Equipment:

Plankton Concentrator - A 4 in. x 15 in. PVC pipe with 53 um mesh nylon screen glued to the base.

Pump - An automatic or manual diaphragm pump capable of delivering at least 10 L/min.

Intake hosing - Use reinforced 3/4-in I.D. x 30-ft tubing.  A small weight will also be necessary to hold the intake end down in strong current.

Outlet hosing - Use clear tubing at least 3/4 I.D. by 10 ft long.

5-gallon Pail - Place a 10-L mark in the pail.  This pail will be necessary to measure the amount of surface water passed through (filtered) the concentrator.

Buffered Formalin - 10% Buffered Sugar Formalin.

Sampling Jars - Small wide mouth jars (pint/500 ml) that can be properly sealed.  Glass is not recommended for obvious reasons.  If there is any chance that the containers will leak, seal them inside plastic bags.

Wash bottle - A bottle with a spout containing tap water that is used to back flush the plankton concentrator (i.e. sample) into the sampling jar/bottle.

Labels & Permanent Marker - Needed to mark veliger samples with site identification, volume filtered, and date of collection.

Rinse Water - Gallon jugs of tap water for rinsing (back-flushing) the concentrators after sampling.

Field Methods:

Below Dams - Carefully enter the tailwater area a few hundred feet below the dam where turbulence is elevated but boating is manageable and safe.  The objective is to obtain a 30-liter cross-sectional, mid-depth composite sample from three locations (10-L each) across the channel (i.e. 25%, 50% and 75% of the channel width). Suspend the weighted intake hose approximately mid-depth or at least 3-m (about 10-ft) below the surface. Pump several liters of river water through the sampling lines to flush out the pumping equipment prior to taking the sample. This includes back-flushing the plankton concentrator with a few liters of site water. Place the plankton concentrator in the five-gallon pail and collect the desired 10-L sub-sample. There is no need to anchor and you will likely drift downstream with each sub-sample.  Between sampling points, keep plankton concentrator in the pail with the previous filtered water.  Then, just prior to taking the next 10-L sub-sample at the next sampling point, carefully remove the concentrator and dump out the filtered river water from the sampling pail and then resume pumping additional river water into the concentrator.   When pumping water into the concentrator run the river water along the cylinder's wall rather than directly onto the nylon screen.

Sample processing - After the third 10-L sub-sample is collected, move the boat to a quiet water area or shoreline to perform the transfer of plankton collected in the concentrator to the sampling bottle.  First, flush plankton, algae, and detritus to one "side" of the concentrator.  Then turn the concentrator upside down and hold it over the wide-mouth jar/bottle.  Flush all material out of the concentrator into the sampling jar/bottle.  This procedure usually requires two people. The concentrator may need to be slowly rotated to help flush material off the PVC walls.  Be sure to save enough room in the sampling jar/bottle to add the preservative.  Add enough preservative to dilute the sample by about 50% with the buffered sugar formalin. Label the jar/bottle with the amount filtered (i.e. 30-L), collection date and sampling location. Store samples in a cooler for transport back to the field station.

Cleaning Concentrator - It is very important to adequately clean the concentrator after each use to help prevent cross-contamination of samples. Use a spray bottle and forcefully back-flush the concentrator with 100-200 ml of tap water to help dislodge particles in the screen.  Then back-flush an additional 1-2 liters of tap water through the screen by pouring water over the screen's surface.  Store concentrator in a clean plastic bag between sampling sites or during storage.

Veliger-containing Tributaries (i.e. St. Croix River) or other non-tailwater Mississippi River Samples - It is desirable to collect a cross-sectional composite sample at three points across the river as described above.  Since turbulence is likely lower (as compared to below a dam) collect sub-samples at 0.2, 0.5 and 0.8 times the river depth (you will need to anchor the boat to collect these samples).  Note, this will result in 9 separate sub-samples (3 depths at 3 locations across the channel).  The sub-sample volume may vary depending upon the expected veliger concentrations.  For the Mississippi River, sub-samples of 3-4 liters (27-36 liters total) are adequate.  For tributary samples, sub-samples of 10-L (90 liters total) are recommended.  However, this may pose a problem if the stream is extremely turbid since the concentrator may become plugged with suspended particulate material including algae.  In these cases you will need to resort to a lower sub-sample volume.  Also note, you will need to mark your pail at the desired sub-sample volume amount if different than 10-L.

Tributaries mouths not known or expected to contain zebra mussel larvae  - A dedicated plankton concentrator (not used in infested waters) should be used to collect these samples. Be sure to mark this concentrator to distinguish it from others. It very important that sampling equipment (pumps and pails) be adequately cleaned with site water prior to its use as described above to help prevent cross-contamination of samples. Collect 3 mid-depth sub-samples across the channel or in the main flow where transect sampling is not possible.  Where possible (i.e. low suspended particulate matter), collect 20 to 30-L sub-samples to yield a total filtered sample of 60 to 90 liters.

Post-Sampling Cleaning - Upon return to the field station, flush several liters of tap water through pumps, tubing, and pails.  Back-flush the plankton concentrator with several liters of tap water if not done if the field.  Store the pails and concentrator in clean plastic garbage bags.  Drain tubing and store dry in a clean location.  Precipitates, fungus growths and other materials inside tubing may require additional cleaning since these surfaces may retain larvae. Use a weak bleach solution and soapy water and run a small sponge through the tubing by attaching the sponge to a strong cord.

Note: Additional cleaning precautions will be necessary if sampling equipment (including the boat, motor and trailer) are used in in-land waters to prevent the introduction of larvae into these systems.  It is recommended that all equipment be thoroughly cleaned and dried out prior to its use un-infested waters, especially in-land lakes or reservoirs.

Recommended Preservative -

Buffered sugar formalin developed by Jim Stoeckel (ILNHS) is recommended. To make up 1 liter of preservative add 100 ml of Formaldehyde (37%) to 900 ml of tap water.  Add 40 g of table sugar and approximately 1-2 g of baking soda (note: the amount of baking soda used may vary according to the hardness of your tap water.  Add baking soda until pH is between 7.5 and 8.  Check the pH again 24 hrs after mixing to make sure it has stabilized.  The preservative should be used at half strength (50% preservative to 50% sample).