A technician samples water from a port in a tube containing mixed layer water (mixolimnion), and deep brine layer water (monimolimnion; bottom) from the Great Salt Lake. The objectives of the microcosm experiment were to: (1) determine if brine shrimp utilize the high organic matter content available at the interface between the two layers, and; (2)determine whether the extremely high methyl mercury levels in the deep brine layer are transferred to to shrimp that live primarily in the mixed layer, but may feed at the interface. The anoxic, reducing conditions in the deep brine layer promote the growth of sulfur reducing bacteria, and these in turn, methylate mercury in the deep waters of the lake.


In the 10-day experiment, two tubes were filled with only mixed layer water, and two received both mixed layer and deep brine layer water. Brine shrimp nauplii were added and allowed to grow into adults. Analyzes of mercury, and the isotopic content (15N and 13C) in the shrimp and seston were done at the end of the experiment.


Photo: October 2009