Lecture Notes: Freshwater Ecology

Introduction

• Previous Topics: Water cycle, aquatic environment classification (marine and freshwater), oceanography (marine), limnology and rheology (freshwater).
• Current Focus: Freshwater ecology fundamentals, types and origins of lakes, limiting factors in freshwater, stratification, and organisms in each stratification.

Freshwater Environment

• Statistics: Only 3% of the world’s water is fresh.
  • 99% of that is frozen in glaciers or aquifers.
  • Only 1% is in lakes, ponds, rivers, and streams.

Importance of Freshwater

1. Convenience and Cost: Essential for domestic and industrial use.
2. Hydrologic Cycle: Acts as a bottleneck in water transfer.
3. Waste Disposal: Provides a cost-effective system.

Study of Freshwater: Limnology

• Definition: Study of freshwater systems and processes (physical, chemical, biological).
• Areas Covered:
  • Lentic: Non-moving water like lakes.
  • Lotic: Moving water like rivers.
  • Estuaries: Transition between river and ocean environments.

Lentic vs. Lotic Environments

• Lentic (Lakes, Ponds, Swamps):

  • Succession: From lakes to ponds to swamps due to factors like sediment deposition, catastrophic events, and water loss.
  • Types: Lakes (large and static), Ponds (small and shallow), Swamps (support vegetation).

• Lotic (Running Water):

  • Succession: Rivulets to brooks to creeks to rivers.
  • Age and Base Level: Determines river age based on erosion and base level.

Stratification and Limiting Factors

• Thermal Stratification:
  • Layers: Epilimnion (warm), Thermocline (rapid temp change), Hypolimnion (cold).
  • Seasonal Turnover: Spring and fall mixing nutrients.
• Light Stratification:
  • Zones: Photic (supports photosynthesis) and Aphotic (supports respiration).

Types of Lakes

• Origins: Tectonic, Volcanic, Glacial, Landslide, Solution, Fluvial, Aeolian, Shoreline, Organic, Anthropogenic, Meteorite.

Freshwater Organisms Classification

• By Habitat: Literal, Limnetic, Benthos.
• By Locomotion: Nekton (swimming), Plankton (drifting), Neuston (surface-dwelling).
• Plankton Types: Phytoplankton (plants), Zooplankton (animals).
• Neuston: Surface film organisms, e.g., water striders.
• Benthos: Bottom dwellers, e.g., crabs, worms.

Plant Life in Freshwater

• Macrophytes: Large aquatic plants, crucial for ecosystem processes like oxygen production, habitat provision.
• Algae and Other Microphytes: Essential for nutrient cycling.

Tasks & Assignments

• Reflect on importance of freshwater, compare lake types, discuss succession causes, and classify organisms.
• Explore specific tasks related to understanding lake dynamics, organism classification, and environmental factors affecting freshwater ecosystems.