Effects of episodic nutrients enrichments on P-limited planktonic communities: Lake Redon ENEX 2013 experiment

Planktonic communities are naturally subjected to episodic nutrient
enrichments that may stress or redress the imbalances in limiting
nutrients. Human-enhanced atmospheric nitrogen deposition has caused
profound N:P imbalance in many remote oligotrophic lakes in which
phosphorus has largely become limiting. These lakes offer an opportunity
to investigate the planktonic community response to nutrient fluctuations
in P-limited conditions. The ENEX experiment in Lake Redon (Pyrenees),
performed during August 2013, aimed to investigate the structural and
stoichiometric effects of pulse nutrient additions on P-limited planktonic
communities. We performed P (PO43-), and N (NH4+ or NO3-) additions to the
summer epilimnetic community of the ultraoligotrophic lake using
self-filling ~100 L enclosures and analysed the response to varying P
availability, N:P imbalance, and N source. The nutrient additions were
gradients within the range of values seasonally found in the lake and
other oligotrophic lakes of the Pyrenees, with a further P level typical
of mesotrophic lakes to provided non-limiting conditions.