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This story was corrected June 6. Wrens were incorrectly identified as a forest interior dwelling species in the original story. Also, the yellow-throated woodpecker should have been identified as the yellow-throated warbler.

From trees with knees to bass-singing frogs to providing flood control, swamps in Southern Maryland have a lot to offer to the region, despite popular culture’s fearful portrait.

Swamps in Southern Maryland do not contain swamp people or ogres, but they do host reptiles and amphibians, birds, mammals, insects, trees and plants.

Wetlands with forests or shrubs are considered swamps, according to the U.S. Environmental Protection Agency.

Forested swamps typically contain trees that exceed 20 feet in height, while shrub swamps contain woody plants that are smaller, usually less than 20 feet high, according to the EPA.

Now how did that get there?

The swamps in Southern Maryland probably formed in three different ways, said retired marine geophysicist Peter Vogt, who worked for the U.S. Naval Research Laboratory in Washington, D.C., and lives in Port Republic.

Vogt said beavers have actually created the most swamp wetlands by damming streams, which flooded low-lying areas and killed off trees that could not handle the abundance of water behind the beaver dam. The trees that could handle the water did survive, or the areas eventually dried out to form meadows, Vogt said.

Some of the swamp wetlands, especially larger, nontidal ones, formed when sea level rise rates slowed down about 6,000 to 7,000 years ago, Vogt said, following the last ice age when major ice sheets in Eurasia and Canada had melted.

“Sediments brought in by streams and rivers began to form deltas, like in the Susquehanna Flats [where that river meets the Chesapeake Bay], very shallow water which eventually silted in completely to form first salt marshes, like in the lower Parker’s Creek [in Calvert County], and upstream from that tidal freshwater swamps and up from that nontidal wetlands,” Vogt said.

An uncommon way that swamps have formed is through alongshore sand movement, usually north to south due to a nor’easter, Vogt said. However, swamps in Flag Ponds Nature Park and Cove Point along the Chesapeake Bay, both near Lusby, demonstrate signs of this formation, Vogt said.

Zekiah — the swamp of braided channels

Zekiah Swamp in Charles County stretches from north to south on the eastern side of the county.

The freshwater swamp flows from Cedarville State Forest east of Waldorf, crosses under Route 5 near Bryantown and empties into a marsh and tidal waters called Allens Fresh near Newburg, becoming the Wicomico River just downstream from there.

One of the unique features of the Zekiah Swamp is that the water channels comprising the swamp braid into 20 to 30 channels while it flows south, said Kyle Rambo, conservation director at Patuxent River Naval Air Station.

“The Zekiah Swamp is meandering — one stream channel, crossing one, then another. It doesn’t have a single stream but multiple streams,” Rambo said.

The freshwater swamp attracts lots of species because it is a continuous, wide stretch of largely undeveloped, untouched habitat.

For example, forest interior-dwelling species, birds that thrive in thick, contiguous full-grown forests, are present in the Zekiah Swamp. Those species include warblers and barred owls.

Rambo said that the fish that live in the swamp are not game fish but species such as the eastern mud minnow, the pickerel and the bullhead catfish.

Turtles fond of slow-moving freshwater also make their home in the Zekiah Swamp, including snapping turtles and mud turtles, Rambo said. The northern water snake and the ribbon snake are also present.

Another notable swamp in Charles County is colloquially called the Bumpy Oak Swamp, located near the intersection of Bumpy Oak Road and the Indian Head Rail Trail in Pomfret.

George M. Jett, a naturalist who volunteers to find species for the Maryland Amphibian and Reptile Atlas, said that swamps are often a habitat where he looks for amphibians because they breed in shallow water that the swamp provides.

The amphibians frogs, toads and salamanders also live in the water as tadpoles before they transform into adults.

Jett said that in Charles County there are about 60 species of herpetofauna, which are reptiles and amphibians, out of 90 that are in the state.

Some of the species include the eastern painted turtle, the rainbow snake and the marbled salamander.

Jett said there are no water moccasin snakes in Southern Maryland, as the only kind of poisonous snake in the region is the copperhead.

Several species of frogs like to inhabit Southern Maryland swamps, including bullfrogs, known for their low-pitched croaks, green tree frogs, pickerel frogs and spring peepers, Jett said.

Local swamps also contain the food that herpetofauna and birds eat, including crayfish, worms, beetles and small fish, Jett said.

Swamps, then, are not just a place with trees and water, but an ecosystem.

The Mattawoman Creek watershed also has spots of swampland and ephemeral pools of water that attract reptiles and amphibians to the area, said Jim Long, president of the Mattawoman Watershed Society.

Another swamp in Charles County is Pages Swamp, which protects the waters flowing into the Port Tobacco River, Long said.

What trees have knees? These!

Battle Creek Cypress Swamp Nature Center in Prince Frederick is one of the northernmost locations for bald cypress trees.

Typically occurring in the southern United States, the bald cypress trees are known for their “knees,” roots that protrude from the waters like small wooden towers.

Shannon Steele, a naturalist at Battle Creek, said scientists debate over why the cypress trees have knees, with opinions ranging from a need for the trees to have aeration, like a snorkel, to storing carbohydrates to providing stability during fluctuations in nutrients.

The cypress trees have needles for leaves, but unlike evergreen trees, they shed their needles completely for winter, hence the “bald” in their name.

The cypress trees have a wide trunk and shaggy bark, grow up to 120 feet high and can be 600 years old, Steele said.

“Only certain trees can tolerate swamps. Another kind, besides cypress trees, is the red maple tree, which is designed to soak up all kinds of water,” Steele said.

Battle Creek Cypress Swamp is drier at this time of the year than in the winter, because the trees are holding in water to feed the leaves and reproductive material.

In the winter, the cypress trees release their water, and the water level rises up closer to the boardwalk that traverses the swamp, Steele said.

The 100-acre swamp does not only have the bald cypress trees, but also several animals and plants.

Spotted turtles, which are black with yellow spots, bask in the sun to absorb heat for their cold-blooded bodies. Green frogs also find the cypress swamp appealing.

Barred owls, wrens, woodpeckers and the prothonotary warbler find a home in the swamp as well. The warblers have predominately yellow feathers with gray or black tail feathers. They nest in holes within the trees, and their call sounds like “sweet, sweet, sweet,” according to the Smithsonian National Zoological Park website.

A source of food for some of the birds, mud minnows are small fish that live in Battle Creek.

Steele said that visitors also can see insects like damselflies and the ebony jewelwing, another kind of damselfly with black wings and a green body.

Walking on the boardwalk of the swamp, one will find small, volcano-like mud hills on the swamp floor.

Burrowing crayfish live in the hills and burrow down into the swamp mud to live in the water underneath the surface.

The swamp contains a plant with a stench called skunk cabbage. Appropriately named, the plant emits a skunky odor that deters predators from eating it.

“This place in general is basically a hidden gem,” Steele said of Battle Creek.

There are several other swamps in Calvert County, including some in the Parkers Creek watershed south of Prince Frederick, as well as some in Flag Ponds Nature Park and in the Cove Point area.

The key to this swamp

Key Swamp is one of the smaller swamps in Southern Maryland, located at Historic St. Mary’s City.

In the 1630s, the swamp received its name from the earliest European settlers, likely not after a landowner but because of the geographical term key, said Timothy Riordan, chief archaeologist at Historic St. Mary’s City.

Key does not refer to the present-day understanding of a key a small island but rather what the early European settlers understood a key, spelled quay back then, to be.

“In the 17th century the meaning of key was an inlet or cove,” Riordan said.

It is assumed, Riordan said, that Key Swamp got its name from that definition.

The swamp borders a creek that empties into the St. Mary’s River, and contains thick vegetation that makes it difficult to travel into its interior parts.

Several species of plants, such as elderberry and pawpaw trees make their home in the swamp, said Mary Alves, horticulturalist and landscape manager for Historic St. Mary’s City.

Pawpaw trees grow narrow, oval-shaped leaves and fruit that are like small bananas, only rounder. They typically grow between 10 feet and 40 feet tall, according to the U.S. Department of Agriculture’s Natural Resources Conservation Service.

Elderberry plants bear blue and purple berries that are edible, though the red berries are toxic and should not be eaten, according to the USDA NRCS. They typically grow between 6 feet and 12 feet tall.

Yet Key Swamp also contains invasive species such as multiflora rose and Japanese honeysuckle, which has led the historic center to seek out assistance to remove the invasive plants.

Alves said that the center has been able to remove some of the invasive species thanks to volunteer groups and goats, but must go through the state’s critical area commission to receive approvals for removal and mitigation because the swamp is within 1,000 feet of tidal waters.

Alves said that the multiflora rose was brought into the country from the Far East as hedgerows for cattle. But instead of staying in one place, the plants spread when birds ate the fruit on the plant and deposited the seeds, spreading them far and wide.

The problem is that invasive species like the multiflora rose have no natural predators, making them too aggressive for the native species to keep them out.

Swamps also are present in St. Mary’s River State Park. Several species of forest interior-dwelling birds find homes in the park because of the thick, contiguous forests, Rambo said.

Some of the birds include the yellow-throated warbler and the hooded warbler. The park is also home to the eastern narrow-mouthed toad, a moist-skinned amphibian rare to Southern Maryland.

Along the banks of the St. Mary’s River that traverses the park, swamp vegetation pops up because rainwater remains in the soil close to the surface, Rambo said.

The skunk cabbage also makes its home here.

Another swamp, called Church Swamp, is in Avenue on private property. According to the U.S. Fish and Wildlife Service’s Wetland Mapper, the swamp contains broad-leaf deciduous trees that shed for the fall and winter months. Portions of the swamp regularly have water, while other parts of the swamp have temporary pools of water.

A reason to protect

Experts who like to venture into the swamps say there are several reasons that swamps should be protected.

The presence of species diversity is one reason experts give to keep around swamps.

Swamps also provide free flood control and purification systems.

In other words, when rain from a storm flows into a swamp, the trees and plants absorb the rainwater so that it does not flood areas downstream.

In that way, less rainwater ends up downstream, and it moves more slowly, making it less likely that it picks up sediment along the way.

Swamps also filter runoff so that less nutrient pollution ends up in rivers, and subsequently the Chesapeake Bay.

“If trees are the lungs of earth, wetlands are the kidneys of the earth,” Rambo said.

One of the consequences of developing near or within swamps is that erosion can deposit sediment in the swamps, which affects the ability of fish and amphibian species to breed, Rambo said. The runoff also can carry pesticides to the water if land near the swamps has been treated with the chemicals.

In addition, clearing areas of contiguous forest, including in swamps, has an impact on birds that live in dense forests. Fragmenting habitats makes it easier for predators, who work the edge of forests, to find their prey. It means there is less sanctuary area, Rambo said.

Jett said that evapotranspiration is another reason why swamps should be kept from development. Evapotranspiration consists of both water that evaporates from bodies of water and water in plants that transpires back into the atmosphere.

“If there is an area with trees, only 5 to 10 percent of the rainwater evaporates, but if the trees are cleared, 90 percent of rainwater evaporates,” Jett said.

A less forested area means that less moisture is retained in the lower parts of the atmosphere, which can result in drier climates and even droughts, Jett said.

Some of the swamps in Southern Maryland are protected via government or land preservation trusts.

The Zekiah Swamp became a Rural Legacy Area, which makes it an area targeted for preservation using state Project Open Space funds. The Rural Legacy Area for Zekiah Swamp totals about 31,000 acres, but several of the properties envisioned for preservation are private properties.

Long said that Pages Swamp could be threatened with a proposal to extend Middletown Road through the swamp.

Battle Creek Cypress Swamp has been protected since 1957 through the nonprofit Nature Conservancy and is managed by the Calvert County Natural Resources Division. The American Chestnut Land Trust protects nearly 3,000 acres of Parkers Creek watershed, including its swamps. Flag Ponds Nature Park is a county-owned park.

Key Swamp is protected since it is part of Historic St. Mary’s City. The swamps in St. Mary’s River State Park are protected as well. Church Swamp in Avenue does not currently have protective covenants, called easements.

“We should protect not just for aesthetic reasons, but our own reasons,” Jett said. “Evapotranspiration affects humans. We have to have vegetation for humans to survive. If we don’t allow habitats to survive, we won’t survive.”

pwarner@somdnews.com