README_NUTR.TXT - Readme file for Nutrient-Chlorophyll Study - NAWQA NECB

FILE FORMATS

The data tables are offered in two formats, Microsoft Excel and ASCII plain 
text. The text files are tables provided in tab-delimited columns with the 
first row being the Column Header Names. The data are preceded by lines of 
documentation or explanatory text. Any row containing such comments starts 
with a '#' sign. 

These ASCII files are easily viewable in a web browser or any word-processing 
program like MS Word or Notepad. However, those programs will not format the 
data into correctly-aligned columns, because the files are tab-delimited (the
columns do not have fixed widths). These tables are provided with the 
intention that they will be easily imported into a spreadsheet or database 
program (such as Quattro Pro, SAS, Access, Paradox, etc.).


WHAT IS A DETECTION?

Until recently (2000), results of laboratory analyses by the USGS were 
reported either as quantified above or below (using the less than, <, symbol) 
a Laboratory Reporting Level (LRL). Recent improvements in laboratory 
analytical techniques, however, enable a chemist to report an estimated 
concentration (E) when a compound meets all identification criteria, but the
concentration value is less than the LRL (Connor and others, 1998; Childress 
and others, 1999).


QUALITY ASSURANCE/QUALITY CONTROL SAMPLES

The water-quality data tables provided on this website are only for
environmental samples (actual surface water samples). In addition to the
environmental samples, the NECB study collected quality assurance/quality
control (qa/qc) samples. For every 10-12 environmental surface-water samples
collected, the following set of quality-control samples were collected:

1. Field blanks for major ions, nutrients, and dissolved organic carbon 
   (DOC). Seven field blanks were collected.
2. Field replicates for major ions, nutrients, and dissolved organic carbon
   (DOC). Five field replicates were collected.

See Socolow and others (2000, p. 22) for an explanation of types of qa/qc 
samples.

The qa/qc sample results are not available on this web site, but a brief 
summary of the qa/qc sample results follows:

	-Concentrations of certain major ions, nutrients, and DOC were 
detected in some of the blank samples. However, these concentrations were 
estimated concentrations below the LRL and lower than the concentrations
in the environmental samples.

	-All relative differences measured in concentrations between 
replicate and environmental samples were within the precision of the method
for the specific analyte at a particular concentration range.


Anyone wishing to obtain the qa/qc data, please contact Sarah Flanagan of
the NECB Study Unit at sflanaga@usgs.gov.


REFERENCES

Childress, C.J.O., Foreman, W.T., Connor, B.F., and Maloney, T.J., 1999, New
reporting procedures based on long-term method detection levels and some 
considerations for interpretations of water-quality data provided by the U.S.
Geological Survey National Water Quality Laboratory: U.S. Geological Survey 
Open-File Report 99-193, available ON-LINE at 
http://water.usgs.gov/owq/OFR_99-193/index.html

Connor, B.F., Rose, D.L., Noriega, M.C., Murtagh, L.K., and Abney, S.R., 
1998, Methods of analysis by the U.S. Geological Survey National Water 
Quality Laboratory--Determination of 86 volatile organic compounds in water
by gas chromatography/mass spectrometry, including detections less than 
reporting limits: U.S. Geological Survey Open-File Report 97-829, 78 p.,
available ON-LINE at http://nwql.usgs.gov/Public/pubs/OFR97-829.html

Socolow, R.S., Zanca, J.L., Murino, Jr., Domenic, and Ramsbey, L.R., 2000, 
Water resources data, Massachusetts and Rhode Island, Water Year 1999: U.S.
Geological Survey Water-Data Report MA-RI-99-1, 401 p.