Indirect link between riverine dissolved organic matter and bacterioplankton respiration in a boreal estuary

• Increasing loading of terrestrially derived dissolved organic matter tends to enhance bacterioplankton respiration (BR) in boreal estuaries, but knowledge on the mechanisms behind this effect is not complete. We determined the stable isotopic signature of the reactive estuarine dissolved organic carbon (DOC) in the Ore estuary (Baltic Sea) by using the Keeling plot method. The delta C-13 ratio of the estuarine labile DOC varied from -26.0 parts per thousand to -18.7 parts per thousand with most values resembling those typical for DOC of coastal phytoplanktonic origin (-18 to -24 parts per thousand), while being distinctly higher than those of DOC from terrestrial sources (-28 parts per thousand to 27 parts per thousand). Furthermore, the delta C-13 of the respired carbon was positively correlated to DOC concentrations, indicating that carbon of marine origin increasingly dominated the reactive substrates when input of organic matter into the estuary became higher. This suggests that riverine organic matter mainly affects BR indirectly, by providing nutrients that stimulate the production of phytoplankton-derived reactive DOC in the estuary. Thus, riverine derived DOC per se may not be as important for coastal CO2 emissions as previously thought.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences (hsv//eng)

Nyckelord

Riverine dissolved organic matter

Dissolved organic carbon

Bacterial respiration

Baltic sea

Carbon isotopes

Bacterioplankton

Primary production

Carbon cycling

Riverine dissolved organic matter

Dissolved organic carbon

Bacterial respiration

Baltic sea

Carbon isotopes

Bacterioplankton

Primary production

Carbon cycling

Publikations- och innehållstyp

ref (ämneskategori)

art (ämneskategori)