Constraining the sources and cycling of dissolved organic carbon in a large oligotrophic lake using radiocarbon analyses

Prosper K. Zigah; Elizabeth C. Minor; Ann P. McNichol; Li Xu; Josef P. Werne

doi:10.1016/j.gca.2017.03.021

Constraining the sources and cycling of dissolved organic carbon in a large oligotrophic lake using radiocarbon analyses

Prosper K. Zigah, Elizabeth C. Minor, Ann P. McNichol, Li Xu, Josef P. Werne

Chemistry & Biochemistry

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Abstract

We measured the concentrations and isotopic compositions of solid phase extracted (SPE) dissolved organic carbon (DOC) and high molecular weight (HMW) DOC and their constituent organic components in order to better constrain the sources and cycling of DOC in a large oligotrophic lacustrine system (Lake Superior, North America). SPE DOC constituted a significant proportion (41–71%) of the lake DOC relative to HMW DOC (10–13%). Substantial contribution of ¹⁴C-depleted components to both SPE DOC (Δ¹⁴C = 25–43‰) and HMW DOC (Δ¹⁴C = 22–32‰) was evident during spring mixing, and depressed their radiocarbon values relative to the lake dissolved inorganic carbon (DIC; Δ¹⁴C ∼ 59‰). There was preferential removal of ¹⁴C-depleted (older) and thermally recalcitrant components from HMW DOC and SPE DOC in the summer. Contemporary photoautotrophic addition to HMW DOC was observed during summer stratification in contrast to SPE DOC, which decreased in concentration during stratification. Serial thermal oxidation radiocarbon analysis revealed a diversity of sources (both contemporary and older) within the SPE DOC, and also showed distinct components within the HMW DOC. The thermally labile components of HMW DOC were ¹⁴C-enriched and are attributed to heteropolysaccharides (HPS), peptides/amide and amino sugars (AMS) relative to the thermally recalcitrant components reflecting the presence of older material, perhaps carboxylic-rich alicyclic molecules (CRAM). The solvent extractable lipid-like fraction of HMW DOC was very ¹⁴C-depleted (as old as 1270–2320 ¹⁴C years) relative to the carbohydrate-like and protein-like substances isolated by acid hydrolysis of HMW DOC. Our data constrain relative influences of contemporary DOC and old DOC, and DOC cycling in a modern freshwater ecosystem.

Original language	English (US)
Pages (from-to)	102-118
Number of pages	17
Journal	Geochimica et Cosmochimica Acta
Volume	208
DOIs	https://doi.org/10.1016/j.gca.2017.03.021
State	Published - Jul 1 2017

Bibliographical note

Funding Information:
We thank the staff at National Ocean Sciences Accelerator Mass Spectrometry Facility for radiocarbon analyses, the captain and crew of the R/V Blue Heron for their help during sampling, and the Repeta laboratory at the Woods Hole Oceanographic Institution for assistance in the HMW protein, lipid, and carbohydrate isolations for radiocarbon analysis. Two anonymous reviewers and the associate editor Orit Sivan provided comments that considerably improved earlier versions of the manuscript. This work was funded by the United States National Science Foundation grant OCE 0825600 to E.C.M. and J.P.W., a graduate student internship fellowship to P.K.Z. by the National Ocean Sciences Accelerator Mass Spectrometry Facility (OCE 0753487), and the Postdoctoral Scholar Program at the Woods Hole Oceanographic Institution to P.K.Z, with funding provided by the National Ocean Sciences Accelerator Mass Spectrometry Facility (OCE 0753487).

Publisher Copyright:
© 2017 Elsevier Ltd

Keywords

Atmospheric CO
Carbohydrate-like substance
Carboxylic-rich alicyclic molecules (CRAM)
Contemporary DOC
Dissolved inorganic carbon
Dissolved organic carbon
Freshwater carbon cycling
Heteropolysaccharides (HPS)
High molecular weight DOC
Lake Superior
Lipid-like fraction
Old DOC
Oligotrophic lake
Protein-like substance
Radiocarbon
Serial thermal oxidation
Solid phase extracted DOC
Stable isotope
Unhydrolysable material

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title = "Constraining the sources and cycling of dissolved organic carbon in a large oligotrophic lake using radiocarbon analyses",

abstract = "We measured the concentrations and isotopic compositions of solid phase extracted (SPE) dissolved organic carbon (DOC) and high molecular weight (HMW) DOC and their constituent organic components in order to better constrain the sources and cycling of DOC in a large oligotrophic lacustrine system (Lake Superior, North America). SPE DOC constituted a significant proportion (41–71%) of the lake DOC relative to HMW DOC (10–13%). Substantial contribution of 14C-depleted components to both SPE DOC (Δ14C = 25–43‰) and HMW DOC (Δ14C = 22–32‰) was evident during spring mixing, and depressed their radiocarbon values relative to the lake dissolved inorganic carbon (DIC; Δ14C ∼ 59‰). There was preferential removal of 14C-depleted (older) and thermally recalcitrant components from HMW DOC and SPE DOC in the summer. Contemporary photoautotrophic addition to HMW DOC was observed during summer stratification in contrast to SPE DOC, which decreased in concentration during stratification. Serial thermal oxidation radiocarbon analysis revealed a diversity of sources (both contemporary and older) within the SPE DOC, and also showed distinct components within the HMW DOC. The thermally labile components of HMW DOC were 14C-enriched and are attributed to heteropolysaccharides (HPS), peptides/amide and amino sugars (AMS) relative to the thermally recalcitrant components reflecting the presence of older material, perhaps carboxylic-rich alicyclic molecules (CRAM). The solvent extractable lipid-like fraction of HMW DOC was very 14C-depleted (as old as 1270–2320 14C years) relative to the carbohydrate-like and protein-like substances isolated by acid hydrolysis of HMW DOC. Our data constrain relative influences of contemporary DOC and old DOC, and DOC cycling in a modern freshwater ecosystem.",

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author = "Zigah, {Prosper K.} and Minor, {Elizabeth C.} and McNichol, {Ann P.} and Li Xu and Werne, {Josef P.}",

note = "Funding Information: We thank the staff at National Ocean Sciences Accelerator Mass Spectrometry Facility for radiocarbon analyses, the captain and crew of the R/V Blue Heron for their help during sampling, and the Repeta laboratory at the Woods Hole Oceanographic Institution for assistance in the HMW protein, lipid, and carbohydrate isolations for radiocarbon analysis. Two anonymous reviewers and the associate editor Orit Sivan provided comments that considerably improved earlier versions of the manuscript. This work was funded by the United States National Science Foundation grant OCE 0825600 to E.C.M. and J.P.W., a graduate student internship fellowship to P.K.Z. by the National Ocean Sciences Accelerator Mass Spectrometry Facility (OCE 0753487), and the Postdoctoral Scholar Program at the Woods Hole Oceanographic Institution to P.K.Z, with funding provided by the National Ocean Sciences Accelerator Mass Spectrometry Facility (OCE 0753487). Publisher Copyright: {\textcopyright} 2017 Elsevier Ltd",

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T1 - Constraining the sources and cycling of dissolved organic carbon in a large oligotrophic lake using radiocarbon analyses

AU - Zigah, Prosper K.

AU - Minor, Elizabeth C.

AU - McNichol, Ann P.

AU - Xu, Li

AU - Werne, Josef P.

N1 - Funding Information: We thank the staff at National Ocean Sciences Accelerator Mass Spectrometry Facility for radiocarbon analyses, the captain and crew of the R/V Blue Heron for their help during sampling, and the Repeta laboratory at the Woods Hole Oceanographic Institution for assistance in the HMW protein, lipid, and carbohydrate isolations for radiocarbon analysis. Two anonymous reviewers and the associate editor Orit Sivan provided comments that considerably improved earlier versions of the manuscript. This work was funded by the United States National Science Foundation grant OCE 0825600 to E.C.M. and J.P.W., a graduate student internship fellowship to P.K.Z. by the National Ocean Sciences Accelerator Mass Spectrometry Facility (OCE 0753487), and the Postdoctoral Scholar Program at the Woods Hole Oceanographic Institution to P.K.Z, with funding provided by the National Ocean Sciences Accelerator Mass Spectrometry Facility (OCE 0753487). Publisher Copyright: © 2017 Elsevier Ltd

PY - 2017/7/1

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N2 - We measured the concentrations and isotopic compositions of solid phase extracted (SPE) dissolved organic carbon (DOC) and high molecular weight (HMW) DOC and their constituent organic components in order to better constrain the sources and cycling of DOC in a large oligotrophic lacustrine system (Lake Superior, North America). SPE DOC constituted a significant proportion (41–71%) of the lake DOC relative to HMW DOC (10–13%). Substantial contribution of 14C-depleted components to both SPE DOC (Δ14C = 25–43‰) and HMW DOC (Δ14C = 22–32‰) was evident during spring mixing, and depressed their radiocarbon values relative to the lake dissolved inorganic carbon (DIC; Δ14C ∼ 59‰). There was preferential removal of 14C-depleted (older) and thermally recalcitrant components from HMW DOC and SPE DOC in the summer. Contemporary photoautotrophic addition to HMW DOC was observed during summer stratification in contrast to SPE DOC, which decreased in concentration during stratification. Serial thermal oxidation radiocarbon analysis revealed a diversity of sources (both contemporary and older) within the SPE DOC, and also showed distinct components within the HMW DOC. The thermally labile components of HMW DOC were 14C-enriched and are attributed to heteropolysaccharides (HPS), peptides/amide and amino sugars (AMS) relative to the thermally recalcitrant components reflecting the presence of older material, perhaps carboxylic-rich alicyclic molecules (CRAM). The solvent extractable lipid-like fraction of HMW DOC was very 14C-depleted (as old as 1270–2320 14C years) relative to the carbohydrate-like and protein-like substances isolated by acid hydrolysis of HMW DOC. Our data constrain relative influences of contemporary DOC and old DOC, and DOC cycling in a modern freshwater ecosystem.

AB - We measured the concentrations and isotopic compositions of solid phase extracted (SPE) dissolved organic carbon (DOC) and high molecular weight (HMW) DOC and their constituent organic components in order to better constrain the sources and cycling of DOC in a large oligotrophic lacustrine system (Lake Superior, North America). SPE DOC constituted a significant proportion (41–71%) of the lake DOC relative to HMW DOC (10–13%). Substantial contribution of 14C-depleted components to both SPE DOC (Δ14C = 25–43‰) and HMW DOC (Δ14C = 22–32‰) was evident during spring mixing, and depressed their radiocarbon values relative to the lake dissolved inorganic carbon (DIC; Δ14C ∼ 59‰). There was preferential removal of 14C-depleted (older) and thermally recalcitrant components from HMW DOC and SPE DOC in the summer. Contemporary photoautotrophic addition to HMW DOC was observed during summer stratification in contrast to SPE DOC, which decreased in concentration during stratification. Serial thermal oxidation radiocarbon analysis revealed a diversity of sources (both contemporary and older) within the SPE DOC, and also showed distinct components within the HMW DOC. The thermally labile components of HMW DOC were 14C-enriched and are attributed to heteropolysaccharides (HPS), peptides/amide and amino sugars (AMS) relative to the thermally recalcitrant components reflecting the presence of older material, perhaps carboxylic-rich alicyclic molecules (CRAM). The solvent extractable lipid-like fraction of HMW DOC was very 14C-depleted (as old as 1270–2320 14C years) relative to the carbohydrate-like and protein-like substances isolated by acid hydrolysis of HMW DOC. Our data constrain relative influences of contemporary DOC and old DOC, and DOC cycling in a modern freshwater ecosystem.

KW - Atmospheric CO

KW - Carbohydrate-like substance

KW - Carboxylic-rich alicyclic molecules (CRAM)

KW - Contemporary DOC

KW - Dissolved inorganic carbon

KW - Dissolved organic carbon

KW - Freshwater carbon cycling

KW - Heteropolysaccharides (HPS)

KW - High molecular weight DOC

KW - Lake Superior

KW - Lipid-like fraction

KW - Old DOC

KW - Oligotrophic lake

KW - Protein-like substance

KW - Radiocarbon

KW - Serial thermal oxidation

KW - Solid phase extracted DOC

KW - Stable isotope

KW - Unhydrolysable material

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M3 - Article

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VL - 208

SP - 102

EP - 118

JO - Geochimica et Cosmochimica Acta

JF - Geochimica et Cosmochimica Acta

ER -

Constraining the sources and cycling of dissolved organic carbon in a large oligotrophic lake using radiocarbon analyses

Abstract

Bibliographical note

Keywords

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