WHAT IS A LAKE?
Lakes are inland bodies of water. Typically water flows downhill through a watershed via rivers and streams and through groundwater. Ocassionally, geologic forces will stop water on its way downhill (by intercepting streams or groundwater) and cause it to pool, forming lakes and ponds. Glaciers and plate tectonics are the main foreces that create lakes.
The Great Salt Lake is at the bottom of a closed basin. Mountains around the lake stop the water from flowing into the Snake River while evaporation keeps lake levels low. Lake Boneville, formed during a much wetter time, historically flowed into the Snake River.
Lakes lifespans are limited, as rivers dump their sediment into them and dead plant material builds up on the lake bottom. Most lakes are less than 10,000 years old.
Man-made lakes are known as reservoirs The primary purpose of lakes in Utah is to store excess spring runoff to use to irrigate during our dry summers
DYNAMICS OF LAKES
Lakes, ponds and reservoirs go through fascinating changes throughout the seasons that are not observed in rivers and streams. Most of these changes are due to the unique properties of water. For example, water becomes more dense as it cools untill it freezes, when it floats. Wind and waves are powerful forces too, allowing for the mixing of lake layers.
During winter, a protective layer of ice forms on the surface. This actually insulates the waters below, allowing fish to survive the winter.
As the ice melts, cooler surface waters mix with the warmer insulated layer below. Nutrients and oxygen are able to spread through out the entire lake body, which allows for plant growth.
As sun heats the lake in the summer, layers once again set up.This time a warm layer of water sits above cooler water below. The lack of mixing can mean lower oxygen levels in the cool, deep layer.
Colder weather cools down the surface of lakes, untill the layers mix and oxygen and nutrients are once again able to circulate throughout the entire lake body.
BIOLOGICAL ASPECTS OF LAKES
Besides fish, there is a fascinating array of “bugs” and plants that are support the ecosystems of water bodies. There are both those we can see and those we can’t.
Phytoplankton are tiny plants that use sunlight and nutrients in lakes to grow. Polluted lakes may host 'algae blooms' which can suck oxygen out of the water and may be toxic to humans and animals.
Zooplankton are small animals that drift in the water column and feed on phytoplankton and smaller zooplankton.The main groups of zooplankton are Rotifers, Cladocerans and Copepods. During poor conditions, they are able to make a resting egg which may sit for decades and still be viable when conditions improve.
Zooplankton are the favorite food of many types of fish and most juvenile fish.
Zooplankton and phytoplankton are found in the limnetic zone, the open water area of the pond or lake where light does not generally penetrate to the bottom.
These animals include many types of insects as well as other animals such as worms, mollusks, and crustaceans.
Macroinvertebrates usually live in the shallow-water area around the edge of the pond amongst aquatic plants (e.g. cattails, water lilies and elodea). They are an important part of the food chain and a food source for larger fish.
Macroinvertebrates are often used as indicator species to determine the health of water. Some species are more sensitive to pollution than others. In ponds and lakes dragonflies and mayflies are indicative of a healthy aquatic community.