The Mill River: An Outdoor Laboratory unit is designed to show students that science (with an emphasis on chemistry) is a tool that can be used to solve environmental problems. Students will learn to ask questions about the Mill River and then design experiments that will answer their questions.
The South Central Regional Water Authority has expressed an interest in seeing the results of our sampling: this should make students realize that their scientific work is taken seriously. Students should complete the unit with a feeling of accomplishment and empowerment.
Even though the unit is very specific — it deals with the Mill River in New Haven, Conn. — it can be used by other science teachers, with modifications, in their own local situations. One important consideration is that any teacher planning an ecological stud should have a good working relationship with local institutions. We will be able to borrow equipment from the Geology Department at Yale University and also from the Regional Water Authority. The advice of the scientists at these institutions will also be invaluable. I also hope to get graduate school volunteers from the Urban Resources Initiative at the Yale Forestry School to work with students in the field.
The unit is designed with modifications both for ninth grade Physical Science students as well as for 11-12th grade chemistry students. Obviously these classes will not be able to visit the Mill River site more than once or twice each marking period because of transportation and scheduling problems, but there will be an on-going group, namely the Science Club. which will be able to go out every Friday afternoon throughout the year, weather permitting. Science Club is a voluntary activity and attracts mostly younger. enthusiastic students who will provide the continuity that this project needs. Since there are fewer of them than in a class, they are also easier to transport and manage.
However, I feel that it is very important for all my students to have the benefit of sampling a “real” river. Before they ever set foot in the field though, they will need to develop a good background both theoretical and practical in the classroom. They will understand and maybe also retain the knowledge if it is developed slowly and from several different angles. including a lot of hands-on activities.
The unit will start with a section on water and its properties. The physical science classes will have several simple labs on surface tension and solubility. The more hands-on activities the better since many ninth graders have not had much experience working in the lab (although more middle schools seem to be emphasizing it now). They need to learn about lab techniques, equipment, and safety. They also need to think clearly about setting up experiments: formulating questions: stating a hypothesis, controlling their variables, and reporting their results.
One simple lab on surface tension is described in the classroom activities section of this unit. It is open-ended allowing students to try their own variations. It also requires graphing the results.
Chemistry students can approach the subject of water on a slightly higher plane than physical science students. They should learn the following: the fact that the bent shape of the water molecule gives it its polar nature; hydrogen bonding and surface tension; and also the solubility of polar and nonpolar substances in water.
Now it’s time to study a hypothetical river — a river with a mysterious fish kill. The American Chemical Society has published an excellent high school text called ChemCom. The first section of the book, which was written by a team of high school chemistry teachers, presents the students with a problem: a massive fish kill has been discovered in the mythical Snake River near the town of Riverwood. Students read “newspaper articles” (they look genuine) about the fish kill and the ensuing anxiety of the townspeople who are dependent on the river for their drinking water.
Interspersed with the newspaper articles in the book are lots of labs and activities for the students so that they can help solve the mystery of the fish kill. This year I modified this unit for the ninth grade Physical Science classes who were quite enthusiastic about solving the problem. I really think that more classroom units should be presented as mysteries. because students love learning in this way.
Among other topics covered in the unit were personal water use, water purification, testing for ions, pH, and dissolved gases. (Although I didn’t use the whole Snake River unit with the chemistry classes, we did do some of the labs.) Finally, the cause of the fish kill was revealed (excess air in the water under the dam had caused air bubbles in the fish gills).
Students then had a town meeting to decide who was responsible for the fish kill and who should pay for the drinking water that Riverwood had to import. They played the roles of the various interest groups in the town such as officials of the power plant at the dam, motel owners, and the Chamber of Commerce, as well as engineers and scientists. The presentations were quite passionate (everyone blamed someone else), but there were also quite a few dispassionate speeches based on the evidence.
At this point my science classes will be ready to visit the Whitney Water Center at the Lake Whitney dam (run by the South Central Regional Water Authority) and learn to sample the waters of the nonmythical Mill River. Education specialists at the Center show students how to test for pH, temperature, dissolved oxygen, turbidity, and alkalinity, using various chemical kits and instruments. For most students this will be their first opportunity to work in a real river: it should be an exciting experience for them. They will record all data on the Whitney Water Center data sheets and we will then discuss it.
The Whitney Water Center visit is an excellent introduction to the unit on the Mill River. Students have now seen a small part of the river ( at the dam) and have done a little water sampling. What is needed now is to have them sort out facts from inferences. They will again form small groups and fill out a sheet labeled THE MILL RIVER that has three headings: FACTS, INFERENCES, and QUESTIONS WE WOULD LIKE TO SOLVE. Then each group will report to the rest of the class who will critique them. A fact might be. “The Mill River is shallow at the dam.” A possible inference is. “The Mill River is polluted.” It is important for students to learn to differentiate between facts and inferences.
Having students think about question they would like to solve helps focus them and directs their thinking. After studying the Snake River unit in ChemCom they will probably want to know if the Mill River fish are healthy and whether there is too much air in the water coming over the dam. They might also want to know what ions are dissolved in the river and whether the water is polluted.
Before we take another Mill River field trip students should learn some map skills. There will be a class set of the U.S. Geological Survey New Haven Quadrangle maps available. After they have learned some basic facts about symbols, scale, and topography, they will locate their homes, the Coop High School, and the downtown Green. Now we will look at the Harbor: how deep is it? Which rivers empty into it?
Then students will focus on the Mill River on the map. Between the Harbor and the dam. how long is it in miles? Which roads cross it? How high are the tides and would salt water move into the river at high tide? Are there marshes? What are meanders? Finally they will make a sketch of the river between the dam and the State Street tide gates, labeling all the parts. The art teacher at the Coop High School will show them how to enlarge a drawing using graph paper. Students also need to know the difference between QUALITATIVE and QUANTITATIVE experiments at this point. Up to now when testing for dissolved ions ( such as chloride and iron) in the lab we have only stated whether they were present or absent — in other words, the results were qualitative. However when we test in the field we will be using instruments which measure results in parts per million (ppm). In water solutions this is the same as milligrams per liter (mg/L). In order to understand the magnitude of these numbers, I will do a dilution series beforehand using food color on the overhead projector, showing that even though the eve can’t detect one ppm. the chemical is present.
Which factors are we going to measure in the Mill River? The following would seem to be the most pertinent (and are also the easiest to detect: dissolved oxygen, temperature, pH, and conductivity. The Geology Department at Yale University will lend us a dissolved oxygen meter; a conductivity meter will come from the Regional Water Authority.
Dissolved oxygen (DO) is probably the most important parameter in measuring the health of river waters. Most fish need a minimum of 4 to 5 ppm of dissolved oxygen to survive, while some fish like trout need about 9 ppm. There is usually more oxygen in a swiftly moving stream than a slowly moving stream because the water mixes with the air. The Mill River below the dam flows rapidly over the cobbles. and, as expected, there is more DO than farther south where it slows down.
So that they will be comfortable doing the DO testing in the field, students will first need to learn how to sample dissolved oxygen in different waters in the lab using both chemical tests and an oxygen meter. Does fresh tap water contain more DO than boiled water? Do the chemical tests correlate with the DO meter results? They should also understand how a dissolved oxygen meter works and how to take care of it (keeping the probe moist).
The dissolved oxygen meter also measures the water temperature in degrees Celsius. Students can then figure out the percent saturation of oxygen if they know the temperature and the DO in ppm. 90 percent dissolved oxygen saturation or better means that the stream is probably healthy. Since students are much more familiar with the Fahrenheit scale than the Celsius scale we will always take the Fahrenheit reading first and let them estimate what it would be in Celsius.
The Snake River unit allowed students to stud the pH of various substances, but this is a good time to go more deeply into the subject. Students should understand that the scale is logarithmic so that each number on the scale represents a ten-fold change in the hydrogen ion concentration. For instance, pH 5 is 10 times more acid than pH 6 and it’s 100 times more acid than pH 7. Normal rain has a pH of 5.0— 5.6 but the average reading for acid rain in the northeastern United States is about 4.3 (Mitchell and Stapp, 1992).
The pH in streams can vary greatly depending on several factors including the bedrock in the watershed. (A limestone bedrock can buffer the acid rain, making it less acid) But the Mill River runs through primarily sandstone and traprock which have less buffering capacity. Will we find that the pH of the river is toward the acid side? Fish and invertebrates have quite specific pH requirements but any river water that has a pH more than 9 or less than 4 will not have a lot of living things.
Students will have already learned to use Universal Indicator paper to test substances, but for the Mill River we will use a portable pH meter which they will quickly discover is much more accurate.
A conductivity meter measures the total amount of dissolved ions in water. The more ions, the greater the flow of electricity and the higher the reading. Distilled water has no dissolved ions and therefore the meter will register 0 ppm because there is no flow of electricity. Seawater, on the other hand, contains a high percent of dissolved sodium chloride as well as other ions so that the conductivity meter readings will be very high. The average salinity of ocean water is about 35 parts per thousand (or 35.000 parts per million).
Long Island Sound is an estuary with many rivers emptying into it: therefore the salinity is not as high as in the open sea. We will first test the conductivity of the New Haven Harbor waters and then move on to the Mill River which is a tidal stream whose lower reaches are flooded twice a day by waters of the Sound. The tide gates at the intersection of State Street and I-91 keep much of the saline water out but some still flows north into the river by East Rock Park. How far does it go? To the Orange Street bridge? Or farther? Students should be able to make predictions based on the tides before they use the conductivity meter at various locations.
Students should also learn to ask themselves about the methodology of sampling: is it better to sample water on the banks of the river or from a bridge? How many samples should we take in each location?
The final question to be asked is “Is the Mill River a healthy river or is it polluted?” To answer this we will look at the animals that live in the water. The absence or presence of these animals, called macroinvertebrates, indicates the environmental quality of any stream. The Izaak Walton League of America, which is dedicated to sports fishing and the improvement of stream quality, has started a program called Save Our Streams (SOS). This program shows volunteers how to survey the biota in a stream in order to rate the water quality. For instance, if stonefly and caddisfly larvae are plentiful the stream is probably healthy: on the other hand, worms and midge larvae indicate polluted conditions.
The students will get to use kick seine nets in the river: they will dislodge bottom dwellers for a distance of three feet upstream. Then we will spread the net on the bank and, using magnifying glasses and tweezers, we will sort the “critters” into groups, using the SOS identification card. This procedure will be repeated at different points along the river.
All this data — dissolved oxygen, temperature, pH, conductivity, and invertebrate populations — needs to be combined into one report. Students can work in groups on this. They should also write down their recommendations and further questions that they have. We will then present the reports to the Regional Water Authority