Using Aquatic Insect Tolerance Values: An Example


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!


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?


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

Collecting in Arivaipa

Arivaipa near first road crossing

Arivaipa near first road crossing

This year, one of my good friends and I decided that we were going to avoid all of the Black Friday nonsense in our city by going on an insect collecting trip.  We were originally planning to go to Sycamore Canyon, an area we’ve both been to many times near Arizona’s border with Mexico.  However, my friend is a fish scientist (ichthyologist for those of you don’t know) and happens to have access to a protected stream where I’ve never been able to collect.  She was granted permission for us to collect from the stream in exchange for our sharing our findings with the land managers.  So, we packed up my tiny SUV bright and early on Black Friday and drove 3 hours to the eastern end of Arivaipa Creek.

Arivaipa is this wonderfully magical place that people have told me about since I arrived in Arizona.  I’m always told stories about it in hushed tones like the place is sacred.  Naturally, I’ve been dying to go.  And Arivaipa really is a special place.  For one, it has flowing water year round, uncommon for small streams in southern Arizona these days.  For another, the creek is relatively clean with minimal runoff from roads and no sewage effluent.  There may be some contamination by heavy metals from nearby mines, but the creek is largely unimpaired.  It is also home to several native fish species, an increasingly rare quality in Arizona.  Because is a sort of last-of-it’s-kind type of place, access to the canyon and the creek is restricted by the Bureau of Land Management.  You can only hike in the Canyon with a permit and you have to cross Nature Conservancy land to get there, so you have to have double permission to enter.  Only 50 people are allowed in the Canyon each day, so getting to go there is a real treat.  And getting permission to collect aquatic insects from a relatively pristine Sonoran Desert stream there is even better!

Arivaipa Creek looking toward the canyon

Arivaipa Creek looking toward the canyon

We couldn’t have asked for a better day!  It was supposed to be very cold in Tucson (it was supposed to get down to 26 degrees that night, which is positively frigid by Tucson standards), so we were a little worried it was going to be uncomfortably cool and we prepared for the worst.  We lucked out and stepped out of the car to a bright, perfectly warm, gorgeous day!  We both strapped on some impeccably clean waders and hauled a bunch of gear to the stream.  we were pleasantly surprised the water wasn’t as cold as we’d expected.  (Granted, I was still happy I was wearing my wool socks under my waders!)  We each strapped on some gear, grabbed our strainers (best aquatic insect  nets ever!), and waded into the stream.

Arivaipa Creek looking upstream

Arivaipa Creek looking upstream

We spent the next 4 hours wandering around in the stream hunched over, peering into the water and dipping our strainers into the creek in an attempt to collect as many different insects as we could.  We were surveying the stream for the land managers after all!  Due to the perfectly warm weather, there were clouds of adult mayflies swarming over the stream and I managed to catch a few of them with my strainer.  We pulled several things out of the water that I’d expected to find in in Arivaipa Creek, things I knew other people had collected there.  We didn’t get any specimens of other things that I was surprised were absent.  My friend and I both had to be back in the early evening, so we couldn’t hike too far downstream.  Thus, we missed out on some of the insects that are typically only found in Arivaipa Canyon, a 10 mile stretch of stream flowing between high, steep rock cliffs, or further downstream.  That’s where all the hellgrammites are.  Sadly we didn’t find a single specimen in the section of the stream where we were collecting.  We did collect some exciting things though!  We were feeling quite pleased with our day by the time we headed back home.  Great day!

(AND, we stopped to the The Thing on the way home.  I’ve been driving past this roadside attraction in Arizona nearly my entire life and I’ve never seen it.  Since we had some time to kill, we stopped, paid our $1, and saw The Thing.  I’ve known what it is since I was a kid, but it was high time I actually visited!)


Vials of insects collected from Arivaipa.

The following week, we sorted through all of our bugs, removed them from the debris (we “picked” them), separated the insects into groups according to genus, and identified them to the genus level.  In all, I collected 23 genera, including water bugs, water scorpions, several caddisflies, lots of beetles (including crawling water beetles – family Haliplidae – my favorite aquatic beetles), and some damselflies.  The most exciting find of the day for me was collecting two different genera of dixid flies in one stream, something I’ve never experienced before.  My friend also caught a beetle I’ve never caught on any of my many Arizona collecting trips, a marsh beetle (family Scirtidae).  Overall I think we collected about 30 different insect species.  That’s pretty good considering we only sampled a very tiny section of the stream during late fall/early winter!

My collecting trip to Arivaipa made me really happy.  Rather than sitting around at home avoiding shopping, I got outside, visited a beautiful place that I’d never been, collected a bunch of great insects, and spent most of a day talking to a good friend.  We got some really great bugs, saw The Thing.  I got to drive through the creek several times where it crossed the road.  (I have a secret dream to be a stunt driver for truck commercials, so I LOVE driving through rivers!)  Much better than spending the day hiding in the house!  Now, where to go next year…


Unless otherwise stated, all text, images, and video are copyright © 2010

Building a Garden Pond for Aquatic Insects, Update

pondThe Biosphere 2 Science and Society Fellows lunch was held in May, so my time as a B2 fellow is officially over and a new cohort will begin in the fall.  The fellowship was a great experience in general, though I am particularly pleased with my blogging experience.  Thanks to everyone who’s been keeping up with my blog for the support and encouragement!  I’m going to keep blogging and hope to make this a permanent part of my scientific life.

I had a chance to check on the pond I built to attract aquatic insects at B2 during the tour of fellows’ projects we made before the lunch.  As promised, this post will be a report on the success of my pond a month after the installation.  It’s terribly overdue as I’m easily distracted by interesting things and kept putting it off, but it’s time to get to it!  If you missed the earlier posts and want to read about the planning and installation of the pond, there are links to all of the pond posts at the bottom of the page.

First, a photo of the condition of the pond the last time I saw it, in mid-May:

my pond

My pond, a month after installation.

Admittedly, there were a few problems with the pond.  The water ended up becoming murkier than I’d hoped.  It may eventually require the installation of a filter to clear the water up because it was hard to see to the bottom of the pond.  It could have been worse though and a month in the hot sun of southern Arizona is enough to cause some major algae problems that my pond didn’t appear to be having.  So, the pond water was pretty good, but could have been better.

The main problem the pond was having was the wind.  During the installation of the pond, the Biosphere 2 courtyard where it is located was quite lovely.  Three weeks later when I went to check on it and again at the fellows lunch, the wind was absolutely ripping through the courtyard.  That courtyard gets a lot of very strong winds apparently.  I’m not sure that the cattails I planted myself had been in the pond long enough to establish a strong root system and the majority of them had been ripped out and were lying across the top of the pond.  I can’t do anything to keep the wind down in the area, but I did replant the cattails that still looked healthy and supported their bases with a lot of rocks.  I’ll have to go back to check on it one more time to see if it worked or whether they fell over again.

The wind was also causing problems for my identification guides.  They were getting whipped around on their hangers and were spread across the courtyard both times I went to check up on the pond.  The ring was entirely missing from one of the guides as well.  I’m going to need to figure out a way to shelter the guides from the wind so that they’re not being strewn all over the area and they’re in a place visitors can actually find them.  Stupid wind!  It’s amazing how much wind that courtyard gets.

pond plants

Plants in the pond.

In spite of these rather minor hiccups, here were several things that made me very happy about the pond too.  First, most of the plants seemed to be doing pretty well.  The submerged plants were still looking good and the horsetails, irises, and reeds remained green and were standing upright in the pond.  This suggests that they rooted sufficiently to withstand the wind.  The floating plants weren’t quite as abundant as they were originally and some had clearly died, but there were several still living in the pond and those all looked bright and healthy.  Overall, the plant situation looked promising.  I’ll want to go back after the winter and see how many plants avoided freezing during the winter, but I think the plants will make it until the first freeze at least.

There were insects in the pond!  There weren’t as many species as I had hoped (the seclusion of the courtyard and/or the wind may have had something to do with it), but there were some beetles and some fly larvae in the pond.  Considering the goal was to attract insects to the pond, this was what I had hoped to see.  I expect the pond likely has more insects in it now as the warm weather prompts many aquatic insects to disperse to new habitats and the monsoons are coming up soon too.  Lots of insects move around once the monsoon rains begin.

Much to my great happiness, there was one insect type missing entirely from the pond: mosquitoes!  There had been many at my house by the time I checked on the pond, so I was very worried that there would be tons of them breeding in the water.  I looked really hard and I didn’t see a single one!  The flow of the water appears to be sufficient to control the mosquitoes, though I’ll definitely want to go check up on that again this summer just to be sure.  Mosquitoes are definitely something I want to avoid.

And finally, the water levels and the flow were both looking good.  The automatic filling system seemed to be doing its job well and the water was still flowing at a good clip.  Hopefully these will continue to work well long into the future.

Overall, I think the pond was looking pretty good the last time I visited it.  I want to go back sometime after the monsoon rains start to check on it again, but the conditions of the pond a month after installation were promising.  The goal of the project was ultimately to create a permanent educational display and so far the pond seems to be holding its own and going strong.  Yay!  My first successful pond!  Now I’m itching to build one in my yard…  :)


Posts in this series:


Unless otherwise stated, all text, images, and video are copyright © 2010

Aquatic Insects and Water Quality

water sampling

The Dragonfly Woman recording data during a sampling trip to an effluent stream. Photo by Dave Walker.

I’ve decided to put off talking about my damselfly research another month or two so the post is closer to the paper release date, so I’m going to talk about another subject today: aquatic insects and water quality.  In my second year of grad school, a professor for a class I was taking recommended that I apply for a job.  A month later, I had a second job in an aquatic ecology lab and was working as an aquatic sampler and insect identification guru.  The project I was hired for originally was for the Environmental Protection Agency and focused on the impacts of effluent (treated wastewater) on the insect populations downstream of wastewater treatment plants in Arizona.  I can’t say that sampling for the project was pleasant and I can attest to the fact that wearing chest waders in poorly treated, reeking wastewater when it is 110 degrees in the shade is quite awful.  However, the project taught me firsthand just how much of an impact water quality has on aquatic insect populations and it is a subject I find fascinating.  In fact, my work in my second job has helped direct my plans for my research program once I have completed my doctorate.  I haven’t talked much about my second job yet in my blog and it’s time to rectify this!  Today I’m going to introduce the subject of aquatic insects and water quality.

Arizona  has a lot of problems with its water.  There are huge demands placed on the little water that is available and streams and rivers have been sucked dry by farmers and growing cities over the last hundred years.  This means that in some sections of several rivers there would be no flow at all if it weren’t for wastewater treatment plants releasing effluent.  So just how to insects respond to wastewater?  The short answer is this: not well.  Aquatic insects are typically adapted to a particular range of conditions.  If those conditions change, such as when effluent is dumped into a stream, the insects must often move to a different habitat or die.  Other insects, things that are very tolerant to polluted waters, may move into the area in their place.  You can therefore see a huge shift in the types of insects living in a clean, relatively pristine stream relative to an effluent dominated stream (a stream nearly completely or completely made up of effluent).  Many types of insects simply can’t live in environments with low water quality – and those that can tell you a lot about how terrible the water quality really is.  In fact, aquatic scientists often use aquatic insects as biological indicators of water quality.  That was exactly what we were doing in the effluent project, using insects to tell us about the quality of water in effluent dominated streams.  I’m not going to go into detail about that project today.  Instead, I’ll illustrate the differences in the insect populations between two streams in the Tucson area, one effluent dominated stream (the Santa Cruz River) and one mostly clean water stream (Sabino Creek in Sabino Canyon) so you can see the shift from dirty water insect populations to clean water populations.

Let’s take a look at an effluent stream first, a dirty stream.  The Santa Cruz River is one of the major “rivers” in Tucson and it is dry most of the year along most of its length.  However, it always flows downstream of the wastewater treatment plants.  The Santa Cruz River is therefore 100% effluent for most of the year.  Effluent, even when it is very well treated, has all kinds of bad things in it.  In my area, the nitrogen levels of the waters released from treatment plants are very high.  Scientists have also discovered many compounds that humans secrete in our wastes, such as pharmaceuticals, flame retardants that are on our clothing, triclosan (an antibiotic used in antibacterial soaps), and many other nasty chemicals.  These don’t get cleaned out of the water with current treatment techniques, so all those chemicals end up in the streams when water is released from treatment plants.  In essence, the biota living in the streams below wastewater treatment plants are bathing in a stew of antibiotics, birth control chemicals, detergents, etc.  You can imagine why this might be a problem.  My labmates have found many of these chemicals in the Santa Cruz River water.  So what kinds of insects do you find there?  We recently took a reporter for the Arizona Daily Star to sample from the river as part of a story about the wastewater treatment plant.  These are the insects we found:

blood worms

Bloodworms, larvae of the non-biting midges (a type of fly). This photo made the front page of the newspaper the day the article ran!

Ah, the lovely bloodworm.  And notice that ALL of the insects in this image are bloodworms.  Not all bloodworms are a sign of troubled waters so you can’t simply say that bloodworms = low water quality.  However, if you find tons of bloodworms and nothing else in a stream, that’s usually a bad sign.  Bloodworms get their name from their red coloration (it has been mostly broken down in the image due to the preservatives used – they’re flaming red when they’re alive) and that red coloration comes from a chemical bloodworms have that almost no other insects have: a hemoglobin-like compound.  If you want to read more about bloodworms and their hemoglobin, please read my post on aquatic insect respiration.  For now all you need to know is that the hemoglobin-like compound allows these insects to live in very low oxygen environments.  Thus, the sheer abundance of these insects and the lack of other insect species tell you something important about this stream: there is hardly any oxygen in the water at least some of the time.  The chemicals in the water probably contribute to the overall inhospitability of the river for insects as well.  Thus, the insects in the stream tell you that this stream has poor water quality.  We found this to be the case at all of the effluent streams we sampled during the EPA study, but this particular wastewater treatment plant had the fewest species of aquatic insects downstream of the plant of all of the streams we tested.

Now let’s compare the low quality stream to one with high water quality, Sabino Creek.  Sabino Canyon is one of the most popular outdoor spaces in the Tucson area in part because it has a gorgeous clear stream that flows through most of the canyon.  We went to Sabino Creek to sample right after we sampled in the Santa Cruz, and these are just some of the insects we found in the creek:


Backswimmer (Family: Notonectidae)


Dragonfly nymph, a clubtail dragonfly (Family: Gomphidae)


Damselfly nymph, a spreadwing damselfly (Family: Lestidae)

Hellgrammite (Corydalus cornutus)

Hellgrammite (Family: Corydalidae)

Creeping water bug

Creeping water bug (Family: Naucoridae)


Dragonfly nymph, a skimmer (Family: Libellulidae)

Notice the difference between this stream and the effluent stream?  Look at how many more species there are!  And some of these, including the hellgrammite and the clubtail dragonfly, only live in pretty clean water and need a lot of oxygen.  Even if you didn’t know that though, you could tell that this is a fairly clean water stream simply by looking at the number of insect species living in it.  There is one caveat, however, when comparing the Santa Cruz River to Sabino Creek.  The river is in the Tucson valley and is located at a lower elevation than Sabino Creek, which means that the types of insects you find in the stream would likely be a bit different even if they had the same quality.  Still, if you compare other effluent streams at similar elevations, or even the Santa Cruz River below the wastewater treatment plant upstream of Tucson at Nogales, it is obvious that the section of the Santa Cruz flowing through Tucson is really nasty.  Sabino Creek is comparatively very clean.  And, the insects in the stream can tell you just how clean the water is because they are excellent indicators of water quality.

This trend, that clean water has much higher insect diversity than polluted water, seems to hold true throughout the world in the majority of aquatic habitats.  For this reason, insects have become very important in water quality studies.  By collecting insects and identifying them, a scientist can say some very profound things about the water quality in that environment even if he doesn’t take any other measurements.  I’ve personally done a lot of work using insects as indicators of water quality through my second job and this work has profoundly impacted how I think about aquatic systems and the insects that call them home.  I’ll definitely be revisiting the topic in the future.


Unless otherwise stated, all text, images, and video are copyright © 2010

Notes From NABS Day 5

meeting logoPhysical, Chemical, and Biological Changes Along the Continuum of an Agricultural Stream: Influence of a Small Terrestrial Preserve

Well, I didn’t quite get this post done the day I meant to, but my day ended up being quite busy.  However, the NABS/ASLO joint meeting of 2010 is now officially over!  That means this will be my last NABS post until I go to another conference.  It’s nice to be back home!  Meetings are exhausting and melt your brain after a while.  They’re fun, but they’re intense – and I never get enough sleep.  No matter how much I enjoy a meeting, I’m always happy to get back home and sleep.  And, if I come away from the experience without any new communicable diseases, I’ll consider it a success.

I’m going to skip the Things I Leaned section for today and jump right into the last talk.  Today, my focus is a talk by Dr. David Houghton that was given on Day 3 of the conference.  Dr. Houghton is an entomologist and Associate Professor at Hillsdale College.  Hillsdale is a small liberal arts college (even smaller than the one I went to as an undergrad!) and Dr. Houghton is in the department of biology there.  Sadly, there aren’t all that many people from these sorts of schools at most of the meetings I go to.  This is doubly sad because Dr. Houghton’s presentation was really interesting and made some excellent points.

In the area in southern Michigan where Dr. Houghton completed his study, the streams used to be surrounded by a wide strip of dense vegetation (the riparian zone).  The area is now an agricultural region.  This means that, rather than large trees and plants that require a lot of water filling the space adjacent the streams, the native plants have been removed and the agricultural fields go right up to the banks.  This has several implications.  The lack of trees means the water is warmer than it was before the trees were removed because there isn’t as much shade on the water.  A lot of chemicals such as pesticides and fertilizers end up in the water any time water flows over the fields and into the streams (i.e. during rains, heavy irrigation, etc).  Those chemicals decrease the water quality, which in turn impacts the plants and animals that live in the water.  Overall, the water quality decreases and with it the number of species that can live in the river.

In general, this situation isn’t good for the stream or any of its biota.  The river needs the forested areas for everything to work properly.  Removing the riparian area means that things in the river change and the “health” of the river goes down.  Stream health is a somewhat vague concept that I don’t want to get into here, but it is essentially a measure of how close to naturalistic conditions an ecosystem is.  Dr. Houghton’s talk began with this introduction.  Then he asked a question: are the small forested areas that are still available along southern Michigan’s streams capable of improving the water downstream so that the area downstream more closely resembles conditions without the influence of agriculture?  This has important implications for conservation of aquatic species.

Dr. Houghton’s study was conducted in the St. Joseph River in southern Michigan.  Like other rivers in the region, the St. Joseph has agricultural fields along the majority of its length with small forested areas near the headwaters.  In particular, Dr. Houghton was interested in one section of the river that had a small terrestrial preserve where the riparian area remained intact.  The river running through the preserve looked better than the area upstream, so he thought the water flowing through the area might be improved such that insects downstream of the preserve would fare better than the insects above the preserve.

To study this, Dr. Houghton chose six sites in the St. Joseph River from which he collected water and insect samples.  Two sites were above the preserve, two were within the preserve, and two were further downstream.  He measured several parameters of the water itself, including the temperature, dissolved oxygen, pH, and conductivity (effectively a measure of the amount of salt compounds in the water).  He also measured the insect populations by collecting adult caddisflies at light traps near the river.  Measuring the water parameters would tell him whether the water running through the preserve or downstream of the preserve was better than the water upstream of the preserve.  Because caddisflies are aquatic as larvae and live in the water for most of their lives, they are strongly impacted by water quality and are excellent indicator species.  Counting the number of individual adults and the number of species (also known as species richness) that came to the light traps would tell Dr. Houghton something about how “healthy” the river is.

His results were interesting.  There was no difference in any of the measurements of water quality Dr. Houghton collected above and below the preserve.  This meant that the river is an agricultural stream for its entire length and the preserve did not improve the water quality downstream.  There were two water parameters that improved within the preserve: the temperature (it went down) and the amount of dissolved oxygen (it went up).  These two changes can likely both be attributed to the amount of shade the river receives in the preserve versus the areas outside.  Shading the water causes the temperature to go down because less sun hits the water.  This in turn causes the dissolved oxygen to go up because cooler water holds more oxygen than warmer water.  However, once the water flowed back out of the preserve, the temperature and the dissolved oxygen went back to the levels seen above the preserve.  The preserve did not appear to be improving the water quality in the river.

Similar results were found using the insect samples.  Dr. Houghton found that 7 species of caddisflies made up 90% of all of the specimens coming to the light traps both within and outside the preserve.  These 7 species all feed in similar ways (they are collector-gatherers and they eat things that are floating in the water, like leaf particles and floating algae that are of the appropriate size) and have the same level of tolerance to pollution.  So, it appears that the majority of the caddisflies in the river were about the same throughout, again suggesting that the preserve didn’t do much to improve the quality of the river.

However, Dr. Houghton did detect one important difference between the caddisflies in the preserve compared to those outside: there were more species of caddisflies inside the preserve, so the species richness improved.  22 species of caddisflies were found only in area of the river where it flowed through the preserve.  Most of these caddisflies fed in a similar way (they are shredders, or insects that tear leaves and algaes into pieces small enough to eat – an important component of decomposition in aquatic systems) and the remaining species were ones that required cooler waters than those found outside the preserve.  None of these species were very abundant and in fact a few of them were represented by only a single specimen, but the species richness was definitely improved within the preserve compared to outside.

Dr. Houghton ended his talk with a question: is the river “healthier” because of the presence of the preserve?  He suggests that the answer to this question depends on what measure of health you are using.  The preserve clearly didn’t change the water quality so that the section downstream of the preserve was different from the area above.  If your measure of river health is whether the water quality and caddisfly populations downstream of the preserve are better than those above, then the preserve does not have any effect.  This could give some policy makers the idea that it’s okay to rip those last few preserves out, making space for more agricultural fields.  However, if your measure of river health is species richness, the presence of the preserve had a huge impact.  The river above and below the preserve had many fewer species of caddisflies than the area within the preserve.  Clearly the preserve is acting as a refuge for species that are unable to live in the more harsh conditions outside of the preserve.  Thus, if your goal is to maintain diversity in the stream, the preserve is very important.  In fact, building new forested areas along the water might further improve the diversity of the river even further.

I thought this talk was excellent.  It was a simple project, but it did everything it needed to accomplish.  Dr. Houghton’s talk also highlighted a couple of important points.  First, when looking for the biological impacts of a system on a species, you need to identify which measurements of health you want to use.  Second, it is good to consider multiple measurements of health within a system.  It would be tragic for any study to say that forested areas near a stream aren’t necessary because they don’t improve the water quality downstream.  I think what makes Dr. Houghton’s study great is the fact that he identified the changes in the species richness of the forested preserve, which showed that the preserve really did have an impact on the river system, if only in the area within the preserve.  It wasn’t exactly the one he might have expected or hoped for, but it does suggest that forested preserves are valuable to river systems and should be protected so that species diversity within the river is maintained.

And that wraps up the Notes from NABS series!  I hope you all enjoyed the glimpse into the research that is currently happening in the aquatic sciences and learned some new things.  Scientific conferences are an excellent place to gain new insights, think about things in new ways, or learn about things you’ve never even considered.  Hopefully I have passed some of these qualities on as they’re just too good to keep to myself.


Posts in this series:
Day 0 – Introduction to the Series
Day 1 – Invasive Crayfish
Day 2 – Giant Water Bug Dispersal
Day 3 – Dragonfly Captive Rearing
Day 4 – Integrating Service-Learning Programs into College Courses
Day 5 – Impact of a Small Preserve on Stream Health


Unless otherwise stated, all text, images, and video are copyright © 2010

Notes from NABS Day 4

meeting logoIncorporating Service Learning Into an Introductory Limnology Course

Greetings from NABS Day 4!  Tomorrow is the last day of the conference, so I’ll only be making one more post in this series.  I’m also headed home, and a bit earlier than originally planned.  A combination of sleep deprivation and general physical and mental exhaustion due to extensive traveling over the last few weeks (I was gone almost a week right before the conference began) has convinced me that I should go home in the morning, skipping the talks on the last day of the conference.  I’m driving home, so it’s important that I travel during the period when I am most alert, which means missing the talks.  So, I will be presenting something from one of the first four days of the conference when I post my final entry for the conference on Saturday.  What can you do?

Things I learned:

— High school students have a lot of fun going out into the field to collect data (though this shouldn’t come as a surprise – my favorite biology lab in high school was one where we documented the ecosystem of a marsh in Colorado, the same marsh where I eventually did my undergraduate biology thesis!)
— Aquatic insect species that are found in many areas across the landscape are usually found at about the same altitude while insects that are found in a wide range of altitudes are typically only found in a small geographic area.
— This is really re-confirming something for me:  conferences are exhausting!

On to my favorite talk of the day!  I attended the Education in Aquatic Sciences session today because this subject is near and dear to my heart.  I LOVE teaching, so any time I can learn more about how to do it better, you know I’ll be there in the front row.  (Okay, okay – so, I was in the second row…)  My favorite talk of the session ended up being my favorite talk of the day, partly because it was an interesting talk and partly because the speaker, Dr. Frank Wilhelm, was completely inspiring.  Dr. Wilhelm is a professor in the University of Idaho’s Fish and Wildlife Resources Department and teaches a course in introductory limnology to undergraduate students.  His talk focused on a service-learning project that he has incorporated into his class and he described how it works.

Service learning is defined as a method of teaching, learning, and reflecting that combines classroom curriculum and meaningful service throughout the community.  In essence, service learning projects allow students to doing something hands-on that is also worthwhile to the community.  Dr. Wilhelm described service learning as a powerful, motivating, and effective approach to teaching and learning and believes it can be broadly applied in college courses focusing on field-based sciences.  He also believes that it engages students in a way that isn’t possible via other teaching methods and helps the students form a strong connection between what they learn in class and the real world.

Here’s how the service learning component of Dr. Wilhelm’s intro limnology course works.  First, he finds someone or a group of people in the community that have a problem they want solved or a question they want answered.  That person or group then becomes the partner for the class that semester.  Dr. Wilhelm gave an example of a partner from the last class he taught.  In his area, there is a small lake that is surrounded by ritzy homes.  However, the lake was absolutely full of vegetation, so full that it was completely useless for any other purposes such as fishing or boating.  The neighborhood asked Dr. Wilhelm to have his students tackle their problem and became the class service learning partner for the semester.

Students are told at the beginning of the term that they will be doing a service learning project as part of the course.  It is a required activity that ends up taking up the final 1/3 of the lab periods of the course.  During the first week, the students are put into groups that become their team for the semester and the entire class is introduced to the problem.  The second week, the partner presents the problem to the class so that the students know the person/people they are helping and the problem they are trying to solve.  They then identify subsections within the main problem that individual groups can tackle during the course.  Teams decide which subsection they want to focus on and define clear objectives, develop methods, make lists of equipment they require (made available by Dr. Wilhelm from his personal supply), and develop a budget that will help them accomplish their goal.  Dr. Wilhelm allows his students nearly complete freedom to decide which aspects of the problem they wish to tackle, how they wish to tackle it, and what sort of data they will need to collect.  His only requirement is that they have to work toward solving the overall goals of the project.

Then he sets them loose out in the field to do their projects!  By his account, this part is a little chaotic, but the students generally have fun and are learning valuable things while they work.  Dr. Wilhelm also said that students use their travel time to discuss issues related to the project, so there isn’t any downtime – they are constantly learning.

Back in the lab, the students analyze the data they collected in the field and make conclusions based on their results.  Then they present their part of the project to the rest of the class in teams.  The students combine their efforts to create a report that they will present to the partner.  And then they present their data to the partner in person, making suggestions for how the partner might solve their problem.

Dr. Wilhelm said that this sort of project is fairly easy to incorporate into a class that could conceivably have a field component.  (I can imagine how well it would fit into my insect behavior and aquatic entomology labs!)  He said that all you need to get started is to identify a partner for the semester, identify the areas of expertise for which you have sufficient knowledge to successfully guide students toward solving the partner’s problem, and spread the word about the program to get people interested.

Dr. Wilhelm believes the program has been a big success.  The partners have been happy with the information the students have provided them.  The students themselves tell Dr. Wilhelm that they really enjoy the project and think it’s the best part of the class.  Dr. Wilhelm thinks his students have become more engaged in the course since he introduced the service learning project as well.  Perhaps the best measure of success is that, in a difficult senior level undergraduate course worth 4 credits that starts at 8AM, he has nearly 100% attendance!  This just doesn’t happen.  He attributes this spectacular feat to the service learning project experience.

Although the talk was simple and not a scientific research talk, I really loved this one.  If nothing else, Dr. Wilhelm obviously cares about his students deeply and wants them to succeed.  He puts a lot of effort into his teaching and is clearly excited by the teaching component of his professorship (a somewhat rare trait at the big public universities!).  It was so inspiring to listen to him talk about his program and how involved the students become, how much they care about what they’re doing during their service learning project.  I’m hoping to incorporate some of the same things into my own courses sometime!

Tomorrow I’ll finish up Notes from NABS with a description of a talk I heard on Day 3 that focused on the effects that a small wildlife preserve has on a river in southern Michigan.  The vegetation that would naturally surround the river (called the riparian area) has been entirely replaced by agricultural fields – except for the area where it flows through the preserve.  Want to know if this preserve helps improve the quality of the water before it flows downstream?  Check back tomorrow!


Posts in this series:
Day 0 – Introduction to the Series
Day 1
– Invasive Crayfish
Day 2 – Giant Water Bug Dispersal
Day 3 – Dragonfly Captive Rearing
Day 4 – Integrating Service-Learning Programs into College Courses
Day 5 – Impact of a Small Preserve on Stream Health


Unless otherwise stated, all text, images, and video are copyright © 2010

Notes from NABS

meeting logoGreetings from a new venue for the Dragonfly Woman!  I’m currently in Santa Fe attending the joint meeting of the North American Benthological Society (NABS) and the American Society of Limnology and Oceanography (ASLO).  I’ve been to NABS meetings in the past and they’re quite fun as far as scientific meetings go.  You spend your days going to scientific talks (and there are TONS, so it’s not hard to find at least one thing you’re interested in during any given time slot) or poster sessions and your evenings socializing with the other members of the society.  The NABS meetings are far and away my favorite meetings to go to of all of the scientific meetings I’ve been to because they’re a reasonable size and really emphasize the social aspects of the society.  As a not-at-all-outgoing person, I appreciate this.  Forced scientific social time is good for me.  :)

This year… well, I can’t say the meeting is going to be quite as fun for me, though I’m sure other people would heartily disagree.  There are double the people at the meeting due to the addition of the ASLO members, and I find the crowds disconcerting.  The social activities are, I’ll admit, a bit overwhelming for me due to the gigantic number of attendees and that makes them far less fun for me.  The meeting is also spread across several buildings for the first time since I’ve been attending the NABS meetings.  This wouldn’t be a problem if the buildings were close together, but some of them are several blocks apart.  This makes scheduling your day a lot more complicated because you can’t just flit from room to room easily like I have in the past.  I feel obligated to sit through talks I’m not as interested in hearing because something better is too far away to get to in time.  And then there are a bunch of little personal touches that the NABS meetings always include that are absent from this meeting, making it feel just a bit less special.  None of these things are the end of the world of course and I’m sure I’ll enjoy the conference anyway, but they do make the meeting marginally less appealing to me than in former years.

The meeting officially started yesterday.  I hadn’t planned to go to the opening ceremonies last night, but even if I had, I wouldn’t have made it to Santa Fe in time.  When estimating how long it would take to get to Santa Fe by car, I stupidly used the time it took to get there from where I used to live in Colorado rather than Tucson, even though I’ve driven both ways a hundred times.  That combined with being hit by an absolutely enormous, blinding storm on the interstate in the dark meant that I arrived much later than planned and completely missed all of the things that happened last night.  But that’s okay.  I did get to see a spectacular sunset shortly before the mother of all storms slammed into my car and that made the drive 100% worth it.  This photo doesn’t even begin to do it justice (it was, after all, taken one handed and out the window of a car going 75 mph on the interstate and I certainly wasn’t taking my eyes off the road long enough to frame the shot properly – not ideal photographic conditions!):


Sunset in New Mexico

Because I missed the official first evening, I consider today day 1 of the conference.  And this means that, as promised, I am going to try to blog every day this week and highlight my favorite talk or poster of the day.  Just as a warning, I might jump outside of the aquatic insect realm this week.  This isn’t an insect meeting and there are tons and tons of other aquatic related topics covered here that I find fascinating, so one non-insect talk might work its way in.  My favorite talk today did at least deal with another freshwater invertebrate: the crayfish.  It was a very interesting talk and I am very excited to share some of the information that was presented.

However, you won’t get to hear about it until tomorrow.  I am going to have a one day delay in getting things posted (Day 1 will be posted on Day 2, etc).  This is to ensure that I have enough time to get a decent post together rather than throwing something up that doesn’t make sense.  I will have a new post every day through Saturday though, so I hope you’ll check back often.  There will be some very interesting and very new science posted over the next 5 days.  It should be worth your while!


Posts in this series:
Day 0Introduction to the Series
Day 1
Invasive Crayfish
Day 2Giant Water Bug Dispersal
Day 3 Dragonfly Captive Rearing
Day 4Integrating Service-Learning Programs into College Courses
Day 5Impact of a Small Preserve on Stream Health


Unless otherwise stated, all text, images, and video are copyright © 2010