Water is an essential element in growing the food we eat. Also, the growing of our food has an effect on Earth's water resources as agricultural runoff contributes to pollution, and diversions for irrigation affect streamflow and deplete aquifers. In this module, we'll look at how water is a critical element in the production of food. We'll also explore some of the impacts that our food systems have on both the quality and quantity of our water resources.
Plants can't grow without water and in this module, we explore how plants use water and where that water comes from. Have you ever considered the fact that you eat a lot of water? All of the food you eat required water to grow, process, and transport. How much water did it take to make grow feed for the cattle that ultimately became the hamburger you had for lunch this week? Or to feed the chicken that laid the egg for your breakfast? Or to grow the coffee beans for your morning latte? Water is an essential component of our food system!
After completing this module, students will be able to:
Detailed instructions for completing assessments are provided with each module.
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If you have any questions, please send them through Canvas e-mail. We will check daily to respond. If your question is one that is relevant to the entire class, we may respond to the entire class rather than individually.
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How much water do you eat? Water is essential for food production. In this unit, you will learn about water as an essential ingredient to grow the food that we eat, including plants and animal products. The concepts of photosynthesis, evapotranspiration, and crop consumptive water use are introduced followed by an overview of the spatial variability of precipitation and the resulting need for irrigation. The final activity will introduce you to virtual water embedded in the food you eat and your water footprint.
The short animated video that follows was produced by the United Nations' Water group for World Water Day and illustrates how much water is embedded in a few different food products. The numbers are given in liters, so it's helpful to remember that there are 3.8 liters per gallon. A liter is a little bigger than a quart. In this module, we'll look at why it takes so much water to produce food and you'll estimate how much water you eat.
World water day 2012
Why is water so important to our food security?
Your bread: 650 liters
Your milk: 200 liters
Your eggs: 135 liters
Your steal: 7000 liters
Your vegetables: 13 liters
Your burger: 2400 liters
ALL YOU EAT NEEDS WATER TO GROW
Agriculture accounts for 70% of our total water use
So. Now. You. Know. Why.
By: FaowaterIf you do not see the video above, please go to YouTube [4] to watch it.
In order to understand why growing food uses so much water, we need to explore the process of evaporation. Evaporation is a hydrologic process that we're all quite familiar with, even if you aren't aware of it. Think about hanging clothes out to dry on the clothesline, or blow-drying your hair. Both of those involve the movement of water from its liquid form to its vapor or gaseous form that we call water vapor, or in other words, both involve the evaporation of water.
In what weather conditions do your clothes dry faster? A hot, dry, windy day, or a cool, cloudy, rainy day? Why do you use a blow drier to dry your hair? Water evaporates faster if the temperature is higher, the air is dry, and if there's wind. The same is true outside in the natural environment. Evaporation rates are generally higher in hot, dry, and windy climates.
The rate at which water evaporates from any surface, whether from a lake's surface or through the stomata on a plant's leaf, is influenced by climatic and weather conditions, which include the solar radiation, temperature, relative humidity, and wind (and other meteorological factors). Evaporation rates are higher at higher temperatures because as temperature increases, the amount of energy necessary for evaporation decreases. In sunny, warm weather the loss of water by evaporation is greater than in cloudy and cool weather. Humidity, or water vapor content of the air, also has an effect on evaporation. The lower the relative humidity, the drier the air, and the higher the evaporation rate. The more humid the air, the closer the air is to saturation, and less evaporation can occur. Also, warm air can “hold” a higher concentration of water vapor, so you can think of there being more room for more water vapor to be stored in warmer air than in colder air. Wind moving over a water or land surface can also carry away water vapor, essentially drying the air, which leads to increased evaporation rates. So, sunny, hot, dry, windy conditions produce higher evaporation rates. We will see that the same factors - temperature, humidity, and wind - will affect how much water plants use, which contributes to how much water we use to produce our food!
Evaporation requires a lot of energy and that energy is provided by solar radiation. The maps below (Figure 4.1.1) illustrate the spatial patterns of solar radiation and of annual evaporation rates in the United States. Notice how the amount of solar radiation available for evaporation varies across the US. Solar radiation also varies with the season and weather conditions. Note that annual evaporation rates are given in inches per year. For example, Denver, Colorado in the lake evaporation map is right on the line between the 30-40 inches and 40-50 inches per year of lake evaporation, so let's say 40 inches per year. On average, if you had a swimming pool in Denver, and you never added water and it didn't rain into your pool, the water level in your pool would drop by 40 inches in a year. Explore the maps and answer the questions below.
Plants need water to grow! Plants are about 80-95% water and need water for multiple reasons as they grow including for photosynthesis, for cooling, and to transport minerals and nutrients from the soil and into the plant.
"We can grow food without fossil fuels, but we cannot grow food without water."
Dr. Bruce Bugbee, Utah State University
We can't grow plants, including fruits, vegetables, and grains, without water. Plants provide food for both us and for the animals we eat. So, we also can't grow cows, chickens, or pigs without water. Water is essential to growing corn as well as cows!
Agriculture is the world's greatest consumer of our water resources. Globally about 70% of human water use is for irrigation of crops. In arid regions, irrigation can comprise more than 80% of a region's water consumption.
The movement of water from the soil into a plant's roots and through the plant is driven by an evaporative process called transpiration. Transpiration is just the evaporation of water through tiny holes in a plant's leaves called stomata. Transpiration is a very important process in the growth and development of a plant.
Water is an essential input into the photosynthesis reaction (Figure 4.1.2), which converts sunlight, carbon dioxide, and water into carbohydrates that we and other animals can eat for energy. Also, as the water vapor moves out of the plant's stomata via transpiration (Figure 4.1.2), carbon dioxide can enter the plant. The transpiration of water vapor out of the open stomata allows carbon dioxide (another essential component of photosynthesis) to move into the plant. Transpiration also cools the plant and creates an upward movement of water through the plant. The figure below (Figure 4.1.2) shows the photosynthesis reaction and the movement of water out of the plant's stomata via transpiration.
As water transpires or evaporates through the plant's stomata, water is pumped up from the soil through the roots and into the plant. That water carries with it, minerals and nutrients from the soil that are essential for plant growth. We'll talk quite a bit more about nutrients later in this module and future modules.
This drawing shows the sunlight shining down on a flower. The roots of the flower are in the soil and there is water in the soil. Carbon dioxide is going into the flower. Water vapor and oxygen are being released from the flower (Transpiration). The chemical formula for photosynthesis is shown as 6 CO2 (Carbon Dioxide) + 6 H2O (Water) an arrow representing light leads to C6H12O6 (Sugar) + 6 O2 (Oxygen).
The amount of water that a crop uses includes the water that is transpired by the plant and the water that is stored in the tissue of the plant from the process of photosynthesis. The water stored in the plant's tissue is a tiny fraction (<5%) of the total amount of water used by the plant. So, the water use of a crop is considered to be equal to the water transpired or evaporated by the plant.
Since a majority of the water used by the crop is the water that is transpired by the plant, we measure the water use of a plant or crop as the rate of evapotranspiration or ET, which is the process by which liquid water moves from the soil or plants to vapor form in the atmosphere. ET is comprised of two evaporative processes, as illustrated in figure 4.1.3 below: evaporation of water from soil and transpiration of water from plants' leaves. ET is an important part of the hydrologic cycle as it is the pathway by which water moves from the earth's surface into the atmosphere.
Remember, evaporation rates are affected by solar radiation, temperature, relative humidity, and the wind. ET, which includes evaporation from soils and transpiration from plants, is also evaporative, so the ET rate is also affected by solar radiation, temperature, relative humidity, and the wind. This tells us that crop water use will also be affected by solar radiation, temperature, relative humidity, and the wind! More water evaporates from plants and soils in conditions of higher air temperature, low humidity, strong solar energy, and strong wind speeds.
The transpiration portion of ET gets a little more complicated because the structure, age, and health of the plant, as well as other plant factors, can also affect the rate of transpiration. For example, desert plants are adapted to transpire at slower rates than plants adapted for more humid environments. Some desert plants keep their stomata closed during the day to reduce transpiration during the heat of a dry desert day. Plant adaptations to conserve moisture include wilting to reduce transpiration. Also, small leaves, silvery reflective leaves, and hairy leaves all reduce transpiration by reducing evaporation.
In summary, the amount of water that a crop needs is measured by the ET rate of a crop. The ET rate includes water that is transpired or evaporated through the plant. And, the ET rate varies depending on climatic conditions, plant characteristics, and soil conditions.
Diagram of Evapotranspiration. At the bottom is soil and below that, available soil water. In the soil are two plants with roots extending into the soil water. There are lines coming up from the soil representing evaporation from the soil. Lines from the plants represent transpiration from leaves. There is a line drawn around all of this, with the sun outside and humidity and temperature flowing in. An arrow from transpiration and evaporation leads to evapotranspiration.
If the ET rate of a crop determines the water use of that crop, we could expect water use of a single crop to vary in similar spatial patterns to evaporation rates. For example, if evaporation rates are very high in Arizona because of the hot, dry climate, you would expect ET rates to be higher for a given crop in that climate. ET is measured by the average depth of water that the crop uses, which is a function of the plant and of the weather conditions in the area. In cool, wet conditions, the plant will require less water, but under hot, dry conditions, the same plant will require more water.
Figure 4.1.4 shows a range of typical water use for crops in California. The graph shows how much water needs to be applied as irrigation to grow different crops. Notice how some crops, like alfalfa, almonds, pistachios, rice, and pasture grass can require four feet or more of water application. Other crops, like grapes, beans, and grains only require about one to two feet of water.
If we moved the plants in Figure 4.1.4 to a cooler and more humid climate, the rate of evaporation would be less and the crop water demand would decline as well. In a hot dry climate, you need to apply more water to the plant to keep it healthy and growing because more water is evaporating from both the soil and through the stomata on the plants’ leaves, so the plant is pulling more water out of the soil via its roots to replace the water transpiring from its leaves.
The source of water for most land plants is precipitation that infiltrates or soaks into the soil, but precipitation varies dramatically geographically. For example, we know that Florida gets a lot more precipitation per year than Arizona. Figure 4.1.5 below shows the average annual precipitation across the United States and around the globe. Notice on the map of the U.S. that the dark orange colors represent areas that get less than ten inches of precipitation per year. And, the darkest green to blue regions receive more than 100 inches or more than eight feet of precipitation per year!
Climate, including the temperature of a region and the amount of precipitation, plays an important role in determining what types of plants can grow in a particular area. Think about what types of plants you might see in a high water resource region versus a low water resource region. A low resource region with respect to water receives lower precipitation, so would have desert-like vegetation, whereas a higher resource region for water would have lusher native vegetation, such as the forests of the eastern US.
Regions that receive enough precipitation to grow crops without irrigation (i.e., those areas shaded green on the map below) would be considered high resource areas with respect to water. A high-resource region is more likely to be a more resilient food production region. In contrast, a low resource region with respect to water would be regions on the map below in the orange-shaded colors. In these regions, extra effort is needed to provide enough water for crops, such as through the development of an irrigation system.
Compare the crop water use values in Figure 4.1.6 with the average annual precipitation in Figure 4.1.5 and you'll see that there are parts of the US where there isn't enough precipitation to grow many crops. In fact, there is a rough line running down the center of the US at about the 100th meridian that separates regions that get more than about 20 inches of rain per year from regions that get less than 20 inches of rain per year. On the map in Figure 4.1.5, this line is evident between the orange-colored areas and the green-colored areas. Generally, west of the 100th meridian there is insufficient precipitation to grow many crops. If a crop's consumptive water use or ET is greater than the amount of precipitation, then irrigation of the crop is necessary to achieve high yields.
In regions where precipitation is insufficient to grow crops, farmers turn to other sources of water to irrigate their crops. Irrigation is the artificial application of water to the soil to assist in the growth of agricultural crops and other vegetation in dry areas and during periods of inadequate rainfall. These sources of water can be from either surface or groundwater. Surface water sources include rivers and lakes, and diversion of water from surface water sources often requires dams and networks of irrigation canals, ditches, and pipelines. These diversions structures and the resulting depletion in river flow can have significant impacts on our river systems, which will be covered in the next part of this module. The pumping of water for irrigation from aquifers also has impacts, which are also discussed in the next part of this module.
Water use for irrigation comprised about 80-90 percent of U.S. consumptive water use in 2005, with about three-quarters of the irrigated acreage being in the western-most contiguous states (from USDA Economic Research Service [10]). For example, in the state of Colorado, irrigation comprised 89% of total water withdrawals in 2010 (Figure 4.1.7). Irrigated agriculture is also very important economically, accounting for 55 percent of the total value of crop sales in the US in 2007 (from USDA Economic Research Service [10]). Globally only about 18 percent of cropland is irrigated, but that land produces 40 percent of the world's food and about 50 percent by value (Jones 2010).
In this activity, you will employ geoscience ways of thinking and skills (spatial thinking and interpretation of the spatial data to characterize specific regions for the geographic facility).
The amount of water used for irrigation varies depending on the climate and on the crop being grown, and it also depends on the irrigation technique used. Just like in your garden or home landscaping there are more or less efficient sprinklers. In many parts of the world flood or surface, irrigation is still used where water flows across a field and soaks into the soil.
Surface or flood irrigation is the least efficient manner of irrigation. When a field is flooded, more water than is needed by the plant is applied to the field and water evaporates, seeps into the ground, and percolates down to the groundwater, where it can be out of reach of the plant's roots. Another problem with flood irrigation is that the water is not always applied evenly to all plants. Some plants might get too much water, and others get too little. On the other hand, flood irrigation tends to use the least energy of any irrigation system.
Furrow irrigation (Figure 4.1.8) is another type of surface irrigation in which water is directed through gated pipe or siphon tubes into furrows between rows of plants. When using furrow irrigation, water is lost to surface runoff, groundwater, and evaporation, and it can be challenging to get water evenly to an entire field.
More efficient methods of irrigation include drip irrigation (Figure 4.1.9) sprinklers (such as center pivots, Figure 4.1.10), and micro-spray (Figure 4.1.11) irrigation. All of these methods, while more efficient, also require significant investments in equipment, pipes, infrastructure (e.g., pumps Figure 4.1.9) and energy. In addition to the high cost, some soil types, irrigation networks, field sizes, and crops pose greater challenges to the implementation of more efficient methods of irrigation. For example, in the Grand Valley of western Colorado, the irrigation network is entirely gravity-fed, meaning that farmers can easily flood and furrow irrigate without the use of pumps. In addition, the fields are small and the soils are very clayey, all of which make using center pivots for row crops particularly challenging and expensive. But, in the same valley, the peach orchards have successfully used micro-spray and drip systems. A major advantage of more efficient irrigation in addition to reduced water consumption is that crop yields are often higher because the water can be applied more directly to the plant when water is needed.
Table 4.1.1 presents data on the top 15 irrigated states in the United States. You can see how many acres of land are irrigated in each state, and how much water is used for irrigation of both surface water and groundwater. Consider the relationship between the amount of irrigated land in a state, the type of irrigation used and the amount of water used.
An acre-foot is a unit of measure for large volumes of water and is the volume of water required to cover one acre of land to a depth of one foot (325,851 gallons). Imagine a football field, including the end zones, one foot deep in water.
State | Irrigated Land (in thousand acres) by type of irrigation |
Surface Water Withdrawals | Groundwater Withdrawals | Total Irrigation Withdrawals | ||||||
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- | Sprinkler | Micro-irrigation | Surface | Total | Thousand acre-feet per year | % of irrigation water from surface water | Thousand acre-feet per year | % of irrigation water from groundwater | Thousand acre-feet per year | Percent of total water withdrawals used for irrigation |
California | 1790 | 2890 | 5670 | 10400 | 16100 | 62% | 9740 | 38% | 25840 | 61% |
Idaho | 2420 | 4.57 | 1180 | 3600 | 11500 | 73% | 4280 | 27% | 15780 | 82% |
Colorado | 1410 | 0.2 | 1930 | 3340 | 9440 | 87% | 1450 | 13% | 10890 | 88% |
Arkansas | 518 | 0 | 4150 | 4670 | 1500 | 15% | 8270 | 85% | 9770 | 77% |
Montana | 753 | 0.64 | 886 | 1640 | 7880 | 98% | 142 | 2% | 8022 | 94% |
Texas | 3770 | 244 | 1910 | 5920 | 1940 | 25% | 5710 | 75% | 7650 | 27% |
Nebraska | 6370 | 0.57 | 2360 | 8730 | 1520 | 24% | 4820 | 76% | 6340 | 70% |
Oregon | 1210 | 97 | 594 | 1900 | 3750 | 64% | 2140 | 36% | 5890 | 78% |
Arizona | 195 | 28.1 | 770 | 993 | 3220 | 63% | 1900 | 37% | 5120 | 75% |
Wyoming | 184 | 4.12 | 892 | 1080 | 4410 | 90% | 490 | 10% | 4900 | 93% |
Utah | 625 | 1.45 | 710 | 1340 | 3060 | 85% | 554 | 15% | 3614 | 72% |
Washington | 1270 | 86.1 | 221 | 1580 | 2630 | 75% | 894 | 25% | 3524 | 63% |
Kansas | 2840 | 18.1 | 217 | 3080 | 179 | 5% | 3230 | 95% | 3409 | 76% |
Florida | 548 | 712 | 731 | 1990 | 1500 | 46% | 1770 | 54% | 3270 | 20% |
New Mexico | 461 | 19.6 | 397 | 878 | 1640 | 54% | 1390 | 46% | 3030 | 86% |
Water is essential to growing food and every bite of food we consume required water to grow, process, and transport. The water necessary to grow, process, and transport food is often referred to as virtual water or embedded water. Virtual water is the entire amount of water required to produce all of the products we use, including our mobile phones and cotton t-shirts. But a global assessment of virtual water reveals that the majority of water that we consume is in the food we eat. If we total up all of the virtual water embedded in everything we use and eat, we can estimate our total water footprint. Water footprints can be used to provide insights into how much water is used every day in all of our activities including producing our food. For example, Figure 4.1.12 shows the amount of water used per person around the globe associated with wheat consumption. When you eat food imported from another region, you are eating the water of that region. The apple from New Zealand, grapes from Chile, and lettuce from California all required water to grow and by consuming those products you’re "eating" that virtual water. The concepts of virtual water and water footprints can be powerful tools for businesses and governments to understand their water-related risks and for planning purposes (water footprint network [12]).
Scroll through this infographic [14] explaining virtual water and then answer the questions below.
Please download the worksheet below for detailed instructions.
You will perform three activities in this assessment:
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.
Please submit your assignment in Module 4 Formative Assessment in Canvas.
Agricultural food production impacts water resources by depleting quantities of both surface water and groundwater and by polluting surface and groundwater with pesticides and fertilizers. Module 4.2 includes a brief introduction to the impacts of agriculture on water resources, followed by two case studies: the Colorado River (flow depletion and salinity) and the Mississippi River (nutrients, eutrophication, and the hypoxic zone in the Gulf of Mexico).
In completing this module, you will be able to:
Agricultural production has significant impacts on both the quality and quantity of surface and groundwater resources around the globe. In this unit, we'll look at how agricultural activities can contribute to water pollution, and we'll also consider how the diversion of irrigation water from both surface and groundwater resources creates significant impacts on those water resources and the ecosystems they sustain. Some of the critical issues connecting agricultural activities with water resource quality and quantity are:
As discussed in the first part of Module 4, in regions where precipitation is insufficient to grow crops, irrigation water is drawn from lakes, rivers, and aquifers to supplement the insufficient or unreliable precipitation. Water diversions for irrigation can have impacts on both surface and groundwater resources.
We saw earlier in this module that the western US receives less precipitation than the eastern US. What does that mean for irrigation needs? The western US withdraws more water from lakes, rivers, and groundwater for irrigation than the eastern US (Figure 4.2.1). These water withdrawals are not without impacts, as we will see throughout the rest of this module. Figure 4.2.1 maps the water withdrawal data we explored in the previous unit. Do you remember the three states in the US that diverted the most water for irrigation in the US? California, Idaho, and Colorado. But Nebraska irrigated more acres than both Idaho and Colorado. In the map in Figure 4.2.1, you can clearly see the states that use the most irrigation water. Next, we'll look at some of the impacts of surface and groundwater withdrawals.
The storage and redistribution of water by dams, diversions, and canals has been a key element in the development of civilizations. Large-scale water control systems, such as on the Nile in Egypt or the Colorado River in the southwestern U.S. make it possible to support large cities and millions of hectares of agricultural land. As the population grows and water diversions increase, serious questions are being raised about the environmental costs of these large water management systems.
Agricultural water withdrawals are placing significant pressure on water resources in water-scarce regions around the globe (Figure 4.2.2). If more than 20 percent of a region's renewable water resources are withdrawn, the region is in a state of water scarcity and the water resources of the region are under substantial pressure. If the withdrawal rises to 40 percent or more, then the situation is considered critical and evidence of stress on the functions of ecosystems becomes apparent. More than 40% of the world's rural population lives in river basins that are physically water-scarce and some regions, such as parts of the Middle East, Northern Africa, and Central Asia, are already withdrawing water in excess of critical thresholds (FAO 2011).
In order to divert water from rivers, diversion structures or dams are usually constructed and create both positive and negative effects on the diverted river system. Dams can provide a multitude of benefits beyond their contribution to storage and diversion for agricultural uses. Dams can contribute to flood control, produce hydroelectric power, and create recreational opportunities on reservoirs. Negative impacts of dams and agricultural diversions include:
This world map shows that water famine especially high in the Southwestern United States and large areas of Africa, the Middle East, and South Asia.
Where surface water supplies are insufficient, groundwater is often used for irrigation (Figure 4.2.3). Agriculture uses about 70% of the groundwater pumped for human use globally and about 53% of the groundwater pumped in the US (USGS: Groundwater use in the United States [20]). In some parts of the world, groundwater is pumped at a faster rate than natural processes recharge the stored underground water. Groundwater use where pumping exceeds recharge is non-renewable and unsustainable.
Another problem that may occur in some aquifers with excessive groundwater pumping is a compaction of the aquifer and subsidence of the ground surface. When the water is pumped from the pore spaces in the aquifer, the pore spaces compress. The compression of millions of tiny pore spaces in hundreds of meters of aquifer material manifests on the surface as subsidence. The ground elevation actually decreases. Subsidence from groundwater pumping is irreversible and leaves the aquifer in a condition where it cannot be recharged to previous levels.
Our reliance on and depletion of groundwater resources is becoming a global concern as aquifers are being pumped at unsustainable rates in the US (Figure 4.2.4) and all over the world. Enhanced irrigation efficiencies and conservation measures are being implemented when possible to prolong the life of some aquifers. Unfortunately, groundwater is often the water resource that we turn to in times of drought or when other surface-water resources have been depleted. For example, in California during the recent drought, farmers drilled wells and used groundwater to save their crops when surface water resources were not available.
This map of the U.S. shows total groundwater withdraws by state, in millions of gallons per day. California has the highest at 20,000 - 60,000. Nebraska follows at 10,000 - 20,000. Texas and Arkansas are 5,000 - 10,000, Mississippi, Florida, Colorado, Kansas, Arizona, Oregon, and Idaho are each 2,000 - 5,000. The rest of the country is 0 - 2000.
Rosenberg, David M., Patrick McCully, and Catherine M. Pringle. "Global-scale environmental effects of hydrological alterations: introduction. [23]" BioScience 50.9 (2000): 746-751.
Runoff from agricultural areas is often not captured in a pipe and discharged into a waterway; rather it reaches streams in a dispersed manner, often via sub-surface pathways, and is referred to as non-point source pollution. In other words, the pollutants do not discharge into a stream or river from a distinct point, such as from a pipe. Agricultural runoff may pick up chemicals or manure that were applied to the crop, carry away exposed soil and the associated organic matter, and leach materials from the soil, such as salts, nutrients or heavy metals like selenium. The application of irrigation water can make some agricultural pollution problems worse. In addition, runoff from animal feeding operations can also contribute to pollution from agricultural activities.
The critical water quality issues linked to agricultural activities include:
Review the following fact sheet on agricultural impacts on water quality:
Protecting Water Quality from Agricultural Runoff, 2005, EPA Fact Sheet on Agricultural Runoff [24]
The Colorado River in the southwestern U.S. is an excellent case study of a river that is highly utilized for irrigation and agriculture. A majority of the Colorado River’s drainage basin has an arid or semi-arid climate and receives less than 20 inches of rain per year (Figure 4.2.5), and yet the Colorado River provides water for nearly 40 million people (including the cities of Los Angeles, San Diego, Phoenix, Las Vegas, and Denver) and irrigates 2.2 million hectares (5.5 million acres) of farmland, producing 15 percent of U.S. crops and 13 percent of livestock (USBR 2012). Much of the irrigated land is not within the boundaries of the drainage basin, so the water is exported from the basin via canals and tunnels and does not return to the Colorado River (Figure 4.2.6).
The net results of all of these uses of Colorado River water (80 percent of which are agricultural) in both the U.S. and Mexico are that the Colorado River no longer reaches the sea, the delta is a dry mudflat, and the water that flows into Mexico is so salty as a result of agricultural return flows that the U.S. government spends millions of dollars per year to remove salt from the Colorado River.
Many farmers in the Colorado River basin are working to use Colorado River water more efficiently to grow our food and food for the animals that we eat. Watch the video below and answer the questions to learn more about farming in the Colorado River basin.
Watch the following video then answer the questions below
Narrator: A drop of water from a sprinkler on a quiet Los Angeles street. A shower head in a Las Vegas hotel. Agricultural land in California's Imperial Valley. Where does all this water come from? The Colorado River. In 1922, representatives from seven states gathered at Bishop’s Lodge New Mexico to sign the Colorado River Compact, an agreement on how to allocate water in this precious river system. But that River had more water then, than it does today. The Colorado River Basin touches the lives of every American. The river system runs through seven states in the US, and two in Mexico, and supplies water for over 36 million people. It also irrigates over five million acres of cropland and provides eighty percent of our winter produce, all from one river. And agriculture is the first to feel the pressure. At the headwaters of the Colorado River, farmers and ranchers are creating a toolbox of resilience. They save water with efficient technology and by building healthy soil.
Brendon Rockey, Rockey Farms, Center, Colorado: My grandpa always had a philosophy on this farm that you have to take care of the soil before the soil can take care of you, and he just felt like we had gotten away from that. That's the number one thing with everybody. is yield, yield, yield. Everybody wants just big production, you know, so that's why you want to dump on the fertilizer, kill off anything that poses a threat. It's all about production. We put more of an emphasis on quality. And what's really nice is when you put the emphasis on quality, the quantity usually comes along with it.
Narrator: And he also uses less water. How? By managing his soil more efficiently and working with nature instead of against it. Brendon rotates his potato crops with green manure, or cover crops, that enhance soil health while reducing his dependence on pesticides, fertilizers, and water.
Narrator: Unhealthy soil lacks life. Often a crust forms on its surface. When a crop is watered, very little soaks into the soil. Instead, it sits on top and is left to evaporate or run off. This land often has to be watered more frequently to get water to the crops. Healthy soils teem with life and are often built when farmers plant a mix of cover crops that add nutrients to the soil. When these plants die they become organic matter which helps store water in the soil. That means farmers can irrigate less, and have more certainty in times of drought.
Brendon Rockey: The reason we got into cover cropping was a response to a drought. Now that we've brought in more diverse crops, that have diverse root systems, which actually help benefit the water use efficiency as well, we've regenerated the soil to the point now where I'm growing a potato crop on about 12 to 14 inches of irrigation water per year. We're focusing on the soil, we're investing in the soil and we're bringing up for the functionality of the soil back to its optimum range.
Mike Jensen, Homegrown Biodynamic Farm, Bayfield, Colorado: A farm after 20 years should have much better soil than when it started. The best thing I do for my land is cover cropping. It rejuvenates the soil keeps everything happy, gets all the flora and fauna in balance. It's not about production this year, it's about production for the next 30 years.
Mike Nolan, Mountain Roots Produce, Mancos, Colorado: One thing I've learned from a bunch of folks, old-timers I've worked with is, do your best to not ever have any bare ground, nothing open, no open soil. I mean even in nature, even in the desert, technically there are things covering the ground. There's things, fungi and bacteria, that are holding the ground together. So what I did about three weeks ago is I planted out this oats crop. I’m not gonna harvest this for the seed or anything, but what it's going to do, it's going to hold moisture in here.
Cynthia Houseweart, Princess Beef Company, Hotchkiss, Colorado: Right now we're in full bloom, but what I like to see is a variety of plants. I don't want to just see straight alfalfa, I want to see grass and, and clover. I don't want bare ground. If we didn't have irrigation water, we would be a desert. This would be sagebrush, cedar trees. This, the water is what creates our livelihood. We graze during the growing season. So the conventional thing is, you move your cows off your pastures, grow them and cut them for hay. What we do instead of cutting them for hay, we graze them.
Narrator: Cynthia waters, using a center pivot. As it moves across her fields, the cattle follow behind eating fresh grass.
Cynthia: And the things they trample in, and their manure, adds to the soil, feeds the soil. It breaks down, turns into humus. The soil becomes more like a sponge and can suck up water that we put on it and rain, so the soil improves, which means the plants grow better and then our cows look better.
Dan James, James Ranch, Durango, Colorado: When you build topsoil, you increase the capillary action of the soils ability to retain water; and the less frequent you're applying your water, the more those roots have to go after that water, as it recedes into the ground. And so now you have all these roots below the surface, and all of a sudden here comes your cow. She comes in and she clips that off. Now your plant’s this high and the plant sheds the same proportion of roots. Now you're adding organic material and you're growing topsoil.
Strengthening the soil is also a concern of Steve Ela, a fruit grower in Hotchkiss Colorado. With precise tools like micro sprinklers and permanent drip irrigation, Steve can use water precisely when and where he needs it most, and his soil is healthy enough to efficiently deliver that water to his crops.
Steve Ela, Ela Family Farms, Hotchkiss, Colorado: For us on the farm it's the difference between using first furrows and the micro specters and now drip. It’s been a bit of an evolution of thinking. So for me it's been, it's not that really one system is better or worse, but it's an evolution of thinking, of trying to manage our water better, trying to use the system of irrigation management and cover cropping to manage our weeds, and also to just only to grow better fruit and healthier trees. Yes, it's expensive on the upfront cost, but it's a system then we can use for 20 years. It's very efficient. I think it probably saves us that much, you know, in water.
Narrator: It's innovation that saves water and money, while increasing soil fertility. It's also innovation that includes technology. Water data delivered by weather satellites, GPS, and even smart sensors like those used by Randy Meaker, a Colorado wheat and corn grower. He uses cover crops to improve his soil and by monitoring soil moisture, he can more effectively use the center pivots to reduce water use.
Randy Meaker: There are huge efforts going on right now, trying to figure out how we and the western United States can solve the shortages of water due to drought conditions. There's two ways to keep water in a bucket and one is to put more water in at the top, the other one is to take less water out at the spigot. People in the lower Basin States, where the population centers are, they're looking for us to supply them more water. But what we're looking for is a responsible use from them. What good is it for me to be restricted if I realize that we're still irrigating lawns, we're still washing cars.
Narrator: Water is the lifeblood of our Western landscape. Farmers and ranchers are as essential to it as the water itself. The water challenges these farmers face are many, but across the country they gather to share their water knowledge and provide each other with valuable support. They build community and grow good food, while stewarding both their land and their water. They are the water stewards of the Colorado River Basin.
Agricultural runoff can contribute pollutants to natural waters, such as rivers, lakes, and the ocean, that can have serious ecological and economic impacts, such as the creation of areas with low levels of dissolved oxygen called dead zones caused by pollution from fertilizers. Nutrients, such as nitrogen and phosphorus, are elements that are essential for plant growth and are applied on farmland as fertilizers to increase the productivity of agricultural crops. The runoff of nutrients (nitrogen and phosphorus) from fertilizers and manure applied to farmland contributes to the development of hypoxic zones or dead zones in the receiving waters through the process of eutrophication (Figure 4.2.7).
Watch the following videos from NOAA’s National Ocean Service that show how dead zones are formed and explain the dead zone in the Gulf of Mexico:
The nutrients that make our crops grow better also fertilize phytoplankton in lakes and the ocean. Phytoplankton are microscopic organisms that photosynthesize just like our food crops. With more nitrogen and phosphorus available to them, they grow and multiply. When the phytoplankton dies, decomposers eat them. The decomposers also grow and multiply. As they’re eating all of the abundant phytoplankton, they use up the available oxygen in the water. The lack of oxygen forces mobile organisms to leave the area and kills the organisms that can’t leave and need oxygen. The zone of low oxygen levels is called a hypoxic or dead zone. Streams flowing through watersheds where agriculture is the primary land use exhibit the highest concentrations of nitrogen (Figure 4.2.8).
The Mississippi River is the largest river basin in North America (Figure 4.2.9), the third largest in the world, and drains more than 40 percent of the land area of the conterminous U.S., 58 percent of which is very productive farmland (Goolsby and Battaglin, 2000). Nutrient concentrations in the lower Mississippi River have increased markedly since the 1950s along with increased use of nitrogen and phosphorus fertilizers (Figure 4.2.10). When the Mississippi River’s nutrient-laden water reaches the Gulf of Mexico, it fertilizes the marine phytoplankton. These microscopic photosynthesizing organisms reproduce and grow vigorously. When the phytoplankton die, they decompose. The organisms that eat the dead phytoplankton use up much of the oxygen in the Gulf’s water resulting in hypoxic conditions. The resulting region of low oxygen content is referred to as a dead zone or hypoxic zone. The dead zone in the Gulf of Mexico at the mouth of the Mississippi River has grown dramatically and in some years encompasses an area the size of the state of Connecticut (~5,500 square miles) or larger. Hypoxic waters can cause stress and even cause the death of marine organisms, which in turn can affect commercial fishery harvests and the health of ecosystems.
The dead zone in the Gulf of Mexico is primarily a result of runoff of nutrients from fertilizers and manure applied to agricultural land in the Mississippi River basin. Runoff from farms carries nutrients with the water as it drains to the Mississippi River, which ultimately flows to the Gulf of Mexico. If a number of nutrients reaching the Gulf of Mexico can be reduced, then the dead zone will begin the shrink.
Since 2008, the Hypoxia Task Force, led by the U.S. Environmental Protection Agency and consisting of five federal agencies and 12 states, has been working to implement policies and regulations with the aim of reducing the size of the dead zone in the Gulf of Mexico. Many of the strategies for reducing nutrient loading target agricultural practices including (USEPA, The [37]Sources [37] and Solutions: Agriculture [37]).
Watch the following video from the US Department of Agriculture about strategies to reduce nutrient loading into the Mississippi River:
EPA website about nutrient pollution and some solutions to nutrient pollution: The Sources and Solutions: Agriculture [38]
Review the graphs below and answer the questions that follow. Figure 4.2.11 presents the size of the hypoxic zone in the Gulf of Mexico from 1985 to 2014. The U.S. Environmental Production Agency led a task force in 2008 that identified a goal to reduce the five-year average of the size of the dead zone to less than 2,000 square miles by 2015.
Water is essential to growing food, and the source of water for food production is either naturally occurring precipitation or irrigation from surface or groundwater. The application of fertilizers and pesticides to crops results in the production of water pollution. We can incorporate water resources into our Coupled Human-Natural System diagram, where the climate of the natural system determines the availability of water for food production. The response in the human system is to develop irrigation systems where necessary and implement conservation and efficiency measures in times of scarcity. Also, the application of fertilizers and pesticides results in water pollution, which impacts the water quality in the natural system.
In the summative assessment for Module 4, you'll apply what you've learned about coupled human and natural water systems to a particular farming scenario in Pawnee County, Kansas. You'll consider the precipitation in Kansas, the crops you could grow with that precipitation and then look at crop yields for different crops using irrigation. Finally, you'll consider the impact on water resources if you were to shift the types of crops grown and irrigation practices on a farm in Pawnee County, KS. The assignment is explained in the worksheet below.
Water is essential to growing food, and the source of water for food production is either naturally occurring precipitation or irrigation from surface or groundwater. The application of fertilizers and pesticides to crops results in the production of water pollution. We can incorporate water resources into our Coupled Human-Natural System diagram, where the climate of the natural system determines the availability of water for food production. The response in the human system is to develop irrigation systems where necessary and implement conservation and efficiency measures in time of scarcity. Also, application of fertilizers and pesticides results in water pollution, which impacts the water quality in the natural system.
In the summative assessment for Module 4, you'll apply what you've learned about coupled human and natural water systems to a particular farming scenario in Pawnee County, Kansas. You'll consider the precipitation in Kansas, the crops you could grow with that precipitation and then look at crop yields for different crops using irrigation. Finally, you'll consider the impact on water resources if you were to shift the types of crops grown and irrigation practices on a farm in Pawnee County, KS. The assignment is explained in the worksheet below.
After completing the worksheet, please complete the Module 4 Summative Assessment in Canvas.
Your assignment will be evaluated based on the following rubric. The maximum grade for the assignment is 40 points.
Criteria | Possible Points |
---|---|
Part 1: Precipitation | |
Precipitation rates from map are correct | 2 |
Part 2: Crops | |
List of crops correctly represents crops that could be grown with natural precipitation | 4 |
Part 3: Irrigation Efficiency and Crop Yield | |
Scenario table correctly populated with results from the Crop Water Allocator | 14 |
Part 4: Discussion and Synthesis | |
Includes correct usage of the concept of water footprints and connection between diet and water consumption. | 5 |
Clearly explains connections between farming, water scarcity, dead zones, and irrigation efficiency. Also demonstrates clearly the connection between increased water consumption and impacts to water resources, including quality and quantity impacts, such as nutrient pollution and groundwater depletions. | 10 |
Well-written, proper spelling and grammar, and uses complete and well-crafted sentences. | 2 |
Logical presentation of topics. Reasonable length. | 3 |
TOTAL | 40 |
This module has introduced some important concepts that tie our food system to the Earth's water resources. Water resources are essential for food production, and food production also has significant impacts globally on both the quantity surface and groundwater and the quality. Growing crops relies on water from either precipitation or irrigation derived from surface and groundwater. Virtual water is embedded in everything you eat, with the amount of water varying, depending on the crop and the climate in which the crop was grown. Crops grown in hot and dry climates consume more water via transpiration as evaporation rates are higher in those climates. Also, some plants need more water than others, for example, rice uses more water to grow than corn. You explored precipitation rates in different parts of the US compared to evaporation rates and considered how much water might need to be applied to certain crops. Computation of your personal water footprint allowed you to compare your lifestyle and resulting water consumption with average water consumption in the US and globally. Also, these computations along with consideration of virtual water in different food products allowed you to draw conclusions about the impacts of different types of diets on the planet's water resources.
In this unit, we've just touched the surface of the very large issue of how agriculture impacts both the quality and quantity of our water resources. We also looked at a few examples of agricultural practices that help to minimize and reduce these impacts.The Colorado River provided an example of a river on which agricultural diversions have severely impacted the quantity of water in the river. We saw that the Colorado River no longer reaches the sea! The breadbasket of the US, the Midwest, contributes nutrient pollution to the Mississippi River, which has, in turn, created a massive dead zone in the Gulf of Mexico. You explored data on the size of the dead zone and proposed strategies to reduce the nutrient loading and thereby reduce the size of the dead zone in the future.
You have reached the end of Module 4! Double-check the to-do list on the Module 4 Roadmap [44] to make sure you have completed all of the activities listed there before moving on to Module 5!
Links
[1] https://www.epa.gov/sites/production/files/2015-09/documents/ag_runoff_fact_sheet.pdf
[2] https://www.e-education.psu.edu/geog3/node/1099
[3] https://www.e-education.psu.edu/geog3/node/1191
[4] https://www.youtube.com/watch?v=U26Na9Xa5Ug&feature=youtu.be
[5] https://commons.wikimedia.org/wiki/File:Photosynthesis.gif
[6] https://creativecommons.org/licenses/by-sa/3.0/deed.en
[7] http://pacinst.org/publication/california-agricultural-water-use-key-background-information/
[8] http://nationalmap.gov
[9] http://12.000.scripts.mit.edu/mission2017/solutions/engineering-solutions/rainwater-harvesting-techniques/
[10] http://www.ers.usda.gov/topics/farm-practices-management/irrigation-water-use/background.aspx
[11] https://pubs.usgs.gov/circ/1405/
[12] http://waterfootprint.org/en/water-footprint/
[13] https://www.pnas.org/doi/10.1073/pnas.1109936109
[14] https://thewaterweeat.com/
[15] https://www.e-education.psu.edu/geog3/sites/www.e-education.psu.edu.geog3/files/Mod4/Geog3_Module4_Formative2.docx
[16] http://waterfootprint.org/en/resources/interactive-tools/personal-water-footprint-calculator/
[17] https://www.yumpu.com/en/document/view/37673587/bozza-scheda-dow04-10
[18] http://water.usgs.gov/edu/wuir.html
[19] http://www.fao.org/fileadmin/templates/solaw/images_maps/map_3.pdf
[20] https://water.usgs.gov/edu/wugw.html
[21] http://water.usgs.gov/edu/wugw.html
[22] https://water.usgs.gov/edu/gwdepletion.html
[23] https://www.e-education.psu.edu/geog3/sites/www.e-education.psu.edu.geog3/files/Mod4/BioScience-2000-Rosenberg-746-51.pdf
[24] https://www.e-education.psu.edu/geog3/sites/www.e-education.psu.edu.geog3/files/Mod4/Ag_Runoff_Fact_Sheet.pdf
[25] https://www.youngfarmers.org/
[26] http://water.epa.gov/type/watersheds/named/msbasin/images/eutro_big.jpg
[27] https://oceantoday.noaa.gov/happnowdeadzone/
[28] https://www.e-education.psu.edu/geog3/node/1275
[29] https://oceanservice.noaa.gov/hazards/hypoxia/
[30] https://www.e-education.psu.edu/geog3/node/1276
[31] https://pubs.usgs.gov/fs/2010/3078/
[32] http://ks.water.usgs.gov/pubs/fact-sheets/fs.135-00.html
[33] https://water.usgs.gov/nawqa/headlines/nut_pest/USGS-Trends-Sprague.pdf
[34] http://www.gulfhypoxia.net/
[35] https://coastalscience.noaa.gov/
[36] http://pubs.usgs.gov/fs/2003/fs-105-03/
[37] https://www.epa.gov/nutrientpollution/sources-and-solutions-agriculture
[38] http://www2.epa.gov/nutrientpollution/sources-and-solutions-agriculture
[39] https://coastalscience.noaa.gov/research/stressor-impacts-mitigation/habhrca/ngomex/
[40] https://www.epa.gov/sites/production/files/2015-03/documents/hypoxia_reassessment_508.pdf
[41] https://www.e-education.psu.edu/geog3/sites/www.e-education.psu.edu.geog3/files/Mod4/Module4_Summative_Revised092518.docx
[42] https://www.e-education.psu.edu/geog3/sites/www.e-education.psu.edu.geog3/files/Mod4/Module4_Summative_Revised092518PDF%202.pdf
[43] https://www.e-education.psu.edu/geog3/sites/www.e-education.psu.edu.geog3/files/Mod4/Module4_SummativeResults.xlsx
[44] https://www.e-education.psu.edu/geog3/node/606
[45] http://pubs.usgs.gov/fs/2010/3078/
[46] https://pubmed.ncbi.nlm.nih.gov/22331890/
[47] http://www2.epa.gov/sites/production/files/2015-03/documents/hypoxia_reassessment_508.pdf
[48] http://www.usbr.gov/lc/region/programs/crbstudy/finalreport/index.html
[49] http://www.arcgis.com/home/item.html?id=0698165058384852b23f31b26ae7cace
[50] https://agwaterconservation.colostate.edu/ag-water-faqs/crop-water-use/
[51] http://waterfootprint.org/en/resources/interactive-tools/product-gallery/
[52] https://youtu.be/h23IHDOKhZc
[53] https://youtu.be/j9JywZGtXA4
[54] https://youtu.be/U26Na9Xa5Ug
[55] https://youtu.be/64W2yh4RsgI
[56] http://www.fao.org/nr/water