Seasonal Variations of Chromophoric Dissolved Organic Matter in a National Estuarine Research Reserve

Guo, Laodong, Linhares, Emma, Mentor, Poster Presentation, Projects, School and College, School of Freshwater Sciences, Student

Emma Linhares, “Seasonal Variations of Chromophoric Dissolved Organic Matter in a National Estuarine Research Reserve”
Mentor: Laodong Guo, Freshwater Sciences
Poster #85

Chromophoric dissolved organic matter (CDOM) is a major component of natural DOM and has been frequently used to elucidate DOM composition and optical properties and their dynamic changes in aquatic environments. CDOM can be characterized using spectroscopic techniques, including fluorescence excitation and emission (EEM) and UV-Visual spectrophotometers, each provides complementary information for the characterization of DOM. In addition, CDOM measurements, when combined with analysis of bulk dissolved organic carbon (DOC) and parallel factor modeling (PARAFAC), can be used to characterize DOM quality, including molecular composition and chemical properties, and to evaluate sources and environmental fate of DOM in aquatic ecosystems. The Mission-Aransas National Estuarine Research Reserve is an ecosystem with many smaller naturally separated areas, which makes it an ideal area to study the effect of environmental change on CDOM composition. Water samples were collected between 2016-2020 through collaboration with researchers in UT-Austin for the measurements of DOC and CDOM, including chromophoric and fluorescent DOM. Abundances of CDOM (absorption coefficient in 254 nm) were significantly correlated with DOC concentrations. Optical properties, such as spectral slope, aromaticity, and UV-absorbance ratio index, exhibit unique seasonal variations, pointing to different DOM sources and hydrological events. Values of humification index were highly variable, indicating different terrigenous DOM sources with different degradation extent, while values of biological index were consistently high, suggesting a dominantly fresh biogenic DOM source. Based on EEM-PARAFAC analysis, three major fluorescent DOM components, two humic-like and one protein-like, were identified in the Estuarine Research Reserve, consistent with results derived from other optical properties. The seasonal and environmental changes in CDOM provide an improved understanding of DOM dynamics and measurements of CDOM should be adopted in the long-term monitoring to obtain important information on water quality and algal blooms in the aquatic system.