Seasonal variability in absorption and fluorescence properties of chromophoric dissolved organic matter in the Barataria Basin, Louisiana, USA

Abstract

Absorption and fluorescence measurements of chromophoric dissolved organic matter (CDOM) were examined along a transect containing 36 sampling stations in the Barataria Basin during high and low conditions to observe seasonal variation in these optical properties. The objectives of this study were (i) to observe CDOM variability in Barataria Basin in variable flow (high and low) conditions, and to characterize the CDOM, (ii) to identify the constituents of CDOM and to model CDOM compositional variability in the Barataria Basin using parallel factor analysis (PARAFAC). CDOM–salinity relationships were non-conservative in lower and upper part of the transect; however a conservative inverse relationship in the middle basin suggest that CDOM could be used as an useful indicator of salinity in the middle Barataria Basin. Larger variations in mean CDOM absorption and fluorescence values have been observed during low flow conditions than that during high flow conditions along the same transect. In general, mean CDOM absorption and fluorescence have shown linear inverse relation with salinity (r2 = 0.5 for high flow; r2 = 0.6 for low flow) and increased upstream along the stations. Using PARAFAC, four components could be identified in the Barataria Basin. Two humic, one non-humic, and one pedogenic component derived from PARAFAC modeling. These components showed the characteristics of the bulk fluorescence properties with an exception of component 3 (non-humic). Component 3 was found similar to autochthonous production of labile organic matter and was supported by elevated levels of chlorophyll-a between stations from 25 to 30. Fluorescence and humification indices along with peak ratios were calculated. In conclusion, CDOM variability in the Barataria Basin was characterized and modeled using the PARAFAC. The results obtained in this study are similar to previously reported results in estuarine environments. This study showed the potential application in characterizing CDOM variability in the Barataria Basin which explained over 99% variability of the water samples consisting of four major constituents. In future studies, water discharges from different water bodies in the Barataria Basin could be traced using CDOM compositional variability observed by EEM-PARAFAC technique.