Science Question

Environmental impact assessment of Cedar Creek, Trexler Park, Lehigh County,Allentown, PA using benthic macroinvertebrates
Introduction
Freshwater ecosystems are among the most degraded ecosystems on Earth. The Great
Lakes, the Black Sea, and the Danube and Yangtze rivers are examples of major
systems that have been severely affected by human impact. Many factors contribute to
the degradation of freshwater systems, including overfishing, direct alterations of the
system, such as dams, and pollution from surrounding human altered landscapes.
Unfortunately, major systems are not the only systems that have been impacted. The
health of small, local systems are also of concern. In this study, we will focus on a small,
local stream, Cedar Creek, to determine whether an artificial !duck pond” that the
creek runs through affects the health (i.e., water quality) of the creek. To do this, we will
conduct a survey of the diversity of benthic macroinvertebrates in the creek.
Methods
This study will take place over three weeks. We will do our fieldwork in the first week.
Identification of benthic macroinvertebrates will take place in the second week. And
data analysis will be done in the third week.
We will conduct our sampling upstream of the duck pond and and downstream of the
duck. Each lab section will survey one site.
WEEK 1
Benthic Macroinvertebrate Survey
Before starting the survey, you will discuss and develop the hypothesis and predictions
that we will be testing.
In order to get an unbiased assessment of benthic macroinvertebrate diversity, we will
sample along a 20m transect tape placed in the middle of the stream from upstream to
downstream. Do this by having one person hold onto the end of the tape (0m mark)
while another person pulls the tape downstream while holding onto the handle,
stopping just beyond the 20m mark. Put the handle on the bottom of the steam and
use rocks if necessary to keep it in place. Make sure the tape is stretched out and is
sitting on the bottom. Use rocks if needed to keep the tape down.
We will sample along the transect every 5m starting at the 0m mark, alternating sides
as you move along the transect. Start on the left side (as you face downstream) of the
transect at the 0m mark.
To make sure that every participates in the project, the class will be broken up into
groups and each group will sample at least one site along the transect.
Follow the following steps to collect samples at each location.
1. Place the kick net on the bottom of the stream with the opening of the net facing
upstream (so that water flows into the net) and manually disturb the substrate in
front of the net by “kicking” so that you scrape off sediment and organisms off the
sediment in a 1m2 area in front of the net. Kick for 30 seconds. Lift the net out of
the water using a slight forward motion to make sure that you do not lose any of the
sample.
2. Wash down the sides of the net to collect the material at the end of the net by
repeatedly dipping the net a few times in the creek while shaking the net with your
hand.
3. On land, add a few centimeters stream water into deep-sided tray. Transfer the
material from the net into the bucket by carefully turning the net inside out and
dipping it into a the water in the bucket. Make sure to agitate the bottom of the net
to dislodge all of the material from the net
4. If any large objects were capture in the net (e.g., sticks, rocks), wash them in the
bucket and discard.
5. Gently mix up the contents of the tray (including and sediment) using your hand in
stirring motion and carefully pour the contents of the bucket through the mesh
sieve. Pour a little at a time and mixed up the contents of the bucket between
pours. We are not collecting the water so you can drain the water onto the ground
or into the stream.
6. If there is sediment in the tray, be careful not to pour the sediment into the sieve.
Stop pouring when you cannot pour anymore water without adding the sediment to
the sieve.
7. Place the sieve upside down into the tray and rinse the sieve using a squirt bottle,
using as little water as possible to minimize dilution of the alcohol that will be used
to preserve the samples. Gently pour the contents of the tray into a 1 L wide-neck,
labeled sample-bottle. Make sure you use the correct bottle (Upstream,
Downstream). All samples from the same location will be poured into the same
bottle.
8. Lastly, fill the bottle 3/4 of the way with the 95% ETOH. Cap the bottle and gently
invert the bottle several times to mix the contents with the ETOH. Then fill the
bottle completely with ETOH and cap. The bottle will then be brought to the lab for
identification in Week 2.
WEEK 2
Identification of Benthic Macroinvertebrates
You will work in groups to identify and count the benthic macroinvertebrates collected
from the streams.
1. Choose a sample bottle and gently swirl it to suspend the contents. Be sure to note
which location (upstream, downstream). Using a turkey baster, remove enough of
the contents to cover the bottom of the sampling tray. Add an equal amount of
water to suspend the organisms and to dilute the ETOH.
2. Fill each compartment in the ice cube tray halfway with water. Sort organisms by
morphology by placing organisms that look alike together in the same
compartment of a plastic ice cube tray. Use a forceps to move the organisms to the
ice cube tray.
3. When you have sorted all the organisms in your sampling tray, rinse out the tray
with tap water and start a new sample (from the same bottle)
4. Continue this until all organisms from that bottle have been sorted by the class.
Add water to the ice cube tray as needed to keep the organisms wet.
5. Use the identification guide to identify the benthic macroinvertebrates the lowest
taxonomic rank on the identification guide and record the number of individuals of
each taxon in your notebook (e.g., the number of individuals of the Order
Ephemeroptera; Appendix I). Alternatively, you could ID the organisms as you
see them and then sort them.
WEEK 3
Data Analysis
Pollution Tolerance Index
Benthic macroinvertebrates can be categorized by how tolerant they are to pollution
(Table 1). Category 1 organisms are pollution intolerant organisms. That is, they cannot
survive in any water that is even minimally polluted. Category 2 organisms are
intermediate in tolerance. They can survive in a wide range of water quality. Category 3
organisms are pollution tolerant. They can survive in fairly polluted water, as well as
clean water.
To calculate the Pollution Tolerance Index (PTI), you need to determine the taxa
richness (not abundance) of each category and then multiply each by appropriate index
value. For example, if there are six Category 1 taxa (pollution intolerant), two Category
2 taxa (intermediate tolerance), and eight Category 3 taxa (pollution tolerant), the PTI =
(6*3)+(2*2)+(8*1)=30. The PTI is then compared to Table 6 to determine water quality.
Table 1. Benthic macroinvertebrates categorized by pollution tolerance used to calculate
Pollution Tolerance Index. The index values for each category is in parentheses.
Category 1: Pollution
intolerant (3)
Category 2: Intermediate
tolerance (2)
Category 3: Pollution tolerant
(1)
Order Ephemeroptera
(mayflies)
Order Odonata (dragonflies,
damselflies)
Family Chironomidae (nonbiting midge)
Order Plecoptera
(stoneflies)
Order Isopoda (sowbug)
Family Simuliidae (black fly)
Order Trichoptera
(caddisflies)
Order Amphipoda (scuds)
Class Turbellaria (flatworms)
Order Megaloptera
(dobsonflies, alderflies)
Family Tipulidae (crane flye)
Class Hirudinea (leeches)
Order Coleoptera (beetles)
Class Bivalivia (clams, mussels)
Class Oligochaeta (aquatic
worms)
Class Gastropoda (righthanded snails)
Order Decapoda (crayfish)
Class Gastropoda (left-handed
lung snails)
Order Diptera, Family
Athericidae (Watersnipe fly)
Family Hydropsychidae (Netspinning caddisflies )
Family Psephenidae (Water
pennies)
Order Hemiptera (true bugs)
Class Collembola (springtails)
Order Trombidiformes (water
mites)
As you can see, our example has excellent water quality. Remember, the PTI is based
on the number of different kinds (taxa) of macroinvertebrates collected, rather than the
number of individuals collected.
Table 3. Pollution Tolerance
Index water quality values.
PTI
Quality
>22
Excellent
17-21
Good
11-16
Fair