Fig. 1. 3D fluorescence spectrogram of humic acid under centrifugal extraction

Fig. 2. 3D fluorescence spectrogram of humic acid under Oscillating extraction

Fig. 3. Variation of fluorescence region integration values under two extraction methods
(a): Changes of regional integral values in centrifugal extraction;(b): Changes of regional integral values in oscillatory extraction

Fig. 4. Variation of F_max values under two extraction methods
(a): Changes of regional integral values in centrifugal extraction; (b): Changes of regional integral values in oscillatory extraction

Fig. 5. Fluorescence components of humic acid under the two extraction methods by PARAFAC model

Fig. 6. Correlation analysis of DOM components in humic acid
(a): Correlation analysis of regional integral values by FRI method; (b): Correlation analysis of F_max values by PARAFAC method

Fig. 7. Principle component analysis of DOM components in humic acid
(a): Principle component analysis of F_max values by PARAFAC method;(b): Principle component analysis of regional integral values under FRI method