Hydrologic connections in Apostle Islands coastal wetlands: Exploring dynamics and resilience to Lake Superior water level fluctuations

Abstract

Coastal wetlands within Apostle Islands National Lakeshore (APIS) represent important reference ecosystems for Lake Superior given their relatively undegraded condition. However, this region lacks climate change-relevant nearshore bathymetric information for coastal wetlands, a gap our study helps fill. Since 2010, the Great Lakes, including Lake Superior, have experienced both extended low water levels and extreme highs. Such extremes are anticipated to increase in frequency and duration, but the exact outcomes are uncertain. Therefore, it is important to explore the resiliency of APIS wetlands against different water level scenarios. We studied seven wetlands with different geomorphic connections to Lake Superior (open, transient, or semi-permanent) and gathered water level and depth data. Using depth measurements, we created topo-bathymetric maps to investigate inundation patterns for various scenarios of Lake Superior water levels. Comparing wetland water levels to those of Lake Superior we found that water level patterns were unique per connection type, but that Lake Superior maintained baseline-water levels for all sites. Additionally, the wetlands we sampled demonstrated resiliency to substantial changes in water levels thanks to both bathymetry deeper than record low Lake Superior levels and sufficient undisturbed upslope habitats. However, the biotic communities within could shift in composition depending on future water level regimes. The increasing magnitude and frequency of Great Lakes water level fluctuations induced by climate change will influence all APIS coastal wetlands, regardless of connection type.