shallow lakes part 2 Flashcards
(15 cards)
What are Alternative Stable States (ASS) in shallow lakes?
Alternative Stable States refer to different possible ecosystem conditions (states) that can persist in a system, such as a lake. For example, a lake can alternate between a clear water, macrophyte-dominated state and a turbid, phytoplankton-dominated state.
How does climate warming relate to alternative stable states in ecosystems?
Gradual climate changes may have little effect until a threshold is crossed, after which ecosystems can shift rapidly into a new, stable state, often altering the ecosystem’s structure and function.
What factors may trigger a regime shift in a shallow lake ecosystem?
Crossing a critical nutrient threshold (e.g., phosphorus levels)
Loss of macrophyte biomass
Increased disturbance (e.g., climate warming, eutrophication)
What happens when macrophyte biomass is lost in shallow lakes?
Habitat shifts
Reduced biodiversity
Decreased water quality
Changes in the physical, chemical, and biological composition of the lake
What is the pristine state of shallow lakes?
Pristine shallow lakes are characterized by clear water and abundant aquatic vegetation (macrophytes). This state is often maintained by feedback mechanisms within the ecosystem.
How do feedback mechanisms contribute to the stability of shallow lakes?
Positive feedback mechanisms can help maintain an ecosystem in a given state. For example, in a clear-water state, macrophytes stabilize sediments and reduce nutrient availability for phytoplankton, reinforcing the clear-water condition.
What is the ecosystem behavior of shallow lakes far from a threshold?
Low variability
High recovery rate
This means that the ecosystem can recover quickly from disturbances and remains relatively stable.
What happens to shallow lakes as they approach a threshold?
High variability
Low recovery rate
Disturbances begin to accumulate, making it harder for the system to return to its original state.
What did Bayley and Prather (2003) discover in their study of shallow lakes in Alberta?
62% of the 148 shallow lakes sampled showed alternative stable states.
Four categories were identified:
High phytoplankton (turbid)
High submerged aquatic vegetation (SAV, clear)
Both high SAV and high phytoplankton
Low SAV and phytoplankton
What factors determine whether a shallow lake is clear or turbid?
Nutrient concentrations, especially phosphorus
Zooplankton populations
Macrophyte biomass
Fish populations
Climatic controls on water depth
What is a trophic cascade, and how can it affect shallow lakes?
A trophic cascade occurs when predators reduce the abundance or alter the behavior of prey, which then releases the next lower trophic level from predation. This can lead to changes in nutrient cycling and primary production, which can shift the ecosystem between states (e.g., from clear water to turbid).
What are the possible states of shallow lakes according to Bayley and Prather’s research?
Turbid (high phytoplankton)
Clear (high submerged aquatic vegetation)
Mixed (high phytoplankton and high SAV)
Low (both low SAV and low phytoplankton)
How do nutrient concentrations, particularly phosphorus, affect shallow lake states?
Phosphorus is a key factor determining whether a shallow lake remains clear or becomes turbid. High phosphorus levels often lead to phytoplankton dominance and a turbid state, while low phosphorus levels promote macrophyte growth and clear water.
What role do zooplankton populations play in maintaining shallow lake stability?
Zooplankton help control phytoplankton populations by grazing on them. If zooplankton are absent or reduced, phytoplankton can proliferate, leading to a shift towards a turbid state.
What happens when fish populations are present in shallow lakes?
Fish populations can disturb the sediment, affect zooplankton populations, and alter macrophyte growth. Fish can also contribute to shifts in the ecosystem, either promoting a turbid state or maintaining a vegetated state, depending on their species and abundance.
