Types of Aquatic Ecosystems

Aquatic ecosystems can be divided into two general types: marine ecosystems and freshwater ecosystems.

Marine Ecosystems

Marine ecosystems cover approximately 71 % of the Earth’s surface and contain approximately 97 % of the planet’s water. They generate 32 % of the world’s net primary production. They are distinguished from freshwater ecosystems by the presence of dissolved compounds, especially salts, in the water. Approximately 85 % of the dissolved materials in seawater are sodium and chlorine. Seawater has an average salinity of 35 parts per thousand (ppt) of water. Actual salinity varies among different marine ecosystems.

Marine ecosystems can be divided into the following zones: oceanic (the relatively shallow part of the ocean that lies over the continental shelf); profundal (bottom or deep water); benthic (bottom substrates); intertidal (the area between high and low tides); estuaries; salt marshes; coral reefs; and hydrothermal vents (where chemosynthetic sulphur bacteria form the food base).

Classes of organisms found in marine ecosystems include brown algae, dinoflagellates, corals, cephalopods, echinoderms, and sharks. Fish caught In marine ecosystems are the biggest source of commercial foods obtained limn wild populations.

Environmental problems concerning marine ecosystems include unsustainable exploitation of marine resources (for example overfishing of certain species), water pollution, and building on coastal areas.

Freshwater Ecosystems

Freshwater ecosystems cover 0, 8 % of the Earth’s surface and contain 0,009 % of its total water. They generate nearly 3 % of its net primary production. Freshwater ecosystems contain 41 % of the world’s known fish species.

There are three basic types of freshwater ecosystems:

· Lentic: slow-moving water, including pools, ponds, and lakes.

· Lotic: rapidly-moving water, for example streams and rivers.

· Wetlands: areas where the soil is saturated or inundated for at least part of the time.

Lake ecosystems can be divided into zones: pelagic (open offshore waters);

profundal; littoral (nearshore shallow waters); and riparian (where the lake meets the sea). Two important subclasses of lakes are ponds, which typically are small lakes that intergrade with wetlands, and reservoirs. Many lakes, or bays within them, gradually become enriched by nutrients and fill in with organic sediments, a process called eutrophication. Eutrophication is accelerated by human activity within the catchment area of the lake.

The major zones in river ecosystems are determined by the river bed’s gradient

or by the velocity of the current. Faster moving turbulent water typically contains greater concentrations of dissolved oxygen, which supports greater biodiversity than the slow moving water of pools. The food base of streams within riparian forests is mostly derived from the trees, but wider streams and those that lack a canopy derive the majority of their food base from algae. Anadromous fish are also an important source of nutrients. Environmental threats to rivers include loss of water, dams, chemical pollution and introduced species.

Wetlands are dominated by vascular plants that have adapted to saturated soil. Wetlands are the most productive natural ecosystems because of the proximity of water and soil. Due to their productivity, wetlands are often converted into dry land with dikes and drains and used for agricultural purposes. Their closeness to lakes and rivers means that they are often developed for human settlement.

Wetlands are the interface between dry or terrestrial habitats and aquatic environments including streams, lakes and seas. Around the Great Lakes they take four basic forms. Swamps are a cross between forest and aquatic ecosystems, inhabited by woody species: conifers, hardwoods or shrubs. Bogs are characterized by acidic, peaty soils with little water movement and feature flora such as blueberries, orchids and carnivorous plants. Fens are similar to bogs, but with more water movement their soils are less acidic. The domi­nant plants are sedges and low shrubs.

Wetlands are important because they act as natural sponges, absorbing water so it moves more slowly through the system. This prevents flooding and shoreline erosion. In the 19th Century people thought that anything obstructing rivers would increase flooding, so they frequently removed islands and wetlands to let water mere more readily through urban areas. Such practices actually increased the problem.

More recently some cities have begun to let wetlands regenerate. Wetland construction is commonly a part of housing developments, though often at the expense of more complex pre-existing natural habitats.

Wetlands are also well-designed to filter out pollution, particularly nitro­gen and phosphorous. They are also useful for removing heavy metals. Indus­tries are experimenting with constructing wetlands for this purpose.

Meanwhile wetlands exceed other temperate habitats in that they produce as much oxygen, per area, as tropical rainforest.

Besides, wetlands provide a natural nursery for many species of native plants and wildlife. More than 40 species of birds nest in Point Pelee’s marsh and 66 species of dragonflies and damselflies breed there. These habitats also pro­vide a major food source for humans and animals. They also offer recreation in the form of canoeing, birdwatching and fishing.

Raid Ecosystem

This is a specific type of freshwater ecosystem that is largely based on the autotrophic algae which provide the base trophic level for all life in the area. The largest predator in a pond ecosystem will normally be a fish and in-between range smaller insects and microorganisms. It may have a scale of organisms from small bacteria to big creatures like water snakes, beetles, water bugs, and turtles.