Metadata for csv dataset,
Nutrient Field-Blank Data From Surface-Water Sites in Historical U.S. Geological Survey Water-Quality Networks, 2002–12	

Column heading followed by description

Station: Sampling station identification number

Date: Date of sample collection

Parameter code: National Water Information System parameter code 
        608 (ammonia as N); 
        613 (nitrite as N); 
        631 (nitrite-plus-nitrate as N); 
        49570 ( total particulate nitrogen); 
        625 (total Kjeldahl nitrogen: ammonia plus organic N); 
        62855 (total nitrogen: ammonia plus nitrite plus nitrate plus organic nitrogen); 
        671 (orthophosphate); 
        665 (total phosphorus)

Method:	A code, briefly described in the table below, for the National Water Quality Laboratory (NWQL) method used to analyze the indicated nutrient.

Remark	A remark from the NWQL for the nutrient concentrations:-    
        "<": The measured value is less than the indicated concentration (detection limit)
    
        "E": The reported value is an estimate

Result:	Concentration in milligrams per liter

Flag: Indicator for potential data screening:
    
        1. No restrictions on data use
    
        2. Alert to use of this record, include cases where the sample collector requested result verification by NWQL, the field-blank result was higher than the associated environmental result, original data were miscoded, or the sample was diluted
    
        3. Suggest disregard this record for reason explained in comment

Recensor note: Note to describe recensoring from reported censor level (as laboratory reporting level [LRL], method detection limit [MDL], interim reporting level [IRL], or mimimum reporting level [MRL]) to the long-term method detection level (LTMDL)

Comment: Description of evidence to support assignment of flag
	

Method code followed by method description
AKP01	Colorimetry, automated segmented flow, alkaline persulfate digestion
CL021	Low-level; colorimetry, automated segmented flow, acid persulfate digestion
CL037	Colorimetry, automated segmented flow, salicylate-hypochlorite
CL039	Low-level: colorimetry, automated segmented flow, salicylate-hypochlorite
CL041	Colorimetry, automated segmented flow
CL043	Low-level: colorimetry, automated segmented flow
CL048	Colorimetry, automated segmented flow, cadmium reduction
CL050	Low-level: colorimetry, automated segmented flow, cadmium reduction
CL053	Colorimetry, automated segmented flow, phosphomolybdate
CL057	Low-level: colorimetry, automated segmented flow, phosphomolybdate
COMB7	Combustion and thermal conductivity
DZ001	Colorimetry, discrete analyzer
KJ008	Colorimetry, automated segmented flow, Kjeldahl digestion
KJ009	Colorimetry, automated segmented flow, Kjeldahl digestion
PHM01	Colorimetry, discrete analyzer, phosphomolybdate
RED01	Colorimetry, discrete analyzer, enzyme reduction-diazotization
RED02	Low-level: colorimetry, discrete analyzer, enzyme reduction-diazotization
SHC02	Colorimetry, discrete analyzer, salicylate-hypochlorite