Multiple linear regression models to predict the formation efficiency of triplet excited states of dissolved organic matter in temperate wetlands

Abstract

The source and composition of dissolved organic matter (DOM) dictates light absorption in surface waters. Sunlight absorption by chromophoric dissolved organic matter (CDOM) forms reactive intermediates and drives global organic carbon processing. Triplet excited states of CDOM ( 3 CDOM*) are primary reactive intermediates formed by sunlight absorption by CDOM.3 CDOM* also produce secondary reactive intermediates, including radicals and reactive oxygen species, which are active in biogeochemical pathways. The efficiency of 3 CDOM* formation (apparent quantum yield, AQY T ) depends on DOM composition, especially DOM molecular weight. This dependence may arise from the greater probability of forming intra-molecular chargetransfer (CT) complexes in high-molecular weight DOM that inhibit 3 CDOM* formation. There are few examples that demonstrate this in field samples. In this report, vegetation, general hydrology, and watershed characteristics for 39 temperate wetlands, which are critical sources of high-molecular weight DOM, from the United States were defined and related to DOM composition and AQY T . The DOM bulk composition was assessed using absorbance and fluorescence spectroscopies. AQY T was estimated under simulated sunlight using the probe 2,4,6-trimethylphenol. Relatively high AQY T values (7%) were observed in wetlands with long hydroperiods and > 50% cropland watershed land cover compared to wetlands with >50% forest watershed land cover (< 1-4%). Low molecular weight DOM (E2/E3 > 7 and SUVA 254 < 3 L mg-C 21 m 21) and autochthonous DOM (b/a > 0.7) had relatively high AQY T estimates ($ 10%), indicating that allocthonous, high-molecular weight compounds produce 3 CDOM* less efficiently than autochthonous DOM. The CT theory of DOM light absorption and internal light-screening offer mechanistic explanations for these trends.Naturally occurring dissolved organic matter (DOM) is a complex mixture of components including aromatics from terrestrial plants and biomacromolecules from primary and secondary aquatic producers (Wilson 1987;Stenson et al. 2003;Nebbioso and Piccolo 2013). Wetlands are integral sources of DOM to the hydrosphere and function as natural reactors in DOM transformation (Watanabe et al. 2012;Raymond and Spencer 2015). The relative inputs of terrestrial and aquatic DOM, and thus DOM composition, changes from headwaters and isolated wetlands (terrene wetlands) to wetlands associated with lake basins and rivers (lentic and lotic wetlands, respectively) (M€ unster and Chr ost 1990;Larson et al. 2014;Yu et al. 2015). In headwater systems with surrounding shrubs, trees, or emergent vegetation, inputs of DOM are dominated by terrestrial sources, such as plant matter and soil organic matter (allochthonous DOM). In contrast, the composition of DOM in systems with large open water regions and long water residence times is dominated by exo-metabolites from photoautotrophs and pelagic heterotrophs as well as products of photo-and microbialdegradation (autochthonous DOM) (M€ unster and Chr ost ...

Photochemical Characterization of Surface Waters from Lakes in the Adirondack Region of New York

“…Directly comparing Φ app,RI determined in this work with literature data was inherently challenging due to inconsistencies in experimental methodology among studies (e.g., differences in light sources, wavelength ranges for R a integration, and probe methods); nevertheless, such a comparison enables constraining the relative photoreactivity of Adirondack lake waters with the noted caveat. Φ app, 3 DOM TMP * for Adirondack lake waters spanned the range of values reported for whole waters (i.e., lakes, − , rivers, , estuaries, , wetlands, ,, stormwater, wastewater effluent ,,,, ) and DOM extracts or fractions isolated from terrestrial and aquatic environments, ,,,, but values were an order of magnitude lower than those measured for dissolved black carbon derived from biomass feedstocks . Furthermore, the mean Φ app, 3 DOM TMP * was higher than those for whole waters from temperate lakes in northern Minnesota and Wisconsin , and mountain lakes in northwestern Italy , but was lower than those measured for Lake Greifensee , and lakes in the Terra Nova Bay area of Antarctica .…”

“…Furthermore, the mean Φ app, 3 DOM TMP * was higher than those for whole waters from temperate lakes in northern Minnesota and Wisconsin , and mountain lakes in northwestern Italy , but was lower than those measured for Lake Greifensee , and lakes in the Terra Nova Bay area of Antarctica . Φ app, 1 O 2 were also on the same order of magnitude as values for whole waters and DOM isolates from a wide range of lakes (e.g., Lake Superior) and rivers, ,,,,,,,,− but the mean Φ app, 1 O 2 fell below those for surface waters from wetland (e.g., prairie potholes , ) and estuaries (e.g., the Florida Everglades) as well as wastewater effluent. ,,,, Φ app, 3 DOM HDO * fell on the lower end of the Φ app of high-energy 3 DOM* (i.e., measured by sorbate probes) for wastewater effluent and whole lake and river waters, ,, but compared well with values determined for Suwannee River DOM isolates under the same irradiation conditions, confirming their similarity in the formation efficiency of high-energy 3 DOM*. Lastly, Φ app, • OH were substantially lower than those for whole waters and DOM isolates from various sources, ,,,,,,,,, in part because the majority of literature Φ app, • OH were measured at shorter excitation wavelengths (e.g., <400 nm).…”

“…Φ app,RI followed the general pattern of Φ app, 3 DOM TMP * (1.3–4.7 × 10 –2 with a mean of 2.8 ± 0.9 × 10 –2 ) ≥ Φ app, 1 O 2 (1.5–3.3 × 10 –2 with a mean of 2.2 ± 0.5 × 10 –2 ) > Φ app, 3 DOM HDO * (0.4–1.2 × 10 –2 with a mean of 0.8 ± 0.2 × 10 –2 ) > Φ app, • OH (1.4–12.9 × 10 –6 with a mean of 6.8 ± 3.2 × 10 –6 ), similar to those observed for whole waters from other aquatic environments. ,,, Φ app, 3 DOM TMP * also showed strong correlations with Φ app, 1 O 2 and Φ app, 3 DOM HDO * (ρ = 0.903–0.918; p < 0.001) as TMP, FFA, and t , t -HDO all directly or indirectly sampled different but overlapping pools of 3 DOM*, ,,,, although their role in triplet energy transfer and oxidation reactions could not be resolved solely based on correlative evidence. The second-order reaction rate constant of TMP with 3 DOM* ( k TMP, 3 DOM TMP * ; 7.2–9.8 × 10 8 M –1 s –1 with a mean of 8.5 ± 0.8 × 10 8 M –1 s –1 ; Table S11) and that of t , t -HDO with 3 DOM* ( k t‑t ‑HDO, 3 DOM HDO * ; 5.9–9.9 × 10 8 M –1 s –1 with a mean of 8.0 ± 1.4 × 10 8 M –1 s –1 ; Table S13) for Adirondack lake waters were close to previous estimates, ,,,,− providing further evidence for the convergence of 3 DOM* reactivity with TMP and t , t -HDO among DOM isolates and whole waters of diverse origins. On average, 55 ± 8% of Φ app, 3 DOM TMP * was attributable to 3 DOM* also capable of sensitizing t , t -HDO isomerization (Table S15), which was consistent with prior work showing that a major fraction (e.g., 46–72%) of high-energy 3 DOM* (i.e., 3 DOM* with E T ≥ 250 kJ mol –1 , ) participated in one-electron transfer TMP oxidation .…”

“…g . , L a k e S u p e r i o r 2 9 ) and rivers, 32,33,92,93,96,98,99,128,134−137 but the mean Φ app, 1 O 2 fell below those for surface waters from wetland (e.g., prairie potholes 79,100 ) and estuaries (e.g., the Florida Everglades 103 ) as well as wastewater effluent. 33,102,131,138,139 Φ app, 3 DOM HDO * fell on the lower end of the Φ app of high-energy 3 DOM* (i.e., measured by sorbate probes 80 ) for wastewater effluent and whole lake and river waters, 32,33,105 but compared well with values determined for Suwannee River DOM isolates under the same irradiation conditions, confirming their similarity in the formation efficiency of high-energy 3 DOM*.…”

“…The photoreactivity of native and altered lake water samples was assessed by measuring the photochemical production of RIs with specific probe compounds, including terephthalic acid (TPA) for • OH , (including lower-energy hydroxylating species − and collectively termed as • OH), furfuryl alcohol (FFA) for 1 O 2 , , 2,4,6-trimethylphenol (TMP) as an electron transfer probe for 3 DOM* ( 3 DOM TMP * ), , and trans , trans -2,4-hexadien-1-ol ( t , t -HDO or sorbic alcohol) as an energy transfer probe for 3 DOM* ( 3 DOM HDO * ) . Probe-spiked samples were irradiated in septum-sealed quartz test tubes (held at ∼30° from the horizontal) inside an Atlas Suntest XLS+(II) solar simulator equipped with a 1700 W xenon arc lamp and a daylight glass 300 nm UV filter.…”