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Marine Ecology Progress Series

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MEPS 561:17-29 (2016)  -  DOI:

Mixing depth and allochthonous dissolved organic carbon: controlling factors of coastal trophic balance

Ulf Båmstedt1,*, Johan Wikner1,2 

1Umeå Marine Sciences Centre, Umeå University, Norrbyn, 905 71 Hörnefors, Sweden
2Department of Ecology and Environmental Science, Umeå University, 901 87 Umeå, Sweden
*Corresponding author:

ABSTRACT: The interacting effects of different mixing depths and increased allochthonous dissolved organic carbon (DOC) on the ratio of heterotrophic to autotrophic production (i.e. trophic balance) was evaluated in a mesocosm study with a stratified water column. An autumn plankton community from the northern Bothnian Sea showed significantly decreased phytoplankton production and somewhat increased bacterial production with added DOC. In addition, increased mixing depth further reduced phytoplankton production. With a deep pycnocline and added DOC, the system became net-heterotrophic, with an average bacteria-to-phytoplankton production ratio of 1.24. With a deep pycnocline without added DOC, the trophic balance was changed to 0.44 (i.e. autotrophic). With a shallow pycnocline, the system remained net-autotrophic irrespective of DOC addition. We propose that increased precipitation in northern Europe due to climate change may result in changed density stratification and increased allochthonous DOC transport to the sea, leading to more heterotrophic coastal aquatic ecosystems. Such a scenario may entail reduced biological production at higher trophic levels and enhanced CO2 emission to the atmosphere.

KEY WORDS: Trophic · Balance · Phytoplankton · Bacterioplankton · Mixing · Depth · DOC · Mesocosm

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Cite this article as: Båmstedt U, Wikner J (2016) Mixing depth and allochthonous dissolved organic carbon: controlling factors of coastal trophic balance. Mar Ecol Prog Ser 561:17-29.

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