Insect Investigations: Aquatic Insects as Indicators of Water Quality

aquatic insects

My mini aquatic insect tank for carrying to classrooms

I promised to post some lesson plans during the semester, but I never had a chance to actually do it.  Today I’m making good on that promise.  As it’s also related to my recent water quality series, I’ll use this post to finish up the series at the same time!

A few weeks ago, I had the opportunity to teach at a top middle school in Tucson, a school that consistently ranks in the top 10 or 20 schools in the nation.  The kids at this school are very smart.  I taught 3 lessons, but the kids were in groups of 5th through 7th graders, all mixed together.  Odd!  These kids were also older than any other kids I’ve worked with over the past semester, so my usual “What is an Insect” presentation just wasn’t going to cut it.  Instead, I planned a presentation on aquatic insects.

One part of my presentation involved the kids doing an activity I developed that focused on using aquatic insects as indicators of water quality.  For the blog here, I’m going to describe how I ran the lesson in the classroom during the hour I had allotted.  However, if anyone wants to use this activity, you can find a more official, printable lesson plan on my Educational Materials page (it will be posted later today – having problems getting it uploaded).  Feel free to use and share it at will!

roaches

The roaches I share with the kids travel in this

I start all of my insect lessons by figuring out how much the kids already know about the characteristics of insects – number of legs, body segments, antennae, and wings and where their skeleton is located.  With the more advanced kids at this school, I also asked about spiders, crustaceans, and other arthropods as well.  Once we covered the basics, I got a hissing cockroach out and let them hold and interact with it.  The group of kids were mature enough to be able to pass the roach around without totally freaking out and dropping one of my little guys on the floor – one benefit of working with older, gifted kids!  We discussed what the roaches eat (they’re decomposers of plants) and how they eat (chewing mouthparts).  Then I got a giant water bug out.  I don’t let kids hold them so they won’t get bitten, but I showed them all the piercing-sucking mouthpart up close.  We compared the mouthparts of the water bug to those of the roach and I had them guess some of the amazing things that giant water bugs are capable of eating.

At that point, they’d seen an aquatic insect up close and several water bugs and water scorpions in the clear container at the front of the room, so they were aware that there are insects that live in water.  I spent a couple of minutes talking about aquatic insects and where they live before introducing the idea of using insects as indicators of water quality.  I briefly told them how aquatic entomologists use tolerance values of insects to determine the water quality of a stream or lake, explained the tolerance value scale, and let them ask questions.  Then we did the activity.

"samples"

The insect "samples" from their "streams"

I had the kids get into four groups and set the tone by telling them that each group was a survey team sampling a different stream in southern Arizona.  They’d collected, sorted, and identified the insects in their samples, but they still needed to calculate the biotic index value to determine how polluted the water was in their stream.  I gave each sampling team an envelope containing 10 cards, the “insects” in their samples.  Each card had a picture, the genus, a common name, and the Arizona tolerance value (see below).  Their job was to calculate the biotic index value by taking the average of the tolerance values for all the insects in their sample.  I also asked them to count the number of species found in their sample and discuss what the number they calculated said about the water quality in their stream.  Then I let them loose!

I let the kids do the math and discuss the results with their groups for about 8 minutes and then got everyone back together.  I had one person from each group share the biotic index value for their stream and what they thought that meant.  After every group shared their results, I told them which specific streams their “insects” were from (I based my cards on actual samples, so they were accurate!) and a few facts about that stream that might impact the water quality.  We discussed their results in light of this new information.  For example, everyone decided that it was natural that the most polluted stream would be the one that only had water in it because a waste water treatment plant dumped its effluent into the streambed.  It was also natural that the stream that had the fewest human visitors was the least polluted.  They also discovered that the number of species was generally higher in less polluted streams than in highly polluted streams and that some insects with very high pollution tolerance values still lived in the cleanest water.  Essentially, they came up with all the ideas I had intended to point out, entirely on their own!

insect cards

The "insects" in the "sample"

The kids were enthralled by the insects that have tolerance values of 11 out of 10, so I ended my presentation by pulling out a water scorpion.  They were an example of and 11, and I let everyone get a close look at it.  I told them a few facts about the insects and we finished the lesson by briefly discussing why that particular insect might be more tolerant to pollution than other insects.  They came up with some great ideas!

All in all, I was happy with the presentation!  I think there was a good mix of live insects and fake insects.  I did some talking, but the kids spent most of the time making observations and doing the activity.  Even though the students at this school might not be the best from which to judge the success of my new activity, the kids seemed to get really into it the activity and asked questions that made it clear that they’d understood the greater implications.  I couldn’t have been happier!  Although my presentation was rather informal, I have some ideas for how to expand the activity to make it a full-blown science lesson that fits into the national science standards for 5-8 graders.  If you’re interested in teaching the activity, check out the lesson plan I’ve posted for more information!

This concludes my series on using aquatic insects as indicators of water quality… for now!  I have a few more topics I’d like to cover, but I think I’ll move on to other subjects for a while and revisit this topic again in the future.

_______________

Unless otherwise stated, all text, images, and video are copyright © 2011 DragonflyWoman.wordpress.com

Advertisements

Using Aquatic Insect Tolerance Values: An Example

EDW

A highly impaired, effluent dominated stream downstream of a wastewater treatment plant. Photo by Dave Walker.

Last Monday I discussed how tolerance values are assigned to aquatic insects so that water resource managers and scientists can use insects as indicators of water quality.  While simply knowing the tolerance value of an invertebrate can tell you something about that animal and where it is likely to live, combining the tolerance values of a whole bunch of invertebrates can tell you some pretty profound things about the body of water in which you found them.  Today I’m going to walk you through a large study that I did with my former employer, one in which we examined the aquatic macroinvertebrates in five effluent dominated streams in Arizona, to show you how tolerance values can be used to determine the water quality in a body of water.

Arizona isn’t known for having tons of water all over the place.  We have a lot of people in some areas and a whole lot of agriculture, so the demands for water are high.  As urban and agricultural uses grow, the amount of total available water will decrease until there is very little left.  Water resource managers are thus looking to other sources of water to meet the needs of Arizonans and our aquatic wildlife and sport fish.  One possible source of water is effluent.  It’s possible that many of Arizona’s aquatic animals, especially fish, will depend on effluent dominated waters (EDWs) for survival in the future.

water sampling

Me recording data during a sampling trip to an EDW. Photo by Dave Walker.

Soon after I started grad school, the Arizona Department of Environmental  Quality (ADEQ) became interested in classifying and comparing the macroinvertebrate assemblages of five Arizona EDWs to determine a) the water quality at the outfall from the waste water treatment plant (WWTP) and further downstream and b) whether they represented viable habitat for Arizona’s aquatic organisms.  They gave a grant to my former employer, who hired several students to help, including me.  All of us spent many hours working in some really awful water collecting insects, measuring basic water chemistry, collecting water and algae samples, and measuring the physical characteristics of the stream.  We collected from two sites in each of five EDWs, once during the winter and again during the summer.   Back at the lab, I directed a team of people who sifted through the enormous samples, removed all the macroinvertebrates, and then handed them over to me to ID.  Once I had everything identified to genus and counted, I calculated the diversity and the Hilsenhoff biotic index (HBI) for each site during the winter and summer.

For now I’m going to ignore diversity and focus on the HBI results.  The HBI is an index of pollution tolerance that was originally developed by William Hilsenhoff in 1977 and updated in two subsequent publications.  It’s used by aquatic scientists and water resource managers all the time!  It’s simple conceptually: you determine the tolerance values of many aquatic macroinvertebrates (as described in my post on tolerance values), take a macroinvertebrate sample in a body of water of interest, identify and count all the animals in the sample, and calculate the average of the tolerance values for every individual in the sample.  The resulting number tells you the overall average tolerance value of the macroinvertebrates in the stream.  You can then compare the values you get to this chart to see how polluted the body of water is:

Tolerance values

Pollution levels according to the Hilsenhoff Biotic Index. Click to make bigger! From Hilsenhoff 1987.

For the project I was involved with, I calculated the HBI for each site for the five different EDWs.  I’m not going to name the exact streams so I don’t end up getting sued (one particular WWTP wasn’t so thrilled about what we said about their effluent…), but here’s what we learned.  First, the WWTPs with the better treatment processes had lower HBI’s than the ones with lower quality treatments.  For example, in the best WWTP, water is treated using extended aeration, activated sludge, secondary clarification, and ultraviolet disinfection.  The average HBI for all sites and dates combined for this site was 7.23.  At the worst WWTP, treatment consists of filtering out the solids, running the water through biofilters to remove nitrogen, chlorinating and de-chlorinating the water, and then dumping it into the stream.  From another couple of studies I worked on, I know that the water coming out of this WWTP is full of pharmaceutical products, flame and fire retardants, and other chemicals – and it smells terrible too.  The average HBI for this site was 9.75, which is just about as high as it gets!

EDW

Sampling at an EDW in southern AZ. Photo by Dave Walker.

There were also some overall trends in the HBI values we calculated for each site and date.  The HBI’s were usually higher near the outfall than further downstream, suggesting that the streambed is acting like a filter or the plants are absorbing pollutants from the streams and improving the water quality as it moves downstream.  For example, in the stream below one of the high quality WWTP’s, the HBI at the outfall was 7.5 but dropped to 6.9 further down.  Also, the HBIs were higher in the summer than the winter, 8.4 and 7.5 respectively in one stream.  The reasons behind these seasonal shifts are complex, but the dissolved oxygen levels in the water played a big role.  Generally, things with high tolerance values tend to be able to survive in much lower oxygen environments than things with low tolerance values, and oxygen levels decrease as water temperature increases.  Thus, invertebrates with tolerance values around 6  were probably just getting by in the winter and couldn’t survive at all in the summer, driving the HBI up during the hot part of the year.

The HBI’s of the five effluent dominated streams ranged from 6.5 at a downstream site in the winter at the best WWTP to 9.8 at a downstream site in the summer at the worst WWTP.  Notice that with the exception of the one instance of an 6.5 HBI that falls into the “fair” category, these streams suffer from extensive organic pollution.  One site earned the HBI of 9.8.  Indeed, we found only three species at that site on that date: bloodworms, drain flies, and sludge worms.  Sounds appetizing doesn’t it?

EDW

This EDW looks nice, but it had some pretty nasty water in it. Photo by Dave Walker.

In the end, the HBI values (along with the diversity index we used and our statistics) led us to one undeniable conclusion: none of the EDWs in Arizona are particularly good habitat for aquatic insects.  The oxygen levels are too low and the nutrient and chemical content too high for most macroinvertebrates.  Fish certainly aren’t going to be able to survive in this water over the long term!  In our report we stated that effluent, at least as it is currently treated, is not of sufficient quality to support habitat for most of Arizona’s aquatic organisms and that improved treatment is the only way to make effluent useful for this purpose.  A disappointing recommendation for the water resource managers I think, but it was obvious to anyone who pulled giant handfuls of bloodworms out of a rank, hot, sandy stream when it was 110 degrees outside that this water is far from clean.  In fact, several of the WWTPs recommend that you wash your skin with potable water and soap if you are exposed to effluent.

I’m continuing with the water quality and macroinvertebrate theme next week.  Hope you’ll check back!

_______________

For more detailed information about the Hilsenhoff Biotic Index, consider reading William Hilsenhoff’s 1987 paper (might be a little hard to get your hands on if you don’t have access to an academic library…):

Hilsenhoff, W.L.  1987.  An improved biotic index of organic stream pollution.  Great Lakes Entomol.  20:31-39.

_______________

Unless otherwise stated, all text, images, and video are copyright © 2011 DragonflyWoman.wordpress.com

Aquatic Insect Tolerance Values

fast flowing, cold water

Sampling insects in a clean, high elevation stream

About 6 months ago, I wrote a post about aquatic insects and water quality that highlighted the differences in the diversity of species in a polluted river compared to a clean mountain stream in Arizona.  Considering how much I enjoy this subject, it’s been far too long since I wrote about it!  It’s time to do something about this sorry state of affairs.  My next few Monday posts are thus going to be about how insects are used as indicators of water quality in streams and lakes.

Aquatic insects are very useful for making environmental policy decisions and in deciding when managers need to step in and actively manage a body of water.  I think it’s useful to know how this works!  But first I should introduce the concept of macroinvertebrates.  If you ever delve into the insects-as-indicators-of-water-quality literature, you’ll see this term over and over again.  Although I tend to talk about insects more than the other invertebrates in streams and lakes, not all invertebrates that live in freshwater habitats are insects.   There are lots of other inverts, including crustaceans (crayfish, shrimp, and their relatives), aquatic worms (earthworms, tube worms, leeches, etc), flatworms, mites, snails, and clams.  The inverts are divided into the microinvertebrates and the macroinvertebrates.  Essentially, anything that you can see with the naked eye is a macroinvertebrate.  Everything else is a microinvertebrate.  I personally don’t find this definition very satisfying because one person’s macroinvertebrate might be another person’s microinvertebrate (e.g. my macroinvertebrate is very small).  Any one person’s cutoff for what makes a macroinvertebrate can change over time and as they gain experience too.  Still, water resource managers love the term macroinvertebrate and everyone uses it, including me.

An example of water full of organic pollution. This is a constructed wetland intended to clean up water coming out of a wastewater treatment plant before being released into the river.

In my first post on using aquatic insects as indicators of water quality, I focused on the changes in diversity that you see along the clean to polluted water continuum and I’ll talk about it again in a future post.  The number of species of macroinvertebrates in a stream is a quick and dirty way to compare bodies of water and determine the relative amount of pollution or impairment because clean streams and lakes tends to have more species in them than highly polluted bodies of water.  It isn’t precise though.  A fairly dirty stream can have almost as many macroinvertebrate species in it as a clean stream under the right conditions.  In this situation, it becomes important to consider the specific species that are found in a body of water. This is where tolerance values come in handy.

Tolerance values tell you how tolerant any given species is to pollution in its habitat (go figure).  The scale most commonly used goes from 0 to 10.  Things with low numbers are very sensitive to pollution.  Things with tolerance value numbers closer to 10 tolerate a lot more pollution in their habitats and can live in some pretty nasty water.  And, just to make everything confusing, sometimes you find super tolerant species with scores that go right off the top of the regular scale.  (They’re like Nigel’s amplifier in Spinal Tap – they go to 11!)

Arivaipa Creek looking toward the canyon

A nearly pristine, low elevation stream

Considering how often tolerance values are used in aquatic research and how valuable they are to water resource agencies and managers, I think it is worthwhile to know where tolerance values come from.  It takes a lot of time and effort, and often a lot of money, to calculate tolerance values for macroinvertebrates, but the concept is very simple.  First, someone (often a water manager for a state’s environmental protection department or a scientist) will take measurements of pollution or other impairments in many different bodies of water.  These could be simple physico-chemical measurements (such as pH, dissolved oxygen, temperature), measurements of embeddedness (how far down into the silt/sand the rocks and pebbles are buried) or periphyton (the algae growing on the surfaces of rocks, soil, and plants in the water), or full water chemistry analysis.  Which measurements are taken will depend on the region, the group doing the work, the funding, and the time available to put toward the project.  After measurements are made, bodies of water are grouped according to the level of pollution/impairment they exhibit, such as pristine, impaired, and polluted.

Next, the researchers send out a hoard of samplers to pull out every invert they can find from as many bodies of water as possible.  Some poor group of technicians then “picks” the samples (separates the inverts from the massive amount of junk that you get in aquatic samples such as leaves, sand, silt, twigs, trash, etc) and passes the inverts off to the identification guru to identify.  After all the water measurements and invert ID work is done, then the researchers compare the species present in each water body to its pollution classification and use statistics and other mathematical tools to look for overall trends.

Rio de Flag

A highly impaired, effluent dominated stream downstream of a wastewater treatment plant. Photo by Dave Walker.

Inverts that are found only in pristine lakes and streams and never in impaired or polluted waters have narrow pollution tolerances and are assigned low pollution tolerance values, usually 3 or less.  Inverts found in impaired and pristine waters but not highly polluted waters have a wider tolerance for pollution.  These inverts prefer clean water, but they can tolerate some pollution in their habitats and are usually assigned mid-range values around 5 or 6.  Things commonly found in highly polluted waters get high scores, between 8 and 10, though they are sometimes found in clean water systems too.  And those things with scores of 11?  Well, they can live in some of the filthiest water you can imagine!  I don’t know about you, but I can imagine (and have worked in) some pretty nasty water, and there are insects living in nearly all of them.

It is important to note that macroinvertebrate pollution tolerance values vary from region to region.  Here in Arizona, we can’t use the pollution tolerance values calculated for inverts on the east coast, even when the species are the same, because our waters and the inverts living in them behave differently than those on the coast.  Thus, every region develops their own pollution tolerance values.  When I’ve done water quality studies using insects as indicators of pollution/impairment in the past, I’ve used a list of tolerance values developed within Arizona that was given to me by the Arizona Department of Environmental Quality.  The tolerance values therefore accurately reflect how inverts in Arizona react to pollution/impairment that occur in Arizona.  The list doesn’t have every species, but you can often use what you know about which waters you find them in and published records of their presence to fill in the gaps.

Sabino Canyon

A normally clean, but impaired, stream a few weeks after the end of a major fire. Photo by Dave Walker.

Next Monday I will go through an example of how scientists and water managers use tolerance values by discussing a project I was involved in a few years ago looking at the insects in Arizona’s effluent dominated streams.  Tolerance values played a huge role in the analysis of our results, and it was an interesting (but disgusting) project.  Until then, have a great week – and don’t forget to enter my latest contest!

_______________

Unless otherwise stated, all text, images, and video are copyright © DragonflyWoman.wordpress.com