Fluorescence index as an indicator of dissolved organic carbon quality in hydrologic flowpaths of forested tropical watersheds

Abstract

Over two hundred samples were collected in tropical headwater forested catchments in the lowland Amazon basin near Juruena, Mato Grosso Brazil. These were analyzed for fluorescence characteristics and DOC concentrations, and represented a range of terrestrial hydrologic flowpaths and firstorder streams during baseflow and stormflow conditions. The fluorescence index (FI) of McKnight et al. (2001) was found to have a significant relationship with DOC concentrations for stream water at baseflow conditions, but FI values within individual terrestrial flowpaths and stormflow varied little for the range of DOC concentrations observed. FI values were seen to increase for increasing residence time of water within the terrestrial ecosystem, while DOC concentration decreased for increasing hydrologic residence time. The FI of terrestrial flow paths indicated that DOC became increasingly characterized by microbially derived carbon for flow paths with longer residence times, on the order through fall and overland flow \ percolating soil water \ groundwater. Base flow samples of stream water had a mean FI value of 1.78, compared with 1.51 and 1.44 for through fall and overland flow, respectively, and 1.65 for percolating soil water. The FI values for stream water at base flow were also seen to vary seasonally, and were inversely proportional to DOC concentrations over time.

Tracking the evolution of stream DOM source during storm events using end member mixing analysis based on DOM quality

“…Similar to our results, Inamdar et al (2011) have demonstrated that litter leachate had the highest HIX, the lowest FI and percent protein-like fluorescence among all DOM sources in a US forested watershed. The highest FI of groundwater for this study was in accordance with that for forested tropical watersheds (Johnson et al, 2011). However, Inamdar et al (2012) observed an elevation of protein-like fraction in groundwater, which was not evident in our study.…”

Ionic Liquid Extraction Unveils Previously Occluded Humic‐Bound Iron in Peat Soil Pore Water

“…We normalized the resulting fluorescence intensities to an external, ultrapure Raman peak water standard (Starna Cells, Atascadero, CA, USA), integrated similarly to the sample Raman peak and collected daily. Excitation-emissions matrices were then analyzed for fluorescence index (FI; Johnson et al, 2011), an index of humification (H P ; He et al, 2013), for an index of DOM redox status (RI) derived from Miller et al (2006), and for a second index of DOM redox status (C a /C c ; Kothawala et al, 2012) using the area in a 10 nm × 10 nm window under the component peak maxima (as a % total EEM fluorescence).…”

Single particle size and fluorescence spectra from emissions of burning materials in a tube furnace to simulate burn pits

“…Chemical characterization and specification of the open-air burning affluent may allow linking to potential health effects [9][10][11][12][13][23][24][25][26]. The excitation-emission matrix (EEM) can identify ultra-trace amounts of particular PAHs, humic substances, dissolved organic carbon (DOC) in different complex samples [27][28][29][30][31][32][33][34], such as the determination of two of the most carcinogenic PAHs, benzo[a]pyrene and dibenzo [a,h] anthracene at a concentrations below 10 ng/L [27]. The 370-nm excited fluorescence intensity ratio between 450 and 500 nm, named as fluorescence index (FI), was found to have a significant relationship with DOC concentrations for polluted stream water [29].…”