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.

Volunteers Pitch In at New Jersey’s Thompson Park

A volunteer effort, lead by the Middlesex County, New Jersey Parks and Recreation Department and the Rutgers Cooperative Extension, recently took place at Thompson Park.

Despite the rainy weather, 78 volunteers and members of the Youth Conservation Corps removed litter from the shoreline of Manalapan Lake, repaired fencing, made improvements to the park’s walking trails, weeded and mulched the park’s rain garden and native plant garden, and installed new plants in the rain garden.

The park’s rain garden was originally designed by Princeton Hydro Senior Water Resource Engineer Dr. Clay Emerson, PE, CFM. Rain gardens are cost effective, attractive and sustainable means to minimize stormwater runoff. They also help to reduce erosion, promote groundwater recharge, minimize flooding and remove pollutants from runoff.

By definition, a rain garden is a shallow depression that is planted with deep-rooted native plants and grasses, and positioned near a runoff source to capture rainwater. Planting native plants also helps to attract pollinators and birds and naturally reduces mosquitos by removing standing water thus reducing mosquito breeding areas.

Rain gardens temporarily store rainwater and runoff, and filter the water of hydrocarbons, oil, heavy metals, phosphorous, fertilizers and other pollutants that would normally find their way to the sewer and even our rivers and waterways.

On the day of the volunteer event, Central New Jersey received 0.44 inches of rain.  “We got to see the rain garden in action, which was really exciting,” said Princeton Hydro Senior Project Manager Kelly Klein, who volunteered at the event.

Volunteers from the following organizations participated:

  • Edison Metro Lions Club
  • Hioki USA Corporation
  • Girl Scout Troop 70306
  • East Brunswick Youth Council
  • Monroe Middle School
  • South Plainfield High School
  • Rutgers University
  • Master Gardeners of Middlesex County
  • Foresters Financial
  • Princeton Hydro

The Middlesex County Parks and Recreation Department’s next public volunteer event is tomorrow (June 2) in Davidson’s Mill Pond Park.

The Princeton Hydro team has designed and constructed countless stormwater management systems, including rain gardens in locations throughout the Eastern U.S. Click here for more information about our stormwater management services.