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Estuaries and Coasts

, Volume 38, Issue 1, pp 192–210 | Cite as

Inorganic Carbon Fluxes in the Inner Elbe Estuary, Germany

  • Thorben AmannEmail author
  • Andreas Weiss
  • Jens Hartmann
Article

Abstract

Estuaries are strong sources for CO2 to the atmosphere. At the same time, they are intense reactors for dissolved matter at the land–ocean interface. The temporal and spatial variations of inorganic carbon fluxes in the inner Elbe estuary were studied based on 18 transects and a budget was constructed. The freshwater part of the Elbe estuary, a potential hotspot for carbon transformation, was evaluated using GIS-derived surface areas, isotopic DIC data and modelled pCO2. Calculation of pCO2 with commonly used constants yield 20 % higher values if compared to thermodynamically modelled results, integrating the actual ionic composition of the sample. With these improved calculations, it could be confirmed that this part is important for carbon turnover. Highest pCO2 values and strongest CO2 efflux per square metre compared to the rest of the inner Elbe estuary were observed. It contributes 10 % of the CO2 fluxes to the atmosphere, and 82 % of seaward transport of dissolved CO2. Overall, the estuary is net heterotrophic and releases 13.2 × 109 mol CO2 year−1 to the atmosphere. About 20 % of the DIC exports from the estuary are attributed to atmospheric CO2 exchange, while 80 % are transported seawards in dissolved form. Additionally, the Elbe estuary is a source for DIC besides CO2. The flux to the coastal zone is increased by about 18 %. Main sources are marshes and sediments. These findings should be considered in North Sea budgets, which to date rely on simple two source mixing of freshwater and seawater to derive riverine DIC inputs. Findings from this study corroborate the anthropogenic impact on carbon fluxes and clearly confirm the necessity to examine the entire estuary including the freshwater part.

Keywords

Carbon cycling Carbon dioxide Estuaries Elbe DIC 

Notes

Acknowledgements

We would like to thank Tom Jäppinen for great assistance during the field campaign and laboratory analysis. Michael Böttcher is acknowledged for providing data of δ13CDIC. We are grateful to captain and crew of the R/V Prandtl for their professional work and to Volker Dzaak for organising the necessary ship time. Climatic data was provided by the German Weather Service (DWD). We like to thank four anonymous reviewers and the editor Alberto Borges for many remarks, which helped us to improve the manuscript. Thorben Amann and Jens Hartmann were funded by the DFG Cluster of Excellence “CliSAP” (EXC177). Andreas Weiss was funded by ESTRADE (Estuary and Wetland Research Graduate School Hamburg) as member of LExI (State Excellence Initiative) and by the DFG Cluster of Excellence “CliSAP” (EXC177).

Supplementary material

12237_2014_9785_MOESM1_ESM.xls (261 kb)
Online Resource Table 1 a Raw data of all conducted surveys including standard deviations (STDEV) of the analysis. Columns S and AL-AM refer to calculated data. b Fitting equations for the modelled DIC and TA concentration distribution in the salinity gradient on the basis of available transect data. (n.d. = not determined). c List of the major tributaries along the inner Elbe Estuary, and their annual mean discharge based on the given time frame. d Detailed CO2 fluxes through the different estuarine zones. Horizontal arrows show CO2 transport in dissolved form, while upright arrows indicate CO2 gas exchange with the atmosphere. All values are given in 106 mol season−1 or 106 mol year−1 unless stated otherwise. e Detailed TA fluxes through the different estuarine zones. Arrows show TA transport. All values are given in 106 mol season−1 or 106 mol year−1 unless stated otherwise. f Detailed DIC fluxes through the different estuarine zones. Horizontal arrows show DIC transport, while upright arrows indicate CO2 gas exchange with the atmosphere. All values are given in 106 mol season−1 or 106 mol year−1 unless stated otherwise. (XLS 261 kb)
12237_2014_9785_MOESM2_ESM.pdf (99 kb)
Online Resource Fig. 1 DIC concentrations from every transect in the salinity gradient. Open circles mark the most seaward measurement of a salinity <1, filled circles mark measurements, where salinity ≥1. The dotted red line indicates the best polynomial or linear fit of the data, while the solid black line depicts the calculated effective DIC concentration. (PDF 98 kb)
12237_2014_9785_MOESM3_ESM.pdf (95 kb)
Online Resource Fig. 2 TA concentrations from every transect in the salinity gradient. Open circles mark the most seaward measurement of a salinity <1, filled circles mark measurements, where salinity ≥1. The dotted red line indicates the best polynomial or linear fit of the data, while the solid black line depicts the calculated effective DIC concentration. (PDF 95 kb)
12237_2014_9785_MOESM4_ESM.pdf (55 kb)
Online Resource Fig. 3 DIC (black line and circles) and TA (blue line and squares) concentrations of all recently conducted surveys along the inner Elbe Estuary. (PDF 54 kb)
12237_2014_9785_MOESM5_ESM.pdf (65 kb)
Online Resource Fig. 4 Calculated saturation indices (SI) for CaCO3 (black line and circles) and the relative fraction of PIC in SPM (grey line and squares) of all recently conducted surveys along the inner Elbe Estuary. (PDF 64 kb)
12237_2014_9785_MOESM6_ESM.pdf (39 kb)
Online Resource Fig. 5 NH4 + concentrations in the inner Elbe Estuary. (PDF 39 kb)

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Copyright information

© Coastal and Estuarine Research Federation 2014

Authors and Affiliations

  1. 1.KlimaCampus, Institute for Geology, University of HamburgHamburgGermany

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