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 LESSON 2 |
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LESSON 2 |
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Streamwatch
Lesson 2 of the Water Resources Module concentrates on surface water bodies, and in particular, streams. A stream is any flowing water body. By looking at the physical, chemical, and biological aspects of water bodies, it is relatively easy to determine their health, assuming you know what to look for. Streams in the local area are fascinating, readily-accessible highways of biodiversity that interconnect many, if not all, living organisms in our environment. Watersheds, mini-ecosystems themselves, are determined by the topography of the earth and connect to each other via these highways of biodiversity.
This stream study is aimed at giving your students the ability to monitor the health of a stream. This important work does not need to be performed by state conservation employees -- in fact, there are too many streams for them alone to monitor. Stream monitoring can be done by any willing adult, or even conscientious students.
Data about a stream can be useful if properly recorded. Therefore, the activities in this section are organized around the data sheets used for Streamwatch. While learning to complete the data sheets, students also learn about critical thinking, measurement, and interactions in the environment, which helps meet the state learning standards. Student data are collected and shared with other schools. Not only can other teachers use your data for comparative study, the data are also available to NYSDEC through our participation in Hudson Basin River Watch. Data will be more useful if you follow HBRW monitoring protocols. (Contact The Catskill Center for more details.)
Weather Conditions
Temperature. Data about the surroundings help put other monitoring data in context. Use an air thermometer to take the temperature. Use the Celsius scale exclusively. We believe students will never grow accustomed to Celsius if they must always convert it to Fahrenheit before they can understand it. By feeling cold water at 10°C and warm air at 20°C, students will learn to relate Celsius temperatures to their own tactile experience as they have done with Fahrenheit.
If your thermometer measures only Fahrenheit, be sure to convert it to Celsius. Here are the conversion formulae, though Fahrenheit should not be used in these activities.
where 5/90.55556 and 9/5=1.8
For example, if your temperature measures 42°F, then subtract 32 and multiply by 5/9 to get °C:
45°F - 32 × 5/9 = 7°C
or if your Celsius thermometer says 7°C, then multiply that by 9/5 and add 32 to get °F:
7°C × 9/5 + 32 = 45°F
Cloud Cover. Determine the percentage of the sky that is covered by clouds. If the sky is either completely cloudy or completely clear, it is easy to tell the percent cloud cover. If there is some blue sky and some clouds, it is more difficult. It can be done by visualizing the sky divided into halves, then quarters, and so on until you can tell what percentage of the sky is clouds.
Precipitation. Depending on how far you are from the headwaters, it may take hours or days for rain to make it into your stream. Therefore, recording past weather conditions is as important as recording whether it is raining during your field trip. To keep things simple, the data sheet asks only whether or not it has rained or snowed in the last 24 hours. Students can make additional notes about the amount or timing of precipitation (e.g., "snowed 10 cm overnight").
Physical Data
Water Temperature. Hold the thermometer at least four inches below the surface of the water for two minutes. Measure in the deep part of the stream, not in shallow areas along the bank, which can be warmed by the sun. Keep the thermometer in the water while reading it, and do not touch the bulb with your warm hands. Note whether the temperature was taken in the shade or in the sunlight and try to be consistent each time.
Depth and Width. Depth and width of the stream, as described here, refer to specific points along the stream and therefore can only be used to examine changes in the stream over time. Depth and width cannot be used in calculating the amount of water flowing in the stream; for that, one must use the full "Total Flow" procedure described in the appended materials. The depth and width measurements are useful for seeing how much the water level rises or falls. Depth and width should always be measured in the same place. Measure the depth at the deepest part of the channel if this can be done safely. Record the width in meters using a measuring tape or a cord marked at one-meter intervals stretched across the stream.
Turbidity and Color. Water color is a separate variable from turbidity (cloudiness), and this should be made "clear" to students. Some liquids, like apple juice or tea, are brown but not turbid. You can see through them easily. Other liquids, like milk, are turbid but not colored. A muddy stream is both turbid and colored (brown). Floating algae can cause water to be turbid and green.
In the Catskills, streams are usually clear and nearly colorless, but storms or erosion can make streams muddy. This is a problem for aquatic life, since it can clog and irritate gills. Sediment particles can also harbor harmful microbes, and when sediment settles in a reservoir it can decrease the capacity of the reservoir.
Judge the turbidity by looking at the bottom of the stream. If rocks half a meter below the surface are not visible, then the stream is "slightly turbid". If rocks 10 centimeters below the surface are not visible, the stream is "very turbid".
Chemical Data
Dissolved oxygen (DO) is required for many fish and invertebrates to survive under water, though some are adapted for low-oxygen environments and can breathe air from the surface. Oxygen dissolves best in cold water, so cold water (resulting from shade along the stream) provides the best habitat for trout.
Dissolved oxygen is most easily measured using a snap-test kit. Follow kit instructions to obtain a measurement. It is difficult to use the comparator accurately, and a consensus among the teacher and several students will help insure accuracy. Other test kits use a titration method; they are more precise but harder to use. The sample can be chemically "fixed" in the field, and the procedure can be completed later, in the classroom. These test kits also pose a greater safety concern, as described in kit instructions. A healthy stream has 9 or more parts per million DO.
Percent oxygen saturation, although it does not in itself determine fish survival, is a good indicator of oxygen depletion because it compensates for temperature. Percent saturation describes how much oxygen is in the water compared to how much it could hold at the present water temperature. Use the chart to find percent oxygen saturation. First find the dissolved oxygen on the bottom scale. Then find the water temperature on the top scale. Draw a line from the oxygen to the temperature. The point where that line crosses the percent saturation scale shows the oxygen saturation of your sample. Saturation should be above 80%.
Acidity, measured in pH units, can be increased by acid rain or certain ecosystems like bogs or hemlock stands. Acidity can kill fish and invertebrates in the stream, and in lesser amounts it may prevent eggs from hatching or interfere with fish gill functions. It can also kill trees and affect other terrestrial organisms. Students should understand that pH ranges from 0 to 14. A pH of 7 is neutral, higher numbers are alkaline (also called basic), and lower numbers are acidic. The lower the number, the more acidic the water is! Most aquatic animals can tolerate a range from 6.5 to 8.
The pH of a water sample can be tested using pH paper or a chemical test kit. The test paper is the easier but less accurate method. Test kits, almost as easy, involve placing a few drops of an indicator solution into a sample vial and then judging the color using a comparator.
Biological Data
There are two methods we use for collecting macroinvertebrates (non-microscopic animals without backbones) from the stream. Most of the species we collect are benthic, meaning they live on the bottom of the stream, on or under rocks. They are abundant in many streams, a fact which surprises those who have never looked for the hidden and camouflaged creatures. Because of their abundance, students can catch quite a few by picking up rocks and searching the undersides of those rocks for invertebrates. They can be removed gently by using fingers or a soft foam brush. (Caution children about the risk of injury to carelessly handled organisms.) The invertebrates are then transferred to plastic containers full of stream water.
In the second collection method, a net is used. Since most of the invertebrates in our streams are benthic, they must be flushed from their hiding places before they can be caught. This is done by kicking the rocks so that they are overturned. Some of the insects will then be floating in the current, which sweeps them quickly into the net, held a few feet downstream from the kick-sampling area. We use two types of net, a D-net (D-shaped or rectangular frame at the end of a pole) and a seine net (stretched between two poles, each held by a different student). Both nets have a flat bottom-edge which fits against the stream bed. The D-net is best suited if there is a lot of current, since it is easier to control, but it is slightly harder to remove insects from.
On the data sheet, students should list the creatures by type, such as mayflies, stoneflies, caddisflies, aquatic worms, etc. In most cases, these broad categories correspond to the taxonomic order, as listed on the appended key from Izaak Walton League. Students do not have to identify individual families or species, but a more advanced key for family-level identification is available from The Catskill Center, if desired.
To ensure an accurate count, the group should avoid counting any insect twice. We divide the class into three small groups, each with its own data sheet, and we combine their results at the end. If the whole class is working together, have one student count all of the insects. The other students bring their insects to that person to be counted and then release them so they can't be counted again.
Use the Screening Criteria for Non-Impacted Streams to assess water quality based on number and type of invertebrates found. There are other, more reliable, methods which take into account more invertebrate groups, finer levels of classification, and the number of individuals within groups found. You may wish to try the Biotic Index Score if you teach middle school students. Our version of the Biotic Index Score was modified from the original. The original required a random sample of 100 macroinvertebrates, but our system will work with any number. Note however that the accuracy is somewhat compromised if you use fewer than 100 specimens.