Freshwater biology

Freshwater habitats support a wide variety of organisms with habitats including rivers, streams, lakes, ponds, and wetlands. Rivers and streams Running water is a type of freshwater habitat that mainly consists of rivers and streams. Running, fast-moving waters have a higher oxygen content, allowing different species to thrive and making pollution easier to combat. The characteristics of the streams and rivers change throughout their journey from the source to the mouth. For example, the water at the source is clearer, has a higher oxygen content, lower temperatures, and heterotrophs common species. In the middle, the width usually expands and the species diversity increases due to temperature and oxygen content changes, including aquatic green plants and algae. The water at the mouth has a lower oxygen concentration and is murkier due to the sediment that has been collected and traveled along the length of the river or stream. This increased sediment decreases the amount of light that is able to penetrate the water and there is less diversity of flora and the lower oxygen lowers the diversity of fauna. Stratification does not occur in running water because of the fast moving water that mixes water with varying oxygen content together. The topmost layer has the most oxygen and as depth increases, the oxygen decreases. Standing water can be divided into three zones based on depth and distance from shore. The littoral zone is the uppermost layer and the warmest water found in lakes and ponds, as the sun directly heats is. Carolina Bays are characterized as elliptical shaped depressions that are surrounded by a sand rim and have a sandy bottom. This depression goes through wet and dry periods, filling with rainwater during the winter and spring months, and drying out in the summer. Carolina Bays often contain rare species, some endemic to the bays. == Freshwater organisms ==

Freshwater organisms are generally divided into the categories of benthic and pelagic organisms, as these are the two zones of life found in the freshwater biome. Freshwater organism can include invertebrates, insects, fish, amphibians, mammals, birds, aquatic plants, aquatic fungi and planktons. Freshwater invertebrates provide an important link in freshwater food chains, transporting the nutrients and energy from producers such as algae and aquatic plants to higher consumers such as fish and amphibians. Around half of fish species live in freshwater environments, the other half living in saltwater. Some fish, such as salmon and some species of shark, are able to travel between the freshwater and saltwater environments, linking the two. Amphibians Amphibians, which include frogs, toads, salamanders, and caecilians, are a group that predominately exist in freshwater habitats. Amphibians are exotherms that possess thing skin, meaning that they rely on water to remain hydrated. Amphibians are Amphibians can act as an indicator of environmental health, as they are easily affected by changes in the environment, such as pollution or climate change. Birds that rely on freshwater habitats include birds such as kingfishers, flamingos, and various types of waterfowl. Many species rely on the plants in these freshwater environments for nesting material, habitat, and food. Additionally, freshwater birds act as a control for fish and insects in freshwater environments. Emergent macrophytes have stalks and leaves that rise above the water surface, while floating-leaved macrophytes are anchored in the lakebed with leaves that rest on the surface. Free-floating macrophytes drift freely on the water, and submerged macrophytes grow completely beneath the surface. Freshwater Fungi Freshwater fungi are fungi that spend their whole, or at least one part of their life cycle in water. Fungi are diverse in freshwater, including fungi from almost all phyla of Fungi, encompassing 3,870 described species (per 2022). They parttake in these ecosystems as decomposers, lichens, parasites, mutualists and more. Ascomycetes are dominating the biodiversity with around 3,000 species, with the majority being sordariomycetes. Chytrids are mostly known from aquatic systems, and encompass 333 described species, where most of these are parasites of planktonic algae. Most freshwater fungi are microscopic, but are important drivers of nutrient cycling and in food webs. == Threats ==

The most common cause of water pollution is stormwater runoff from developed areas, like pavement and rooftops. Stormwater runoff is moving rain and snowmelt that has not been absorbed. As human populations increase and industrialize, the demand for groundwater is increasing, but the pollution of groundwater is also increasing. The pollution of groundwater is easy to achieve due to the slow circulation of water, even slower than that of lakes and ponds. The water must navigate through small holes in the aquifer rock, moving on average only a couple of inches each day. The rate of groundwater recharge is the time it takes for groundwater to replenish itself and extremely slow, leading to water shortages, as humans remove water from aquifers faster than the rate of recharge. Due to such slow circulation of water, groundwater can remain polluted for decades, as the natural purification processes are so slow. ==See also==