Donald W. Schloesser
USGS, Great Lakes Science Center, Ann Arbor, MI
"Restoration of burrowing mayflies (Hexagenia spp.) in the Laurentian Great Lakes"
One goal of the Great Lakes Water Quality Agreement between the United States and Canada is to restore ecosystem health to international waters of the Laurentian Great Lakes. This legislation was established in response to decades of pollution that negatively impacted ecosystem components. One such component was the mayfly, Hexagenia spp. that disappeared from many near shore waters of the Great Lakes in the 1950s in response to low oxygen caused by nutrient enrichment, subsequent growth of fertilized plants, and decomposition of plant tissues as they settled to bottom substrates where mayflies live. In response to decades of nutrient enrichment, waste water treatment was initiated in the 1970s and scientists have been looking for signs of mayfly restoration ever since. In 1992, adult mayflies were observed in open waters of western Lake Erie. In 1993, the USGS's Great Lakes Science Center repeated a benthic survey performed in the 1930s, 1960s, and 1980s and verified the presence of mayflies in Lake Erie. Sporadic surveys between 1995 and 1999 revealed mayfly populations at abundance similar to those found in the 1930s (ca.400/m2). In 2000, USGS initiated systematic surveys specifically designed to assess mayfly restoration in Lake Erie. Mayfly surveys revealed a cycle of mayfly abundance that resemble a 'boom-and-bust' pattern of an organism that reproduces until it is limited by some environmental factor which causes a sudden 'crash' in abundance to occur. To date, data reveal three to four-year cycles of high abundance followed by a sudden decrease in abundance. This has led to a working hypothesis that mayfly populations in western Lake Erie are partially 'self-regulating.' Continued surveys, further laboratory testing of the density-dependent hypothesis, and verification of oxygen models will reveal when mayflies will be totally restored to Lake Erie. If the density-dependent hypothesis is proven correct, inclusion of respiration by benthic fauna into widely used eutrophication models to monitor pollution abatement could improve understanding of lake restoration efforts in Lake Erie, the Great Lakes, and other water bodies throughout the world.
Thursday, December 8, 2011
Classroom Building B118
Students, Staff, and Faculty are welcome. Light refreshments will be served.
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