Aquatics

1. Aquatics Freshwater Ecosystems LAKES AND PONDS

2. What is an Ecosystem • An ecosystem is a complex set of relationships among the living resources, habitats, and residents of an area. • It includes plants, animals, microorganisms, water, soil, and people. • Everything that lives in an ecosystem is dependent on the other species and elements that are also part of that ecological community. • If one part of an ecosystem is damaged or disappears, it has an impact on everything else.

3. Freshwater Ecosystems • Only 3% of the Earth’s water is fresh. • 99% of this is either frozen in glaciers and pack ice or is buried in aquifers (an aquifer is an underground bed or layer of permeable rock, sediment, or soil that yields water). • The remainder is found in lakes, ponds, rivers, streams, and wetlands.

4. Freshwater Ecosystems • Freshwater contains little to no dissolved salt. • The plant and animal life depends on the depth of the water, how fast the water moves, the amount of nutrients, sunlight, and oxygen available. • There are two general terms that categorize freshwater ecosystems, lentic and lotic. Lentic: Refers to standing bodies of water (lakes, ponds, and inland wetlands). Lotic: Refers to flowing systems (streams and rivers).

5. Lakes • Lakes are large, natural bodies of standing water formed when precipitation runoff or groundwater seepage fills depressions in the Earth’s surface. • Deep lakes contain 4 distinct zones, each with its characteristic community of organisms. • The 4 zones are: • Littoral Zone • Limnetic Zone • Profundal Zone • Benthic Zone

6. Littoral Zone • The zone close to shore. • Light reaches all the way to the bottom. • The producers are plants rooted to the bottom and algae attached to the plants and to any other solid substrate. • The consumers include: • Tiny crustaceans • Flatworms • Insect larvae • Snails • Frogs, fish, and turtles

7. Limnetic Zone • The layer of open water where photosynthesis can occur. • Located away from shore • Surrounded by the littoral zone and above the profundal zone.

8. Net Primary Production • As one descends deeper in the limnetic zone, the amount of light decreases until a depth is reached where the rate of photosynthesis becomes equal to the rate of respiration. At this level, net primary production no longer occurs. • Net Primary Production: the rate at which a plant or an ecosystem produces new plant biomass by growth and reproduction. NPP is equal to gross primary production minus respiration • Biomass: plant materials and animal waste used as fuel

9. Organisms in Limnetic Zone • Producers: • Plankton • Consumers: • Microscopic Crustaceans • Nekton • Nekton refers to the aggregate of actively swimming aquatic organisms in a body of water (usually oceans or lakes) able to move independently of water currents.

10. Profundal Zone • Many lakes (but few ponds) are so deep that not enough light reaches here to support net primary productivity. • This zone depends on the drifting down of organic matter from the littoral and limnetic zones. • The profundal zone is chiefly inhabited by primary consumers that are either attached to or crawl along the sediments at the bottom of the lake. • The sediments underlying the profundal zone also support a large population of bacteria and fungi. These decomposers break down the organic matter reaching them, releasing inorganic nutrients for recycling.

11. Benthic Zone • The benthic zone is the very bottom of the lake. • Organisms living in this zone are called benthos. • Organisms here tend to tolerate cooler temperatures well. • For the profundal and benthic zones, low levels of photosynthesis result in low levels of dissolved oxygen. • Benthic organisms can be divided into two categories based on whether they make their home on the ocean floor or an inch or two into the ocean floor. • Those living on the surface of the ocean floor are known as epifauna.Those who live burrowed into the ocean floor are known as infauna.