Restoring the Northernmost Freshwater Tidal Marsh on the Delaware River

By Kelsey Mattison, Marketing Coordinator

Located in Hamilton Township, New Jersey, Mercer County’s John A. Roebling Memorial Park offers residents in the surrounding area a freshwater marsh with river fishing, kayaking, hiking, and wildlife-watching. The park contains the northernmost freshwater tidal marsh on the Delaware River, Abbott Marshland. Since the mid-1990s, many public and private partnerships have developed to help support the preservation of this important and significant marsh.

Tidal marshes, like the 3,000-acre Abbott Marshlands, contain valuable habitat for many rare species like River Otter, American eel, Bald Eagle, and many species of wading birds. Unfortunately, the Abbott Marshland has experienced a significant amount of loss and degradation, partially due to the introduction of the invasive Phragmites australis, or, Common Reed.

Phragmites australis

Phragmites australis is a species of grass that has a non-native invasive form that creates extensive strands in shallow water or on damp ground. The reed tends to colonize disturbed wetlands and then spreads very rapidly, outcompeting desirable native plant species. Once it is established, it forms a monoculture with a dense mat and does not allow any opportunity for native plants to compete. This impairs the natural functioning of the marsh ecosystem by altering its elevations and tidal reach which impacts plant and animal communities. Over the last century, there has been a dramatic increase in the spread of Phragmites australis, partly due to development impacts that resulted in disturbances to wetlands.

For the Mercer County, Princeton Hydro put together a plan to reduce and control the Phragmites australis, in order to increase biodiversity, to improve recreational opportunities, and to improve visitor experience at the park. This stewardship project will replace the Phragmites australis with native species with a goal to reduce its ability to recolonize the marsh. In September, our Vice President Mark Gallagher and Senior Project Manager Kelly Klein presented our plan to the public at the Tulpehaking Nature Center.

Vice President Mark Gallagher presenting on the project at the Tulpehaking Nature Center.

Princeton Hydro conducted a Floristic Quality Assessment to identify invasive areas and performed hydrologic monitoring to understand tidal stage elevations. Phase 1 of the restoration process occurred this fall and included herbicide applications to eradicate the Phragmites australis. The herbicide used, Imazapyr, is USEPA and NJDEP approved and our field operation crew applied it using our amphibious vehicle called a Marsh Master. For harder to reach areas, we used our airboat.

According to a USDA report, Imazapyr has been extensively studied, and when properly applied, it has no impact to water quality, aquatic animal life, birds, or mammals, including humans. It works by preventing plants from producing a necessary enzyme called acetolactate synthase.

The goal of this wetland restoration project is to enhance plant diversity, wildlife habitat, and water quality in John A. Roebling Memorial Park. In late spring of 2019, we will revisit the site to continue spraying the Phragmites australis. By Spring of 2020, we expect to see native species dominating the landscape from the newly exposed native seed bank with minimal Phragmites australis. Stay tuned for more photos from the field when our Field Crew returns to the site for Phase II in early Spring!   

View of John A. Roebling Memorial Park from the access road.

For more information about Princeton Hydro’s invasive species removal and wetland restoration services, visit: bit.ly/InvasivesRemoval 

Kelsey Mattison is a recent graduate of St. Lawrence University with a degree in English and environmental studies and a passion for environmental communication. Through her extracurricular work with various nonprofit organizations, Kelsey has developed expertise in content writing, storytelling, verbal communication, social media management, and interdisciplinary thinking. Her responsibilities at Princeton Hydro include social media management, proposal coordination, editorial overview, and other marketing tasks. As a member of the Princeton Hydro team, she aims to further its mission by taking creative approaches to communicating about our shared home: Planet Earth.