Freshwater Tidal Marsh
Approximately 53-60 continuous acres
The Lynn Farm's freshwater tidal marsh bordering Accokeek Creek constitutes nearly half of the property and is contiguous with some of the most diverse and
intact tidal marshes in the Potomac River drainage. The marsh's vegetation and habitat conditions require further inventory and assessment. Vegetative composition likely aligns with water levels. The most species-rich portion is often the mixed marsh zone above the water line, featuring grasses, ferns, sedges, rushes, and widflowers. Shrubs occur where the marsh transitions to upland habitats.
Freshwater tidal marshes in the Atlantic Plain region are home to a number of rare plant species, including the globally rare Sensitive Joint-Vetch (Aeschynomene
virginica). This diminutive annual plant has been observed in the Crow's Nest Preserve marsh and so may be present in the Lynn Farm marsh as well. (See
Appendix C for a Sensitive Joint-Vetch fact sheet.)
Observed problem weeds include Japanese Stiltgrass (Microstegium viminium) at the marsh edges and a large patch of exotic Phragmites (Phragmites australis) in the marsh's interior and along the marsh's southeastern edge. The exotic invasive Water Dayflower (Murdannia keisak), pervasive in nearby mixed marsh zones, may
also be present. The highly invasive exotic aquatic Hydrilla (Hydrilla verticillata) occurs in abundance near open water. Control of this water-borne plant will be
difficult unless targeted in the entire marsh ecosystem. This will require coordinating with stewards of adjacent and nearby properties and educating boaters to ensure the plant is not reintroduced via root and stem fragments on boats launched in Accokeek Creek.
The tidal marsh faces increased salinity levels due to chronic sea level rise (Strauss). Over time, the increased salinity will likely alter vegetative composition toward oligohaline marsh conditions.
Note: Aerial photographs suggest that the Phragmites patch has expanded from approximately 12,000 square feet in 2008 to 26,000 square feet in 2016. Given the potential for distortion in aerial photography, this estimate should be field checked.
Tidal marsh-upland interface at the Lynn Farm, July 2016. Standard best management practices recommend maintaining semi-forested buffers along marsh and upland interfaces to help protect water quality.
Tidal marsh at the Lynn Farm, June 2016. Shrub growth occurs where the tidal marsh transitions to upland habitats.
Tidal marsh along Accokeek Creek, July 2016. Further upstream from the Lynn Farm are a rare freshwater tidal marsh zone dominated by American lotus (Nelumbo lutea) in the boundary between marsh and open water. Wild rice (Zizania aquatica) dominates the zone beyond the Lotus, as evident in the photo above.
Mixed marsh zone in the Crow's Nest Natural Areas Preserve, July 2016. The mixed marsh zone above the water line is typically the most species-rich portion of freshwater tidal marshes, featuring a wide variety of wildflowers, ferns, grasses, and sedges.
Restoration & Management Implications
• The tidal marsh warrants further vegetation inventory and assessment, including for possible occurrences of the globally rare Sensitive Joint- Vetch, an annual species. Any Sensitive Joint-Vetch populations would be of interest to scientists and conservationists as this plant is a priority for research, protection, and recovery programs.
• Chronic sea level rise will affect habitat conditions in the tidal marsh over time (Strauss), potentially converting it to oligohaline conditions. Additional input from experts as it pertains to planning for and adapting to these changes is needed before addressing specific management implications here.
• Management and restoration actions in this area should be timed to avoid the marsh bird nesting period since the marsh provides breeding habitat for numerous ground-nesting bird species of conservation concern. The marsh bird breeding
period in Virgina's coastal plain is generally regarded to be April 15 – Sept. 1. Avoiding activity during the turtle nesting period may also be necessary (the
nesting period varies by species but it generally spans late April to mid July in Virginia).
• Any efforts by the DCR to control invasive exotic Phragmites should be supported. Where DCR budgets do not allow for control, privately funded control efforts may be needed to prevent this fast growing exotic species from compromising the
Lynn Farm's highest quality habitat zone. Control efforts should also attend to any Phragmites occurring outside the large circular patch visible in aerial photographs, including along the marsh's southeastern edge.
• Tidal marsh edges, subject to increased light levels and disturbed edge conditions from recent logging, should be monitored for weed invasion.
• The tidal marsh's large size means access to open water will require a lengthy boardwalk. A shorter boardwalk would provide access to the mixed marsh, the most plant species-diverse zone.