Summertime Sadness: Hurricanes and Water Quality

Reference: Mallin, M.A., M.H. Posey, G.C. Shank, M.R. McIver, S.H. Ensign, and T.D. Alphin. Hurricane effects on water quality and benthos in the Cape Fear watershed: natural and anthropogenic impacts. Ecological Applications 9: 350-362.[0350:HEOWQA]2.0.CO;2

Hurricane madness and water quality nastiness!

A little over a month ago, Hurricane Florence slowly churned its way across the Atlantic and barreled into the Carolinas. It made landfall near Wilmington, NC and crawled its way inland at a snail’s pace, dumping unprecedented amounts of rain in the region. The power outages were widespread, and the flooding was catastrophic. Many of the rivers in the region broke water level records, as water rose and swelled riverbanks, and eventually flowed out to sea.

Flooded farm after Hurricane Florence in Duplin Country, NC. Source: Wikipedia

With hurricanes and flooding like this, we scientists wonder: “How bad will this be for water quality, and how can we limit the nastiness?” To understand the nastiness, we must begin with what’s on the land. Rain and floodwaters rinse the land and wash debris, pollution, and other materials into larger rivers or lakes. In southeastern North Carolina, the Cape Fear region where Hurricane Florence hit is known for its darkly colored, blackwater swamps, where organic materials (leaves, twigs, and other plant or animal debris) collect over time and slowly decay. The decay process also uses up oxygen in the water, so these blackwater swamps have naturally low dissolved oxygen levels.

Figure 2: Darkly colored, blackwater swamp on the Black River, NC. Source: Nick Iraola, UNCW Aquatic Ecology Lab

This region is also home to a large number of swine and poultry farms that store their animal waste in open lagoons, not to mention the Duke Energy Sutton Plant that stores coal ash (a toxic byproduct of burning coal) in a basin next to the river. Reports after the storm confirmed that 32 waste lagoons at 27 swine farms were discharging into floodwaters, and that the Sutton Plant’s dam that withheld coal ash had broken at several points, spilling its contents into floodwaters.

Learning lessons from past hurricanes.

While the Cape Fear region is still being assessed after Florence, we can look at previous hurricanes that have hit the region and compare the impacts of those storms to Florence. In 1996, Hurricane Fran made landfall near Wilmington, NC, and progressed up the Cape Fear. According to USGS, Fran dropped about 6-20 inches of rainfall throughout the region, whereas Florence dropped 20-30 inches. UNCW’s Center for Marine Science was able to collect ‘before’ and ‘after’ Hurricane Fran water quality data at over a dozen stations throughout the region.

Shawty got low, low, low, low – DO!

After Fran, the researchers noticed light was not able to travel very far into the water column in the river, a result of the darkly stained swamp water and mud water flooding into the rivers. While the swamp water already has low dissolved oxygen, less light also means less phytoplankton (microscopic algae). This is important because phytoplankton add dissolved oxygen to the water during photosynthesis.

The researchers found that dissolved oxygen levels at all sites in the Cape Fear region fell to 0-2 mg/L, from a safe level of 5 mg/L! At these low levels, fish and other aquatic life struggle to get the oxygen they need to survive, resulting in widespread death of fish and critters living at the bottom of these water bodies. Several stations showed significant declines in bottom dwelling critters after Fran, with recovery taking as long as 2-4 months.

Fish kill, most commonly a result of low dissolved oxygen. Source: Wikipedia

The research team realized there might be more to this low dissolved oxygen issue. Two rivers in the Cape Fear region, the Black River and Northeast Cape Fear River were compared. They both contained blackwater swamps, the land draining into those rivers were about the same size, and both contained swine and poultry farms. The team studied how much oxygen was being used up by decay, and noticed that it was six times higher in the Northeast Cape Fear River compared to the Black River! Dissolved oxygen was 80% lower in the Northeast Cape Fear compared to the Black River! How can this be!?

It so happens that at least four swine waste lagoons breached into floodwaters in the Northeast Cape Fear River, compared to only one reported in the Black River. All that untreated animal waste was decaying in the river, causing oxygen to be depleted in massive amounts. The other major issue with untreated waste is all the bacteria and disease-causing organisms that enter the environment as well, that make animals and humans sick, yuck!

Swine farm. Source: Wikipedia
Can we prevent the nastiness after hurricanes?

So, let’s revisit our two questions: how bad will hurricanes be for water quality, and how can we limit the nastiness? It’s clear that the impacts will vary based on what’s on the land where the hurricane hits, and some of the nastiness may be unavoidable. For the Cape Fear, swamp water flooding into the rivers and lowering the dissolved oxygen are a negative but natural consequence of a hurricane. However, swine and poultry farms, coal power plants, septic and wastewater treatment centers, and other human development may add more nastiness to the water, as seen in the aftermath of Hurricane Florence.

If there’s a lesson to be learned, it may be that hurricanes are a natural disaster that will have natural and expected negative consequences. Our call to action is to have policies and practices in place to reduce further degrading water quality from human activities. These include making sure human wastewater and sewer systems are properly designed and equipped with backup generators to prevent spills via power outages. The current methods of treating and containing swine and poultry farm waste should be redesigned for already existing farms to account for potential flooding, in addition to placing stronger consideration on building new farms outside of these flood prone areas. Human and animal waste magnified the disastrous effects on water quality after Hurricane Fran. We’ll be destined to suffer the same consequences if we don’t learn the lessons that nature has provided.


Coastal Review Online. “Florence: Nasty Water, Mounting Damage.” North Carolina Health News, 28 Sept. 2018,

Mallin, M.A., M.H. Posey, G.C. Shank, M.R. McIver, S.H. Ensign, and T.D. Alphin. Hurricane effects on water quality and benthos in the Cape Fear watershed: natural and anthropogenic impacts. Ecological Applications 9: 350-362.[0350:HEOWQA]2.0.CO;2

“Precipitation, Total Inches.” USGS 02105769 CAPE FEAR R AT LOCK #1 NR KELLY, NC, USGS, 2018,

Wagner, Adam. “HURRICANE FLORENCE: Environmental Woes Follow Storm’s Floodwaters.” Wilmington Star News, 25 Sept. 2018,


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Nick Iraola

Nick has a Master of Science in Marine Science from UNC Wilmington. His master's thesis research pertained to eutrophication and nutrient cycling within an urban blackwater lake in Wilmington, NC. Currently, Nick works for the Cape Fear Public Utility Authority testing drinking and waste water for safe consumption and discharge (respectively!!). Nick also works as a part-time research scientist at UNCW's Center for Marine Science in the Aquatic Ecology Laboratory and the Nutrient Analysis Core Facility. When he's not sciencing, Nick enjoys running, swimming, cooking, sailing, and catching up with friends and family. His favorite candy is Reese's pb cups, because what is there not to like!?

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