eco 12

Aquatic Ecosystems Overview

  • Aquatic ecosystems are the last set of biomes covered in this lecture.

  • Three David Attenborough Living Planet videos available for deeper insights:

    • Sweet Freshwaters

    • Intertidal Environments and Estuaries

    • Open Ocean and Pelagic Ecosystems

  • Importance of watching these videos emphasized for broader understanding of biomes.

Types of Aquatic Ecosystems

  • Aquatic ecosystems comprise both fully aquatic and fully terrestrial systems.

  • Wetlands support standing water for part of the year with submerged roots supporting diverse vegetation.

    • Classified based on dominant vegetation, similar to terrestrial biomes.

Types of Wetlands

  • Swamps

    • Characterized by woody plants and shrubs, typically in regions like the Orinoco Delta in southern U.S.

    • Large emergent trees with roots adapted to prolonged submersion.

  • Marshes

    • Dominated by reeds, rushes, and grasses.

    • Associated with estuaries where fresh water meets the sea; sediments are deposited in still environments.

  • Bogs

    • Contain large amounts of sphagnum mosses.

    • Located at the nexus between taiga and tundra in the Northern Hemisphere.

    • High peat content, which is undecomposed sphagnum moss.

  • Fens

    • Found in Europe and parts of the U.S.; often human-made.

    • Dominated by sedges and rushes and developed to supply water to agricultural land.

  • Mangroves

    • Studied by Dr. Anushka Rajkuran; found in tropical estuarine systems.

    • Replace marshes in tropical regions.

Functions and Benefits of Wetlands

  • Wetlands provide critical ecological services:

    • Water purification: trap sediments and decompose toxic wastes from agricultural runoff.

    • Wetlands are increasingly used for water quality remediation in sewage treatment.

    • Flood risk reduction: act as reservoirs that buffer against flooding during high tides and storm surges.

    • Biodiversity: rich in a variety of animal life across all trophic levels.

Coverage of Aquatic Ecosystems

  • Aquatic ecosystems cover 71% of the Earth's surface, including marine and freshwater environments.

  • Classification of aquatic ecosystems into three basic types:

    1. Freshwater

    2. Marine

    3. Brackish Water

Freshwater Ecosystems

  • Freshwater environments have very low salt concentrations.

  • Comprising lakes, ponds, rivers, and streams:

    • Represent only 1% of Earth's water, with only 0.3% available on the surface.

Classification of Lakes

  • Oligotrophic Lakes:

    • Nutrient-poor, deep, clear water, often cold, commonly found in mountainous areas.

  • Eutrophic Lakes:

    • Nutrient-rich, shallower, murkier water due to high phytoplankton growth, often warmer found at lower elevations.

  • Mesotrophic Lakes:

    • Transition between oligotrophic and eutrophic conditions.

Seasonal Dynamics of Lakes

  • Lakes exhibit seasonal changes leading to stratification:

    • Epilimnion: Warm upper layer due to sun exposure.

    • Thermocline: Rapid temperature change layer.

    • Hypolimnion: Cold, dense bottom layer.

  • Seasonal mixing:

    • Wind-driven mixing occurs in autumn and spring, while winter often leads to ice cover.

Zonation in Lakes

  • Littoral Zone: Shallow, light-available area supporting rooted vegetation.

  • Limnetic Zone: Upper part of open water where light penetrates, including:

    • Pelagic Zone: surface waters.

    • Profundal Zone: deeper, dark area where photosynthesis cannot occur.

  • Benthos: bottom substrate layer, varying from hard (rocks) to soft (mud).

Streams and Rivers

  • Rivers and streams are continuously flowing bodies of water, originating in higher elevations (headwaters) and emptying into larger bodies (mouth).

  • Characteristics change along the river's course:

    • Headwaters: Clear, fast-moving, rocky substrate, oxygen-rich, low in nutrients.

    • Downstream: Slower, sediment-rich, murky, wide rivers with high nutrient content, supporting diverse plant and animal life.

Interaction of Freshwater and Seawater

  • Estuaries: Defined as partially enclosed bodies of water where freshwater meets seawater, subject to salinity fluctuations due to tides.

    • Highly productive ecosystems with abundant nutrients, supporting various life forms.

Types of Estuaries

  • Salt Wedge Estuary: High flow of freshwater over denser seawater; saltwater underlies freshwater.

  • Partially Mixed Estuary: Moderate freshwater input with significant seawater mixing.

  • Well Mixed Estuary: Low freshwater input, achieving a gradient of salinity from fresh to saline.

  • Fjord Estuary: Characterized by trapped seawater with limited freshwater inputs.

Biodiversity in Estuaries

  • Estuaries are critical nurseries for marine fish, with many species depending on these environments at different life stages.

  • High diversity of salt marsh grasses, algae, phytoplankton, mangroves (in tropics).

  • Organisms may include:

    • Burrowing worms, annelids, crabs, and various fish species.

    • Waterfowl use estuaries as feeding and breeding grounds.

  • Adaptations required to cope with fluctuating salinity, causing osmotic stresses on organisms.

Importance of Estuaries

  • Constant nutrient and sediment input from rivers enhances productivity.

  • Examples include the life cycles of shrimp and certain fish, emphasizing their reliance on estuaries for growth and reproduction.