Definition: | study city where data is collected | unique site identifier | refers to the first, second, etc. synoptic event in a given city | date of sample analysis | lab at which sample was analyzed for FDOM. FIU= Florida International University, ISU=Idaho State University, SERC=Smithsonian Environmental Research Center | Fluorescence index. Calculated as emission intensity (470 nm/520 nm) at 370 nm excitation. Ratio ~1.2 reflects terrestrially derived fulvic acids, ~1.8 reflects microbially derived fulvic acids. Values range from ~1.2 (terrestrial) to ~1.9 (microbial). References: McKnight et al. 2011, Fellman et al. 2010. Limnol. Oceanogr., 55(6): 2452–2462 | Biological index. The ratio of emission intensity at 380 nm divided by 430 nm at excitation 310 nm. An indicator of autotrophic productivity. High values (>1) correspond to recently produced DOM of autochthonous origin. Ranges from 0.6 (low productivity) to >1 (high productivity). Reference: Fellman et al. 2010. Limnol. Oceanogr., 55(6): 2452–2462 | humification index. The area under the em spectra 435–480 nm divided by the peak area 300–345 nm1435–480 nm, at ex 254 nm. indicator of humic substance content or extent of humification. Higher values indicate an increasing degree of humification. (Note - Ohno 2002 method corrects for secondary inner filter effects, is concentration independent, and ranges between 0 and 1). Values range from 0 (less humic) to 1 (more humic). Reference: Ohno et al. 2002. | absorbance at 254nm. Strongly correlated with aromaticity. This is typically normalized by DOC concentration as specific UV absorbance at 254 nm (SUVA254). Caution needed in interpreting these, as values can be influenced by sample pH, nitrate, and iron. Reference: Weishaar et al. 2003. Environ. Sci. Technol. 2003, 37, 20, 4702–4708 | Nonlinear slope of absorbance from 275 to 295nm. Proxy for DOM molecular weight. Very sensitive to photobleaching. Reference: Helms et al. 2008 Absorption spectral slopes and slope ratios as indicators of molecular weight, source,and photobleaching of chromophoric dissolved organic matter. Limnol. Oceanogr.,53(3) 955–969 | Nonlinear slope of absorbance from 350 to 400nm. Typically higher slope values indicate low molecular weight material and/or decreasing aromaticity. References: Blough and Del Vecchio (2002), Helms et al. ( 2008) | Slope ratio. Best-fit slope of ln(abs) from 275-295 divided by best-fit slope of ln(abs) from 250 to 400n. Negatively correlated with average molecular weight. Very sensitive to photobleaching, which increases Sr values. Values range from 0.7 (blackwater) to 10 (open ocean). Reference: Helms et al. 2008. | E2:E3. Ratio of Absorbance at 250 to absorbance at 365. Negatively correlated with molecular weight and aromaticity. Reference: Penghui Li & Jin Hur (2017) Critical Reviews in Environmental Science and Technology, 47:3, 131-154. De Haan and De Boer (1987) | C1 component (microbial humic-like) from PARAFAC model based on CURB synoptic sampling in Atlanta, Boston, Miami, and Salt Lake City | C2 component (terrestrial humic-like) from PARAFAC model based on CURB synoptic sampling in Atlanta, Boston, Miami, and Salt Lake City | C3 component (terrestrial humic-like) from PARAFAC model based on CURB synoptic sampling in Atlanta, Boston, Miami, and Salt Lake City | C4 component (protein-like) from PARAFAC model based on CURB synoptic sampling in Atlanta, Boston, Miami, and Salt Lake Cit4 | C5 component (benzoic acid-like) from PARAFAC model based on CURB synoptic sampling in Atlanta, Boston, Miami, and Salt Lake City | Percentage of C1 (microbial humic-like) component from PARAFAC model based on CURB synoptic sampling in Atlanta, Boston, and Miami | Percentage of C2 component (terrestrial humic-like) from PARAFAC model based on CURB synoptic sampling in Atlanta, Boston, and Miami | Percentage of C3 component (terrestrial humic-like) from PARAFAC model based on CURB synoptic sampling in Atlanta, Boston, and Miami | Percentage of C4 component (protein-like) from PARAFAC model based on CURB synoptic sampling in Atlanta, Boston, and Miami | Percentage of C5 component (benzoic acid-like) from PARAFAC model based on CURB synoptic sampling in Atlanta, Boston, and Miami |