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
2. A second drains S-W to the Gulf of Mexico
3. The Third drains east to the Atlantic
More realistic view
The state’s freshwater systems are divided into 104 watersheds.
Five Major Watersheds
1 ) Great Lakes Basin – only 1% of this basin lies within PA.
Erie Basin – includes Conneaut, Elk, and Walnut Creeks
Genesee Basin - drains into Lake Ontario
Five Major Watersheds
2) Ohio River Basin – PA’s 2 nd largest watershed. Headwaters in the Ohio River and Allegheny & Mongahela Rivers that meet in Pittsburgh.
This basin includes :
Tionesta Creek, Mahoning Creek, Stony Creek River, the Lower and Upper Youghiogheny Rivers, Beaver River, and the Upper Ohio River.
Five Major Watersheds
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
Five Major Watersheds
4) Potomac Basin – Does not flow through Pennsylvania, but a portion of its basin is located within the state.
PA tributaries include :
Marsh, Wills, Tonaloway, Licking, Rock, Conocochegue, and Antietam Creeks
Five Major Watersheds
5) Delaware Basin – Pa’s third largest watershed
Tributaries include :
Upper, Middle, and Lower Lehigh Rivers
Maiden and Brandy Wine Creeks
Three dominant groups of organisms in stream communities.
1. Algae – and other Protists
Algae – producers or autotrophs
Animal-like Protists including:
Ciliates and paramecia – eat bacteria and algae
Amoeba – Protist – engulf their food
Protists – are called saprotrophs – feed on decayed organic matter . Some Protists are called raptors because they eat other Protists.
Common types :
Insects – flies and beetles occur in almost every stream
The larval stage of flies and beetles live in water. Adult forms live on land.
Exception – water strider stays on the surface of the water.
Some flies are shredders – eat tissue of other organisms/organic matter and wood. Other flies are predators eating their prey whole or piercing its tissue and sucking out the fluid.
Mollusks – feed on algae and plants. Are primary consumers.
Amphibians – salamanders and frogs – go through various life stages in the stream.
Frogs – predators – insect eaters – with a sticky tongue adaptation
Salamanders and Newts – insect eaters and their larvae
Fish – are the dominant freshwater vertebrate
Grazers – algae eating fish
Strainers or Suckers depending on how they feed
Predator fish – Pike, Pickeral, Gars, Bullhead
Detritivores – feed on shredding sediments and filter their food from those sediments.
Factors That Affect Freshwater Ecosystems
Interactions between the biotic and abiotic factors determine the numbers and kinds of organisms in the fresh water ecosystem.
Abiotic factors that affect biodiversity
1 – temperature
2 – current & velocity
3 – substrate
4 – stream order
5 – amount of sunlight
6 – turbidity
7 – quantities of dissolved substances
8 – ph
9 – organic matter
Streams form over time as runoff flows along tiny channels called rills. Rills flow into larger streams and eventually into rivers.
The smallest streams are called first order streams with flow into second order streams which flow into third order streams which flow into fourth order streams and so on.
In Pennsylvania 80% of all streams are first and second order streams.
The size or order of a stream relates directly to the organisms that inhabit the ecosystem.
1 st order streams - largest insect populations and little if any fish
3rd order streams – are dominated by plants and game fish
Larger streams – contain diverse populations of algae, fish, and other aquatic organisms.
Temperature differences are caused by:
1 – velocity of the water
2 – depth
3 – amount of vegetation near stream banks
4 – seasonal changes – for example snow melt
5 – natural springs
Temperature affects the kinds and numbers of species in a stream.
Carp and catfish can live in a wide range of temperatures.
Protists, algae, and trout survive only in certain temperatures.
Current and Velocity
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.
Substrate is the material that organisms live in, on, or around. It contains both organic and inorganic particles.
Organic substrate – contains algae and other small particles of matter.
Inorganic substrate – contains rocks, pebbles, silt, sand, and mud that make up the stream channel.
Most invertebrates live in or under the rocky substrate. Freshwater sponges live their lives attached to the tops and sides of rocks. Other sponges attach to the sides and bottom of the stream.
Some organisms live in the substrate. One type of dragonfly larva lives in the sandy substrate of riverbeds and gathers the oxygen it needs by way of a siphon.
Bullheads often live deep within gravelly substrates.
In some cases, stream organisms use plants as substrates. Example: midge flies.
The amount of light a stream receives also affects the biodiversity of the stream.
Plants rely on photosynthesis to make their energy. An area in a stream that is darker generally has fewer organisms.
The amount of sunlight that penetrates a body of water depends on the stream’s clarity or turbidity.
Turbidity reflects the amount of suspended matter in the water. Suspended material in the water includes: silt, clay, small organisms (plankton), and organic debris.
Factors that affect stream turbidity includes :
Increase in erosion
Periods of high water
Large amounts of melting snow
Also affects turbidity.
Cold snowmelt entering the stream carries large amounts of sediment.
Warm stream waters promote plankton growth.
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
Phosphorus – plant growth
In excess nitrogen and phosphorus stimulate plant and algae growth.
Excess algal growth is called an algal bloom. Algal blooms deplete oxygen levels in the water and can result in the death of many organisms .
Streams contain dissolved oxygen and carbon dioxide.
Dissolved oxygen is important in determining the biodiversity of a stream.
Oxygen enters the water from the air.
The amount of oxygen dissolved in the stream depends on the temperature of the water.
Cooler water holds more dissolved oxygen than does warm water.
The amount of dissolved oxygen also depends on photosynthesis and respiration.
Beetles get oxygen directly from the water or use air tubes to get oxygen from the air. Worms and other invertebrates absorb oxygen through their skins.
The streams current also affects the oxygen level. Slower stream current means less oxygen is available to organisms in the water.
Organisms have adapted to compensate for the lower amount of oxygen.
Organisms have adapted to compensate for a lower amount of oxygen.
1 – Many organisms can increase the current that flows over their respiratory structures.
Mayflies move their gills back and forth to increase the available oxygen.
2 – Some insects have small holes in their shells that enable them to create a current through their bodies when oxygen levels are low.
The decomposition of organic matter also affects the oxygen content of the water. Oxygen is used up during decomposition. This process occurs faster in warmer water.
Most of the carbon dioxide in stream water comes either from the atmosphere or groundwater.
Decomposition and respiration are the other two sources. Oxygen is used up during decomposition. This process occurs faster in warmer water.
As plants photosynthesize and organisms absorb carbonate minerals from the water, carbon dioxide is removed from a stream.
Most organic matter in a stream is used for food.
Organic matter includes :
Bits of leaves
Too many nutrients can decrease the oxygen levels. Too few nutrients cause organisms to begin to travel to other parts of the stream in search of food.
The Ph of a solution is the measure of its concentration of specific hydrogen ions.
Ph ranges for 0-14
Ph of 7 is neutral
Ph higher than 7 is a base
Ph lower than 7 is an acid
Pure water has a Ph of 7 and is neutral.
Most rain water is slightly acidic.
Most stream organisms can tolerate small changes in ph. However, if a stream becomes acidic populations of organism will become reduced.
PA pH Balance
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.