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Abstract
Predicted climate-induced changes in the Great Lakes include increased variability in water levels, which may shift periphyton habitat. Our goal was to determine the impacts of water level changes in Lake Superior on the periphyton community assemblages in the Keweenaw Peninsula with different surface geology. At three sites, we identified periphyton assemblages as a function of depth, determined surface area of periphyton habitat using high resolution bathymetry, and estimated the impact of water level changes in Lake Superior on periphyton habitat. Our results suggest that substrate geology influences periphyton community assemblages in the Keweenaw Peninsula. Using predicted changes in water levels, we found that a decrease in levels of 0.63 m resulted in a loss of available surface area for periphyton habitat by 600 to 3000 m2 per 100 m of shoreline with slopes ranging 2 to 9°. If water levels rise, the surface area of substrate will increase by 150 to 370 m2 per 100 m of shoreline, as the slopes above the lake levels are steeper (8–20°). Since periphyton communities vary per site, changes in the surface area of the substrate will likely result in a shift in species composition, which could alter the structure of aquatic food webs and ecological processes.
Highlights
Since the 1950s, the climate of the Great Lakes continues to change: air temperatures have increased by 1.3 ◦ C, precipitation has increased 14% with less snow and more rain, and summer lake surface temperatures have increased by 2.5 ◦ C [1]
We selected three sites in the Keweenaw Peninsula based on nearshore geology and accessibility: McLain State Park (ML) had loose sand and gravel with patches of Freda Sandstone bedrock; Hunter’s Point Park (HP) contained basalt andesite lava flows and Copper Harbor
If Lake Superior water levels change, the surface area of periphyton habitat will change in the Keweenaw Peninsula to varying degrees based on bathymetry
Summary
Since the 1950s, the climate of the Great Lakes continues to change: air temperatures have increased by 1.3 ◦ C, precipitation has increased 14% with less snow and more rain, and summer lake surface temperatures have increased by 2.5 ◦ C [1]. Models predict that climate-induced changes in the Great Lakes include an increased variability in lake levels [2]. Water levels in Lake Michigan and Lake Huron are nearly 1 m higher compared to the long-term average since 1918 [3]. Fluctuating water levels fundamentally affect the biophysical and chemical properties of the Great Lakes [4] including lake circulation, aquatic communities, ecosystem productivity, fish and wildlife habitat quality, and the availability and quality of water for human use [5,6,7]. Microbial communities in aquatic ecosystems may quickly change in response to increased air and water temperatures. Warmer water temperatures may change the composition of periphyton communities, which may disturb ecological processes and function
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