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5.3: Summary and Final Tasks

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    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.

    Reminder - Complete all of the Module 4 tasks!

    You have reached the end of Module 4! Double-check the to-do list on the Module 4 Roadmap to make sure you have completed all of the activities listed there before moving on to Module 5!

    References and Further Reading

    • Dubrovsky, N.M. and P.A. Hamilton, 2010, Nutrients in the Nation’s Streams and Groundwater: National Findings and Implications, USGS Fact Sheet 2010-3078 (
    • FAO, 2011, The State of the World’s Land and Water Resources for Food and Agriculture (SOLAW) - Managing systems at risk. Food and Agricultural Organization of the United Nations, Rome and Earthscan, London.
    • Goolsby, D.A., and Battaglin, W.A., 2000, Nitrogen in the Mississippi Basin--Estimating sources and predicting flux to the Gulf of Mexico: U.S. Geological Survey Fact Sheet 135-00, 6 p.
    • Hoekstra, A.Y. and M.M. Mekonnen, 2012. The water footprint of humanity, Proceedings of the National Academy of Science, vol. 109, no. 9, pp. 3232-3237 (
    • Jones, J.A.A., 2010, Water Sustainability: A Global Perspective, Hodder Education, 452 pp.
    • Mississippi River Gulf of Mexico Watershed Nutrient Task Force, 2013, Reassessment 2013: Assessing Progress Made Since 2008, Accessed from
    • U.S. Bureau of Reclamation (USBR), 2012, Colorado River Basin Water Supply and Demand Study,

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