By SOLVE Jesuit Volunteer Corps Northwest Member, Charlie
‘Tis the season for macroinvertebrate surveying in the SOLVE Green Team scene and the students at Valley Catholic High School were the most recent to jump on this buggy bandwagon when they sampled Johnson Creek on Wednesday.
For those of you who aren’t avid Green Team Blog followers and this is your first post you’ve read on macroinvertebrate sampling, here is a brief crash course: Macroinvertibrates (or as we call them, “macros”) are basically bugs (truly, anything without a backbone, which is what “invertebrate” means) that you can see with your naked eye (more or less what “macro” means). Surveying the macros in our streams can give us a pretty holistic indication of how healthy our stream is. Temperature and chemical tests might also give us a good idea of health, but these things often fluctuate over the course of the day and the macros living in the stream itself have to deal with these fluctuations. Therefore taking a look at who is living in the stream along with the knowledge of who is pollution tolerant and pollution sensitive can paint a clearer picture of stream health, and can give an idea of how well our restoration efforts are affecting the aquatic community.
The Method: Students sampled by swishing their nets in and around the vegetation growing on the sides of the bank, dislodging anything that might be crawling on the grass and reeds. Since Johnson Creek is very marshy and slow-moving, like many of the other streams in the Tualitin River Valley, we were unable to take samples from the bottom of the stream, this also had to do with the depth and muddiness of the creekbed. Students did, however, have no reservations about getting in the creek (sometimes past their waders…) to get great samples.
Okay, with that out of the way, let’s get to the exciting part: what did we find??? Insect-wise, students found a lot of damselfly larvae wiggling at the bottom of their samples. Also a lot of aquatic diving beetles were found swimming around the sample tray, and midge larvae twitching around the water. All of these are generally in fairly slow-moving stream environments (like Johnson Creek). Students also found several case-making caddisfly larvae with cases constructed out of sticks and blades of grass. These were exciting to find as these insects are pretty pollution sensitive. However students also found a lot of aquatic worms, snails, and a few leeches which are very pollution tolerant groups of invertebrates. Some other cool finds included a dragonfly larva, a couple of crayfish, and some students found a large gelatinous egg-mass belonging to Northwestern Salamanders! Thank you, amphibian expert, Kris Taylor, for identifying the egg mass!
It’s difficult to make any conclusive statements about the health of the stream from this one survey since this is the first survey at the stream and we don’t know what the invertebrate populations of the stream was historically. However the pollution sensitive caddisfly were exciting to see and might indicate that the stream is not completely degraded, but at the same time we did find a lot of pollution tolerant macros. We will save this data and in future years will use it to compare to future surveys of the stream to see how well Valley Catholic’s restoration efforts of Johnson Creek are improving the quality of the watershed and the health of the stream.
Thank you, Clean Water Services, for funding this project!