Metadata

Description
Total organic carbon (TOC) concentrations were analyzed by a high-temperature combustion method with a Shimadzu TOC-5000A TOC analyzer. In advance the analysis, samples were acidified with 3M HCl, and purged with N2 gas to remove inorganic C. Ancillary physical and chemical parameters were measured using standar methods as part of on-going estuarine water quality monitoring program http://www.serc.fiu.edu/wqmnetwork. Detailed methods will be found elsewhere. For escitation-emission matrix (EEM) measurements, fluorescences spectra were measured with a Jobin-Yvon-Horiba (France) Spex Fluoromax-3 fluorometer equipped with a 150-W continuous output xenon arc lamp under condition of 5.7-nm excitation and 2-nm emission slit widths and a 0.25 second response time. Forty-four emission scans were acquired at excitation wavelengths (lamda ex) between 240 and 455 nm at 5 nm intervals. Them emission wavelengths were scanned from lamda ex + 10 nm to lamda ex + 250 nm at 2 nm intervals (Coble et al., 1993 and Coble, 1996). All fluorescence spectra were acquired in ratio mode, whereby the sample (emission signal, S) and reference (excitation lamp output, R) signals were collected and the ratio (S/R) was calculated. The ratio mode eliminates the influence of possible fluctuation and wavelength dependency of excitation lamp output. Several post-acquisition steps were involved in the correction of the fluorescence spectra. First, an inner filter corrections was applied to the fluorescence data according to McKnight et al. (2001). After inner filter corrections the sample EEM underwent spectral subtraction of the Milli-Q water to remove most of the effects due to Raman scattering. Instrument bias related to wavelength dependent efficiencies of the specific instrument's optical components (gratings, mirrors, etc.) were then corrected by applying multiplication factors, supplied by the manufacturer, for both excitation and emission wavelengths for the range of observations. Finally, the fluorescence intensity values were converted to quinine sulfate unit (QSU;1QSU=1 ngL-1 of quinine sulfate monohydroxide) to facilitate inter-laboratory comparisons (Coble et al., 1993). From the 370 nm scan a fluorescence index (FI) was calculated (McKnight et al., 2001). Milli-Q water was used as a reference for all fluorescence analysis. UV-visible measurements of the water samples were carried out with 1cm quartz UV-visible cells at room temperature (20 degrees C), using a Varian CARY 50 Bio UV-visible spectrophotometer. Milli-Q water was used as the reference.

References:
Battin, T J 1998. Dissolved organic matter and its optical properties in a blackwater tributary of the upper Orinoco river, Venezuela. Organic Geochemistry, 28: 561-569.

Chen, Meilian L. 2010. Comparative study of dissolved organic matter from groundwater and surface water in the Florida costal Everglades using multi-dimensional spectrofluorometry combined with multivariate statistics. Applied Geochemistry, 25: 872-880.

De Souza Sierra, M M 1997. Spectral identification and behavior of dissolved organic fluorescence material during estuarine mixing processes. Marine Chemistry, 58: 51-58.

Donard, O F 1989. High-sensitivity fluorescence spectroscopy of Mediterranean waters using a conventional or a pulsed laser excitation source. Marine Chemistry, 27: 117-136.

Helms, John R. 2008. Absorption spectral slopes and slope ratios as indicators of molecular weight, source, and photobleaching of chromophoric dissolved organic matter. Limnology and Oceanography, 53(3): 955-969.

Lu, X Q 2003. Molecular characterization of dissolved organic matter in freshwater wetlands of the Florida Everglades. Water Research, 37: 2599-2606.

McKnight, Diane M 2001. Spectrofluorometric characterization of dissolved organic matter for indication of precursor organic material and aromaticity. Limnology and Oceanography, 46: 38-48.

Stedmon, Colin A. 2003. Tracing dissolved organic matter in aquatic environments using a new approach to fluorescence spectroscopy . Marine Chemistry, 82: 239-254.

Weishaar, James L. 2003. Evaluation of Specific Ultraviolet Absorbance as an Indicator of the Chemical Composition and Reactivity of Dissolved Organic Carbon . Environmental Science and Technology, 37: 4702-4708.

Yamashita, Youhei 2010. Dissolved organic matter characteristics across a subtropical wetland's landscape: Application of optical properties in the assessment of environmental dynamics. Ecosystems, 13: 1006-1019.

Instrumentation
Whatman 0.7um glass fiber filers, Shimadzu TOC-5000A Analyzer, Jobin Yvon Horiba (France) Spex Fluoromax-3 fluorometer, Varian CARY 50 Bio UV visible spectrophotometer