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Effects of CO2 perturbation on phosphorus pool sizes and uptake in a mesocosm experiment during a low productive summer season in the northern Baltic Sea

Effects of CO2 perturbation on phosphorus pool sizes and uptake in a mesocosm experiment during a low productive summer season in the northern Baltic Sea
Effects of CO2 perturbation on phosphorus pool sizes and uptake in a mesocosm experiment during a low productive summer season in the northern Baltic Sea
Studies investigating the effect of increasing CO2 levels on the phosphorus cycle in natural waters are lacking although phosphorus often controls phytoplankton development in many aquatic systems. The aim of our study was to analyse effects of elevated CO2 levels on phosphorus pool sizes and uptake. The phosphorus dynamic was followed in a CO2-manipulation mesocosm experiment in the Storfjärden (western Gulf of Finland, Baltic Sea) in summer 2012 and was also studied in the surrounding fjord water. In all mesocosms as well as in surface waters of Storfjärden, dissolved organic phosphorus (DOP) concentrations of 0.26?±?0.03 and 0.23?±?0.04?µmol?L?1, respectively, formed the main fraction of the total P-pool (TP), whereas phosphate (PO4) constituted the lowest fraction with mean concentration of 0.15?±?0.02 in the mesocosms and 0.17?±?0.07?µmol?L?1 in the fjord. Transformation of PO4 into DOP appeared to be the main pathway of PO4 turnover. About 82?% of PO4 was converted into DOP whereby only 18?% of PO4 was transformed into particulate phosphorus (PP). PO4 uptake rates measured in the mesocosms ranged between 0.6 and 3.9?nmol?L?1?h?1. About 86?% of them was realized by the size fraction <?3?µm. Adenosine triphosphate (ATP) uptake revealed that additional P was supplied from organic compounds accounting for 25–27?% of P provided by PO4 only. CO2 additions did not cause significant changes in phosphorus (P) pool sizes, DOP composition, and uptake of PO4 and ATP when the whole study period was taken into account. However, significant short-term effects were observed for PO4 and PP pool sizes in CO2 treatments >?1000?µatm during periods when phytoplankton biomass increased. In addition, we found significant relationships (e.g., between PP and Chl a) in the untreated mesocosms which were not observed under high fCO2 conditions. Consequently, it can be hypothesized that the relationship between PP formation and phytoplankton growth changed with CO2 elevation. It can be deduced from the results, that visible effects of CO2 on P pools are coupled to phytoplankton growth when the transformation of PO4 into POP was stimulated. The transformation of PO4 into DOP on the other hand does not seem to be affected. Additionally, there were some indications that cellular mechanisms of P regulation might be modified under CO2 elevation changing the relationship between cellular constituents.
1726-4170
3035-3050
Nausch, Monika
13fc1e68-8ca3-4078-99eb-171ccafcd7b9
Bach, Lennart Thomas
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Czerny, Jan
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Goldstein, Josephine
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Grossart, Hans-Peter
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Hellemann, Dana
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Hornick, Thomas
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Achterberg, Eric Pieter
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Schulz, Kai-Georg
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Riebesell, Ulf
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Nausch, Monika
13fc1e68-8ca3-4078-99eb-171ccafcd7b9
Bach, Lennart Thomas
f758bd38-4d84-4fbf-af78-e8cc0120b69a
Czerny, Jan
8f08fb1e-1e69-4e8b-bb64-cd8d4ce7fb8b
Goldstein, Josephine
37490162-504e-457c-a5b2-5ec24e9fad3b
Grossart, Hans-Peter
652f54d6-e6e2-435d-b86f-d9127549473f
Hellemann, Dana
442ad186-f42e-4582-9229-74dfbc36b8f8
Hornick, Thomas
db60fd83-bd5d-4ce0-8d24-9a7b7b9f5cd1
Achterberg, Eric Pieter
685ce961-8c45-4503-9f03-50f6561202b9
Schulz, Kai-Georg
4436e85e-fcc8-4483-b21a-96bffa8adc22
Riebesell, Ulf
2218bcf4-b444-4a1a-b268-9875762de458

Nausch, Monika, Bach, Lennart Thomas, Czerny, Jan, Goldstein, Josephine, Grossart, Hans-Peter, Hellemann, Dana, Hornick, Thomas, Achterberg, Eric Pieter, Schulz, Kai-Georg and Riebesell, Ulf (2016) Effects of CO2 perturbation on phosphorus pool sizes and uptake in a mesocosm experiment during a low productive summer season in the northern Baltic Sea. Biogeosciences, 13 (10), 3035-3050. (doi:10.5194/bg-13-3035-2016).

Record type: Article

Abstract

Studies investigating the effect of increasing CO2 levels on the phosphorus cycle in natural waters are lacking although phosphorus often controls phytoplankton development in many aquatic systems. The aim of our study was to analyse effects of elevated CO2 levels on phosphorus pool sizes and uptake. The phosphorus dynamic was followed in a CO2-manipulation mesocosm experiment in the Storfjärden (western Gulf of Finland, Baltic Sea) in summer 2012 and was also studied in the surrounding fjord water. In all mesocosms as well as in surface waters of Storfjärden, dissolved organic phosphorus (DOP) concentrations of 0.26?±?0.03 and 0.23?±?0.04?µmol?L?1, respectively, formed the main fraction of the total P-pool (TP), whereas phosphate (PO4) constituted the lowest fraction with mean concentration of 0.15?±?0.02 in the mesocosms and 0.17?±?0.07?µmol?L?1 in the fjord. Transformation of PO4 into DOP appeared to be the main pathway of PO4 turnover. About 82?% of PO4 was converted into DOP whereby only 18?% of PO4 was transformed into particulate phosphorus (PP). PO4 uptake rates measured in the mesocosms ranged between 0.6 and 3.9?nmol?L?1?h?1. About 86?% of them was realized by the size fraction <?3?µm. Adenosine triphosphate (ATP) uptake revealed that additional P was supplied from organic compounds accounting for 25–27?% of P provided by PO4 only. CO2 additions did not cause significant changes in phosphorus (P) pool sizes, DOP composition, and uptake of PO4 and ATP when the whole study period was taken into account. However, significant short-term effects were observed for PO4 and PP pool sizes in CO2 treatments >?1000?µatm during periods when phytoplankton biomass increased. In addition, we found significant relationships (e.g., between PP and Chl a) in the untreated mesocosms which were not observed under high fCO2 conditions. Consequently, it can be hypothesized that the relationship between PP formation and phytoplankton growth changed with CO2 elevation. It can be deduced from the results, that visible effects of CO2 on P pools are coupled to phytoplankton growth when the transformation of PO4 into POP was stimulated. The transformation of PO4 into DOP on the other hand does not seem to be affected. Additionally, there were some indications that cellular mechanisms of P regulation might be modified under CO2 elevation changing the relationship between cellular constituents.

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Accepted/In Press date: 25 April 2016
e-pub ahead of print date: 24 May 2016
Published date: 24 May 2016
Organisations: Ocean and Earth Science

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Local EPrints ID: 399110
URI: http://eprints.soton.ac.uk/id/eprint/399110
ISSN: 1726-4170
PURE UUID: a5aa7603-cee6-4362-87bc-5fb70fe4dfdf

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Date deposited: 04 Aug 2016 12:35
Last modified: 09 Jan 2022 08:38

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Contributors

Author: Monika Nausch
Author: Lennart Thomas Bach
Author: Jan Czerny
Author: Josephine Goldstein
Author: Hans-Peter Grossart
Author: Dana Hellemann
Author: Thomas Hornick
Author: Kai-Georg Schulz
Author: Ulf Riebesell

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