Algal Blooms Return to the Chowan River
July 10, 2017
For the third year in a row, dense populations of blue-green algae have turned parts of the Chowan River into the color of pea soup.
These algal blooms stink. They also take up large amounts of oxygen when they decay, suffocating aquatic life and leading to fish kills.
The Chowan River hasn’t seen consistent algal blooms like this since 1972, when North Carolina had its first large-scale algal bloom outbreak.
It happens with the right cocktail of conditions: hot, sunny days, slow-moving water and excess nutrients (think lawn fertilizer). In 1972, conditions were right, and the algal bloom that occurred led to fish kills and fish disease. For the residents of the Chowan River watershed, the algal bloom was an economic nightmare. Fish kills hit the area’s recreational and commercial fish industry hard, and unsightly waters drove visitors away.
Reisdents worked with environmental quality regulators in Virginia and North Carolina to clean up the watershed. Many of the streams and rivers that flow into the Chowan River begin in Virginia, so both states needed to take action. The Chowan River flows through northeast North Carolina and delivers freshwater to the Albemarle Sound, the country’s largest freshwater sound. The Albemarle Sound's health depends on the rivers that flow into it, and when the Chowan River blossoms with algae, the algae may infect the Albermarle Sound too. The culprit behind the 1972 algal bloom was nutrients.
Contaminants like manure, fertilizer and wastewater sewage contain phosphorous and nitrogen, which fuel algae growth. Upstream from the Chowan River, wastewater treatment plants, farms and factories were leaching nitrogen and phosphorous. The algae fed on the nutrients and grew with a vengeance. Thus, the algal bloom.
Both Virginia and North Carolina encouraged best management practices for nearby nutrient-generators, in order to clean up the watershed. The Chowan River recovered, and for 30 years it has enjoyed a breather from consistent algal blooms. But the last three years have been worrisome to water quality experts like Mark Powell of the Albemarle Resource Conservation and Development Council.
“The main question is why the blooms have come back,” said Powell. “We don’t know yet. We’re hoping to do a land-use study to answer that question.”
Powell said that it’s unlikely the blooms are coming from the same sources as in the 1970s. Most nutrient clean-up efforts and practices are still in place today. But Powell said it’s possible that clear-cutting forests next to rivers is leading to lower water quality. A buffer of trees and shrubs along rivers filter nutrients and prevent contaminants from leaching into the water.
According to Powell, bigger buffers lead to better water quality. The Chowan River doesn’t have state laws protecting its buffers, though the official recommendation is 50 feet of forest buffer. Powell said a buffer of 200 feet would be ideal for parts of the Chowan River.
“Algal blooms are just a symptom,” said Powell. “We’ve got to do a better job of conserving these riparian forests and leaving buffers that are sufficient enough to protect water quality.”
Individuals can do their part too. This can include using a reasonable amount of fertilizer on lawns, and watching the weather to make sure the fertilizer doesn’t get swept downstream during a heavy rain. Cleaning up after pets is another way to keep nutrients out of water sources.
Algal blooms may become a familiar part of the summer season, as hotter days and less forest cover create ideal conditions for an algae feeding frenzy.
To learn more about algal blooms, check out the North Carolina Department of Environmental Quality's page.
- Rossie Izlar
Rossie Izlar is the associate producer of Sci Tech Now North Carolina, a weekly show highlighting the latest science stories from North Carolina and across the nation.