By Dana Krejcarek and Jessie Good
In this unit students will be introduced to the GLOBE Program and work specifically with the Hydrology unit. GLOBE (Global Learning and Observations to Benefit the Environment) is an international, environmental program where students, teachers, and scientists are able to share information. Students will gain an understanding of the importance of water quality through various hands-on and inquiry-based activities. They will learn how to perform the water quality tests and be able to collect, analyze, and compare their data to the data from other schools. The data will be used to develop a model that can be used as a teaching tool for students to share their findings with their classmates. The presentation will be used as an alternative assessment using a given rubric. Both the modeling project and the presentation will help students understand the connection of water quality to their lives.
- Water chemistry is an important aspect of habitat requirements
- Temperature can affect other water chemistry factors
- Water chemistry affects species diversity
- Instruments can enhance what your senses tell you about what is in water
- Data are used to pose and answer questions
- Graphs and maps are valuable tools for visualizing data
- Accuracy and precision are important when taking measurements
- The soil stores water, and its water content is related to the growth of vegetation
- Where rainfall goes depends on your site characteristics
- Higher temperatures and longer periods of sunshine increase evapotranspiration
- Water flows can change over time
- Water balance can be modeled using temperature, precipitation, and latitude data
- Making observations
- Applying field sampling techniques
- Calibrating scientific equipment
- Following directions in methods and test kits
- Recording and reporting data accurately
- Reading a scale
- Communicating orally
- Communicating in writing
- Asking Questions
- Forming and testing hypotheses
- Designing experiments, tools, and models
- Using water quality measurement equipment
- Using tools to enhance the senses
- Creating and reading graphs
- Calculating averages
- Making comparisons over space and time
- Analyzing data for trends and differences
- Using the GLOBE database
Student and Teacher Background Information:
We do not just drink water; we are water. Water constitutes 50 to 90 percent of the weight of all living organisms. It is one of the most abundant and important substances on the Earth. Water sustains plant and animal life, plays a key role in the formation of weather, helps to shape the surface of the planet through erosion and other processes, and covers roughly 70% of the Earth's surface. Water continually circulates between the Earth's surface and its atmosphere in what is called the hydrologic cycle. The hydrologic or water cycle, is one of the basic processes in nature. Responding to heat from the sun and other influences, water from the oceans, rivers, lakes, soils and vegetation evaporates into the air and becomes water vapor. The water vapor rises into the atmosphere, cools, and turns into liquid water or ice, forming clouds. When the water droplets or ice crystals get large enough, they fall back to the surface as rain or snow. Once on the ground, water does one of three things; some of it filters into the soil and is either absorbed by plants or percolates downward to groundwater reservoirs. Some runs off into streams and rivers and eventually into the oceans. Some evaporates.
The water in a lake, the snow on a mountain, the humid air or the drop of morning dew are all part of the same system. The total annual water loss from the surface of the planet equals the Earth's total annual precipitation. Changing any part of the system, such as the amount of vegetation in a region or land uses, affects the rest of the system.
Despite its abundance, we cannot use most of Earth's water. If we represent the Earth's water as 100 liters, 97 of them would be seawater. Most of the remaining three would be ice. Only about 3 mL out of the whole 100 liters would be water that we can consume; that water is pumped from the ground or taken from fresh water rivers and lakes.
Water participates in many important chemical reactions, and most substances are soluble in water. Due to its effectiveness as a solvent, truly pure water rarely occurs in nature. Water carries many natural and human-introduced impurities as it travels through the hydrologic cycle. These impurities give each water its distinctive chemical makeup, or quality. Rain and snow capture small dust particles or aerosols from the air, and sunlight causes emissions from the burning of gasoline and other fossil fuels to react with water to form sulfuric and nitric acids. These pollutants return to Earth as acid rain or snow. The acids in the water slowly dissolve rocks, placing dissolved solids in water. Small but visible pieces of the rocks and soils also enter the water, resulting in suspended solids and making some waters turbid. When water percolates into the ground, it is in very close contact with rocks and more minerals dissolve into the water. These impurities dissolved or suspended in water determine its quality.
In this investigation, students will measure the following seven key indicators of water quality:
Light, essential for growth of green plants, travels further in clear water than in either turbid water that contains suspended solids or colored water. Two methods that are commonly used to measure the transparency, or degree to which light penetrates into water, are the Secchi disk and turbidity tube. Secchi disk transparency was first measured in 1865 by Father Pietro Angelo Secchi, scientific advisor to the Pope. This simple and widely used measurement is the depth at which a 20-cm black and white disk lowered into water just disappears from view, and reappears again when raised. An alternate measure of transparency is obtained by pouring water into a tube with a pattern similar to that of a Secchi disk on the bottom and noting the depth of water in the tube when the pattern just disappears from view. The Secchi disk is used in deeper, still waters; the turbidity tube can be used with either still or flowing waters and can be used to measure shallow water sites or the surface layer of deep water sites.
Sunlight provides the energy for photosynthesis, the process by which plants grow by taking up carbon, nitrogen, phosphorus and other nutrients, and give off oxygen. Thus penetration of sunlight into a water body determines the depth to which algae and other plants can grow, and the relative amount of growth.
Transparency decreases as color, suspended sediments, or algal abundance increases. Water is colored by the presence and action of some bacteria, phytoplankton, and other organisms, by chemicals leached from soil, and by decaying plant matter. Therefore, the amount of plant nutrients coming into a body of water from sources such as sewage treatment plants, septic tanks, fertilizer run-off, and wind and water born plant debris affects transparency. Suspended sediments often come from sources such as agriculture, construction, storm runoff and resuspension of bottom sediments.
Most natural waters have transparency ranging from 1 meter to a few meters. A low value, under 1 meter, would be expected in a highly productive body of water. A low value can be due as well to a high concentration of suspended solids. Extremely clear, unproductive lakes or coastal waters can have transparency up to 30 - 40 m as can the areas around coral reefs.
2. Water Temperature
Water temperature is largely determined by the amount of solar energy absorbed by the water and the surrounding soil and air. More solar heating leads to higher water temperatures. Water that has been used in manufacturing and discharged into a water body may also increase water temperature. Water evaporating from the surface can lower the temperature of the water but only for a very thin layer at the surface. We need to measure water temperature to understand the patterns of change over the year because the temperature of a water body strongly influences the amount and diversity of its aquatic life. Lakes that are relatively cold and have little plant life in winter bloom in the spring and summer when water temperatures rise and the nutrient-rich bottom waters mix with the upper waters. One also finds periods of mixing in the fall. Because of this mixing and the warmer water temperatures, the spring overturn is followed by a period of rapid growth of microscopic aquatic plants and animals. Many fish and other aquatic animals also spawn at this time of year when the temperatures rise and food is abundant. Shallow lakes are an exception to this cycle, as they mix throughout the year. One concern is that warm water can be fatal for sensitive species, such as trout or salmon, which require cold, oxygen-rich conditions.
3. Dissolved Oxygen
Water is a molecule made of two hydrogen atoms and one oxygen atom - hence, H2O. However, mixed in with the water molecules of any body of water are molecules of oxygen gas (O2) that have dissolved in the water. Dissolved oxygen is a natural impurity in water. Aquatic animals, such as fish and the zooplankton they feed on, do not breathe the oxygen in water molecules; they breathe the oxygen molecules dissolved throughout the water. Without sufficient levels of dissolved oxygen in the water, aquatic life suffocates. Dissolved oxygen levels below 3 mg/L are stressful to most aquatic organisms.
In the atmosphere, roughly one out of every five molecules is oxygen; in water, about one to ten molecules in every million molecules are oxygen. Vigorous mixing of air and water, such as in turbulent streams, increases the amount of oxygen dissolved in water. So does photosynthesis by aquatic plants. Oxygen is consumed by fish, zooplankton, and the bacteria that decompose organic materials. Organic materials such as dead plant and animal matter enter streams naturally in water draining from forests and grass or crop lands. Another source of organic matter is outfalls from sewage treatment plants. Whatever the source, we tend to find low dissolved oxygen levels, well under half the saturated value, in slow-moving streams near sources of organic matter. In addition, warm water holds less oxygen than cold water, so critical periods for fish and zooplankton tend to occur in summer. For example, at 25° C, dissolved oxygen solubility is 8.3 mg/L, whereas at 4° C the solubility is 13.1 mg/L.
pH is a measure of the acid content of water. The pH of a water influences most of its chemical processes. Pure water with no impurities (and not in contact with air) has a pH of 7. Water with impurities will have a pH of 7 when its acid and base content are exactly equal and balance each other out. At pH values below 7 we have excess acid, and at pH levels above 7 we have excess base in the water.
The pH scale is different from the concentration scale we use for other impurities. It is logarithmic, which means that a one-unit change in pH represents a factor of ten change in the acid content of the water. Thus water with a pH of 3 has ten times the acid content of water with a pH of 4, which in turn has ten times the acid content of water with a pH of 5.
Natural, unpolluted rain has a pH between 5 and 6, so even rain water from the least polluted place on Earth has some natural acidity. This natural acidity is the result of carbon dioxide from the air dissolving in the rain drops. Distilled water which is in equilibrium with the air will have this same pH. The most acidic rain has a pH of about 4, though urban fogs with pH of less than 2 have been measured. Most lakes and streams have pH's in the range of 6.5 to 8.5. One can find waters that are naturally more acidic in areas with certain types of minerals in the soil, (e.g., sulfides). Mining activity can also release acid-causing minerals to a stream. Naturally basic waters are found typically in areas where the soil contains minerals such as calcite or limestone.
The pH of a water body has a strong influence on what can live in it. Salamanders, frogs and other amphibian life are particularly sensitive to low pH. Most insects, amphibians, and fish are absent in water bodies with pH below 4.
5. Electrical Conductivity
Pure water is a poor conductor of electricity. It is the impurities in water, such as dissolved salts, that enable water to conduct electricity. Since we lack the time or money to analyze water for each substance, we have found a good indicator of the total level of impurities in fresh water to be its electrical conductivity - how well a water passes electrical current. The more impurities in water, the greater its electrical conductivity.
For most agricultural and municipal uses, we want water that has a total dissolved solids content well below 1000-1200 parts impurity per million parts water by weight (ppm), or an electrical conductivity (ability to pass electrical current) below about 1500-1800 microSiemens/cm (Note that 1 ppm = 1mg/L). Above these levels, one can expect damage to sensitive crops. For household use, we prefer water with a total dissolved-solids content below about 500 ppm, or below a conductivity of about 750 microSiemens/cm. The residues left on "clean" dishes just out of the automatic dishwasher are a product of dissolved solids in water. Manufacturing, especially of electronics, requires impurity-free water. Pure, alpine snow from remote areas has a conductivity of about 5-30 microSiemens/cm.
The sea is salty; it has a much higher dissolved solids content than do fresh waters. Salinity is a measure of that saltiness and is expressed in parts impurity per thousand parts water. The average salinity of the Earth's oceans is 35 parts per thousand (35 ppt). Sodium and chloride, the components of common table salt (NaCl), contribute the most to the salinity. Since the proportion of chloride in seawater changes little from place to place we can also measure the chloride content, referred to as chlorinity, to estimate the total salinity. In bays and estuaries we can find a wide range of salinity values, since these are the regions where freshwaters and seawater mix. The salinity of these brackish waters is between that of freshwater, which averages0.5 ppt, and seawater.
Every continent on Earth also has inland lakes that are saline. Some of the more prominent examples are the Caspian Sea in Central Asia, the Great Salt Lake in North America, and several lakes in the Great Rift Valley of East Africa. Some of these are even more saline than seawater. Waters acquire salinity because rivers carry salts that originated from the weathering or dissolving of continental rocks. When water evaporates the salts stay behind, resulting in a buildup of dissolved material. At some point the water becomes saturated with solids, they precipitate out as solids, and they settle out of the water. Whereas the ocean's salinity changes slowly, over many millennia, the salinity of inland waters can change more quickly when rainfall or snowmelt patterns change.
The salt content of a water body is one of the main factors determining what organisms will be found there. Thus fresh waters and saline waters are inhabited by quite different organisms. Plants and animals that live in or use freshwater (below 1 ppt) generally have a salt content inside their cells that is greater than the water they inhabit or use. They tend to give off salts as waste products. Saltwater plants and animals have a salt content equal to or less than the salinity of the surrounding water, and thus have different mechanisms for maintaining their salt balance. In brackish waters (salinity values of 1 - 10 ppt) we find plants and animals that can tolerate changes in salinity.
Plants in both fresh and saline waters require three major nutrients for growth: carbon, nitrogen and phosphorus. In fact, most plants tend to use these three nutrients in the same proportion, and cannot grow if one is in short supply. Carbon is relatively abundant in the air as carbon dioxide which dissolves in water, so a lack of either nitrogen or phosphorus generally limits the growth of aquatic plants. In some cases trace nutrients such as iron can also be limiting, as can sunlight. Nitrogen exists in water bodies in numerous forms: dissolved molecular nitrogen (N2), organic compounds, ammonium (NH4+), nitrite (NO2-) and nitrate (NO3-). Of these, nitrate is usually the most important. Nitrite is usually only present in suboxic waters (low dissolved oxygen levels). The nitrate form of nitrogen found in natural waters comes naturally from the atmosphere in rain, snow, fog or dry deposition, or from the decay of organic material in soil and sediments. It can also come from agricultural runoff; farmers add nitrogen fertilizer to crops, some of which drains out of the soil when it rains.
When an excess amount of a limiting nutrient such as nitrogen is added to a lake or stream the water becomes enriched and further growth of algae and other plants ensues. We call this process of enriching the water eutrophication. The resulting excess plant growth can cause taste and odor problems in lakes used for drinking water, can cause nuisance problems for users of the water body, or can adversely affect fish and other aquatic animals. Concerns about excess nitrogen or phosphorus in lakes and coastal waters are often associated with sewage discharges. Concentrations of nitrate should always be expressed as elemental nitrogen. Thus nitrate is expressed as nitrate nitrogen (NO3 -N) in milligrams per liter (that is, 14 g of nitrogen per mole of NO3-) and never as NO3 (that is 62 g per mole NO3-). Most natural waters have nitrate levels under 1 mg/L nitrate nitrogen, but concentrations up to 10 mg/L nitrate nitrogen are found in some areas.
The Importance of Measurements
- What is the condition of the Earth's many surface waters - the streams, rivers, lakes, and coastal waters?
- How do these conditions vary over the year?
- Are these conditions changing from year to year?
Through the GLOBE Hydrology Investigation, students, together with students at other GLOBE schools, address these questions by continuous, widespread monitoring of natural waters. Our knowledge of national and global trends in water quality is based on sampling at a very few representative sites. This sampling has generally been done only a few times. For example, our information on many lakes is based on sampling done only once or twice more than ten years ago. Before we can assess changes, we need reliable information on current conditions. When changes are already underway, comparison of affected and unaffected areas can help us understand what is happening.
Measures of dissolved oxygen and pH directly indicate how hospitable a body of water is to aquatic life. Again, it is interesting to both follow the annual cycle of dissolved oxygen, alkalinity and pH, and to make comparisons between different water bodies. We can ask such questions as: are dissolved oxygen levels always at the maximum allowed by the temperature of the water, or are they depressed during part of the year? If they are low, we want to know the cause. We can see if pH becomes depressed right after a rain or when there is a lot of snowmelt running off into the lake or stream. If we do find a depression in pH, we would expect that this water had a low level of alkalinity. In fact, we should expect that waters with a low alkalinity would have a depression in pH following rainfall or snowmelt. But we must make the measurement to confirm whether or not that really happens.
Students should collect these GLOBE measurements with at least two societal goals in mind. First, we want to develop a better understanding of our local land and water resources. This knowledge can help us make more intelligent decisions about how we use, manage and enjoy the resources. Second, we want to assess the extent to which human activities are affecting the quality of our water and thus affecting how we will be able to use it in the future. In most countries current measurement programs cover only a few water bodies at a few times during the year. We hope the measurements you make in the GLOBE program will help fill this gap and improve our understanding of the health of Earth's natural waters.
Lesson 1: Introduction to Hydrology Unit
A. Students will receive a copy of a letter from the GLOBE Program entitled: Scientists' Letter to the Students
Dear GLOBE Students,
We are the principal scientists on the GLOBE Hydrology and Water Chemistry investigation, and we welcome you to the program. You are participating in a scientific program that addresses a critical gap in our knowledge about the Earth.
Hydrology is the study of water, one of the most critical resources on Earth. Water is essential to all life. You and your fellow students in schools around the world will collect what should be the broadest set of measurements on water quality compiled to date. This GLOBE program will result in more bodies of water being sampled at the same time than ever before. We hope you find this planetary connection exciting, challenging and important.
In measuring the quality of water on your study site, you will learn much about an important part of your local environment and how it changes throughout the year.
We are very interested in your data and are excited about using the data to answer questions about planetary and local hydrology. So please let us hear from you. As the year progresses, you will hear from us with suggestions about how to interpret your data. We hope that together we can find answers to important water-quality questions.
Very truly yours,
Dr. Roger C. Bales and Dr. Martha H. Conklin
This letter can used as a discussion tool to help make the students aware of the importance of gathering accurate data that will be used by real scientists.
B. Hand out a copy of the Meet the Scientists Interview
Meet Dr. Roger C. Bales and Martha H. Conklin
Roger C. Bales and Martha H. Conklin teach and conduct research in hydrology and water resources at the University of Arizona in Tucson, Arizona, U.S.A.
GLOBE: You are co-principal investigators for GLOBE's Hydrology measurements and you're married to each other?
Dr. Conklin: Right. We have a two-year old girl and just had a little boy in January.
GLOBE: You are a husband-and-wife scientific team. How did you meet?
Dr. Conklin: We met at graduate school. We were both interested in water chemistry.
GLOBE: Water is H20. What is your interest in its chemistry?
Dr. Bales: It's the impurities in water that are of interest and concern.
Dr. Conklin: You won't find pure water in nature because it is a universal solvent. All kinds of materials either dissolve in it or are deposited into it. A purpose of GLOBE is to understand what occurs in water and what happens when substances like chemicals are added to it.
Dr. Bales: According to the head of the U.S. Environmental Protection Agency, about 40% of the surface waters in this country are not fishable and swimmable. Often it's the smaller bodies of water, including many in agricultural areas, that are substandard. You would think that somebody is monitoring their quality, but in most cases, that's not so. Through GLOBE, we'll get information on many more streams, rivers and lakes.
Dr. Conklin: There are many water bodies around the world and each is unique. Students taking measurements is a wonderful way to gather information.
GLOBE: Why do you need students to collect data? Why not have scientists or graduate students collect it?
Dr. Bales: We're only a few people. Even if we went to twice as many places, we still wouldn't have much coverage.
GLOBE: Are you concerned about things that are put in water by natural sources? By human sources? By both?
Dr. Bales: Both. Impurities-and by impurities I don't mean anything that's necessarily bad, just anything other than H20--can get in the water because rocks, dust and gases dissolve. Some impurities come from the atmosphere in rainfall or snowfall, which then enter streams and lakes. Some impurities come when humans dump waste into streams or lakes.
GLOBE: You mentioned the exposure of water to rocks. Do rocks dissolve in water?
Dr. Conklin: Yes, but very slowly. You can see the long-term-effect in old mountain ranges like the Appalachians. They're weathered and not so high.
GLOBE: Why would bodies of water near agriculture be polluted?
Dr. Bales: Growing crops involves the use of fertilizers and pesticides. You want the fertilizer and pesticides to stay in the field for the crops or to control pests. Unfortunately, rainwater and irrigation water carry some of those away to streams and lakes. Or into the ground water.
GLOBE: Have students collected data for hydrologists before?
Dr. Conklin: Students have collected data on lake and river systems, but not on GLOBE's scale.
GLOBE: Tell us a little about yourselves. Where you were born? Where did you grow up?
Dr. Bales: I was born in Lafayette, Indiana, and graduated from high school in Bloomington, Indiana. I got a degree from Purdue University in civil and environmental engineering. Then I took a master's degree in the same fields at the University of California in Berkeley.
Dr. Conklin: I was born in New Jersey, but soon my family moved to Illinois. Then we moved to Europe, which was quite a contrast. We lived in Holland for five years, where I became interested in science. Then I went to boarding school in England for two years, then came back and finished high school outside Boston.
GLOBE: Did anyone discourage you from pursuing science because you were a woman?
Dr. Conklin: No. I went to mainly all-girl schools, so there was never any question about whether girls could do science or math.
GLOBE: When did you get into hydrology?
Dr. Conklin: In graduate school. I became interested in what reactions occur in atmospheric droplets. So I studied water chemistry.
GLOBE: What was happening?
Dr. Conklin: We had just discovered that acid fogs occur, which are worse than acid rain. A rain droplet falls through the atmosphere quickly, picking up pollutants in the air, but fog droplets can be in the air for hours. They absorb more pollutants, and animals and people are more likely to breathe them.
GLOBE: What do you do for fun and recreation?
Dr. Bales: Play with our kids. We also have two Labrador retrievers and a cabin in the mountains above Tucson. I'm an avid hiker, mountain climber and skier, and we still do as much of that as we can, as well as ride our bicycles.
GLOBE: Have you had an Archimedes-like "Eureka!" when you made a discovery on something you'd been working on?
Dr. Conklin: I'm an experimentalist, not a theorist. I do laboratory experiments to try to understand processes that occur. I get excited when the data from lab experiments do not match what I think is going to happen. The fun thing is trying to figure out what actually is happening.
GLOBE: As a scientist you find failed experiments beneficial?
Dr. Conklin: Right. They are much more beneficial than if they turned out the way I thought they would. If it turns out that the results are different, that implies that my hypothesis is incorrect and I have to come up with a new one. That's the exciting thing about science.
GLOBE: So science would be almost boring if the hypothesis was always correct?
Dr. Conklin: Terribly boring!
GLOBE: When you understand the mechanism of something, does that mean that you can predict what will happen?
Dr. Bales: Exactly. Once we understand why things happen, we can say, "Well, if we have changes in the future, this is how the stream is going to respond." I'm in the business of predicting how streams or lakes respond to things like climate variability, global climate change or acid deposition.
GLOBE: What is acid deposition?
Dr. Bales: That's when rain or snow has a very low pH because it has dissolved strong acids from the atmosphere, many of which are produced by human activity. Acid rain plays havoc with a number of ecological niches.
GLOBE: I think of acid as something that burns the skin. Yet acid rain doesn't feel different from any other kind of rain. What is it about acid rain that makes it acid rain?
Dr. Bales: It's a strong acid that's mixed with water. It has a lower pH than natural rainfall. It's not as acidic as lemon juice or battery acid or something like that. But it could be as acidic as vinegar. In extreme cases, fog water could be as acidic as lemon juice. The main source of the acidity is the burning of fossil fuels such as gasoline, coal, and natural gas.
GLOBE: And the emissions from the burning of these fossil fuels get into the atmosphere and interact with the water?
Dr. Bales: Rainfall or snowfall scavenges these acids out of the atmosphere and they come back down to Earth. What goes up, comes down.
GLOBE: What are the rewards of science? What do you get out of it?
Dr. Bales: You feel you're contributing to an understanding of society's potential problems, and hopefully you're contributing to solutions. We examine the past, as in the case of Greenland, in order to get a clue to what the future may hold. How our environment may change as we burn more fossil fuels and change our atmosphere and waters.
Dr. Conklin: One of the most exciting things about science is that I keep getting new knowledge and in doing so, I also keep meeting new people. If I don't know something about a field, I'll find someone who does. So I also make new friends.
Dr. Bales: People need to make intelligent decisions about the Earth, even if they do so just as voters. So when I teach students about climate warming, about air pollution, about water pollution so they understand the Earth a little better, I find that very rewarding.
GLOBE: Don't you already know enough? What drives you to want to know more?
Dr. Conklin: Environmental systems have so many components to them that it's impossible for one person to ever know enough to understand them totally, but the more you know, the better your guesses are about what's happening to them.
GLOBE: Did you have heroes when you were growing up?
Dr. Conklin: One reason I'm interested in environmental science is that I always felt a need to make the world a better place. So if I have heroes it's the scientists who have tried to do that. Two are Linus Pauling, who got Nobel Prizes in both chemistry and peace, and Albert Einstein.
GLOBE: Do you have international colleagues?
Dr. Bales: Of course. We can't do everything ourselves and they can't do everything themselves, so we cooperate and share resources and data.
GLOBE: As scientists, what are your days like? Do you have labs?
Dr. Conklin: My average day now is working in my office, teaching, interacting with students, preparing classes, writing, analyzing my students' data, working on the computer a lot. I go into the lab to see how people are doing.
GLOBE: It sounds like more and more scientific work is occurring on the computer. Is that true?
Dr. Conklin: Yes, collecting data is not enough. You have to understand it. So a lot of data analysis is done on the computer.
Dr. Bales: Most days, I spend a few hours preparing and teaching class. Then I spend an hour or two at the computer, corresponding with other scientists, reading and commenting on my students' work, or outlining things for my collaborators. Then I spend an hour or two with my graduate students. The rest gets taken up by meetings and university business.
GLOBE: Have you any funny anecdotes about your work?
Dr. Bales: I work a lot in mountain snowcaps because most of the water there falls as snow rather than rainfall, at least in the western U.S. And it seems ironic that I went to school all these years to get a Ph.D. only to go out and spend days digging holes in the snow with a shovel! When my mother sent me to college, she didn't tell me I'd be digging holes someday.
GLOBE: So scientists can measure the introduction of impurities into the atmosphere by examining ice core samples that have been around for 100, 10,000 or even 100,000 years?
Dr. Bales: Yes. In fact, I spent four weeks last summer on the Greenland ice sheet drilling ice cores. I slept in a tent on the ice for about 12 days.
GLOBE: So you're surrounded by ice. Anything else?
Dr. Bales: It's all white and blue. Snow and sky. Of course, the sun didn't set because we were way up north in the summer or spring. We were drilling ice cores and wanted to get done as soon as possible before a storm came in. You see the advent of the Industrial Revolution in the ice. A period of over three hundred years is very clear in the ice cores we did last summer. We also see forest fire signals in the ice core.
GLOBE: How do you hope students will benefit from GLOBE?
Dr. Conklin: I hope students learn how to determine the health of an environmental system. Society assumes that we can keep dumping pollutants and somehow the environment will take care of them. I hope that by checking their water systems and so on, students have some sense of whether they are healthy or polluted. I also hope they learn how to make good measurements.
GLOBE: Why should a student today consider entering your field?
Dr. Conklin: Water is one of our most important resources. Hydrology is a very good field that will become more important as clean water becomes scarcer.
Dr. Bales: Students want to do something that is not only interesting and gets them outdoors, but also contributes to a better environment and a better society. Our profession definitely does that because water is fundamental to all life on Earth.
GLOBE: Do you have any advice for students who want to get involved in Earth sciences or hydrology in particular?
Dr. Conklin: I hate to say it, but learn the basics. Math, physics, chemistry, biology. And learn how to ask questions, because those who ask the right questions will make the most important discoveries. And also learn how to write.
GLOBE: Why do you have to learn how to write?
Dr. Conklin: You could be brilliant, but if you can't communicate your results to other people, no one will know about them.
Dr. Bales: And learn as much about nature by direct experience as you can.
Students could work in groups to read and discuss the interview with the key hydrologists. The importance of this activity is to provide the scientists' background as well as to provide key concepts regarding water.
C. Assignment: Students should complete the following study guide from the hydrology introduction activities.
- What is hydrology?
- Why do we study hydrology?
- Why doesn't water exist as pure water in nature?
- Why would water bodies near agricultural areas be polluted?
- What is acid deposition?
- What do the hydrologists find rewarding in their studies of water?
- Briefly explain the water cycle.
- How is the transparency of water studied?
- List the names of five of the water chemistry tests.
- Why are water quality measurements important?
Study Guide: Teacher Answer Key
1. What is hydrology?
The study of water
2. Why do we study hydrology?
Water is essential to all life
3. Why doesn't water exist as pure water in nature?
Because water is the universal solvent and has the chemical properties to dissolve many substances
4. Why would water bodies near agricultural areas be polluted?
Growing crops involves the use of fertilizers and pesticides
5. What is acid deposition?
When the pH of rain or snow is low because of dissolved gases from the atmosphere
6. What do the hydrologists find rewarding in their studies of water?
They feel that they are contributing to an understanding of society's potential problems, and hopefully also contributing to the solutions
7. Briefly explain the water cycle.
The movement of water from the atmosphere to the land to the groundwater to the oceans and back again
8. How is the transparency of water studied?
Through the use of a Secchi disk or turbidity tube
9. List the names of five of the water chemistry tests.
Temperature, pH, dissolved oxygen, electrical conductivity, and nitrates
10. Why are water quality measurements important?
Information on current conditions is necessary prior to developing potential methods of analyzing change
Lesson 2: Water Walk Activity
To become familiar with the hydrology of the Sheboygan River
Students will visit the Sheboygan River at the Black Wolf Run Golf Course site, and conduct a visual survey to discover information about local land use and water quality, and then document their findings. The students will use this initial investigation to raise questions about local land use and/or water chemistry issues that may require further study.
- Surface water exists in many forms, such as: ponds, lakes, and rivers.
- Water characteristics are closely related to the characteristics to the surrounding land
- Water moves from one location to another
- Surface water has many observable characteristics, such as: color, smell, flow, and shape.
Materials and Tools:
- Drawing materials and tools needed for creating pictures
- Still or video cameras for photography
- Compass or measuring devices
- Clear containers for observing water clarity and color
Your body of water is part of a catchment basin. A watershed delineates a catchment basin, the area drained by a river and its tributaries. The topography of the area determines the shape of the watershed. The surrounding land and the uses of this land - towns, cities, highways, agricultural, livestock, timber harvesting, natural vegetation, etc.- influences the water chemistry of bodies of water within the watershed.
Many factors can affect the characteristics of the water in a river system, lake, or pond. Characteristics of water include: temperature, color, shape, etc. In this acivity, you will be collecting data about water quality as measured by dissolved oxygen, pH, alkalinity and electrical conductivity. Field observations increase the students' ability to conceptualize links between land characteristics and water characteristics. This activity is an introduction to your hydrology study site and lays the foundation for subsequent hydrology learning activities and the hydrology lessons.
What To Do and How To Do It
- Ask students about their knowledge of local bodies of water. Begin with questions such as:
Is there a lake, river, pond or stream that you visit?
What is your favorite past-time at this place?
Why is this body of water important to you?
- Take your students to the Hydrology Study Site. Remind them of safety issues.
- Assign teams of students to survey different sections of the site. In teams composed of a journalist, a mapper, a sketcher, and a photographer, students should begin to document what they observe about their section. What is the appearance, smell, nature of the water in their section? Bordering lands should be noted: urban, agricultural, industrial, residential, wooded, swamp, etc. Students should map the general contours and characteristics of their sections and record the wildlife and plants in and around its water. What is the slope of the land adjacent to their section of water?
- Back in the classroom, students should create a composite display of all the maps. Look for similarities and differences and discuss observed patterns. Based on their observations, encourage students to think about how the water got to this location, how it flows through the study site, where it goes from there, how the area surrounding the water influences the quality of the water particularly during periods of rain, snowmelt, flooding, etc. What questions do they have? Record them on a poster on the classroom wall.
- In addition, ask the students to discuss some of the following:
What land use activities did you observe and list? How do you think these activities would change the water characteristics? Would these activities influence water quality?
What type of water appearance was recorded most often and what might this indicate about the water quality?
Was there evidence of human uses of the water? Evidence of wildlife and other animals using the water?
Have students create a visual display of what they know about their body of water, including surrounding land uses and their impacts on the quality of the water (both positive and negative) in ways that affect fish and animals, including humans, that depend on the water. Students will use this poster in their class presentations shared at the end of the unit.
Lesson 3: Connecting Ideas from the Water Walk Activity
A. Activity: Think / Pair / Share
Students should list the main ideas they learned from the water walk activity in their notebook, and then share these ideas with a partner.
Students should then share their ideas with the entire class through a group discussion lead by the instructor.
B. Activity: World-Wide Water Cycle Web
Overview: This activity will allow students to apply prior knowledge and to establish new knowledge regarding the water cycle.
Individual sheets of paper labeled:
Atmosphere, Ocean, Lake, Biosphere, Stream, Groundwater, Earth surface
Four different colors of yarn to represent:
Precipitation, Evaporation/Transpiration, Runoff, and Infiltration
Place the labeled sheets of paper representing the major parts of the water cycle in different locations around the classroom.
Connect the components of the water cycle using the major physical and chemical processes represented by colored yarn.
Explain and Think It Over
1. Using the water web and your knowledge of systems, define the primary sources of input and output of water for a stream.
Define the key parts and properties of a stream.
What properties of a stream can we measure to document changes in input and output.
2. Humans interact with the hydrologic cycle on a daily basis. Develop a brief summary of ways in which humans interact with the Earth's dynamic water system using your knowledge of the water cycle.
Write a one-page paper summarizing the water cycle, and how water quality issues are important to your life. Use your background knowledge of the six-traits of good writing, and focus this paper on voice as a trait.
Lesson 4: Water Quality Tests
To have students:
- learn how to use each of the hydrology instruments correctly
- explore the ranges of measurements possible with each instrument
- use each instrument as directed in the test
- understand the importance of quality control.
Groups of students will rotate among measurement stations for each of the water chemistry tests that will be performed by the class. They will practice using the instrument or kit and activity for that particular measurement, exploring sources of variation and error. The activity concludes with students testing water samples brought from a variety of places (home, yard, puddles, brooks, etc.).
If you have enough instruments and kits, you may want to focus on a subset of the measurements during a given class period in order to simplify the discussion.
Two class periods
- Quality assurance
- Quality control
- Following directions carefully
- Performing measurements
Materials and Tools
- One bucket of tap water
- Copies of Hydrology Investigation Student Activity Sheets
In addition you will need the following materials for particular tests:
- Transparency: green food color, spoonful of silt
- pH: samples of vinegar water, distilled water, milk, juice, soda pop, etc.
- Temperature: ice
- Conductivity: distilled water, salt
- Salinity: distilled water, salt, ice
- Nitrate: lawn fertilizer
Ask students to bring in water samples from the home and/or yard.
Set up measurement stations for each of the tests your students will be performing. For each station you will need:
Equipment and instruments to perform the measurement
One copy of the test instructions to be posted at the station
Copies of the Hydrology Investigation Student Activity Sheet.
Draw a bucket of tap water at the beginning of the day and allow it to sit until class. Record the time on a piece of tape attached to the bucket.
Fill a Dissolved Oxygen sample bottle at the same time and preserve the sample as directed in the activity. Record the time on the sample bottle label.
A quality assurance and quality control (QA/QC) plan is necessary to ensure test results are as accurate and precise as possible. Accuracy refers to how close a measurement is to true value. Precision means the ability to obtain consistent results. Desired accuracy, precision and reliability are ensured by:
- careful calibration, use, and maintenance of testing equipment
- following the specific directions of a test exactly as described
- repeating measurements to ensure that they are within acceptable limits
- minimizing contamination of samples, stock chemicals and testing equipment
- keeping track of samples
Together these steps help make the data you collect valid, valuable and meaningful.
Calibration is a procedure used to check the accuracy of testing equipment. To assure that the equipment is functioning properly, a solution of known value is tested. Calibration procedures vary among the measurements and are detailed in each test.
Consult Material Science Data (MSDS) sheets that come with the kits and buffers. Also consult your local school district's safety procedure guidelines.
What To Do and How To Do It
- Divide the students into small groups. Checking each others work, students should take turns reading directions, making measurements, and recording the data.
- Students rotate through each station learning the instruments and tests.
- (Alternative activity)
Compare the results they obtained on samples from various places. Help them make sense of their results by placing data on a map of the water sources and considering the history of each sample in terms of well water, city water, pool, pond, puddle or brook. This is also a good time to stress the importance of accurate measurements when you make comparisons. Is the difference real or measurement error? This is also the time to discuss why we didn't test these samples for DO and temperature and how we might test for them.
Student Activity Sheet
Transparency is the measurement of water clarity. How clear the water is at your site will depend on the amount of soil particles suspended in the water and on the amount of algae or other growth at your site. Transparency may change seasonally with changes in growth rates, in response to precipitation runoff, or for other reasons. The clarity of your water determines how much light can penetrate. Since plants require light, transparency becomes an important measurement in determining productivity of your water site.
In the field you would measure transparency in one of two ways; with a Secchi disk in deep, still waters or with a turbidity tube if your site has shallow or running water. For the lab practice station, we will use the turbidity tube.
What To Do and How to Do It
- Ask each student to fill the turbidity tube with tap water until the image disappears. Record the depth of the water in the tube in cm.
2. Compare data from several students. Ask students to formulate hypotheses on variations in their data.
3. Try the tube again testing variables such as: amount of light in the room, tube in sunlight and shadow, with and without sunglasses, turning the tube to try and detect the image at the bottom, letting the water stand in the tube for 15-20 seconds.
4. Once students have established the depth using tap water, pour the water into a bucket and mix a few grams of silt into the water.
5. Ask students to fill the turbidity tube with the silty water until the image disappears. Record the depth of the water in the tube in cm. Compare the readings from several students.
6. Put a few drops of green food coloring in tap water.
7. Have each student fill the turbidity tube with colored water until the image disappears.
Student Activity Sheet
Water temperature is the temperature of a body of water such as a stream, river, pond, lake, well, or drainage ditch as it appears in nature. Water bodies can vary greatly in temperature, according to latitude, altitude, time of day, season, depth of water, and many other variables. Water temperature is important because it plays a key role in chemical, biological and physical interactions within a body of water. For example, high temperatures may be an indicator of increased plant production. The temperature of the water determines what aquatic plants and animals may be present since all species have their natural limits of tolerance to upper and lower temperatures. Water temperature can therefore help us to understand what may be happening within the water body without directly measuring hundreds of different things within the body of water.
What To Do and How To Do It
- Following the steps in the Water Temperature Test, each member of the group should take a turn measuring the temperature of the same sample with the same thermometer. Make sure everyone in the group can read the thermometer. Compare your readings. Are they within 0.5° C of each other? Why? Why not? If not, repeat this exercise with another water sample until you are obtaining readings within 0.5° C of each other.
- With each member of the team using a different thermometer and following the steps of the water temperature test, measure the temperature of a single water sample and compare your readings. Do you get readings within 0.5° C of each other? Why? Why not? If not, your thermometers may need calibration.
- Following the steps in the water temperature test, measure the temperatures of water from the hot and cold water taps, ice water, and the water that has been standing in the bucket.
- Discuss the range of measurements possible with each of the thermometers.
- Can you take temperatures below the freezing mark? Why? Why not?
- Can you take the temperature of boiling water with the thermometer provided? Why? Why not?
Student Activity Sheet
Dissolved Oxygen Station
All living things depend on oxygen to survive. In a water environment molecules of oxygen gas dissolve in the water. This is called dissolved oxygen (DO). In air, 20 out of every 100 molecules are oxygen. In water, only 1-5 molecules out of every million molecules are oxygen. This is why dissolved oxygen is measured in parts per million (ppm). Different species of aquatic organisms require different amounts of oxygen, but generally aquatic organisms require at least 6 ppm for normal growth and development.
Water temperature and altitude influence how much oxygen water can hold; i.e., the "equilibrium" value. In general, warmer water cannot hold as much oxygen as colder water. Similarly, at higher altitudes water cannot hold as much oxygen as waters at lower altitudes. Look for these patterns in the Temperature and Altitude Tables in the DO protocol. This is why we use a distilled water standard in the protocol and correct for temperature and altitude.
The actual amount of DO in a water may be higher or lower than the equilibrium value. Bacteria in the water consume oxygen as they digest decaying plant or animal materials. This can lower the DO levels of the water. In contrast, algae in lakes produce oxygen during photosynthesis which can sometimes result in higher DO levels in summer.
What To Do and How To Do It
- Following the steps in the Dissolved Oxygen Test, each member of the group takes a turn measuring the DO of the same sample. Compare your readings. Are they within 0.2 mg/L of each other? Why? Why not? If not, repeat this exercise with another water sample until you obtain readings within 0.2 mg/L of each other.
- If your water faucets have aerators on them, test a water sample freshly drawn from the faucet, one that was drawn at the beginning of the day and allowed to sit undisturbed in a bucket, and the preserved sample drawn at the same time. Record the time at which you tested the water in the bucket. How long has it been since the water was drawn? Compare the readings. Are they different? Why? Why not? What might account for the differences?
Student Activity Sheet
pH is an indicator of the acid content of water. The pH scale ranges from 1 (acid) to 14 (alkaline or basic) with 7 as neutral. The scale is logarithmic so a change of one pH unit means a tenfold change in acid or alkaline concentration. For instance, a change from 7 to 6 represents a solution 10 times more acidic; a change from 7 to 5 is 100 times more acidic, and so on. The lower the pH the more acidic the water. The pH of a water body has a strong influence on what can live in it. Immature forms of salamanders, frogs, and other aquatic life are particularly sensitive to low pH.
What To Do and How To Do It
- Following the steps for pH paper in the pH test, each member of the group takes a turn measuring the pH of the same sample. Compare your readings. Are they within 1.0 pH units of each other? Why? Why not? If not, repeat this exercise with another water sample until you are obtaining readings within 1.0 pH units of each other.
- Without calibrating the pH meter, but following the steps for the meter given in the pH test, take turns measuring the pH of a different water sample. Record these numbers.
- Calibrate the pH meter and repeat the measurements again following the directions carefully to avoid contaminating samples. Alternatively, students could use one calibrated meter and one that has not been calibrated if there is enough equipment. Record your readings.
- Compare the data obtained using different methods. Discuss possible reasons for the differences.
- Take the pH of familiar liquids such as distilled water, vinegar, tap water, milk, juice, soda pop, etc. using pH paper.
Student Activity Sheet
Electrical Conductivity Station
Electrical conductivity is a measure of the ability of a water sample to carry an electrical current. Pure water is a poor conductor of electricity. It is the impurities in water, such as dissolved salts, that enable water to conduct electricity. Therefore, conductivity is often used to estimate the amount of dissolved solids in the water since it is much easier than evaporating all the water molecules from a sample and weighing the solids that remain.
Conductance is measured in a unit called the microSiemen/cm. Sensitive plants can be damaged if they are watered with water that has electrical conductivity levels above about 2200-2600 microSiemens. For household use, we prefer water with conductivity below 1100 microSiemens. Manufacturing, especially of electronics, requires pure water.
What To Do and How To Do It
- Following the steps in the Electrical Conductivity test, each member of the group takes a turn measuring the conductivity of the same tap water sample. Compare your readings. Are they within 40 µSiemens/cm of each other? Why? Why not? If not, repeat this exercise with another water sample until you are obtaining readings within 40 µSiemens/cm of each other.
- Measure the conductivity of familiar liquids such as vinegar, drinking water, milk, juice, soda pop, etc.
- What is the range of conductivity readings? Create a conductivity scale and plot the value obtained for each sample.
Student Activity Sheet
Salinity Station - for Salt or Brackish Water
Salinity is the measurement of dissolved salts in salty or brackish water. It is measured in parts per thousand (ppt). Salinity may vary with precipitation, snow melt, or proximity to a freshwater source such as a river mouth.
The hydrometer is an instrument which measures the specific gravity or density of a fluid. Its design is based on the principle, recognized by the Greek mathematician Archimedes, that states that the weight loss of a body in a liquid equals the weight of the liquid displaced. The denser your liquid, therefore, the less the weighted bulb must sink to displace its own weight.
Why do you need to take a temperature reading with your hydrometer reading? Water becomes more dense as it approaches freezing - then less dense as it becomes ice. Since we want to measure the effect of dissolved salts on density, we must control the temperature variable.
What To Do and How To Do It
- Fill a 500 mL cylinder with fresh water to the 500 mL line.
- Gently place the hydrometer into the cylinder (do not drop).
- Read the scale on the hydrometer at the bottom of the meniscus.
- Remove the hydrometer and add 7.5 grams of salt to the cylinder. Stir.
- Use a thermometer to measure the temperature in the cylinder 10 cm below the surface.
- Use the hydrometer to measure the density of the fluid in the cylinder.
- Add 10 grams of salt to your mixture.
- Measure the temperature and salinity of the fluid.
Student Activity Sheet
Nitrogen is one of the three major nutrients needed by plants. Most plants cannot use nitrogen in its molecular form (N2). In aquatic ecosystems blue-green algae are able to convert N2 into ammonia (NH3) and nitrate (NO3-) which can then be used by plants. Animals eat these plants to obtain nitrogen that they need to form proteins. When the plants and animals die, protein molecules are broken down by bacteria into ammonia. Other bacteria then oxidize the ammonia into nitrites (NO2-) and nitrates (NO3-). Under suboxic conditions nitrates can then be transformed by other bacteria into ammonia (NH3), beginning the nitrogen cycle again.
Typically nitrogen levels in natural waters are low (below 1 ppm nitrate nitrogen). Nitrogen released by decomposing animal excretions, dead plants, and animals is rapidly consumed by plants. In water bodies with high nitrogen levels eutrophication can occur. Nitrogen levels can become elevated from natural or human-related activities. Ducks and geese contribute heavily to nitrogen in the water where they are found. Man-made sources of nitrogen include sewage dumped into rivers, fertilizer washed into streams or leached into groundwater, and runoff from feedlots and barnyards. Nitrate levels are measured in milligrams per liter nitrate nitrogen.
What To Do and How To Do It
- Following the steps in the Nitrate test, measure the nitrate level of the water sample. Compare the readings of several students. Are they within 0.2 mg/L of each other? If not, discuss possible reasons for error. Repeat the readings until you obtain readings within 0.2 mg/L.
- Measure the nitrate level in a number of different water samples: runoff from a golf course, other pond water, a stock tank, river, etc.
- Add a few grains of fertilizer to your sample. Test again. What is the difference?
- Discuss possible sources of nitrogen in your water samples.
Lesson 5: Field Trip to Test Site
- Students will run the various water quality tests at the Sheboygan River test site.
- Students should follow the directions for each of the tests, and record their data.
How to Measure Transparency
Make sure that Secchi disk and turbidity tube measurements are made in the shade with the sun to your back to make an accurate and reproducible reading. If there is no shade available, use an umbrella or a large piece of cardboard to shade the particular area where the measurement is being made. For the turbidity tube the shadow of the observer should be adequate. Different individuals may see the Secchi disk or the bottom of the turbidity tube disappear at different water depths. For this reason, whenever possible the transparency observation should be made by three different students and each of their observations submitted to the GLOBE Student Data Server.
- Lower the disk slowly into the water until it just disappears. If possible, grab the rope at the surface of the water and mark this point on the rope (e.g. use a clothes pin). If it is not possible to mark the rope at the water surface, mark the rope a known distance above the water.
- Then raise the Secchi disk until it just reappears into view. Grab the line at the surface of the water when the Secchi disk reappears and mark this point (or some known distance above the water). The rope should now be marked at two points. There should only be a few centimeters difference between these two points.
- Record both depths on your Hydrology Investigation Data Work Sheet to the nearest 1 cm.
- If the two depths differ by more than 10 cm, repeat the measurement, recording the new depths on your Hydrology Investigation Data Work Sheet.
- Using the Cloud Cover Protocol, determine the cloud cover. Determine the distances between where each observer marked the rope and the water surface. Record both on your Hydrology Investigation Data Work Sheet. If the rope was marked at the water surface enter 0.
- Submit your depths along with the cloud cover and distance from the mark to the water surface to the GLOBE Student Data Server. Note: Enter data for each observer, not the average of the different observations.
Note: If the Secchi Disk reaches the bottom of your study site and you can still see it, simply record the depth to the bottom by referring to the point where the rope is at the water surface and put a greater than (>) symbol in front of the measurement both on your data work sheet and when you submit the value to the GLOBE Student Data Server.
- Pour sample water into the tube until the image at the bottom of the tube is no longer visible when looking directly through the water column at the image. Rotate the tube while looking down at the image to see if the black and white areas of the decal are distinguishable.
- Record this depth of water on your Hydrology Investigation Data Work Sheet to the nearest 1 cm.
- Submit your depth to the GLOBE Student Data Server. Enter data for each observer, not the average of the different observations.
Note: If you can still see the image on the bottom of the tube after filling it, simply record the depth as > the depth of the tube.
How to Measure Water Temperature
- Tie one end of a piece of string securely to the end of the thermometer and the other end to a rubber band. Slip the rubber band around the wrist so that the thermometer is not lost if it is accidentally dropped in the water.
- Hold the end of the thermometer (opposite the bulb) and shake it several times to remove any air in the enclosed liquid. Note the temperature reading.
- Immerse the thermometer to a depth of 10 cm in the sample water for three to five minutes.
- Raise the thermometer only as much as is necessary to read the temperature. Quickly note the temperature reading. If the air temperature is significantly different from the water temperature or it is a windy day, the thermometer reading may change rapidly after it is removed from the water; try to take the reading while the bulb of the thermometer is still in the water. Lower the thermometer for another minute or until it stabilizes. Read it again. If the temperature is unchanged, proceed to Step 5.
- Record this temperature along with the date and time on the Hydrology Investigation Data Work Sheet.
- Take the average of the temperatures measured by the student groups. If all measured values are within 1.0o C of the average, submit the average value to the GLOBE Student Data Server. Otherwise, repeat the measurement.
How to Measure Dissolved Oxygen
- Rinse the sampling bottle and hands with sample water three times. Rinse vial three times in distilled water.
- Replace the cap on the bottle.
- Submerge the bottle in sample water and remove the cap. Allow the container to fill.
- Tap the bottle to release air bubbles.
- While the bottle is submerged, replace the cap. Remove the capped bottle from the water.
- Check to ensure that no bubbles are present in the bottle. If bubbles are found, repeat the sampling procedure.
Sample Preservation and Testing Procedure
- Use a dissolved oxygen test kit that meets the specifications in the Toolkit of the GLOBE Program Teacher's Guide. Follow the instructions carefully. If a scoop is used to measure powdered chemicals, do not allow the scoop to come in contact with the liquid.
- Record the values from the student groups on the Hydrology Investigation Data Work Sheet.
- Take the average of the DO values measured by the student groups. If the values are all within 1 mg/L of the average, submit the average DO value to the GLOBE Student Data Server. Otherwise repeat the measurement.
- Put all liquids in waste bottle.
DO test kits involve two overall parts - sample preservation (stabilization) and sample testing. The preservation part involves the addition to the sample of a chemical that precipitates in the presence of dissolved oxygen, followed by addition of a chemical that produces a colored solution. The testing part involves dropwise addition of a titrant solution until the color disappears. The DO value is calculated from the volume of titrant added.
How To Measure pH
In order to measure the pH of your water sample using the pH meter you need to: (1) prepare buffer solutions, (2) calibrate the instruments, (3) recheck your instrument by measuring the buffers in the field, and (4) measure the pH of your sample in the field.
Calibration should be performed before each set of measurements. This procedure can be performed in the classroom before you go out in the field.
Step 1: Prepare the Buffer Solutions
Pre-mixed buffer solutions can be stored for 1 year, as long as they have not been contaminated. If you are using the powdered pillow buffer, then dissolve it in distilled water as described below. If you are using pre-mixed buffer solutions, measure 50 mL into a graduated cylinder and proceed to step 4.
For each pH buffer (4, 7, and 10):
- Write the buffer pH and date on two pieces of masking tape. Place one on a clean, dry 100 mL beaker and the other on a 50 mL bottle or well cleaned baby food jar.
- Using a graduated cylinder, measure 50 mL of distilled water and pour it into the beaker.
- Over the beaker, completely cut open one end of a pillow of buffer powder, then squeeze and shake the pillow to release the powder into the water. Make sure all the powder is released into the water. Stir with stirring rod or spoon until all the powder dissolves.
- Pour the buffer solution into the labeled bottle. Cap the bottle tightly. Discard after a month.
- Continue preparing the other buffers, repeating steps 1-4 for each.
pH Measurement Procedure
- Rinse the electrode and the surrounding area with distilled water using the squeeze bottle. Blot the area dry with a soft tissue.
- Fill a clean, dry 100 mL beaker to the 50 mL line with the water to be tested.
- Immerse the electrode in the water. Be sure that the entire electrode is immersed, but avoid immersing it any further than necessary.
- Stir once and then let the display value stabilize.
- Once the display value is stable, read the pH value and record it in the Hydrology Investigation Data Work Sheet.
- Repeat steps 1 through 5 for another sample as a quality control check. The two pH values should agree to within 0.2 which is the accuracy of this technique.
- Rinse the probe with distilled water, blot it dry with soft tissue, replace the cap on the probe, and turn the instrument off.
How to Measure Conductivity
- Remove cap from the meter and press the ON/OFF button to turn the tester on.
- Rinse the electrode with distilled water and blot it dry.
- Fill a clean, dry, 100 mL beaker with water to be tested.
- Immerse the electrode in the water sample. See Figure HYD-P-4.
- Gently stir the sample for a few seconds, then allow the display value to stabilize.
- Read the display value and record its value on the Hydrology Investigation Data Work Sheet.
- Take the average of the electrical conductivity values measured by the student groups. If the recorded values are all within 40 microSiemens/cm of the average, report the average value to the GLOBE Student Data Server. If you have more than three groups and there is one outlier (a value far different from the rest), discard that value and calculate the average of the other values. If they are now all within 40 microSiemens/cm of this new average, report this new average to the GLOBE Student Data Server. If there is a wide scatter in results, discuss the procedure and the potential sources of error with the students, but do not report a value to the GLOBE Student Data Server. Repeat the protocol if possible to produce a reportable measurement.
How to Measure Nitrate
- Use a nitrate measurement kit that meets the GLOBE Instrument Specifications in the Toolkit. Rinse the sample tubes in the kit at least 3 times with sample water before starting the measurement.
- Nitrate nitrogen plus nitrite nitrogen: Follow the manufacturer's nitrate instructions in the kit. The kits are based on the technique of adding a reagent that reacts with nitrate to form nitrite. The nitrite reacts with a second reagent to form a color. The intensity of the color is proportional to the amount of nitrate in the sample. The concentration is determined by comparing the sample color, after addition of reagents, to a color comparator included in the kit. If the kit calls for shaking the sample, be sure to shake for the specified period of time. Failure to follow the times specified in the directions will result in inaccurate measurements.
- Have at least 3 students in the group read the color comparator. Record the nitrate concentration for each student group on the Hydrology Investigation Data Work Sheet. (Note: Hold the comparator up to a light source such as a window, the sky or a lamp. Do not hold it up to the sun.)
- Take the average of the three readings. If the recorded values are all within 1 mg/L of the average, record the average on the Hydrology Investigation Data Work Sheet. If they are not within 1 mg/L of the average have the students reread the color comparator, then record and average the new values. (Note: do not reread if more than 5 minutes has elapsed.) If your remaining values are now all within 1 mg/L of the new average, record this new average on the Hydrology Investigation Data Work Sheet. If there is still one outlier (a value far different from the rest) discard that value and calculate a new average of the other values. If there is still wide scatter (more than 1 mg/L) in results, discuss the procedure and the potential sources of error with the students, but do not report a value to the Data Server. Repeat the protocol to produce a reportable measurement.
- Nitrite nitrogen: Follow the manufacturer's instructions for nitrite. It is the same procedure, except the reagent to reduce nitrate to nitrite is not used.
- Repeat steps 3 and 4 to obtain nitrite values.
Note: Test results should be reported as mg/L nitrate nitrogen (NO3- N; the same units as your standards), and not as mg/L nitrate (NO3-).
For general information: To convert mg/L nitrate to mg/L nitrate nitrogen divide by 4.4, the ratio of their molecular weights. For example: 44 mg/L NO3- is equivalent to 10 mg/L NO3-N. To convert mg/L nitrite to mg/L nitrite nitrogen divide by 3.3, the ratio of their molecular weights.
Lesson 6 - Analyze and Compare Data Results
Answer the following questions using the class data:
- Examine the data from the test results. How do the
- What is the data trend?
- Would you expect the data to change seasonally?
- Are there any unusual data points?
- What is the relationship between temperature and dissolved oxygen?
- Are other tests related to temperature?
- Would dissolved oxygen levels show seasonal fluctuations?
- What other ideas can you gather from the results of these tests?
- What do you feel is the overall condition or health of this stream?
- What things could be done to help change the stream's conditions?
See the following websites for additional graphing activities
Assignment: List the concepts that you learned from this unit so far. Design a preliminary model for your class presentation.
Lesson 7 - Work on Project
Develop a poster board or model to use for the presentation
Time: two class periods
Lesson 8 - Begin class presentations
(Grade the oral reports using a rubric)
This rubric developed for evaluation gives the teacher, other students, and the students themselves a chance to reflect on their results. In this evaluation process, students are given the chance to improve on their entire learning process so that they can benefit as lifelong learners, community citizens, and young adults.
Expresses Ideas Clearly
- Consistently communicates information effectively by providing a clear main idea or theme with support that contains rich, vivid, and powerful detail.
- Consistently communicates information by providing a clear theme with sufficient support and detail.
- Sporadically communicates information by providing a clear main idea with sufficient support and detail.
- Rarely communicates information by providing a clear main idea with sufficient support and detail.
Effectively Communicates with Different Audiences
- Demonstrates an ability to adjust tone and style to a wide and highly diverse range of audiences.
- Demonstrates the ability to adjust tone and style to different audiences.
- Demonstrates the ability to communicate with a restricted range of an audiences.
- Does not demonstrate the ability to adjust tone and style to different audiences.
Effectively Communicates in a Variety of Ways
- Demonstrates an ability to creatively and effectively use many diverse methods of communication.
- Demonstrates an ability to effectively use diverse methods of communication.
- Demonstrates an ability to use only a few methods of communication.
- Demonstrates an ability to use only one or two methods of communication.
Effectively Communicates for a Variety of Purposes
- Demonstrates an ability to communicate for a wide and diverse variety of purposes.
- Demonstrates an ability to communicate for different purposes.
- Demonstrates an ability to communicate for a restricted range of purposes.
- Does not demonstrate an ability to change the purpose of communications.
Creates Quality Products
- Consistently creates products that exceed conventional standards.
- Consistently creates products that clearly meet conventional standards.
- Sporadically creates products that meet conventional standards.
- Rarely, if ever, creates products that meet conventional standards.