Chromophoric dissolved organic matter (CDOM) refers to the portion of organic material that is optically active in natural water systems. The optical properties of CDOM allow us to examine the levels and processing of this part of the carbon pool in these ecosystems. The distribution and characteristics of the absorbent and fluorescent components of CDOM were determined in 64 freshwater lakes in the Pacific Northwest. There have been very few studies of CDOM in this region. Lakes were sampled from June-August 2018. Analyses used excitation-emission matrix spectroscopy (EEM) and parallel factor analysis (PARAFAC) for the fluorescent component. Dissolved organic carbon (DOC) values ranged from 0.3-15.4 mg/L, fluorescence intensities from 7.4 x 10-2-18 Raman units, and absorption coefficients (at 350 nm) from 0.12-40 m-1, showing wide variability across the region. No distinguishable trends were observed between high and low altitude lakes, or between urban and rural areas. Low DOC levels and CDOM fluorescence intensities in 11 of the lakes indicated low biological productivity and carbon stored in the waters of these systems. Comparison of fluorescence intensities (ex: 350, em: 450) and absorption coefficients with DOC levels had positive, linear dependencies (p &lt; 0.05; R2 coefficients &gt; 0.6). This suggests the optically active portion of the organic carbon pool is relatively constant across the lakes. CDOM molecular weight and aromaticity were assessed through calculations of spectral slopes and flu/abs ratios. Fluorescence and humification indices were used to identify recent production of fluorescent organic material and the fraction of humic substances. Three characteristic peaks were identified in EEM’s through the traditional peak picking method, two terrestrial humic-like components and one protein-like component. This assessment was enhanced through application of PARAFAC which identified three fluorescent components and their concentrations across the data set. This study demonstrates the utility of the EEM-PARAFAC method in characterizing the fluorescent components of DOM in freshwater lakes in the Pacific Northwest.

Optical properties of chromophoric dissolved organic matter (CDOM) in Pacific Northwest lakes

2019 Fall National Meeting

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