Lecture 10

Question 1

What role does light play in aquatic ecosystems?

Answer 1

Light serves as the primary energy source for photosynthesis.

Question 2

What does Lambert-Beer’s law describe?

Answer 2

The attenuation of light intensity with depth.

Question 3

What factors affect light extinction?

Answer 3

Water clarity

Phytoplankton density

Turbidity

Question 4

How is turbidity measured?

Answer 4

Using Secchi disk depth, where higher turbidity corresponds to a shallower depth at which the disk disappears.

Question 5

What is photosynthetically active radiation (PAR)?

Answer 5

Light in the wavelength range of 400-700 nm used for photosynthesis.

Question 6

What defines the euphotic zone?

Answer 6

The depth where PAR reaches 1% of surface light.

Question 7

How do stratified water layers affect light penetration?

Answer 7

Surface layers may allow more light penetration, while deeper layers with higher turbidity reduce light further.

Question 8

What are the primary limiting factors for photosynthesis in aquatic systems?

Answer 8

Light, inorganic carbon, water, temperature, and nutrients (N, P, Fe, Si).

Question 9

What does the photosynthesis equation describe?

Answer 9

6 CO₂ + 6 H₂O + light → C₆H₁₂O₆ + 6 O₂. It outlines the conversion of carbon dioxide and water into glucose and oxygen using light energy.

Question 10

How do light conditions affect photosynthesis efficiency?

Answer 10

Algae adapted to low light perform better in dark conditions but are less efficient in high-light environments.

Question 11

What is PAR and its role in photosynthesis?

Answer 11

Photosynthetically Active Radiation (400-700 nm) is the light spectrum usable by plants and algae for photosynthesis.

Question 12

What does the light adaptation parameter (Ik) indicate?

Answer 12

It indicates the light intensity needed to reach maximum photosynthetic rate (Pmax). A large Ik means high irradiance is needed; a small Ik means lower light is sufficient.

Question 13

How does temperature influence algal growth?

Answer 13

Growth rate increases up to an optimal temperature (Topt) and decreases steeply beyond it.

Question 14

What is the significance of sedimentation in algal models?

Answer 14

Sedimentation represents a mortality term, as algae that sink below the euphotic zone cannot photosynthesize and die.

Question 15

How does respiration respond to changes in temperature?

Answer 15

Respiration increases with temperature until Topt, after which it declines rapidly.

Question 16

How does nitrogen cycle through aquatic systems?

Answer 16

Nitrogen cycles between its inorganic forms (NH₄⁺, NO₂⁻, NO₃⁻) through processes like assimilation, ammonification, nitrification, and denitrification.

Question 17

Why is NH₄⁺ preferred by phytoplankton over NO₃⁻?

Answer 17

Ammonium (NH₄⁺) is more bioavailable and requires less energy for uptake compared to nitrate (NO₃⁻).

Question 18

What is ammonification?

Answer 18

The process by which bacteria decompose organic nitrogen into ammonia (NH₃) or ammonium (NH₄⁺).

Question 19

What is nitrification, and why does it require oxygen?

Answer 19

Nitrification is the oxidation of NH₄⁺ to NO₂⁻ and then to NO₃⁻ by bacteria (e.g., Nitrosomonas and Nitrobacter). It requires oxygen as an electron acceptor.

Question 20

What conditions favor denitrification?

Answer 20

Anoxic conditions (absence of oxygen) favor denitrification, where NO₃⁻ is reduced to N₂ gas.

Question 21

How does pH affect ammonia volatilization?

Answer 21

High pH levels shift the equilibrium towards gaseous ammonia (NH₃), increasing its volatilization from water.

Question 22

What are biogeochemical nitrogen cycles’ roles in ecosystems?

Answer 22

They regulate the availability of bioavailable nitrogen, which is crucial for primary production and ecosystem health.

Question 23

How does human activity affect nitrogen cycling?

Answer 23

Activities like agriculture and wastewater discharge increase nitrogen loads, contributing to eutrophication.