Forest harvest contribution to Boreal freshwater methyl mercury load

Kronberg, Rose-Marie; Drott, Andreas; Jiskra, Martin; Wiederhold, Jan G.; Björn, Erik; Skyllberg, Ulf

doi:10.1002/2015gb005316

Cited by 46 publications

(51 citation statements)

References 88 publications

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“…through forest harvest (clear-cut), after which increased Hg concentrations in water, zooplankton, and fish have been observed [9,16,17,18,19,20]. In two accompanying studies we reported that forest harvest lead to an enhanced MeHg formation in soils and an increased MeHg transport from the same study sites [21,22].…”

Section: Introductionmentioning

confidence: 71%

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

Jiskra

Wiederhold

Skyllberg

et al. 2017

Environ. Sci.: Processes Impacts

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Terrestrial runoff represents a major source of mercury (Hg) to aquatic ecosystems. In boreal forest catchments, such as the one in northern Sweden studied here, mercury bound to natural organic matter (NOM) represents a large fraction of mercury in the runoff. We present a method to measure Hg stable isotope signatures of colloidal Hg, mainly complexed by high molecular weight or colloidal natural organic matter (NOM) in natural waters based on pre-enrichment by ultrafiltration, followed by freeze-drying and combustion. We report that Hg associated with high molecular weight NOM in the boreal forest runoff has very similar Hg isotope signatures as compared to the organic soil horizons of the catchment area. The mass-independent fractionation (MIF) signatures (ΔHg and ΔHg) measured in soils and runoff were in agreement with typical values reported for atmospheric gaseous elemental mercury (Hg) and distinctly different from reported Hg isotope signatures in precipitation. We therefore suggest that most Hg in the boreal terrestrial ecosystem originated from the deposition of Hg through foliar uptake rather than precipitation. Using a mixing model we calculated the contribution of soil horizons to the Hg in the runoff. At moderate to high flow runoff conditions, that prevailed during sampling, the uppermost part of the organic horizon (Oe/He) contributed 50-70% of the Hg in the runoff, while the underlying more humified organic Oa/Ha and the mineral soil horizons displayed a lower mobility of Hg. The good agreement of the Hg isotope results with other source tracing approaches using radiocarbon signatures and Hg : C ratios provides additional support for the strong coupling between Hg and NOM. The exploratory results from this study illustrate the potential of Hg stable isotopes to trace the source of Hg from atmospheric deposition through the terrestrial ecosystem to soil runoff, and provide a basis for more in-depth studies investigating the mobility of Hg in terrestrial ecosystems using Hg isotope signatures.

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Section: Introductionmentioning

confidence: 71%

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

Jiskra

Wiederhold

Skyllberg

et al. 2017

Environ. Sci.: Processes Impacts

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“…Not surprisingly, Hg mass positively correlated with depth of sampled mineral horizons (P = 0.01), explaining 45% of the variance in Hg mass across these soil pits. Compared to Hg mass in these Arctic tundra soils, mass estimates in temperate forest areas generally show smaller pool sizes, in the range of 120 to 170 g/ha in eastern Germany (Schwesig et al, 1999), 213 g/ha in the northeastern United States (Yu et al, 2014), 53 g/ha in mineral soils of a Minnesota forest (Grigal et al, 2000), and 12 to 80 g/ha in Swedish boreal forests (Kronberg, Drott, et al, 2016). Although comparisons across sites are challenging because different studies reference results to different soil depths, remote Arctic tundra soils show some of the highest Hg pools in soils compared to most temperate soils.…”

Section: Active-layer Hg Pool Sizes In Northern Alaska Arctic Tundra mentioning

confidence: 93%

Mercury in Active‐Layer Tundra Soils of Alaska: Concentrations, Pools, Origins, and Spatial Distribution

Olson

Jiskra

Biester

et al. 2018

Global Biogeochemical Cycles

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Tundra soils serve as major sources of mercury (Hg) input to the Arctic Ocean via river runoff and coastal erosion; yet little information is available on tundra soil Hg concentrations, pool sizes, origins, and dynamics. We present a detailed investigation of Hg in the active layer (upper ~100 cm subject to seasonal thaw) of tundra soils across 11 sites in Alaska. Soil Hg concentrations in organic horizons (151 ± 7 μg/kg) were in the upper range of temperate soil organic horizons, and concentrations in mineral horizons (98 ± 6 μg/kg) were much higher than in temperate soils. Soil Hg concentrations declined from inland to coastal sites, in contrast to a hypothesized northward increase expected because of proximity to coastal atmospheric mercury depletion events. Principle component analyses and elemental ratios results show that exogenic sources dominated over geogenic sources—in A‐horizons (66 ± 4%) and mineral B‐horizons (51 ± 1%). 14C age‐dating suggested recent origins of Hg in surface soils but showed that mineral soils (more than 7,300 years old) must have accumulated atmospheric inputs across millennia leading to high soil concentrations and pools. We estimated a total Northern Hemisphere active‐layer tundra soil Hg pool of 184 Gg (range of 136 to 274 Gg), suggesting a globally important Hg storage pool. Tundra soils are subject to seasonal thaw and freeze dynamics, thereby providing large inputs to rivers, lakes, and the Arctic Ocean. Understanding processes that mobilize Hg from tundra soils will be critical to understanding future Arctic wildlife and human Hg exposures.

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“…This suggests that non-essential Hg in these aquatic consumers is associated with the retention of equally non-essential terrestrial OM, from a nutritional point of view (Grey et al, 2001;Jansson et al, 2007;Cole et al, 2011;Karlsson et al, 2012;Lau et al, 2012). The OM-Hg interactions have been intensively studied with a general consensus that OM mobilizes total Hg and MeHg from soil to waters (Skyllberg et al, 2000;Shanley & Bishop, 2012;Kronberg et al, 2016). The high abundance of cladocerans across oligotrophic lakes is strongly exposed to terrestrial food sources (Berggren et al, 2014) and, once ingested, Hg may be equally transferred via such terrestrial as well as algal food sources, as seen in this study.…”

Section: Discussionmentioning

confidence: 99%

“…Increasing DOC concentrations derived from terrestrial sources can themselves potentially increase Hg bioaccumulation in estuarine ecosystem food webs (French et al, 2014;Jonsson et al, 2014;Jonsson et al, 2017). This is also relevant in boreal ecosystems as common forest harvest activities can enhance terrestrial OM input to lake (Meunier et al, 2016), resulting in increased DOC concentrations (O'Driscoll et al, 2006;Glaz et al, 2015), and sometimes higher Hg and/or MeHg input from terrestrial to aquatic ecosystems (Eklöf et al, 2013;Kronberg et al, 2016). This can increase Hg bioaccumulation in food webs (Bishop et al, 2009;Hongve et al, 2012;Wu et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

Terrestrial diet influences mercury bioaccumulation in zooplankton and macroinvertebrates in lakes with differing dissolved organic carbon concentrations

Kainz

Åkerblom

et al. 2019

Science of The Total Environment

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Dietary uptake is a key step in conveying both toxic mercury (Hg; particularly as highly bioavailable methylmercury, MeHg) and essential dietary biochemicals, such as polyunsaturated fatty acids (PUFA), across trophic levels within aquatic food webs. Using stable isotopes and fatty acids we evaluated the role of food sources in size-fractioned plankton and littoral macroinvertebrates for the bioaccumulation of total Hg and MeHg in six oligotrophic and one mesotrophic Swedish lakes with differing concentrations of dissolved organic carbon (DOC). We found that the consumption of both algal and terrestrial diets (assessed by PUFA and long-chain saturated fatty acids, respectively) predicted >66% of the Hg concentration variability in meso-(100-500 µm) and macrozooplankton (>500 µm) in oligotrophic lakes. In the mesotrophic lake, total Hg bioaccumulation in higher trophic level biota, carnivorous macroinvertebrates was also significantly related to terrestrial diet sources (R 2 =0.65, p<0.01). However, lake pH and DOC correlated to total Hg bioaccumulation and bioconcentration across all lakes, suggesting the consumption of different diet sources is mediated by the influence of lake characteristics. This field study reveals that using dietary biomarkers (stable isotopes and fatty acids) together with the physico-chemical lake parameters pH and nutrients together improve our ability to predict Hg bioaccumulation in aquatic food webs. Fatty acids used as dietary biomarkers provide correlative evidence of specific diet source retention in consumers and their effect on Hg bioaccumulation, while pH and nutrients are the underlying physico-chemical lake parameters controlling differences in Hg bioaccumulation between lakes.

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Forest harvest contribution to Boreal freshwater methyl mercury load

Cited by 46 publications

References 88 publications

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

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

Mercury in Active‐Layer Tundra Soils of Alaska: Concentrations, Pools, Origins, and Spatial Distribution

Terrestrial diet influences mercury bioaccumulation in zooplankton and macroinvertebrates in lakes with differing dissolved organic carbon concentrations

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