EGU23-13399, updated on 26 Feb 2023
EGU General Assembly 2023
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Recent inorganic carbon increase in a temperate estuary driven by water quality improvement and enhanced by droughts

Louise Rewrie1, Yoana Voynova1, Justus Beusekom1, Arne Körtzinger2, Gregor Ollesch3, and Burkard Baschek4
Louise Rewrie et al.
  • 1Institute of Carbon Cycles, Helmholtz-Zentrum Hereon, 21502 Geesthacht, Germany.
  • 2GEOMAR, Helmholtz-Zentrum für Ozeanforschung Kiel, 24148 Kiel, Germany
  • 3Flussgebietsgemeinschaft Elbe (FGG Elbe), 39104 Magdeburg, Germany
  • 4Deutsches Meeresmuseum, 18439 Stralsund, Germany

Estuaries are an important component of the global carbon budget as sites of removal and transformation for carbon between land and coastal ocean. Drought conditions can lengthen river and estuarine water residence time, which can extend the retention and alter the cycling of organic carbon and nutrients. To better understand the functioning of an estuary under the current threat of climate change related droughts, we use the Elbe Estuary as an example, examining a period since 1997, when annual mean DIC in the mid to lower Elbe Estuary increased significantly, and with focus on the drought conditions since 2014. 

The recent (1997-2020) significant DIC increase by 6 to 15 µmol L-1 yr-1 we found is due to increase in upper estuary POC content of 8-14 µmol L-1 yr-1 in late spring and summer (May-August). The significant increase in POC was associated with dominating autotrophy (with negative AOU and pH > 9), and an overall improvement in water quality shown in significant (> 50%) decrease in BOD7 since 1997. We found that microbial respiration of organic matter from upstream regions accounted for most of the DIC produced in the mid-estuary, therefore, the increased POC is efficiently remineralized to DIC by the mid-estuary region.

The Elbe River and estuary was subject to significantly lower river discharge between 2014 and 2020 (468 ± 234 m3 s-1), nearly 40% of the long-term average (1960-2020, 690 ± 441 m3 s-1). In addition, May was the only month with a significant negative trend in mean monthly river discharge from 1997, and down to 264 ± 19 m3 s-1 by 2020, a discharge usually observed during summer and early autumn. During the recent drought period (2014-2020), the internal gain in the carbon load as DIC in the mid to lower estuary was significantly higher, by up to 3 times, compared to the non-drought period (1997-2013). This suggests that the drought in the Elbe watershed caused a significant reduction in the average river discharge in May, likely increasing the residence time in the estuary, subsequently permitting a longer period for remineralisation of POC and greatest production of DIC in the mid-lower Elbe Estuary.

How to cite: Rewrie, L., Voynova, Y., Beusekom, J., Körtzinger, A., Ollesch, G., and Baschek, B.: Recent inorganic carbon increase in a temperate estuary driven by water quality improvement and enhanced by droughts, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-13399,, 2023.