Baltimore’s famed Inner Harbor has been the National Aquarium’s home for more than 40 years. Once a natural habitat of shallow mud flats fringed by tidal salt marsh grasses and surrounded by forest, the Inner Harbor is a classic example of a shoreline that has been dredged out, paved over, and built up—changed and developed in ways that inhibit the natural processes that support clean water. 

Revitalizing the waterfront is a key component in the National Aquarium’s BLUEprint master plan. Leaders at the National Aquarium, which spans two piers jutting into the harbor, had a vision to return natural habitat to the water surrounding its campus. Using floating wetlands to re-create the natural Chesapeake Bay microhabitats that were once plentiful in the heart of Baltimore City: the Aquarium’s waterfront campus project promotes clean water, attracts native species, and connects people with nature right outside its doors. This vision for the Aquarium’s waterfront campus fits into a broad citywide effort to restore the harbor and improve its ecological health.

Currently, a floating wetland prototype is in place, serving as both a successful example of how these installations can support wildlife and as an educational tool for the Aquarium’s What Lives in the Harbor program, which gives Baltimore City Public Schools’ sixth graders hands-on learning opportunities to engage with a slice of the Chesapeake Bay, the United State’s largest estuary.

The National Aquarium looks forward to sharing their plans for the Waterfront Campus during the Association of Zoos and Aquariums’ Annual Conference in Baltimore in late August and early September!

Five Lessons From Floating Wetlands

When the National Aquarium first started experimenting with floating wetland technology in 2010, the goals were to reintroduce wetland habitat into the Inner Harbor and promote healthy water. What lessons have we learned?

When the National Aquarium installed a 200-square-foot floating wetland in the harbor in 2010, it was the first time this technology had been introduced into a brackish tidal system anywhere in the United States. Before that, floating wetlands were traditionally used in stormwater retention ponds. Over the past 12 years, the Aquarium’s Conservation team has refined the floating wetland design to develop a model that best fits the specific needs of the Inner Harbor, evaluating its progress through scientific research. 

Based upon their ongoing work with and maintenance of the floating wetland, the Aquarium’s Director of Field Conservation, Charmaine Dahlenburg, and Conservation Technician, Langston Gash, summarized five lessons learned so far.

Not All Floating Wetlands are Created Equal

The Aquarium’s 2010 floating wetland faced overuse from Canada geese, an accumulation of invasive dark false mussels and a failed anchor system. It was retired in 2013. Another version, installed in 2012, was tested and retired a short time later due to similar challenges. Version three was installed in 2015 and remains in place today. It’s being used for nutrient uptake studies but will soon be retired.

Using information gained from the first three floating wetlands, the Aquarium began rethinking the technology and developing a custom floating wetland unique to the needs of the Inner Harbor. In August 2017, this new floating wetland prototype—version four—was introduced.

This prototype is custom-designed with four key components our previous floating wetlands lacked: elevation changes to allow for a variety of high and low marsh shrubs and grasses; a center channel with moving water that mimics shallow-water habitat for native wildlife; an aeration system to mix the upper portion of the water column surrounding the prototype while also providing the mechanism to control where the prototype sits in the water column through a pontoon ballast system; and a structure made from materials designed to withstand the harbor’s brackish water and Baltimore’s four seasons.

“While this 400-square-foot prototype continues to perform well, our next challenge is figuring out how to scale it up to cover about 15,000 square feet while minimizing costs,” said Charmaine.

The Harbor Experiences Extreme Water Quality Events

Baltimore’s Inner Harbor commonly experiences two types of water quality events—algal blooms and sulfur bacterial blooms—that can turn the water unusual colors, change the way it smells, and negatively impact wildlife.

As part of the Maryland Department of Natural Resources’ Eyes on the Bay project, the Aquarium continuously collects and reports core water quality parameters in the harbor. This 24/7 monitoring provides important, near real-time data about water quality events as they are happening.

In one instance, the Aquarium measured levels of chlorophyl from an algal bloom that were so high, Charmaine thought the equipment may be malfunctioning. For our area, a healthy level of chlorophyl in a body of water is 15 micrograms per liter. Fifty micrograms per liter is considered a significant amount of chlorophyl, while 100 micrograms per liter is considered extreme. On January 15, 2020, the Aquarium’s devices, called sondes, recorded chlorophyl levels averaging 400 micrograms per liter. One reading reached 670 micrograms.

“When I contacted the manufacturer of the probe, they said they’d never seen readings that high,” Charmaine recalled. “Over the history of the Eyes on the Bay program, of all the data collected across the state of Maryland, the Aquarium’s sondes in the Inner Harbor have recorded the top 1,000 to 2,000 chlorophyl readings, which is significant.”

Algal blooms are caused by excess nutrients, like nitrogen and phosphorus, entering the water through human activities. This rapid growth in algae creates a chain reaction leading to extended periods of low dissolved oxygen when the algae die and consume oxygen as they decompose. Unfortunately, aquatic animals struggle to survive in these conditions.

“If you see animals swimming at the surface of the harbor, it can be a red flag that they’re struggling for oxygen due to an extreme water quality event,” said Langston.

Aeration is Key

The aeration system on the floating wetland prototype—which taps into the system used inside the Aquarium—offers stability for animals when dissolved oxygen levels are low during water quality events.

Charmaine said that as soon as the aeration system was turned on in 2017, the team noticed wildlife responding to it. “Fish tend to accumulate around the aerators by the hundreds or thousands,” she said. “It’s clearly creating a microhabitat that’s beneficial for wildlife.”

To evaluate the aeration component of the wetland, the team is conducting a study to compare water quality data from the center channel of the floating wetland with data from another part of the harbor. While this research is continuing, the preliminary data is positive, showing cooler, more stable temperatures in the channel where dissolved oxygen levels are higher thanks to the aeration system.

The Harbor is Teeming with Hidden Life

“Qualitatively, we know our floating wetland provides habitat for aquatic life; we can see the diversity,” said Charmaine, mentioning the pumpkinseed sunfish, gizzard shad, snapping turtles, and ghost anemones seen on and around the wetland recently. “However, we needed to find a way to quantitatively assess the Harbor’s biodiversity.”

Following Maryland Sea Grant’s biodiversity and biofilm project, Charmaine, Langston, and researchers from the Institute of Marine and Environmental Technology submerge acrylic disks in the Inner Harbor to analyze the communities that grow on them. These biofilms are the foundation of the food chain and attract other animals.

Each month, the team collects three disks from the harbor, records video of four random sections under a microscope, and then views the video to count and identify the organisms. Samples scraped from the disks are further analyzed using DNA barcoding, a process conducted in partnership with volunteers at Baltimore Underground Science Space and IMET.

Langston, who was first involved with the Aquarium as an intern at IMET, reported that in 2017, a total of 248 different species were identified on the acrylic disks through DNA barcoding.

The Harbor is Restorable

Charmaine said the Charles River Conservancy in Boston, Mass., is a good model for Baltimore; the two cities and their waterways have key similarities, along with some differences.

Three freshwater rivers empty into Boston Harbor, part of Massachusetts Bay, which connects directly to the Atlantic Ocean. Baltimore’s Inner Harbor, on the other hand, is further inland and more isolated. It connects to the Patapsco, which flows into the Chesapeake Bay, which then flows into the ocean.

In the 1980s, Boston was under a court order to upgrade its sewer system, as Baltimore has been since 2002. Boston upgraded its wastewater treatment plant to prevent raw sewage from entering their waterways; they also turned a city dump into a park and wildlife refuge, similar to Baltimore’s Masonville Cove. A new, 43-mile-long park connects Boston’s neighborhoods to its waterfront. And while swimming in Boston’s harbor had been prohibited since the 1950s, it no longer is.

“We don’t know what the coming years will bring here in Baltimore,” Charmaine said. “We are digging deep into the beneficial science of floating wetland technology. Living shorelines and floating wetlands are certified for pollution mitigation in non-tidal areas; we hope to prove that our prototype provides similar, measurable benefits in tidal areas.”

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