Riverine sources of bioreactive macroelements and their impact on bacterioplankton metabolism in a recipient boreal estuary

Författare

Summary, in Swedish

The loading of macroelements such as, dissolved organic carbon (DOC), total
nitrogen (N) and total phosphorus (P) from terrestrial soils to aquatic systems is
increasing in the northern hemisphere. This phenomenon has several ecological
and biogeochemical consequences for inland and coastal water systems, which are
linked to bacterial cycling of DOC, N and P. During growth, bacteria assimilate
macroelements into biomass (a process known as bacterial production), removing
DOC, N and P from the water column and channelling these elements to
consumers. Bacteria can also utilize organic carbon as a source of energy for
respiration. For this purpose they take up oxygen dissolved in the water and
release CO2 to the atmosphere. Increases in bacterial production have
consequences for aquatic food web structures, whereas increases in bacterial
respiration have implications for greenhouse gas emissions and for oxygen
concentrations of estuarine waters. Currently, it is still unclear the degree to which
land derived macroelements can be utilized by bacteria. Moreover, it is also not
understood how bacterial metabolism (production and respiration) will respond to
increased terrestrial macroelement fluxes.
In this thesis, I aimed to determine the fraction of the terrestrially derived
macroelement loading that can be utilized by bacteria. Moreover, I investigated
whether riverine inflows of DOC, N and P, alone or combined, limited the
metabolism of bacteria in estuarine waters. I found that on average only 2% of the
DOC exported from land was utilized by bacteria for production of biomass during
a seven-day period. This share amounted to approximately 50% in the case P,
which was thus the macroelement mostly available to bacteria among the three
macroelements studied. Yet, the relatively low DOC quality increased downstream
for rivers with long river water residence time and high catchment proportions of
agricultural and urban land. These riverine catchment features are thus important
to predict the export of oxygen consuming organic carbon (C) from rivers to
estuaries.
The DOC transported in the Öre river, was less important for support of
bacterial respiration than nutrients. These findings agree well with predictions of
DOC quality for the Öre river, based on the its catchment features. Riverine
nutrients stimulated primary production at the Öre estuary, which in turn supplied
organic carbon to bacteria. In general, bacterial production in the Öre estuary was
limited by P, while bacterial respiration was limited by organic C. In light of
predicted increases of riverine macroelement deliveries and expected reductions of
estuarine primary production, bacterial production will likely increase, as well as
the bacterial respiration of riverine delivered organic C. Both estuarine bacterial
production and respiration are expected to increase the most in response to
combined increases of riverine deliveries of DOC, N and P.
In summary, land derived macroelements can be substantially available to
freshwater and estuarine bacteria and impact their metabolism. Given the large
role of bacteria in food web structures and aquatic CO2 emissions, continued
changes in the input of terrestrial macroelements may have large implications for
boreal aquatic ecosystems.

Ämne

  • Natural Sciences

Nyckelord

  • Dissolved organic carbon
  • DOC bioreactivity
  • nutrient bioavailability
  • dissolved organic matter
  • bacterioplankton production
  • bacterial respiration
  • aquatic ecology

Status

Published

ISBN/ISSN/Övrigt

  • ISBN: 978-91-7753-589-8
  • ISBN: 978-91-7753-588-1

Försvarsdatum

9 mars 2018

Försvarstid

10:00

Försvarsplats

Lecture hall “Världen”, Geocentrum I, Sölvegatan 10, Lund