DELUGE - Disturbance and Ecohydrological Legacies in Upland Great-lakes Ecosystems: An Ecosystem Scale experiment to study coastal critical zone

Coastal ecosystems along the Great Lakes play an important role in critical element cycling between land and lake ecosystems. Because lake water levels are highly dynamic, the dominant ecosystems (marsh, swamp, upland forest) constantly respond to the varying water line. Flood pulses are important controls on plant community zonation, as well as their respective biogeochemical functions, setting the boundary between herbaceous wetlands, forested wetlands, and/or upland forest based on the respective flooding tolerance. Because lake levels are predicted to increase in future decades (e.g. 2040-2049 vs. 2010-2019), shifts in ecosystem boundaries are expected but the change in ecosystem function is currently unknown.

To understand the impact these flood pulses have on soil biogeochemistry and plant function, we are implementing an ecosystem-scale manipulative experiment to create increasingly intense flood pulses by pumping water across an elevation gradient from forested wetland to upland (DELUGE - Disturbance and Ecohydrological Legacies in Upland Great-lakes Ecosystems). We follow a before-after-control-impact design using two diked parcels in the Ottawa National Wildlife Refuge at the coast of Lake Erie, one of which will be untreated and serve as a reference. The main objective is to gain a mechanistic understanding of how the effects of freshwater flooding and subsequent drainage propagate through water, soils, microbes, and plants to cause ecosystem state changes such as tree mortality and changes in biogeochemical cycling. Here we present the experimental design, site characterization, and results from sensor-based baseline measurements which started in June, 2025. Results from DELUGE will be incorporated into multi-scale process and Earth system models, with the overarching goal of an improved predictive understanding of coastal ecosystems.