The Great Subterranean Spring of Minneapolis, Minnesota, USA, and the Potential Impact of Subsurface Urban Heat Islands

Anthropogenic subsurface urban heat islands (SUHIs) in groundwater under cities are known worldwide. SUHIs potentially threats to springs because much spring biota, like trout, amphipods, and rare plants, is cold stenothermal. The city of Minneapolis, Minnesota, USA, has a SUHI documented by the temperature an underground spring, dubbed Little Minnehaha Falls, inside Schieks Cave, which located 23 m below central core city. In 2000, that was elevated 11°C above regional background temperatures (8°C) at this latitude (45°N). A thermometric survey cave nearby tunnel seepages 2007 found abandoned drill hole through bedrock ceiling discharging with 17.9°C. By comparison, deep water table closer natural for region. unusually warm thereby localized strata cave. This strongest signal anthropogenic warming state Minnesota attributed vertical conduction from basements pavements. Minneapolis unique among forms collection gallery surface, whereas literature almost exclusively based on data observation wells.