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

Nausch, M., Bach, Lennart T., Czerny, Jan, Goldstein, J., Grossart, H. P., Hellemann, Dana, Hornick, T., Achterberg, Eric P., Schulz, Kai G. 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 (BG), 13 (10). pp. 3035-3050. DOI 10.5194/bg-13-3035-2016.

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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 aquatic systems. The aim of our study was to analyze effects of elevated CO2 levels on phosphorus pool sizes and uptake. Therefore, we conducted a CO2-manipulation mesocosm experiment in the Storfjärden (western Gulf of Finland, Baltic Sea) in summer 2012. We compared the phosphorus dynamics in different mesocosm treatments but also studied them outside the mesocosms in the surrounding fjord water.

In the 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 μmol L−1 and 0.17 ± 0.07 μmol L−1 in the mesocosms and in the fjord, respectively. Uptake of PO4 ranged between 0.6 and 3.9 nmol L−1 h−1 of which ~ 86 % (mesocosms) and ~ 72 % (fjord) were 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. About 18 % of PO4 was transformed into POP, whereby the major proportion (~ 82 %) was converted into DOP suggesting that the conversion of PO4 to DOP is the main pathway of the PO4 turnover.

We observed that significant relationships (e.g., between POP and Chl a) in the untreated mesocosms vanished under increased fCO2 conditions. Consequently, it can be hypothesized that the relationship between POP formation and phytoplankton growth changed under elevated CO2 conditions. Significant short-term effects were observed for PO4 and particulate organic phosphorus (POP) pool sizes in CO2 treatments > 1000 μatm during periods when phytoplankton started to grow.

Document Type: Article
Additional Information: WOS:000378354900012
Keywords: EASTERN GOTLAND BASIN; NODULARIA SPUMIGENA; ORGANIC-MATTER; FILAMENTOUS CYANOBACTERIA; OCEAN ACIDIFICATION; NITROGEN-FIXATION; PCO(2) LEVELS; ELEVATED CO2; PEECE-III; SEAWATER
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-CH Chemical Oceanography
OceanRep > The Future Ocean - Cluster of Excellence
OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-BI Biological Oceanography
Kiel University
Refereed: Yes
Open Access Journal?: Yes
DOI etc.: 10.5194/bg-13-3035-2016
ISSN: 1726-4170
Projects: SOPRAN, KOSMOS, BIOACID
Expeditions/Models/Experiments:
Date Deposited: 22 Dec 2015 13:14
Last Modified: 04 May 2017 10:38
URI: http://oceanrep.geomar.de/id/eprint/30745

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