Initial Publication Date: October 15, 2021

Student Guides

Download the student guide as a PDF:

Student Guide - Nitrogen and the Water Cycle (Acrobat (PDF) 1.3MB Oct28 21)
Student Guide - Antibiotics and the Water Cycle (Acrobat (PDF) 1.7MB Oct28 21)
Student Guide - Mercury and the Water Cycle (Acrobat (PDF) 1.5MB Oct28 21)

Water connects all elements of Earth's ecosystems, and human activities – biological, economic, and even recreational – change the chemical and biological nature of water. As such, maintaining the quality of water for humans and other organisms is a wicked problem, that is, a complex societal challenge that is impossible to fully solve. As we experience a growing world population, increasing consumption of resources, and global climate change, the problem of downstream water pollution becomes ever more complex. Many human activities impact water quality, including agriculture and food production in rural areas, sewage and wastewater disposal in urban areas, the generation of electricity, manufacturing and other industrial processes, and even the use of lifesaving pharmaceuticals that ultimately end up in our water.

Water supports life and is essential for our economy, but everything we do is likely to impact the quality of our water supply in some way. How do we provide for the water-related needs of a growing population, while ensuring an adequate supply of clean water for our neighbors and for future generations?

Clean Water and Sanitation is one of the 17 U.N. Sustainable Development Goals (opens in a new tab)., the interrelated goals that help international policymakers identify targets and actions for ending poverty, reducing inequality, and protecting the planet. Sustaining resources and improving quality of life for more people on our planet requires planning that crisscrosses issues, time, and space. It is not difficult to imagine how clean water (Goal #6) is directly related to many of the other goals. Water is health, comfort, and security, and nobody on the planet can live without an adequate supply of clean water.

To begin to understand what makes water quality a "wicked problem," consider the Mississippi River Watershed. This vital region in the central U.S. is really a system of people living in cities, growing food, integrated with the natural environment, an essential player in regional and global trade, and a set of complex societal and environmental challenges that need to be solved. In this exercise, you will explore the way complex problems intertwine natural systems with human activities that provide for our physical health and economic well-being.

By the end of the exercise, you will be able to:

Locate and describe interactions between human and natural systems.
Diagram key components of a complex system focused on water quality and identify different stakeholder perspectives or interests associated with water use.
Explain how differing power dynamics among stakeholders creates conflict and the potential for social/environmental injustice.

What do we mean by a "system," and how can it help us analyze complex problems?

A "system" is an interconnected group of parts that define a unified whole (Wikipedia). We can study ecosystems (interrelated organisms and the components of their natural environment), social systems (human communities and their physical infrastructure), economic systems (people and institutions involved in the production and distribution of goods and services), and many other types of natural and human-created systems. In order to analyze a system, you must be able to identify the critical (or key) components of the system and understand how they interact. You also need to have some idea of how a disruption in one part of the system causes a reaction in other parts of the system. We will explore this in more detail by looking at water pollution in the Mississippi River Watershed, a complex integration of natural and human systems.

The Mississippi River Watershed as a Complex System

The Mississippi River system is vast. The headwaters of the Mississippi River begin in Minnesota and courses through 10 states, before it discharges into the Gulf of Mexico. The Mississippi River is the second longest river in the United States at 2,202 mi (3,544 km). The longest river is the Missouri River at 2,341 mi (3,768 km), but because it drains into the Mississippi, the Mississippi River drainage basin or watershed, is actually considered the largest. Covering an area over 1,245,000 mi²(3,220,000 km²), the Mississippi River Watershed encompasses over 40% of the contiguous U.S. and is one of the largest drainage basins in the world. Practically, that means any rainwater (or melting snow) that falls in a 32 state area is carried downstream to the Gulf of Mexico.

Clearly such a large region contains lots of people, industry, and farmland, not to mention the major cities of Minneapolis, St. Louis, Memphis, and New Orleans. The sheer size of the Mississippi River Watershed means that human activities — like the intensive agriculture required for our food supply, livestock, and global trade —are intimately connected to the natural and human systems that move water downstream and keep the water clean for the plants and animals inhabiting it. Since all water (for example, rainwater, snowfall, surface streams, groundwater, and water vapor in the atmosphere) is connected, the "fingerprint" from human activities like farming, waste disposal, transportation, or even just urban street runoff, all moves downstream. When the chemical or biological fingerprint has a negative impact, that's downstream pollution.

Pollutants in the Mississippi River Watershed

Depending on the pollutant your instructor has selected, you may only need to read about a specific pollutant.

The Water Cycle and Nitrogen in the Mississippi River Valley

Show Water Cycle and Nitrogen in the Mississippi River Valley

To illustrate the "wicked" nature of maintaining water quality downstream, we're going to zero in on a significant pollutant in the Mississippi River system: nitrogen. Like water, nitrogen is everywhere. It comprises most of the air we breathe and is a component of all living matter, making it critical to life on Earth. Humans have dramatically increased the amount of nitrogen that is biologically available by harnessing it as fertilizer. As it moves and changes chemically, too much nitrogen in the wrong place and in the wrong form can be a pollutant. But because it's so abundant, so essential, and it is created and distributed by such a wide range of human activities, it provides a useful illustration of a wicked problem associated with a common chemical pollutant in river systems.

Before we identify how and where nitrogen problems arise from human activities, we need to understand where those activities interact with the water cycle. You've probably been learning about water and the water cycle since you were a child. Figure 1 illustrates the movement and change of water and several ways that the natural movement of water intersects with human activities. It's clear that there are lots of opportunities for human systems and natural systems to interact around water.

Watch this video for a quick refresher on the water cycle (opens in a new tab) andthis video on human aspects of the water cycle (opens in a new tab).

Watch these brief videos

Watch this video that illustrates one kind of interaction: connecting fertilizer runoff with drinking water (opens in a new tab).
And finally,view this interactive story of nutrient pollution in the Mississippi River watershed (opens in a new tab).

The Water Cycle and Antibiotics in the Mississippi River Valley

Show Water Cycle and Antibiotics in the Mississippi River Valley

To illustrate the "wicked" nature of maintaining water quality downstream, we are going to zero in on a significant pollutant in the Mississippi River system: antibiotics.

Before we identify how and where antibiotics problems arise from human activities, we need to understand where those activities interact with the water cycle. You have probably been learning about water and the water cycle since you were a child. Figure 1 illustrates the movement and change of water and several ways that the natural movement of water intersects with human activities. It is clear that there are lots of opportunities for human systems and natural systems to interact around water.

Watch this video for a quick refresher on the water cycle (opens in a new tab) and this video on human aspects of the water cycle (opens in a new tab).

Sources of Antibiotics in waterways

Alexander Flemming first discovered antibiotics in 1928 with the increased use and production occurring around WW2. Antibiotics are used to treat bacterial infections; however, the effectiveness and easy access to antibiotics have also led to their overuse and some bacteria have evolved resistance to them. The World Health Organization has classified antimicrobial resistance as a widespread "serious threat [that] is no longer a prediction for the future, it is happening right now in every region of the world and has the potential to affect anyone, of any age, in any country." Antibiotics get into waterways through waste disposal and through urine and excrement since not the entire drug used during human or animal metabolism. Today, beside human medicinal usage, antibiotics are used in concentrated animal feeding operations (CAFO) as a prophylactic to keep animals health in tight quarters and to increase meat production.

Watch these brief videos

What are Antibiotics (opens in a new tab)
What is a CAFO? (opens in a new tab)

Other resources

TEDx Factory Farms, Antibiotics, and Superbugs (opens in a new tab)
Industrial Farming from PBS (opens in a new tab)

The Water Cycle and Mercury in the Mississippi River Valley

Show Water Cycle and Mercury in the Mississippi River Valley

To illustrate the "wicked" nature of maintaining water quality downstream, we are going to zero in on a significant pollutant in the Mississippi River system: mercury.

Before we identify how and where mercury problems arise from human activities, we need to understand where those activities interact with the water cycle. You have probably been learning about water and the water cycle since you were a child. Figure 1 illustrates the movement and change of water and several ways that the natural movement of water intersects with human activities. It is clear that there are many opportunities for human systems and natural systems to interact around water.

Watch this video for a quick refresher on the water cycle (opens in a new tab) and this video on human aspects of the water cycle (opens in a new tab).

Sources of Mercury in Waterways

Mercury finds its way into our waterways mainly from burning coal (Figure 2). When coal is burned mercury trapped in the coal is released into the atmosphere where is gets deposited into the waterways downwind from the plants. In aquatic ecosystems, some inorganic mercury is converted to methylmercury, which is the toxic version of mercury. Methylmercury bioaccumulates when it enters aquatic food webs, at which point it is taken up by algae and other microorganisms (Figure 3). Methylmercury concentrations increase with successively higher trophic levels in the food web via a process called bioaccumulation. In general, fish at the top of the food web that consume other fish tend to accumulate the highest methylmercury concentrations. Mercury also enters the water cycle when coal ash from coal combustion is stored at locations near power plants.

Mercury is a potent neurotoxin that bioaccumulates in fish to levels concerning for human health and the health of other wildlife consuming fish. This is the primary reason for issuing fish consumption advisories. In the first half of the last century, mercury was released by the Chisso Corporation from wastewater in the bay in Minamata, Japan. The fish and shellfish in the bay were the primary sources of protein in diet for the small town, and their consumption resulted in mercury poisoning among the residents. The resulting neurological diseases caused the deaths of cats, dogs, pigs, and humans for up to 36 years after the release. (Japan's Minamata Disease - Mercury poisoning of a town (opens in a new tab))

Watch these brief videos