Food web structure mediates ecosystem resilience in response to storm event pulses of nutrient loading

Abstract:

Over the last decade the frequency and intensity of storms have increased in the Midwest due to climate change. Ecosystem resilience, the ability of an ecosystem to return to a reference state following a disturbance, can alter the effect of storm-related disturbances such as nutrient loading pulses into a lake. The structure of lake food webs can influence ecosystem resilience to nutrient loading by amplifying or reducing the disturbance through trophic interactions. We hypothesized that a simple food web structure would decrease ecosystem resilience to algal blooms following pulse nutrient loading disturbances by decreasing nutrient cycling pathways and diminished top-down control. We tested this hypothesis by constructing food webs in paired experimental ponds with low, intermediate, and high degrees of trophic linkages. One pond in each food web treatment received a pulse addition of nutrients similar to the load expected in a large storm event, while the other pond served as a reference ecosystem. We measured the response of algal biomass and ecosystem metabolism to the pulse perturbations in the manipulated ponds and compared them to the dynamics in the reference ecosystem. Overall, the ecosystems with more diverse trophic linkages had increased ecosystem resilience to the nutrient pulse. In configurations with only simple food chains, the degree of top-down control on algal biomass was proportional to how rapid and severe the ecosystem response was to the nutrient pulse. Food webs with more complex trophic linkages and a high degree of benthic-pelagic coupling were the most resilient to the perturbation. This series of whole ecosystem experiments provide evidence that food web structure can mediate the ecosystem response to pulse disturbances such as the nutrient loading associated with storm events.