Rivers and the organisms that live within them need nutrients to survive and grow. In our rivers, the two most important nutrients are phosphorus and nitrogen. These nutrients fuel the growth of algae and other aquatic plants that form the foundation of the river’s food web. Plants consume the nutrients, aquatic insects eat the plants, fish eat the insects, and birds and bigger fish eat the smaller fish. In a healthy river, this balance ensures all organisms can thrive.
Eutrophication: How Excess Nutrients Hurts Rivers
However, when there’s too much nitrogen or phosphorus in the river, the balance is tipped, and water quality declines. Excessive nutrients in rivers are so common that there’s a specific term for it: eutrophication. Eutrophication can trigger a chain reaction of harmful effects that can be difficult to reverse.
Algae Deplete Dissolved Oxygen
Algae also affects dissolved oxygen levels, oxygen that fish and insects need to breathe. During the photosynthetic period of the day, the oxygen level climbs to over 100% saturation, but then at night, it drops to nearly zero. Without enough oxygen, organisms must either move to more survivable parts of the river or perish. Slow or immobile organisms cannot escape. When the overgrowth of algae consumes all the nutrients, or blocks out so much sunlight it cannot sustain itself, a mass die-off occurs. All the decomposing algae consumes the remaining oxygen and washes downstream.
Human Activities Drive Excess Nutrients
While some nutrients and algae are necessary for a healthy ecosystem, eutrophication is largely driven by human activity. On a national scale, the primary source of nutrients in waterways comes from agriculture. In urban areas, the main source of nutrients comes from wastewater treatment plants. Although the treated water is clean and sanitized, it still contains nutrients that are hard to remove. Other human sources of nutrient pollution come from fertilizers, industrial discharges, soil erosion, and accidental or illicit discharges.
Efforts to Address Nutrient Pollution in Illinois
In Illinois, treatment plants—either working individually or as watershed groups—are actively studying the effects of phosphorus pollution in our watersheds. They have submitted detailed reports to the Illinois Environmental Protection Agency (IEPA), outlining safe phosphorus levels and strategies for improving water quality. These strategies include upgraded treatment methods, dam removals, and stream restoration projects. All of these will likely be necessary to return the health of the rivers to target levels.
How You Can Help Protect Our Rivers
While many public and private agencies are working to solve the issue, homeowners can also play a role in protecting our rivers. Here are some ways you can help:
- Apply fertilizer properly: When applying fertilizer, make sure to follow instructions on the packaging. If rain is forecasted within a few days, avoid applying fertilizer. Nitrogen fertilizer is water soluble and easily gets into rivers. Don’t overapply—it is harmful to your plants and is more likely to wash into rivers.
- Prevent soil erosion: Because phosphorus fertilizer binds to soil, it reaches rivers through soil erosion. Plus, soil naturally contains nutrients. Make sure your plants are holding the ground in place. If you have a seasonal garden, use cover crops, mulch, or tarping during non-growing periods to protect the soil.
- Manage fall leaves: Fall leaf litter is a significant source of phosphorus. When leaf litter collects on impervious surfaces (roads, sidewalks, and parking lots), rainfall leaches nutrients from the leaves and washes them into rivers via storm drains. Instead of piling leaves on the curb for collection consider leaving them in your yard (which also contributes to natural fertilization of your lawn) or mulch the leaves and use as compost. If those aren’t good options for you, wait until after forecasted rain to rake them to the curb.
- Stabilize stream banks: If a stream runs through your property, ensure the banks are stabilized with rocks or native plants to reduce erosion, and consider planting a native buffer strip along the shore to absorb runoff and filter pollutants stormwater runoff.
- Garden with native plants: Native plants absorb both water and nutrients well, and have deep roots that hold and enrich the soil. Try converting some or all of your yard to native landscaping, or build a rain garden.
Conclusion: A Shared Responsibility for Healthier Rivers
Protecting the health of our rivers is a shared responsibility. While large-scale efforts are underway to address nutrient pollution, individual actions can also make a difference. By being mindful of how we manage fertilizers, prevent soil erosion, and manage our leaves, we can all contribute to healthier rivers and streams. Together, we can help restore the natural balance in our waterways, ensuring clean water and a thriving ecosystem for future generations.
Written by Alex Handel – Environmental Scientist, The Conservation Foundation
