Lecture 7 Flashcards
1
Q
Winter stratification
A
- Densest water sinks to the bottom
- This will usually be the warmest, shielded by the ice surface
2
Q
Spring stratification
A
- Top layers warms, the wind can fully mix the water (Spring circulation)
3
Q
Summer stratification
A
- The surface becomes so warm and dense that the wind can’t fully mix the water
4
Q
Autumn stratifcation
A
- The surface layer cools down, the difference in layer density decreases and the wind is ale to fully mix the lake (Autumn circulation)
5
Q
Dimictic lakes
A
Alternating peroiods of stratification and circulation
6
Q
Ecological succession
A
- How a community of organisms changes over time
7
Q
Algae and Zooplankton ecological succession
A
- Winter - low light and cold temp limits growth. Zooplankton overwinters
- Spring - Higher light and temp lead to algal growth, zooplankton wakes up and feast
- Summer - Zooplankton over-grazing leading to overall population crash
- Autumn - Algal and zooplankton rebound
- Onset of winter - Algal and Zooplankton decline
8
Q
Overwintering strategies
A
Copepods - diapouse
Cladocerans - resting eggs in sediment
Rotifers - resting eggs
9
Q
Algal species ecological succession
A
- Initially, edible, small and fast growing algae
- Post clear water, late summer when nutrients get trapped in hypolimnen. Algae become P-limited and replaced by low p-tolerant pennate diatoms
- Pennate diatoms get Si limited and replaced by canobacteria (which gets N limited)
- REplaced by N-fixing cyanobacteria
- Eukaryotes return as light and productivtiy declines
10
Q
Copepod strategies for low algal food
A
Lipid storage
Adults become carnivores and eat smaller cladocearns
11
Q
Zooplankton community
A
- Initially, small cladoceans, too cold for rotifers. Copepods increasing
- Replaced by larger cladoceans which drive algal crash
- With algal crash, large cladoceans die off. The rest wait it out
- With algal regrowth, mixed and diverse community feast on cyanobacteria
12
Q
Plankton Ecology Group (PEG)
A
- Developed for temperate lakes
- Modes successions
- Omits microbial loop - which bacterias peak during clear water phase
13
Q
PEG fails
A
- Fais in humic lakes - food web largely driven by microbial loop
- Fails in tropical lakes - high food and temp all year round. some lakes mix daily
14
Q
PEG Oligiotrophic lake model
A
Slower dynamics lead to only one zooplankton peak and smaller algae peaks
15
Q
Deep chlorophyll maxima
A
- Balance for light and nutrients
