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Effects of Meltwater on the Arctic Coastal Microbial Food Web: An Experiment With Isotopic Labeling From Young Sound, NE Greenland.

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Title: Effects of Meltwater on the Arctic Coastal Microbial Food Web: An Experiment With Isotopic Labeling From Young Sound, NE Greenland.
Authors: Puts, IC1,2,3,4 (AUTHOR) isolde.puts@umu.se, Mostovaya, A1,2 (AUTHOR), Henson, HC1,2 (AUTHOR), Allais, L1 (AUTHOR), de Kluijver, A5 (AUTHOR), Thyrring, J1,2 (AUTHOR), Middelboe, M6,7 (AUTHOR), Holding, JM1,2,8 (AUTHOR)
Source: Journal of Geophysical Research. Biogeosciences. Mar2026, Vol. 131 Issue 3, p1-15. 15p.
Subject Terms: *Meltwater, *Bacterial growth, *Food chains, *Fjords, *Runoff, *Glacial melting, *Ocean
Geographic Terms: Greenland, Arctic regions
Abstract: The Arctic Ocean freshwater content is predicted to increase by 30%–50% during the 21st century, and especially coasts receive substantial amounts of freshwater from melting glaciers and thawing permafrost. The resulting increase in sediment and carbon inputs from rivers is changing seawater chemistry along Arctic coasts, potentially disrupting food web processes. Here, we test how sediment‐rich river runoff carrying glacial meltwater affects the microbial food web in a Greenlandic fjord, by separating the effects of freshening alone from those combined with river‐ and land‐derived compounds (river discharge). After enriching seawater with 13C‐HCO3− and freshening it by 16% with either Milli‐Q or river water, we monitored the response of natural microbial producers in both treatments. We tracked bacterial and algal biomass and production over 14 days and assessed fatty acids and their δ13C signatures. The results show that meltwater enriches the marine environment with silicon and nitrogen. Furthermore, a 16% dilution with river water stimulates bacterial —but not algal— production and biomass. The observed effects of meltwater are possibly due to impacts of labile organic carbon, inorganic (micro) nutrient inputs, or even the increased silicate concentration supporting biosilicifying bacteria. Still, the specific environmental factors supporting the increased bacterial activity remain speculative. Given the limited research on meltwater effects on microbial processes, we highlight key knowledge gaps and provide guidance for future experimental setups. Overall, we show that increased river discharge carrying meltwater enhances bacterial production, potentially impacting the entire ecosystem and emphasizing the significant influence of terrigenous freshwater inputs on coastal environments. Plain Language Summary: Rivers transport increasing amounts of freshwater from melting glaciers and thawing permafrost into the Arctic Ocean. This meltwater often carries sediments, micronutrients, and minerals that coastal microscopic life uses to grow. Currently, it is not understood how this runoff changes coastal water chemistry or how it affects coastal microscopic life, which is important for the rest of the ecosystem. In this experiment, we test how river water affects the growth of various sea‐living microbes (algae and bacteria). We do this by adding either pure freshwater or sediment‐rich glacial meltwater to labeled seawater containing natural microbes, and monitoring their growth, biomass, and fatty acids over 14 days. The experiment shows that meltwater rivers bring silicon, and potentially micronutrients and low amounts of bioavailable carbon to the coast, which stimulates the growth of bacteria, but not algae growth. This is an important observation because it shows that freshwater inputs impact coastal environments and could potentially affect the entire coastal ecosystem. Key Points: We test how sediment‐rich river‐runoff carrying glacial meltwater affects the microbial food‐web in a Greenlandic fjordMeltwater enriches the marine environment with silicon, and low amounts of nitrogen and likely highly bio‐available organic carbonA 16% dilution with river water stimulates bacterial biomass [ABSTRACT FROM AUTHOR]
Copyright of Journal of Geophysical Research. Biogeosciences is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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Items – Name: Title
  Label: Title
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  Data: Effects of Meltwater on the Arctic Coastal Microbial Food Web: An Experiment With Isotopic Labeling From Young Sound, NE Greenland.
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  Data: <searchLink fieldCode="AR" term="%22Puts%2C+IC%22">Puts, IC</searchLink><relatesTo>1,2,3,4</relatesTo> (AUTHOR)<i> isolde.puts@umu.se</i><br /><searchLink fieldCode="AR" term="%22Mostovaya%2C+A%22">Mostovaya, A</searchLink><relatesTo>1,2</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Henson%2C+HC%22">Henson, HC</searchLink><relatesTo>1,2</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Allais%2C+L%22">Allais, L</searchLink><relatesTo>1</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22de+Kluijver%2C+A%22">de Kluijver, A</searchLink><relatesTo>5</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Thyrring%2C+J%22">Thyrring, J</searchLink><relatesTo>1,2</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Middelboe%2C+M%22">Middelboe, M</searchLink><relatesTo>6,7</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Holding%2C+JM%22">Holding, JM</searchLink><relatesTo>1,2,8</relatesTo> (AUTHOR)
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  Data: <searchLink fieldCode="JN" term="%22Journal+of+Geophysical+Research%2E+Biogeosciences%22">Journal of Geophysical Research. Biogeosciences</searchLink>. Mar2026, Vol. 131 Issue 3, p1-15. 15p.
– Name: Subject
  Label: Subject Terms
  Group: Su
  Data: *<searchLink fieldCode="DE" term="%22Meltwater%22">Meltwater</searchLink><br />*<searchLink fieldCode="DE" term="%22Bacterial+growth%22">Bacterial growth</searchLink><br />*<searchLink fieldCode="DE" term="%22Food+chains%22">Food chains</searchLink><br />*<searchLink fieldCode="DE" term="%22Fjords%22">Fjords</searchLink><br />*<searchLink fieldCode="DE" term="%22Runoff%22">Runoff</searchLink><br />*<searchLink fieldCode="DE" term="%22Glacial+melting%22">Glacial melting</searchLink><br />*<searchLink fieldCode="DE" term="%22Ocean%22">Ocean</searchLink>
– Name: SubjectGeographic
  Label: Geographic Terms
  Group: Su
  Data: <searchLink fieldCode="DE" term="%22Greenland%22">Greenland</searchLink><br /><searchLink fieldCode="DE" term="%22Arctic+regions%22">Arctic regions</searchLink>
– Name: Abstract
  Label: Abstract
  Group: Ab
  Data: The Arctic Ocean freshwater content is predicted to increase by 30%–50% during the 21st century, and especially coasts receive substantial amounts of freshwater from melting glaciers and thawing permafrost. The resulting increase in sediment and carbon inputs from rivers is changing seawater chemistry along Arctic coasts, potentially disrupting food web processes. Here, we test how sediment‐rich river runoff carrying glacial meltwater affects the microbial food web in a Greenlandic fjord, by separating the effects of freshening alone from those combined with river‐ and land‐derived compounds (river discharge). After enriching seawater with 13C‐HCO3− and freshening it by 16% with either Milli‐Q or river water, we monitored the response of natural microbial producers in both treatments. We tracked bacterial and algal biomass and production over 14 days and assessed fatty acids and their δ13C signatures. The results show that meltwater enriches the marine environment with silicon and nitrogen. Furthermore, a 16% dilution with river water stimulates bacterial —but not algal— production and biomass. The observed effects of meltwater are possibly due to impacts of labile organic carbon, inorganic (micro) nutrient inputs, or even the increased silicate concentration supporting biosilicifying bacteria. Still, the specific environmental factors supporting the increased bacterial activity remain speculative. Given the limited research on meltwater effects on microbial processes, we highlight key knowledge gaps and provide guidance for future experimental setups. Overall, we show that increased river discharge carrying meltwater enhances bacterial production, potentially impacting the entire ecosystem and emphasizing the significant influence of terrigenous freshwater inputs on coastal environments. Plain Language Summary: Rivers transport increasing amounts of freshwater from melting glaciers and thawing permafrost into the Arctic Ocean. This meltwater often carries sediments, micronutrients, and minerals that coastal microscopic life uses to grow. Currently, it is not understood how this runoff changes coastal water chemistry or how it affects coastal microscopic life, which is important for the rest of the ecosystem. In this experiment, we test how river water affects the growth of various sea‐living microbes (algae and bacteria). We do this by adding either pure freshwater or sediment‐rich glacial meltwater to labeled seawater containing natural microbes, and monitoring their growth, biomass, and fatty acids over 14 days. The experiment shows that meltwater rivers bring silicon, and potentially micronutrients and low amounts of bioavailable carbon to the coast, which stimulates the growth of bacteria, but not algae growth. This is an important observation because it shows that freshwater inputs impact coastal environments and could potentially affect the entire coastal ecosystem. Key Points: We test how sediment‐rich river‐runoff carrying glacial meltwater affects the microbial food‐web in a Greenlandic fjordMeltwater enriches the marine environment with silicon, and low amounts of nitrogen and likely highly bio‐available organic carbonA 16% dilution with river water stimulates bacterial biomass [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
  Label:
  Group: Ab
  Data: <i>Copyright of Journal of Geophysical Research. Biogeosciences is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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RecordInfo BibRecord:
  BibEntity:
    Identifiers:
      – Type: doi
        Value: 10.1029/2025JG008921
    Languages:
      – Code: eng
        Text: English
    PhysicalDescription:
      Pagination:
        PageCount: 15
        StartPage: 1
    Subjects:
      – SubjectFull: Meltwater
        Type: general
      – SubjectFull: Bacterial growth
        Type: general
      – SubjectFull: Food chains
        Type: general
      – SubjectFull: Fjords
        Type: general
      – SubjectFull: Runoff
        Type: general
      – SubjectFull: Glacial melting
        Type: general
      – SubjectFull: Ocean
        Type: general
      – SubjectFull: Greenland
        Type: general
      – SubjectFull: Arctic regions
        Type: general
    Titles:
      – TitleFull: Effects of Meltwater on the Arctic Coastal Microbial Food Web: An Experiment With Isotopic Labeling From Young Sound, NE Greenland.
        Type: main
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              M: 03
              Text: Mar2026
              Type: published
              Y: 2026
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