Freshwater Ecosystem Notes

Freshwater Ecosystems

Introduction

• Freshwater ecosystems comprise a variety of organisms that depend on the physico-chemical and biological characteristics of the freshwater environment.

• Two main categories:

  • Lentic: stagnant waters (lakes, ponds, swamps)

  • Lotic: flowing waters (streams, springs, rivers, brooks)

Importance of Freshwater

• Only 2.5% of the world's water is freshwater, and less than 1% is accessible.

• Freshwater is essential for all life on Earth and vital to human well-being.

• It supports energy, food, and health, which are indispensable for human development.

• Freshwater ecosystems provide crucial regulating services:

  • Water purification

  • Flood mitigation

  • Treatment of human and industrial wastes

• Freshwater is needed for:

  • Drinking water

  • Agriculture

  • Irrigation

  • Industry

  • Power generation

• 10% of the world’s animal species live exclusively in freshwater habitats.

Lentic Aquatic Systems

• Contain stagnant waters represented by lakes, ponds, and swamps.

Lake Formation Processes

• Earth movement

• Glaciation

• Volcanic activity

• Erosion

• Deposition

• Human biological activity

Zones of Lake Based on Light Penetration

• Trophogenic Zone:

  • The upper portion of the lake where photosynthesis occurs.

  • P > R (Production exceeds Respiration)

  • Also referred to as the Euphotic Zone.

• Tropholytic Zone:

  • Consumption of energy exceeds its production.

  • P < R (Production is less than Respiration)

  • Also referred to as the Profundal Zone.

• Compensation Level:

  • Where Photosynthesis equals Respiration.

  • $P = R$

  • Varies diurnally and seasonally with changes in light penetration.

Thermal Stratification

• Epilimnion:

  • Upper, warm layer.

  • Typically well mixed.

• Metalimnion:

  • Layer of water in which the temperature declines rapidly with depth.

• Hypolimnion:

  • Bottom layer of colder water.

• Temperature example:

  • Epilimnion: 22°C

  • Metalimnion: 5°C

  • Hypolimnion: 4°C

• Winter: High $O<em>2$ concentration at 0m depth, Medium $O</em>2$ concentration at 16m depth, Low $O_2$ concentration at 24m depth

• Autumn: High $O<em>2$ concentration at 0m depth, Medium $O</em>2$ concentration at 16m depth, Low $O_2$ concentration at 24m depth

• Spring: High $O<em>2$ concentration at 0m depth, Medium $O</em>2$ concentration at 16m depth, Low $O_2$ concentration at 24m depth

• Summer: High $O<em>2$ concentration at 0m depth, Medium $O</em>2$ concentration at 16m depth, Low $O_2$ concentration at 24m depth

Zones of Lake Based on Organisms

• Littoral Zone:

  • Home of rooted plants.

  • Greater variety of consumers than the other zones.

• Limnetic Zone:

  • Composed of plankton, nekton, and sometimes neuston.

• Profundal Zone:

  • Consists of bacteria and fungi.

  • Three groups of animal consumers:

    • Blood worms

    • Small clams

    • Phantom larvae

• Benthic Zone:

  • Most of the organisms are invertebrates.

Lake Types Based on Nutrient Levels

• Oligotrophic:

  • Nutrients are poor in supply.

  • Clear blue water.

• Mesotrophic:

  • Lakes of intermediate productivity.

• Eutrophic:

  • Nutrients are good in supply.

  • Shallow, murky water.

Lotic Aquatic Systems

• Contain flowing waters represented by streams, springs, rivers, and brooks.

• Continuous unidirectional flow.

• Volume of water keeps changing, which brings about changes in the velocity of water currents.

• Water acts as an effective agent (transfer, transport & dilution).

Zones of River

• Crenon:

  • Uppermost zone at the source of the river.

• Rhithron:

  • Upstream portion of the river that follows the crenon.

• Potamon:

  • Remaining downstream stretch of river.

Energy Sources

• Autochthonous:

  • Result of photosynthesis and the destruction of detritus.

• Allochthonous:

  • Stored in photosynthetically formed organic matter within the drainage basin or brought to the lake or stream in various forms.

Human Impacts on Freshwater

• Overexploitation of freshwater sources

• Pollution

• Agricultural Run-Off

• Climate Change

• Habitat destruction

• Introduction of invasive species

Government Policies/Programs

• Philippine Fisheries Code (Republic Act No. 8550, amended by RA 10654)

• The Clean Water Act (Republic Act No. 9275)

• The National Integrated Protected Areas System (NIPAS) Act (Republic Act No.7586)

• The Watershed Management Program

• The Manila Bay Rehabilitation Program