Speaker: Marc Schallenberg, University of Otago, Dunedin, New Zealand
Place: Forum Chriesbach, FC-D24

The non-linear stressor-response relationship with hysteresis is the basis for alternative stable state theory in lakes. Quantifying these relationships in lakes should improve the forecasting of lake responses to increasing and decreasing stressor levels, allowing better decisions and investments to be made regarding lake management. However, stressor-response relationships may take many forms (including linear, logistic, exponential, etc) and may or may not exhibit hysteresis. In this talk, I will explore different types of lake stressor-response relationships as supported by evidence from studies on New Zealand lakes. Examples include (1) the relationship of nitrogen availability to algal biomass in a large, oligotrophic lake (Lake Taupo), (2) the relationship between nitrogen loading and the health of macrophyte communities in coastal lagoons, and (3) the relationship between phosphorus availability and algal blooms in medium-sized, warm monomictic lakes. I will discuss how the stressor-response framework for lake management requires a robust lake typology and how multiple stressors (i.e., eutrophication, climate change, invasive species) are likely to influence stressor-response relationships.

Short Bio: Marc Schallenberg received his PhD from McGill University in 1993 and has been a Research Fellow at the University of Otago, Dunedin, New Zealand since 1994. He has studied over 100 lakes throughout New Zealand, the Sub-Antarctic Islands and in Antarctica. He heads the Southern Lakes Research Group at the University of Otago, which studies many fundamental and applied aspects of lake science and which also contributes advice on lake monitoring and policy development. He is in Switzerland to gauge interest among Swiss lake researchers on a future collaboration to study the functioning and management of deep, pre-alpine lakes in Switzerland, Italy and New Zealand.