Effects of nutrient limitation of post bloom phytoplankton composition, productivity and photophysiology were investigated at 3 locations (M: mid, J: jetty, G: glacier front) in a high Arctic fjord (Kongsfjorden, 79˚N) during June 2015. Glacial melt water intensified stratification during this period in all locations, whereas nitrate concentrations were low (average 0.2±μM), indicating post bloom conditions. Short term (60 h) nitrate addition experiments revealed increasing N-limitation of surface phytoplankton at central Kongsfjorden. This coincided with a pronounced change in the flagellate dominated phytoplankton community, replacing large (10 μm) chrysophytes (85% of chl-a) with smaller (5-2 μm) haptophytes (60% of chl-a) and prasinophytes (20% of chl-a). These changes were less pronounced at station G, where average surface nutrient concentrations were higher. Surface chl-a concentrations (5 m) were variable and showed no clear trends during the onset of nutrient limitation and changes in taxonomic composition. Furthermore, chl-a normalized maximum carbon fixation rates and water column productivity showed no significant trends. The initial rate of carbon fixation correlated to irradiance and surface salinity, in addition to chrysophyte chl-a. Active fluorescence (FRRf) derived chl-a normalized photosynthetic characteristic were more strongly associated to changes in taxonomic composition and chl-a than to environmental variables and N-limitation. FRRf based photosynthesis characteristics showed opposing trends compared to the carbon incorporation experiments, changing the electron requirement for carbon fixation from 7.7± in the beginning of June to 17± electrons at the end of June. We concluded that N-limitation caused pronounced changes in phytoplankton composition and size structure, with minor effects on chlorophyll-a and water column productivity.
|Publication status||Published - 2017|
|Event||IASC Conference Prague - Prague , Czech Republic|
Duration: 3-Apr-2017 → 7-Apr-2017
|Conference||IASC Conference Prague|
|Period||03/04/2017 → 07/04/2017|