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U.S. GEOLOGICAL SURVEY
Data Series 345

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Review and Revision of Environmental and Biological Sample Data

Because this report includes a wide array of data types, different approaches were used for the review and revision of sample data. Most data were entered into various USGS databases and reviewed by study unit personnel. After review and verification, data were retrieved and compiled. These datasets were reviewed again by NEET members in order to check for consistency between study units. This standardized process occurred for the following datasets: nutrients, field parameters, chlorophyll, and habitat. The algal and invertebrate data were standardized by a laboratory review and revision processes prior to release (Moulton and others, 2000). All ancillary data were generated using standardized GIS procedures and reviewed prior to release.

Quality-control samples designed to measure bias and variability in the field included blank and replicate samples (Mueller and others, 1997). Field blanks are used to monitor for possible contamination or bias during sample collection and consist of subjecting analyte-free water to all aspects of normal sample collection, processing, and handling. Replicate samples are subsamples of a single, larger sample and are used to characterize the reproducibility of sample processing and the analytical process. Quality-control samples in the laboratory are routinely analyzed as part of the quality-assurance plan described by Maloney (2005). These samples include standard reference materials, laboratory reagent blanks, spikes, and surrogates. Biological community data were collected, as presented above, using standardized protocols (Moulton and others, 2002). These protocols address all field procedures to ensure that a sample is collected, processed, and shipped in an appropriate manner. The laboratory procedures used to process all algal samples, including all quality-control procedures, are presented in Charles and others (2002). Invertebrate samples were processed using standard quality-control procedures outlined in Moulton and others (2000).

A total of 16 blank samples were analyzed for nutrients and 15 for carbon. Reported values for all blank samples were near or less than detection limits. The mean percentage of differences between nutrient replicate samples ranged from 1.6 to 5.6 for all nutrient species (table 3). Thus, the variation in sample results due to variability in handling or laboratory analysis was small. The mean percentage of difference between particulate carbon-nitrogen replicate samples ranged from 0.4 to 6.8 percent. Thus, the variation in particulate carbon-nitrogen sample results due to variability in handling or laboratory analysis was larger than the variation for nutrient samples.

Variability in concentrations of replicate benthic and seston chlorophyll a samples also was examined (table 3). The mean percentage of difference for replicate benthic samples ranged from 6.5 to 11.4. The variation in values between replicate samples was small and was not very different from the variability in the nutrient and carbon-nutrient replicate samples. The mean percentage of difference for seston chlorophyll a replicate samples was only 4.8 percent.

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