From the Headwaters to the Bay
Pennsylvania is truly blessed with abundant and diverse natural resources. From
fertile farmlands in the south to the forested mountains in the north we have it all.
Nowhere is this diversity more apparent than in our aquatic resources. There are
45,000 miles of rivers and streams, and an untold number or lakes and ponds in
Pennsylvania with more than 160 different kinds of fish living there. Many of these
waters start as a trickle in the mountain and end up as a large river that flows out to
a bay. The physical, chemical, and biological changes create vastly diverse habitats
throughout the Commonwealth of Pennsylvania.
To understand these aquatic ecosystems, you must first understand the concept of a
watershed. A watershed is a region or area bounded by highlands and draining to a
particular waterway. A watershed is also referred to as a basin. Everyone lives in a
watershed, even if you live in a desert. You are technically in a watershed. The water
in these systems can trace its origin to the precipitation that falls on the ground.
Imagine a raindrop falling to the ground. It could infiltrate, evaporate, be absorbed
by plants, or runoff. If that drop were to runoff the ground until it found a body of
water, in would be in the watershed of that body of water.
Many of you live in the Ridley Creek watershed. Some of you may live in the Crum
Creek watershed.
Both of those creeks drain into the Delaware River. The Delaware River watershed
is one of the six major watersheds in Pennsylvania. Since it separates Pennsylvania
from New Jersey, it covers eastern portion of the state. The Susquehanna River
watershed runs through the center of our state and is therefore covers the most
area in Pennsylvania.
Small streams form from the collection of water running downhill. Many of these
small streams start in the mountains or from underground spring that well up to the
surface. These are referred to as headwater stream since they are at the head of the
system and have no tributaries. These are also called first order streams. When two
first order streams come together they form a 2nd order stream. When 2nd order
streams come together they become a third order waterway. It goes up from there.
If you trace the Mississippi Rive back to its origins it could be classified as a 10 order
waterway.
Topography plays a big role in the character of headwater streams. Since many of
these streams are located high on step mountain ridges, the water flows fast and
takes with it some of the surrounding landscape. Surrounding layers of rocks, soil
and minerals are eroded by the force of the water.
Streams that drain areas with a limestone (containing the mineral calcite) bedrock
geology are better able to buffer or neutralize the effects of acidic precipitation.
Most of the state’s headwater streams are found in areas of sandstone bedrock and
are less able to counter the effect of these acids.
The vegetation that surrounds headwater streams plays an important role. Since the
stream are not as wide as a large river, trees growing on both sides of the stream
provide shade keeping the water cold. Headwater stream are therefore often called
cold water streams and generally stay under 65 degrees Fahrenheit, even in the
summer month. The surrounding canopy also provides the bulk of the productivity
for the food web in these streams. Studies have shown that as much as 70 -80
percent of the energy input in head water streams comes from leaves. The larvae
and nymphs of insects such as stoneflies, craneflies, mayflies and some caddisflies
shred these leaves. These insects are very specialized in their shape and function.
They in turn provide food for the fish that call these waters their home. Among them
are the slimy and mottled sculpins, blacknose and longnose dace and brook trout.
These fish require high amounts of dissolved oxygen. Since more oxygen can be held
in colder waters then warm waters, these fish are referred to as cold water fish. The
shade and mixing of oxygen by the fast moving streams keeps oxygen levels high to
support these species. As these streams wind downward the stream slows and algae
can grow on the rocks. The nymphs and larvae of insects, such as mayflies and
caddisflies graze on the algae. These insect larvae are important food sources for
predatory insects and fish like trout.
The stream enters a valley and is joined by another stream. Water temperature
during the summer edge into the 70oF range. This is now considered a cool water
stream. Fish such as redbreast sunfish, rock bass and smallmouth bass are found.
Insects such as burrowing mayflies, caddisflies, whirligig beetles, hellgrammites,
dragonflies and damselflies are found in these waters.
At the end of the valley the stream has grown into a small river. Smallmouth bass
are still caught here, but the water is different. The water flows slower, so weeds are
more plentiful. During the summer months it warms into the high 70o range, so
catfish, muskies and walleys are often found. Streams change to rivers by getting
wider and deeper. This causes the water to move slower and gain more heat.
Additionally since these water ways are wider, less of the water is shaded by trees
on the river bank. This is an important reason as to why rivers are warmer than
streams. Because they are warmer and slower, they hold less oxygen. This is why
the aquatic life changes. Water temperatures can now reach 80os in the hot summer
months.
As small rivers join to form a big river like the Susquehanna or Delaware, Algae
becomes more abundant and aquatic plants can now root on the bottom. Carp,
crappie, bluegills and bullhead catfish can be found. Insects are fewer since they find
it tough to survive in the deep mud bottom of slow wide rivers. Plankton is very
plentiful and the main component of these warm water food webs. Ponds and lakes
have similar characteristics are also considered warm water habitats.
As the river enters the bay it begins to lose all of its previous identity. The fresh
water of the river mixes with the salt water from the near ocean. This mixed water
is known as brackish water and creates an ecosystem know as an estuary. Estuaries
like the Delaware and Chesapeake Bay (Maryland) are extremely diverse and
productive ecosystem providing homes for many species of fish, reptiles, amphibian,
birds and mammals.
From the Headwaters to the Bay
Questions
1. How many different fish are found in PA. Why do your think there are so many
different kinds?
2. Describe a watershed. Name two watersheds that you live in.
3. Name the six major watershed of Pennsylvania.
4. What is stream order?
5. Describe a headwater stream and explain why they are named as such.
6. Why do certain fish and other aquatic organism need to cold water habitats? Name
four examples of cold water organisms.
7. Why are cold water streams cold?
8. Where does most of the productivity come from in a cold water stream?
9. How do cold water and cool water stream differ physically and biologically?
10. What the physical changes from a stream to a large river? How does this affect what
lives there.
11. List four warm water species.
12. What is the base of the food chain in a warm water ecosystem?
13. What is an estuary? Name one