Many drainage patterns in the west are dendritic because of massive sedimentary rock layers.
The drainage patterns in the south -central part of the state tend to be rectangular primarily because of ancient faults the formed during the formation of the Appalachian Mountains.
The south-east drainage patterns are trellis patterns. These patterns form as a result of folding that occurred when the Appalachian’s formed. Erosion of the rock material left resistant rock layers alternating with non-resistant rock layers. Streams now flow in the non-resistant rock valleys.
In Potter County there is an unnamed hill marks the boundary between three of Pennsylvania’s major drainage basins.
1.One drains to the north through the St. Lawrence River
3) Susquehanna/Chesapeake Basin – largest watershed in PA covering 46% of the state. The largest river is the Susquehanna with has its headwaters in New York’s Otsego Lake and its mouth at Chesapeake Bay.
Major tributaries include :
Lackawanna, Conestoga, West Branch Susquehanna, and Juniata Rivers, Also Loyalsock and Tuscarora Creeks
Streams are unidirectional meaning they flow in one direction.
In this way they carry their load as well as nutrients stream organisms need. If they do not “capture” their nutrients quickly, they must wait for the stream to bring more.
The flow of water exerts a force on organisms in the stream.
Mollusks can resist this force. Its muscular foot enables it to attach itself to rocks, plants, and the streambed itself.
Some fish are streamlined so they can move with or against the current.
Keep in mind that the velocity of the stream is an abiotic factor.
A stream’s velocity changes with its course and its depth. The widening of a river and a smoothing of its bed actually cause an increase in average stream velocity towards its mouth. Stream velocity is lower at the water’s surface and where the water meets the stream meets the channel bed. Stream velocity is most rapid in the middle of the water column due to least resistance.
Most species of fish are unaffected by the velocity and can live nearly anywhere. Insects are usually restricted to calmer waters.
Some of a streams load is a dissolved load or materials dissolved in the stream’s water. Some of the dissolved load enters the stream as the water flows into the riverbed. Most of the dissolved load enters the stream from groundwater.
Some of the dissolved load includes:
These elements are essential to the organisms that live in the stream.
Magnesium – plant growth
Calcium – critical in fish bones and mollusk shells
Potassium – plant growth
Silicon – used by microscopic diatoms to make their shells and by sponges to make their spicules
Short term acidic effects include fish kills and decreases in insect populations .
Acid mine drainage results in the deaths of many bottom dwelling organisms.
Acid mine drainage is not only acidic, but contains heavy metals and other pollutants. These substances settle to the bottom of the stream channel and becomes trapped in the sediments. These substances enter organisms through the process of diffusion.
Pennsylvania’s streams are susceptible to acidification for three reasons :
1 – Pennsylvania receives some of the most acidic rainfall in the U.S.
2 – Rocks in Pennsylvania contain minerals that contribute to acidification.
3 – Pennsylvania has many coalmines.
Fortunately many streams buffer or prevent large changes in Ph.