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USGS scientists returned in August, 2021, to map an area of Lake Superior that has been - and continues to be - greatly impacted by a legacy of copper mining in the region.  Millions of tons of waste material from the mines, locally known as “stamp sands”, were dumped into coastal waters along the Keweenaw Peninsula of Michigan during the early 20th century. 

This article is part of the January-March 2022 issue of the Sound Waves newsletter.

 

The super abundance of crushed basaltic rock caused the shoreline to accrete 100s of meters lakeward until mining largely ceased in the 1930s.  Subsequent erosion has redistributed the dark-colored, metal-rich stamp sands along the shore, creating a wide beach ridge down drift of the original dump site, filling a navigation channel, and burying biologically productive areas of lake floor.  With funding from the Great Lakes Restoration Initiative (GLRI), the USGS has worked with partners at the US Army Corps of Engineers and Michigan Tech University since an initial survey in 2018 (https://www.usgs.gov/center-news/mapping-stamp-sands-lake-superior) to determine the extent and volume of stamp sands near Buffalo Reef located in Grand  Traverse Bay.

Bathymetric map of Grand Traverse Bay, Lake Superior.
 Bathymetric map of Grand Traverse Bay, Lake Superior.  The 2018 data are shown in gray hillshade, with the combined 2021 preliminary data superimposed in color.  Index map at lower right shows the extent of each survey. 

The 2021 survey was a joint effort between the Woods Hole Coastal and Marine Science Center (WHCMSC) and the Great Lakes Science Center (GLSC).  Scientists, equipment and research vessels were mobilized from each Center during the 11-day survey between Aug 5-16.  GLSC scientists Anthony Arnold, Sam Pecoraro and Chris Wright collected multibeam bathymetry and backscatter data in areas close to the beach using a Norbit iWBMSh (400 kHz) onboard the RV Desmid.  WHCMSC scientists Walter Barnhardt, Brian Andrews, Alex Nichols, Eric Moore, Seth Ackerman and Patrick Berube also collected multibeam data in broader offshore areas using a dual-head Reson T20-P (400 kHz) onboard the RV Rafael.  The two research teams worked simultaneously in adjacent areas of the lake, surveying along closely spaced tracklines to achieve maximum data quality in water depths as shallow as 1.5 m.  For the final 3 days of the survey, the RV Rafael switched to collecting photographs, video and sediment samples of the lake floor using the SEABOSS.  The combined geophysical, photographic and sampling data from both teams will support efforts to determine changes in substrate since a baseline survey in 2005 and the previous USGS survey in 2018, and to develop new methods of assessing the concentration of stamp sands in bottom sediments.   

 Detailed bathymetric maps of Buffalo Reef
Detailed preliminary bathymetric maps of Buffalo Reef.  Improvements in grid resolution between the 2018 (left) and 2021 (right) surveys were facilitated by decreasing line spacing from 50 meters to 35 meters or less between adjacent lines.  
man standing on a boat deck surrounded by equipment
Patrick Berube prepares the SEABOSS for deployment in Lake Superior. 
two men standing on two boats
The RV Desmid (foreground) alongside the RV Rafael during sampling operations on Lake Superior.

 

Physical conditions of the lakefloor are tightly coupled with production of fisheries for lake trout and lake whitefish that are important to the regional fishing economy and tribes. The objectives of this project are to fully characterize the spatial distribution of benthic substrates, including legacy mine wastes, to help federal/state/local/tribal partners decide on the best mitigation measures.  By defining the geologic framework of the coastal system, the USGS will produce actionable information for improving the resilience of coastal environments and infrastructure to future storms and lake-level changes.  The data collected on this survey will also serve to advance emerging methodologies that integrate autonomous underwater vehicles (AUVs), machine learning techniques and computer modeling to efficiently map and quantify bottom types, fish habitats and benthic organisms.   

magnified mixed sediment shown under a microscope
Sample of mixed sediment shown under a microscope at 7.5x magnification.  Dark-colored, coarse-grained stamp sands are readily distinguishable from light-colored, finer-grained native sand.  Scale bar at bottom right for reference.

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