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Reporting Alkalinity and ANC

The U.S. Geological Survey (USGS) recommends that alkalinity and acid neutralizing capacity (ANC) be reported in milliequivalents per liter (or microequivalents per liter), if possible. Alternatively, report alkalinity and ANC in milligrams per liter as calcium carbonate.

USGS policy states that reported values of alkalinity and ANC should include all digits known with certainty, plus one digit that is uncertain. That last digit is called the Least Significant Digit (LSD). The same USGS policy also recommends that the analytical results be stored in the USGS database with one additional uncertain digit (LSD+1) because the extra digit may contain useful information when large datasets are evaluated. Published data, however, should be reported only to the LSD.

Using the typical levels of uncertainty associated with alkalinity and ANC titrations, and when following the methods recommended by the USGS National Field Manual (section 6.6.4), the following reporting guidance has been developed. If reporting alkalinity, ANC, carbonate, bicarbonate, and hydroxide in milligrams per liter:

Hydroxide, carbonate, and bicarbonate concentrations cannot be negative. Alkalinity and ANC, however, may be negative because they are a measure of the sample's H+ deficiency relative to a solution of carbon dioxide in water. A negative alkalinity or ANC simply indicates the presence of some amount of mineral acidity. Report negative values of alkalinity and ANC with the same number of significant figures you would use if the values were positive.

Report the average value for duplicate samples or the median when more than two replicate samples are used for quality control and the value falls within the appropriate quality-assurance criterion for variability.

Parameter Codes

For USGS database users, use the parameter and method codes in the tables below to assign values to alkalinity, ANC, carbonate, bicarbonate, and hydroxide. For more information, consult the USGS parameter and method code dictionaries.

Constituent Units Filtered? Method Field or
Lab
Parameter
Code
Alkalinity    mg/L   
as CaCO3
filtered inflection point field 39086
lab 39087
Gran field 29802
lab 29803
fixed endpoint field 00418
lab 00421
ANC mg/L
as CaCO3
unfiltered inflection point field 00419
lab 00416
Gran field 29813
fixed endpoint field 00410
lab 00417
Carbonate mg/L
as CO32-
filtered inflection point field 00452
lab 29809
Gran field 63788
lab 63789
fixed endpoint field 29807
lab 29808
unfiltered inflection point field 00447
lab 00446
Gran field 29798
fixed endpoint field 00445
lab 00448
Bicarbonate mg/L
as HCO3-
filtered inflection point field 00453
lab 29806
Gran field 63786
lab 63787
fixed endpoint field 29804
lab 29805
unfiltered inflection point field 00450
lab 00449
Gran field 29797
fixed endpoint field 00440
lab 00451
Hydroxide mg/L
as OH-
filtered inflection point field 71834
lab 29812
Gran field 29800
fixed endpoint field 29810
lab 29811
unfiltered inflection point field 71832
lab 71831
Gran field 29799
fixed endpoint field 71830
lab 71833

Method and Parameter Codes for Alkalinity and ANC

Method codes have been created for field-derived alkalinity and ANC values to record the type of titrator used in the titration. These method codes also record the type of titration method (inflection point, Gran, or fixed endpoint). Use the following method codes for alkalinity and ANC:

Constituent Units Filtered? Method Field or
Lab
Parameter
Code
Method Code
Hach Digital
Titrator
 Buret 
Titrator
Alkalinity    mg/L   
as CaCO3
filtered inflection point field 39086 TT061 TT062
Gran field 29802 TT056 TT057
fixed endpoint field 00418 TT054 TT055
ANC mg/L
as CaCO3
unfiltered inflection point field 00419 TT065 TT066
Gran field 29813 TT058 TT059
fixed endpoint field 00410 TT063 TT064

Method and Parameter Codes for CO32-, HCO3-, and OH-

USGS method codes have been created to make a distinction between the available speciation methods for calculating carbonate and bicarbonate concentrations. They are:

Choose parameter and method codes from the following tables. Note that each table is for a different titration method.

Inflection Point Method, Field
Constituent Units Filtered? Parameter
Code
Speciation
Method
Method Code
Hach Digital
Titrator
 Buret 
Titrator
Carbonate    mg/L   
as CO32-
filtered 00452 advanced ASM01 ASM02
simple SSM01 SSM02
unfiltered 00447 advanced ASM09 ASM10
simple SSM09 SSM10
Bicarbonate mg/L
as HCO3-
filtered 00453 advanced ASM01 ASM02
simple SSM01 SSM02
unfiltered 00450 advanced ASM09 ASM10
simple SSM09 SSM10
Hydroxide mg/L
as OH-
filtered 71834 advanced ASM01 ASM02
simple SSM01 SSM02
unfiltered 71832 advanced ASM09 ASM10
simple SSM09 SSM10

Gran Titration Method, Field
Constituent Units Filtered? Parameter
Code
Speciation
Method
Method Code
Hach Digital
Titrator
 Buret 
Titrator
Carbonate    mg/L   
as CO32-
filtered 63788 advanced ASM03 ASM04
simple SSM03 SSM04
unfiltered 29798 advanced ASM11 ASM12
simple SSM11 SSM12
Bicarbonate mg/L
as HCO3-
filtered 63786 advanced ASM03 ASM04
simple SSM03 SSM04
unfiltered 29797 advanced ASM11 ASM12
simple SSM11 SSM12
Hydroxide mg/L
as OH-
filtered 29800 advanced ASM03 ASM04
simple SSM03 SSM04
unfiltered 29799 advanced ASM11 ASM12
simple SSM11 SSM12

Fixed Endpoint Titration Method, Field
Constituent Units Filtered? Parameter
Code
Speciation
Method
Method Code
Hach Digital
Titrator
 Buret 
Titrator
Carbonate    mg/L   
as CO32-
filtered 29807 advanced ASM05 ASM06
simple SSM05 SSM06
unfiltered 00445 advanced ASM07 ASM08
simple SSM07 SSM08
Bicarbonate mg/L
as HCO3-
filtered 29804 advanced ASM05 ASM06
simple SSM05 SSM06
unfiltered 00440 advanced ASM07 ASM08
simple SSM07 SSM08
Hydroxide mg/L
as OH-
filtered 29810 advanced ASM05 ASM06
simple SSM05 SSM06
unfiltered 71830 advanced ASM07 ASM08
simple SSM07 SSM08

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Page Last Modified: Friday - Jan 4, 2013 at 15:49:54 EST