CONTROL OF BENTHIC AND HYPORHEIC STREAM BIOFILMS BY THE LIGHT:PHOSPHORUS SUPPLY RATIO – A MESOCOSM EXPERIMENT

Streams around the world suffer heavily from various facets of anthropogenic land use activities. As a consequence, their ecological status is frequently deteriorated, e.g. through the inputs of excessive loads of dissolved nutrients and increased light availability at the streambed due to riparian deforestation. The light-nutrient hypothesis (LNH) is a stoichiometric framework that allows the prediction of thresholds for primary producer growth. We here tested its applicability in a small European river saturated in reactive nitrogen through human land use effects. We performed a flume mesocosm experiment in a small German river characterized by low dissolved phosphorus concentrations, but high nitrate loads. We applied a gradient of soluble reactive phosphorus concentrations (12 levels from < 10 to 220 µg P L^-1) at constant light conditions, thereby creating a wide range of light:phosphorus ratios. The biomass of benthic microbial communities (biofilms) decreased exponentially with the molar light:SRP ratio within one week, as predicted by the LNH. In contrast to the benthic (light exposed) biofilms, the hyporheic biofilm community did not respond according to the predictions of the LNH.  Our results demonstrate that the LNH approach is applicable for benthic biofilm growth in anthropogenically impacted, nitrogen-enriched stream ecosystems, and may help to derive management decisions for sustainable nutrient and light input levels.

Presentation Preference: Oral

Primary Presenter: Rizwan Ullah, Helmholtz Center for Environmental Research-UFZ (rizwan.ullah@ufz.de)

Authors:

Rizwan Ullah, Department River Ecology, Helmholtz Centre for Environmental Research – UFZ, Brueckstrasse 3a, 39114 Magdeburg, Germany  (rizwan.ullah@ufz.de)

Anika Große, Department Aquatic Ecosystem Analysis and Management, Helmholtz Centre for Environmental Research – UFZ, Brueckstrasse 3a, 39114 Magdeburg, Germany  (anika.grosse@ufz.de)

Nuria Perujo, Department River Ecology, Helmholtz Centre for Environmental Research – UFZ, Brueckstrasse 3a, 39114 Magdeburg, Germany  (nuria.perujo-buxeda@ufz.de)

Daniel Graeber, Department Aquatic Ecosystem Analysis and Management, Helmholtz Centre for Environmental Research – UFZ, Brueckstrasse 3a, 39114 Magdeburg, Germany  (daniel.graeber@ufz.de)

Patrick Fink, University of Cologne, Institute for Zoology, Zuelpicher Strasse 47b, 50674 Koeln, Germany  (patrick.fink@ufz.de)