Mayflys, Crayfish and Snails Oh My
By Olivia Espinoza, Land Steward
I grew up with a lake in my backyard. As a kid, I would spend most of my days down by the water hanging over my dock watching the fish and crawdads zoom by in front of me. Back then, I didn’t think too much about these critters and what else might be living in the mud and rocks. These days, I think a little bit more about what is going on down there though. As an adult, I still find myself being drawn to water. I still love to jump off that dock every summer and splash around in a stream with my kids and I see the same fascination in them that I know I had myself.
Two years ago I had the opportunity to be a volunteer stream monitor for Great Parks of Hamilton County. This was a great way to bring my past fascination of crayfish and bugs to a whole new light. I had the opportunity to play in a stream and collect valuable information at the same time. I enjoyed it so much that when I was hired to work for Cincinnati Nature Center one of my first questions was if I could start a stream monitoring program here as well. If you’re not familiar with stream monitoring, it is a way to collect data on the quality of a stream by using macroinvertebrates and other aquatic life. These macroinvertebrates are considered “bioindicators.” This means they are species that can be used to monitor the health of an environment.
A macroinvertebrate is an invertebrate (without a backbone) that is large enough to be seen with the naked eye, such as a crustacean, mollusk or aquatic insect. Many of the macroinvertebrates we look at spend part of their life cycle as aquatic organisms. We collect them from the stream while most of them are in their larval and nymph stages.
There are several reasons we can use these little guys to help us determine the health of our streams. For one, they can spend up to a year in a stream and are often abundant. Macroinvertebrates are effective barometers of a streams health because they have varying tolerances of pollution and are sensitive to changes in water quality. Chemical water tests are limited because they only tell us what’s in the water at the specific moment the sample is collected. They don’t give an indication of what was in the water an hour ago or last week. Macroinvertebrates are constantly surrounded by water and any pollutants that may be in the water. If pollutants were in the water last week or yesterday, the quantity and diversity of macros present would reflect this. They have less mobility when compared to fish or other organisms that can readily move away from pollution. These small aquatic organisms are collected from our streams and observed to determine which types are present and how frequently they occur. The organisms are always returned to the water and we then use the data to determine the health of that portion of the stream.
Here at Cincinnati Nature Center we monitor our streams once a month from April to September. We use a small 3x3 foot seine that is placed in a riffle section of the creek with the water flowing into it. We choose the riffle section of the stream because it’s an area of fast, shallow flow. It also has increased oxygen content and larger substrate. So we then pick up the large rocks in front of the seine and rub the little critters off in the water so they flow into the net. Then kick up the gravel, sand and silt to free any other macros that might be living in the sediment. It’s pretty easy, which is one reason it is so ideal to use them as indicators. It also doesn’t require any chemical analysis, which makes it a simple and cost-effective method of testing a stream’s health.
There are three categories of stream macroinvertebrates; pollution intolerant, moderately pollution intolerant and pollution tolerant. Group 1 is the pollution intolerant species. This group consists of caddisfly larvae, dobsonfly larvae, mayfly nymphs, gilled snails, adult riffle beetle, stonefly nymphs and the water penny larvae. This group requires higher dissolved oxygen levels, neutral pH, and cold water. Group 2 is the moderately intolerant species. This group consists of beetle larvae, clams, crane fly larvae, crayfish, damselfly larvae, dragonfly larvae, scuds, sow bugs, fishfly larvae, alderfly larvae and atherix. Group 3 is the pollution tolerant species. This group consists of aquatic worms, blackfly larvae, leeches, midge larvae and pouch snails. This group can tolerate low oxygen levels, lower/higher pH and warmer water.
After the insects are collected, identified and recorded we can take the data and determine the rating for that particular stream. The ratings are simply; excellent, good, fair or poor. To determine the stream rating, we look at the diversity of species, as well as the number of species within each group. The greater the diversity the healthier the stream!
The Nature Center is currently monitoring Avey’s Run, Long Branch Creek and O’Bannon Creek. All three streams are rated “good.” If one of our streams suddenly rated “poor” when we know that it generally rates “good” this would give us an idea that maybe something happened that we are unaware of; for instance recent active construction, or an oil or gas spill. Streams are sensitive systems and they serve as important wildlife and fish passage corridors. Many organisms depend on healthy streams and we can all do something even from our own homes to help improve the water quality of our streams, lakes and rivers. We are all a part of a watershed, which is an area of land that includes a particular river, lake or stream that storm water flows into. So even if your house is not right beside a stream things like fertilizing your lawn, over-salting your driveway, pesticides, herbicides, etc.., can impact stream quality. So next time you go for a walk take a bag with you to pick up litter, or plant a tree in your yard, reduce the amount of chemicals you use in your yard and the amount of electricity you use in your homes. You can also help our streams here at the Nature Center by staying on trails and not walking in the streams. You never know, you may just save a caddisfly!
Ohio Department of Natural Resources: http://watercraft.ohiodnr.gov/sqmMichigan’s Clean Water Corp: http://www.wupcenter.mtu.edu/education/stream/Macroinvertebrate.pdfhttps://environment.arlingtonva.us/streams/macroinvertebrates/