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What's the Nonpoint? Assessing Nonpoint Source Water Quality Threats Nationwide

This article is from Issue Freshwater - Vol. 18 No. 1.

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Nonpoint source water pollution comes from large areas or landscapes such as roadways, farms, and urban and suburban communities. Scientists know this type of pollution exists, but it is difficult to identify and control the sources.  In this study, scientists were interested in determining how the threat from nonpoint source water pollution varies in watersheds across the United States.

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Reflection Section Answer Guide

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Additional Resources for this Article:
Meet the scientists that contributed to this article:

"Thinking About Science Themes" covered in this article:
When scientists want to figure out the total impact of a number of unlike variables on another variable, they need a standard way to measure the variables. In this research, for example, the scientists wanted to know how a combination of variables might impact the level of water pollution risk in an area. These variables had different units of measurement. A unit of measurement is a standardized quantity of a physical property, such as inches, meters, degrees Celsius, etc. Different units of measurement cannot be added together. As an example, consider how we measure percentage of cloud cover and air temperature. Adding the percentage of cloud cover to the air temperature produces a senseless number. In this research, the scientists divided the range of measurement for each variable into five equal categories. Each category represented 20 percent of the entire range of values. A category representing an equal percentage of the whole is called a percentile. Then, the scientists assigned a number from 1 to 5 for each measured value. A value in the lowest 20 percent of the range, for example, was given a score of 1. A measurement in the highest 20 percent of the range was given a score of 5 (figure 1). This process standardized the relative value of each variable so that the values could be compared and summed.
Specific "Thinking About Science" Themes:
  • The Scientific Process

"Thinking About Environmental Themes" covered in this article:
Congress passed the Federal Water Pollution Control Act in 1972. Since the actís passage, water pollution coming from point sources has been reduced. Point sources of pollution are those that directly release pollution into a water source and may include factories and wastewater treatment plants. This reduction was possible because it is easy to identify point sources of pollution (figure 2). Nonpoint sources of pollution, in contrast, are not easily identified or controlled. These sources are not easily identified or controlled because nonpoint sources of pollution include things like farms, roadways, and urban and suburban communities (figure 3). The scientists in this study were interested in better understanding the risk of water pollution from nonpoint sources across the entire United States.
Specific "Thinking About the Environment" Themes:
  • Nonpoint Source Pollution
  • Water

NSE Standards covered in this article:
  • Abilities necessary to do scientific inquiry (A)
  • Abilities of technological design (E)
  • History of science (G)
  • Motions and forces (B)
  • Nature of science (G)
  • Personal health (F)
  • Populations and ecosystems (C)
  • Populations, resources and environments (F)
  • Properties and changes of properties in matter (B)
  • Science and technology in society (F)
  • Science as a human endeavor (G)
  • Structure and function in living systems (C)
  • Structure of the earth system (D)
  • Transfer of energy (B)
  • Understandings about science and technology (E)
  • Understandings about scientific inquiry (A)