Environmental Engineering Seminar: Lake Superior Topics

Environmental Engineering Seminar Series
GLRC 202 3:00pm

Rasika Gawde, PhD student, Environmental Engineering

“Hydrodynamics and Thermal Structure in Lake Superior Impacts of an Episodic Climate Anomaly”

In recent years, 3D hydrodynamic models have been widely applied in a predictive capacity to all the Great Lakes to study ecosystem response to long-term climate change. But, an alternative aspect of climate change, observed as intermittent climatic anomalies, has not received equal interest. An isolated, positive anomaly observed in local air temperature measurements in March 2012 presents a unique opportunity to study the latter in Lake Superior’s ecosystem. Here, a 3D hydrodynamic model, Environmental Fluids Dynamics Code (EFDC), is applied for two consecutive summers, one preceded by the spring anomaly (2012) and the second preceded by average spring air temperatures (2011), to analyze the impact of this climatic anomaly on the thermal regime of the lake. This modeling effort is supported by a rich, comprehensive dataset of surface water temperatures and vertical temperature profiles measured during the April to September period of 2011 and 2012. Impacts of the temperature anomaly were observed along temporal and spatial scales; e.g. the 6°C increase in lake-wide surface water temperatures at the start of summer 2012 as compared to 2011 as well as on the physical processes; e.g. an early onset of thermal stratification (4 weeks in advance) in 2012. These shifts in thermal regimes will in turn affect ecological processes.

Marcel Dijkstra, PhD student, Environmental Engineering

“Ecosystem function in Lake Superior: Impacts of an episodic climate anomaly”

Climate change may become manifest over differing time scales: one characterized by long term, incremental changes as recorded in historical averages and the other by short term variability, e.g. the magnitude, timing, frequency and duration of episodic, extreme events. The ecological impact of extreme weather events may be particularly severe, simply because they are extreme, but also because ecosystems have rarely been exposed to such events. Due to the inherent unpredictability of extreme events, few studies have reported on the attendant ecosystem response. Here, the effects of an episodic air-temperature anomaly that occurred in Spring 2012 are reported and compared to those of 2011, a year with essentially average temperature conditions. Impact of this extreme weather event on the lake’s thermal regime and ecological forcing conditions (e.g. light, temperature and nutrients) cascaded through the system. This resulted in elevated annual primary production with a distinctive temporal distribution characterized by high productivity in early summer followed by a collapse in September (brought on by nutrient depletion resulting from extended thermal stratification). The benefits of increased annual primary production to the higher food web may be offset by cataclysmic drops in production.