Abstract
We employed a coupled physical-biogeochemical modelling framework for the reconstruction of the historic (H), pre-industrial state of a coastal system, the German Bight (southeastern North Sea), and we investigated its differences with the recent, control (C) state of the system. According to our findings: i) average winter concentrations of dissolved inorganic nitrogen and phosphorus (DIN and DIP) concentrations at the surface are ∼70–90% and ∼50–70% lower in the H state than in the C state within the nearshore waters, and differences gradually diminish towards off-shore waters; ii) differences in average growing season chlorophyll a (Chl) concentrations at the surface between the two states are mostly less than 50%; iii) in the off-shore areas, Chl concentrations in the deeper layers are affected less than in the surface layers; iv) reductions in phytoplankton carbon (C) biomass under the H state are weaker than those in Chl, due to the generally lower Chl:C ratios; v) in some areas the differences in growth rates between the two states are negligible, due to the compensation by lower light limitation under the H state, which in turn explains the lower Chl:C ratios; vi) zooplankton biomass, and hence the grazing pressure on phytoplankton is lower under the H state. This trophic decoupling is caused by the low nutritional quality (i.e., low N:C and P:C) of phytoplankton. These results call for increased attention to the relevance of the acclimation capacity and stoichiometric flexibility of phytoplankton for the prediction of their response to environmental change.
| Original language | English |
|---|---|
| Pages (from-to) | 1311-1323 |
| Number of pages | 13 |
| Journal | Science of the Total Environment |
| Volume | 639 |
| Early online date | 26 May 2018 |
| DOIs | |
| Publication status | Published - 15 Oct 2018 |
Funding
Wera Leujak (UBA) and Annika Grage (previously NLWKN, now BSH) are gratefully acknowledged for their contributions to the conceptual development of the ‘historical state’. We thank Sonja van Leeuwen (previously CEFAS, now NIOZ) for providing data on riverine fluxes and Johannes Pätsch (UHH) for providing the suspended particulate matter climatology. This is a contribution by the Helmholtz Society through the PACES program. OK was supported by the German Federal Ministry of Education and Research (BMBF) through the MOSSCO project ( 03F0667A , 03F0667B , and 03FO668A ); the German Research Foundation (DFG) through the priority program 1704 Dynatrait ( KE 1970/1-1 ); and the NLWKN through the project ‘WRRL - Referenz- und Zielzustände für Chlorophyll a & Nährstoffe - Modellbasierte Überprüfung’. FG received funding from the German Environmental Protection Agency (UBA), in the frame of the project ‘Implementation of Descriptor 5 Eutrophication to the MSFD’, SN: 3713225221. MK was financially supported by the Cluster of Excellence ‘CliSAP’ (EXC177), Universität Hamburg, funded by DFG. The authors gratefully acknowledge the computing time granted by the John von Neumann Institute for Computing (NIC) and provided on the supercomputer JURECA ( Jülich Supercomputing Centre, 2016 ) at Jülich Supercomputing Centre. This study greatly benefited from the open source code and/or free software including FABM, GETM, GOTM, NCO, CDO, NetCDF, Python, LATE X and Kubuntu, developers of which are gratefully acknowledged. Station data presented in Fig. 5 were provided by Niedersächsichser Landesbetrieb für Wasserwirtschaft, Küsten- und Naturschutz (Norderelbe); Alfred Wegener Institute and K. Wiltshire (Helgoland and Sylt); J.E.E. van Beusekom (Sylt); Bundesamt für Seeschifffahrt und Hydrographie (T11); Landesamt für Landwirtschaft, Umwelt und ländliche Räume des Landes Schleswig-Holstein (Norderney). A representative subset of the model output can be accessed at: https://cera-www.dkrz.de/WDCC/ui/cerasearch/entry?acronym=MAECS_biogeochemistry_CH .
Keywords
- acclimation
- adaptation
- eutrophication
- pristine conditions
- reconstruction