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How Can Nutrients Become Pollutants in Bodies of Water?

Overloading our water system with nutrients can be just as harmful as other types of pollutants. Human activity is responsible for production of many excess nutrients, which can severely interfere with the normal balance of aquatic ecosystems.

  1. Water Cycle

    • All the water on earth is constantly cycling through lakes, streams, oceans and the atmosphere. This means that water-borne nutrients also travel, and can end up far away from their starting point.

    Role of Nutrients

    • Bodies of water need nutrients to support life, and exist in a stable balance where nutrients are present only at the necessary levels. However, human activities result in large amounts of excess nutrients, which can easily find their way into the water system.

    Sources of Excess Nutrients

    • Excess nutrients may come from fertilizer on yards or farms, sewage, livestock operations, burning fossil fuels or commonly used chemicals. The two major nutrients that have historically created problems are nitrogen and phosphorus.

    Problems Caused by Excess Nutrients

    • An overload of nutrients creates excessive growth. Algae exposed to a high load of nutrients grow vigorously and complete their life cycle quickly. A lake filled with dead algae will have very low oxygen content, since oxygen is consumed as the algae decomposes. This may cause other organisms to die, creating a lake or pond that is choked with dead material.

    Long-Term Effects

    • Over time, a lake or pond that is receiving large doses of nutrients may fill completely with dead and decaying matter. The water can no longer maintain the proper balance of nutrients to support life. This decreases habitat for water-dwelling organisms. Some algal species that proliferate when excess nutrients are present give off harmful toxins that can impact not only a particular body of water, but also nearby ecosystems.

    Strategies for Prevention

    • Prevention is difficult, since activities that generate excess nutrients are widespread. However, creating buffers between contaminated runoff and pristine water bodies is helpful. Using low levels of fertilizer and non-phosphate detergents can also help reduce nutrient loads. Proper water treatment is another important step.

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