Lakes: standing bodies of water range from ponds a few square meters in area to lakes covering thousands of square kilometers. Temperature lakes may have a seasonal thermocline; tropical lowland lakes have a thermocline year-round. Salinity, oxygen concentration, and nutrient content differ greatly among lakes and can vary with season. Wetlands: habitat that is inundates by water at least some of the time and that supports plants adapted to water-saturated soil.
Some wetlands are inundated at all times, whereas others flood infrequently. Wetlands are home to a diverse community of invertebrates, which in turn support a wide variety of birds. Wetlands are among the most productive biomes on Earth. Their water-saturated soils favor the growth of plants such as floating pond lilies and emergent cattails, many sedges, tamarack, and black spruce, which have adaptations enabling them to grow in water or in soil that is periodically anaerobic owing to the presence of unaerated water.
Streams and Rivers: The most prominent physical characteristic of streams and rivers is their current. Headwater streams are generally cold, clear, turbulent, and swift. Streams and rivers are stratified into vertical zones. The salt and nutrient content of streams and rivers increases from the headwaters to the mouth. Damming and flood control impair the natural functioning of stream and river ecosystems and threaten migratory species such as salmon. Estuaries: is a transition area between river and sea.
Seawater flows up the estuary channel during a rising tide and flows back down during the falling tide. Salinity varies spatially within estuaries, from nearly that of fresh water to that of seawater. Estuarine flow patterns combined with the sediments carried by river and tidal waters create a complex network. Intertidal zones: periodically submerged and exposed by the tides, twice daily on most marine shores. Upper zones experience longer exposures to air and greater variations in temperature and salinity.
Oxygen and nutrient levels are generally high and are renewed with each turn of the tides. Oceanic Pelagic Zone: a vast realm of open blue water; constantly mixed by wind-driven oceanic currents. Because of higher water clarity, the photic zone extends to greater depths than in coastal marine waters. The most abundant heterotrophy in this biome are zooplankton. This zone also includes free-swimming animals, such as large squids, fishes, sea turtles, and marine mammals. Coral Reefs: are formed largely from the calcium carbonate skeletons of corals.
Shallow-reef-building corals live in the photic zone of relatively stable tropical marine environments with high water clarity. Marine Benthic Zone: consists of the seafloor below the surface waters of the coastal, or neritic, zone and the offshore, pelagic zone. Except for shallow, near-coastal areas, the marine benthic zone receives no sunlight. oxygen is present at sufficient concentrations to support a diversity of animals. Photosynthetic organisms, mainly seaweeds and filamentous algae, are limited to shallow benthic areas with sufficient light to support them.