Take me to the river bottom
It’s not every day you see people in wetsuits heading toward a river in the heart of a big city.
But last spring, scientists from the Partnership for the Delaware Estuary waded into the waters of the Schuylkill River to install experimental nature-based infrastructure offshore from Bartram’s Garden, a park in Southwest Philadelphia.
The project, supported in part by the Delaware Watershed Conservation Fund, might be the first to pilot creating a living shoreline with beds of freshwater mussels — as opposed to saltwater shellfish. The aim is to make the river cleaner for people and more welcoming for aquatic wildlife.
Thanks to new funds made available through the Bipartisan Infrastructure Law, the Delaware fund will now provide an additional $4.9 million each year for the next five years to support more innovative projects like this one that use nature-based infrastructure to improve wildlife habitat, sustain ecological functions in the face of climate change, and directly engage communities.
The Partnership’s project is the poster child — it does all three.
It’s alive
Nature-based solutions, like living shorelines, are designed to help protect human and natural communities by replicating nature, rather than working against it.
An approach that’s been implemented in many places, including New York Harbor, is building oyster reefs to decrease wave energy and erosion in coastal areas. Another Delaware Watershed Conservation Fund grantee, the American Littoral Society, did just that off Bayshore Beach on the Delaware Bay as part of a project to restore horseshoe crab breeding habitat.
Living shoreline projects like the those in New York Harbor in Bayshore Beach capitalize on the natural tendency of saltwater shellfish, like oysters and ribbed mussels, to stick to each other and to other surfaces. When they stick together, they are less vulnerable to predators and the whim of currents.
But freshwater mussels are a different animal.
“They don’t attach, they burrow,” explained Josh Moody, Restoration Programs Manager for the Partnership for the Delaware River Estuary.
If you want to create an oyster reef, you just need to provide something stable for oysters to latch onto, like a cage full of oyster shells. But how do you create conditions that encourage freshwater mussels to stick around, and multiply?
Getting to the bottom of it
The goal of the Partnership’s pilot project is to get to the bottom of that question. They know freshwater mussels need moderate water flow to bring in food and remove waste, but too much scour from fast-moving water makes it difficult for mussels to stay put, particularly in the urban corridor where the riverbed has been altered over time from development.
“We thought, let’s try to install a few innovative structures in configurations that are appropriate for dissipating energy, stock the site with freshwater mussels, monitor them, and see which works better,” Moody explained.
After two years of research and development, the Partnership installed a few dozen galvanized steel cages filled with shells in the Schuylkill River. The cages are lashed together with anchor poles and heavy duty zip ties to create three 20-foot long structures — one shaped like a W, one like V, and one like a lowercase ‘e’.
Gimme shelter
The different designs are all all intended to do the same thing: give the mussels shelter from fast current, while allowing them to move around a bit and potentially gather in groups, as mussels like to do. The goal of the project is to figure out which structure does it best.
A couple of months after installing the structures, the scientist stocked 25 freshwater mussels adjacent to each one, and at a control site away from the structures for comparison.
Now, they’re giving them some space.
“Once you put the mussels in the water, you want to give them time to settle in,” he explained. Over the summer, they’ll go back to check on the mussels, but to minimize disturbance, they have outfitted a subset of them with Passive Integrated Transponders, or PIT tags.
“That way we can wave the reader over the site to check that they are still present. If we don’t get a ping, we can check by hand for a shell,” Moody said.
At the end of monitoring phase, in late 2022, they’ll dig up all of the mussels to determine how many stayed in place, and measure how much they grew.
In other words, to see which of the structures made the mussels feel most at home.
Habitat engineers
Why go to all this trouble? Oyster reefs help protect shorelines by dissipating wave energy. But what good are mussels in a river bottom?
“Freshwater mussels are habitat engineers,” Moody explained. Where healthy and abundant, they make rivers and streams more hospitable for other species by stabilizing the bottom, recycling nutrients, and providing complex habitat for larval fish to feed and hide out in, and for bottom plants like wild celery to grow in.
They also make rivers and streams healthier for people by filtering out polluting particles.
Mussels don’t discriminate when it comes to filter-feeding — they filter both the good and the bad, including bacteria and phytoplankton, from the water column as they feed. The result is clearer water that leads to more light for photosynthesis by bottom plants.
Projects like this one can also inform efforts to conserve mussels in other places— a growing need. Freshwater mussels have experienced drastic declines in the U.S. over the last century due the loss, fragmentation, and degradation of aquatic habitats from interacting stressors, including agricultural runoff, development, and dam construction.
We need mussels, but they need our help too.
Location, location, location
Now you’re probably wondering if and when your community can install a freshwater-mussel living-shoreline project. The Partnership is looking into that, too. Their project has a second goal to develop a living shoreline feasibility model that will help identify sites where natural and nature-based features are likely to succeed based on four sets of metrics: physical conditions, ecological baseline, site access, and community resources.
Take the Bartram’s Garden site as an example. In terms of physical condition, Moody said there’s a clear need for natural stabilization in this stretch of the Schuylkill: it’s a high-scour area, with “mucky” sediment at the bottom. In surveys, they did find low numbers of freshwater mussels, giving them an ecological basis to proceed.
Ultimately, they hope to stabilize the river bottom conditions enough so the site will support robust mussel populations and submerged aquatic plants, increasing both the habitat value and water quality.
Accessibility wise, the site is ideal because the shoreline is unarmored, meaning there are no physical structures like walls between the land and the river. That’s rare in urban areas.
Community focus
Moody explained that the “community resources” metric is designed to measure both the potential benefits from a living-shoreline project in a given community, and the potential barriers to success.
High-scoring communities can come in all shapes and sizes. One could be a place with high capital-resource availability and active community stewardship of existing natural areas. Another could be a place where the community would benefit more from the added green-infrastructure protection, and has the potential to leverage environmental-justice funding.
Or it could be a place like Bartram’s Garden, a 45-acre urban botanical garden with a mission focusing on conservation, watershed management, sustainability, education, and food sovereignty, with a four-acre community farm that grows 15,000 pounds of produce each year.
Mussel power
Eventually, the Partnership will be growing freshwater mussels at Bartram’s Garden, too. The Partnership is building a hatchery on the property to provide the natural resources needed to supply future living-shoreline installations in the urban corridor. It will also give visitors a way to actually see the living aspect of living shorelines that are usually underwater.
While Bartram’s Garden will host the hatchery for mussel propagation, the Partnership is also working with other organizations throughout the Delaware River Basin, and beyond, to develop a network of mussel rearing sites — typically, a healthy pond. These sites serve as weigh stations where baby mussels can be temporarily raised to “harden them” to field conditions before they get relayed to their final restoration project sites.
The goal is to produce half a million baby mussels a year: it will take a village, and it will benefit a watershed.
This story is part of an ongoing series highlighting projects supported by the Delaware Watershed Conservation Fund that together show, when it comes to creating a sustainable future for wildlife and people, the whole is great than the sum of its parts.
