When bodies of surface water are green, it’s often an indication of overgrowth of harmful algae, and nutrient pollution is often to blame.
Researchers are tracking the color shifts to estimate quality of surface water bodies
In the age of satellite photography, scientists can simply look at rivers to draw some accurate conclusions about their water quality. A study published recently in the journal Geographical Research Letters explains how it works.
According to researchers, a third of rivers in the United States have changed color since 1984 as a result of human activities. To determine the magnitude of the change, the research team examined tens of thousands of one-mile stretches of river in the U.S. using satellite imagery.
What River Color Says about River Health
Researchers found that 11,629 miles of river had turned greener or moved toward the violet end of the spectrum, while some stretches had shifted red. Approximately 5% of U.S. rivers are a healthy blue, and approximately 66% of American rivers are yellow, indicating a high soil content. A river’s color is an important clue to its health. Leading causes of color changes in rivers include:
- Nutrient-rich agricultural runoff that feeds algae blooms
- Untreated wastewater discharge
- Dams
- Soil erosion mitigation efforts
- Higher water temperatures associated with anthropogenic climate change
Professor Tamlin Pavelsky, a co-author of the study, explained that a green tint on the Ohio River, for example, indicates a severe algae problem fed by agricultural runoff, while rivers that become less yellow show that regulations to stop soil erosion are doing some good.
While some greenish-tinted rivers fall within the normal range, green is generally the most concerning color because it often shows the presence of the algae that cause eutrophication, which depletes oxygen from water bodies, killing aquatic life and destroying aquatic ecosystems. And it’s not just aquatic ecosystems that suffer. Algae blooms often are toxic, causing harm to humans on land. According to the study, 2% of yellow U.S. rivers have gone green.
The problem isn’t confined to the U.S. A study published in early 2020 mapped eutrophication worldwide, finding that 31% of the catchments studied showed high levels of what appeared to be algal growth. Nearly 76% of harmful growth was caused by phosphorus in agricultural areas in North America, South America, and Europe. Undesirable algal growth due to nitrogen enrichment was found in North Africa, some Mideast regions, and India.
Solutions to Preserve River Health
What steps can be taken to prevent eutrophication? Farmers can apply fertilizer more precisely, manage drainage, and assure ground cover throughout the year. In another strategy, buffer strips of native plants can be established around agricultural fields to rid runoff of excessive nutrient load. The use of recycled wastewater for irrigation can cut down on fertilizer requirements. Because the reused wastewater already contains some nitrogen and phosphorus, less fertilizer is needed, reducing the risk of fertilizer runoff.
While there are many prevention and remediation strategies that can be implemented at the farm level, there also are some more technical options.
- Domestic and industrial wastewater can be treated to higher quality standards before being returned to the environment. By improving effluent quality, businesses with a high-COD wastewater — food and beverage, for example — can protect local water sources while avoiding expensive treatment surcharges or penalties.
- Wastewater can be treated at the point of need with a treatment technology called the membrane aerated biofilm reactor (MABR), which removes excessive nutrient load.
- Resource-recovery operations can be added to wastewater treatment plants to transform nitrates and phosphorus from wastewater into desirable commercial fertilizer.
If you want to meet local standards and protect America’s rivers, consider improving your waste management practices. Fluence’s Aspiral™ wastewater treatment units, featuring MABR technology, are ideal for domestic, industrial, or even remote agricultural applications. Aspiral™ can help you meet regulatory standards for effluent and its low energy consumption makes decentralized treatment viable even on alternative energy, off the grid.
Contact Fluence to learn more about our sustainable solutions and discuss your water treatment needs with our experts.
