Secrets of Tidal Creeks

Tidal creeks are the link from stormwater runoff to the estuaries and the ocean. Researchers are studying the dynamics of tidal creeks and what lives in them, so communities can better protect this unique, fragile and vital habitat for coastal life.

WILMINGTON — I found William Hurst this sunny, weekday morning on his dock, repairing fishing nets. He’s using a giant net threader, which in a way resembles a knitting needle on steroids. The net is hung on nails that are attached to a wooden frame. William then examines it bit by bit, searching for holes. 

“I know it seems tedious, but I’m always excited as I do this because I know I’ll be heading out into the creek soon,” Hurst says, as he scrutinizes the net. “Oh I love the creek, I grew up on it, my people grew up on it, and it’s just a way of life."

The creek Hurst is referring to is Hewlett’s Creek. It’s a tidal creek near Wilmington. His family has owned the property along the creek where the dock was built since before the Civil War. Hurst has fished and crabbed these waters for most of his 80-plus years. And yet, after all that time, he still marvels at how the creek is alive and changing every day. In some cases, it changes by the hour.

“When you came here, none of that mud was showing but now the tide has gone out and the bottom is showing and it has only been an hour,” says Hurst, as he walks out on the dock and points out how the creek has changed. “Occasionally we’ll see two eagles and you can watch them take the fish from the osprey. They’ll let the osprey fish and catch and then the eagles will take it.”

The vibrant ecosystem of Hewlett’s Creek is what’s known as a tidal creek. That means the water level rises and falls with the tides. But what makes tidal creeks even more unique is that their water is in constant mix. A tidal creek combines salt water from the estuary with stormwater runoff from the land. In fact, you could call tidal creeks the aquatic link between the land and the sea.

“There’s a lot going on in this little package,” explains Troy Alphin, Senior Research Associate with the Center of Marine Science at the University of North Carolina at Wilmington. “The creek is only four to five kilometers long from the mouth to the headwaters, and within that you’ve got a variety of habitats including marshes, oysters, open sand flats and channels.”

And that variety of habitats supports a host of organisms that depend on the tidal creek system for refuge as well as food.

“Tidal creeks are very valuable because they provide ecosystem services that we don’t get from a lot of other systems,” says Gloria Putnam with North Carolina Sea Grant. “Tidal creeks provide nurseries for animals as well as refuge, food and even storm protection for the land. Tidal creeks are very dynamic; they are constantly changing, and because they are so closely tied to the land and the sea, tidal creeks are a sentinel of coastal health.”

“What’s happening in tidal creeks might tell us something about what will happen in the larger estuary and so we need to learn more about the processes in tidal creeks,” explains Alphin. “The biggest thing that is happening around these creeks is development and so what is happening here is happening everywhere. So we need to know the impacts here so we know what is coming down the road for the larger estuaries.”

Scientists say the oyster beds in Hewlett’s Creek are key to understanding what’s happening in this tidal creek and the dozens of other tidal creeks along the North Carolina coast. The oyster beds in Hewlett’s Creek have been closed to harvesting for almost 10 years because pollution is creating high bacteria levels.

But North Carolina Sea Grant is supporting oyster research in the creek. The creeks oyster beds are not only viewed as a way to monitor the health of the creek but also to study whether creating shellfish beds in tidal creeks would help to preserve the creek while at the same time help grow the shellfish industry.

Scientists pull up bags of oysters to examine the size, growth rate and condition of oysters living in the oyster beds. And before the bags are brought to the lab for study, scientists also record what is in, around, and under the oyster system. That’s because a lot of creatures live under the oyster beds and the abundance and density of those communities is also an indicator of the health of the creek.

Initial findings show that while oysters can survive in tidal creeks, they are stressed. One indicator of that stress is the small amount of soft tissue that researchers found in one of the oysters. Researchers also found a pea crab, which is a parasitic crab, inside the oyster. Those stresses appear to come from stormwater runoff on land, but no one is certain and more study is needed.

And that’s where Byron Toothman’s work comes in.

The research biologist with the North Carolina Coastal Reserve and the National Estuarine Research Reserve is working with four monitoring stations strategically placed in estuaries at the mouths of tidal creeks around Wilmington. That includes Hewlett’s Creek. The devices were installed in 1996 and collect data every 15 minutes. The stations provide a way for researchers to know what flows into the creeks by the hour, the day and even over several years.

“The multi-parameter water quality sound is a pretty basic device used to deploy instruments,” explains Toothman, as he shows off a metal tube that looks a lot like a torpedo. The tubes are attached to poles in the estuaries.

“Right now we have it set up to record dissolved oxygen, turbidity, PH levels, temperature, specific conductivity and salinity,” Toothman explains, removing the cap at the bottom to expose the instruments. “There is a battery higher up on the tube, along with a circuit board that can retain data for 45 days.”

Those are all different aspects of water quality, including turbidity, which measures the cloudiness of the water from dissolved particles. PH measures the acidity of the water. Water that is highly acidic does not support life. And conductivity measures the ability of water to conduct electricity. A failing sewage system would raise the water’s conductivity because of the presence of organic materials such as phosphates and nitrates. An oil spill would lower conductivity.

Alphin says the goal of his work is to track how land use changes may correlate with changes to the tidal creeks.

Back on the dock, as he completes repairs to the fishing net, William Hurst believes all of the science happening around him will help folks to understand what is happening to Hewlett’s Creek and how it can be preserved. Hurst knows the creek will never be like it was, but he says, “I can remember as a boy before there were outboard motors, and then you had to pole, or row or sail, up and down the creek. There wasn’t as much human impact on the creek as there is now and we need to take care of it.”

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