Aquatic Ecosystems

Aquatic Ecosystems The major kinds of aquatic environments are streams and rivers, lakes, wetlands, estuaries, and oceans. Each of these can be subdivided further with respect to many factors.

Aquatic Ecosystems In aquatic ecosystems, depth, water temperature, flow rate, and oxygen and nutrient concentrations are the dominant physical factor Many of the producers in many aquatic ecosystems are single-celled algae Aquatic ecosystems have been classified by salinity, water movement, and depth Unlike terrestrial ecosystems, defining aquatic ecosystems according to vegetation would be impossible.

Flowing Water: Streams and Rivers All aquatic ecosystems interact with the terrestrial biomes that surround them Streams receive runoff, groundwater, and organic matter from the surrounding land A variety of organisms live their lives in both aquatic and terrestrial environments

Flowing Water: Streams and Rivers Could you name some other interactions between aquatic ecosystems and terrestrial biomes? Frogs and salamanders, for example, have aquatic larval stages and terrestrial adult stages Some terrestrial animals feed on organisms that grow in streams and lakes Many organisms with aquatic larval stages, such as mosquitoes, feed on terrestrial organisms

Flowing Water: Streams and Rivers Stream and river systems are referred to as lotic systems Flowing water erodes Rivers and streams are created by erosion Most streams and rivers are older than lakes – although they move around more lotic systems-applied to flowing water systems

Flowing Water: Streams and Rivers Streams form wherever precipitation exceeds evaporation Streams grow with distance as they join together with rivers

Flowing Water: Streams and Rivers River continuum concept-ecosystems are more complex and more productive downstream because water flows more slowly and becomes warmer and richer in nutrients. The River Continuum Concept describes the physical processes (geology, climate) outside of a river that effect the biological processes (vegetation) along a river, which effect the physical and biological processes within a river (temperature, nutrients).

Flowing Water: Streams and Rivers Riffle areas are where water runs rapidly over a rocky substratum Water is well oxygenated in riffles

Flowing Water: Streams and Rivers Pools are deeper stretches of more slowly moving waters Pools tend to accumulate silt and organic matter

Flowing Water: Streams and Rivers Are these two areas productive or unproductive? Both areas tend to be unproductive because the nutrients needed for life are washed away in riffles, whereas the oxygen and sunlight needed for life are lacking in pools.

Flowing Water: Streams and Rivers Streams lack the richness and diversity of life Toward the headwaters of rivers, the productivity of algae and other photosynthetic organisms tend to be low Riparian zones are transitional areas between the aquatic system and adjacent land Riparian zones are influenced by seasonal flooding and elevated water tables

Flowing Water: Streams and Rivers Much of the food web of headwater ecosystems depends on leaves and other organic matter Organic material that enters the aquatic ecosystem the outside is termed allochthonous leaves and other organic matter fall or washes into streams from surrounding vegetation uh-lok-thuh-nuhs

Flowing Water: Streams and Rivers The larger the river , the more its organic material is autochtonous, originating where it is found

Flowing Water: Streams and Rivers As you move downstream, rivers become wider, slower moving, more nutrient laden, and more exposed to sunlight Nutrients and sunlight support growth of algae and plants

Flowing Water: Streams and Rivers Lotic systems are sensitive to any modification of their water flow Rates of flow, water temperature, and sediment patterns are all altered Could you name one major modification?

Flowing Water: Streams and Rivers Dams are built for flood control, to provide water for irrigation, or to generate electricity Water behind dams becomes warmer, and bottom habitats become choked with silt, destroying habitat for fish and other aquatic organisms Using dams for flood control changes the seasonal cycles of flooding Dams disrupt the natural movement of aquatic organisms

Standing Water: Lakes and Ponds Referred to as lentic systems, distinguished by non-flowing waters Range in size from small, temporary rainwater to lakes that are about a mile in depth Example: Lake Baikal, in Russia, contains about 1/5th of all the fresh water at the surface of the earth.

Standing Water: Lakes and Ponds Many lakes and ponds are formed by the retreat of glaciers Glaciers leave behind gouged-out basins and blocks of ice buried in glacial deposits Example: The Great Lakes of North America formed in glacial basins

Standing Water: Lakes and Ponds Lakes are also formed in geologically active regions Vertical shifting of blocks of the earth’s crust creates basins w/in water accumulates

Standing Water: Lakes and Ponds Oxbow lakes are broad bends of the former river cut off by shifts in the main channel

Standing Water: Lakes and Ponds Lakes are subdivided into several ecological zones, each of which has distinct physical conditions Littoral zone Limnetic zone Benthic Zone

Standing Water: Lakes and Ponds Littoral zone is the shallow zone around the edge of a lake or pond w/in which one finds rooted vegetation Limnetic zone is the open water where producers are floating single-celled algae, phytoplankton.

Standing Water: Lakes and Ponds The sediments at the bottoms of lakes and ponds make up the benthic zone The benthic zone provides habitat for burrowing animals and microorganisms

Standing Water: Lakes and Ponds Are lakes and ponds permanent? Most temporary ponds can dry out each year Most small temperate lakes that formed when glaciers retreated will gradually refill in w/ sediment until there is no open water What will happen to the former aquatic ecosystem? Small temporary ponds can dry out each year, often multiple times during a season Most small temperate lakes that when glaciers retreated will gradually fill in with sediment until there is no open water The formerly aquatic ecosystem will slowly change into a terrestrial ecosystem, first a wet meadow and later the natural terrestrial biome of the region

Wetlands Areas of land consisting of soil that is saturated w/ water and supports vegetation specifically adapted to such conditions

Wetlands What are some examples of wetlands? Swamps, marshes, and bogs Salt marshes and mangrove wetlands associated w/ marine envrionments

Wetlands Most of the plants can tolerate low oxygen concentrations in the soil. Many are specialized for anoxic conditions and grow nowhere else Wetlands provide important habitat for a wide variety of animals Wetlands protect coastal areas from the ravages of hurricanes and other storms Wetland sediments immobilize potentially toxic or polluting substances dissolved in water

Estuaries Estuaries are found at the mouths of rivers Are unique because of their mix of fresh and salt water Are abundantly supplied w/ nutrients and sediments carried downstream by rivers Estuaries tend to be areas of sediment deposition Supports high biological productivity

Marine Aquatic Systems Oceans cover the largest portion of the earth Variation in marine environments comes from differences in temperature, salinity, depth, currents, substrata, and tides What does depth influence? Depth influences light and pressure.

Marine Aquatic Systems The littoral zone (also called the intertidal zone) extends between the highest and lowest tidal water levels Exposed periodically to air Ecological conditions w/in the littoral zone change rapidly as the tide flows in or out

Marine Aquatic Systems The neritic zone extends to depths of about 200m, which correspond to the edge of the continental shelf Region of high productivity The sunlit surface layers of water are close enough to the nutrients in the sediments below that strong waves can move them to the surface

Marine Aquatic Systems The oceanic zone is beyond the neritic zone where the seafloor drops rapidly to great depths In the oceanic zone, nutrients are sparse and production is strictly limited The seafloor beneath the oceanic zone is the benthic zone.

Marine Aquatic Systems Both the neritic and oceanic zones are subdivided vertically into a photic zone In the photic zone, there is sufficient light for photosynthesis

Marine Aquatic Systems Organisms in the aphotic zone depend mostly on organic material raining down from above

Marine Aquatic Sytems What other ecosystem could be compared to the open ocean? What other ecosystem could be compared to the tropical rainforest?

Marine Aquatic Sytems Coral reefs are like tropical rainforests, both in the richness of their biological production and the diversity of their inhabitants Reef-building corals are found in shallow waters of warm oceans Coral reefs usually surround volcanic islands, where they are fed by nutrients eroding from the rich volcanic soil and by the deep water currents forced upward by the profile of the island

Marine Aquatic Sytems Coral reefs are doubly productive because photosynthetic algae w/in their tissues generate carbon energy that fuels the coral’s rates of growth