Fig. 2.

PCA score plots from the combined fraction's mass spectra using the Electrospray ionization (ESI)− mode (as Fig. 1b). The first and the second principal components (t1 and t2) are shown. Each year is represented with a different symbol. In picture legend 1: year 2005; 2: year 2006; 3: year 2007; 4: year 2008.