Freshwater biomes include lakes and ponds (stagnant water) and rivers and streams (flowing water). These include wetlands, which will be discussed later.
LAKE AND PONDS
Lakes and ponds are part of terrestrial landscapes and are therefore associated with abiotic and biotic factors affecting these terrestrial biomes. Lakes and ponds can vary in size from a few square meters to thousands of square kilometers. Temperature is an important abiotic factor affecting life in lakes and ponds. Thermal stratification of lakes and ponds occurs in the summer when the upper layer of water is heated by the sun and does not mix with deeper, colder water. Light can enter the photic zone of the lake or pond.
Zooplankton (very small animals that swim in water) such as rotifers and small crustaceans consume this phytoplankton. At the bottom of lakes and ponds, bacteria in the aphotic zone destroy dead organisms that sink to the bottom. Nitrogen and phosphorus are major limiting nutrients in lakes and ponds. Because of this, are determinants of phytoplankton growth.
With large amounts of nitrogen and phosphorus (eg., from effluents and runoff from meadows and manure farms ), algal growth increases, resulting in a large accumulation of algae known as aquatic algal blooms. As a result, the lake or pond becomes aphotic and the photosynthetic plants rooted at the bottom of the lake cannot survive. As the algae die and decompose, the water becomes severely oxygen-depleted, animals die and the death zones are formed.
RIVERS AND STREAMS
Rivers and streams are constantly moving bodies of water that carry large volumes of water from their source or headwaters to a lake or ocean. The largest rivers include the Nile in Africa, the Amazon in South America, and the Mississippi in North America.
The abiotic properties of rivers and streams vary throughout the river or stream. Streams start at a point of origin called a water source. The channel (the width of the river or creek) is narrower than anywhere else along the river or creek. Because of this, the current here is usually faster than anywhere else in the river or stream.
Fast-moving water causes minimal accumulation of silt at the bottom of the river or stream, leaving the water clear. Photosynthesis here is mainly attributed to algae growing on the rocks; The fast current inhibits the growth of phytoplankton.
An additional energy boost could come from leaves or other organic matter falling into the river or streams from trees and other plants bordering the water.
Plants and animals have adapted to this fast-flowing water. For example, leeches (Phylum Annelida) have elongated bodies and suckers on each end. These suction cups will attach to the substrate and hold the leech in place. Freshwater trout species are a major predator in these fast-flowing rivers and streams.
As the river or stream moves away from its source, the width of the channel gradually widens and the flow decreases. This slow-moving water, caused by the decreasing slope and increasing volume as the tributaries flow together, exhibits more sedimentation. Phytoplankton can remain suspended, therefore the water will not be as clear as near the spring. The water is also warmer. Worms (Phylum Annelida) and insects (Phylum Arthropoda) hide in the mud. Higher-order predatory vertebrates (phylum Chordata) include waterfowl, frogs, and the fish.
Wetlands differ from lakes because wetlands are shallow bodies of water that can periodically dry up. Emerging vegetation consists of wetland plants that are rooted in the soil but they have portions of leaves, stems and flowers that extend above the water surface.