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


Summary, in English

The loading of terrestrially derived macroelements, such as dissolved organic carbon (DOC), total nitrogen (N), and total phosphorus (P), to inland and estuarine waters is increasing in the northern hemisphere. These
macroelements often limit heterotrophic bacterioplankton metabolism (production and respiration), which in turn influence food web structures, exchange of greenhouse gases between the atmosphere and aquatic systems and oxygen consumption in estuarine ecosystems. In order to predict the impact of increasing macroelement inflows on the function and structure of boreal aquatic ecosystems it is vital to understand the potential sources of macroelements and their regulation of bacterioplankton metabolism. In this thesis, I aimed to determine whether terrestrially derived macroelement loadings to inland and estuarine waters can be utilized by bacterioplankton. In addition, I assessed how riverine influxes of DOC, N and P, alone or combined, regulate estuarine bacterioplankton metabolism. For this purpose, I applied a bioassay
approach to measure bacterioplankton respiration (BR) and production (BP) on samples from boreal freshwaters and estuarine systems. Terrestrially derived macroelement availability in brown-water lakes increased from DOC to N to P and averaged 2%, 31% and 49%, respectively. Although extremely low, relative
DOC bioreactivity increased with downstream transit for rivers with long water residence time and high fractions of urban and agricultural land use. Riverine bioreactive DOC was not the primary source of energy supporting bacterioplankton respiration at the Öre estuary, confirming the low bioreactive DOC exports expected for the Öre river. Instead riverine nutrients showed a more important effect on BR through stimulation of primary production, which in turn derived the organic carbon utilized by the bacterioplankton in the estuary.
However, BP at the Öre estuary was in general limited by P and BR by carbon. In light of expected increases in riverine loadings of DOC and P, and decreases of estuarine primary production, estuarine BP is expected to increase, as well as estuarine BR of riverine DOC inputs. These bacterioplankton responses may be
exacerbated by combined increases of riverine inflows of DOC, N and P. In summary, terrestrially derived macroelements can have a substantial impact on freshwater and estuarine bacterioplankton metabolism. Given the large role of bacterioplankton on the structure and function of aquatic systems, continuous changes in the input of terrestrial macroelements may have large consequences for boreal aquatic ecosystems.


  • Natural Sciences


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




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

Defence date

9 March 2018

Defence time


Defence place

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