A regional analysis of the physical and biological effects of Tropical Cyclone Irene on lake ecosystems across northeastern United States and eastern Canada

Background/Question/Methods

On August 27^th and 28^th of 2011, Tropical Cyclone Irene made landfall along the New Jersey coast and proceeded up the east coast and through New England and eastern Quebec, Canada.   These areas experienced heavy rain (>200 mm in 24-hours) and windy conditions (up to 28 m s^-1 sustained winds) as the storm passed.  This study documents the regional impact of Tropical Cyclone Irene on thermal structure and ecosystem metabolism in nine lake ecosystems in the northeastern United States and eastern Canada using high-frequency data from meteorological and aquatic environmental sensors.  Physical lake characteristics such as thermal stability were calculated using measurements of wind speed, water temperature profiles, and basin morphometry.  Metabolism metrics (e.g., gross primary productivity and community respiration) were estimated by fitting a metabolism model to diel patterns of dissolved oxygen in the water column.  The study lakes span a gradient of lake morphometry, watershed characteristics, and productivity.  Here, we assess the impact of a single storm event on multiple lakes across a large geographic area. 

Results/Conclusions

Across lakes, thermal stability declined 9-100% within 48 hours after the storm. The impact on thermal stability was predicted by both storm magnitude and the total amount of rainfall that fell in the watershed and on the lake’s surface relative to volume (potential volume replacement).  Together, these metrics suggest that storm magnitude is an important driver of the rate of change in stability but that the watershed context and potential runoff are important drivers of mixing. Prior to Irene, primary production was tightly coupled to respiration across all lakes; however, after the storm, primary production was decoupled from respiration.  This pattern suggests that, after Irene, lake and reservoir ecosystems received increased terrestrial organic material that fueled ecosystem-wide increases in allochthonous-driven community respiration and net heterotrophy.  Predictions derived from climate models suggest that eastern North America will experience an increase in intense rain events which would likely result in elevated loadings of water, nutrients, sediments, and organic matter to lakes.  Effective management practices and protection or restoration of regional water resources will require addressing the impact of intense storms, and results from this study indicate that watershed characteristics are likely to mediate the impact that such storms will have on lakes.