Source tracing of natural organic matter bound mercury in boreal forest runoff with mercury stable isotopes

Jiskra, Martin; Wiederhold, Jan G.; Skyllberg, Ulf; Kronberg, Rose-Marie; Kretzschmar, Ruben

doi:10.1039/c7em00245a

Cited by 77 publications

(107 citation statements)

References 93 publications

(98 reference statements)

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“…However, under different flow paths such as runoff vs. baseflow, the exact source(s) of Hg can vary. It should be noted that mobilization of Hg associated with DOM can occur through the release of DOM-Hg complexes from soil OM without inducing additional MDF (Jiskra et al 2017). The binary mixing model results show that Hg in soil and river water is mainly derived from previous dry deposition into the watersheds, which is consistent with other studies in vegetated ecosystems examining both soil (Demers et al 2013;Enrico et al 2016;Obrist et al 2017) and surface-water samples (Jiskra et al 2017;Woerndle et al 2018).…”

Section: Transport and Sources Of Mercury In Riverssupporting

confidence: 89%

“…Recent studies measuring the natural abundance of Hg stable isotope ratios have shown that the source(s) of Hg in surface water can be constrained by examining the isotopic composition of aqueous Hg. Both MDF and odd-MIF can vary depending on the hydrological conditions and atmospheric deposition of Hg in the watersheds (Jiskra et al 2017;Woerndle et al 2018). Thus, Hg isotope analyses may potentially help distinguish changes in the source(s) of Hg during extreme flooding events in blackwater river ecosystems if water sampling is conducted during the period of rapid changes in river hydrographs (Phillips and Slattery 2007;Majidzadeh et al 2017).…”

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confidence: 99%

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Concentration and isotopic composition of mercury in a blackwater river affected by extreme flooding events

Tsui

Uzun

Ruecker

et al. 2020

Limnology & Oceanography

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Torrential rain and extreme flooding caused by Atlantic hurricanes mobilize a large pool of organic matter (OM) from coastal forested watersheds in the southeastern United States. However, the mobilization of toxic metals such as mercury (Hg) that are associated with this vast pool of OM are rarely measured. This study aims to assess the variations of total Hg (THg) and methylmercury (MeHg) levels and the isotopic compositions of Hg in a blackwater river (Waccamaw River, SC, U.S.A.) during two recent extreme flooding events induced by Hurricane Joaquin (October 2015) and Hurricane Matthew (October 2016). We show that extreme flooding considerably increased filtered THg and MeHg concentrations associated with aromatic dissolved organic matter. During a 2‐month sampling window each year (October–November), we estimate that about 27% (2015) and 78% (2016) of the average amount of Hg deposited atmospherically during these 2 months was exported via the river. The isotopic composition of Hg in the river waters was changed only slightly by the substantial inputs of runoff from surrounding landscapes, in which mass‐dependent fractionation (as δ202Hg) decreased from −1.47 to −1.67‰ and mass‐independent fractionation (as ∆199Hg) decreased from −0.15 to −0.37‰. The slight variations in Hg isotopic composition during such extreme flooding events imply that sources of Hg in the river are nearly unchanged even under the very high wet deposition of Hg derived from the intensive rainfall. The majority of Hg exported by the river (74–85%) is estimated to have been derived from dry deposition to the watersheds. An increase in frequency and intensity of Atlantic hurricanes is expected in the next few decades due to further warming of ocean surface waters. We predict that increased hurricanes will mobilize more dry‐deposited Hg and in situ produced MeHg from these coastal watersheds where MeHg can be extensively bioaccumulated and biomagnified in the downstream aquatic food webs.

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Section: Transport and Sources Of Mercury In Riverssupporting

confidence: 89%

mentioning

confidence: 99%

Concentration and isotopic composition of mercury in a blackwater river affected by extreme flooding events

Tsui

Uzun

Ruecker

et al. 2020

Limnology & Oceanography

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“…Although the short‐term (1–2 years) decomposition period does not infer long‐term accumulation trend, the continual coverage of newly deposited litter can block external Hg uptake by the decomposing litter underneath (X Wang, Lin, et al, ) and possibly cause Hg loss in the decomposing litter through C and N mineralization. Reemission of Hg 0 by biologically mediated reduction can lead to a positive shift of δ 202 Hg on forest floor without significant MIF (M. Jiskra et al, , ; Kritee et al, , ; Woerndle et al, ). The more positive δ 202 Hg (~1–1.5‰ shift) in surface soil than in fresh litter confirms such Hg loss during long‐term litter decomposition mediated biologically because of negligible MIF shifts (Figures a–d).…”

Section: Resultsmentioning

confidence: 99%

Effects of Precipitation on Mercury Accumulation on Subtropical Montane Forest Floor: Implications on Climate Forcing

et al. 2019

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Processes facilitated by precipitation play an important role on mercury (Hg) accumulation on forest floor and therefore key to Hg cycling in forest ecosystems. Sites along the windward slope of 1,250 to 2,400 m at Mt. Ailao, Southwestern China, have higher precipitation than the leeward slope sites. In this study, measurements of Hg concentration and associated stable isotope composition for soil, fresh, and degraded litterfall samples were made at sites along two slopes of Mt. Ailao to quantify the direct and indirect effects of precipitation on Hg accumulation on forest floor. Higher soil Hg concentrations, larger litterfall Hg depositions, and faster litter decomposition rates were observed on the windward slope (1,250-2,400 m). Data of Hg isotopic signatures suggest that Hg in surface soils is mainly derived from litterfall Hg input. Precipitation enhances litterfall Hg deposition by increasing litter biomass production, reduces litter decomposition rate, facilitates short-term Hg uptake to decomposing litter, and potentially increases microbial activity that increases Hg loss via microbial reduction or runoff. Structural equation modeling results support that the indirect effect of precipitation on increased biomass production merge as the most important factor controlling soil Hg variation. Given the climate forcing on global precipitation pattern and vegetation growth cycle, Hg biogeochemical cycling is likely to continue to evolve under the changing climate.Plain Language Summary Precipitation has direct and indirect effects on Hg accumulation and transformation on forest floor. The direct effect is that atmospheric Hg enters into forest floor via precipitation, throughfall, and cloud water deposition. In addition, precipitation likely has an indirect effect on Hg accumulation by influencing litter biomass production and postdepositional processes of Hg, such as litter decomposition, Hg reemission, and surface runoff. The objective of this study is to better quantify the direct and indirect effects of precipitation on Hg accumulation on forest floor. The study sites are located along the leeward and windward slopes of Mt. Ailao in Southwest China. Precipitation intensity is the main variable at the same altitude between two slopes. Our results showed that influences from precipitation on soil Hg accumulation are largely through the indirect effects caused by influencing litterfall Hg deposition. We also suggest that the changed precipitation pattern can force variations of litterfall Hg deposition and soil Hg accumulation globally.

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“…It has long been suggested that OM mediates the transport of Hg from terrestrial to the adjacent aquatic environment. Negatively charged surfaces of OM are enriched with carboxyl functional groups (RCOO − ), and thiolates (RS − ) in OM behave as ligands to form a transition metal thiolate complex, which leads to a strong binding affinity with trace metals including Hg [34][35][36] . These associations among OM, thiolates, and THg contents can explain the positive relationships among them as observed in the Svalbard fjords ( Fig.…”

Section: Discussionmentioning

confidence: 99%

Input of terrestrial organic matter linked to deglaciation increased mercury transport to the Svalbard fjords

Kim

Kwon

Lee

et al. 2020

Sci Rep

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Deglaciation has accelerated the transport of minerals as well as modern and ancient organic matter from land to fjord sediments in Spitsbergen, Svalbard, in the European Arctic Ocean. Consequently, such sediments may contain significant levels of total mercury (THg) bound to terrestrial organic matter. The present study compared THg contents in surface sediments from three fjord settings in Spitsbergen: Hornsund in the southern Spitsbergen, which has high annual volume of loss glacier and receives sediment from multiple tidewater glaciers, Dicksonfjorden in the central Spitsbergen, which receives sediment from glacifluvial rivers, and Wijdefjorden in the northern Spitsbergen, which receive sediments from a mixture of tidewater glaciers and glacifluvial rivers. Our results showed that the THg (52 ± 15 ng g −1) bound to organic matter (OM) was the highest in the Hornsund surface sediments, where the glacier loss (0.44 km 3 yr −1) and organic carbon accumulation rates (9.3 ~ 49.4 g m −2 yr −1) were elevated compared to other fjords. Furthermore, the δ 13 C (-27 ~-24‰) and δ 34 S values (-10 ~ 15‰) of OM indicated that most of OM were originated from terrestrial sources. Thus, the temperature-driven glacial melting could release more oM originating from the meltwater or terrestrial materials, which are available for THg binding in the European Arctic fjord ecosystems. Increasing temporal trends of total mercury (THg) concentration in the sediments of the Arctic continental shelves and lakes have recently been reported 1,2. These increasing levels have been proposed to be caused by the long-distance transport of anthropogenic mercury (Hg) from industrialized countries to the Arctic, given its long atmospheric lifetime of 0.3 to 2 years 3,4. In addition, it has been shown that ' Atmospheric Mercury Depletion Events' (AMDE) in the spring can lead to high Hg deposition in the Arctic Ocean. Reactive Hg (Hg 2+) is rapidly formed through in situ oxidation of gaseous Hg° by halogens (i.e., atomic Br and radical BrO), which are generated by solar irradiation through O 3 destruction 5-7. However, previous measurements of atmospheric Hg deposition in the Arctic regions have revealed relatively low deposition rates of <5 µg m −2 yr −1 8. Recent studies have suggested that natural processes governing Hg release via riverine transport 9 , soil runoff, and/or discharge of water coming from thawing permafrost 10 could be important sources of Hg to the Arctic environments. Fjords on Svalbard, the main island of the Svalbard archipelago, is among the most studied fjord systems in the world 11. Previous studies have focused on the effects of local and/or long-range transport, oceanic currents, and long-term sediment deposition rates (i.e., geological and chemical processes that control Hg distribution in surface and core sediments) 4,12-17 on spatial distribution and the extent of accumulation of Hg in the fjord sediment. Recent studies have shown that fjords are effective sequesters of organic carbon among other marine

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Source tracing of natural organic matter bound mercury in boreal forest runoff with mercury stable isotopes

Cited by 77 publications

References 93 publications

Concentration and isotopic composition of mercury in a blackwater river affected by extreme flooding events

Concentration and isotopic composition of mercury in a blackwater river affected by extreme flooding events

Effects of Precipitation on Mercury Accumulation on Subtropical Montane Forest Floor: Implications on Climate Forcing

Input of terrestrial organic matter linked to deglaciation increased mercury transport to the Svalbard fjords

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