Study Notes for Midterm Review on Aquatic Ecosystems and Biogeochemistry

Light and Aquatic Ecosystems

  • Definitions:

    • "Photo" means light.

    • "A" means without.

  • Zones in Aquatic Ecosystems:

    1. Photic Zone:

    • Definition: The upper layer of a body of water that receives enough sunlight for photosynthesis.

    • Importance: Supports the growth of phytoplankton and other photosynthetic organisms.

    1. Aphotic Zone:

    • Definition: The layer of water that is too deep for sunlight to penetrate.

    • Importance: No photosynthesis occurs; organisms rely on other forms of energy.

  • Processes Performed by Phytoplankton:

    • Photosynthesis: They convert light energy into chemical energy, producing oxygen and organic material that forms the base of the aquatic food web.

Salinity and Aquatic Ecosystems

  • Impact of Rainfall on Salinity:

    • Rain, being freshwater, decreases the salinity levels when it enters aquatic systems.

  • Effects of Evaporation and Precipitation Rates on Salinity:

    1. Faster Evaporation than Precipitation:

    • Result: Salinity levels would rise as water evaporates and leaves behind dissolved salts.

    1. Faster Precipitation than Evaporation:

    • Result: Salinity levels would decrease as freshwater influx dilutes the salt concentration.

pH and Aquatic Ecosystems

  • pH Scale Overview:

    • Scale: Ranges from 0 to 14.

    • Acidic: pH < 7

    • Neutral: pH = 7

    • Alkaline: pH > 7

    • Acid Rain's Impact:

    • Acid Rain can lower the pH of aquatic habitats, affecting organisms that thrive in a specific pH range.

    • Question: Would acid rain increase or decrease the pH?

      • Answer: Decrease the pH.

The Water Cycle

  • Key Processes in the Water Cycle:

    1. Evaporation: Water changes from liquid to vapor.

    2. Condensation: Water vapor cools and forms droplets, leading to cloud formation.

    3. Evapotranspiration: The combined process of evaporation from the land and transpiration from plants.

    4. Water Storage:

    • In atmospheric bodies and groundwater.

Biogeochemical Cycles

  • Definition of Biogeochemical Cycles:

    • Natural processes that recycle nutrients in various chemical forms from the environment to organisms and then back to the environment.

  • Main Biogeochemical Cycles:

    1. Carbon Cycle:

    • Involves the movement of carbon between the atmosphere, land, oceans, and living things.

    1. Nitrogen Cycle:

    • Describes the processes by which nitrogen and its compounds are interconverted in the environment and in living organisms.

    1. Water Cycle:

    • Describes the continuous movement of water on, above, and below the surface of the Earth.

  • Purpose of Biogeochemical Cycles:

    • To maintain the balance of matter on Earth. Consistent movement of matter rather than energy, which decreases as it moves up the food chain.

    • Conclusion: Matter remains constant in an ecosystem, ensuring stability while energy levels diminish as they are transferred from one organism to another.

Evaluating Biogeochemical Cycles

  • Exercises on Matter and Energy in Ecosystems:

  1. As energy moves through an ecosystem, the amount of energy Decreases.

  2. Three Examples of Biogeochemical Cycles:

    • 1. Carbon Cycle

    • 2. Nitrogen Cycle

    • 3. Water Cycle