EESS Winter Seminar Series - Patricia Glibert, Professor, Center for Environmental Science, University of Maryland
EESS Winter Seminar Series - Patricia Glibert, Professor, Center for Environmental Science, University of Maryland, "Complexities in the dynamics of eutrophication and oligotrophication – from the phytoplankton to the ecosystem scale", Abstract: While eutrophication is occurring globally, the responses of an ecosystem to eutrophication are complicated for a number of reasons. The most recognized responses to eutrophication are hypoxia and increases in harmful algae, but changes can be far more complex due to multiple reinforcing feedbacks leading to non-linear and often, abrupt ecosystem changes over time. Nutrient ratios have long been thought to infer system regulation only when nutrient concentrations are at levels limiting to the phytoplankton assemblage. A prevailing view has considered nutrient ratios to be ecologically irrelevant unless concentrations are in these limiting ranges. This talk addresses the theme that nutrient ratios do play important roles in shaping aquatic food webs whether nutrients are limiting are not. Four aspects will be emphasized. First, nutrient ratios are changing globally due to anthropogenic activities. Second, physiological regulation by nutrients continues by cells even in the “super-saturation” range of the kinetic curve; kinetic responses are dynamic. This has importance consequences for biomass composition, i.e. food quality. Third, Imbalances in stoichiometry may destabilize the dynamics of consumers, shifting systems to new conditions via changes in food quality and via altered biogeochemical cycling. Finally, positive (and negative) reinforcing feedbacks can shift ecosystems to new stable states; such shifts can be gradual or abrupt and communities may not return to their original state once nutrient loads have been reduced. Management efforts targeting single nutrient removal strategies may have unintended consequences for aquatic ecosystems.