FIG. 4.

(a) Comparison of absorbance-normalized BCP (i.e., increment in BCP from the addition of irradiated HS relative to nonirradiated control, divided by the absorbance coefficient at 300 nm) after the 43-h incubation for different humic substance extraction types. (b) Comparison of the average absorbance-coefficient-normalized BCP for the 43-h incubation, among the different HS sample sources [i.e., (HPOA + HPIA)/2 and (HA + FA)/2]. Abbreviations: Allocht (predominantly allochthonous), Mix (mixed source), Autocht (predominantly autochthonous). See Table 1 for more details about the HSs.