262 Advances in Ecohydrogeology (Posters)

Ecohydrogeology is the unifying, synthetic field of study integrating the approaches from the ecological and hydrogeological sciences in the study of groundwater-related ecosystems, habitats, and organisms. We encourage submissions of research that advances the science, stewardship, and policy at the intersection of ecology and hydrogeology.

Wednesday, 22 October 2025
8:00 AM - 5:30 PM
HBGCC, Hall 1

From Muskrats to Mudflats, the Changing Ecohydrology of an Interdunal Wetlands in the Lake Michigan Dunes, USA

Paper number: 262-2
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

We have studied the ecohydrology of an ~1.25ha interdunal wetland, an imperiled ecosystem, in a Lake Michigan coastal dune complex at Saugatuck Harbor Natural Area, Allegan County, Michigan, USA since 2016. A sand aquifer ~70m thick underlies the wetlands, connecting it to Lake Michigan-Huron (Lake MH). Previous research documents the ecosystem shifts between open dune and wetlands due to fluctuating Lake MH water levels. The wetland appears and expands in response to rising water levels, then contracts and transitions to open dune vegetation when water levels decrease. In 2020, Lake MH water levels reached record highs. The wetland’s pools were over 3’ deep, providing habitat for muskrats to build lodges. Lake levels have since dropped and been below the lake-wide historic average, 176.57m, since mid-October 2024, causing the pools to dry. The wetlands’ subtle microtopography of low-relief ridges and depressions still hosts dominant hydrophytic vegetation, including Cladium mariscoides, Spiraea tomentosa, and Calamovilfa canadensis. However, vegetation quadrat sampling shows the density of these species has decreased since 2024 while more upland/dune vegetation species have appeared. Sampling surface water pools and groundwater in the wetland’s monitoring wells indicates groundwater also contributes to the wetland’s hydrology. In April 2025 we installed two HOBO data loggers in a centrally-located monitoring well to collect detailed water level measurements. The U.S. Drought Monitor indicated abnormally dry conditions beginning early May 2025, transitioning to moderate drought in early July 2025. Approximately 14.5cm of rain fell during this time. A strong diurnal pattern of falling groundwater levels during the day and rising levels during the night appeared in late May, indicating daytime evapotranspiration losses and nightly groundwater replenishment. This pattern was punctuated by rain, causing temporary ponding during the event and increased groundwater levels post-event. Overall groundwater levels still decreased over 13cm from April–late July as evapotranspiration demands exceeded groundwater and precipitation replenishment. Daily water levels decreased ~1.6cm/day at temperatures ~24˚C while higher temperatures ~32˚C resulted in ~2.2 cm/day of water loss, suggesting greater evapotranspiration losses with higher temperatures. Climate change models predict higher summer temperatures with fewer rain events and potential increased drought during the growing season. Hence, this imperiled ecosystem faces significant challenges given the amount of water needed to support it, especially under changing climatic conditions.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-413582

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