Archive of Spotlight Feature Articles

Great Lakes Exploration: Lake Huron’s Sinkholes

By Katie Coakley, Cooperative Institute for Limnology and Ecosystems Research Summer Fellow

Isolated sinkhole (93m)

Misery Bay Sinkhole

Ariel View of Misery Bay Sinkhole

Ariel View of Misery Bay Sinkhole (20m)

How were the sinkholes discovered?

During a 2001 Lake Huron Thunder Bay National Marine Sanctuary survey, Dr. Dwight Coleman (Institute for Exploration) first discovered a series of offshore freshwater underwater sinkholes at a depth of approximately 100 meters, formed by a unique series of environmental processes. Sinkholes on land and in shallow nearshore areas have been known to local residents for some time; however the unique ecosystems represented in these systems have not been studied. Lake Huron experienced a period of low levels between 10,000 and 6,000 years ago, exposing its limestone bedrock to erosion by groundwater. Sinkhole formation began as acidic water dissolved away passages and holes in the limestone rock, resulting in weak ceiling structures prone to collapse.

Why are sinkholes of interest to NOAA?

An understanding of these systems is important to NOAA in determining the groundwater volume these systems may contribute to Lake Huron lake levels (important to Great Lakes shipping), unraveling the mystery of these unique microbial ecosystems and analyzing compounds found in the sinkholes for potential pharmaceutical applications.

How will NOAA study these sinkholes?

NOAA’s Office of Ocean Exploration in collaboration with NOAA’s Great Lakes Environmental Research Laboratory, recently funded the $284,315 proposal: “Exploration of shallow and deep water submerged sinkhole ecosystems in Thunder Bay National Marine Sanctuary, Lake Huron: habitat and life.” The goal is to produce a detailed physical, chemical and biological picture of an unknown landscape found beneath the waters of Lake Huron. Project scientists will use National Undersea Research Program remotely operated vehicles operated by the University of Wisconsin - Milwaukee teamed with divers to map and study the Middle Island and Isolated Sinkholes in Lake Huron.

Has there been much progress on this project?

Currently, much of the project’s efforts are extended to the study of the Isolated Sinkhole, a 55 m by 40 m karst sinkhole with a maximum depth of 3 m. The following chart summarizes data from Isolated Sinkhole’s vent water as compared to standard Lake Huron water data.

Parameter (Units)	Lake Water	Vent Water
Conductivity (µS/cm)	140	1700
Temperature (ºC)	3.5	7.0
Chloride (mg/L)	13	175
Sulfate (mg/L)	16	1457
Total Phosphorus (mg/L)	0.004	3.230
Dissolved organic carbon (mg/L)	3.5	9.8
Particulate organic carbon (mg/L)	0.9	405

Conditions found in vent environments are markedly different that those found throughout the familiar waters of Lake Huron. A higher conductivity in vent water is attributed to the increased levels of Chloride and Sulfate, both indicators of biogeochemical condition. Phosphorus is a limiting nutrient for primary production throughout the Great Lakes; therefore, additional work could prove a link between sinkhole discharge and surrounding water quality in Lake Huron. Heightened levels of DOC and POC also aid in fueling unique biogeochemical process within the sinkhole, providing an environment suitable for living organisms. Recent studies at the Middle Island sinkhole indicate that microbial life in these systems relies on sulfate and methane for respiration rather than the typical oxygen respiration cycle.

What are future outcomes of studying Lake Huron’s sinkholes?

Scientists are collecting groundwater samples to test for and identify chemosynthetic (sulfur reducing) microbes and determine the age of water flowing out of the sinkholes. These samples will lend insight into physical conditions; nutrient chemistry; and microbial biomass, diversity, and process in a largely unstudied environment. Additionally, benthic sampling of prominent microbial mats has the potential to yield microbes for pharmaceutical application.

Steve Ruberg, Lead PI (Physico-Chemical Mapping and Instrumentation, GLERL) and Team:

Nathan Hawley (Oceanography, GLERL)
Tyrone Black (Michigan Department of Environmental Quality, Karst Geology)
Mark Baskaran (Wayne State - Geochemistry, Groundwater Discharge)
Bopi Biddanda (Grand Valley State University, Aquatic Ecology)
Scott Kendal (Grand Valley State University, Chemistry and Instrumentation)
Steve Nold (University of Wisconsin-Stout, Molecular Ecology)
Tom Johengen (University of Michigan, Nutrient Chemistry) Jeff Gray (Thunder Bay National Marine Sanctuary Support, Outreach and Diving)
Val Klump (University of Wisconsin-Milwaukee, Geochemistry)
Rob Paddock (University of Wisconsin-Milwaukee, Underwater Vehicles)
Ivar Babb (NOAA’s Undersea Research Program/ University of Connecticut).

+ View underwater video of Middle Island Sinkhole[.wmv file] (13,591kb) Total time: 5 min 28 secs

The NOAA Great Lakes Environmental Research Laboratory is one of 7 Federal research laboratories within the Oceanic and Atmospheric Research line office of NOAA. GLERL was formed in 1974 to provide a focus for NOAA's environmental and ecosystem research in the Great Lakes and coastal marine environments. GLERL scientists play a critical role in academic, state, federal, and international partnerships, and GLERL research provides information and services to support decisions that affect the environment, recreation, public health and safety, and the economy of the Great Lakes and coastal marine environments.

The Cooperative Institute for Limnology and Ecosystem Research is a center of excellence that serves as a focal point for collaborations between the National Oceanic & Atmospheric Agency and University researchers in the Great Lakes region. The research mission of the institute is to improve the understanding of the fundamental physical, chemical, biological, ecological, social, and economical processes operating in the Great Lakes region. CILER also promotes educational training opportunities in the region, through opportunities such as postdoctoral fellows positions and student summer fellowship program.

7/22/08

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