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Sediment Sampling: What Is a PONAR Grab Sampler?


The PONAR grab sampler is the main bottom sampling device used on vessels to study the composition of the bottom sediments of a lake or river.  The grab sampler provides a means to obtain a somewhat quantitative and undisturbed sample of the bottom material. It takes a bite of known surface area and penetration depth, provided that the bottom material is neither too hard or nor too soft. It is called a grab sampler because of the manner in which it obtains samples.

Early studies on Lake Michigan used oceanographic and freshwater grab samplers that were not satisfactory. Research scientists from the Great Lakes Research Division of the University of Michigan devised a new sampler, the PONAR grab sampler, that was first available for sale in 1966. The sampler is named after Great Lakes scientists, Charles E. Powers, Robert A. Ogle, Jr., Vincent E. Noble, John C. Ayers, and Andrew Robertson.

The PONAR grab sampler consists of two opposing semi-circular jaws that are normally held open by a trigger mechanism. The sampler is lowered to the bottom where contact with the bottom sets off the trigger and a strong spring snaps the jaws shut trapping a sample of the bottom inside. Fine copper screen covers the top of the jaws so that the trapped material will not wash out as the sampler is retrieved.

For the full article, including a description of how the bottom material is studied, go to  

Source:  Excerpted from the Instructor’s Manual on Bottom Sampling and used with permission from Annis Water Resources Institute (AWRI).

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