Notes on Aquatic Ecosystems

Aquatic Ecosystems Overview

  • Aquatic Environments: Defined primarily by depth and water movement rather than temperature or moisture.
    • They are categorized into freshwater (lakes, ponds, rivers) and marine (oceans, seas) environments.

Key Concepts

  • Factors Influencing Aquatic Systems:

    • Water depth, salinity, nutrient availability, light penetration.

  • Types of Life Zones:

    • Saltwater and freshwater life zones.

  • Human Activities Impacting Aquatic Systems:

    • Pollution, damming rivers, overfishing, climate change.

Saltwater Life Zones

  • Open Ocean: Vast water body, low productivity.
  • Coastal Zone: Rich in nutrients, includes shipping channels and beaches.
  • Intertidal Zones: Areas between high and low tide; rich in nutrients and biodiversity.
  • Estuaries: Where freshwater meets saltwater; highly productive.
  • Coral Reefs: Biodiverse and productive ecosystems found in warm, shallow waters.
  • Mangroves: Salt-tolerant trees found along coastlines that provide critical habitat.

Coral Reefs

  • Formed in shallow areas of the tropics, overall productivity is very high.
  • Corals host symbiotic algae, enhancing nutrient cycling.
  • Threatened by climate change, acidification, and overfishing.

Freshwater Life Zones

  • Types of Water Bodies:
    • Standing Water (Lentic): Includes lakes and ponds.
    • Flowing Water (Lotic): Streams and rivers.

Types of Lakes

Oligotrophic Lakes
  • Characterized by low nutrient levels, clear water, and steep shorelines.
  • Sparse vegetation and low fish populations.
Eutrophic Lakes
  • Rich in nutrients, high productivity, and dense fish populations.
  • Typically characterized by warm, shallow waters that support abundant plant life.

Zones in Lakes and Ponds

  • Littoral Zone: Area near the shore, shallow, with rooted vegetation.
  • Limnetic Zone: Open water, dominated by phytoplankton.
  • Profundal Zone: Deep water where sunlight does not penetrate, with low oxygen levels.
  • Benthic Zone: Bottom sediments, habitat for many organisms.

Water Layer Dynamics

  • Epilimnion: Warm, upper layer of water; well-oxygenated.
  • Hypolimnion: Cooler, deeper layer; often anoxic.
  • Thermocline: Transition layer with rapid temperature changes.

Circulation Patterns in Lakes

  • Seasonal temperature changes cause water density changes, leading to mixing events known as overturns in spring and fall.
  • Stratification: Warmer surface water floats on cooler, denser layers underneath.

Freshwater Wetlands

  • Defined as areas that are either permanently or seasonally flooded.
  • Types:
    • Swamps: Trees found in periodically flooded areas.
    • Marshes: Dominated by herbaceous plants.
    • Bogs: Acidic waters, specialized flora.
    • Fens: Alkaline settings, rich plant diversity.

River Ecosystems

  • River Continuum Concept: Describes how biological communities change along river gradients from headwaters to large rivers.
    • Changes in shredder and collector species are notable.

Impact of Dams

  • Dams disrupt natural river flow, impacting habitats, water temperature, and oxygen levels; can lead to increased mercury in aquatic life due to bioaccumulation.