Groundwater Plume Mapping in a Submerged Sinkhole in Lake Huron

A multidisciplinary exploratory project team from the Institute for Exploration, the Great Lakes Environmental Research Laboratory, Grand Valley State University, and the University of Michigan located and explored a submerged sinkhole in Lake Huron during September 2003. A CTD system and an ultra-short baseline (USBL) acoustic navigational tracking system integrated with an open frame remotely operated vehicle (ROV) provided high-resolution depth, temperature, and conductivity maps of the sinkhole and plume. Samples were also peristaltically pumped to the surface from a depth of 92 meters within and outside of the sinkhole plume. A 1-2 m thick cloudy layer with a strong hydrogen sulfide odor characterized the water mass close to the plume. Relative to ambient lake water, water samples collected within this layer were characterized by slightly higher (4-7.5 °C) temperatures, very high levels of chloride and conductivity (10-fold) as well as extremely high concentrations of organic matter (up to 400 mg C/L), sulfate, and phosphorus. Our observations demonstrated the occurrence of unique biogeochemical conditions at this submerged sinkhole environment.