FOSS Ecoscenarios: Delaware Water Gap National Recreation Area
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INTRODUCTION
Biome: Freshwater lakes and rivers
The Delaware River is the largest free-flowing river in the eastern United States. It is one of the
few remaining free-flowing rivers in North America. There are no dams to block this river as it
winds between mountain ridges and down river valleys to the ocean.
The Delaware River has long attracted people with its beauty and natural resources. The LenniLenape Indians are the earliest known inhabitants in the region. They made their home here long
before the arrival of European settlers.
The Delaware Water Gap National Recreation Area (NRA) covers 64.3 kilometers (km) of the
middle Delaware River, bordering the states of New Jersey and Pennsylvania and running down
through Delaware and Maryland.
A water gap is a geologic feature where a river has carved through a mountain
ridgeline. The Delaware Water Gap is a water gap that cuts through a large ridge of
the Appalachian Mountains near the state line between Pennsylvania and New Jersey. The water
gap is at the southern end of the national recreation area.
Courtesy of National Park Service
The Delaware Water Gap cuts through a large ridge of the Appalachian
Mountains.
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A watershed is an ecosystem that contains a set of streams and rivers that all drain into a single
larger body of water. The body of water could be a wetland, lake, pond, and groundwater (water
stored underground). The watershed can also include cities, factories, mines, and farmland. These
human developments can affect the health of the watershed ecosystem.
The Delaware River watershed is the area where any water that falls as precipitation or is added
by humans will eventually drain into the Delaware River. Watersheds vary in size, depending on
the area being observed. The Delaware River watershed is quite large. It covers 21,789 square
kilometer (km2) of Delaware, New York, New Jersey, and Pennsylvania. Delaware Water Gap is
just a small part of this enormous watershed.
In early colonial times, Dutch settlers moved to the area to mine the mountains for copper. Not
knowing the implications, they dumped human waste directly into the water. Thousands of
people died every year from diseases spread by water, like typhoid and dysentery.
The watershed was the location of many important historical events. Forts were built during the
French and Indian War along the ridge tops. Remnants of Revolutionary and Civil War
cemeteries can still be found in the surrounding forests. In the late 1800s, the area became a
popular resort and vacation area for tourists from Philadelphia and New York City.
Courtesy of National Park Service
Small streams throughout the watershed feed into the Delaware
River. Trails run through riparian forests along the riverbanks.
As factories and cities grew within the watershed, the river became very polluted. Pollution refers
to substances introduced by industry and other human activity that can harm an ecosystem. By
the 1940s, the Delaware River was so polluted with chemicals and human waste that no fish
could survive in it. Scuds and zooplankton feed on decaying material at the bottom of the river
and ingest toxic chemicals. These toxins move up the food chain, until the top-level consumers
(bald eagles, black bears, and humans) end up with high levels of pollutants in their bodies. This
process is called bioaccumulation.
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Efforts to clean up the Delaware River watershed were unsuccessful until 1962, when the
governors of New York, New Jersey, Delaware, and Pennsylvania agreed to work together. Each
state agreed to make decisions that were best for the entire watershed.
The Delaware Water Gap was established as a National Recreation Area in 1965, for public
recreation and to preserve scenic and scientific resources. In 1978, part of the Delaware Water
Gap was designated a National Wild and Scenic River. The National Park Service manages all
National Recreation Areas.
The Delaware Water Gap NRA offers many ecosystem services. The river provides drinking
water for about 15 million people. A healthy watershed creates habitat for many aquatic
organisms, including fish and crustaceans that humans eat.
Today, over 60 million people live within a day’s drive of the Delaware Water Gap. Common
recreation activities include boating, fishing, canoeing, and swimming. In 1994, 4.4 million
people visited the Delaware Water Gap, compared to 3.4 million in Yellowstone National Park
that same year. Recreation activities raise over $70 million for the park every year and create
income for neighboring towns.
Courtesy of National Park Service
The Delaware Water Gap is a popular
spot for water sports, such as fishing.
Water quality in the Delaware River is a constant issue. The health of the ecosystems depends on
a continuous supply of clean water. The Delaware River is now one of the cleanest rivers in the
United States, but its future may be in danger. Many people are concerned that natural gas drilling
(also known as fracking) could contaminate the watershed. In 2010, the states within the
Delaware River watershed banned fracking within the watershed. However, recently
Pennsylvania and New Jersey have begun working toward allowing drilling within their parts of
the watershed.
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Ecosystem Services
• Aesthetic value: The beauty of the Delaware Water Gap landscape draws many visitors and is a
source of inspiration and happiness for many people.
• Food: Freshwater ecosystems like the Delaware Water Gap are home for man, fish, and
crustaceans species that humans eat.
• Fresh water: The Delaware River provides drinking water for about 15 million people living in
New York, New Jersey, Pennsylvania, and Delaware. Fresh water is also required for irrigation
and plumbing.
• Habitat refuge: Healthy rivers and riparian zones are essential habitat for many aquatic and
terrestrial organisms.
• Natural resources: About 36 percent of the Delaware watershed could be mined for natural gas.
• Primary Production: Phytoplankton within the freshwater biome and along the riparian zones
offer significant primary production.
• Recreation and tourism: River recreation activities such as boating and camping are an
important ecosystem service and raise over $70 million for the park every year.
• Water cycle: Major watersheds like the Delaware River watershed are significant reservoirs of
freshwater for supporting the water cycle.
• Water regulation: A healthy watershed is able to regulate and maintain clean fresh water.
ABIOTIC DATA
Freshwater lakes and rivers are found within every terrestrial biome on Earth. Many of the abiotic
factors of a particular lake or river are influenced by the terrestrial biome they are found within.
The Delaware River runs through a temperate deciduous forest ecosystem.
Summers at Delaware Water Gap are warm and humid. Average summer air temperatures range
between 17 degrees Celsius (°C) and 23°C. The water temperature is usually a few degrees colder
than the air temperature. Thunderstorms and dense fog are common in the summer. An upstream
reservoir in New York sometimes releases excess water that is colder than the river. These large
volumes of cold water flow down the river and cool the entire river.
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The Delaware Water Gap has cold winters. Snow and ice storms are common. Air temperatures
range between -2°C and 2.5°C. Water temperature drops to freezing (0˚C), and most of the river
is covered in ice. Underneath the ice, the river continues to flow and many of the aquatic
organisms continue to thrive.
Delaware River water depth is measured in Montague, New Jersey. Normally, the water is 1.5–2
meters (m) deep, but during floods the water can reach 7.5 m deep. Floods occur because of
stormy weather or because water has been released from an upstream reservoir.
The flow of the Delaware River is generally smooth and quick. Areas of shallow streams and
quiet pools are excellent locations for spotting animal life. These features help circulate more
oxygen in the water which helps many aquatic animals. The river bottom consists of pebbles and
cobbles deposited by ancient glaciers.
The Delaware River is still affected by pollution. There are two main types of pollution: point
source pollution and nonpoint source pollution. Point source pollution comes from an identifiable
source like a pipe or factory smokestack. Federal laws like the Clean Water Act have regulated
many forms of point source pollution. Nonpoint source pollution comes from many different
sources that aren’t always identifiable. Storm water runoff and accumulation of runoff from farms
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or lawns are examples of nonpoint source pollution. This form of pollution is much harder to
control because there are so many contributing sources.
BIOTIC DATA
As in all freshwater biomes, phytoplankton are the dominant producers in the Delaware River
ecosystem. In the Delaware River, examples of phytoplankton include diatoms, freshwater algae,
and cyanobacteria. Phytoplankton provide food for many other organisms in the ecosystem.
Other producers include aquatic plants like yellow pond lilies.
Cyanobacteria are very sensitive to changes in water nutrient levels. An increase in nitrogen from
agricultural runoff can cause algae and bacteria to grow rapidly. This is called an algal bloom.
When the massive population of cyanobacteria dies, the decomposition process can consume all
the oxygen in the water. This can decrease the amount of oxygen available to other organisms in
the water.
Annual primary productivity is the amount of energy provided by the producers to the ecosystem
each year. Freshwater ecosystems, like the Delaware Water Gap NRA, have moderate annual
primary productivity compared to other biomes. The rate of primary productivity changes
depending on the temperature, depth, and quality of the water.
Freshwater ecosystems, like the Delaware Water Gap NRA, have intermediate levels of
primary productivity, as compared to other ecosystems.
The rocks, vegetation, and mud of the stream bottom are covered with organisms. Tiny
crustaceans called scuds swim through the vegetation. Aquatic snails scrape algae off submerged
plant stems and rocks. Freshwater mussels live in the muddy stream bottom. They eat by
siphoning water and mud and filtering out plankton, algae, and detritus. In the early summer, tiny
black tadpoles feed on plankton and algae. If they survive, they will grow to become amphibians
like toads, salamanders and frogs.
The surface of a summer pond might be covered in small insects. Mayflies spend most of their
lives as nymphs, clinging to underwater plants and eating algae and detritus. When they molt and
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emerge as adults, they live only a few hours or days. Water shrews feed on aquatic insects as well
as small fish, spiders, snails, and amphibians.
A buffer of native vegetation protects the river. The buffer zone of trees, shrubs, and sedges
protects the waterway by trapping and filtering pollutants as the groundwater flows through the
roots underground. The thick canopy of trees shades the water and helps produce the cooler
water temperatures and low light levels preferred by brook trout. The hemlock trees form an
important bird-breeding habitat, especially for songbirds. Along the banks of streams and calm
pools, narrow-leaf cattails grow. They provide shelter and protection for many small animals.
On the shore, you will find many small animals. Beavers haul branches from the surrounding
forest into the water to build their lodges and dams. Common map turtles bask on the partially
submerged logs of beaver dams. Minks forage along the riverbank and live in abandoned beaver
lodges.
Courtesy of National Park Service
A bald eagle on the lookout for a fish dinner.
Crayfish scavenge along the muddy shoreline. Mallard ducks forage for aquatic plants and
invertebrates. Great Blue Herons patiently hunt fish and other small animals.
Within the water, brook trout lurk in the shade. They live in the gravelly riverbeds where the
water is clear and cool. They are a major predator of bottom-dwelling invertebrates and landdwelling insects that fall into the water. Channel catfish live and feed along the muddy bottoms of
ponds and rivers. Smallmouth bass swim in deeper water, and catch larger prey like frogs and
smaller fish. Still larger animals, like bald eagles, river otters, and black bears, eat these predatory
fish.
Recently, population increases of invasive species like bighead carp and northern snakehead fish
are dramatically changing the ecosystem. Bighead carp are consumers of phytoplankton. As their
populations increase, they outcompete other plankton-eating native species for food. Meanwhile,
northern snakehead fish are voracious predators that will eat almost any animal in its path.
Predation by snakehead fish is decreasing many native populations throughout the American MidAtlantic and Midwestern freshwater ecosystems of the United States.
FOSS Populations and Ecosystems Course, Second Edition
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