Characterization of bulk and chromophoric dissolved organic matter in the Laurentian Great Lakes during summer 2013

Abstract

The Laurentian Great Lakes contain ~21% of earth's surface freshwater and are experiencing dramatic decadal-scale changes to their water quality, biogeochemistry and ecosystem functions. We report here the first data set of dissolved organic carbon (DOC) and chromophoric dissolved organic matter (DOM), including UV-visible absorbance and derived optical properties and fluorescence excitation-emission matrices (EEMs), for open-lake surface-waters from each of the Great Lakes. Concentrations of DOC ranged from 86 to 240 µmol/L and the absorption coefficient at 254-nm (a 254) varied from 2.67 to 10.47 m-1 in Great Lakes waters. UV-visible and fluorescence characterization indicated that the DOM in open-lake waters in all the Great Lakes was primarily autochthonous. Both DOC and a 254 increased from Lake Superior to Lakes Erie and Ontario where aromaticity, molecular-weight and humification-degree of DOM were also higher. These variations are consistent with both the water transport pathway and the trend of increasing human population and relative watershed drainage area along the Great Lakes. Parallel factor analysis on fluorescence-EEM data revealed three terrestrial humic-like DOM components (C1, C2 and C4) and one protein-like DOM component (C3). Open Lake Huron had the highest protein-like/humic-like DOM ratio (C3/C1), while sites in Lakes Erie and Ontario had lower C3/C1 ratios, indicating a greater proportional influence of terrestrial DOM. Changes in DOM composition along the water transport pathway in the Great Lakes indicate varying impacts from terrestrial inputs and human activities in the different lake systems.

Yields and Characterization of Dissolved Organic Matter From Different Aged Soils in Northern Alaska

“…Values of BIX varied from 0.44 to 0.82 (Table ), which are within the ranges reported for natural DOM in aquatic environments (e.g., 0.6–0.95 in Gironde Estuary, reported by Huguet et al, ; 0.64–1.02 [averaging 0.87 ± 0.13] in fog water samples, reported by Birdwell and Valsaraj, ; 0.63–0.77 [averaging 0.71 ± 0.04] in Green Bay, reported by DeVilbiss et al, ; and 0.84–0.97 [averaging 0.90 ± 0.04] in Laurentian Great Lakes, reported by Zhou, Guo, et al, ) and increased consistently with the age of soil, indicating the production of autochthonous or microbially derived DOM during SOM degradation within permafrost. This result is consistent with the increase in protein‐like components in old soil and changes in the C3/C1 and C3/C2 ratios among different aged soils (Table ).…”

“…The HIX values ranged from 3.87 to 6.33 and increased in general with increasing soil 14 C age, except for the oldest soil (1.12; Table ). These HIX values observed in soil‐DOM samples are higher than those measured for DOM in Green Bay waters (1.95 ± 0.69; DeVilbiss et al, ) and in the Great Lakes (1.56 ± 0.53; Zhou, Guo, et al, ), but seem to be lower than those measured in Gironde Estuary waters (2–17; Huguet et al, ). Values of FIX were similar (0.98–1.15) among the four bulk soil‐DOM samples and did not show a clear trend with soil 14 C ages (Table ).…”

“…The spectral slope ( S 275–295 ) values ranged from 0.0108 to 0.0152 nm −1 for the bulk soil‐DOM with an average of 0.0127 ± 0.0018 nm −1 (Table ). These spectral slope values are much lower than those measured for aquatic environments (e.g., 0.0130–0.0361 [averaging 0.0183 ± 0.0056] nm −1 in estuarine waters in Atlantic coast; Helms et al, ; 0.0173–0.0292 [averaging 0.0218 ± 0.0025] nm −1 in Green Bay; DeVilbiss et al, ; and 0.0242–0.0352 [averaging 0.0299 ± 0.0025] nm −1 in the Laurentian Great Lakes; Zhou, Guo, et al, ) and suggested that soil‐derived DOM not only had high aromaticity but also contained more higher molecular weight DOM components since spectral slope values are inversely related to DOM molecular weight (Helms et al, ; Twardowski & Donaghay, ). As shown in Table , the DOM from the most aged soil sample (AVR09‐05) appeared to have the lowest S 275–295 value and thus contain more HMW DOM than the other three younger ones.…”

“…Although a 254 values of bulk soil‐DOM differed by over a factor of 5, they are broadly correlated with bulk DOC concentration ( n = 4, R 2 = 0.96, p < 0.05). The a 254 ‐based SUVA 254 values in the bulk leachate ranged from 8.7 m 2 /g‐C to as high as 31.7 m 2 /g‐C for the most aged soil sample (Table ), showing higher aromaticity for the soil‐DOM derived from permafrost compared to DOM in natural water samples (e.g., 1.4–12.2 [averaging 7.4 ± 3.0] m 2 /g‐C for fulvic acid, humic acid, and hydrophobic acid from rivers, lakes, and seawater; Weishaar et al, ; 2.6–10.6 [averaging 7.5 ± 2.4] m 2 /g‐C in estuarine waters in Atlantic coast; Helms et al, ; 4.7–8.7 [averaging 6.4 ± 0.9] m 2 /g‐C in Green Bay; DeVilbiss et al, ; and 2.2–3.6 [averaging 2.7 ± 0.3] m 2 /g‐C in the Laurentian Great Lakes; Zhou, Guo, et al, ). The SUVA 254 values measured in this study are also higher than those values of 7–9 in soil water extraction of aged Alaska permafrost (Whittinghill et al, ).…”

Do invasive quagga mussels alter CO2 dynamics in the Laurentian Great Lakes?

“…Recently, carbon cycling and magnitude of CO 2 fluxes across the air-water interface in lakes and inland waters have received increasing attention15161718, although studies on carbon dynamics in the Great Lakes remain scarce1719.…”