Measuring Stream Quality via Bugs!

Introduction:

Streams and rivers are vital components of our ecosystems, serving as habitats for diverse species, sources of drinking water, and recreational areas for communities. However, these freshwater systems are increasingly threatened by multiple pollution points, habitat destruction & modification, and climate change. We have already observed the effects of habitat modification on a stream ecosystem during the species diversity lab. Regarding pollution, the sources can be classified into three categories:

• Inorganic toxins: These can include acids, solid waste (i.e., garbage), heavy metals (i.e., lead, mercury, cadmium, copper, etc.) & other elements such as sulfur & chlorine. This type of pollution is normally the sole reason an aquatic community will have a total lack of insects.
• Organic toxins: These can include agricultural fertilizers, livestock & human waste. Typically, organic toxins decrease the amount of free oxygen dissolved in water. This will have the effect of allowing life forms such as various worms, bacteria & other harmful microorganisms, that can survive in low-oxygen environments, to take over the aquatic ecosystem.
• Physical: Examples of physical stressors include sedimentation (i.e., can make a river muddy) & heat. Excess sediment such as mud/clay, silt & sand leads to lowered visibility, reduced feeding opportunities, & destroy streambed habitats that provide shelter & places for fish to lay eggs. This type of pollution can occur naturally (i.e., storms eroding more land sediment than normal) or anthropogenically (i.e., land habitat manipulation). A warmer river decreases the dissolved oxygen content of water.

Typically, an array of quantitative techniques is used to obtain measurements of pollutant levels in streams. In this lab, you will gain experience in using qualitative observations to assess the condition of a local stream by catching and observing bugs!

Materials:

• Forceps
• White collection pan
• Mesh window screen
• Magnifying glass
• Insect identification book (optional)

Hypothesis:

Once you arrive at the field site, compose a hypothesis regarding your prediction of stream quality solely based on visual area observations before doing any sampling.

Procedure:

1. Organize into groups & head to the field site as designated by your instructor.
2. Have one group member hold the screen vertically into the stream such that water can pass through it (while standing on the dry banks). Do not submerge the entire screen. Do your best to ensure that excess debris (such as sticks and leaves) are not flowing in the chosen area. Also, do your best to ensure the bottom of the screen is as flat as possible on the stream bed.
3. Have another group member measure approximately one meter upstream from the screen. In this area, agitate the bottom of the stream (a stick or meter stick can be good for this) for around thirty seconds. After the agitation has stopped, wait approximately two minutes while the water flow carries debris towards the screen.
4. After two minutes, lift the screen out of the stream & place it on a flat, nearby surface.
5. Use the forceps to pluck all collected material from the screen into the white collection pan. Make sure there’s some standing water in the tray to allow any collected insects to survive.
6. Use the magnifying glass to observe any organisms that are actively moving. Record the type & quantity of these in the data table below. Like with the Species Diversity lab, you don’t have to know the exact species name. Recording basic traits such as color, number of legs, any wings, relative size, etc. is sufficient. Expect to observe mostly small insects (multiple body segments & six legs) although worms & snails can also be had.
7. Lastly, walk along a short stretch of the stream & record the presence (or absence) of any fish in the area.
8. Once the data table is completed, now the stream quality can be assessed. The categories of stream quality are summarized below.

Stream Quality Categories:

Notes:

Good – A high population & variety of organisms indicates consistent high-quality water with minimal to no history of contamination.

Fair – Some species require good quality water. A somewhat lower variety of organisms can suggest a past water quality issue (& that the stream could be in a recovery phase).

Poor – The low level & variety of organisms suggest only the most resistant/tolerant species can live in the water.

Dead – If the water is clear, but no organisms seem to be present, this suggests an inorganic toxin issue.

Data Table

Post-Lab Questions:

1. What do the collected organisms indicate about the quality of the studied stream?

2. Would you agree with the results from question #1 just by looking at the stream? In other words, would you accept or reject your initial hypothesis from the end of the first page?

3. List three actions that take place on land that can affect the quality of the studied stream.

4. Given the surrounding area of the stream studied and how it’s used, name two potential pollution control techniques to improve stream quality.

5. What are three potential sources of error during this experiment that could potentially give misleading results about stream quality?