easily from a field measurement.

Example salinity correction:

Consider a DO measurement made in water with a 

temp-erature of 20.0 °C, an atmospheric pressure of 750 mm 

of mercury, and a specific conductance of 8,000 μS/cm. The 

freshwater oxygen solubility from table 6.2–2 (at end of chapter) is 8.97 mg/L for that temperature and pressure; the salinity 

correction factor from table 6.2–4 (at end of chapter) is 0.9733 

for that temperature and specific conductance. The solubility 

of oxygen under these conditions then is

8.97 mg/L x 0.9733 = 8.73 mg/L (1)

The presence of dissolved ions in the water decreases the 

oxygen solubility.

If calibrating an instrument that lacks an internal salinitycompensation algorithm, the user could elect to adjust the 

DO instrument to read 8.73 mg/L for a 100-percent saturation 

condition.

If the DO measurement made with a sensor under the 

above conditions was 7.50 mg/L and the DO instrument did 

not have an internal salinity-compensation algorithm, then 

the actual DO concentration should be reported as 7.50 mg/L 

multiplied by 0.9733, or 7.30 mg/L.

Example percent-saturation calculation:

To express results as percent saturation, use the following 

equation:

 ( )

 ( / ) 100

 ( / )

DO percent saturation

measured DO mg L

DO mg L at percent saturation

=

× 100 -

(2)

For a salinity-corrected DO measurement of 7.30 mg/L 

for a sample in which the oxygen solubility (salinity corrected) 

is 8.73 mg/L as in the above example, the percent DO 

saturation would be the dividend of 7.30 divided by 8.73, 

multiplied by 100, which equals 83.6 percent. Note that for 

measurements made with the spectrophotometric method, 

salinity-correction factors are not applied to the measured 

concentration because salinity does not interfere with spectrophotometric DO analyses.
18 Chapter A6.2. Dissolved Oxygen

Acknowledgments

The information in the U.S. Geological Survey (USGS) 

National Field Manual (NFM) is based on existing manuals, 

various reference documents, and a broad spectrum of 

expertise provided by USGS colleagues. Authors of previous 

versions of NFM chapter A6.2 were S.A. Rounds, F.D. Wilde, 

G.F. Ritz, M.A. Sylvester, R.T. Iwatsubo, D.B. Radtke, and 

M.E. Lewis, whose expertise and integrity provided the 

groundwork for this and future versions of this chapter. The 

persistence and spirit that all of our USGS colleagues brought 

to the development of a national field manual were invaluable.

The following USGS colleagues provided detailed 

technical content and reviews that improved the quality of 

this report: Gerolamo Casile, Kimberly Beisner, Irene Fisher, 

Allison Leninger, Cherie Miller, Timothy Oden, Patrick 

Rasmussen, and Stanley Skrobialowski. Editorial and production assistance from Marilyn Billone, Sandy Cooper, Elizabeth 

Good, Cathy Knutson, Katharine Schindler, and Dale Simmons is greatly appreciated. These individuals contributed to 

the accuracy, quality, and usability of the NFM, and demonstrated much patience as we traversed the difficult task of 

developing the new format.

Special thanks are extended to Franceska Wilde (USGS), 

who led the effort for the NFM from its inception until her 

retirement in 2014; the USGS NFM Steering Committee 

(Gerolamo Casile, Alissa Coes, Michael Manning, 

Cherie Miller, Timothy Oden, Lisa Olsen, Michael Rosen, 

and Stanley Skrobialowski); Cherie Miller, who led the effort 

from 2016 to 2018; and Gerolamo Casile, who assumed 

responsibility for the NFM in 2018.

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https://www.ysi.com/parameters/dissolved-oxygen.
20 Chapter A6.2. Dissolved Oxygen Table 6.2–2. Solubility of oxygen in freshwater at various temperatures and pressures. [Solubility shown in milligrams per liter; values are based on equations published by Benson and Krause (1980, 1984); Temp. (°C), temperature in degrees Celsius; solubility values for atmospheric pressures from 600 to 695 millimeters of mercury are after the values for 0-40 °C] Temp. (deg C) Atmospheric pressure, in millimeters of mercury 700 705 710 715 720 725 730 735 740 745 750 755 760 765 770 775 780 785 790 795 0.0 13.46 13.56 13.65 13.75 13.85 13.94 14.04 14.14 14.23 14.33 14.43 14.52 14.62 14.72 14.81 14.91 15.01 15.10 15.20 15.30 0.5 13.27 13.37 13.46 13.56 13.65 13.75 13.84 13.94 14.03 14.13 14.23 14.32 14.42 14.51 14.61 14.70 14.80 14.89 14.99 15.08 1.0 13.09 13.18 13.28 13.37 13.46 13.56 13.65 13.75 13.84 13.93 14.03 14.12 14.22 14.31 14.40 14.50 14.59 14.69 14.78 14.87 1.5 12.91 13.00 13.09 13.19 13.28 13.37 13.46 13.56 13.65 13.74 13.84 13.93 14.02 14.11 14.21 14.30 14.39 14.48 14.58 14.67 2.0 12.73 12.82 12.91 13.01 13.10 13.19 13.28 13.37 13.46 13.56 13.65 13.74 13.83 13.92 14.01 14.10 14.20 14.29 14.38 14.47 2.5 12.56 12.65 12.74 12.83 12.92 13.01 13.10 13.19 13.28 13.37 13.46 13.55 13.64 13.73 13.82 13.91 14.00 14.10 14.19 14.28

3.0 12.39 12.48 12.57 12.66 12.75 12.84 12.93 13.02 13.10 13.19 13.28 13.37 13.46 13.55 13.64 13.73 13.82 13.91 14.00 14.093.5 12.23 12.31 12.40 12.49 12.58 12.67 12.75 12.84 12.93 13.02 13.11 13.19 13.28 13.37 13.46 13.55 13.63 13.72 13.81 13.904.0 12.07 12.15 12.24 12.33 12.41 12.50 12.59 12.67 12.76 12.85 12.93 13.02 13.11 13.20 13.28 13.37 13.46 13.54 13.63 13.724.5 11.91 11.99 12.08 12.17 12.25 12.34 12.42 12.51 12.59 12.68 12.77 12.85 12.94 13.02 13.11 13.20 13.28 13.37 13.45 13.545.0 11.75 11.84 11.92 12.01 12.09 12.18 12.26 12.35 12.43 12.52 12.60 12.69 12.77 12.86 12.94 13.03 13.11 13.19 13.28 13.365.5 11.60 11.69 11.77 11.86 11.94 12.02 12.11 12.19 12.27 12.36 12.44 12.52 12.61 12.69 12.78 12.86 12.94 13.03 13.11 13.196.0 11.46 11.54 11.62 11.70 11.79 11.87 11.95 12.04 12.12 12.20 12.28 12.37 12.45 12.53 12.61 12.70 12.78 12.86 12.94 13.036.5 11.31 11.39 11.48 11.56 11.64 11.72 11.80 11.88 11.97 12.05 12.13 12.21 12.29 12.37 12.46 12.54 12.62 12.70 12.78 12.867.0 11.17 11.25 11.33 11.41 11.49 11.58 11.66 11.74 11.82 11.90 11.98 12.06 12.14 12.22 12.30 12.38 12.46 12.54 12.62 12.707.5 11.03 11.11 11.19 11.27 11.35 11.43 11.51 11.59 11.67 11.75 11.83 11.91 11.99 12.07 12.15 12.23 12.31 12.39 12.47 12.558.0 10.90 10.98 11.06 11.14 11.21 11.29 11.37 11.45 11.53 11.61 11.69 11.76 11.84 11.92 12.00 12.08 12.16 12.24 12.32 12.398.5 10.77 10.84 10.92 11.00 11.08 11.16 11.23 11.31 11.39 11.47 11.54 11.62 11.70 11.78 11.86 11.93 12.01 12.09 12.17 12.249.0 10.64 10.71 10.79 10.87 10.94 11.02 11.10 11.18 11.25 11.33 11.41 11.48 11.56 11.64 11.71 11.79 11.87 11.94 12.02 12.109.5 10.51 10.59 10.66 10.74 10.81 10.89 10.97 11.04 11.12 11.19 11.27 11.35 11.42 11.50 11.57 11.65 11.73 11.80 11.88 11.95

10.0 10.39 10.46 10.54 10.61 10.69 10.76 10.84 10.91 10.99 11.06 11.14 11.21 11.29 11.36 11.44 11.51 11.59 11.66 11.74 11.8110.5 10.26 10.34 10.41 10.49 10.56 10.64 10.71 10.78 10.86 10.93 11.01 11.08 11.16 11.23 11.30 11.38 11.45 11.53 11.60 11.68

11.0 10.15 10.22 10.29 10.37 10.44 10.51 10.59 10.66 10.73 10.81 10.88 10.95 11.03 11.10 11.17 11.25 11.32 11.39 11.47 11.5411.5 10.03 10.10 10.17 10.25 10.32 10.39 10.47 10.54 10.61 10.68 10.76 10.83 10.90 10.97 11.05 11.12 11.19 11.26 11.34 11.41

12.0 9.91 9.99 10.06 10.13 10.20 10.27 10.35 10.42 10.49 10.56 10.63 10.71 10.78 10.85 10.92 10.99 11.06 11.14 11.21 11.2812.5 9.80 9.87 9.94 10.02 10.09 10.16 10.23 10.30 10.37 10.44 10.51 10.58 10.66 10.73 10.80 10.87 10.94 11.01 11.08 11.1513.0 9.69 9.76 9.83 9.90 9.97 10.04 10.11 10.19 10.26 10.33 10.40 10.47 10.54 10.61 10.68 10.75 10.82 10.89 10.96 11.0313.5 9.59 9.65 9.72 9.79 9.86 9.93 10.00 10.07 10.14 10.21 10.28 10.35 10.42 10.49 10.56 10.63 10.70 10.77 10.84 10.9114.0 9.48 9.55 9.62 9.69 9.76 9.82 9.89 9.96 10.03 10.10 10.17 10.24 10.31 10.37 10.44 10.51 10.58 10.65 10.72 10.7914.5 9.38 9.44 9.51 9.58 9.65 9.72 9.78 9.85 9.92 9.99 10.06 10.13 10.19 10.26 10.33 10.40 10.47 10.53 10.60 10.67
References Cited 21

Table 6.2–2. Solubility of oxygen in freshwater at various temperatures and pressures.—Continued[Solubility shown in milligrams per liter; values are based on equations published by Benson and Krause (1980, 1984); Temp. (°C), temperature in degrees Celsius; solubility values for atmospheric pressures from 600 to 695 millimeters of mercury are after the values for 0-40 °C]

Temp. 

(deg C)

Atmospheric pressure, in millimeters of mercury

700 705 710 715 720 725 730 735 740 745 750 755 760 765 770 775 780 785 790 795

15.0 9.27 9.34 9.41 9.48 9.54 9.61 9.68 9.75 9.81 9.88 9.95 10.02 10.08 10.15 10.22 10.29 10.35 10.42 10.49 10.5615.5 9.18 9.24 9.31 9.38 9.44 9.51 9.58 9.64 9.71 9.78 9.84 9.91 9.98 10.04 10.11 10.18 10.24 10.31 10.38 10.4416.0 9.08 9.14 9.21 9.28 9.34 9.41 9.47 9.54 9.61 9.67 9.74 9.80 9.87 9.94 10.00 10.07 10.13 10.20 10.27 10.3316.5 8.98 9.05 9.11 9.18 9.24 9.31 9.37 9.44 9.50 9.57 9.64 9.70 9.77 9.83 9.90 9.96 10.03 10.09 10.16 10.2217.0 8.89 8.95 9.02 9.08 9.15 9.21 9.28 9.34 9.41 9.47 9.54 9.60 9.66 9.73 9.79 9.86 9.92 9.99 10.05 10.1217.5 8.80 8.86 8.92 8.99 9.05 9.12 9.18 9.24 9.31 9.37 9.44 9.50 9.57 9.63 9.69 9.76 9.82 9.89 9.95 10.0118.0 8.70 8.77 8.83 8.90 8.96 9.02 9.09 9.15 9.21 9.28 9.34 9.40 9.47 9.53 9.59 9.66 9.72 9.78 9.85 9.9118.5 8.62 8.68 8.74 8.80 8.87 8.93 8.99 9.06 9.12 9.18 9.24 9.31 9.37 9.43 9.50 9.56 9.62 9.69 9.75 9.8119.0 8.53 8.59 8.65 8.72 8.78 8.84 8.90 8.96 9.03 9.09 9.15 9.21 9.28 9.34 9.40 9.46 9.53 9.59 9.65 9.7119.5 8.44 8.50 8.57 8.63 8.69 8.75 8.81 8.87 8.94 9.00 9.06 9.12 9.18 9.25 9.31 9.37 9.43 9.49 9.55 9.6220.0 8.36 8.42 8.48 8.54 8.60 8.66 8.73 8.79 8.85 8.91 8.97 9.03 9.09 9.15 9.21 9.28 9.34 9.40 9.46 9.5220.5 8.28 8.34 8.40 8.46 8.52 8.58 8.64 8.70 8.76 8.82 8.88 8.94 9.00 9.06 9.12 9.18 9.25 9.31 9.37 9.4321.0 8.19 8.25 8.31 8.37 8.43 8.49 8.55 8.61 8.67 8.73 8.79 8.85 8.92 8.98 9.04 9.10 9.16 9.22 9.28 9.3421.5 8.11 8.17 8.23 8.29 8.35 8.41 8.47 8.53 8.59 8.65 8.71 8.77 8.83 8.89 8.95 9.01 9.07 9.13 9.19 9.2522.0 8.04 8.09 8.15 8.21 8.27 8.33 8.39 8.45 8.51 8.57 8.63 8.68 8.74 8.80 8.86 8.92 8.98 9.04 9.10 9.1622.5 7.96 8.02 8.08 8.13 8.19 8.25 8.31 8.37 8.43 8.48 8.54 8.60 8.66 8.72 8.78 8.84 8.89 8.95 9.01 9.0723.0 7.88 7.94 8.00 8.06 8.11 8.17 8.23 8.29 8.35 8.40 8.46 8.52 8.58 8.64 8.69 8.75 8.81 8.87 8.93 8.9823.5 7.81 7.86 7.92 7.98 8.04 8.09 8.15 8.21 8.27 8.33 8.38 8.44 8.50 8.56 8.61 8.67 8.73 8.79 8.84 8.9024.0 7.73 7.79 7.85 7.90 7.96 8.02 8.08 8.13 8.19 8.25 8.30 8.36 8.42 8.48 8.53 8.59 8.65 8.70 8.76 8.8224.5 7.66 7.72 7.77 7.83 7.89 7.94 8.00 8.06 8.11 8.17 8.23 8.28 8.34 8.40 8.45 8.51 8.57 8.62 8.68 8.7425.0 7.59 7.65 7.70 7.76 7.81 7.87 7.93 7.98 8.04 8.10 8.15 8.21 8.26 8.32 8.38 8.43 8.49 8.54 8.60 8.6625.5 7.52 7.58 7.63 7.69 7.74 7.80 7.85 7.91 7.97 8.02 8.08 8.13 8.19 8.24 8.30 8.35 8.41 8.47 8.52 8.5826.0 7.45 7.51 7.56 7.62 7.67 7.73 7.78 7.84 7.89 7.95 8.00 8.06 8.11 8.17 8.22 8.28 8.33 8.39 8.44 8.5026.5 7.38 7.44 7.49 7.55 7.60 7.66 7.71 7.77 7.82 7.88 7.93 7.99 8.04 8.10 8.15 8.20 8.26 8.31 8.37 8.4227.0 7.32 7.37 7.43 7.48 7.53 7.59 7.64 7.70 7.75 7.81 7.86 7.91 7.97 8.02 8.08 8.13 8.19 8.24 8.29 8.3527.5 7.25 7.30 7.36 7.41 7.47 7.52 7.57 7.63 7.68 7.74 7.79 7.84 7.90 7.95 8.01 8.06 8.11 8.17 8.22 8.2728.0 7.19 7.24 7.29 7.35 7.40 7.45 7.51 7.56 7.61 7.67 7.72 7.77 7.83 7.88 7.93 7.99 8.04 8.10 8.15 8.2028.5 7.12 7.18 7.23 7.28 7.33 7.39 7.44 7.49 7.55 7.60 7.65 7.71 7.76 7.81 7.87 7.92 7.97 8.02 8.08 8.1329.0 7.06 7.11 7.16 7.22 7.27 7.32 7.38 7.43 7.48 7.53 7.59 7.64 7.69 7.74 7.80 7.85 7.90 7.95 8.01 8.0629.5 7.00 7.05 7.10 7.15 7.21 7.26 7.31 7.36 7.42 7.47 7.52 7.57 7.62 7.68 7.73 7.78 7.83 7.89 7.94 7.99
22 Chapter A6.2. Dissolved Oxygen Table 6.2–2. Solubility of oxygen in freshwater at various temperatures and pressures.—Continued [Solubility shown in milligrams per liter; values are based on equations published by Benson and Krause (1980, 1984); Temp. (°C), temperature in degrees Celsius; solubility values for atmospheric pressures from 600 to 695 millimeters of mercury are after the values for 0-40 °C] Temp. (deg C) Atmospheric pressure, in millimeters of mercury 700 705 710 715 720 725 730 735 740 745 750 755 760 765 770 775 780 785 790 795 30.0 6.94 6.99 7.04 7.09 7.14 7.20 7.25 7.30 7.35 7.40 7.46 7.51 7.56 7.61 7.66 7.71 7.77 7.82 7.87 7.92 30.5 6.88 6.93 6.98 7.03 7.08 7.13 7.19 7.24 7.29 7.34 7.39 7.44 7.49 7.55 7.60 7.65 7.70 7.75 7.80 7.85 31.0 6.82 6.87 6.92 6.97 7.02 7.07 7.12 7.17 7.23 7.28 7.33 7.38 7.43 7.48 7.53 7.58 7.63 7.69 7.74 7.79 31.5 6.76 6.81 6.86 6.91 6.96 7.01 7.06 7.11 7.16 7.21 7.27 7.32 7.37 7.42 7.47 7.52 7.57 7.62 7.67 7.72 32.0 6.70 6.75 6.80 6.85 6.90 6.95 7.00 7.05 7.10 7.15 7.20 7.25 7.30 7.36 7.41 7.46 7.51 7.56 7.61 7.66 32.5 6.64 6.69 6.74 6.79 6.84 6.89 6.94 6.99 7.04 7.09 7.14 7.19 7.24 7.29 7.34 7.39 7.44 7.49 7.54 7.59

33.0 6.59 6.64 6.69 6.74 6.79 6.84 6.89 6.93 6.98 7.03 7.08 7.13 7.18 7.23 7.28 7.33 7.38 7.43 7.48 7.5333.5 6.53 6.58 6.63 6.68 6.73 6.78 6.83 6.88 6.93 6.98 7.02 7.07 7.12 7.17 7.22 7.27 7.32 7.37 7.42 7.4734.0 6.48 6.53 6.57 6.62 6.67 6.72 6.77 6.82 6.87 6.92 6.97 7.02 7.06 7.11 7.16 7.21 7.26 7.31 7.36 7.4134.5 6.42 6.47 6.52 6.57 6.62 6.67 6.71 6.76 6.81 6.86 6.91 6.96 7.01 7.06 7.10 7.15 7.20 7.25 7.30 7.3535.0 6.37 6.42 6.47 6.51 6.56 6.61 6.66 6.71 6.76 6.80 6.85 6.90 6.95 7.00 7.05 7.09 7.14 7.19 7.24 7.2935.5 6.32 6.36 6.41 6.46 6.51 6.56 6.60 6.65 6.70 6.75 6.80 6.84 6.89 6.94 6.99 7.04 7.08 7.13 7.18 7.2336.0 6.26 6.31 6.36 6.41 6.45 6.50 6.55 6.60 6.65 6.69 6.74 6.79 6.84 6.88 6.93 6.98 7.03 7.08 7.12 7.1736.5 6.21 6.26 6.31 6.35 6.40 6.45 6.50 6.54 6.59 6.64 6.69 6.73 6.78 6.83 6.88 6.92 6.97 7.02 7.07 7.1137.0 6.16 6.21 6.26 6.30 6.35 6.40 6.44 6.49 6.54 6.59 6.63 6.68 6.73 6.77 6.82 6.87 6.92 6.96 7.01 7.0637.5 6.11 6.16 6.20 6.25 6.30 6.35 6.39 6.44 6.49 6.53 6.58 6.63 6.67 6.72 6.77 6.81 6.86 6.91 6.95 7.0038.0 6.06 6.11 6.15 6.20 6.25 6.29 6.34 6.39 6.43 6.48 6.53 6.57 6.62 6.67 6.71 6.76 6.81 6.85 6.90 6.9538.5 6.01 6.06 6.10 6.15 6.20 6.24 6.29 6.34 6.38 6.43 6.47 6.52 6.57 6.61 6.66 6.71 6.75 6.80 6.84 6.8939.0 5.96 6.01 6.05 6.10 6.15 6.19 6.24 6.29 6.33 6.38 6.42 6.47 6.52 6.56 6.61 6.65 6.70 6.75 6.79 6.8439.5 5.91 5.96 6.01 6.05 6.10 6.14 6.19 6.23 6.28 6.33 6.37 6.42 6.46 6.51 6.56 6.60 6.65 6.69 6.74 6.7840.0 5.87 5.91 5.96 6.00 6.05 6.09 6.14 6.19 6.23 6.28 6.32 6.37 6.41 6.46 6.50 6.55 6.59 6.64 6.69 6.73
References Cited 23

Temp.

(deg C)

Atmospheric pressure, in millimeters of mercury

600 605 610 615 620 625 630 635 640 645 650 655 660 665 670 675 680 685 690 695

0.0 11.53 11.62 11.72 11.82 11.91 12.01 12.11 12.20 12.30 12.40 12.49 12.59 12.69 12.78 12.88 12.98 13.07 13.17 13.27 13.360.5 11.36 11.46 11.56 11.65 11.75 11.84 11.94 12.03 12.13 12.22 12.32 12.41 12.51 12.60 12.70 12.80 12.89 12.99 13.08 13.181.0 11.21 11.30 11.39 11.49 11.58 11.68 11.77 11.86 11.96 12.05 12.15 12.24 12.34 12.43 12.52 12.62 12.71 12.81 12.90 12.991.5 11.05 11.14 11.24 11.33 11.42 11.52 11.61 11.70 11.79 11.89 11.98 12.07 12.17 12.26 12.35 12.44 12.54 12.63 12.72 12.812.0 10.90 10.99 11.08 11.18 11.27 11.36 11.45 11.54 11.63 11.72 11.82 11.91 12.00 12.09 12.18 12.27 12.37 12.46 12.55 12.642.5 10.75 10.84 10.93 11.02 11.11 11.20 11.29 11.39 11.48 11.57 11.66 11.75 11.84 11.93 12.02 12.11 12.20 12.29 12.38 12.473.0 10.61 10.70 10.79 10.88 10.96 11.05 11.14 11.23 11.32 11.41 11.50 11.59 11.68 11.77 11.86 11.95 12.03 12.12 12.21 12.303.5 10.47 10.55 10.64 10.73 10.82 10.91 10.99 11.08 11.17 11.26 11.35 11.43 11.52 11.61 11.70 11.79 11.87 11.96 12.05 12.144.0 10.33 10.42 10.50 10.59 10.68 10.76 10.85 10.94 11.02 11.11 11.20 11.28 11.37 11.46 11.54 11.63 11.72 11.81 11.89 11.984.5 10.19 10.28 10.36 10.45 10.54 10.62 10.71 10.79 10.88 10.97 11.05 11.14 11.22 11.31 11.39 11.48 11.57 11.65 11.74 11.825.0 10.06 10.15 10.23 10.32 10.40 10.48 10.57 10.65 10.74 10.82 10.91 10.99 11.08 11.16 11.25 11.33 11.42 11.50 11.59 11.675.5 9.93 10.02 10.10 10.18 10.27 10.35 10.43 10.52 10.60 10.68 10.77 10.85 10.94 11.02 11.10 11.19 11.27 11.35 11.44 11.526.0 9.80 9.89 9.97 10.05 10.14 10.22 10.30 10.38 10.47 10.55 10.63 10.71 10.80 10.88 10.96 11.04 11.13 11.21 11.29 11.376.5 9.68 9.76 9.84 9.93 10.01 10.09 10.17 10.25 10.33 10.42 10.50 10.58 10.66 10.74 10.82 10.91 10.99 11.07 11.15 11.237.0 9.56 9.64 9.72 9.80 9.88 9.96 10.04 10.12 10.20 10.29 10.37 10.45 10.53 10.61 10.69 10.77 10.85 10.93 11.01 11.097.5 9.44 9.52 9.60 9.68 9.76 9.84 9.92 10.00 10.08 10.16 10.24 10.32 10.40 10.48 10.56 10.64 10.72 10.80 10.87 10.958.0 9.33 9.40 9.48 9.56 9.64 9.72 9.80 9.88 9.95 10.03 10.11 10.19 10.27 10.35 10.43 10.51 10.58 10.66 10.74 10.828.5 9.21 9.29 9.37 9.44 9.52 9.60 9.68 9.76 9.83 9.91 9.99 10.07 10.14 10.22 10.30 10.38 10.46 10.53 10.61 10.699.0 9.10 9.18 9.25 9.33 9.41 9.48 9.56 9.64 9.71 9.79 9.87 9.95 10.02 10.10 10.18 10.25 10.33 10.41 10.48 10.569.5 8.99 9.07 9.14 9.22 9.29 9.37 9.45 9.52 9.60 9.67 9.75 9.83 9.90 9.98 10.05 10.13 10.21 10.28 10.36 10.43

10.0 8.88 8.96 9.03 9.11 9.18 9.26 9.33 9.41 9.49 9.56 9.64 9.71 9.79 9.86 9.94 10.01 10.09 10.16 10.24 10.3110.5 8.78 8.85 8.93 9.00 9.08 9.15 9.23 9.30 9.37 9.45 9.52 9.60 9.67 9.75 9.82 9.89 9.97 10.04 10.12 10.19

11.0 8.68 8.75 8.82 8.90 8.97 9.04 9.12 9.19 9.26 9.34 9.41 9.48 9.56 9.63 9.71 9.78 9.85 9.93 10.00 10.0711.5 8.58 8.65 8.72 8.79 8.87 8.94 9.01 9.08 9.16 9.23 9.30 9.38 9.45 9.52 9.59 9.67 9.74 9.81 9.88 9.96

12.0 8.48 8.55 8.62 8.69 8.77 8.84 8.91 8.98 9.05 9.12 9.20 9.27 9.34 9.41 9.48 9.56 9.63 9.70 9.77 9.8412.5 8.38 8.45 8.52 8.59 8.67 8.74 8.81 8.88 8.95 9.02 9.09 9.16 9.23 9.31 9.38 9.45 9.52 9.59 9.66 9.7313.0 8.29 8.36 8.43 8.50 8.57 8.64 8.71 8.78 8.85 8.92 8.99 9.06 9.13 9.20 9.27 9.34 9.41 9.48 9.55 9.6213.5 8.19 8.26 8.33 8.40 8.47 8.54 8.61 8.68 8.75 8.82 8.89 8.96 9.03 9.10 9.17 9.24 9.31 9.38 9.45 9.5214.0 8.10 8.17 8.24 8.31 8.38 8.45 8.52 8.58 8.65 8.72 8.79 8.86 8.93 9.00 9.07 9.14 9.20 9.27 9.34 9.4114.5 8.01 8.08 8.15 8.22 8.29 8.35 8.42 8.49 8.56 8.63 8.69 8.76 8.83 8.90 8.97 9.04 9.10 9.17 9.24 9.3115.0 7.93 7.99 8.06 8.13 8.20 8.26 8.33 8.40 8.47 8.53 8.60 8.67 8.74 8.80 8.87 8.94 9.00 9.07 9.14 9.21

Table 6.2–2. Solubility of oxygen in freshwater at various temperatures and pressures.—Continued[Solubility shown in milligrams per liter; values are based on equations published by Benson and Krause (1980, 1984); Temp. (°C), temperature in degrees Celsius]
24 Chapter A6.2. Dissolved Oxygen Temp. (deg C) Atmospheric pressure, in millimeters of mercury 600 605 610 615 620 625 630 635 640 645 650 655 660 665 670 675 680 685 690 695 15.5 7.84 7.91 7.97 8.04 8.11 8.17 8.24 8.31 8.37 8.44 8.51 8.57 8.64 8.71 8.77 8.84 8.91 8.97 9.04 9.11 16.0 7.76 7.82 7.89 7.95 8.02 8.09 8.15 8.22 8.28 8.35 8.42 8.48 8.55 8.61 8.68 8.75 8.81 8.88 8.95 9.01 16.5 7.67 7.74 7.80 7.87 7.93 8.00 8.07 8.13 8.20 8.26 8.33 8.39 8.46 8.52 8.59 8.65 8.72 8.79 8.85 8.92 17.0 7.59 7.66 7.72 7.79 7.85 7.92 7.98 8.05 8.11 8.17 8.24 8.30 8.37 8.43 8.50 8.56 8.63 8.69 8.76 8.82 17.5 7.51 7.58 7.64 7.70 7.77 7.83 7.90 7.96 8.03 8.09 8.15 8.22 8.28 8.35 8.41 8.47 8.54 8.60 8.67 8.73 18.0 7.43 7.50 7.56 7.62 7.69 7.75 7.81 7.88 7.94 8.01 8.07 8.13 8.20 8.26 8.32 8.39 8.45 8.51 8.58 8.64

18.5 7.36 7.42 7.48 7.55 7.61 7.67 7.73 7.80 7.86 7.92 7.99 8.05 8.11 8.18 8.24 8.30 8.36 8.43 8.49 8.5519.0 7.28 7.34 7.41 7.47 7.53 7.59 7.66 7.72 7.78 7.84 7.90 7.97 8.03 8.09 8.15 8.22 8.28 8.34 8.40 8.4719.5 7.21 7.27 7.33 7.39 7.45 7.52 7.58 7.64 7.70 7.76 7.82 7.89 7.95 8.01 8.07 8.13 8.20 8.26 8.32 8.3820.0 7.13 7.20 7.26 7.32 7.38 7.44 7.50 7.56 7.62 7.68 7.75 7.81 7.87 7.93 7.99 8.05 8.11 8.17 8.24 8.3020.5 7.06 7.12 7.18 7.24 7.31 7.37 7.43 7.49 7.55 7.61 7.67 7.73 7.79 7.85 7.91 7.97 8.03 8.09 8.15 8.2121.0 6.99 7.05 7.11 7.17 7.23 7.29 7.35 7.41 7.47 7.53 7.59 7.65 7.71 7.77 7.83 7.89 7.95 8.01 8.07 8.1321.5 6.92 6.98 7.04 7.10 7.16 7.22 7.28 7.34 7.40 7.46 7.52 7.58 7.64 7.70 7.76 7.82 7.88 7.94 7.99 8.0522.0 6.85 6.91 6.97 7.03 7.09 7.15 7.21 7.27 7.33 7.39 7.45 7.50 7.56 7.62 7.68 7.74 7.80 7.86 7.92 7.9822.5 6.79 6.85 6.90 6.96 7.02 7.08 7.14 7.20 7.26 7.31 7.37 7.43 7.49 7.55 7.61 7.67 7.72 7.78 7.84 7.9023.0 6.72 6.78 6.84 6.90 6.95 7.01 7.07 7.13 7.19 7.24 7.30 7.36 7.42 7.48 7.53 7.59 7.65 7.71 7.77 7.8223.5 6.66 6.71 6.77 6.83 6.89 6.94 7.00 7.06 7.12 7.17 7.23 7.29 7.35 7.40 7.46 7.52 7.58 7.63 7.69 7.7524.0 6.59 6.65 6.71 6.76 6.82 6.88 6.94 6.99 7.05 7.11 7.16 7.22 7.28 7.33 7.39 7.45 7.51 7.56 7.62 7.6824.5 6.53 6.59 6.64 6.70 6.76 6.81 6.87 6.93 6.98 7.04 7.10 7.15 7.21 7.27 7.32 7.38 7.44 7.49 7.55 7.6125.0 6.47 6.52 6.58 6.64 6.69 6.75 6.81 6.86 6.92 6.97 7.03 7.09 7.14 7.20 7.25 7.31 7.37 7.42 7.48 7.5325.5 6.41 6.46 6.52 6.57 6.63 6.69 6.74 6.80 6.85 6.91 6.96 7.02 7.08 7.13 7.19 7.24 7.30 7.35 7.41 7.4626.0 6.35 6.40 6.46 6.51 6.57 6.62 6.68 6.73 6.79 6.84 6.90 6.95 7.01 7.07 7.12 7.18 7.23 7.29 7.34 7.4026.5 6.29 6.34 6.40 6.45 6.51 6.56 6.62 6.67 6.73 6.78 6.84 6.89 6.95 7.00 7.06 7.11 7.16 7.22 7.27 7.3327.0 6.23 6.28 6.34 6.39 6.45 6.50 6.56 6.61 6.67 6.72 6.77 6.83 6.88 6.94 6.99 7.05 7.10 7.15 7.21 7.2627.5 6.17 6.23 6.28 6.33 6.39 6.44 6.50 6.55 6.60 6.66 6.71 6.77 6.82 6.87 6.93 6.98 7.04 7.09 7.14 7.2028.0 6.12 6.17 6.22 6.28 6.33 6.38 6.44 6.49 6.54 6.60 6.65 6.70 6.76 6.81 6.87 6.92 6.97 7.03 7.08 7.1328.5 6.06 6.11 6.17 6.22 6.27 6.33 6.38 6.43 6.49 6.54 6.59 6.64 6.70 6.75 6.80 6.86 6.91 6.96 7.02 7.0729.0 6.01 6.06 6.11 6.16 6.22 6.27 6.32 6.37 6.43 6.48 6.53 6.59 6.64 6.69 6.74 6.80 6.85 6.90 6.95 7.0129.5 5.95 6.00 6.06 6.11 6.16 6.21 6.27 6.32 6.37 6.42 6.47 6.53 6.58 6.63 6.68 6.74 6.79 6.84 6.89 6.9530.0 5.90 5.95 6.00 6.05 6.11 6.16 6.21 6.26 6.31 6.37 6.42 6.47 6.52 6.57 6.63 6.68 6.73 6.78 6.83 6.8830.5 5.85 5.90 5.95 6.00 6.05 6.10 6.16 6.21 6.26 6.31 6.36 6.41 6.46 6.52 6.57 6.62 6.67 6.72 6.77 6.82

Table 6.2–2. Solubility of oxygen in freshwater at various temperatures and pressures.—Continued[Solubility shown in milligrams per liter; values are based on equations published by Benson and Krause (1980, 1984); Temp. (°C), temperature in degrees Celsius]
References Cited 25

Temp.

(deg C)

Atmospheric pressure, in millimeters of mercury

600 605 610 615 620 625 630 635 640 645 650 655 660 665 670 675 680 685 690 695

31.0 5.79 5.85 5.90 5.95 6.00 6.05 6.10 6.15 6.20 6.25 6.31 6.36 6.41 6.46 6.51 6.56 6.61 6.66 6.71 6.7731.5 5.74 5.79 5.84 5.90 5.95 6.00 6.05 6.10 6.15 6.20 6.25 6.30 6.35 6.40 6.45 6.50 6.55 6.61 6.66 6.7132.0 5.69 5.74 5.79 5.84 5.89 5.94 5.99 6.04 6.10 6.15 6.20 6.25 6.30 6.35 6.40 6.45 6.50 6.55 6.60 6.6532.5 5.64 5.69 5.74 5.79 5.84 5.89 5.94 5.99 6.04 6.09 6.14 6.19 6.24 6.29 6.34 6.39 6.44 6.49 6.54 6.5933.0 5.59 5.64 5.69 5.74 5.79 5.84 5.89 5.94 5.99 6.04 6.09 6.14 6.19 6.24 6.29 6.34 6.39 6.44 6.49 6.5433.5 5.54 5.59 5.64 5.69 5.74 5.79 5.84 5.89 5.94 5.99 6.04 6.09 6.14 6.19 6.24 6.28 6.33 6.38 6.43 6.4834.0 5.50 5.54 5.59 5.64 5.69 5.74 5.79 5.84 5.89 5.94 5.99 6.04 6.08 6.13 6.18 6.23 6.28 6.33 6.38 6.4334.5 5.45 5.50 5.55 5.59 5.64 5.69 5.74 5.79 5.84 5.89 5.94 5.98 6.03 6.08 6.13 6.18 6.23 6.28 6.32 6.3735.0 5.40 5.45 5.50 5.55 5.59 5.64 5.69 5.74 5.79 5.84 5.88 5.93 5.98 6.03 6.08 6.13 6.18 6.22 6.27 6.3235.5 5.35 5.40 5.45 5.50 5.55 5.59 5.64 5.69 5.74 5.79 5.84 5.88 5.93 5.98 6.03 6.08 6.12 6.17 6.22 6.2736.0 5.31 5.36 5.40 5.45 5.50 5.55 5.60 5.64 5.69 5.74 5.79 5.83 5.88 5.93 5.98 6.02 6.07 6.12 6.17 6.2236.5 5.26 5.31 5.36 5.41 5.45 5.50 5.55 5.60 5.64 5.69 5.74 5.78 5.83 5.88 5.93 5.97 6.02 6.07 6.12 6.1637.0 5.22 5.27 5.31 5.36 5.41 5.45 5.50 5.55 5.60 5.64 5.69 5.74 5.78 5.83 5.88 5.93 5.97 6.02 6.07 6.1137.5 5.17 5.22 5.27 5.31 5.36 5.41 5.45 5.50 5.55 5.60 5.64 5.69 5.74 5.78 5.83 5.88 5.92 5.97 6.02 6.0638.0 5.13 5.18 5.22 5.27 5.32 5.36 5.41 5.46 5.50 5.55 5.60 5.64 5.69 5.73 5.78 5.83 5.87 5.92 5.97 6.0138.5 5.09 5.13 5.18 5.22 5.27 5.32 5.36 5.41 5.46 5.50 5.55 5.59 5.64 5.69 5.73 5.78 5.83 5.87 5.92 5.9739.0 5.04 5.09 5.13 5.18 5.23 5.27 5.32 5.36 5.41 5.46 5.50 5.55 5.59 5.64 5.69 5.73 5.78 5.82 5.87 5.9239.5 5.00 5.05 5.09 5.14 5.18 5.23 5.27 5.32 5.37 5.41 5.46 5.50 5.55 5.59 5.64 5.69 5.73 5.78 5.82 5.8740.0 4.96 5.00 5.05 5.09 5.14 5.18 5.23 5.28 5.32 5.37 5.41 5.46 5.50 5.55 5.59 5.64 5.69 5.73 5.78 5.82

Table 6.2–2. Solubility of oxygen in freshwater at various temperatures and pressures.—Continued[Solubility shown in milligrams per liter; values are based on equations published by Benson and Krause (1980, 1984); Temp. (°C), temperature in degrees Celsius]
26 Chapter A6.2. Dissolved Oxygen Table 6.2–4. Salinity correction factors for dissolved oxygen in water (based on specific conductance). [Factors are dimensionless; values are based on equations published by Benson and Krause (1984); Temp. (°C), temperature in degrees Celsius] Temp. (deg C) Specific conductance, in microsiemens per centimeter at 25 degrees Celsius 0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 10,000 11,000 12,000 13,000 14,000 0.0 1.0000 0.9961 0.9922 0.9882 0.9843 0.9804 0.9764 0.9724 0.9684 0.9644 0.9604 0.9564 0.9524 0.9483 0.9443 1.0 1.0000 0.9961 0.9923 0.9884 0.9845 0.9805 0.9766 0.9727 0.9687 0.9648 0.9608 0.9568 0.9528 0.9488 0.9448 2.0 1.0000 0.9962 0.9923 0.9885 0.9846 0.9807 0.9768 0.9729 0.9690 0.9651 0.9611 0.9572 0.9532 0.9493 0.9453 3.0 1.0000 0.9962 0.9924 0.9886 0.9847 0.9809 0.9770 0.9732 0.9693 0.9654 0.9615 0.9576 0.9536 0.9497 0.9458 4.0 1.0000 0.9962 0.9925 0.9887 0.9849 0.9811 0.9772 0.9734 0.9696 0.9657 0.9618 0.9579 0.9541 0.9502 0.9462 5.0 1.0000 0.9963 0.9925 0.9888 0.9850 0.9812 0.9774 0.9736 0.9698 0.9660 0.9622 0.9583 0.9545 0.9506 0.9467

6.0 1.0000 0.9963 0.9926 0.9889 0.9851 0.9814 0.9776 0.9739 0.9701 0.9663 0.9625 0.9587 0.9549 0.9510 0.94727.0 1.0000 0.9963 0.9927 0.9890 0.9853 0.9816 0.9778 0.9741 0.9703 0.9666 0.9628 0.9590 0.9552 0.9514 0.94768.0 1.0000 0.9964 0.9927 0.9891 0.9854 0.9817 0.9780 0.9743 0.9706 0.9669 0.9631 0.9594 0.9556 0.9519 0.94819.0 1.0000 0.9964 0.9928 0.9892 0.9855 0.9819 0.9782 0.9745 0.9708 0.9672 0.9634 0.9597 0.9560 0.9523 0.9485

10.0 1.0000 0.9964 0.9928 0.9893 0.9856 0.9820 0.9784 0.9747 0.9711 0.9674 0.9637 0.9601 0.9564 0.9527 0.9489

11.0 1.0000 0.9965 0.9929 0.9893 0.9858 0.9822 0.9786 0.9750 0.9713 0.9677 0.9640 0.9604 0.9567 0.9530 0.9494

12.0 1.0000 0.9965 0.9930 0.9894 0.9859 0.9823 0.9787 0.9752 0.9716 0.9680 0.9643 0.9607 0.9571 0.9534 0.949813.0 1.0000 0.9965 0.9930 0.9895 0.9860 0.9825 0.9789 0.9754 0.9718 0.9682 0.9646 0.9610 0.9574 0.9538 0.950214.0 1.0000 0.9965 0.9931 0.9896 0.9861 0.9826 0.9791 0.9756 0.9720 0.9685 0.9649 0.9613 0.9578 0.9542 0.950615.0 1.0000 0.9966 0.9931 0.9897 0.9862 0.9827 0.9793 0.9758 0.9723 0.9687 0.9652 0.9617 0.9581 0.9545 0.951016.0 1.0000 0.9966 0.9932 0.9898 0.9863 0.9829 0.9794 0.9760 0.9725 0.9690 0.9655 0.9620 0.9584 0.9549 0.951317.0 1.0000 0.9966 0.9932 0.9898 0.9864 0.9830 0.9796 0.9761 0.9727 0.9692 0.9657 0.9622 0.9587 0.9552 0.951718.0 1.0000 0.9967 0.9933 0.9899 0.9865 0.9831 0.9797 0.9763 0.9729 0.9695 0.9660 0.9625 0.9591 0.9556 0.952119.0 1.0000 0.9967 0.9933 0.9900 0.9866 0.9833 0.9799 0.9765 0.9731 0.9697 0.9663 0.9628 0.9594 0.9559 0.952420.0 1.0000 0.9967 0.9934 0.9901 0.9867 0.9834 0.9800 0.9767 0.9733 0.9699 0.9665 0.9631 0.9597 0.9562 0.952821.0 1.0000 0.9967 0.9934 0.9902 0.9868 0.9835 0.9802 0.9769 0.9735 0.9701 0.9668 0.9634 0.9600 0.9566 0.953122.0 1.0000 0.9968 0.9935 0.9902 0.9869 0.9836 0.9803 0.9770 0.9737 0.9704 0.9670 0.9636 0.9603 0.9569 0.953523.0 1.0000 0.9968 0.9935 0.9903 0.9870 0.9838 0.9805 0.9772 0.9739 0.9706 0.9672 0.9639 0.9605 0.9572 0.953824.0 1.0000 0.9968 0.9936 0.9904 0.9871 0.9839 0.9806 0.9774 0.9741 0.9708 0.9675 0.9642 0.9608 0.9575 0.954125.0 1.0000 0.9968 0.9936 0.9904 0.9872 0.9840 0.9808 0.9775 0.9743 0.9710 0.9677 0.9644 0.9611 0.9578 0.954526.0 1.0000 0.9968 0.9937 0.9905 0.9873 0.9841 0.9809 0.9777 0.9744 0.9712 0.9679 0.9647 0.9614 0.9581 0.954827.0 1.0000 0.9969 0.9937 0.9906 0.9874 0.9842 0.9810 0.9778 0.9746 0.9714 0.9681 0.9649 0.9616 0.9584 0.955128.0 1.0000 0.9969 0.9938 0.9906 0.9875 0.9843 0.9812 0.9780 0.9748 0.9716 0.9684 0.9651 0.9619 0.9586 0.955429.0 1.0000 0.9969 0.9938 0.9907 0.9876 0.9844 0.9813 0.9781 0.9750 0.9718 0.9686 0.9654 0.9621 0.9589 0.9557
References Cited 27

Table 6.2–4. Salinity correction factors for dissolved oxygen in water (based on specific conductance).—Continued[Factors are dimensionless; values are based on equations published by Benson and Krause (1984); Temp. (°C), temperature in degrees Celsius]

Temp. 

(deg C)

Specific conductance, in microsiemens per centimeter at 25 degrees Celsius

15,000 16,000 17,000 18,000 19,000 20,000 21,000 22,000 23,000 24,000 25,000 26,000 27,000 28,000 29,000

0.0 0.9402 0.9361 0.9321 0.9280 0.9239 0.9198 0.9157 0.9116 0.9074 0.9033 0.8992 0.8950 0.8909 0.8867 0.88261.0 0.9408 0.9367 0.9327 0.9286 0.9246 0.9205 0.9164 0.9124 0.9083 0.9042 0.9001 0.8960 0.8918 0.8877 0.88362.0 0.9413 0.9373 0.9333 0.9293 0.9252 0.9212 0.9172 0.9131 0.9091 0.9050 0.9009 0.8969 0.8928 0.8887 0.88463.0 0.9418 0.9378 0.9339 0.9299 0.9259 0.9219 0.9179 0.9139 0.9099 0.9058 0.9018 0.8978 0.8937 0.8897 0.88564.0 0.9423 0.9384 0.9345 0.9305 0.9266 0.9226 0.9186 0.9146 0.9107 0.9067 0.9027 0.8986 0.8946 0.8906 0.88665.0 0.9428 0.9389 0.9350 0.9311 0.9272 0.9233 0.9193 0.9154 0.9114 0.9075 0.9035 0.8995 0.8955 0.8915 0.88756.0 0.9433 0.9395 0.9356 0.9317 0.9278 0.9239 0.9200 0.9161 0.9122 0.9082 0.9043 0.9004 0.8964 0.8924 0.88857.0 0.9438 0.9400 0.9361 0.9323 0.9284 0.9246 0.9207 0.9168 0.9129 0.9090 0.9051 0.9012 0.8973 0.8933 0.88948.0 0.9443 0.9405 0.9367 0.9329 0.9290 0.9252 0.9213 0.9175 0.9136 0.9098 0.9059 0.9020 0.8981 0.8942 0.89039.0 0.9447 0.9410 0.9372 0.9334 0.9296 0.9258 0.9220 0.9182 0.9143 0.9105 0.9067 0.9028 0.8989 0.8951 0.8912

10.0 0.9452 0.9415 0.9377 0.9340 0.9302 0.9264 0.9226 0.9188 0.9150 0.9112 0.9074 0.9036 0.8998 0.8959 0.8921

11.0 0.9457 0.9419 0.9382 0.9345 0.9308 0.9270 0.9233 0.9195 0.9157 0.9119 0.9082 0.9044 0.9006 0.8968 0.8929

12.0 0.9461 0.9424 0.9387 0.9350 0.9313 0.9276 0.9239 0.9201 0.9164 0.9126 0.9089 0.9051 0.9014 0.8976 0.893813.0 0.9465 0.9429 0.9392 0.9355 0.9319 0.9282 0.9245 0.9208 0.9171 0.9133 0.9096 0.9059 0.9021 0.8984 0.894614.0 0.9470 0.9433 0.9397 0.9361 0.9324 0.9287 0.9251 0.9214 0.9177 0.9140 0.9103 0.9066 0.9029 0.8992 0.895415.0 0.9474 0.9438 0.9402 0.9366 0.9329 0.9293 0.9257 0.9220 0.9183 0.9147 0.9110 0.9073 0.9036 0.8999 0.896216.0 0.9478 0.9442 0.9406 0.9370 0.9334 0.9298 0.9262 0.9226 0.9190 0.9153 0.9117 0.9080 0.9044 0.9007 0.897017.0 0.9482 0.9446 0.9411 0.9375 0.9340 0.9304 0.9268 0.9232 0.9196 0.9160 0.9123 0.9087 0.9051 0.9014 0.897818.0 0.9486 0.9451 0.9415 0.9380 0.9345 0.9309 0.9273 0.9238 0.9202 0.9166 0.9130 0.9094 0.9058 0.9022 0.898519.0 0.9490 0.9455 0.9420 0.9385 0.9349 0.9314 0.9279 0.9243 0.9208 0.9172 0.9136 0.9101 0.9065 0.9029 0.899320.0 0.9493 0.9459 0.9424 0.9389 0.9354 0.9319 0.9284 0.9249 0.9214 0.9178 0.9143 0.9107 0.9071 0.9036 0.900021.0 0.9497 0.9463 0.9428 0.9394 0.9359 0.9324 0.9289 0.9254 0.9219 0.9184 0.9149 0.9114 0.9078 0.9043 0.900722.0 0.9501 0.9467 0.9432 0.9398 0.9363 0.9329 0.9294 0.9260 0.9225 0.9190 0.9155 0.9120 0.9085 0.9049 0.901423.0 0.9504 0.9470 0.9436 0.9402 0.9368 0.9334 0.9299 0.9265 0.9230 0.9196 0.9161 0.9126 0.9091 0.9056 0.902124.0 0.9508 0.9474 0.9440 0.9406 0.9372 0.9338 0.9304 0.9270 0.9236 0.9201 0.9167 0.9132 0.9097 0.9063 0.902825.0 0.9511 0.9478 0.9444 0.9411 0.9377 0.9343 0.9309 0.9275 0.9241 0.9207 0.9172 0.9138 0.9104 0.9069 0.903426.0 0.9515 0.9481 0.9448 0.9415 0.9381 0.9347 0.9314 0.9280 0.9246 0.9212 0.9178 0.9144 0.9110 0.9075 0.904127.0 0.9518 0.9485 0.9452 0.9419 0.9385 0.9352 0.9318 0.9285 0.9251 0.9217 0.9183 0.9149 0.9115 0.9081 0.904728.0 0.9521 0.9488 0.9455 0.9422 0.9389 0.9356 0.9323 0.9289 0.9256 0.9222 0.9189 0.9155 0.9121 0.9087 0.905329.0 0.9524 0.9492 0.9459 0.9426 0.9393 0.9360 0.9327 0.9294 0.9261 0.9228 0.9194 0.9161 0.9127 0.9093 0.9060
28 Chapter A6.2. Dissolved Oxygen Temp. (deg C) Specific conductance, in microsiemens per centimeter at 25 degrees Celsius 30,000 31,000 32,000 33,000 34,000 35,000 36,000 37,000 38,000 39,000 40,000 41,000 42,000 43,000 44,000 0.0 0.8784 0.8742 0.8701 0.8659 0.8617 0.8575 0.8533 0.8491 0.8449 0.8407 0.8365 0.8323 0.8281 0.8239 0.8197 1.0 0.8795 0.8753 0.8712 0.8670 0.8629 0.8587 0.8546 0.8504 0.8462 0.8421 0.8379 0.8337 0.8296 0.8254 0.8212 2.0 0.8805 0.8764 0.8723 0.8682 0.8641 0.8599 0.8558 0.8517 0.8476 0.8434 0.8393 0.8351 0.8310 0.8268 0.8227 3.0 0.8815 0.8775 0.8734 0.8693 0.8652 0.8611 0.8570 0.8529 0.8488 0.8447 0.8406 0.8365 0.8324 0.8283 0.8242 4.0 0.8825 0.8785 0.8745 0.8704 0.8664 0.8623 0.8582 0.8542 0.8501 0.8460 0.8419 0.8379 0.8338 0.8297 0.8256 5.0 0.8835 0.8795 0.8755 0.8715 0.8675 0.8635 0.8594 0.8554 0.8513 0.8473 0.8433 0.8392 0.8351 0.8311 0.8270

6.0 0.8845 0.8805 0.8766 0.8726 0.8686 0.8646 0.8606 0.8566 0.8526 0.8485 0.8445 0.8405 0.8365 0.8325 0.82847.0 0.8855 0.8815 0.8776 0.8736 0.8697 0.8657 0.8617 0.8577 0.8538 0.8498 0.8458 0.8418 0.8378 0.8338 0.82988.0 0.8864 0.8825 0.8786 0.8746 0.8707 0.8668 0.8628 0.8589 0.8549 0.8510 0.8470 0.8431 0.8391 0.8351 0.83119.0 0.8873 0.8834 0.8796 0.8757 0.8718 0.8678 0.8639 0.8600 0.8561 0.8522 0.8482 0.8443 0.8404 0.8364 0.8325

10.0 0.8882 0.8844 0.8805 0.8766 0.8728 0.8689 0.8650 0.8611 0.8572 0.8533 0.8494 0.8455 0.8416 0.8377 0.8338

11.0 0.8891 0.8853 0.8815 0.8776 0.8738 0.8699 0.8661 0.8622 0.8583 0.8545 0.8506 0.8467 0.8428 0.8389 0.8351

12.0 0.8900 0.8862 0.8824 0.8786 0.8748 0.8709 0.8671 0.8633 0.8594 0.8556 0.8517 0.8479 0.8440 0.8402 0.836313.0 0.8908 0.8871 0.8833 0.8795 0.8757 0.8719 0.8681 0.8643 0.8605 0.8567 0.8529 0.8490 0.8452 0.8414 0.837514.0 0.8917 0.8879 0.8842 0.8804 0.8767 0.8729 0.8691 0.8654 0.8616 0.8578 0.8540 0.8502 0.8464 0.8426 0.838815.0 0.8925 0.8888 0.8851 0.8813 0.8776 0.8739 0.8701 0.8664 0.8626 0.8588 0.8551 0.8513 0.8475 0.8437 0.840016.0 0.8933 0.8896 0.8859 0.8822 0.8785 0.8748 0.8711 0.8674 0.8636 0.8599 0.8561 0.8524 0.8486 0.8449 0.841117.0 0.8941 0.8905 0.8868 0.8831 0.8794 0.8757 0.8720 0.8683 0.8646 0.8609 0.8572 0.8535 0.8497 0.8460 0.842318.0 0.8949 0.8913 0.8876 0.8840 0.8803 0.8766 0.8730 0.8693 0.8656 0.8619 0.8582 0.8545 0.8508 0.8471 0.843419.0 0.8957 0.8921 0.8884 0.8848 0.8812 0.8775 0.8739 0.8702 0.8666 0.8629 0.8592 0.8556 0.8519 0.8482 0.844520.0 0.8964 0.8928 0.8892 0.8856 0.8820 0.8784 0.8748 0.8711 0.8675 0.8639 0.8602 0.8566 0.8529 0.8493 0.845621.0 0.8972 0.8936 0.8900 0.8864 0.8828 0.8793 0.8757 0.8720 0.8684 0.8648 0.8612 0.8576 0.8539 0.8503 0.846722.0 0.8979 0.8943 0.8908 0.8872 0.8837 0.8801 0.8765 0.8729 0.8693 0.8658 0.8622 0.8585 0.8549 0.8513 0.847723.0 0.8986 0.8951 0.8915 0.8880 0.8845 0.8809 0.8774 0.8738 0.8702 0.8667 0.8631 0.8595 0.8559 0.8523 0.848724.0 0.8993 0.8958 0.8923 0.8888 0.8853 0.8817 0.8782 0.8747 0.8711 0.8676 0.8640 0.8605 0.8569 0.8533 0.849725.0 0.9000 0.8965 0.8930 0.8895 0.8860 0.8825 0.8790 0.8755 0.8720 0.8685 0.8649 0.8614 0.8578 0.8543 0.850726.0 0.9006 0.8972 0.8937 0.8903 0.8868 0.8833 0.8798 0.8763 0.8728 0.8693 0.8658 0.8623 0.8588 0.8552 0.851727.0 0.9013 0.8979 0.8944 0.8910 0.8875 0.8841 0.8806 0.8771 0.8736 0.8702 0.8667 0.8632 0.8597 0.8562 0.852728.0 0.9019 0.8985 0.8951 0.8917 0.8883 0.8848 0.8814 0.8779 0.8745 0.8710 0.8675 0.8641 0.8606 0.8571 0.853629.0 0.9026 0.8992 0.8958 0.8924 0.8890 0.8856 0.8821 0.8787 0.8753 0.8718 0.8684 0.8649 0.8615 0.8580 0.8545

Table 6.2–4. Salinity correction factors for dissolved oxygen in water (based on specific conductance).—Continued[Factors are dimensionless; values are based on equations published by Benson and Krause (1984); Temp. (°C), temperature in degrees Celsius]
References Cited 29

Temp. 

(deg C)

Specific conductance, in microsiemens per centimeter at 25 degrees Celsius

45,000 46,000 47,000 48,000 49,000 50,000 51,000 52,000 53,000 54,000 55,000 56,000 57,000 58,000 59,000

0.0 0.8155 0.8112 0.8070 0.8028 0.7986 0.7944 0.7901 0.7859 0.7817 0.7775 0.7733 0.7691 0.7648 0.7606 0.75641.0 0.8170 0.8128 0.8086 0.8045 0.8003 0.7961 0.7919 0.7877 0.7835 0.7793 0.7751 0.7709 0.7668 0.7626 0.75842.0 0.8185 0.8144 0.8102 0.8061 0.8019 0.7978 0.7936 0.7894 0.7853 0.7811 0.7770 0.7728 0.7686 0.7645 0.76033.0 0.8200 0.8159 0.8118 0.8077 0.8035 0.7994 0.7953 0.7911 0.7870 0.7829 0.7788 0.7746 0.7705 0.7664 0.76234.0 0.8215 0.8174 0.8133 0.8092 0.8051 0.8010 0.7969 0.7928 0.7887 0.7846 0.7805 0.7764 0.7723 0.7682 0.76415.0 0.8230 0.8189 0.8148 0.8108 0.8067 0.8026 0.7986 0.7945 0.7904 0.7863 0.7823 0.7782 0.7741 0.7700 0.76606.0 0.8244 0.8204 0.8163 0.8123 0.8082 0.8042 0.8002 0.7961 0.7921 0.7880 0.7840 0.7799 0.7759 0.7718 0.76787.0 0.8258 0.8218 0.8178 0.8138 0.8098 0.8057 0.8017 0.7977 0.7937 0.7897 0.7857 0.7816 0.7776 0.7736 0.76968.0 0.8272 0.8232 0.8192 0.8152 0.8112 0.8073 0.8033 0.7993 0.7953 0.7913 0.7873 0.7833 0.7793 0.7753 0.77139.0 0.8285 0.8246 0.8206 0.8167 0.8127 0.8088 0.8048 0.8008 0.7969 0.7929 0.7889 0.7850 0.7810 0.7770 0.7731

10.0 0.8299 0.8259 0.8220 0.8181 0.8141 0.8102 0.8063 0.8023 0.7984 0.7945 0.7905 0.7866 0.7826 0.7787 0.7748

11.0 0.8312 0.8273 0.8234 0.8195 0.8156 0.8117 0.8077 0.8038 0.7999 0.7960 0.7921 0.7882 0.7843 0.7804 0.7764

12.0 0.8324 0.8286 0.8247 0.8208 0.8170 0.8131 0.8092 0.8053 0.8014 0.7975 0.7936 0.7898 0.7859 0.7820 0.778113.0 0.8337 0.8299 0.8260 0.8222 0.8183 0.8145 0.8106 0.8067 0.8029 0.7990 0.7952 0.7913 0.7874 0.7836 0.779714.0 0.8349 0.8311 0.8273 0.8235 0.8197 0.8158 0.8120 0.8082 0.8043 0.8005 0.7966 0.7928 0.7890 0.7851 0.781315.0 0.8362 0.8324 0.8286 0.8248 0.8210 0.8172 0.8134 0.8095 0.8057 0.8019 0.7981 0.7943 0.7905 0.7867 0.782816.0 0.8374 0.8336 0.8298 0.8260 0.8223 0.8185 0.8147 0.8109 0.8071 0.8033 0.7995 0.7958 0.7920 0.7882 0.784417.0 0.8385 0.8348 0.8310 0.8273 0.8235 0.8198 0.8160 0.8123 0.8085 0.8047 0.8010 0.7972 0.7934 0.7896 0.785918.0 0.8397 0.8360 0.8322 0.8285 0.8248 0.8210 0.8173 0.8136 0.8098 0.8061 0.8023 0.7986 0.7948 0.7911 0.787319.0 0.8408 0.8371 0.8334 0.8297 0.8260 0.8223 0.8186 0.8149 0.8112 0.8074 0.8037 0.8000 0.7963 0.7925 0.788820.0 0.8419 0.8383 0.8346 0.8309 0.8272 0.8235 0.8198 0.8161 0.8124 0.8087 0.8050 0.8013 0.7976 0.7939 0.790221.0 0.8430 0.8394 0.8357 0.8321 0.8284 0.8247 0.8211 0.8174 0.8137 0.8100 0.8064 0.8027 0.7990 0.7953 0.791622.0 0.8441 0.8405 0.8368 0.8332 0.8296 0.8259 0.8223 0.8186 0.8150 0.8113 0.8076 0.8040 0.8003 0.7967 0.793023.0 0.8451 0.8415 0.8379 0.8343 0.8307 0.8271 0.8234 0.8198 0.8162 0.8126 0.8089 0.8053 0.8016 0.7980 0.794324.0 0.8462 0.8426 0.8390 0.8354 0.8318 0.8282 0.8246 0.8210 0.8174 0.8138 0.8102 0.8065 0.8029 0.7993 0.795725.0 0.8472 0.8436 0.8400 0.8365 0.8329 0.8293 0.8257 0.8222 0.8186 0.8150 0.8114 0.8078 0.8042 0.8006 0.797026.0 0.8482 0.8446 0.8411 0.8375 0.8340 0.8304 0.8269 0.8233 0.8197 0.8162 0.8126 0.8090 0.8054 0.8018 0.798327.0 0.8491 0.8456 0.8421 0.8386 0.8350 0.8315 0.8280 0.8244 0.8209 0.8173 0.8138 0.8102 0.8066 0.8031 0.799528.0 0.8501 0.8466 0.8431 0.8396 0.8361 0.8326 0.8290 0.8255 0.8220 0.8184 0.8149 0.8114 0.8078 0.8043 0.800729.0 0.8510 0.8476 0.8441 0.8406 0.8371 0.8336 0.8301 0.8266 0.8231 0.8196 0.8160 0.8125 0.8090 0.8055 0.8019

Table 6.2–4. Salinity correction factors for dissolved oxygen in water (based on specific conductance).—Continued[Factors are dimensionless; values are based on equations published by Benson and Krause (1984); Temp. (°C), temperature in degrees Celsius]
30 Chapter A6.2. Dissolved Oxygen Temp. (deg C) Specific conductance, in microsiemens per centimeter at 25 degrees Celsius 0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 10,000 11,000 12,000 13,000 14,000 30.0 1.0000 0.9969 0.9939 0.9908 0.9877 0.9845 0.9814 0.9783 0.9751 0.9720 0.9688 0.9656 0.9624 0.9592 0.9560 31.0 1.0000 0.9970 0.9939 0.9908 0.9877 0.9846 0.9815 0.9784 0.9753 0.9721 0.9690 0.9658 0.9626 0.9595 0.9563 32.0 1.0000 0.9970 0.9939 0.9909 0.9878 0.9847 0.9817 0.9785 0.9754 0.9723 0.9692 0.9660 0.9629 0.9597 0.9565 33.0 1.0000 0.9970 0.9940 0.9909 0.9879 0.9848 0.9818 0.9787 0.9756 0.9725 0.9694 0.9662 0.9631 0.9600 0.9568 34.0 1.0000 0.9970 0.9940 0.9910 0.9880 0.9849 0.9819 0.9788 0.9757 0.9727 0.9696 0.9665 0.9633 0.9602 0.9571 35.0 1.0000 0.9970 0.9940 0.9911 0.9880 0.9850 0.9820 0.9790 0.9759 0.9728 0.9698 0.9667 0.9636 0.9605 0.9573

Temp. 

(deg C)

Specific conductance, in microsiemens per centimeter at 25 degrees Celsius

15,000 16,000 17,000 18,000 19,000 20,000 21,000 22,000 23,000 24,000 25,000 26,000 27,000 28,000 29,000

30.0 1.0000 0.9969 0.9939 0.9908 0.9877 0.9845 0.9814 0.9783 0.9751 0.9720 0.9688 0.9656 0.9624 0.9592 0.956031.0 1.0000 0.9970 0.9939 0.9908 0.9877 0.9846 0.9815 0.9784 0.9753 0.9721 0.9690 0.9658 0.9626 0.9595 0.956332.0 1.0000 0.9970 0.9939 0.9909 0.9878 0.9847 0.9817 0.9785 0.9754 0.9723 0.9692 0.9660 0.9629 0.9597 0.956533.0 1.0000 0.9970 0.9940 0.9909 0.9879 0.9848 0.9818 0.9787 0.9756 0.9725 0.9694 0.9662 0.9631 0.9600 0.956834.0 1.0000 0.9970 0.9940 0.9910 0.9880 0.9849 0.9819 0.9788 0.9757 0.9727 0.9696 0.9665 0.9633 0.9602 0.957135.0 1.0000 0.9970 0.9940 0.9911 0.9880 0.9850 0.9820 0.9790 0.9759 0.9728 0.9698 0.9667 0.9636 0.9605 0.9573

Temp.

(deg C)

Specific conductance, in microsiemens per centimeter at 25 degrees Celsius

30,000 31,000 32,000 33,000 34,000 35,000 36,000 37,000 38,000 39,000 40,000 41,000 42,000 43,000 44,000

30.0 0.9032 0.8998 0.8964 0.8931 0.8897 0.8863 0.8829 0.8795 0.8760 0.8726 0.8692 0.8658 0.8623 0.8589 0.855431.0 0.9038 0.9005 0.8971 0.8937 0.8904 0.8870 0.8836 0.8802 0.8768 0.8734 0.8700 0.8666 0.8632 0.8597 0.856332.0 0.9044 0.9011 0.8977 0.8944 0.8910 0.8877 0.8843 0.8809 0.8776 0.8742 0.8708 0.8674 0.8640 0.8606 0.857233.0 0.9050 0.9017 0.8984 0.8950 0.8917 0.8884 0.8850 0.8817 0.8783 0.8749 0.8716 0.8682 0.8648 0.8614 0.858034.0 0.9056 0.9023 0.8990 0.8957 0.8923 0.8890 0.8857 0.8824 0.8790 0.8757 0.8723 0.8690 0.8656 0.8622 0.858835.0 0.9061 0.9028 0.8996 0.8963 0.8930 0.8897 0.8864 0.8830 0.8797 0.8764 0.8731 0.8697 0.8664 0.8630 0.8597

Table 6.2–4. Salinity correction factors for dissolved oxygen in water (based on specific conductance).—Continued[Factors are dimensionless; values are based on equations published by Benson and Krause (1984); Temp. (°C), temperature in degrees Celsius]
References Cited 31

Temp. 

(deg C)

Specific conductance, in microsiemens per centimeter at 25 degrees Celsius

45,000 46,000 47,000 48,000 49,000 50,000 51,000 52,000 53,000 54,000 55,000 56,000 57,000 58,000 59,000

30.0 0.8520 0.8485 0.8450 0.8416 0.8381 0.8346 0.8311 0.8276 0.8241 0.8207 0.8172 0.8137 0.8102 0.8066 0.803131.0 0.8529 0.8494 0.8460 0.8425 0.8391 0.8356 0.8321 0.8287 0.8252 0.8217 0.8182 0.8148 0.8113 0.8078 0.804332.0 0.8537 0.8503 0.8469 0.8435 0.8400 0.8366 0.8331 0.8297 0.8262 0.8228 0.8193 0.8159 0.8124 0.8089 0.805433.0 0.8546 0.8512 0.8478 0.8444 0.8410 0.8375 0.8341 0.8307 0.8272 0.8238 0.8204 0.8169 0.8135 0.8100 0.806634.0 0.8555 0.8521 0.8487 0.8453 0.8419 0.8385 0.8351 0.8317 0.8282 0.8248 0.8214 0.8180 0.8145 0.8111 0.807735.0 0.8563 0.8529 0.8496 0.8462 0.8428 0.8394 0.8360 0.8326 0.8292 0.8258 0.8224 0.8190 0.8156 0.8122 0.8087

Table 6.2–4. Salinity correction factors for dissolved oxygen in water (based on specific conductance).—Continued[Factors are dimensionless; values are based on equations published by Benson and Krause (1984); Temp. (°C), temperature in degrees Celsius]
32 Chapter A6.2. Dissolved Oxygen

Appendix A. Example comparison between spectrophotometric and optical 

dissolved-oxygen meter data

Table 6.2–A1. Data for comparison between spectrophotometric and optical dissolved-oxygen meter methods.

[DO, dissolved-oxygen concentration; mg/L, milligrams per liter; ND, no data]

Date Time Well Meter reading, 

DO in mg/L

Hach Indigo 

Carmine, 

DO in mg/L

CHEMetrics 

Rhodazine D, 

DO in mg/L

6/21/2016 12:56 GSA 167 0.01 0.05 ND

6/21/2016 12:57 GSA 167 0.01 ND 0.05

6/21/2016 12:58 GSA 167 0.01 ND 0.08

6/21/2016 13:00 GSA 167 0.01 ND 0.05

6/21/2016 13:03 GSA 167 0.01 0.02 ND

6/21/2016 13:03 GSA 167 0.01 ND 0.09

6/21/2016 13:03 GSA 167 0.01 0.03 ND

6/21/2016 13:05 GSA 167 0.01 ND 0.05

6/21/2016 13:06 GSA 167 0.01 ND 0.04

6/21/2016 13:07 GSA 167 0.01 ND 0.04

6/21/2016 13:10 GSA 167 0.01 0.04 ND

6/21/2016 13:12 GSA 167 0.01 ND 0.07

6/21/2016 13:14 GSA 167 0.01 ND 0.05

6/21/2016 13:14 GSA 167 0.01 ND 0.04

6/23/2016 11:02 GSA 167 0.07 ND 0.07

6/23/2016 11:06 GSA 167 0.06 0.07 ND

6/23/2016 11:11 GSA 167 0.05 0.06 ND

6/23/2016 11:12 GSA 167 0.05 0.03 ND

6/23/2016 11:13 GSA 167 0.05 ND 0.06

6/23/2016 11:15 GSA 167 0.05 ND 0.06

6/23/2016 11:16 GSA 167 0.05 0.06 ND

6/23/2016 11:17 GSA 167 0.05 ND 0.09

6/23/2016 11:18 GSA 167 0.05 ND 0.07

6/23/2016 11:19 GSA 167 0.04 0.05 ND

6/23/2016 11:22 GSA 167 0.04 ND 0.07

6/23/2016 11:22 GSA 167 0.04 0.09 ND

6/23/2016 11:23 GSA 167 0.04 ND 0.1

7/26/2016 11:17 GSA 167 0.06 0.08 ND

7/26/2016 11:18 GSA 167 0.06 ND 0.08

7/26/2016 11:19 GSA 167 0.06 ND 0.07

7/26/2016 11:20 GSA 167 0.06 ND 0.07

7/26/2016 11:21 GSA 167 0.06 0.06 ND

7/26/2016 11:22 GSA 167 0.06 0.08 ND

7/26/2016 11:22 GSA 167 0.05 0.07 ND
Appendix 1. 33

Date Time Well Meter reading, 

DO in mg/L

Hach Indigo 

Carmine, 

DO in mg/L

CHEMetrics 

Rhodazine D, 

DO in mg/L

7/26/2016 11:23 GSA 167 0.05 ND 0.07

7/26/2016 11:24 GSA 167 0.05 ND 0.06

7/26/2016 11:26 GSA 167 0.05 0.05 ND

7/26/2016 11:29 GSA 167 0.05 ND 0.09

7/28/2016 10:57 GSA 167 0.04 0.04 ND

7/28/2016 10:58 GSA 167 0.05 ND 0.05

7/28/2016 11:00 GSA 167 0.04 ND 0.07

7/28/2016 11:00 GSA 167 0.04 0.04 ND

7/28/2016 11:00 GSA 167 0.05 ND 0.05

7/28/2016 11:01 GSA 167 0.05 0.05 ND

7/28/2016 11:03 GSA 167 0.05 ND 0.06

7/28/2016 11:04 GSA 167 0.05 ND 0.07

7/28/2016 11:05 GSA 167 0.04 ND 0.06

7/28/2016 11:07 GSA 167 0.04 ND 0.05

Table 6.2–A2. Calibration data for readings in table 6.2–A1.

[mm of Hg, millimeters of mercury; °C, degrees Celsius; DO, dissolved oxygen; Conc, concentration; mg/L, milligrams per liter]

Date

Barometric 

pressure, 

in mm of Hg

Temperature, 

in °C

100% DO 

saturation, 

in mg/L

Initial Conc, 

in mg/L

Adjusted 

Conc, in mg/L

Meter 

reading in 

zero solution, 

in mg/L

2-point 

calibration

(yes/no)

In situ meter 

type

6/21/2016 622.5 21.58 7.18 7.18 7.18 0.02 no AT600 serial 

449415

6/23/2016 621.8 22.75 7.01 6.88 7.02 0.01 no AT600 serial 

449680

7/26/2016 623.5 22.80 6.99 6.98 6.98 0.02 no Smart Troll

7/28/2016 623.0 22.25 7.10 7.10 7.08 0.02 no Smart Troll

Table 6.2–A1. Data for comparison between spectrophotometric and optical dissolved-oxygen meter methods.—Continued

[DO, dissolved-oxygen concentration; mg/L, milligrams per liter; ND, no data]


U.S. Geological Survey—Dissolved Oxygen—Techniques and Methods 9–A6.2

ISSN 2328-7055 (online)

https://doi.org/10.3133/tm9A6.2