Climate change predictions include increasing precipitation and run-off events that expose phytoplankton communities to coloured dissolved organic matter (cDOM) and nutrient pulses of varying intensity and frequency. The consequence of different nutrient/cDOM pulse regimes on phytoplankton communities and the role of legacy effects related to the characteristics of previous exposure regimes, remain largely unresolved. To investigate this, we implemented add-on bottle experiments with water collected from a mesocosm experiment conducted in lake Erken (Sweden) with the following treatments: low intensity-daily pulses (daily), a single pulse with high intensity (extreme) and a control without additions. The same total amount of cDOM and nutrients was added to the daily and extreme treatments over a period of 3 weeks, which was then followed by a 2 week recovery period without further additions. At the end of both periods, water from all mesocosm treatments was filled into microcosms and either exposed to a second single nutrient pulse that corresponded to the extreme mesocosm treatment or left as controls. The microcosms were incubated for 8 days in the lab and changes in phytoplankton biomass and composition were analyzed. Preliminary results show that the phytoplankton responses differed between the mesocosm source treatments, most likely due to differences in initial phytoplankton composition and abundance. Hence, our results suggest that legacy effects may be important in the prediction of phytoplankton community response to extreme nutrient and cDOM pulses.

Primary Presenter: Gabriela Agreda-Lopez, Uppsala University (gagredal@gmail.com)

Authors:

Gabriela Agreda-Lopez, Uppsala University  (gagredal@gmail.com)

Berenike Bick, Uppsala University  (berenike.bick@ebc.uu.se)

Stella Berger, Leibniz-Institute of Freshwater Ecology and Inland Fisheries  (stella.berger@igb-berlin.de)

Silke Langenheder, Uppsala University  (silke.langenheder@ebc.uu.se)