River VL 10

Question 1

What’s the name of the world’s largest, oldest and most biotically diverse lake?

Answer 1

Lake Baikal which holds 20% of earth’s liquid fresh water.

Question 2

Describe the seasonal plankton dynamics in lake Baikal. What is special about it?

Answer 2

Lake Baikal’s plankton dynamics is an inter-annual coupled two year cycle
* Phytoplankton(winter) [P(w)] decline due to competitor phytoplankton(summer) [P(s)].
* P(w) population collapses and P(s) population rises
* Consumers (e.g. zooplankton) put P(s) under a top-down pressure between day 200-400 (start of 2. Winter).
* Second peak of P(w) (in second year) is suppressed by the still high density of the Consumers which nourished from P(s).

Lake Baikal - boreal deep stratifying dimictic lake

Question 3

Why was lake Stechlin thermally polluted?

Answer 3

Lake Stechlin was part of the cooling cycle of a nuclear power plant.
* 10°C warmer than average surface water temperature at the entrance.
* average surface water temperature increased by 1°C.
* lake water residence time was shortened to less than 300 days (naturally >40 years)

Lake Stechlin - temperate deep stratfying dimictic lake

Question 4

Rank the biodiversity of meromictic, monomictic, dimictic and polymictic lakes:

Answer 4

1) Polymictic Lakes: (often shallow structure)
* Highest biodiversity due to frequent mixing, which ensures consistent nutrient availability and diverse habitats.

2) Dimictic Lakes: (deeper lakes)
* High biodiversity with seasonal mixing, providing a variety of thermal and nutrient conditions throughout the year.

3) Monomictic Lakes:
* Moderate biodiversity, with a single mixing period each year that still supports nutrient distribution but less frequently than polymictic or dimictic lakes.

4) Meromictic Lakes:
* Lowest biodiversity, as permanent stratification limits nutrient circulation and creates stable but less diverse habitats.