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BIOL215 Lecture 23 Notes.pdf

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Biology (Sci)
BIOL 215
Neil Price

BIOL215 Lecture 23 Notes Primary production in aquatic systems cannot harvest like terrestrial production - not effective here. 14 Have to use C method Photosynthesis confined to the upper layers of the lake or ocean Light decays exponentially as it penetrates into any body of water Photosynthesis is roughly proportional to light; greater rate of photosynthesis at higher depths Sometimes photosynthesis is weaker at the surface of water (ocean). This is known as photo-inhibition where light levels are too strong and actually inhibitory Difference between Clear Lake and lake Tahoe (very few coloured matter) is that rate of photosynthesis can penetrate deeper if less coloured matter is absorbing the light If we were to measure the relative amount of light that penetrated to the depth were photosynthesis is almost zero, it corresponds to about 1% of the light at the surface; 1% light depth. Below that depth, there is too little light to allow photosynthesis to occur Light is obviously important in affecting photosynthesis in the sea but it is NOT the primary limiting factor for photosynthesis in lakes and oceans Resources seem to be strongly depleted across most of the world's oceans. Two important resources, phosphate and nitrate vary as a function of depth. It seems that phosphate and nitrate are in very small concentration up to the 1% light level where it increases after that. However, this low concentration results in limited resources to phytoplankton to survive and thrive Although there is a high reservoir of resources in the deep sea, it cannot get to the surface very easily because of the density difference between the light surface layer and the deep bottom layers There seems to be some recent change in the NPP occurring in the ocean. This is due to an increase in ocean temperature. As temperature increase, organisms grow faster and metabolize more and have more NPP, but this increase in temperature will add to increase this density surface between the light surface layer to the deep bottom layer, thus creating a larger gap between resources and so, over the years, NPP anomaly has shown to decrease since 1999's average In much of the ocean, nitrogen is the primary limiting nutrient for phytoplankton primary production - although there have been surprisingly few experimental tests of this hypothesis Phosphorus is rarely the limiting nutrient in the open ocean while nitrogen is the primary limiting nutrient Silica can be a limiting nutrient particularly where diatoms are present because diatoms use silica to form their exoskeleton The addition of additional supplies of nitrogen or iron will increase the NPP production Unlike most other elements in the sea, iron doesn't come from the deep waters but actually comes in the form of dust from deserts into the ocean In lakes, phosphorous becomes a very important resource typically from human usage of dishwashing detergents. However, recent environmental studies show that such phosphates have proven harmful to our natural habitats. Phosphates promote the grown of algae and various aquatic weeds in bodies of water Based on lake 227 and other experiments, the suggestion is that productivity is regulated by phosphorous in freshwater ecosystem Lakes that receive lots of P from the surrounding landscape contain lots of phytoplankton At very high phosphorous concentrations, you not only see "Green-soup" lakes, but the level of phosphorous influences the types of phytoplankton that grows When nitrogen is scarce and phosphorous is high, blue-green algae are competitively superior Blue-green algae are superior in acquiring nitrogen because they are able to use nitrogen gas (nitrogen fixation) to obtain nitrogen for growth. They are only type for primar
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