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Tidal Freshwater Wetlands

Written on: September 19th, 2017 in Wetland Assessments

You may already be aware that saltwater wetlands are influenced by ocean tides, and that freshwater wetlands located further inland are not influenced by tides.

But, did you know that there are freshwater wetlands that are actually still influenced by the ocean’s tides?

These wetlands, commonly called tidal freshwater wetlands, are in some ways similar to other wetland types. For example, tidal freshwater wetlands provide many of the same services that other wetland types provide, including floodwater storage, improvements to water quality, and wildlife habitat.

Tidal freshwater wetlands also experience some of the same problems that other wetland types experience, including the presence of invasive species like the common reed (Phragmites australis), and the presence of development or agriculture in the area surrounding the wetland.

However, tidal freshwater wetlands are also different in many ways from other wetland types. Though not an all-inclusive list, here are two big ways that tidal freshwater wetlands differ from their other wetland counterparts:

  1. Landscape: Part of what makes tidal freshwater wetlands different is their location in the landscape. These wetlands are located just far enough away from the ocean where salinity (i.e., how salty the water is) is extremely low, and freshwater flows into these wetlands from headwaters further upstream. Yet, these wetlands are still just close enough to the ocean to experience high and low tides. Other wetland types are either located closer to the ocean and are therefore saltier or are even further inland and do not experience tides.
    Freshwater tidal wetland location verses saltwater tidal wetland location

    Shown above is an aerial view of the Leipsic River in Kent County, Delaware. Circled in red on the left is an example of an area with tidal freshwater wetlands, and circled in red on the right is an example of an area with saltwater tidal wetlands. Notice that the freshwater tidal wetlands are further upstream (i.e., further from the Delaware Bay, inland) than saltwater wetlands.

  2. This flowering plant is pickerelweed (Pontedaria cordata), a common plant found in both non-tidal and tidal freshwater wetlands but not in salt marshes.

    Plant Community: Tidal freshwater wetlands tend to have a lot of the same plant species as non-tidal freshwater wetlands, such as arrow arum (Peltandra virginica), annual wild rice (Zizania aquatica), big cordgrass (Spartina cynosuroides), water smartweed (Polygonum punctatum), pickerelweed (Pontedaria cordata), broadleaf arrowhead (Sagittaria latifolia) and spatterdock (Nuphar species); however, these plant communities differ greatly from those found in salt marshes. Smooth cordgrass (Spartina alterniflora) or saltmeadow cordgrass (Spartina patens) commonly dominates salt marsh communities, whereas they are often completely absent in tidal freshwater wetlands. Additionally, tidal freshwater wetlands usually have much more plant diversity than salt marshes, meaning that there tends to be a higher number of species present in tidal freshwater wetlands compared with salt marshes.

    These two pictures show the contrast between common plant communities in Right: A salt marsh (Leipsic River watershed, summer 2013), and Left: A tidal freshwater marsh (Red Lion watershed, summer 2017).

Now that you know a little bit about these wetlands, your next question might be: do we, WMAP, assess the condition of tidal freshwater wetlands in Delaware? Our answer: Yes!

Throughout this summer (2017), we have been assessing wetlands in the Red Lion watershed in New Castle County. Many of our tidal wetland sites thus far have been freshwater tidal wetlands. We can determine if a site is a freshwater or saltwater tidal wetland by measuring the salinity of the water, looking at the plant community, and looking at its position in the landscape using aerial photos.

To learn more about other wetland types that we have in Delaware, visit the Delaware Wetlands website and our blog post about Delaware’s Unique Wetlands.


Delaware’s Crayfish

Written on: September 19th, 2017 in Wetland Animals

Did you know that Delaware has multiple species of crayfish? While crayfish may look like small lobsters, they are actually distant cousins. The most differentiating feature is that lobsters live in saltwater, and crayfish, crawfish, crawdads, or whatever you would like to call them, live in fresh to brackish waters. Some crayfish species living in […]

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Blue Carbon – a benefit to protecting tidal wetlands

Written on: September 19th, 2017 in Wetland Assessments

Guest Writer: Kari St.Laurent, Delaware National Estuarine Research Reserve Wetlands are more than just a beautiful photo opportunity. If you are a reader of this blog, you are probably aware that tidal wetlands can protect shorelines from storm surge, reduce nutrients, and provide habitat for critters like shellfish, crabs, and fish. These benefits are collectively […]

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NVF-Yorklyn Cleanup and Redevelopment – an unprecedented partnership

Written on: September 13th, 2017 in Wetland Restorations

Guest Writer: John G. Cargill, IV, DNREC Division of Watershed Stewardship/Division of Waste and Hazardous Substances The National Vulcanized Fiber (NVF) plant located in Yorklyn, Delaware has a rich history with humble beginnings in grist, snuff, lumber, and cotton. By the mid 1800s, production in the valley shifted to paper, and by the early 1900s […]

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Beneficial Reuse of Dredge Material on a Tidal Marsh

Written on: May 24th, 2017 in Beneficial Use

What is one way to give a marsh a lift with the challenge of rising seas? Spray the muddy material that has been dredged up from the bottom of a creek in a thin layer on top of the marsh. But how much mud is too much, and can the plants survive? These are a […]

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Keeping an Eye on the Rising Tide: SSIM

Written on: May 24th, 2017 in Wetland Assessments

Coastal wetlands are a hallmark feature of the Delaware’s Bayshore, making up about 23% of all wetland types in the state. Because of the many beneficial services these wetlands provide, such as wave energy reduction, the survival of coastal wetlands is an important part of protecting our seaside communities from threats associated with the changing […]

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Floating Wetlands

Written on: May 24th, 2017 in Outreach

Guest Writer: Phil Miller, DNREC’s Nonpoint Source Program We’ve all heard about wetlands before but have you ever heard of a floating wetland? Floating wetlands are artificial islands with plants on top and roots below. Similar to a natural wetland, they improve water quality by soaking up nutrients, such as nitrogen and phosphorus. These two nutrients […]

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Re-Engineering Nature in Delaware Tax Ditches

Written on: May 22nd, 2017 in Wetland Restorations

Guest Writer: Melissa Hubert, DNREC’s Drainage Program Fun fact, did you know that there are 234 tax ditch organizations scattered across Delaware that provide water management services to over 100,000 residents and nearly half of the state-maintained roads? These watershed based organizations are responsible for maintaining over 2,000 miles of ditch channel to ensure the […]

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Shoreline Stabilization Solutions for You!

Written on: May 22nd, 2017 in Living Shorelines

Where to Begin and an Expedited Permitting Process. Guest Writers: Julie Molina, Katie Huegel and Matt Jones of DNREC’s Wetlands & Subaqueous Lands Section Delaware’s coastal communities face constant challenges from shoreline erosion. Historically, tidal wetlands act as the natural solution for shoreline stabilization. Tidal wetlands provide protection against shoreline erosion, a mechanism for flood […]

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Making the Great Cypress Swamp Great Again

Written on: March 16th, 2017 in Wetland Restorations

Guest Writer: Andrew Martin, Field Ecologist, Delaware Wild Lands The Great Cypress Swamp once covered nearly 60,000 acres. Although a long history of ditching and draining for agriculture and development has reduced its vast expanse, the Swamp remains Delmarva Peninsula’s largest contiguous forest and largest freshwater wetland. For the last 50 years, Delaware Wild Lands […]

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