Why Insects Make Great Water Quality Indicators

giant water bug

Giant water bug, AZ tolerance value = 8

I’ve had a lot of time to think during my trip out of town for a family emergency (it’s going to have a happy ending, but does mean all recycled photos today) and I spent some of it thinking about what insects-and-water-quality post I should do next.  I had several ideas about what I might write about.  Perhaps I should talk about diversity and water quality or the metrics and bioassessment tools that are used by state and federal water quality managers.  Suddenly it occurred to me that I haven’t ever discussed one of the most important topics!  I’ve never explained WHY insects are such great indicators of water quality and why using them in this manner is so popular with researchers and water quality managers.  Today I’m going to do just that!  Really should have done this post ages ago, but sometimes inspiration doesn’t hit at convenient times.

There are several reasons why using insects as bioindicators of water quality is so popular.  One of the most important is that aquatic macroinvertebrates are found in nearly every body of inland (non-marine) water, so they are ubiquitous.  A little puddle of water in a rock the desert?  Yep, there are bugs in there.  A huge river in the Amazon?  Lots of bugs there!  A stream with a pH of 2 (highly acidic for those of you unfamiliar with the pH scale)?  Even there  – and I’ll talk about the insects I found in just such a stream in a future post.  There are insects that can live in pools of petroleum, hot springs that would boil a human alive, and water that’s hundreds or thousands of times saltier than the ocean.  All in all, there are very few biological organisms that you can find in so many different aquatic habitats.  As a result, insects and other macroinvertebrates are the darlings of water quality researchers while many other aquatic plants and animals are completely ignored.

Hydrophilid lateral

Water scavenger beetle, AZ tolerance value = 7

Macroinvertebrates are also useful as indicators because they are abundant.  If there are insects in a body of water, there are usually lots of insects in that body of water, even in highly polluted water.  This means that you can get a decent sample without severely impacting their populations in most places.  This isn’t always the case with some of the bigger animals like fish.

Sometimes you need a tissue sample to see how water quality is impacting aquatic wildlife, such as an analysis of the amount of lead being absorbed by the wildlife in a stream.  You often need fairly large tissue samples to run these sorts of tests, so the bigger the animal the better.  Fish are perfect, but they’re not found in every body of water.  Microorganisms such as algae, bacteria, and protozoans abound in many types of water, but they’re very small.  If you need even a small tissue sample the size of, say, a bloodworm, imagine how many bacteria you need to collect from the water to create a big enough sample!  Not only are insects abundant and ubiquitous, but they’re a lot bigger than most other abundant and ubiquitous organisms.  This makes them more useful as indicators.

Skinny legs

Water scorpion, AZ tolerance value = 11

Insects are easy to collect compared to a lot of other things too.  Consider how difficult it is to sample fish!  You can use a rod and reel and spend days collecting 10 or 12 fish, carry a massively heavy electroshocking unit with its associated risk of electrocution if something goes wrong, or poison all the fish in an area with a chemical like rotenone (which can also kill insects and amphibians).  You could always just sample the water directly, but the last thing you want to do in a remote location is carry gallons of water to your vehicle.  Insect samples are easy!  One aquatic insect net and a decent sized bottle containing alcohol is enough to collect the sample and get it back to the car.  Lightweight, portable sampling equipment is preferable to heavy gear, particularly if you have to hump it into remote locations on foot, and sampling insects is one of the lightest choices.

Water quality analyses of any sort are very expensive.  While it might seem like the easiest way to determine whether a body of water is polluted, analyzing the water itself is particularly spendy.  There are so many man-made and naturally occurring compounds that could be in water that you can run hundreds of tests on a single sample looking for every possible pollutant.  Even running a very simple set of analyses looking at nitrogen, phosphorous, and carbon compounds, biological oxygen demand, and a few other parameters can cost nearly $1000.  Insect samples are also expensive to process and analyze, but they’re not as expensive as water analysis, maybe $300 per sample as opposed to $500-$1000 or more.  For any given budget, you can collect more insect samples than you can water samples, so insect sampling is often preferred.

predaceous diving beetle

Predaceous diving beetle, AZ tolerance value = 7

Finally, one of the things that makes aquatic insects and other macroinvertebrates such great indicators is that they live in the water all the time and are reasonably long-lived.  Pollution can and sometimes does occur steadily over time (imagine a wastewater treatment plant outfall or a paper mill dumping waste into a river), but a single event can cause massive problems in a body of water.  Sometimes, every trace of the pollutant has disappeared from the water by the time a researcher can collect a water sample from the stream.  However, many of the insects were in the stream during the pollution event!  This means that, even if you can no longer find the pollutant in the water, or never even knew a pollution event occurred, the organisms in the stream can show you that something is wrong.  You might not be able to figure out exactly what caused the problem, but you can at least see that there was a problem and start looking for possible sources.

All in all, I think it makes sense to use aquatic macroinvertebrates to assess water quality!  They make fantastic indicator species for so many reasons that they have become one of the best tools researchers have for determining water quality.  They’ve proven themselves in countless studies and their use has become a standard part of sampling protocols for many state and federal water quality agencies.  They’ve become very important to a lot of people.  As an aquatic insect lover, it makes me happy that my favorite bugs matter.  And really, who doesn’t love an aquatic insect?  :)

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

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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!

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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.

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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!

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

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

Backswimmer (Family: Notonectidae)

dragonfly

Dragonfly nymph, a clubtail dragonfly (Family: Gomphidae)

damselfly

Damselfly nymph, a spreadwing damselfly (Family: Lestidae)

Hellgrammite (Corydalus cornutus)

Hellgrammite (Family: Corydalidae)

Creeping water bug

Creeping water bug (Family: Naucoridae)

dragonfly

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.

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Unless otherwise stated, all text, images, and video are copyright © 2010 DragonflyWoman.wordpress.com.

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.

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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

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