Absorption spectroscopy of colored dissolved organic carbon in Georgia (USA) rivers: the impact of molecular size distribution

Abstract

Dissolved organic carbon (DOC) was collected in six rivers that transect the coastal plain of Georgia in July 1999 and February 2000. DOC concentrations ranged from 4.9 to 40.7 g m-3 and from 7.1 to 40.5 g m-3, respectively. The absorption coefficient at 440 nm was highly correlated with DOC concentration, suggesting that the optical parameter may be utilized for rapid estimation of DOC in these waters. The isolated DOC was separated into fractions of operationally defined molecular size, using an ultrafiltration technique that yielded three fractions: <10 ("small"), 10-50 ("medium") and >50 ("large") kilodalton. The smallest fraction was the most abundant (>50%) in 4 rivers in July and in all rivers in February, and considerably more abundant than in previous years. The wavelength-dependent absorption of the total DOC and its fractions showed approximately uniform shape of a curve declining exponentially with the increase of wavelength. The average slope of logarithmically transformed curves was 0.0151 and 0.0159 nm-1, for the material collected in July and February, respectively and showed a dependence on DOC molecular size. In unfractionated DOC samples, the mass-specific light absorption determined at 440 nm was on average 0.33 m2 g-1 in July, and 0.26 m2 g-1 in February. The mass-specific absorption coefficient in all fractions ranged between 0.085 and 1.347 m2 g-1 in July and between 0.085 and 1.877 m2 g-1 in February, and was positively correlated with the molecular size of the measured samples. The results of the reported study clearly suggest that the specific absorption coefficient of the yellow substance is an outcome of the relative contribution of its different size fractions

Spatio-seasonal variability of chromophoric dissolved organic matter absorption and responses to photobleaching in a large shallow temperate lake

“…7a and b) as has been shown in previous studies (e.g. Stedmon et al, 2000;Del Castillo and Coble, 2000;Yacobi et al, 2003;Rochelle-Newall et al, 2004;Zhang et al, 2007a;Kowalczuk et al, 2003).…”

“…The structural modifications in DOM and its coloured fractions that are in part conveyed through variation in S CDOM result from interplay between the input of allochthonous DOC from the catchment, the production of autochthonous DOC from the microbial digestion of phytoplankton cells and the rate at which these materials are degraded biologically and photochemically (Zhang et al, 2009b;Yamashita and Tanoue, 2004;Vantrepotte et al, 2007;Nelson et al, 1998;Yamashita et al, 2013). Newly produced autochthonous CDOM typically has a higher S CDOM coefficient compared to humic-rich allochthonous material (Bracchini et al, 2010).…”

Quantifying fluxes and characterizing compositional changes of dissolved organic matter in aquatic systems in situ using combined acoustic and optical measurements

“…We do not propose that in situ optical parameter measurements replace conventional discrete sampling, but rather that it be used to interpolate between or extrapolate beyond the discrete samples. Importantly, for DOM, simultaneous measurement of spectral absorption and DOM fluorescence provides an opportunity to characterize DOM in terms of its absorption spectral slope and the ratio of fluorescence to absorption parameters related to the chemical composition of DOM (Carder et al 1989, Blough and Green 1995, Yacobi et al 2003.…”

Variation in colloidal chromophoric dissolved organic matter in the Damariscotta Estuary, Maine

“…Thus, compositional differences in small and large colloidal material may account for some of the spectral slope variability. The relationship between S and molecular weight has been investigated by Mopper et al (1996) and Yacobi et al (2003) using ultrafiltration. Although the findings by Yacobi et al (2003) support the simple inverse relationship between molecular weight and S, Mopper et al (1996) suggest that the relationship between S and size is variable.…”

“…The relationship between S and molecular weight has been investigated by Mopper et al (1996) and Yacobi et al (2003) using ultrafiltration. Although the findings by Yacobi et al (2003) support the simple inverse relationship between molecular weight and S, Mopper et al (1996) suggest that the relationship between S and size is variable. Mopper et al (1996) report that the average spectral slope of colloidal material was significantly lower than the bulk CDOM slope in highly productive coastal waters, whereas the opposite was found in deep nonproductive oceanic waters.…”