Ecological regime shifts may occur when the critical threshold of an extrinsic (e.g. climate, nutrient loading) or intrinsic (e.g. food web interactions, biogeochemical cycling) driver is met and results in a shift in the structure of a community (Andersen et al. 2009). When interactions among abiotic and biotic components are not directly proportional, the response of the system is defined as non-linear (Burkett et al. 2005). Often, ecological response to environmental disturbance occurs within a bounded range; however, slight differences in threshold values can trigger a reaction outside the predicted response of the system invoking a non-linear response (Burkett et al. 2005). These shifts are typically enduring and involve a change in the internal dynamics that prevent the system from rebounding to a previous state (Biggs et al. 2009), affecting the structure, function, and ultimately the resiliency of the system (Burkett et al. 2005).
We are investigated the response of lake algal communities to changes in glacial meltwater influx from the Renland Ice Cap (Scoresby Sund, East Greenland) through the Holocene to assess whether these influxes always elicit similar responses, or alternatively, non-linear or threshold responses. In order to assess these influences we are measuring sedimentary algal pigments and diatom assemblage structure and turnover in a glacier-fed lake, Bunny Lake as well as in nearby Raven Lake, which does not receive glacier meltwater. We are modeling lake level changes that have occurred throughout the late Holocene to determine if glaciers altered diatom habitat and algal community structure. Our results suggest that changes in the magnitude and composition of meltwater were unique during the LIA and elicited a non-linear threshold response absent during other periods of glacier advance.
Photos: Bunny Lake (top) and Raven Lake (below) courtesy of Aaron Medford.
This work is a collaboration with fellow Climate Change Institute colleagues: Dr. Jasmine Saros, Dr. Brenda Hall and Aaron Medford.
Support for this work was provided by Correll Fellowship, University of Maine Chase Distinguished Research Assistantship, University of Maine Graduate Student Government Fund, University of Maine School of Biology and Ecology for teaching assistantships.