Baltimore's Inner Harbor is about to dramatically enlarge one of its newest attractions — one meant to draw crabs and fish as well as tourists.



For weeks now, teams of young and adult volunteers have been assembling what promoters say will be Maryland's largest floating wetland, to be anchored along the bulkhead off the World Trade Center.



It's a 10-fold enlargement of a tiny, checkerboard array of grassy floats tethered by the trade center tower since summer 2010. Those initial wetlands, plus one launched at the same time by the National Aquarium, marked the mostly symbolic beginning of an ambitious campaign to clean up Baltimore's degraded harbor and make it swimmable and fishable by the end of the decade.



Now, the Waterfront Partnership, a nonprofit group of Inner Harbor businesses, has teamed up with Biohabitats, a local ecological restoration firm, to deploy a much larger array of floating vegetation that organizers hope will build on what they've learned from the earlier efforts – and give a boost to the harbor cleanup effort as well. They plan to deploy them on April 20.



Floating wetlands are among a handful of experiments being tried by nongovernmental groups to see if they improve the harbor's water quality. Last year, Blue Water Baltimore, the local watershed watchdog group, joined with local engineering firm KCI Technologies Inc. to put a solar-powered water-mixing device in the water off Fells Point. And Biohabitats has installed a contraption in another spot that enlists algae in cleaning the water.



The original eight small wetland frames launched two years ago by the Waterfront Partnership – with a grant from Blue Water Baltimore — had to be replaced late last summer because Hurricane Irene had battered them to the point of disintegration. Still organizers called them a success.



"If you saw those islands last year, the plants were just lush and green and amazing," said Laura Bankey, the aquarium's conservation director.



Those plants, a variety of marsh grasses, feed on the nutrients flushed into the water from wastewater plant discharges, sewage leaks and storm runoff — all of which make the harbor, like the rest of the Chesapeake Bay, prone to algae blooms and even fish kills in spring and summer.



Daniel Terlizzi, a water quality specialist with the University of Maryland's Sea Grant program, said his analysis of the plants growing on the floats indicates they were pulling at least two pounds of nitrogen out of the water for every 100 pounds of vegetation.



While that may not seem like much, given how seriously polluted the harbor is with nutrients, Terlizzi said the wetlands are providing even more ecological benefits below the water's surface. Within weeks, the floats teemed with aquatic life, from tiny worms to barnacles and juvenile eels and crabs.



Hundreds of thousands of tiny dark false mussels, smaller than a pinky nail, attached themselves to the underside of the floats, where their filter feeding further cleaned the water.



A camera the aquarium stationed underwater by its floating wetland also captured video of fish lurking beneath them, some nibbling at the dangling roots.



A few ducks nested or hung out above water, on the islands — a less welcome form of life, because the birds tended to flatten and kill the grass. The new floats will have low plastic fencing around them to discourage waterfowl.



The flotilla of 50 new wetland floats has been built by students from the Living Classrooms Foundation in Fells Point and by volunteers from T. Rowe Price, the investment firm with offices in the Inner Harbor.



One day last week, Christopher Streb of Biohabitats showed five students from the foundation's Fresh Start program how to assemble the rectangular frames. The training program for troubled youths teaches them carpentry and job skills and helps them work toward getting general education diplomas.



Streb, an ecological engineer, demonstrated how narrow strips of wood are bolted together over black plastic mats, into which smooth cordgrass and marsh mallow are to be planted just before they're launched. The floats get extra buoyancy from empty plastic drink bottles embedded in the mats — castoff containers that were retrieved from the trash floating in the Inner Harbor.



"So when you're out at the Inner Harbor with your girlfriend, are you going to tell them you built this?" Streb asked the students helping him with one frame.



No one responded, but Tevin Mitchell, 20, from East Baltimore, later marveled at the tiny mussels clinging to the bottom of an old wetland mat.



"There's a lot of them," he said.



Adam Lindquist, coordinator of the Waterfront Partnership's Healthy Harbor campaign, said he loves hearing the gentle sounds of insects chirping in the wetland grasses in summer.



"You can come down in the evening and it's … like you're out in the woods," he said. "You don't (normally) get crickets at the Inner Harbor."



Even so, scientists studying the wetlands say they haven't been able to quantify their impacts on water quality so far.



"It was just really difficult to measure and we were unable to measure," the aquarium's Bankey said. "We believe obviously that putting more filter feeders in the water is a good thing but proving that is a very difficult thing."



Organizers say they intend to continue the scientific monitoring. But they acknowledge that floating wetlands alone can't be relied on to remedy the harbor's woes. Much work remains to clean up pollution and trash flowing into the northern branch of the Patapsco River from throughout the city and much of Baltimore County.



But Terlizzi said he believes they're already having a different sort of impact.



"If I go out to the wetlands systems in the Inner Harbor to collect a sample, I've got a dozen or more people stopping me to ask me what it is, what it does," he said. "People in my trade call that a teachable moment."



To create more of those moments and reach more people, the partnership plans to put up a sign along the water's edge to explain the floating wetland.



"The real benefit of these things is making people aware of the potential of the harbor," the partnership's Lindquist said. "There is life in the harbor."



Tim.wheeler@baltsun.com



