Advanced Benthic Collection

Choose the Best Habitats

Your goal is to collect macroinvertebrates from three different riffle areas. (If the riffles are as wide as the stream then multiple samples could be collected within the same riffle.) The riffles should have different characteristics (i.e. different composition but mostly cobble and gravel and different velocities). Often different types of riffles hold different varieties of macroinvertebrates, so to properly assess the biological conditions you need to collect a representative sample. Of course your choices of habitats will ultimately depend upon what your reach provides. Once you’ve chosen your location always approach from the downstream end, sampling the site farthest downstream first. This approach insures that the sample is representative of its location and reduces the chances of biasing your second and third sample.

Get Into Position

Select an area approximately the same width (or slightly less) than the width of your kick-net. Most two-pole screen-barrier kick-nets have about 1-meter or 3-foot width. The width of the single-pole rectangular kick-net is about ¼ to ½ meter. So if you are using a smaller diameter-net you will need to collect more samples (2-3 samples using the rectangular kick-net is equivalent to 1 sample with the screen-barrier kick-net). The net holder will place the net snugly against the bottom of the streambed; rocks can be removed if necessary to make sure you have a close-fit. Once you are satisfied with the position, line the front of the net with rocks heavy enough to hold the net in-place. However, be careful to choose rocks that are not too heavy or too wide or high. Large rocks will damage the net and will influence how the macroinvertebrates flow into the net thus making capture less successful. The net holder now tips the kick-net backward at about a 45-degree angle from the water’s surface. This provides greater surface area and more even flow into the net. If the net is held to high some of the macroinvertebrates will wash around the sides and not be captured in the net. While holding the kick-net backwards the net-holder must make sure that water does not wash over the top of the net. Have one 3 ½ to 5-gallon bucket ready before you begin collecting the sample. The bucket will be needed during sample collection.

Begin Disturbing the Streambed

The second person approaches the sample area from upstream and determines the approximate sample-size. Once the area is delineated, the sampler begins disturbing the streambed directly in front of the net. The process starts with rock rubbing. First, pick-up all large rocks (cobble size and larger) and inspects them. You are looking for snails, clams and caddisfly cases. These animals often cling very tightly to the rocks and are not removed by just a simple rub with the hands or a small brush. If the rocks have any of these animals, remove them from the rocks and place them inside the bucket. Move the rocks you picked-up towards front and slightly into the net; brush all sides of the rocks with your hands or a small vegetable-brush to dislodge other clinging macroinvertebrates. Continue the rock rubbing process until the larger sized stones have been thoroughly cleaned. If the rocks cannot be lifted from the streambed, simply rub them where they lay. As much as possible the rock rubbing should proceed from the upstream portion of the sample area towards the front of the net. After the rocks are rubbed they should be placed aside (outside of the sample area) so they are not rubbed a second time. Some volunteer programs choose a timed approach to rock rubbing since this is a rather intensive and somewhat time consuming step. The recommended time frame for adequate rock rubbing is four minutes (or less) depending upon the abundance of cobbles and boulders within your sample area. If you choose a timed approach you should make a note on the survey data sheet and record the time frame you use. After you are satisfied that all or most of the larger rocks have been cleaned you will disturb the remainder of the streambed using a kicking method. Position yourself upstream from the net inside your sample area and begin shuffling your feet back and forth from one side of the sample area to the other. Slowly move towards the net while kicking from side to side. The action dislodges macroinvertebrates from smaller size gravels and also disturbs those that might be burrow themselves down into the soft bottom sediments. While you’re moving from side to side and forward you are also pressing your feet downward in an attempt to make a depression in front of the kick-net. If you have chosen a timed approach then you should limit your kick-time as well. The recommended kick-time is two minutes, so your entire sample should take about six minutes to collect.

Remove the Kick-Net from the Streambed and Capture the Collection

This is a very important step; since the sample collection is laborious you do not want to lose any of the macroinvertebrates collected by sloppy procedures here. Very slowly remove the rocks that have acted as anchors to hold the kick-net in place, rub them off while you remove the rocks, or you may choose to rub them before using them to anchor the kick-net in place. While the net-holder grabs and holds the top of the net in-place the kicker grabs the bottom edge of the net near the handles. The net is removed with a scooping motion, the kicker moved slightly forward and upward while the holder keeps the net steady so that no macroinvertebrates are lost from washing over the top of the kick-net. Both persons then pick-up the net and roll it into a loose cylinder, securing the ends and taking it to the shoreline. The collection bucket should be at the ready to accept the contents of the kick-net.

Place the Net into the Bucket

Slightly unwind the net so that it fits inside the bucket. With a smaller bucket or a spray bottle, wash the contents of the kick-net into the bucket. It will take several minutes and several washes to knock loose most of the macroinvertebrates. Between each attempt, remove the net and check for macroinvertebrates that have not been dislodged. Often these hardy clingers are found near the edges of the kick-net along the bottom-side and in the seams of the net. Be sure to check the opposite side for macroinvertebrates that may have crawled in an attempt to escape. You must be very careful not to overfill the bucket. If the bucket begins to fill with stream water more than about two-thirds its heights, remove some of the water by seining it through the kick-net (hold the net tightly on the bucket and pour off the water) so that the water is poured off and the macroinvertebrates remain in the bucket. The process is complete when you are satisfied that the kick-net has been thoroughly washed and most of the macroinvertebrates are now in the bucket.

Remove the Captured Macroinvertebrates from the Bucket and Begin Sorting

The goal of this step is to remove all captured macroinvertebrates so that they can be observed, identified and counted. WV Save Our Streams recommends that you use several shallow white trays, some of which can be divided to collect the macroinvertebrates as they are removed. The best way to start is by trapping the macroinvertebrates as they are poured from the bucket. Before starting the steps below, remove all larger materials that may have been collected with your sample from the bucket. Make sure to check these for macroinvertebrates before they are discarded. At certain times of the year leaves and other debris are very plentiful in the stream and this material must be sorted. (It is common to find many kinds of macroinvertebrates in leaf-packs; this material is one of their favorite places to live.) The best way to deal with the leaves is to remove as many as possible, place them in smaller bucket or container and wash them to remove the macroinvertebrates. Pay close attention to the leaves that appear chewed and have begun to decay. Newly fallen leaves are less likely to have many macroinvertebrates.

There are several ways to complete the last step. You can use a second bucket with your kick-net on top, and then pour the captured organisms over the net so that they are trapped against the net. The pouring is stopped periodically so that the macroinvertebrates can be removed from the net and placed into the collection trays. Small forceps are the best tool for this job; however the macroinvertebrates can also be removed by hand. The easiest method is to use a wash bucket or EZ-strainer. The EZ-strainer is available in a variety of mesh sizes and fits nicely inside a 3 ½ or 5-gallon bucket. Your collections are poured directly into the EZ-strainer, or into a second bucket and then into the strainer if additional washing is necessary. For advanced volunteer monitoring groups, WV Save Our Streams recommends that volunteer groups sort, count and identify the samples after they are preserved. Complete family-level identification can be difficult, but not impossible for experienced volunteer monitors. The preservative should be at least 70% denatured ethyl alcohol, which is the percentage after the collection (debris and macroinvertebrates) has been added. Rubbing alcohol works very well as a temporary preservative.