Aquatic Insects as Indicators of Water Quality


Photo above: Cybister fimbriolatus: Dysticidae (predaceous diving beetle) would have a tolerance score of 5.

Author: Dr. Hope Q. Liu (Biology)

Aquatic insects, also called benthic macroinvertebrates, are ideal bioindicators of water quality. What the heck is a benthic macroinvertebrate? Benthic means “bottom of a body of water” and macroinvertebrate means you can see the insect with your eye and insect has no backbone. Benthic macroinvertebrates are used as bioindicators of water quality because they are sensitive to environmental changes and its presence or lack thereof determines clean water or polluted water. 

How can an aquatic insect like a dragonfly, which lives in the air, help us determine the quality of the water? Aquatic insect adults lay their eggs in the water. The eggs hatch and the immature form lives in the water, sometimes for years, before transforming into winged adults. The composition of the aquatic insects population (aka bioindicators) is used to ascertain water quality and reveal pollution impact. Much like plants are assigned conservation numbers, aquatic insects have a numeric designation, too. This designation is called a Tolerance score and ranges from 0-10 with zero being the least tolerant to pollution.

Peltodytes edentulus: Haliplidae, benthic macroinvertebrate, aquatic insects

Photo above: Peltodytes edetulus: Haliplidae (crawling water beetle) would have a tolerance score of 7.

Photo to the right: This Hydropsychidae (common net spinning caddisfly) nymph would have a tolerance score of 4.

Hydropsychidae , caddisfly

Aquatic insects are a great starting point to get a sense of the water quality.  To assess a body of water using water sampling would require repeated testing visits to the site. Aquatic insects are not highly mobile and reside in the body of water for long periods of time. This means monitoring and testing the water isn’t needed as often.

For example, you are monitoring the water quality of Stream A. You sample the water for aquatic insects in June 2015, June 2016 and June 2017 and find diverse insect populations – stoneflies, caddisflies, beetles, dragonflies – and then you sample 

again in June 2018 and only find beetles and dragonflies. Generally, stoneflies and caddisflies are less tolerant to pollution when compared to beetles and dragonflies, so you deduce that somehow the water was polluted over the past year and wiped out those populations. You determine, based on talking to people along the stream, that the paper mill accidentally polluted the water in November 2017.

Now, let’s imagine you are sampling Stream A using water samples and laboratory tests. You sample in January, March, June and September of 2015-2018. Based on the tests, you determine the water is clean. Because you didn’t sample in November or December of 2017, there were no indicators showing the stream was polluted.

Now that you know WHY aquatic insects are great indicators of water quality, you may be wondering what they look like and how you can identify them. Purdue Extension publishes a Bioindicators of Water Quality Guide that provides detailed instructions for using bioindicators to determine the water quality. Using this excellent guide, the insects and their conservation values (known as a Tolerance Value) can be identified and calculated to estimate the water quality. Remember, there are other factors that impact the ability of aquatic insects to live in water, such as temperature, sediment, etc. Generally, where possible, it’s always best to collect other water data such as pH, temperature, and dissolved oxygen.

Additionally, the University of Wisconsin Extension offers citizen science training for monitoring water quality using benthic macroinvertebrates. For more information on that, check out the Water Action Volunteers (WAV) site. These classes will teach you how to sample bodies of water using a combination of tests, including aquatic insects.

Entomology Today has an article about insects and mites and what they tell us about water quality





Confluence, our Water Ways in art


The Blanchardville Public Library’s summer theme is “Library’s Rock”  which makes the art exhibit depicting the hydrologic cycle perfect. Ten community artists came together (confluence) to create a beautiful and educational exhibit illustrating elements of the hydrologic cycle — our “water ways.”

Land use and water quality

All land uses have an effect on water flow and water quality; some are positive, some are negative. In healthy ecosystems receiving little human disturbance, most rainfall soaks into the soil rather than running off the ground, stream flows are fairly steady, and water quality is good. In built-up areas with pavement and buildings or agricultural areas where land is bare rainfall causes runoff and poorer water quality. In fact, land use practices are the most important water quality factor.

Runoff

Runoff is the water draining off the land; it is a natural and necessary part of the landscape. Water will follow the rules of gravity and move from a higher point to a lower point. If the water is filtered through native plants’ roots, it is important for recharging our groundwater. Negative runoff situations arise when the land becomes bare. When the water runs off hard surfaces and accumulates contaminants. In urban areas, these hard surfaces are pavement and concrete. In rural areas, solid surfaces are created by bare land. Other runoff occurs in cropped lands via drain tiles or land tilled too close to a stream. These negative situations are mitigated with good conservation farming practices, maintaining native wetlands, planting native plants along streams, and ensuring stormwater is filtered before it enters our waterways.

Photo to the right: As the streambanks build up with erosion, the water channels scoop out the sides causing the land to cave. Drone photo by Jim Hess

Livestock create a direct channel for water runoff and the resulting erosion, emptying topsoil and manure into the stream.

Erosion

Karst

Karst is a topography characterized by carbonate rock (limestone, dolomite, gypsum) that easily dissolves in rainwater forming cracks, sink holes and even large cave systems. Water quickly moves through the cracks in karst and enters the groundwater. These cracks act as direct conduits for pollutants to enter our groundwater, wells, springs, and streams. There are many regions in the world that have karst geology, southwestern Wisconsin is one of them so are areas of Mexico, Germany, and Florida to name a few.

Lafayette County is sensitive to water pollutants because of our karst landscape. Whenever material above the aquifer is permeable, pollutants can readily sink into groundwater supplies and our drinking water supplies. Good conservation practices can ease the statistic that croplands are responsible for 96% of nitrates leached into groundwater.

Karst landscape is particularly easy to see in the winter. Where the road cuts through the earth you can see the beautiful icicles! This is the water seeping through the rocks, then freezing.

Groundwater

Groundwater is the water found underground in the cracks and spaces in soil, sand, and rock. It is stored in and moves slowly through geologic formations called aquifers. Groundwater is a necessary resource; it supplies drinking water for 51% of the total U.S. population and 99% of the rural population.

Groundwater is also a limited resource. It’s difficult to think this is possible when we currently average 34.5” every year, but only about 25% of all rainfall in the U.S. becomes groundwater. In the past that average has fluctuated from 21-44”annually.

Agriculture is the largest consumer of freshwater resources. In the United States 64% of groundwater is drawn down to irrigate crops. 

Karst

Well Depth and Construction

The safety of the water in your home is dependent upon proper well location and construction.  The well casing needs to extend into a confined aquifer, which must be quite deep in our karst landscape. As you can see from these diagrams, if the casing doesn’t extend deep enough, your water could be receiving contaminants from one half to one mile away from your home. The well should be located so rainwater flows away from it. Rainwater can pick up harmful bacteria and chemicals on the land’s surface.

Surface Water

Surface water is freshwater you see on the top or surface of the landscape. It includes rivers, streams, creeks, lakes, and reservoirs; these are vitally important to our everyday life. The amount and location of surface water changes, varying in response to climate and human activities.

Surface water represents only about 3% of all water on Earth. Freshwater lakes account for a mere 0.29% of the Earth’s freshwater. Lake Baikal in Asia has 20% of all fresh surface water; another 20% is stored in the Great Lakes.  What a precious resource we have near us!!

Runoff and erosion have negative effects for surface water and eventually our groundwater. Excess nitrogen and phosphorus from runoff causes the algal blooms on our lakes, subsequent deaths of animals, and a loss of tourism dollars. Excess nitrogen in the streams where livestock drink can cause disease. Pesticides are dangerous too and are found in surface water 97% of the time near agricultural areas and 61% of the time in other landscapes.

Karst
Karst

This shows how surface water is filtered thru confined and unconfined aquifers.

In karst landscape, it’s imperative your well supplying your drinking water is deep enough to draw from a confine aquifer.

Hydrologic Cycle

The hydrologic cycle is the way water moves through our world. Water falls to the ground in the form of precipitation which either evaporates into the atmosphere, soaks into the ground, or runs off into surface waters like lakes, rivers and oceans. The water that infiltrates into the ground is either picked up by plants and organisms that transpire it into the air or it becomes groundwater. Groundwater is stored in an aquifer. Some water spends hundreds of years beneath the surface in deep aquifers; other groundwater is drawn back to the surface through manmade wells. Shallow aquifers feed into our surface water through seeps or springs in the ground. All the water that evaporates enters the atmosphere, becomes clouds and the cycle continues.

The main elements of the hydrologic cycle are:

  1. Evaporation
  2. Precipitation
  3. Transpiration
  4. Runoff
  5. Infiltration

 

Precipitation

Precipitation is water released from clouds. It is visible to us in the form of rain, freezing rain, sleet, snow, or hail and is the primary method for water in the air to be delivered to earth. Most precipitation falls as rain. In our area, we expect an average of 34.5” of rainfall each year. Clouds are small droplets of water too small to fall to the ground. They create a vapor that appears as white fluffy objects in the sky. How many types of clouds can you name?

Evaporation

Evaporation is the process by which water changes from a liquid to a gas or vapor. Studies have shown the oceans, seas, lakes, and rivers provide nearly 90% of the moisture in the atmosphere via evaporation, with the remaining 10 percent being contributed by plant transpiration. Once evaporated, a water molecule spends about 10 days in the air.

hydrologic cycle

Transpiration

Transpiration is how we describe plants’ breathing. Plants’ roots draw water and nutrients up into the stems and leaves; some of this water is returned to the air by transpiration. Transpiration rates vary widely depending on weather conditions. During dry periods, transpiration can contribute to the loss of moisture in the upper soil zone, which can have an effect on food-crop fields.

An acre of corn gives off about 3,000-4,000 gallons of water each day, and a large oak tree can transpire 40,000 gallons per year. Keeping the numerous oak savannas in Lafayette County healthy would be very good for us!!

Watershed

A watershed is the land where all the water drains off of it before entering into a particular water body. Watersheds can vary in size and are determined by topography (the peaks and valleys). In southwestern Wisconsin, we are located in the Upper Mississippi watershed. Everything we do on our land here travels to the Mississippi River and eventually reaches the Gulf of Mexico either from overland flow or through underground channels. Major watersheds like the Upper Mississippi are made up of many little watersheds. In fact each creek or pond has its own defined watershed.

What watershed do you live in?

Lafayette County, watersheds, conservation

A depiction of the watersheds in Lafayette County. Courtesy SWWRPC

Freshwater ecosystem

Freshwater ecosystems – such as wetlands, lakes and ponds, rivers, streams, and springs – are a critical part of the global water cycle. The water in these ecosystems is our surface waters; the ones our watershed catches and directs to our drinking water source.

Freshwater is also imperative to the survival of humans. We cannot stay alive without fresh water, yet we are facing a number of threats to our supply: 1) runoff from agricultural and urban areas, 2) draining of wetlands for agricultural uses and development, 3) overexploitation (i.e. high capacity wells) and pollution, and 4) invasion of exotic species.

All freshwater ultimately depends on the continued healthy functioning of organisms interacting in the aquatic environment. These organisms include fish, aquatic insects, amphibians, turtles, water fowl, and mammals such as otters and beavers. Freshwater is home to 40% of the world’s fish species. At present, more than 20% of these fish species are extinct or imperiled.

Fish living in our creeks and streams need clean, fresh water to survive. Lafayette County is home to one of the best smallmouth bass fishing places in the U.S. Yellowstone Lake is also a source of pride and brings in tourism. 

 

 

There are three basic types of freshwater ecosystems:

  • Lentic: slow moving water, including pools, ponds, and lakes.
  • Lotic: faster moving water, for example streams and rivers.
  • Wetlands: areas where the soil is saturated or inundated for at least part of the time.

What types of freshwater ecosystems do you have near where you live?

Insects are great indicators of safe, clean water because they are not highly mobile; they reside in the water for long periods of time. Insects offer a method of testing water less often and more accurately. Many of them are not tolerant of pollution and will die off when the waters become contaminated.

 

Freshwater ecosystem

Ducks and waterfowl are indicators of the environment. If they’re in trouble, we’ll soon be in trouble. They rely on wetland areas for food and nesting. The primary threat to waterfowl is the loss of wetland quality and function by agricultural activities that aren’t complying with conservation practices.

Freshwater ecosystem

Streambank Erosion

As topsoil erodes from higher elevation it collects along the streambanks which funnels water flow to continue cutting into and eroding the banks.

Where water is not slowed down it erodes the land, sending the topsoil to the streams where it builds up our stream bank sides or silts in our lakes. Our hilly Driftless Area landscape is conducive to erosion. Losing soil and nutrients to streams isn’t good for the farmers or the environment. Soil is precious and losing it hurts a farm’s productivity.

Streambanks historically were feathered out to allow water to ebb and flow. The steep-sided banks we often see in our streams are the topsoil from the ridge tops and hillsides that drained to the valley streams and built up along the edges. Once the streambanks are built up with this excess topsoil, water cannot gently flow but rather is blasted through the channels. This creates more and more erosion. With every turn of the stream the water grooves out more and more soil; eventually the hollowed out bank crumbles. This topsoil becomes nutrient-laden sediment, clogging our streams and lakes, and de-oxygenating the water. Insects and fish cannot thrive and the ecosystem begins to fail.

streambanks
streambanks

The stream in the photo on the left has been feathered to prevent the sides being “cut out” by the water flow. These steep banks of the right hand photo are caused by topsoil eroding down from higher ground and depositing along the streambanks. Then the water cuts into the banks.

Wetlands and Infiltration

The negative effects of runoff and erosion are prevented by the deep roots of native plants. Wetlands adjacent to streams are important and positive for healthy, safe, and clean water. The root systems of native plants reach deep into the soil, many of them stretching 12-20 feet downward. Nonnative plants do not have long roots. The root length allows more microbes to exist in the soil; these microbes are responsible for absorbing the additional nutrients from crops and livestock waste and pesticide runoff from urban areas.

Nonnative plants do not have the same nutrient-absorbing abilities as our natives. Their root structure is short; this means they are dependent on water supplied by precipitation. Native roots extend far into the soil where they can extract water in times of drought. This increases their importance as they can continue to filter surface water when other plants have died. This filtration service is the most significant method for purifying our drinking water.

wetlands
wetlands
wetlands
wetlands