Principal components analysis (PCA) was used to examine the relationship between patterns of microbial
activity (as indicated by absorbance readings) on disturbed and undisturbed sites (Goldbeck 1986). PCA is
an indirect gradient analysis that reduces a multidimensional data set into a smaller number of axes. Based on
correlations between patterns of activity in soil samples, data points are plotted along principal components
axes, highlighting the relationship between samples (Pielou 1984, Gauch 1982, Chapter 4). Since no environmental
data are included in the analysis to further distinguish sites, further interpretation is necessary to
determine whether ordination axes have biological meaning. Average well color development (AWCD) was
calculated by averaging absorbance for each of the 95 carbon sources on a single plate (Garland and Mills
1991). The absorbance of the control well was subtracted from the 95 readings to account for dye reduction from the possible introduction of exogenous nutrients.