Aquatic ecosystems make up the majority of planet Earth. But there are many types of aquatic ecosystems, each with its own physical environment and threats from human impacts.
Lakes and Ponds
Lakes and ponds are aquatic ecosystems with standing bodies of water. They can range in size from less than a square acre to covering thousands of square kilometers. Light, temperature and oxygen vary in lakes depending on their location, size and depth. For example, temperate lakes only have a seasonal thermocline, while tropical lowland lakes have a thermocline year round. Human impacts have caused algae blooms, oxygen depletion, and fish kills in lakes where they have produced runoff from fertilized land, as well as dumping wastes and pollution into the lakes.
A wetland is an aquatic ecosystem that is covered in water at least part of the time during the year. Plants that live in wetlands have to be adapted to living in a constant water-saturated soil. Some wetlands are covered in water at all times, while others are seasonal. Both types of wetlands are used by migratory birds, reduce flooding, and help purify water for drinking. But draining and filling for farmland have destroyed up to 90 percent of the wetlands in the United States.
Streams and Rivers
The well-known characteristic of streams and rivers is the current. Headwater streams are usually cold and turbulent, while downstream is usually calm and warmer. Rivers usually occur when several streams join. Damming of streams and rivers had led to problems for this aquatic ecosystem. Damming and agricultural use of water has led many rivers to dry up before they even reach the ocean. Others carry pollutants to the ocean and create dead zones.
Estuaries are the changeover area between the river and ocean. Seawater can flow into this aquatic ecosystem, which allows many species to reproduce in these waters. In fact, many species spend their entire lives in this brackish water. Majority of crabs and shrimp humans consume come from estuaries. Unfortunately, pollution that has been carried from upstream converges into this ecosystem and has resulted in destroying the water quality worldwide.
Oceans have many different aquatic ecosystems within it. They include Intertidal, Ocean Pelagic, coral reefs, and Marin Benthic zones. Coral Reefs are largely calcium carbonate skeletons of corals. Corals reefs are located in shallow seas. Intertidal zones are high in oxygen and nutrient levels and are renewed with each tide. Oceanic Pelagic Zone is the vast sea of open blue water. The Marine Benthic Zone consists of the sea floor below oceanic pelagic zones, which receives no sunlight. Overfishing and pollution are the main human impacts for the ocean. Many ocean fish stocks are being so overfished that they are on the brink of collapse.