Using a drive-rod operated piston corer, UC Davis scientists analyzing sections of Clear Lake sediment are learning valuable details about the past 200 to 300 years of the heavily polluted Northern California lake's history. Mercury contamination, in both its organic and its inorganic forms, is of primary concern. Interestingly, the scientists have found that although extraction of 72 percent of the mercury adjacent to the lake occurred during the late 1800s, the vast majority of the mercury found in the lakebed sediment was deposited from 1927 to 1944. It turns out, says Jesse Becker, a researcher at the UC Davis Clear Lake Environmental Research Center, the earlier mercury mining practices were far more labor-intensive but moved much less earth than later mining that employed open-pit mining techniques using heavy machinery. The later mining, which yielded 1,100 metric tons of mercury, caused 10 times the loading of mercury into Clear Lake than the earlier mining, which yielded 3,000 metric tons of mercury. The power of heavy machinery to "expose soils to erosion and consequently to alter the lake environment appears to be considerably greater than overgrazing, clearance of lands for agriculture, limited mining and urbanization," Becker says in a paper coauthored by UC Davis researchers including Peter Richerson and Thomas Suchanek. The findings were presented recently at the Society for Environmental Toxicology and Chemistry meeting.