Leaving a mark on ecosystems

By monitoring water quality in the state’s estuaries, Carolina researchers are better understanding the lasting effects that hurricanes have on ecosystems beyond immediate flooding and storm surge.

What happens to the water quality in coastal estuaries during a hurricane?

That’s the question researchers in Hans Paerl’s lab are trying to answer. Specifically, researchers are looking at the impacts of microscopic algae on the functioning of the estuaries along North Carolina’s coast and at how hurricanes impact the algae.

By monitoring water quality in the state’s estuaries and the impacts of major storms on the water, researchers are better understanding the lasting effects that hurricanes have on ecosystems beyond immediate flooding and storm surge.

As part of the UNC Institute of Marine Sciences in Morehead City, Paerl’s lab has a unique opportunity to study those effects of hurricanes. The 35 named storms that have hit the North Carolina’s coast in the past two decades have given the researchers a wealth of data.

Longevity of monitoring data is rare when it comes to water quality, so much so that researchers from other parts of the country use the information collected by the Paerl lab team for their own studies.

In the aftermath of a hurricane, researchers have found visual changes that happen every time, such as the water changing from translucent to opaque as terrestrial matter is brought in by the storm. But many of the nonvisual effects are less consistent.

“When we looked across these 35 storms, the impact seemed to vary storm by storm by storm,” said Nathan Hall, a research associate in the lab. “So, if you compared for any one parameter — these 35 storms against the baseline — there are very few parameters that showed a significant increase or decrease after the storms.”

Their findings have potentially significant ramifications.

The Paerl lab team has found that levels of dissolved organic carbon in the water always increase after a storm.

Most of that organic carbon is then broken down by bacteria and released as carbon dioxide gas into the atmosphere, turning it into a greenhouse gas, Hall said. A severe hurricane could potentially make estuaries a net-source of carbon dioxide.

The second consistent finding revolves around the microalgae studied at the lab. During a hurricane, water and nutrients rush up the estuary and essentially flush phytoplankton from the upper estuaries into the lower estuaries. Researchers have found no change in the biomass of the algae, but their location changes with each storm.

“The reason we care about how the phytoplankton are moved around by the storms is because they can shade out seagrasses, lead to low oxygen problems that cause fish kills or kill fish directly by producing toxins,” Hall said.

By Aaron Moger, University Communications