Water Resources Division Nomenclature Conventions for Reporting Concentrations of Ammonium Ions and Ammonia in Natural Waters



In Reply Refer To:                              August 26, 1993
Mail Stop 412


OFFICE OF WATER QUALITY TECHNICAL MEMORANDUM NO. 93.12

Subject:  PROGRAMS AND PLANS--Water Resources Division
          Nomenclature Conventions for Reporting Concentrations
          of Ammonium Ions and Ammonia in Natural Waters

According to firmly established nomenclature conventions in the 
Water Resources Division (WRD) and in other State and Federal 
agencies, the sum of ammonium ions [NH4+] and solvated ammonia 
[NH3 (aq)] concentrations determined in natural water samples 
are reported as "ammonia."  The fact that this convention is 
misleading--ammonium ions are the predominant species in most 
unpolluted natural water systems where pH is typically less 
than 9--has understandably led to some confusion within the WRD.  
For the record, the WRD conventions for naming these species in 
our data bases and reports are outlined below.

1.  The sum of ammonium ions [NH4+] and solvated (un-ionized) 
    ammonia [NH3 (aq)] are reported as "ammonia."

2.  Until December 1, 1991, the National Water Quality 
    Laboratory's SPN software reported the sum of ammonium ions 
    and solvated ammonia concentrations as "ammonium."  Since 
    December 1, 1991, the sum has been reported as ammonia.

3.  If concentrations of solvated ammonia [NH3 (aq)] are of 
    interest, they can be estimated from reported concentrations 
    of "ammonia," pH, and temperature of samples at the time of 
    collection, using the equilibrium constant for solvated 
    ammonia and ammonium ions at the appropriate temperature.  If 
    estimated solvated ammonia concentrations are included in a 
    report, they must be clearly identified as such.  Values of 
    pH, temperature, and the equilibrium constant used to estimate 
    these concentrations should be included in the report.




                                  David A. Rickert
                                  Chief, Office of Water Quality

This memorandum does not supersede any previous Office of Water 
Quality Technical Memorandum.

Key Words:  Ammonia, nomenclature

Distribution:  A, B, S, FO, PO