Degradation of sterols and terrigenous organic matter in waters of the Mackenzie Shelf, Canadian Arctic

Rontani, J.‐F.; Charrìère, Bruno; Sempéré, Richard; Doxaran, David; Vaultier, Frédéric; Vonk, Jorien E.; Volkman, John K.

doi:10.1016/j.orggeochem.2014.06.002

Cited by 60 publications

(78 citation statements)

References 76 publications

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“…Photo-oxidation degradation products, although probably underestimated, only stand at 10 % (on average across all samples) of the remaining sitosterol amounts. While autoxidation processes appeared to play only a minor role during the degradation of sitosterol in the cold Mackenzie River (Arctic) (Rontani et al, 2014b), it is worth questioning the role that temperature plays in OM degradation, and wondering if it influences one degradation process over the others: do the temperatures found in the Rhône River, warmer than those of the Mackenzie, favor autoxidation? However, the low autoxidation state in the Mackenzie River could also be attributed to the presence of significant proportions of fresh sitosterol-producing phytoplanktonic species (Tolosa et al, 2013).…”

Section: Discussionmentioning

confidence: 99%

“…After evaporation to dryness under a stream of N 2 , the derivatized residues were taken up in 100 µL BSTFA (to avoid desilylation of fatty acids) and an appropriate amount of ethyl acetate, depending on the concentration in lipids in each sample, in order to get the best possible GC-EIMS reading. It should be noted that under these conditions steran-3β,5α,6β-triols were silylated only at C3 and C6 and thus need to be analyzed with great care (Rontani et al, 2014b). A different treatment was used to quantify hydroperoxides and their ketonic and alcoholic degradation products.…”

Section: Chemical Treatment Of the Samplesmentioning

confidence: 99%

“…This assumption was well supported by the detection of significant proportions of compounds deriving from betulin autoxidation (data not shown). Recently, it has been demonstrated that autoxidation plays a key role in the degradation of terrestrial (Rontani et al, 2014b) and marine (Rontani et al, 2014a) vascular plant debris in seawater. There is clearly a growing body of evidence suggesting that autoxidation reactions can strongly impact the preservation of particulate organic matter in the environment and should be considered carefully alongside other removal processes such as biodegradation when constructing carbon cycles and evaluating carbon budgets.…”

Section: -Sterolsmentioning

confidence: 99%

“…Probably due to high compartmentalization effects, preservation of these compounds seems to be enhanced in higher plant debris. It was recently proposed that homolytic cleavage of photochemically produced hydroperoxides in riverine POM could be catalyzed by some redoxactive metal ions released from SPM in the mixing zone of riverine and marine waters (Rontani et al, 2014b). Due to the presence of significant amounts of hydroperoxides in higher plant residues, the involvement of intensive autoxidation of this material in the Rhône estuary is thus likely.…”

Section: Hydroperoxide Stability In Spmmentioning

confidence: 99%

“…However, coastal sediments have shown very little trace of a terrestrial OM signature (Hedges and Keil, 1995;McKee et al, 2004), which implies that either global carbon fluxes and budgets are wrong, or, as is more likely, that terrestrial POM undergoes a rapid and intense degradation upon its arrival at sea (Hedges et al, 1997). The belief that terrestrial POM is refractory to all sorts of decomposition has been recently challenged through studies in the Mediterranean Sea (Bourgeois et al, 2011) and northern Canada (Rontani et al, 2014b), showing that wellpreserved TPOM is heavily degraded upon leaving river systems. This is why we intend to study the chemical structure and degradation state of TPOM in the Rhône River, in order to better understand how such an intense degradation can be possible at sea, while it was not during freshwater transport.…”

Section: Introductionmentioning

confidence: 99%

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Seasonal survey of the composition and degradation state of particulate organic matter in the Rhône River using lipid tracers

et al. 2015

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Abstract. Lipid tracers including fatty acids, hydroxyacids, n-alkanols, sterols and triterpenoids were used to determine the origin and fate of suspended particulate organic matter (POM) collected in the Rhône River (France). This seasonal survey (April 2011 to May 2013) revealed a yearround strong terrestrial higher-plant contribution to the particulate organic matter (POM), with significant algal inputs observed in March and attributed to phytoplanktonic blooms likely dominated by diatoms. Major terrigenous contributors to our samples are gymnosperms, and more precisely their roots and stems, as evidenced by the presence of high proportions of ω-hydroxydocosanoic acid (a suberin biomarker). The high amounts of coprostanol detected clearly show that the Rhône River is significantly affected by sewage waters.Specific sterol degradation products were quantified and used to assess the part of biotic and abiotic degradation of POM within the river. Higher-plant-derived organic matter appears to be mainly affected by photo-oxidation and autoxidation (free radical oxidation), while organic matter of mammal or human origin, evidenced by the presence of coprostanol, is clearly more prone to bacterial degradation. Despite the involvement of an intense autoxidation-inducing homolytic cleavage of peroxy bonds, a significant proportion of hydroperoxides is still intact in higher plant debris. These compounds could affect the degradation of terrestrial material by inducing an intense autoxidation upon its arrival at sea.

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Section: Discussionmentioning

confidence: 99%

Section: Chemical Treatment Of the Samplesmentioning

confidence: 99%

Section: -Sterolsmentioning

confidence: 99%

Section: Hydroperoxide Stability In Spmmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Seasonal survey of the composition and degradation state of particulate organic matter in the Rhône River using lipid tracers

et al. 2015

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Biogeochemical drivers of the fate of riverine mercury discharged to the global and Arctic oceans

Zhang

Jacob

Dutkiewicz

et al. 2015

Global Biogeochemical Cycles

112

121

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Rivers discharge 28 ± 13 Mmol yr À1 of mercury (Hg) to ocean margins, an amount comparable to atmospheric deposition to the global oceans. Most of the Hg discharged by rivers is sequestered by burial of benthic sediment in estuaries or the coastal zone, but some is evaded to the atmosphere and some is exported to the open ocean. We investigate the fate of riverine Hg by developing a new global 3-D simulation for Hg in the Massachusetts Institute of Technology ocean general circulation model. The model includes plankton dynamics and carbon respiration (DARWIN project model) coupled to inorganic Hg chemistry. Results are consistent with observed spatial patterns and magnitudes of surface ocean Hg concentrations. We use observational constraints on seawater Hg concentrations and evasion to infer that most Hg from rivers is sorbed to refractory organic carbon and preferentially buried. Only 6% of Hg discharged by rivers (1.8 Mmol yr À1) is transported to the open ocean on a global basis. This fraction varies from a low of 2.6% in East Asia due to the barrier imposed by the Korean Peninsula and Japanese archipelago, up to 25% in eastern North America facilitated by the Gulf Stream. In the Arctic Ocean, low tributary particle loads and efficient degradation of particulate organic carbon by deltaic microbial communities favor a more labile riverine Hg pool. Evasion of Hg to the Arctic atmosphere is indirectly enhanced by heat transport during spring freshet that accelerates sea ice melt and ice rafting. Discharges of 0.23 Mmol Hg yr À1 from Arctic rivers can explain the observed summer maximum in the Arctic atmosphere, and this magnitude of releases is consistent with recent observations. Our work indicates that rivers are major contributors to Hg loads in the Arctic Ocean.

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Autoxidation as a major player in the fate of terrestrial particulate organic matter in seawater

et al. 2017

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The Rhône River plays a major role in the Mediterranean Sea, being both its main freshwater source and its major particulate matter provider. This survey of the fate of terrestrial particulate organic matter (POM) was conducted along the salinity gradient of the Rhône River plume, between 2012 and 2014. It revealed that autoxidation acts rapidly and intensely upon the POM's arrival at sea, with α‐amyrin and β‐amyrin autoxidation rates going from 12.9 ± 2.9% to 45.0 ± 6.4% and 10.7 ± 4.0% to 50.3 ± 4.4%, respectively, between fresh water (salinity 0) and seawater (salinity 38). These compounds, being unambiguous markers of the terrestrial origin of POM, allow us to unequivocally characterize the POM as terrestrial. While it was originally believed that a desorption of redox‐active trace metal ions was the favoring factor that kick‐started this intense autoxidation, this study evidences no trace metal desorption in the Rhône River mixing zone and hence no correlation between high autoxidation rates and the presence of trace metal ions. Autoxidation rates however were very well correlated with salinity levels within the river plume, with r2 reaching 0.801, 0.962, and 0.943 for sitosterol, α‐amyrin, and β‐amyrin, respectively, in November 2014.

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Degradation of sterols and terrigenous organic matter in waters of the Mackenzie Shelf, Canadian Arctic

Cited by 60 publications

References 76 publications

Seasonal survey of the composition and degradation state of particulate organic matter in the Rhône River using lipid tracers

Seasonal survey of the composition and degradation state of particulate organic matter in the Rhône River using lipid tracers

Biogeochemical drivers of the fate of riverine mercury discharged to the global and Arctic oceans

Autoxidation as a major player in the fate of terrestrial particulate organic matter in seawater

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