Delaware National Estuarine Research Reserve

Source: NOAA


The Delaware National Estuarine Research Reserve (DNERR) consists of two unique components, one on Blackbird Creek and the other on the St. Jones River. Freshwater wetlands, ponds and forest lands dominate the Blackbird Creek component. The St. Jones component is dominated by salt marsh and open water habitats of the Delaware Bay.

The reserve monitors long-term changes in weather and aquatic conditions in the estuary. The reserve’s research and monitoring programs address key management issues, such as biodiversity and the impacts of land-use on estuarine habitats, ecological impacts on horseshoe crab populations from migratory shorebirds, beach replenishment activities in relation to habitat preservation/reclamation, and eutrophication and contaminants in the estuary.

The reserve offers a wide variety of educational programs for the general public, school groups, private and nonprofit organizations, educators and coastal decision makers. Coastal decision-maker workshops have included such topics as land-use planning and smart growth, energy resource conservation and development for the next decade and acoustical bay bottom mapping

The Delaware Reserve is part of the National Estuarine Research Reserve System (NERRS), a network of estuarine habitats protected and managed for the purposes of long-term research, education, and coastal stewardship. Established by Congress in 1972 as part of the Coastal Zone Management Act (CZMA), the NERRS is administered as a partnership between the National Oceanic and Atmospheric Administration (NOAA) and the coastal states.

Blackbird Creek

caption Blackbird Creek. (Source: NOAA)

The more landward Upper Blackbird Creek Reserve is 477 hectares (1,180 acres) in designated size, distributed along 9.2 kilometers (5.7 miles) of low-salinity brackish or freshwater tidal creek, starting about 9.3 km (5.8 mi) upstream from where Blackbird Creek empties into the lower Delaware River.

The Blackbird Reserve contains 50 parcels of land held by 46 private landowners, plus the DNERR and one other state agency. Within the Blackbird Reserve’s designated boundaries about 85.8 ha (212 ac) of tidal marshes, upland fields, woodlots, and croplands were purchased by the DNERR in 1990, but the remaining majority of the Reserve is still in private ownership. An additional 74.1 ha (183 ac) of tidal marsh, woodlands, and croplands, across Blackbird Creek from the DNERR property and within the Reserve’s designated boundaries, was purchased in 1996 by DNREC’s Division of Fish and Wildlife (as part of the Division’s Cedar Swamp Wildlife Area), and is available for use in DNERR activities.

Much of the expansive tidal marshes and upland borders along Lower Blackbird Creek, downstream of the Upper Blackbird Creek Reserve’s designated boundaries, are owned and managed by the Division of Fish and Wildlife. This area primarily consists of a large parcel known as The Rocks (which is also part of the Cedar Swamp State Wildlife Area). Upstream of the Reserve, in non-tidal areas west of Rt. 13, are extensive areas of forested wetlands containing unique coastal plain ponds, much of it within Blackbird State Forest, which is owned and managed by the Delaware Department of Agriculture’s Forestry Section. Blackbird Creek’s watershed is still primarily agricultural or forested, although low-density residential development is increasing.


The wetlands vegetation of the Upper Blackbird Creek estuary is characterized by two major zones. Zone I covers the eastern most seaward quarter of the component. This zone, known as the saltmarsh cordgrass marsh, is dominated by saltmarsh cordgrass. Some fringes of this zone have common reed.

Other associated species found at slightly higher elevations are saltmeadow cordgrass, big cordgrass, salt grass, salt wort, high tide bush and groundsel bush.

Most of the lower Blackbird Creek estuary has been overrun by phragmites, forming a dense, monotypic cover over vast expanses of wetlands.


Black duck, mallard and wood duck are among the most common nesting bird species at the Blackbird Creek Component. During the spring and fall migration periods, extensive use is made of the area by most waterfowl in the mid-Atlantic region, including Canada geese, greenwinged teal, bluewinged teal, gadwall, pintail, wigeon and shoveler. Wading birds, shorebirds and raptors also frequent the area for breeding, migration, feeding and resting. The most common species include great blue heron, great egret, snowy egret, glossy ibis, yellowlegs, sandpipers, kestrels, marsh hawk, osprey and bald eagle.

The forests support deer, raccoon, fox, skunk, opossum, rabbit and squirrel, while large numbers of muskrat occur in the brackish and freshwater wetlands, together with beaver and river otter in lesser numbers. Insects, snakes, turtles, frogs, toads and salamanders are all residents of the component, utilizing both aquatic and terrestrial environments.

The estuary provides important nursery and feeding habitat for several species of fish, including white and channel catfish, weakfish, hogchoker, white perch, black drum, bay anchovy, menhaden, spot and eel, together with a diversity of benthic organisms including blue crabs. In the more landward recesses of the Reserve, where the waters are essentially fresh, American eel, eastern minnow, redfin pickerel, golden and spottail shiners, creek chubsucker, pirate perch, brown bullhead, white and channel catfishes, yellow and white perches, pumpkinseed, bluegill sunfishes and tessellated darter all gather.


The Blackbird Creek component is within the Coastal Plain Province, approximately 25 miles south of the Appalachian Piedmont Fall Zone, and displays essentially the same geological characteristics as those described in the St. Jones component.

St. Jones River

caption St. Jones River boundary map. (Source: NOAA)

The more seaward Lower St. Jones River Reserve is about 1518 ha (3750 ac) in designated size, distributed along 8.8 km (5.5 mi) of medium-salinity tidal river situated at the lower end of the St. Jones River watershed, with the river discharging into mid-Delaware Bay.

The St. Jones Reserve contains 35 parcels of land held by 23 private land-owners, plus the DNERR and one other state agency. Within the St. Jones Reserve’s designated boundaries, about 282.8 ha (698.5 ac) of tidal marshes, upland fields, woodlots, and croplands were purchased or protected by the DNERR in 1991-92 [with 174.7 ha (431.3 ac) purchased through fee-simple acquisition, and 108.1 ha (267.2 ac) protected through conservation easement, but the remaining majority of the Reserve is still in private ownership.

The Lower St. Jones River Reserve is home to the new DNERR education/research facility (containing a small but well equipped laboratory for DNERR researchers) which opened in May of 1999. A marsh boardwalk for interpretive and research activities has already been constructed on the DNERR property. Adjacent to the Lower St. Jones River Reserve on its eastern side is the Ted Harvey Conservation Area, owned and managed by DNREC’s Division of Fish and Wildlife, consisting of 817 ha (2019 ac) of woodlands, upland fields, croplands, freshwater ponds and wetlands, coastal wetland impoundments, and Delaware Bay shoreline. While the Ted Harvey Conservation Area is not within the DNERR’s designated boundaries, it is nonetheless available through cooperative arrangements with the Division of Fish and Wildlife for use in DNERR research and educational activities.

The Division of Fish and Wildlife’s Roberts Tract, a 71.2 ha (176 ac) parcel of the Little Creek State Wildlife Area, borders the St. Jones Reserve at its western end; in conjunction with the Division’s Ted Harvey Conservation Area, the Roberts Tract provides conservation-oriented land ownership on both upstream and downstream ends of the St. Jones Reserve.

The John Dickinson Plantation and Mansion, owned and managed by the Delaware Division of Historical and Cultural Affairs, provides another 106.4 ha (262.8 ac) of protected area within the Reserve’s designated boundaries, adjacent to the DNERR property’s western border. A small-boat ramp and fishing pier at Scotton Landing, owned and managed by the Division of Fish and Wildlife, provides good boat and water access to the main channel of the St. Jones River towards the Reserve’s western end.

On its far eastern end, the Lower St. Jones River Reserve also contains about 1036 ha (2560 ac) of Delaware Bay bottom and nearshore waters, running for 3.2 km (2.0 mi) along the Ted Harvey Conservation Area’s bay shoreline and extending outward 3.2 km (2.0 mi) into the open bay.

The St. Jones River watershed has significant development in upstream non-tidal areas, where urbanized Dover (Delaware’s state capital) dominates the middle and upper watershed. However, downstream portions of the St. Jones River watershed, where the Lower St. Jones River Reserve is located, are still primarily agricultural, with the Dover Air Force Base nearby. The two DNERR component sites are about 32 km (20 mi) apart.


Much of the area adjacent to the river is vegetated by intertidal persistent emergent wetlands. In the Lower St. Jones River watershed, over 90 percent of the tidal wetlands are considered to be classified as Zone 1 (dominated by saltmarsh cordgrass). Patches of Zone II (dominated by saltmeadow cordgrass and saltgrass) combine to form a salt hay community scattered throughout the component's higher elevations.

Big cordgrass and common reed are found along creekside levees and in the backmarsh near the upland edge. Wetland areas upstream of Route 113 at Scotton Landing are vegetated primarily by mixed stands of Spartina alternifora and Spartina cynosuroides, two types of cordgrass. Wetland shrub species, groundselbush and marsh elder, also occur in tidal wetland areas of higher elevation. A limited amount of palustrine forested wetlands occur at the head of the numerous tidal creek tributaries to the St. Jones River.


Nearly 100 species of birds may be found on the reserve site at certain times of the year. Ducks, geese, wading birds, shorebirds, raptors, upland game birds and songbirds all utilize the reserve. Particular importance is attached to black duck, mallard, gadwall, bluewinged teal, wood duck, bobwhite quail, ringnecked pheasant, American woodcock, mourning dove and recently reintroduced turkey, because of their importance as game birds and their occurrence as nesting species in the wetlands and upland fringe.

Avian species such as the blacknecked stilt, black tern, American avocet and black skimmer are relative newcomers to the area. Important raptors have been seen on the site, including osprey, peregrine falcon, Cooper's hawk, red-tailed hawk, rough-legged hawk, Northern harrier (marsh hawk) and great horned owl. In addition, at least 11 species of warblers and over 20 species of shorebirds frequent the site in varying numbers during migration periods.

All mammals common in Delaware can be found in the wetlands and forest fringes of the Lower St. Jones River. White-tailed deer, cottontail rabbit, gray squirrel, raccoon, red fox, opossum and woodchuck are abundant, as well as muskrat, mink and otter. Many reptiles and amphibians occur on the component. Six species of turtles, several types of snakes, frogs, toads and salamanders have been seen on the component.

Peregrine Falcons and the threatened Bald Eagles have been sighted at the reserve.


The St. Jones River component is within the Coastal Plain Province approximately 45 miles south of the Appalachian Piedmont Fall Zone. The Piedmont-type rocks are covered by a thick wedge of unconsolidated and semi-consolidated sedimentary rocks. The oldest and most extensive of these sediments are at the base of the Potomac Formation and are about 120 million years old. It consists of color-banded clays with interbedded sands that eroded off the ancestral Appalachian Mountains.

The Magothy Formation was deposited next with its very distinct white sands and black lignite suggesting a transitional environment from stream deposits to marine, much like that found in a delta. Layered on top of the Magothy are marine formations of Cretaceous through Eocene age with the Piney Point Formation being the youngest. Above this is a nonconformity, which represents a gap in the sedimentary record during which no sediments have been preserved (Oligocene age.)

Later, the sea again covered most of Delaware and deposited Chesapeake Group (Miocene age). This group consists of interbedded silts and sands and reaches a thickness of 400 feet at the St. Jones. Many of the sandy layers contain important supplies of water for municipal and industrial use in the Dover area. The repeated advance and retreat of continental glaciers during the past one to two million years (Pleistocene age) caused dramatic changes in relative sea level and the configuration of streams draining from the glaciers. The deposits from meltwater runoff supplies most of the sands and gravel for construction. Sand and gravel are the most important mineral resources in Delaware with the most potential source for Kent County being in and around the St. Jones River Component area.

Cultural History

The St. Jones River component is endowed with a rich pre-history and a historic 18th Century plantation setting adjacent to the Delaware Bay. The cultural and historical resources of the Reserve have been intensively studied, resulting in the identification of 32 archaeological sites in the St. Jones River Component.

With the arrival of Europeans during the 1600s, Delaware began a process of change that would have an enormous effect on the land as the Native Americans had known it. Forests, rivers, and marshes were altered drastically with the expanding land-use of local farm communities. The land now within the St. Jones River Component's best known owner was John Dickinson (1732-1808), a signer of the Federal Constitution. An area resident in his youth, Dickinson later administered his property from his home in Wilmington. Between 1760 and 1808, the land felt his influence through the decisions he made as a farmer, manager, and owner of more than 5,000 acres in Kent County. Of particular importance were his decisions involving crop production, woodland management, and changes in the management of the nearby St. Jones River and adjoining marsh.

Throughout history, individuals, slaves, tenants, farmers, and others were engaged in crabbing, fishing, oystering, trapping and other wetland enterprises to help put food on their tables. By 1830, these activities became more commercialized and led to over-harvesting. The legacy of this over-harvesting can still be seen in the scarcity of some marsh species today. In addition to tapping wetland resources for food, local farmers pastured livestock on the marsh and made hay from its vegetation.

Landowners in the 1700s considered the marsh to be more of a liability than an asset. Mosquitoes and swamp gasses were unpleasantries often complained about by residents and visitors alike. Though the St. Jones River was ditched and dredged many times, there was probably little thought of changing anything but the river's course.

In John Dickinson's time, the majority of houses and farm buildings in the area were built of log and frame construction. Wood was also the primary source of fuel for home use. European settlers continued to clear woodlands for the creation of farms and by the 1800s deforestation had taken its toll. Only remnants remain today of once endless forests. As forests dwindled, legislation was passed which limited the cutting of trees. John Dickinson responded to deforestation in his time by limiting the number of trees that were cut down on his property. Dickinson encouraged the use of trees already fallen to save the remaining woodlands.

As the 1800s progressed, farmers in this area turned to raising corn and livestock on lands that were worn out by poor farming methods and erosion. Declining productivity pressed some farmers into clearing marginal lands. Agricultural practices of the times, along with continuing deforestation. created more silt flowing into rivers and marshes. Erosion in some areas raised the soil level in the marsh enough to change the types of vegetation which grew there.


caption Delaware Reserve weather station. (Source: NOAA)

A major priority of the reserve is to coordinate, facilitate and conduct management-oriented research, which will provide information useful for local, regional and national coastal management decision making. The creation of permanent field sites for management-oriented research is an important step towards a more comprehensive and integrated program of research, monitoring and management.

The Delaware National Estuarine Research Reserve's two components expand researchers' opportunities to perform long-term studies in representative ecological zones of the Delaware Estuary. The components provide the opportunity to observe and explain basic functions of, and changes in, the natural systems, and apply this information to other estuarine systems along the mid-Atlantic coast. These areas will be managed in part to maintain their relatively undisturbed character to serve as controls to compare to other areas outside the reserve, and in part may be modified or manipulated to accommodate research needs and maximize their research utility.

The goals of the Research Reserve's environmental research and monitoring program are to:

  • Establish and manage key (core) areas of the reserve for long-term use as outdoor field laboratories, maintained for such purpose by the help of buffer areas.
  • Coordinate research projects with other research efforts in the Delaware Estuary and Delaware's Inland Bays to streamline scientific efforts, maximize efficient use of resources and funds and avoid unnecessary duplication of efforts.
  • Enhance scientific understanding of estuarine ecosystem processes and functions to enable better identification of management issues and response options.
  • Gather and make available information needed by reserve managers and coastal decision makers for improved understanding and management of estuarine ecosystems.
  • To better our understanding of ecological values and processes of estuaries nationwide, by comparing the Delaware Estuary to other estuarine areas.
  • Identify priority natural resources, gather baseline information on them and establish indicators of change.
  • Identify priority habitat management needs, gather information about how to best meet the needs and provide technical guidance to implement the desired actions.
  • Monitor the impacts of human stresses on the estuarine environment and the effectiveness of pollution control strategies.
  • To better our understanding of human exploitation of the estuarine environment through time.
  • Identify critical habitat requirements of living natural resources.
  • Evaluate land-use practices and management strategies in terms of their impacts and effectiveness.
  • Publication of research results.

Partners and Supporters

The Delaware Reserve is a partnership between the Delaware Department of Natural Resources and Environmental Control (DNREC) and the National Oceanic and Atmospheric Administration (NOAA). DNREC’s Division of Soil and Water Conservation administers the program within the Delaware Coastal Programs Section.

Further Reading

Disclaimer: This article is taken wholly from, or contains information that was originally published by, the National Oceanic and Atmospheric Administration. Topic editors and authors for the Encyclopedia of Earth may have edited its content or added new information. The use of information from the National Oceanic and Atmospheric Administration should not be construed as support for or endorsement by that organization for any new information added by EoE personnel, or for any editing of the original content.



(2006). Delaware National Estuarine Research Reserve. Retrieved from


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