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Aquatic Ecosystems

This is a lecture on the basics of ocean and aquatic ecosystems.
by

Katherine LaCommare

on 26 March 2013

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Transcript of Aquatic Ecosystems

Lakes and temperature Metalimnion and Thermocline Nutrients Temperature impacts the amount of DO. Colder temperatures will generally have higher DO’s. Warmer temperatures will have lower DO levels. (Think boiling water!) Dissolved Oxygen (DO) Lake Structure Light
Temperature
Dissolved Oxygen
Nutrients (Nitrogen and Phosphorous)
Substrate Like terrestrial systems, aquatic ecosystems have biological and abiological components. This is a list of key abiotic factors. These are important because they often get altered by human actions. But some, like Lake Lansing in Haslett, are not. Garbage “patches” Oceans are threatened by several human activities. They are threatened by habitat destruction, water pollution, garbage "patches", ocean warming and ocean acidification. Threats to the ocean The main threats to the surface ocean are pollution and overfishing. We don't know enough about the deep ocean to know what might threaten it. Watch this video about the deep ocean. The open and deep ocean Substrate is another important abiotic factor of a lake ecosystem. The composition of matter at the bottom of a water body can affect fish spawning and turbidity (water clarity). Humans can impact substrate by adding sediment to our waterways. Substrate Nutrients (Eutrophication) This figure describes the differences between an oligotrophic - young nutrient poor lake and a eutrophic - older “well nourished” lake. Some of these systems are quite pristine. Objective: Describe freshwater ecosystems. Freshwater ecosystems include lakes, ponds, vernal ponds, rivers streams and wetlands. http://www.pmel.noaa.gov/co2/files/pteropodpics1_med.jpg http://www.pmel.noaa.gov/co2/files/pteropodpics1_med.jpg Ocean warming and acidification Coral Reefs Objective: Understand the basic features of our ocean ecosystems, explain why they are important and understand the threats facing them. Nutrients (eutrophication) An estuary is a partially enclosed body of water where fresh water from rivers and streams mixes with salt water from the ocean. Estuaries are areas of transition between the land and the sea. They are often called bays, harbors, inlets or sounds.

Estuaries are very productive ecosystems. They have a lot of primary productivity and therefore can sustain long food chains and a lot of secondary (herbivore and carnivore) biomass. Humans rely heavily on estuaries for the seafood that they produce. Estuaries and coastal wetlands Mangrove ecosystems are a treed, wetland ecosystem found along subtropical coastlines. This video states some important statistics about mangroves and discusses why they are so important.
Mangrove ecosystems are threatened by coastal development and habitat destruction. Mangrove ecosystems The Ocean Planet 71% of our planet is covered by oceans.
97% of the water on our planet is ocean water. The ocean has two main horizontal zones.
The coastal zone is heavily impacted by terrestrial influences. The open ocean is also called the pelagic zone. This is the vast area of open and deep ocean. The ocean is divided into many zones. Each with its own unique ecosystems. It has 3 main vertical zones. The top euphotic zone which is the zone where there is enough light for photosynthesis to occur. 40% of the world’s photosynthetic activity occurs in the euphotic zone of the ocean. The bathyal zone which has some light. It is not totally dark. And the abyssal zone which is completely dark. The abyssal zone is the least explored and most mysterious and certainly has some of the coolest organisms on the planet. Coral reefs are perhaps one of THE most important ocean ecosystems. Coral reefs are a rock-like ecosystem. The “rocky” structures are “built” by small, colonial and sessile animals that have calcium carbonate skeletons. Coral reefs are important because they create habitat for fish and therefore provide fish for people. Many coastal countries and communities rely on these fish as their major source of protein. They are tremendously diverse ecosystems and rival rainforests in the amount of diversity that they have. Barrier reefs can protect terrestrial communities from storms because they provide a break-water. Unfortunately, coral reefs are very threatened ecosystems. Overuse, overfishing and destructive fishing practices destroy reef habitats. Excessive CO2 in the atmosphere contributes to ocean warming and ocean acidification - both threats to coral communities. And, coral reefs are sensitive to ocean pollution. Ocean garbage patches are noteworthy phenomena. They were first discovered in 1997. They are giant rotating “patches” of plastic and other solid wastes in the middle of the ocean. The two most notable are in the North Pacific Ocean near Hawaii. The largest is twice the size of the state of Texas. There are four other patches in the world’s other oceans. 80 – 90% of the trash in these patches is plastic and it is hypothesized that roughly 80% of it is land-based trash. Most of the plastic has been broken down, over time, to very small pieces of plastic, about the size of a grain of rice. These pieces of plastic are so small that garbage patches are not actually visible from above the surface of the water. Ocean garbage patches are noteworthy phenomena. They were first discovered in 1997. They are giant rotating “patches” of plastic and other solid wastes in the middle of the ocean. The two most notable are in the North Pacific Ocean near Hawaii. The largest is twice the size of the state of Texas. There are four other patches in the world’s other oceans. Scientists are concerned that this trash threatens wildlife. It threatens wildlife in two ways. When organisms digest the plastic, it is not food and can make them sick and even kill them. If it doesn’t hurt them immediately, some of the chemicals in the plastic can be selectively absorbed by the organisms and bioaccumulate and biomagnify in the food chain. Ocean acidification means that animals that rely on carbonate to build their skeletons will have a harder time forming those shells. This view of the earth illustrates that the planet is mostly ocean. Freshwater Ecosystems But, looks can be deceiving. Even "pristine" aquatic system are heavily impacted by humans. Freshwater systems, especially lakes, also have zones. Like the ocean, these zones are distinguished by the influence of land, light and temperature. In temperate lakes, seasonal changes in temperature cause lake "turn-over". This process plays an important role in mixing oxygen and nutrients in the water. Dissolved oxygen (DO) is the amount of oxygen (O2) dissolved Water Dissolved oxygen (DO) is one characteristic that makes water usable or unusable to aquatic organisms. Fish use oxygen that enters the water through mixing at the surface – through turbulence, diffusion or as an output of photosynthesis. Water bodies that flow quickly and are cooler in temperature, like headwater streams, contain more dissolved oxygen than slow, warm stagnant bodies of water. The aquatic community is often dictated by the DO level, because different critters have different tolerances. Some, like trout, are very sensitive to low DO levels, and will be replaced by more tolerant organisms like catfish which can exist where the DO level is low. Generally, a DO of < 2 ppm is too low. A pond, on the other hand, would be considered eutrophic. The water would be warm, have a lot of nutrients, a lot of phytoplankton and the water would not be very clear This mountain lake, which is fed primarily by glaciers, would be considered oligotrophic. The water would be very clear, cold and have very little nutrients. Just like for soil, nutrients are present in aquatic systems too. Nitrogen and phosphorous are two important nutrients.

Water systems can be described as nutrient “poor” – oligotrophic – or nutrient “rich” – eutrophic based on the amount of nutrients present. Oligotrophic and eutrophic are relative terms. Lake Superior is the most oligotrophic Great Lake. Lake Erie is the most eutrophic. As water bodies age, they become eutrophic. This process – of lake succession – is known as eutrophication. It is the process by which water bodies receive nutrients that stimulate plant growth and slowly change the system from one that is considered nutrient poor to one that is nutrient rich. Nutrients start on land as leaf-litter, animal waste and other organic matter. When water runs over the land it picks up pieces of these solids and their nutrients. Eutrophication is a natural process, but, there is a more insidious form: cultural eutrophication. Cultural eutrophication is human induced. We’ll talk more about this in our pollution lecture. Rooted aquatic plants. Phytoplankton The Littoral zone is heavily influenced by land processes. The Limnetic Zone is equivalent to open water of the ocean. It is the water near the surface where light readily penetrates. It is often warmer than the rest of the water column. The benthic area is the bottom of the lake. Just like the ocean, lakes have a thermocline. This is a narrow depth range in which the temperature changes quickly. On this graph, temperature is on the top axis and depth is the vertical axis. The temperature drops from near 24 degrees to 4 degrees over a 5oo m range. Follow this figure by starting in June. In June, the lake is highly stratified. The top is warm; the bottom is cold. Because of the thermocline, there is no mixing. This means that oxygen does not mix, that phytoplankton does not mix and nutrients don't mix. As you move into the fall, the temperature of the lake evens out. The thermocline is lost and the lake mixes from top to bottom. In the spring, the lake will mix again. This process mixes oxygen and nutrients into the whole water column which is healthy for the ecosystem. http://video.nationalgeographic.com/video/environment/habitats-environment/habitats-oceans-env/coral-reefs/
Follow this link to a video about coral reefs:
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