Aquatic Ecosystem
Environment
Aquatic Ecosystem
An aquatic ecosystem is an ecosystem where the main habitat is water. The major differences between various aquatic zones arise due to:
- Salinity
- Levels of dissolved nutrients
- Water temperature
- Depth of sunlight penetration
Types of Aquatic Ecosystem
Freshwater Ecosystem
- Salt content is less than 5 ppt.
- Two types:
- Lentic (static water): pond, lake, bogs, swamps
- Lotic (running water): springs, streams, rivers, mountain brooks
Brackish Water Ecosystem
- Salt concentration between 5 to 35 ppt.
- Includes estuaries, salt marshes, mangrove swamps.
- Estuaries: where river water meets sea water, mixed by tides; highly productive.
Marine Ecosystem
- Salt concentration 35 ppt or more.
- Includes shallow seas and open oceans.
Aquatic Organisms (Based on Zone of Occurrence)
Neuston
- Live at air–water interface.
- Examples: floating plants, water striders, beetles.
Periphyton
- Attached to stems/leaves of rooted plants or other substrates.
- Includes sessile algae and small animals.
Plankton
- Microscopic plants (phytoplankton) and animals (zooplankton).
- Found in all aquatic ecosystems except fast-moving streams.
Nekton
- Strong swimmers; can overcome currents.
- Example: fish.
Benthos
- Organisms living at the bottom of the water body.
- Example: sea grass communities.
Corals
- Corals are living animals with symbiotic algae (zooxanthellae).
- Corals get their colour from algae.
- Two types: hard corals (reef-builders) and soft corals.
- Found mainly in shallow tropical waters.
- Types of reefs: fringing, barrier, patch, atoll.
Factors Affecting Aquatic Productivity
Temperature
- Water temperature changes slowly due to high specific heat.
- Aquatic species have narrow tolerance ranges.
Sunlight
- Determines plant distribution.
- Zones:
- Photic zone: light penetrates; supports photosynthesis.
- Aphotic zone: insufficient light; only respiration occurs.
Dissolved Oxygen (DO)
- Enters water through air–water interface and photosynthesis.
- Used up by respiration of organisms and decomposition.
Transparency
- Affected by silt, clay, phytoplankton.
- Determines light penetration and photosynthesis.
Lake Ecosystem
Zones
- Littoral zone (shallow edges)
- Open-water zone (deep water)
- Benthic zone (lake floor)
Classification Based on Salinity
- Freshwater lakes
- Brackish lakes
- Saline lakes
Classification Based on Nutrients
- Oligotrophic (low nutrients)
- Mesotrophic (moderate)
- Eutrophic (high nutrients)
Eutrophication
- Natural eutrophication: slow nutrient enrichment over time.
- Cultural eutrophication: accelerated by human activities (fertilizers, sewage).
- Leads to algal blooms.
Algal Blooms
- Rapid growth of algae due to excess nutrients.
- Some algae produce toxins harmful to fish, birds, mammals, humans.
Estuarine Ecosystem
- Formed where river meets sea.
- Ecotone between freshwater and marine systems.
- Highly productive; act as natural filters.
- Examples: tidal marshes, lagoons, deltas.
Formation of Estuaries
- Rising sea levels
- Sand movement and sandbar formation
- Glacial and tectonic processes
Mangroves
- Found on tropical/subtropical coasts.
- Adapted to saline conditions.
- Protect coasts from cyclones and tsunamis.
Key Features
-
Pneumatophores for respiration
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Vivipary (seeds germinate on tree)
-
Abundant along eastern India (Ganga, Mahanadi, Godavari, Krishna, Cauvery deltas)
Wetland Ecosystem
- Swamps, marshes, mangroves.
- Periodically inundated areas supporting aquatic flora/fauna.
- Nutrient-rich and highly productive.
Functions of Wetlands
- Habitat for diverse species
- Filtration of sediments
- Nutrient recycling
- Water purification
- Flood control
- Groundwater recharge
- Shoreline protection
Adaptations in Aquatic Organisms
- Floating plants/animals: lightweight bodies
- Osmoregulation: tolerance to varying salt levels
- Streamlined bodies for swimming
- Deep-sea organisms show bioluminescence
- Dependence on upper sea zones for food
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Subject: Environment
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