Oxygen is essential for cellular respiration in most organisms. In an aquatic environment, oxygen availability is influenced by a variety of chemical and physical factors. Some of the factors that affect the amount of oxygen dissolved in water are: •
Temperature: As water becomes warmer, its ability to hold oxygen decreases. •
Photosynthetic activity: In bright light, aquatic plants are able to produce more oxygen. •
Decomposition activity: As organic material decays, microbial processes consume oxygen. •
Mixing and turbulence: Wave action, waterfalls, and rapids all aerate water and increase the oxygen concentration. •
Salinity: As water becomes more salty, its ability to hold oxygen decreases. 1. Which environment has the greater concentration of dissolved oxygen: salt water or fresh water? Your answer: Fresh water
Fresh water can hold more oxygen than salt water.
2. Which environment has the greater concentration of dissolved oxygen: warm water (31°C) or cool water (18°C)? Your answer: cool water
Cool water can hold more dissolved oxygen than warm water. Now you know why the fish died in a hot aquarium. 3. Which environment has the greater concentration of dissolved oxygen: a clear pond or a pond with a heavy algal mat? Explain. Your answer: a
Clear water holds more dissolved oxygen than water with a heavy algal mat. Although photosynthesis in the algal mat will produce a great deal of oxygen, the decay of so much organic matter will result in a net depletion of oxygen.
Primary productivity is a term used to describe the rate at which plants and other photosynthetic organisms produce organic compounds in an ecosystem. There are two aspects of primary productivity: •
Gross productivity = the entire photosynthetic production of organic compounds in an ecosystem. •
Net productivity = the organic materials that remain after photosynthetic organisms in the ecosystem have used some of these compounds for their cellular energy...
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