The most diverse ecosystem, where life originated and the first organisms were found. Water is essential for all living beings.
Distribution of Water:
- Oceans contain more than 95% of Earth’s water.
- Freshwater resources are mainly found in rivers (0.00015%) and lakes (0.01%).
- Total Water on Earth: Approximately 71% of the Earth’s surface is covered by water.
- Saltwater: The vast majority of Earth’s water, about 96.5%, is saltwater found in oceans and seas.
- Freshwater: Only 2.5% of Earth’s water is freshwater.
- Freshwater Distribution: Glaciers and Ice Caps: 69% of freshwater is locked up in glaciers and ice caps, making it inaccessible for immediate use.
- Groundwater: 30% of freshwater exists underground.
- Surface Water: Less than 1% of freshwater is found in lakes, rivers, and swamps.
- Usable Freshwater: Only about 1% of the total water on Earth is readily available for human, plant, and animal life.
Types of Aquatic Ecosystems:
- Freshwater ecosystems: Low salt concentration (< 500 mg/L), include rivers, streams, ponds, lakes, swamps, and marshes.
- Saltwater ecosystems: High salt concentration (average 3.5% or 35 ppt), include oceans and bays.
Aquatic Biodiversity: A rich variety of plants and animals, from algae to large fish, including zooplankton, small fish, aquatic insects, and amphibians.
Study of Freshwater Habitats: Limnology.
Types of Freshwater Habitats:
- Lentic: Still waters (lakes, ponds) with longer water residence time (average 10 years) and slower flow velocity (0.001 to 0.01 m/s).
- Lotic: Running waters (rivers, streams) with shorter water residence time (average 2 weeks) and faster flow velocity (0.1 to 1 m/s).
Key Differences:
- Lentic: Thermal stratification (epilimnion, thermocline, hypolimnion) due to density differences.
- Lotic: Characterized by stream orders and patterns influencing flooding and soil erosion.
Catchment Area: The land and water area contributing runoff to a common point (lake or stream). Also called drainage basin or watershed.
Lentic Ecosystems (Still Waters)
Bodies of standing water like lakes, ponds, swamps, and marshes.
Zones
- Littoral Zone: Shallow, near-shore area with abundant light and rooted plants. High biodiversity, including algae, macrophytes, insects, amphibians, and small fish.
- Limnetic Zone: Open water area where light penetrates. Dominated by phytoplankton and zooplankton. Habitat for fish that feed on plankton.
- Profundal Zone: Deep water area with low light and no plants. Inhabited by decomposers and some fish adapted to low oxygen levels.
Characteristics:
- Water Residence Time: Long (average 10 years).
- Flow Velocity: Low (0.001 to 0.01 m/s).
- Thermal Stratification: Present due to density differences caused by temperature variations.
- Epilimnion: Upper, warm, well-mixed layer.
- Thermocline: Also known as Metalimnion. Zone of rapid temperature change, acting as a barrier between layers.
- Hypolimnion: Lower, cold, less oxygenated layer.
- Water Movement: Primarily influenced by wind and temperature. Multi-directional.
- Suspended Solids: Autochthonous (from within the lake, like algae) and allochthonous (from outside, like leaves).
- Light: Penetration depth depends on turbidity, influencing plant growth and primary productivity.
- Dissolved Gases: Oxygen levels vary with depth and productivity. Bottom sediments can be anoxic.
- Dissolved Solids: Influenced by catchment area and biological activity.
Lotic Ecosystems (Flowing Waters)
Moving water bodies like rivers, streams, and springs.
Zones:
- Riffles: Shallow, fast-flowing areas with rocky substrate. High oxygen content. Inhabited by algae, invertebrates, and fish adapted to strong currents.
- Pools: Deeper, slower-moving areas with finer sediment. Lower oxygen levels. Habitat for diverse fish and invertebrates.
Characteristics:
- Water Residence Time: Short (average 2 weeks).
- Flow Velocity: High (0.1 to 1 m/s).
- Stream Order: Classification based on origin and flow, influencing characteristics and biodiversity.
- Stream Patterns: Dendritic, radial, etc., determining soil erosion and flooding risks.
- Currents: Influenced by gradient and substrate, not wind.
- Suspended Solids: Mainly from erosion and litter input.
- Light: Penetration affected by turbidity.
- Temperature: Follows air temperature, influenced by origin, depth, substrate, and tributaries.
- Dissolved Gases: High oxygen due to turbulence. Low oxygen indicates pollution.
- Dissolved Solids: Vary from source to mouth, influenced by geology, climate, and rainfall.
Biodiversity
- Lentic: High biodiversity due to varied habitats. Supports a wide range of plants, invertebrates, fish, and other animals.
- Lotic: Lower biodiversity compared to lentic, but unique species adapted to flowing water thrive. Benthic organisms abundant.
