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Biogeosciences An interactive open-access journal of the European Geosciences Union
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Preprints
https://doi.org/10.5194/bg-2020-160
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2020-160
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  02 Jun 2020

02 Jun 2020

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A revised version of this preprint was accepted for the journal BG and is expected to appear here in due course.

The relative importance of photodegradation and biodegradation of terrestrially derived dissolved organic carbon across four lakes of differing trophic status

Christopher M. Dempsey1, Jennifer A. Brentrup2, Sarah Magyan1, Lesley B. Knoll3, Hilary M. Swain4, Evelyn E. Gaiser5, Donald P. Morris6, Michael T. Ganger1, and Craig E. Williamson7 Christopher M. Dempsey et al.
  • 1Gannon University, Biology Department, Erie, PA, USA
  • 2University of Vermont, Rubenstein Ecosystem Science Laboratory, Burlington, VT, USA
  • 3University of Minnesota, Itasca Biological Station and Laboratories, Lake Itasca, MN, USA
  • 4Archbold Biological Field Station, 123 Main Dr., Venus, FL, USA
  • 5Florida International University, Department of Biological Sciences and Institute of Environment, Miami, FL, USA
  • 6Lehigh University, Earth and Environmental Sciences Department, Bethlehem, PA, USA
  • 7Miami University, Global Change Limnology Laboratory, Department of Biology, Oxford, OH, USA

Abstract. Outgassing of carbon dioxide (CO2) from freshwater ecosystems comprises 12–25 % of the total carbon flux from soils and bedrock. This CO2 is largely derived from both biodegradation and photodegradation of terrestrial dissolved organic carbon (DOC) entering lakes from wetlands and soils in the watersheds of lakes. In spite of the significance of these two processes in regulating rates of CO2 outgassing, their relative importance remains poorly understood in lake ecosystems. In this study, we used groundwater from the watersheds of one subtropical and three temperate lakes of differing trophic status to simulate the effects of increases in terrestrial DOC from storm events. We assessed the relative importance of biodegradation and photodegradation in oxidizing DOC to CO2. We measured changes in DOC concentration, the optical characteristics of the DOC (SUVA320 and Sr), dissolved oxygen, and dissolved inorganic carbon (DIC) in short-term experiments from May–August, 2016. In all lakes, photodegradation led to larger changes in DOC and DIC concentrations and optical characteristics than biodegradation. A descriptive discriminant analysis showed that in brown-water lakes, photodegradation led to the largest declines in DOC concentration. In these brown-water systems, ~ 30 % of the DOC was processed by sunlight and ~ 2 % was photo mineralized. In addition to documenting the importance of photodegradation in lakes, these results also highlight how lakes in the future may respond to changes in DOC inputs.

Christopher M. Dempsey et al.

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Christopher M. Dempsey et al.

Christopher M. Dempsey et al.

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Short summary
We looked at how terrestrial dissolved organic carbon from the watersheds of four different lakes responded to both biodegradation (i.e. microbes) and photodegradation (i.e. sunlight). The traditional paradigm is that biodegradation is more important than photodegradation. Our research shows that on short time scales (i.e. 7 days), sunlight is more important than microbes in degrading DOC. Interestingly, the lakes had different responses to sunlight based on their trophic status.
We looked at how terrestrial dissolved organic carbon from the watersheds of four different...
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