Water Resources

Water should be valued, understood, and cared for as a vital Earth resource.
Exists within Earth's subsystems: hydrosphere, geosphere, atmosphere, and biosphere, interconnected through the hydrologic cycle.

Contains Earth's oceans, lakes, streams, underground water, and ice.
The hydrologic cycle describes water movement across Earth's surface and subsystems.

Hydrogeology: Studies groundwater distribution, availability, and flow within aquifers.

Oceans hold 97.5% of Earth's water.
Freshwater accounts for only 2.5%, with breakdown:
- Glaciers: 68.7%
- Groundwater: 30.1%
- Permafrost: 0.8%

Cover 71% of Earth's surface.
Oceans are divided geographically into five regions and multiple seas, gulfs, bays, and straits.
- Recognized Oceans: Atlantic, Pacific, Indian, Arctic, and Southern Oceans (added by the International Hydrographic Organization in 2000).
Salinity: Defined by the concentration of sodium and chlorine ions.
Oceans have three main zones:
- Surface Layer: Warm, low-density water (up to 100m deep) housing most marine life.
- Thermocline: Rapid temperature decreases with depth, up to 1500m at high latitudes.
- Deep Zone: Cold, covering 80% of the ocean’s water.

Surface currents: Driven by air movement; clockwise in the Northern Hemisphere, counterclockwise in the Southern Hemisphere.
Thermohaline circulation: Driven by temperature and salinity differences.

Glaciers are permanent ice bodies, while ice sheets are expansive masses (over 50,000 km²).
- Freshwater content: 24 million km³, 90% in Antarctica.
- Remaining glaciers are in Greenland, North America, and Scandinavia.

A soil, rock, or sediment frozen for over two consecutive years, spanning from a few meters to 150 meters deep.
- Contains 300,000 km³ of freshwater (0.8% of Earth's total freshwater).

Streams, lakes, wetlands: Collect water from rainfall, melting snow, and groundwater flow.
- Account for 0.3% of Earth's total water resources.

Streams: Moving body of surface water that flows downslope toward sea level, with clearly-defined passageways called channels.
Tributaries - smaller streams
- Key components include drainage basins (the area collecting water), drainage divides, and interfluves (landforms between streams).
- Surface runoff: Water movement downhill during heavy rain (overland flow) or within stream channels (stream flow).

Rivers: Large streams, make up 1.6% of surface water, with an estimated total volume of 2120 km³.

Lakes: Large inland water bodies (fresh or saline), with ponds as smaller, shallow lakes.
- Represent 67% of the total surface water.
Wetlands: Areas where water covers the land for significant periods.
- Types:
  - Marshes: Shallow wetlands near lakes and oceans (e.g., Candaba Wetland in Pampanga).
  - Swamps: Wetlands with lush trees and vegetation in low-lying areas beside slow-moving rivers.
  - Estuaries: Coastal water bodies where freshwater meets saltwater (e.g., Pampanga River in Manila Bay).
- Functions:
  - Trap pollutants and water, replenish groundwater, slow stream flow to reduce flooding and erosion, and harbor biodiversity.

Freshwater found in the rock and soil layers beneath the surface
30.1% of Earth's freshwater is stored in groundwater.
Porosity: The capacity of aquifers to hold water, higher in sand and gravel. Low porosity in basalt and diorite
Permeability: The ability of water to pass through; high in sandstone, limestone, and highly fractured rocks. Low permeability in clay and mud

Zone of Aeration or Unsaturated Zone: Layer beneath the surface in which spaces between particles are filled mainly with air.
Zone of Saturation: Spaces filled with water, below the aeration zone.
Water Table: The boundary between the aeration and saturation zones.
Capillary Fringe: Layer directly above water table

Unconfined aquifers: Water freely rises to its natural level.
Confined aquifers: Water is trapped under pressure between impermeable rocks (aquicludes).