Small changes in phosphorus additions alter the aromaticity of Chromophoric dissolved organic matter (CDOM) in lakewater
Résumé
Although the impacts of eutrophication on freshwater biodiversity are
relatively well known, how eutrophication impacts the quality of
dissolved organic carbon (DOC) is less known, despite its importance for
microbial nutrition. Chromophoric dissolved organic matter (CDOM) is the
fraction of the bulk DOC pool that absorbs light and shifts in the
absorption and fluorescence of this component indicate an alteration in
the quality of the DOC present. Here we looked at the impact of small
phosphorus additions on CDOM absorption and fluorescence in a series of
16, newly constructed and filled, experimental lakes (Plateforme
Planaqua, UMS CEREEP, France). Eight of the lakes received small
additions (+ 100 µM) of phosphorus during late spring and summer
2015. We show that there was a distinct seasonal pattern to DOC and to
all measured CDOM parameters, regardless of nutrient status. We also
show that despite a lack of significant difference between the lakes in
terms of DOC concentrations, there were striking differences in the
carbon-normalised CDOM parameters. For example, we observed a
significant increase in the carbon normalized absorption at 254 nm
(SUVA254) in the lakes with addition of P, this was also the case for
fluorescence (ex350/em450) normalized to carbon concentration. These
changes were also accompanied by shifts in the relative intensities of
the components in the fluorescence excitation-emission matrices (EEM).
We propose that even small shifts in phosphorus availability can induce
strong shifts in carbon quality and that this may well have
repercussions up the food web should this more aromatic CDOM prove to be
less bioavailable. These results also imply that the brownification
observed in lakes in northern Europe may also be partially due to small
shifts in nutrient concentrations combined with increased carbon and
suspended solids imports from the surrounding catchments.
Auteurs, date et publication :
Auteurs Emma Rochelle-Newall , Lydie Blottière , Colombe Consortium
Date : 2018
Volume : 20
Pages : 9464