Comparison of the heterogeneity within bulk sediment humic substances from a stream and reservoir via selected operational descriptors

The heterogeneity within a bulk humic substances (HS) of two sediment HS from different sources (stream and reservoir) was compared using selected operational descriptors for ultrafiltration (UF) fractions. The operational descriptors investigated included the specific UV absorbance (SUVA), the C/N ratio, the ratio of humic-like/fulvic-like fluorescence (HLF/FLF), the humification index (HIX), the molecular weight (MW) and the organic carbon normalized pyrene binding coefficient (Koc). The UF fractions exhibited a linear or a log-linear trend with respect to MW for most operational descriptors. The two sediment HS exhibited similar patterns in the fluorescence excitation–emission matrix (EEM). The trends among some operational descriptors of the UF fractions based on one HS source were not the same as those obtained from the other HS source. For the C/N ratio, HLF/FLF, and the pyrene binding reactivity, the UF fractions of the stream sediment HS had higher values than those of the reservoir sediment HS UF fractions. For SUVA and HIX, however, a single relationship was presented with MW irrespective of HS sources. This indicates that SUVA and HIX may be more related to MW of the sediment HS than to the chemical nature and/or the source. A common strong correlation between HLF/FLF and pyrene Koc was also observed for the UF fractions of the two HS, suggesting that HLF/FLF might serve as a good descriptor to predict the extent of pyrene binding independent of sediment source.