Project 12

Determination of critical thresholds for ecosystem resilience from perturbation experiments.

Based in: University of Geneva, Switzerland.

Objectives: Perturbation experiments are the most straightforward way to measure critical slowing down (www.early-warning-signals.org), the most reliable empirical indication that the system approaches a critical transition. It has been shown in simple perturbation (pulse) experiments that the difference in return time varies greatly between a situation where a system is far from - vs. close to - a transition. We will start by making use of LakeLab which offers experimental control, while being large enough to approach natural levels of complexity. This ESR will manipulate the physical stability of the water column, mimicking the effect of storms. Experimental design in LakeLab will be following criteria from “optimal design”, which allows parameters to be estimated with minimum variance and bias. The response in metabolism and the phytoplankton community will be studied at both low and high nutrient levels, since theory predicts that eutrophication reduces resilience and brings systems closer to a tipping point. The next and final level of (natural) complexity will be studied by performing whole lake manipulations. Resilience and critical slowing down have rarely been studied at whole ecosystem level. The ESR will closely work with lake and reservoir managers and study response and resilience of the ecosystem. Preference will be given to systems where radical restoration measures are planned, for example installation of artificial mixing, or use of hydrogen peroxide to selectively remove cyanobacteria.

This student will be primarily based in Univeristy of Geneva supervised by Prof. Bastiaan Ibelings, and co-supervised by and spend study time with Prof. Rita Adrian, IGB Berlin, Germany. The PhD will will be a double degree awarded by University of Geneva and Free University of Berlin.