Transformation of riverine nutrients and dissolved organic matter from source to sea

Transformations of nutrients and organic matter are of considerable importance in large rivers on their way to the sea, but studies investigating a river system from source to sea are scarce. We tested the hypotheses: (1) dissolved nutrients are incorporated by phytoplankton and transferred into particles with increasing river length, (2) lignin- and polyphenol-like terrestrial components will decrease from upstream to downstream regions, (3) oxygen and aromatic content and molecular mass of DOM will decrease towards the tidal and coastal parts, and (4) chlorophyll a concentration and salinity are important environmental drivers of nutrient dynamics and DOM composition. We investigated the Elbe River in Central Europe from the headwaters via the lowland river and the tidal region towards the coastal waters in the North Sea. Chlorophyll a concentration and oxygen saturation increased longitudinally in the river but showed distinct minima in the estuary upstream of the salinity gradient. Dissolved nutrients were taken up by algae in the freshwater part but were released again at algal die-off, and a part of the nitrate was used for denitrification. Organic carbon was dominated by lignins and polyphenols of terrestrial origin in the upstream region. The O:C ratio, the number of double bounds, aromaticity, and molecular mass decreased with increasing river stretch. The proportion of organic nitrogen components increased in the estuary and coastal regions. Overall, our unique data set helps understanding the dynamic transfer of nutrients and a distinct variability of DOM composition along the land-ocean gradient.

Presentation Preference: Oral

Primary Presenter: Norbert Kamjunke, Helmholtz Centre for Environmental Research (norbert.kamjunke@ufz.de)

Authors:

Norbert Kamjunke, Helmholtz Centre for Environmental Research - UFZ  (norbert.kamjunke@ufz.de)

Peter Herzsprung, Helmholtz Centre for Environmental Research - UFZ  (peter.herzsprung@ufz.de)

Wolf von Tuempling, Helmholtz Centre for Environmental Research - UFZ  (wolf.vontuempling@ufz.de)

Oliver Lechtenfeld, Helmholtz Centre for Environmental Research - UFZ  (oliver.lechtenfeld@ufz.de)

Anna Matousu, Institute of Hydrobiology, Biology Centre CAS  (anna.matousu@gmail.com)

Petr Znachor, Institute of Hydrobiology, Biology Centre CAS  (znachy@gmail.com)

Tina Sanders, Helmholtz-Zentrum hereon GmbH  (tina.sanders@hereon.de)

Holger Brix, Helmholtz-Zentrum hereon GmbH  (holger.brix@hereon.de)

Ingeborg Bussmann, Alfred-Wegener-Institut, Helmholtz Centre for Polar and Marine Research  (Ingeborg.Bussmann@awi.de)

Markus Weitere, Helmholtz Centre for Environmental Research - UFZ  (markus.weitere@ufz.de)