shallow lakes part 1 Flashcards
(14 cards)
What is special about shallow lakes as lentic ecosystems?
Numerically dominant (often temporary)
High biodiversity, especially in wetland and littoral habitats
Humans depend on these systems for agriculture, industry, water storage, and recreation
Generally stable, though stability can be variable
What is the definition of a shallow lake?
A shallow lake (or pond) is a permanent standing body of water where light penetrates to the sediments. Often, macrophytes cover the entire basin.
Where are shallow lakes commonly found?
In lowland areas, especially glaciated regions and floodplains
Formed by glacial activity, permafrost actions, river erosion, or wind
Many have been created by humans for agriculture, industry, water storage, and recreation
What are some key characteristics of shallow lakes?
High nutrient loading (especially in lowlands)
Nutrient recycling occurs quickly, regulating light and production
Macrophytes and periphyton dominate, leading to high biodiversity, especially when nitrogen-to-phosphorus ratio (N
) > 10:1
No hypolimnion, often polymictic (mixes frequently)
What factors influence macrophyte (aquatic plant) growth in shallow lakes?
Colonization is variable
Turbidity and light attenuation are important
Shifts between macrophyte and phytoplankton dominance can occur
What are the different macrophyte growth forms?
Floating unattached
Floating attached (less than 2-3 meters)
Submerged
Emergent (less than 1 meter)
What is the pristine state of shallow lakes, and why is restoration challenging?
Pristine shallow lakes have clear water and abundant macrophytes.
Nutrient loading has altered many systems, making restoration difficult due to changes in nutrient cycling and ecosystem dynamics.
How do habitat size and isolation affect biodiversity in shallow lakes?
Richness increases with lake size
Fish-poor, vegetated lakes have higher biodiversity than fish-dominated, unvegetated lakes of the same size
Vegetated states are more common in smaller lakes, and their occurrence decreases with lake size
How do macroinvertebrates and fish interact with macrophytes in the littoral zones?
Macroinvertebrates, like Daphnia sp., graze on phytoplankton and filter water
These invertebrates are prey for fish
Dense macrophyte growth provides habitat for both grazers and epiphytes (organisms living on plants)
What factors control macrophyte dominance in shallow lakes?
Reduced wave action or currents, leading to increased sedimentation
Uptake of phosphorus and nitrogen by macrophytes
Zooplankton refugia
Large surface area for epiphytes
High metabolism of macrophyte habitat and decaying organic matter (can restrict fish by decreasing dissolved oxygen and pH)
What factors control phytoplankton dominance in shallow lakes?
Less zooplankton grazing due to lack of refugia
Sediment suspension reduces light and disturbs substrate
Strong competition by algae and cyanobacteria
High nutrient levels and dense phytoplankton tend to persist once established
What other mechanisms can control shallow lake dynamics?
Fish introductions that disturb sediments
Winterkill of piscivorous fish species (increasing pressure on zooplankton)
Herbivory by waterfowl and muskrats
Human interventions like herbicide application, mechanical cutting, and biomass removal
What are “Alternative Stable States” in shallow lakes?
These are states in which the ecosystem can exist in multiple stable conditions, such as a fish-dominated, turbid state or a macrophyte-dominated, clear water state.
Understanding these states is important to avoid irreversible shifts.
What is “hysteresis” in the context of shallow lake ecosystems?
Hysteresis refers to the phenomenon where it takes more effort (or “work”) to return an ecosystem to its original state after a disturbance than it took to cause the initial disturbance.
