Molecular composition of organic matter controls methylmercury formation in boreal lakes

Bravo, Andrea G.; Bouchet, Sylvain; Tolu, Julie; Björn, Erik; Mateos‐Rivera, Alejandro; Bertilsson, Stefan

doi:10.1038/ncomms14255

Cited by 246 publications

(220 citation statements)

References 51 publications

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“…As for THg, MeHg revealed a good distribution on the funnel plot and no asymmetry ( z = 0.66, p = 0.51). Negative relationships were found for only 8% (7/85) of all cases for THg (Brigham et al, ; Fagnani et al, ; Noh et al, ; Porvari & Verta, ; Vidon et al, ) and 12% (7/59) for MeHg (Bravo et al, ; Brazeau et al, ; Guedron et al, ; Porvari & Verta, ; Riscassi et al, ).…”

Section: Resultsmentioning

confidence: 99%

“…The most likely explanation is that biological processes responsible for the production of 1 mole of MeHg do not necessarily result in a 1:1 change in DOC concentration, hence reducing the coupling with DOC. Moreover, the origin and molecular composition of OM are critical parameters to understand Hg methylation and accumulation in lakes and rivers (Bravo et al, , ). Although Hall et al () found no significant relationship with DOC for MeHg, they did find significant relationships with HPOA and SUVA 254 , confirming the importance of the type and quality of DOC.…”

Section: Discussionmentioning

confidence: 99%

“…We propose that a better understanding of the molecular underpinnings of the DOC and Hg cycling in freshwaters may shed new light on Hg–DOC coupling. There is a growing interest in using DOC characterization techniques to improve our understanding of Hg dynamics in freshwaters, including SUVA 254 (and other wavelength), HPOA (Burns et al, ; Dittman et al, ), parallel factor analysis modeling of DOC fluorescence (Jiang et al, ; Lescord et al, ), semiquantitative analytical methods by a pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS) (Bravo et al, ), and fully quantitative liquid chromatography (LC)–MS or GC–MS analyses. Such analyses may help better quantifying Hg affinity with DOC under varying environmental conditions.…”

Section: Discussionmentioning

confidence: 99%

“…For the difference between Hg–DOC and Hg–Aromatic portion of DOC (UV 254 , SUVA 254 , UV 420 , and UV 320 ) in objective 3, we ran a multivariate model with DOC type as random (repeated) variable nested within the Study using the function rma.mv in the metafor package (Viechtbauer, ). We used studies that measured both DOC and a measure of aromaticity, which led to 10 studies with 16 pairwise comparisons for THg (Bravo et al, ; Burns et al, ; Dittman et al, ; Eklöf et al, ; Eklöf et al, ; Jeremiason et al, ; MacMillan et al, ; Navratil et al, ; Riscassi et al, ; Riscassi & Scanlon, ) and 4 studies with 6 pairwise comparisons for MeHg (Bravo et al, ; Eklöf et al, ; Jeremiason et al, ; MacMillan et al, ). The most widespread measure of aromaticity was SUVA 254 , which is the specific UV absorbance at 254 nm divided by DOC concentration (UV 254 /DOC).…”

Section: Methodsmentioning

confidence: 99%

“…Indeed, Hg–DOC relationships have been repeatedly observed across space (Braaten et al, ; Luo et al, ; MacMillan et al, ) and time (Burns et al, ; de Wit et al, ; Gerson & Driscoll, ) scales. MeHg–DOC relationships have been found to be weaker than THg–DOC relationships in the literature (Burns et al, ; Hall et al, ; Lescord et al, ), which could be due to the origin and molecular composition of DOC (Bravo et al, , ) or to photodemethylation of MeHg in presence of DOC (Girard et al, ). Stronger relationships with Hg have been found for the aromatic fraction of DOC as measured by SUVA 254 or UV 254 (Burns et al, ; Riscassi & Scanlon, ) or by specific families of compounds measured by fluorescence and analyzed by parallel factor analysis (Jiang et al, ) than for bulk DOC concentrations.…”

Section: Introductionmentioning

confidence: 98%

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Global Meta‐Analysis on the Relationship Between Mercury and Dissolved Organic Carbon in Freshwater Environments

2019

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In freshwater ecosystems, several studies have shown a strong linear relationship between total mercury (THg) or methylmercury (MeHg) and dissolved organic carbon (DOC) concentrations. Variations in this linear relationship have been reported, but the magnitude and causes of this variation are not well known. The objective of this study was to conduct a meta‐analysis to quantify and understand the global variation of this mercury (Hg)–DOC association. This meta‐analysis included 54 studies in lentic and lotic ecosystems for a total of 85 THg–DOC and 59 MeHg–DOC relationships. There was an increase in Hg with DOC concentrations in water with a global average slope of 0.25 (confidence interval (CI): 0.20–0.35) ng/mg for THg and 0.029 (CI: 0.014–0.044) ng/mg for MeHg. Relationships were stronger for (1) North American studies, (2) natural environments compared to those disturbed by anthropogenic activities, (3) spatial studies compared to temporal studies, (4) filtered samples (THg only), and (5) the aromatic fraction of DOC compared to the bulk DOC. Coupling with DOC was stronger for THg than for MeHg. Ecosystem type (lentic vs. lotic), geographical coordinates, and publication year did not influence the strength of relationships. Overall, we show that there is a strong but variable coupling between carbon and mercury cycles in freshwater ecosystems globally and that this link is modulated regionally by geographic location, temporal scale, and human activity, with implications for understanding these rapidly changing biogeochemical processes in response to global change.

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

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Global Meta‐Analysis on the Relationship Between Mercury and Dissolved Organic Carbon in Freshwater Environments

2019

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Investigating molecular changes in organic matter composition in two Holocene lake‐sediment records from central Sweden using pyrolysis‐GC/MS

et al. 2017

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Organic matter (OM) is a key component of lake sediments, affecting carbon, nutrient, and trace metal cycling at local and global scales. Yet little is known about long‐term (millennial) changes in OM composition due to the inherent chemical complexity arising from multiple OM sources and from secondary transformations. In this study we explore how the molecular composition of OM changes throughout the Holocene in two adjacent boreal lakes in central Sweden and compare molecular‐level information with conventional OM variables, including total carbon, total nitrogen, C:N ratios, δ13C, and δ15N. To characterize the molecular OM composition, we employed a new method based on pyrolysis‐gas chromatography/mass spectrometry (Py‐GC/MS), which yields semiquantitative data on >100 organic compounds of different origin and degradation status. We identify large changes in OM composition after deglaciation (circa 8500 ± 500 B.C.), associated with early landscape development, and during the most recent 40–50 years, driven by degradation processes. With molecular‐level information we can also distinguish between natural landscape development and human catchment disturbance during the last 1700 years. Our study demonstrates that characterization of the molecular OM composition by the high‐throughput Py‐GC/MS method is an efficient complement to conventional OM variables for identification and understanding of past OM dynamics in lake‐sediment records. Holocene changes observed for pyrolytic compounds and compound classes known for having different reactivity indicate the need for further paleo‐reconstruction of the molecular OM composition to better understand both past and future OM dynamics and associated environmental changes.

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Mercury in the Black Sea: New Insights From Measurements and Numerical Modeling

Rosati

Heimbürger

Canu

et al. 2018

Global Biogeochemical Cycles

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Redox conditions and organic matter control marine methylmercury (MeHg) production. The Black Sea is the world's largest and deepest anoxic basin and is thus ideal to study Hg species along the extended redox gradient. Here we present new dissolved Hg and MeHg data from the 2013 GEOTRACES MEDBlack cruise (GN04_leg2) that we integrated into a numerical 1‐D model, to track the fate and dynamics of Hg and MeHg. Contrary to a previous study, our new data show highest MeHg concentrations in the permanently anoxic waters. Observed MeHg/Hg percentage (range 9–57%) in the anoxic waters is comparable to other subsurface maxima in oxic open‐ocean waters. With the modeling we tested for various Hg methylation and demethylation scenarios along the redox gradient. The results show that Hg methylation must occur in the anoxic waters. The model was then used to simulate the time evolution (1850–2050) of Hg species in the Black Sea. Our findings quantify (1) inputs and outputs of Hg T (~31 and ~28 kmol yr −1 ) and MeHg T (~5 and ~4 kmol yr −1 ) to the basin, (2) the extent of net demethylation occurring in oxic (~1 kmol yr −1 ) and suboxic water (~6 kmol yr −1 ), (3) and the net Hg methylation in the anoxic waters of the Black Sea (~11 kmol yr −1 ). The model was also used to estimate the amount of anthropogenic Hg (85–93%) in the Black Sea.

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Molecular composition of organic matter controls methylmercury formation in boreal lakes

Cited by 246 publications

References 51 publications

Global Meta‐Analysis on the Relationship Between Mercury and Dissolved Organic Carbon in Freshwater Environments

Global Meta‐Analysis on the Relationship Between Mercury and Dissolved Organic Carbon in Freshwater Environments

Investigating molecular changes in organic matter composition in two Holocene lake‐sediment records from central Sweden using pyrolysis‐GC/MS

Mercury in the Black Sea: New Insights From Measurements and Numerical Modeling

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