Lake Superior After Dark

Ponar Dredge research on Lake Superior, on the RV Lake Guardian for Michigan Tech Great Lakes Research Course. On Station at Ashburton Bay - we arrive off Pic Island near Ashburton Bay at sunset; our goal is to collect bottom sediment samples, in triplicate, at nine stations along an onshore-offshore transect with depths ranging from 15 to 200 meters; we're in the lee of the Canadian north shore here and the waves have calmed considerably; the moon is up in the hills to the east; this is going to be a long night.

You will see the operation of the ponar dredge, washing and filtering of the sample: The PONAR dredge - our target here is Diporeia, a shrimp-like organism a few millimeters in length that plays a critical role in the diet of lake white fish (directly) and lake trout (through small fish called sculpins). Diporeia live at and just below the sediment surface and transfer material and energy from sedimented algae and dead organic matter to positions higher in the food web. This is called the benthic (=bottom) pathway. Diporeia are disappearing from all of the Great Lakes except Lake Superior, perhaps due to competition for food with zebra mussels. Here we collect bottom sediments and organisms with a PONAR dredge, wash the samples to separate the mud and the animals and then place the organisms on ice for counting later in the shipboard laboratory. Subsamples of the collection are separated from organic detritus and preserved for later measurement of lipids (i.e. energy content; value to the food chain) and pollutant concentration (e.g. pesticide content; contribution to biomagnification).

You can learn more and see photos at:
http://www.cee.mtu.edu/great_lakes/images2/spotlight_ponar.html

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Category:

Education

Tags:

• Ponar Dredge
• lake superior
• RV Lake Guardian
• Michigan Tech
• Great Lakes Research