ABIOTIC

The pH of a stream or lake depends on the kinds of rocks and soil that water contacts. Proper pH is an important life requirement for all aquatic organisms. Aquatic invertebrates with external skeletons or shells made of calcium are extremely sensitive to a water’s pH below neutral, and are a very important part of the aquatic food chain. At the low end of the pH range, naturally occurring metals dissolve into the water. These metals may interfere with the body functions of fish, and can influence the development of eggs and larva. This leads to a lower natural production, if any at all. Ultimately the population declines, the food chain collapses, and the community suffers.

Fish require dissolved oxygen for respiration. They extract the oxygen dissolved in the water through their gills or across their skin. Temperature, water velocity, wind, water depth, the number of organisms using the oxygen, and plant growth influence DO in water. The Do needs for many aquatic insects and fish differ, but some ranges overlap. Fish such as black nosed dace, brook and brown trout, and certain stoneflies have similar oxygen. This is why certain groups of fish can be found living together. Generally, dissolved oxygen levels in aquatic habitats must be greater the 6.5 mg/l for fish and aquatic organisms to survive.

Fish can’t maintain internal body temperature like humans. Fish have very specific temperature requirements. Water temperature can influence oxygen concentration, metabolism (body functions), reproduction and growth. Water temperature can be influenced by the speed of the water. Fish are usually found in the “ideal range”, for example, 75 degrees would be considered lethal for brook trout, but fish like channel catfish and largemouth bass need temperatures that high to survive.

Fish can live for long periods of time without food, however long term survival of a fish population requires abundant food. When studying the health of a water system, it is important not only to look at the fish, but the food they eat as well. The first link in the aquatic food chain are plant, ranging from single celled phytoplankton, to algae or larger submerged plants. The plants are then eaten by smaller aquatic insects and other invertebrates. These insects are eaten by larger insects, or fish (consumers) in the food chain. Finally, large predatory fish eat the smaller fish and insects.

Fish need shelter from predators. Fish living in fast moving waters need a place to rest from the current. Vegetation growing in the water can provide important shelter. All the components in a fishes habitat must come together in just the right amounts for it to survive. You can see that if any one of the conditions changes, the resident fish may have a tough time of it. Water pollution can throw off this delicate balance.

Water that has had the delicate balance upset is called “impaired” In Pennsylvania, there are two major kinds of pollution: agricultural runoff, and abandoned mine drainage (AMD) These forms of pollution put excess nutrients, siltation, and metals into our waters. Even thought there are many other forms of pollution sources, none of the others combined affects as many stream miles or acres of lakes as these three. Not Cheetos

Agricultural runoff occurs when rain or melting snow, carries soil, pesticides, and fertilizers from fields into nearby waters. When soil is carried into a stream or river it suspends in the water, making it cloudy, or it settles at the bottom as silt. Silt in the water can damage fishes gills and make it hard to breath for fish. Cloudy water also absorbs more sunlight, than clear water (this may cause the water temp. to rise). Silt that settles at the bottom of the stream is known as sediment. Because some fish find food at the bottom of the stream, and an increase in sediment can kill invertebrates by suffocating them, thus lowering the amount of food the fish have. Sediment can also smother fish eggs and alter natural repopulation patterns. Sediment can also fill in living spaces and destroy natural habitat. “TURBITITY”=cloudiness, which is the amount of sediment in the water.

Nutrients like nitrogen and phosphorus also enter our waters from farms. Manure and other fertilizers are used to increase crop production. When these nutrients reach our streams and lakes, they have the same affect on the aquatic plants. Aquatic plants and algae growth can reach nuisance levels. Livestock can also affect aquatic communities. Stream banks erode where livestock enter the water to drink or cross to reach other pastures. This adds silt into the water. Manure is also directly deposited into the stream. To protect crops, farmers use pesticides to remove pests. Most pesticides are designed to kill insects and are poisonous to aquatic life. This can affect the food chain.