2014
Tsui, Martin Tsz-Ki; Blum, Joel D.; Finlay, Jacques C.; Balogh, Steven J.; Nollet, Yabing H.; Palen, Wendy J.; Power, Mary E.
Variation in Terrestrial and Aquatic Sources of Methylmercury in Stream Predators as Revealed by Stable Mercury Isotopes Journal Article
In: Environmental Science & Technology, vol. 48, no. 17, pp. 10128–10135, 2014.
Abstract | Links | BibTeX | Tags: Mercury Isotope, Methylmercury
@article{Tsui2014,
title = {Variation in Terrestrial and Aquatic Sources of Methylmercury in Stream Predators as Revealed by Stable Mercury Isotopes},
author = {Martin Tsz-Ki Tsui and Joel D. Blum and Jacques C. Finlay and Steven J. Balogh and Yabing H. Nollet and Wendy J. Palen and Mary E. Power},
url = {https://angelo.berkeley.edu/wp-content/uploads/sites/59/2015/01/Tsui_MethylMercuryinStream_EnvSciTech2014.pdf},
doi = {10.1021/es500517s},
year = {2014},
date = {2014-08-08},
journal = {Environmental Science & Technology},
volume = {48},
number = {17},
pages = {10128–10135},
abstract = {Mercury (Hg) is widely distributed in the environment, and its organic form, methylmercury (MeHg), can extensively bioaccumulate and biomagnify in aquatic and terrestrial food webs. Concentrations of MeHg in organisms are highly variable, and the sources in natural food webs are often not well understood. This study examined stable isotope ratios of MeHg (mass-dependent fractionation, as δ202HgMeHg; and mass-independent fractionation, as Δ199HgMeHg) in benthic invertebrates, juvenile steelhead trout (Oncorhynchus mykiss), and water striders (Gerris remigis) along a stream productivity gradient, as well as carnivorous terrestrial invertebrates, in a forested watershed at the headwater of South Fork Eel River in northern California. Throughout the sampling sites, δ202HgMeHg (after correction due to the effect of MeHg photodegradation) was significantly different between benthic (median = −1.40‰; range, −2.34 to −0.78‰; total number of samples = 29) and terrestrial invertebrates (median = +0.51‰; range, −0.37 to +1.40‰; total number of samples = 9), but no major difference between these two groups was found for Δ199HgMeHg. Steelhead trout (52 individual fishes) have MeHg of predominantly aquatic origins, with a few exceptions at the upstream locations (e.g., 1 fish collected in a tributary had a purely terrestrial MeHg source and 4 fishes had mixed aquatic and terrestrial MeHg sources). Water striders (seven pooled samples) derive MeHg largely from terrestrial sources throughout headwater sections. These data suggest that direct terrestrial subsidy (e.g., terrestrial invertebrates falling into water) can be important for some stream predators in headwater streams and could represent an important means of transfer of terrestrially derived MeHg (e.g., in situ methylation within forests, atmospheric sources) to aquatic ecosystems. Moreover, these findings show that terrestrial subsidies can enhance MeHg bioaccumulation of consumers in headwater streams where aqueous MeHg levels are very low.},
keywords = {Mercury Isotope, Methylmercury},
pubstate = {published},
tppubtype = {article}
}
Mercury (Hg) is widely distributed in the environment, and its organic form, methylmercury (MeHg), can extensively bioaccumulate and biomagnify in aquatic and terrestrial food webs. Concentrations of MeHg in organisms are highly variable, and the sources in natural food webs are often not well understood. This study examined stable isotope ratios of MeHg (mass-dependent fractionation, as δ202HgMeHg; and mass-independent fractionation, as Δ199HgMeHg) in benthic invertebrates, juvenile steelhead trout (Oncorhynchus mykiss), and water striders (Gerris remigis) along a stream productivity gradient, as well as carnivorous terrestrial invertebrates, in a forested watershed at the headwater of South Fork Eel River in northern California. Throughout the sampling sites, δ202HgMeHg (after correction due to the effect of MeHg photodegradation) was significantly different between benthic (median = −1.40‰; range, −2.34 to −0.78‰; total number of samples = 29) and terrestrial invertebrates (median = +0.51‰; range, −0.37 to +1.40‰; total number of samples = 9), but no major difference between these two groups was found for Δ199HgMeHg. Steelhead trout (52 individual fishes) have MeHg of predominantly aquatic origins, with a few exceptions at the upstream locations (e.g., 1 fish collected in a tributary had a purely terrestrial MeHg source and 4 fishes had mixed aquatic and terrestrial MeHg sources). Water striders (seven pooled samples) derive MeHg largely from terrestrial sources throughout headwater sections. These data suggest that direct terrestrial subsidy (e.g., terrestrial invertebrates falling into water) can be important for some stream predators in headwater streams and could represent an important means of transfer of terrestrially derived MeHg (e.g., in situ methylation within forests, atmospheric sources) to aquatic ecosystems. Moreover, these findings show that terrestrial subsidies can enhance MeHg bioaccumulation of consumers in headwater streams where aqueous MeHg levels are very low.
2013
Tsui, Martin Tsz Ki; Blum, Joel D.; Finlay, Jacques C.; Balogh, Steven J.; Kwon, Sae Yun; Nollet, Yabing H.
Photodegradation of methylmercury in stream ecosystems Journal Article
In: Limnology and Oceanography, vol. 58, no. 1, pp. 13–22, 2013.
Abstract | Links | BibTeX | Tags: Methylmercury, photodegradation
@article{Tsui2013,
title = {Photodegradation of methylmercury in stream ecosystems},
author = {Martin Tsz Ki Tsui and Joel D. Blum and Jacques C. Finlay and Steven J. Balogh and Sae Yun Kwon and Yabing H. Nollet},
url = {https://angelo.berkeley.edu/wp-content/uploads/sites/59/Tsui_2013_LimonolOcean.pdf},
doi = {10.4319/lo.2013.58.1.0013},
year = {2013},
date = {2013-01-01},
journal = {Limnology and Oceanography},
volume = {58},
number = {1},
pages = {13–22},
abstract = {Photodegradation is an important sink for highly toxic methylmercury (MeHg) in aquatic ecosystems. Lakes have been extensively studied for MeHg photodegradation, but much less is known about streams, mainly because of the heterogeneity in sunlight availability along stream reaches and because there has been a lack of tools with which to integrate this longitudinal variability. We utilize odd-mass anomalies of stable Hg isotopes (i.e., Δ199Hg) as a proxy for estimating the relative extent of MeHg photodegradation in streams. In a northern California stream network, levels of MeHg in water and biota increased with increasing stream size in headwater and intermediate streams (drainage areas ranging from 0.6 to 150 km2), but MeHg levels decreased substantially in larger streams (drainage areas up to 1212 km2). In smaller streams, the increase of MeHg levels is attributed to increasing in situ MeHg production and is accompanied by only a small increase in Δ199Hg, indicating that the rate of MeHg photodegradation is low relative to the rate of in situ MeHg production. In larger streams, decreasing MeHg levels coincided with significant increases in Δ199Hg of MeHg (an average increase of 1.5‰ ± 0.5‰},
keywords = {Methylmercury, photodegradation},
pubstate = {published},
tppubtype = {article}
}
Photodegradation is an important sink for highly toxic methylmercury (MeHg) in aquatic ecosystems. Lakes have been extensively studied for MeHg photodegradation, but much less is known about streams, mainly because of the heterogeneity in sunlight availability along stream reaches and because there has been a lack of tools with which to integrate this longitudinal variability. We utilize odd-mass anomalies of stable Hg isotopes (i.e., Δ199Hg) as a proxy for estimating the relative extent of MeHg photodegradation in streams. In a northern California stream network, levels of MeHg in water and biota increased with increasing stream size in headwater and intermediate streams (drainage areas ranging from 0.6 to 150 km2), but MeHg levels decreased substantially in larger streams (drainage areas up to 1212 km2). In smaller streams, the increase of MeHg levels is attributed to increasing in situ MeHg production and is accompanied by only a small increase in Δ199Hg, indicating that the rate of MeHg photodegradation is low relative to the rate of in situ MeHg production. In larger streams, decreasing MeHg levels coincided with significant increases in Δ199Hg of MeHg (an average increase of 1.5‰ ± 0.5‰
2012
Tsui, Martin Tsz Ki; Blum, Joel D.; Kwon, Sae Yun; Finlay, Jacques C.; Balogh, Steven J.; Nollet, Yabing H.
Sources and transfers of methylmercury in adjacent river and forest food webs Journal Article
In: Environmental Science & Technology, vol. 46, no. 20, pp. 10957–10964, 2012.
Abstract | Links | BibTeX | Tags: forest food web, Methylmercury, river food web
@article{Tsui2012,
title = {Sources and transfers of methylmercury in adjacent river and forest food webs},
author = {Martin Tsz Ki Tsui and Joel D. Blum and Sae Yun Kwon and Jacques C. Finlay and Steven J. Balogh and Yabing H. Nollet},
url = {https://angelo.berkeley.edu/wp-content/uploads/sites/59/Tsui_2012_EnvirScieTech.pdf},
doi = {10.1021/es3019836},
year = {2012},
date = {2012-10-04},
journal = {Environmental Science & Technology},
volume = {46},
number = {20},
pages = {10957–10964},
abstract = {Nearly all ecosystems are contaminated with highly toxic methylmercury (MeHg), but the specific sources and pathways leading to the uptake of MeHg within and among food webs are not well understood. In this study, we report stable mercury (Hg) isotope compositions in food webs in a river and an adjacent forest in northern California and demonstrate the utility of Hg isotopes for studying MeHg sources and cross-habitat transfers. We observed large differences in both δ202Hg (mass-dependent fractionation) and Δ199Hg (mass-independent fractionation) within both food webs. The majority of isotopic variation within each food web could be accounted for by differing proportions of inorganic Hg [Hg(II)] and MeHg along food chains. We estimated mean isotope values of Hg(II) and MeHg in each habitat and found a large difference in δ202Hg between Hg(II) and MeHg (∼2.7‰) in the forest but not in the river (∼0.25‰). This is consistent with in situ Hg(II) methylation in the study river but suggests Hg(II) methylation may not be important in the forest. In fact, the similarity in δ202Hg between MeHg in forest food webs and Hg(II) in precipitation suggests that MeHg in forest food webs may be derived from atmospheric sources (e.g., rainfall, fog). Utilizing contrasting δ202Hg values between MeHg in river food webs (−1.0‰) and MeHg in forest food webs (+0.7‰), we estimate with a two-source mixing model that ∼55% of MeHg in two riparian spiders is derived from riverine sources while ∼45% of MeHg originates from terrestrial sources. Thus, stable Hg isotopes can provide new information on subtle differences in sources of MeHg and trace MeHg transfers within and among food webs in natural ecosystems.},
keywords = {forest food web, Methylmercury, river food web},
pubstate = {published},
tppubtype = {article}
}
Nearly all ecosystems are contaminated with highly toxic methylmercury (MeHg), but the specific sources and pathways leading to the uptake of MeHg within and among food webs are not well understood. In this study, we report stable mercury (Hg) isotope compositions in food webs in a river and an adjacent forest in northern California and demonstrate the utility of Hg isotopes for studying MeHg sources and cross-habitat transfers. We observed large differences in both δ202Hg (mass-dependent fractionation) and Δ199Hg (mass-independent fractionation) within both food webs. The majority of isotopic variation within each food web could be accounted for by differing proportions of inorganic Hg [Hg(II)] and MeHg along food chains. We estimated mean isotope values of Hg(II) and MeHg in each habitat and found a large difference in δ202Hg between Hg(II) and MeHg (∼2.7‰) in the forest but not in the river (∼0.25‰). This is consistent with in situ Hg(II) methylation in the study river but suggests Hg(II) methylation may not be important in the forest. In fact, the similarity in δ202Hg between MeHg in forest food webs and Hg(II) in precipitation suggests that MeHg in forest food webs may be derived from atmospheric sources (e.g., rainfall, fog). Utilizing contrasting δ202Hg values between MeHg in river food webs (−1.0‰) and MeHg in forest food webs (+0.7‰), we estimate with a two-source mixing model that ∼55% of MeHg in two riparian spiders is derived from riverine sources while ∼45% of MeHg originates from terrestrial sources. Thus, stable Hg isotopes can provide new information on subtle differences in sources of MeHg and trace MeHg transfers within and among food webs in natural ecosystems.
2010
Tsui, Martin Tsz Ki; Finlay, Jacques C.; Balogh, Steven J.; Nollet, Yabing H.
In Situ Production of Methylmercury within a Stream Channel in Northern California Journal Article
In: Environmental Science & Technology, vol. 44, no. 18, pp. 6998–7004, 2010.
Abstract | Links | BibTeX | Tags: Methylmercury, phosphorus removal, stream channel
@article{Tsui2010,
title = {In Situ Production of Methylmercury within a Stream Channel in Northern California},
author = {Martin Tsz Ki Tsui and Jacques C. Finlay and Steven J. Balogh and Yabing H. Nollet},
url = {https://angelo.berkeley.edu/wp-content/uploads/sites/59/Tsui_2010_EnvirSciTech.pdf},
doi = {10.1021/es101374y},
year = {2010},
date = {2010-08-18},
urldate = {2010-08-18},
journal = {Environmental Science & Technology},
volume = {44},
number = {18},
pages = {6998–7004},
abstract = {Natural stream ecosystems throughout the world are contaminated by methylmercury, a highly toxic compound that bioaccumulates and biomagnifies in aquatic food webs. Wetlands are widely recognized as hotspots for the production of methylmercury and are often assumed to be the main sources of this neurotoxin in downstream ecosystems. However, many streams lacking wetlands in their drainage basins (e.g., montane and semiarid regions in the western United States) have significant methylmercury contamination, and the sources of methylmercury in these streams remain largely unknown. In this study, we observed substantial production of methylmercury within a highly productive stream channel in northern California (South Fork Eel River) within a drainage basin lacking wetlands. We found that in situ methylmercury production is positively related to phosphorus removal and water temperature within the stream channel, supporting hypothesized biological mediation of in situ mercury transformation. Moreover, our data suggest that epiphytic microbial communities on a dominant filamentous alga (Cladophora glomerata) could play a role in in situ methylmercury production. Because peak in situ methylmercury production coincides with the period of the highest biological productivity during summer baseflow, methylmercury produced internally may be efficiently routed into local stream food webs. Our study provides strong evidence that stream channels, especially those associated with high primary productivity, can be important for regulating the bioavailability and toxicity of this global contaminant.},
keywords = {Methylmercury, phosphorus removal, stream channel},
pubstate = {published},
tppubtype = {article}
}
Natural stream ecosystems throughout the world are contaminated by methylmercury, a highly toxic compound that bioaccumulates and biomagnifies in aquatic food webs. Wetlands are widely recognized as hotspots for the production of methylmercury and are often assumed to be the main sources of this neurotoxin in downstream ecosystems. However, many streams lacking wetlands in their drainage basins (e.g., montane and semiarid regions in the western United States) have significant methylmercury contamination, and the sources of methylmercury in these streams remain largely unknown. In this study, we observed substantial production of methylmercury within a highly productive stream channel in northern California (South Fork Eel River) within a drainage basin lacking wetlands. We found that in situ methylmercury production is positively related to phosphorus removal and water temperature within the stream channel, supporting hypothesized biological mediation of in situ mercury transformation. Moreover, our data suggest that epiphytic microbial communities on a dominant filamentous alga (Cladophora glomerata) could play a role in in situ methylmercury production. Because peak in situ methylmercury production coincides with the period of the highest biological productivity during summer baseflow, methylmercury produced internally may be efficiently routed into local stream food webs. Our study provides strong evidence that stream channels, especially those associated with high primary productivity, can be important for regulating the bioavailability and toxicity of this global contaminant.