Data from Selected U.S. Geological Survey National Stream Water-Quality Monitoring Networks (WQN)
USGS Digital Data Series DDS-37

By Richard B. Alexander, James R. Slack, Amy S. Ludtke, Kathleen K. Fitzgerald, and Terry L. Schertz

WQ_DEFS.TXT

Explanation of total constituent analyses performed on National Stream Quality Accounting Network and Hydrologic Benchmark Network water-quality samples

[The total form reflects different characteristics of the analytical methods and the water-suspended sediment mixture of the samples. Explanations are modified from USGS annual State data reports]

_____________________________________________________________________________
Term                       Explanation                         Applicable 
                                                               constituents            
_____________________________________________________________________________

Total   The total amount of constituent in a representative    Nitrogen1,
         water-suspended sediment sample, regardless of the     phosphorus,
         constituent's physical or chemical form.  The          Kjeldahl
         analytical procedure assures measurement of at least   (organic plus
         95 percent of the constituent present in both the      ammonia)
         dissolved and suspended phases of the sample.          nitrogen, and
                                                                 carbon.

"Total" The determination represents the amount of a consti-   Nitrite,
         tuent in a water sample present in the "dissolved"     nitrate plus
         form.  The analytical method was performed on water-   nitrite2,
         suspended sediment samples "decanted" in the           ammonia, and
         laboratory (Skougstad and others, 1979) to avoid       orthophosphate
         measurement interferences associated with particulate 
         material.  The results of these analyses are not 
         statistically separable from analytical results based 
         on "dissolved" samples obtained by filtering a water-
         suspended sediment sample in the field using a 0.45 
         micrometer membrane filtration device (see memorandum 
         QW93_04).

Total    The amount of a given constituent remaining in solu-  Trace elements
 recov-   tion after a representative suspended-sediment
 erable   sample has been digested by a method (usually using  
          a dilute acid solution) that results in dissolution 
          of only readily soluable substances.  Complete dis-
          solution of all particulate matter is not achieved 
          by the digestion treatment, and the determination 
          represents quantities that are less than 95 percent 
          of the total amount.
_____________________________________________________________________________

     1  Total nitrogen is calculated as the sum of total Kjeldahl nitrogen 
and "total" nitrate+nitrite determinations.

     2  In cases where "total" nitrate+nitrite laboratory analyses were not 
performed (i.e., beginning on 10-1-94), the results of laboratory analyses 
of dissolved nitrate+nitrite were automatically substituted by the U.S. 
Geological Survey's water-quality data storage and retrieval system, the
National Water Information System.


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Last modified: Thu Jan 16 15:00:27 EST 1997