All samples are collected using a hydraulic winch and Ponar dredge. The Ponar dredge samples a bottom area of about 0.053 m2 to a depth that varies with the type of sediment and the ability of the dredge to penetrate it. Under the current program four replicate sample grabs are collected at each sampling site. The contents of the dredge are brought to the surface and placed in a large plastic bucket. Water is then added to the sample to create a slurry. The contents of each grab sample bucket are washed over Standard No. 30 stainless steel mesh screen (0.595 mm openings). Each sample is carefully washed with a fine spray to remove as much of the substrate as possible. All material remaining on the screen after washing is preserved in a solution of approximately 20%26#37; buffered formalin containing Rose Bengal dye for laboratory analysis.
The benthic macroinvertebrate sampling methodology used in this program is described in Standard Methods for the Examination of Water And Wastewater, 20th ed. 1998 American Public Health Association, Washington D.C. (See pages 10-60 through 10-74.)