Review and Revision of the Environmental Sample Data The first
step in preparing the data for analysis was to review all the
records and make any necessary revisions. The initial review
involved checking data codes to ensure that the sample type was
properly identified for each record. The primary types for
nutrient data are environmental samples, replicate samples, and
blank samples. Replicates and blanks are quality-control (QC)
samples. Nutrient QC data were described and analyzed by Mueller
and Titus (2005). A few cases of inconsistent or obviously
erroneous sample coding were noted and corrected. For example,
25 records with nutrient concentration data were coded as plant
or animal tissue samples, and 8 obvious environmental samples
were incorrectly coded as various QC sample types. Also, three
samples coded as blanks were found to be switched with related
samples that were coded as environmental. Data for some
environmental samples were stored in more than one record in the
database. These records were