Molybdenum geochemistry in a seasonally dysoxic Mo-limited lacustrine ecosystem

Jennifer B. Glass, Anthony Chappaz, Brooke Eustis, Alan C. Heyvaert, David P. Waetjen, Hilairy E. Hartnett, Ariel D. Anbar

    Research output: Contribution to journalArticle

    20 Citations (Scopus)

    Abstract

    Lakes are important for storage of the essential micronutrient molybdenum (Mo) during its transfer from the continents to the oceans, but little is known about the major sources and sinks for Mo in lacustrine ecosystems. We studied Mo cycling in Castle Lake, a small subalpine lake in the Klamath-Siskiyou Mountains of Northern California underlain primarily by mafic and ultramafic rocks where primary productivity is limited by Mo bioavailability. The deeper water of the lake becomes dysoxic (9-90μM dissolved oxygen) during the summer. This study was undertaken to identify the sources of Mo to Castle Lake and establish a Mo budget. We measured Mo concentrations in a suite of bulk solids (lake sediments, soils and bedrock) and aqueous samples (sediment porewaters, soil runoff, spring waters, snow and ice) from Castle Lake and its watershed. Lake sediments have elevated Mo (7-36ppm) compared to soils and bedrock (0.2-2ppm) and Mo/Al values were nearly two orders of magnitude higher than the crustal abundance. Sediment porewaters had higher Mo (4-15nM) than lake water (2-4nM), soil runoff (0.1-6.2nM), snowmelt (≤0.1nM), lake ice (0.3-2.2nM) and local spring waters (0.03-2.72nM). Bulk lake sediments had negative δ98/95Mo values, ranging from -0.5 to -1.0‰ (±0.1). We used the numerical model PROFILE to estimate the net reaction rate of Mo in the porewater. Model calculations ruled out diagenesis as a source of Mo to lake sediments; diagenetic Mo always represented ≤5% of the total Mo content in sediment. We also ruled out dissolved Mo inputs from groundwater and watershed inflow as important sources of Mo. Two whole-lake experimental Mo additions in the 1960's could have contributed a sizeable amount of Mo to the lake sediments, but only over a short period. Atmospheric deposition of anthropogenic Mo from extensive copper smelting that occurred south of Castle Lake from 1896 to 1919 and from major Californian urban centers today were negligible Mo sources. Mo flux from the sediments (0.4-0.5nmolcm-2yr-1) was roughly equal to Mo fluxes from surface inflow and outflow, whereas Mo burial fluxes were significantly higher (11.5nmolcm-2yr-1). Because dissolved Mo fluxes were minimal, and atmospheric Mo deposition was estimated to be a minor source of Mo (<1nmolcm-2yr-1), the largest source of Mo is non-detrital particulate matter (~12nmolcm-2yr-1), likely a mixture of organic matter and Fe-Mn oxyhydroxides as supported by Mo isotopic data.

    Original languageEnglish (US)
    Pages (from-to)204-219
    Number of pages16
    JournalGeochimica et Cosmochimica Acta
    Volume114
    DOIs
    StatePublished - Aug 1 2013

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    Geochemistry
    Molybdenum
    molybdenum
    Ecosystems
    geochemistry
    ecosystem
    Lakes
    Sediments
    lacustrine deposit
    lake
    Fluxes
    Soils
    porewater
    Springs (water)
    spring water
    Ice
    Watersheds
    Runoff
    sediment
    bedrock

    ASJC Scopus subject areas

    • Geochemistry and Petrology

    Cite this

    Molybdenum geochemistry in a seasonally dysoxic Mo-limited lacustrine ecosystem. / Glass, Jennifer B.; Chappaz, Anthony; Eustis, Brooke; Heyvaert, Alan C.; Waetjen, David P.; Hartnett, Hilairy E.; Anbar, Ariel D.

    In: Geochimica et Cosmochimica Acta, Vol. 114, 01.08.2013, p. 204-219.

    Research output: Contribution to journalArticle

    Glass, Jennifer B. ; Chappaz, Anthony ; Eustis, Brooke ; Heyvaert, Alan C. ; Waetjen, David P. ; Hartnett, Hilairy E. ; Anbar, Ariel D. / Molybdenum geochemistry in a seasonally dysoxic Mo-limited lacustrine ecosystem. In: Geochimica et Cosmochimica Acta. 2013 ; Vol. 114. pp. 204-219.
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    abstract = "Lakes are important for storage of the essential micronutrient molybdenum (Mo) during its transfer from the continents to the oceans, but little is known about the major sources and sinks for Mo in lacustrine ecosystems. We studied Mo cycling in Castle Lake, a small subalpine lake in the Klamath-Siskiyou Mountains of Northern California underlain primarily by mafic and ultramafic rocks where primary productivity is limited by Mo bioavailability. The deeper water of the lake becomes dysoxic (9-90μM dissolved oxygen) during the summer. This study was undertaken to identify the sources of Mo to Castle Lake and establish a Mo budget. We measured Mo concentrations in a suite of bulk solids (lake sediments, soils and bedrock) and aqueous samples (sediment porewaters, soil runoff, spring waters, snow and ice) from Castle Lake and its watershed. Lake sediments have elevated Mo (7-36ppm) compared to soils and bedrock (0.2-2ppm) and Mo/Al values were nearly two orders of magnitude higher than the crustal abundance. Sediment porewaters had higher Mo (4-15nM) than lake water (2-4nM), soil runoff (0.1-6.2nM), snowmelt (≤0.1nM), lake ice (0.3-2.2nM) and local spring waters (0.03-2.72nM). Bulk lake sediments had negative δ98/95Mo values, ranging from -0.5 to -1.0‰ (±0.1). We used the numerical model PROFILE to estimate the net reaction rate of Mo in the porewater. Model calculations ruled out diagenesis as a source of Mo to lake sediments; diagenetic Mo always represented ≤5{\%} of the total Mo content in sediment. We also ruled out dissolved Mo inputs from groundwater and watershed inflow as important sources of Mo. Two whole-lake experimental Mo additions in the 1960's could have contributed a sizeable amount of Mo to the lake sediments, but only over a short period. Atmospheric deposition of anthropogenic Mo from extensive copper smelting that occurred south of Castle Lake from 1896 to 1919 and from major Californian urban centers today were negligible Mo sources. Mo flux from the sediments (0.4-0.5nmolcm-2yr-1) was roughly equal to Mo fluxes from surface inflow and outflow, whereas Mo burial fluxes were significantly higher (11.5nmolcm-2yr-1). Because dissolved Mo fluxes were minimal, and atmospheric Mo deposition was estimated to be a minor source of Mo (<1nmolcm-2yr-1), the largest source of Mo is non-detrital particulate matter (~12nmolcm-2yr-1), likely a mixture of organic matter and Fe-Mn oxyhydroxides as supported by Mo isotopic data.",
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    AU - Glass, Jennifer B.

    AU - Chappaz, Anthony

    AU - Eustis, Brooke

    AU - Heyvaert, Alan C.

    AU - Waetjen, David P.

    AU - Hartnett, Hilairy E.

    AU - Anbar, Ariel D.

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    N2 - Lakes are important for storage of the essential micronutrient molybdenum (Mo) during its transfer from the continents to the oceans, but little is known about the major sources and sinks for Mo in lacustrine ecosystems. We studied Mo cycling in Castle Lake, a small subalpine lake in the Klamath-Siskiyou Mountains of Northern California underlain primarily by mafic and ultramafic rocks where primary productivity is limited by Mo bioavailability. The deeper water of the lake becomes dysoxic (9-90μM dissolved oxygen) during the summer. This study was undertaken to identify the sources of Mo to Castle Lake and establish a Mo budget. We measured Mo concentrations in a suite of bulk solids (lake sediments, soils and bedrock) and aqueous samples (sediment porewaters, soil runoff, spring waters, snow and ice) from Castle Lake and its watershed. Lake sediments have elevated Mo (7-36ppm) compared to soils and bedrock (0.2-2ppm) and Mo/Al values were nearly two orders of magnitude higher than the crustal abundance. Sediment porewaters had higher Mo (4-15nM) than lake water (2-4nM), soil runoff (0.1-6.2nM), snowmelt (≤0.1nM), lake ice (0.3-2.2nM) and local spring waters (0.03-2.72nM). Bulk lake sediments had negative δ98/95Mo values, ranging from -0.5 to -1.0‰ (±0.1). We used the numerical model PROFILE to estimate the net reaction rate of Mo in the porewater. Model calculations ruled out diagenesis as a source of Mo to lake sediments; diagenetic Mo always represented ≤5% of the total Mo content in sediment. We also ruled out dissolved Mo inputs from groundwater and watershed inflow as important sources of Mo. Two whole-lake experimental Mo additions in the 1960's could have contributed a sizeable amount of Mo to the lake sediments, but only over a short period. Atmospheric deposition of anthropogenic Mo from extensive copper smelting that occurred south of Castle Lake from 1896 to 1919 and from major Californian urban centers today were negligible Mo sources. Mo flux from the sediments (0.4-0.5nmolcm-2yr-1) was roughly equal to Mo fluxes from surface inflow and outflow, whereas Mo burial fluxes were significantly higher (11.5nmolcm-2yr-1). Because dissolved Mo fluxes were minimal, and atmospheric Mo deposition was estimated to be a minor source of Mo (<1nmolcm-2yr-1), the largest source of Mo is non-detrital particulate matter (~12nmolcm-2yr-1), likely a mixture of organic matter and Fe-Mn oxyhydroxides as supported by Mo isotopic data.

    AB - Lakes are important for storage of the essential micronutrient molybdenum (Mo) during its transfer from the continents to the oceans, but little is known about the major sources and sinks for Mo in lacustrine ecosystems. We studied Mo cycling in Castle Lake, a small subalpine lake in the Klamath-Siskiyou Mountains of Northern California underlain primarily by mafic and ultramafic rocks where primary productivity is limited by Mo bioavailability. The deeper water of the lake becomes dysoxic (9-90μM dissolved oxygen) during the summer. This study was undertaken to identify the sources of Mo to Castle Lake and establish a Mo budget. We measured Mo concentrations in a suite of bulk solids (lake sediments, soils and bedrock) and aqueous samples (sediment porewaters, soil runoff, spring waters, snow and ice) from Castle Lake and its watershed. Lake sediments have elevated Mo (7-36ppm) compared to soils and bedrock (0.2-2ppm) and Mo/Al values were nearly two orders of magnitude higher than the crustal abundance. Sediment porewaters had higher Mo (4-15nM) than lake water (2-4nM), soil runoff (0.1-6.2nM), snowmelt (≤0.1nM), lake ice (0.3-2.2nM) and local spring waters (0.03-2.72nM). Bulk lake sediments had negative δ98/95Mo values, ranging from -0.5 to -1.0‰ (±0.1). We used the numerical model PROFILE to estimate the net reaction rate of Mo in the porewater. Model calculations ruled out diagenesis as a source of Mo to lake sediments; diagenetic Mo always represented ≤5% of the total Mo content in sediment. We also ruled out dissolved Mo inputs from groundwater and watershed inflow as important sources of Mo. Two whole-lake experimental Mo additions in the 1960's could have contributed a sizeable amount of Mo to the lake sediments, but only over a short period. Atmospheric deposition of anthropogenic Mo from extensive copper smelting that occurred south of Castle Lake from 1896 to 1919 and from major Californian urban centers today were negligible Mo sources. Mo flux from the sediments (0.4-0.5nmolcm-2yr-1) was roughly equal to Mo fluxes from surface inflow and outflow, whereas Mo burial fluxes were significantly higher (11.5nmolcm-2yr-1). Because dissolved Mo fluxes were minimal, and atmospheric Mo deposition was estimated to be a minor source of Mo (<1nmolcm-2yr-1), the largest source of Mo is non-detrital particulate matter (~12nmolcm-2yr-1), likely a mixture of organic matter and Fe-Mn oxyhydroxides as supported by Mo isotopic data.

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