A freshwater biome is one in which the salt concentration is extremely low, generally below 1 percent. Freshwater biomes include ponds, lakes, streams, rivers and wetlands. Plants in freshwater biomes thrive from the bottom of shallow lakes or ponds, to the edges of streams, to spongy marshes. Lifeforms can be in the water, along natural or human-created drainage systems, streams, springs, in natural or temporary water systems created by floods.
What Are Autotrophs?
An autotroph is an organism with the ability to manufacture its own food, generally by photosynthesis (photoautotrophs), although more information is being gathered about chemoautotrophs that use chemical energy to feed themselves. Autotrophs, classified as "producers," are vital to the cycle of life, since they support the food chain from the bottom up. Plants are autotrophs, as are certain bacteria and some one-celled amoeba.
What Are Heterotrophs?
A heterotroph is an organism that requires external organic matter produced by other organisms to feed on, because it is unable to synthesize its own food. Unlike autotrophs, heterotrophs are classified as "consumers." They can be single-celled organisms or multi-celled. All animals (herbivores, carnivores, and omnivores), some fungi, and many (but not all) bacteria are heterotrophs. Heterotrophs feed on -- and cannot survive without -- autotrophs.
Four Freshwater Autotrophs
Phytoplankton are photosynthetic autotrophs. They not only feed themselves but they produce oxygen and serve as food for heterotrophs. Grassy pondweed is an autotroph that lives in northern wetlands in North America. Cattails are common autotrophs in wetlands, and provide shelter, as well as food, for many wetland animals. True watercress grows in cool water, generally in springs or brooks.
Four Freshwater Heterotrophs
Zooplankton can be single-celled organisms or larger animals. They feed on other forms of plankton as well as organic waste. The common carp is a freshwater fish that is a freshwater heterotroph. The great egret is a resident of wetlands around the world. Birds feast on the insects in freshwater biomes. Insects such as the damselfly thrive in freshwater biomes like ponds, streams and wetlands. They eat small fish in addition to other insect larvae and tadpoles.
Eight of Many
Countless other autotrophs and heterotrophs thrive in the world's freshwater systems. Many of the life forms, however, are threatened by the same dangers that threaten the water systems themselves -- pollution, development and incursion of human habitats into formerly wild places.