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Engineering LibreTexts

5.1.7: Formative Assessment - Turning Water into Food

  • Page ID
    48211
  • Instructions

    Please download the worksheet below for detailed instructions.

    You will perform three activities in this assessment:

    1. Watch the video below, Turning water into food, and answer the questions on the worksheet as you watch the video
    2. Visit water footprint calculator website, compare how your water footprint changes with varying levels of meat consumption, and answer questions on the worksheet. This portion of the assessment will be included in the weekly discussion and not included in the assessment quiz.
    3. Perform a comparison of the virtual water embedded in different food products and answer questions on the worksheet.

    Video: Turning water into food, Bruce Bugbee | TEDxUSU (16:32)

    Click for a transcript of the turning water into food video.

    This is my globe. I've had this globe for over thirty years to analyze the three-dimensional relationships among the continents and the water and the nations. Political boundaries have changed over the decades, but the fundamental relationships haven't changed. Like many globes like this, my globe has raised mountains. And I always thought those mountains were diminished on my globe so that it would make it easier to manufacture. Till one day, I looked up the height of Mount Everest and the diameter of the earth, and I got out my micrometers to check how much these were diminished. And to my amazement, they were embellished. They're considerably embellished. It was a very disturbing day for me. If the mountains are embellished, the oceans are similarly thin. And it turns out, if you take all the water on our blue planet, roll it up into a sphere, it comes out to the size of a ping-pong ball, a ping-pong ball!

    But it doesn't stop there. Even though this is small, ninety-seven and a half percent of the water on our planet is saltwater. We can't drink it, we can't irrigate our crops with it. The two-and-a-half percent that's freshwater is the size of this small blue marble. Now, if I took this marble, I should put it up here on Greenland because 99% of our freshwater is frozen in glaciers, mostly Greenland and Antarctica. The 1% that's left is the size of a mustard seed. This mustard seed recycles and recycles and sustains life on the planet. We use about a gallon of water every day in the water we drink and in the food we eat. We use about another 20 gallons a day in washing things - washing our clothes and domestic use. But we use several hundred gallons of water every day, indirectly, in the food we eat. That amount dwarfs all the other uses.

    In the United States, we dedicate 70% of our water resources to agriculture. I have spent much of my professional life studying how to improve water efficiency in agriculture and I'm joined in this effort by hundreds of colleagues around the world. The challenge is enormous. We can grow food without fossil fuels, but we cannot grow food without water. We think about our carbon footprint. We ought to be thinking about our water footprint, and even more importantly, we ought to be thinking about our global food print. The type of food that we eat has a bigger impact on the environment than the cars we drive. Eating a hamburger is equivalent in water use to taking an 80-minute shower.

    To understand where water goes, it's useful to review the Earth's water cycle. As you can see from the globe, 70% of the planet surface is oceans, 30% is land. So the water cycle starts with one fundamental thing. The Sun shines on the oceans and water evaporates. This is an amazing process. All the salts are left behind. It’s distilled water coming out of the ocean. Anybody that has boiled a pot of water on their stove to dryness knows it takes an enormous amount of energy to evaporate water. The Sun does this every day for free, no fossil fuels, no fancy apparatus. Here's an amazing fact, more Sun shines on the earth in an hour than all of the people use in a year. So this water vapor from the ocean blows over to the land, falls on the land as rain, and soaks into the ground. It eventually runs back to the oceans in the rivers. We have a few thousand years of experience in ways to reuse this water. We built dams, we drill wells, we pump the water back up to the surface. It's still liquid water. The microbes in the soil have purified it. We drill more wells, we use it again. Eventually, it slips out of our grasp and runs back to the ocean. This is all liquid water. There’s two fates, the second one is shown here.

    Now let's plant some seeds. The roots grow from the seeds and the water that used to go into the ocean is short cycled back to the roots of the plants. The Sun is hot. The same energy that falls on the ocean, falls on the plant leaves. To stay cool and hydrated, they evaporate water. It goes into the air, back to the ocean, falls as rain, and become saltwater again. We have far less control over this water vapor than we do over the liquid water that we can reuse. Without a continuous supply of water vapor, the plants dehydrate and food production stops. We irrigate to keep the plants hydrated. We have developed an amazing array of instruments to precisely tell when and how much to irrigate crops. They get just what they need, no more no less. In some older systems, 50% of the water evaporated from the soil surface and didn't get into the plants, went back to the ocean. In some of our modern systems we now have subsurface drip irrigation that can deliver 90% of the water right to the plants.

    Every drop is precious. We call these efforts, more crop per drop. Even with our best efforts, we can't keep up, we can't grow the food we need to feed a hungry planet. So we access aquifers deep in the ground. These aquifers are called fossil aquifers because they formed a long time ago, they're difficult to recharge. We drill deep wells and pump that water up to the surface and irrigate the plants. These aquifers are being depleted far more rapidly than our fossil fuel reserves.

    So how much crop can we get per drop? Let's take a look at these wheat plants over here. Wheat and rice are the biggest crops for direct human consumption on the planet. These two crops provide the vast majority of our calories. This wheat was developed here at Utah State University. My colleagues and I hybridized tall high yielding wheat with very short wheat to get a short high yielding wheat. We did this with NASA funding because we wanted to work with NASA to develop a life support system for space, that we could grow our own food in space independent of the planet. We've grown this wheat many times on the international space station and some of the astronauts turned out to be amazing photographers. This is a picture of this wheat at harvest on the International Space Station. That picture in the background is not a photo-shopped image of my globe. We grow this wheat hydroponically and if you haven't ever seen hydroponic wheat, here it is, the roots absorbing the water, going up to the tops of the plant. And if you’re a student in the lab, you know how much water this wheat takes every day. We developed this for a fast rate of development. This wheat is only three weeks old from transplanting to this tub. It'll be ready to harvest in five weeks. That's almost twice as fast as wheat in the field. Surprisingly, hydroponic wheat doesn't require any more water than field wheat. In fact, it’s often is less because there's no evaporation from the soil surface, there's no leaks, all the water goes through the plant. Even with perfect efficiency of every input, it still takes a hundred gallons of water to grow enough wheat to make a loaf of bread. A hundred gallons of water.

    To emphasize this point, my students built this simulated hundred-gallon tank of water. If we put a faucet on this and dripped it into this tank into a plot big enough to grow that wheat, it would be empty about the time the wheat was ready to harvest. This greatly exceeds all the other household units it uses even when it's perfect. So why is this water use so enormous for plants? Plant physiology is a lot like human physiology. So let's consider breathing. We exhale water vapor to get oxygen. These plants lose water in order to get carbon dioxide. Every square millimeter of the surface of these plants is covered with tiny pores called stomata. The word stomata comes from the Greek word for mouth, so these stomata open to let carbon dioxide in, and they automatically lose water vapor. There's a hundred times more water vapor inside a leaf than there is carbon dioxide in the air and that's why the water use requirement is so enormous. Water has to come out to let the CO2 in. Saving water by closing the stomates is a lot like asking people to save water by stopping breathing. We can't do it. Humans have it easy. There are six hundred times more oxygen in the air than there is carbon dioxide, so that means plants need 600 times more water to grow.

    For all the interest in global warming, carbon dioxide is a trace gas, point zero four percent. If we took the air molecules in this auditorium and made them fluorescent, we'd have a hard time finding the carbon dioxide molecules. There is only four carbon dioxide molecules for every 10,000 air molecules. It's one of the great wonders of the world that plants can find those carbon dioxide molecules and make our food, make high-energy food.

    To better understand the effect of diet on the environment, let's analyze the land area required to grow the food for one person. So we're joined with this scientist, who has an advanced degree from the Playmobil Institute. And because of our studies with NASA, we've many times analyzed how much land he needs. This green felt represents the land area he needs to grows his own food. It's a small amount of land. If everything's perfect, he grows the food 365 days a year. He can sustain himself on this amount of land. Now we're going to send him into space. After all, we're trying to make a life support system for space. He's got to have some shelter, so we give him a house. But the house covers some of the land. Every photon is precious, so he's got to have a green roof on his house. Now he's ready, growing his own food. But he's going into the vacuum of space. So we're gonna give him a transparent dome, seal it up, recycle every drop of the water, grow the plants at just the right rate so the carbon dioxide and oxygen are in perfect balance, call up Morton Thiokol, put a big rocket under this, off it goes into space. He can go anywhere in the solar system and be self-sustaining, long as he doesn't go too far away from the Sun. What if he gets up one morning and says, “If you please, I would like an egg for breakfast”. He can't do it. We need additional land area to feed this chicken, to give him the egg. What if he says, “I'd like a glass of milk for lunch”? We need even more land area to feed the cow. If he eats the equivalent of 25 percent of his calories from animal products, which is the national average, it more than doubles the land area.

    We'll get up each day, my colleagues in animal science, my colleagues in plant science, and work to make water use efficiency in agriculture better, but small changes in our diets can have a much bigger effect than years of our research. Please think about your global food print the next time you think about putting food in the garbage disposal. Please think about that mustard seed and those fossil aquifers, and consider eating less meat. This is the diet for a small planet thank you.

    Submitting Your Assignment

    Please submit your assignment in Module 4 Formative Assessment in Canvas.

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