earth science

• Hydrosphere


  One of the Earth's subsystems that constitutes all the available water supply present on Earth, in all its forms

  
• The hydrosphere exists in the other subsystems independently, it comprises at least 75% of the Earth's surface

  
• Water budget


  The finite amount of water on the Earth, slowly added by volcanic eruptions and meteors from space, that has lasted for billions of years

  
• Residence time


  The average length of time spent by a water molecule in a reservoir. Generally, water molecules in larger reservoirs have longer residence time

  
• Reservoir types and water forms

  • Saltwater reservoir
  • Freshwater reservoir
• Saltwater reservoir


  Saltwater constitutes at least 97% of the total water supply on Earth. Because of its saltiness, it must be distilled and refined before it can be used for consumption
• Ocean


  • A very large body of saltwater that surrounds the entire land
  • The total volume of the world's oceans is approximately 1.35 × 10^9 km^3
  • The Earth contains five (5)—or four (4), depending on the reference material—oceans
• Salinity


  The measure of a saltwater's saltiness. Ocean water has a varied salinity between 33 and 37 ppm (parts per million), mostly from sodium chloride (NaCl) existing as both sodium and chloride ions
• Major ocean zones / saltwater profile

  • Surface layer/zone
  • Thermocline
  • Deep zone

  
• Surface current/circulation


  Movement of saltwater caused by surface air currents, depending on the hemisphere, on the surface zone, creating slow, broad drifts confined at depths of 50–100 m

  
• Thermohaline/ deep currents circulation/current


  Movement of water in the deep zone caused by the active processes within the zone caused by differences in density, which are controlled by both temperature and salinity

  
• Freshwater reservoir


  Most of the freshwater (a form of water that is not saline) on Earth are stored in glaciers and ice sheets in regions mostly inaccessible by man. The ones that are usable and potable are found on shallow surfaces and underground

  
• Glacier


  • A permanent body of solidified water (i.e., ice) primarily composed of recrystallized snow compacted together. Glaciers form on land, and they are made up of fallen snow that gets compressed into ice over many centuries. They move slowly downward from the pull of gravity. Most of the world's glaciers exist in the polar regions, in areas like Greenland, the Canadian Arctic, and Antarctica
• Ice sheet


  • Mass glacial ice covering more than 50,000 km^2 in total land area, commonly seen in Greenland and Antarctica. Ice sheets contain about 99% of the fresh water on Earth, and are sometimes called continental glaciers
• Permafrost


  • Any part of the lithosphere and/or the pedosphere that has been frozen for more than two (2) years. Mostly found in polar regions, permafrost can be as deep as 150 m and has amassed storage of at least 300,000 km^3 worth of freshwater

  
• Surface water


  • Streams
  • Rivers
  • Lakes
  • Reservoirs
• Streams


  • A moving body of surface water flowing downslope from higher elevations toward sea level via clearly defined channels, carrying dissolved substances and sediments. Land areas that allow water to flow into streams are known as watersheds or drainage basins. Stream and river waters contribute to surface runoffs, aiding the transport of sediments and dissolved substances. A stream has an interaction with groundwater, depending on how the stream water flows
• Rivers


  • Streams with considerably more volume of surface water flowing in well-defined channels. Rivers constitute at least 0.0006% of the global water supply (about 1.6% of the surface water supply), estimating at around 2,120 km^3 worth of freshwater
• Lakes


  • Large inland bodies of water, either fresh or saline. Essentially flat on the water's surface, it is exposed to the atmosphere and formed in places with deep depressions (i.e., low areas) by water being supplied by inlet rivers and/or streams, overland flow, and/or groundwater. Lakes are the largest surface freshwater reservoirs, despite freshwater being the smallest water type on Earth
• Wetlands


  • Land areas whose surfaces are covered primarily with water, whose biological life also adapted to its presence (i.e., water). Highly sensitive, any changes in the wetlands' waters drastically affect life in them
• Wetland types


  • Marshes
  • Swamps
  • Estuaries
• Groundwater


  • Freshwater found in the rock and soil layers deep within the soil's surface. As a freshwater source, it is the largest liquid freshwater source, as glaciers and ice sheets are the largest solid freshwater source on Earth. Groundwater sources can be seen as hollow caves located underground, or it can be encased in stone layers. Such rock layers with water are called aquifers
• Humans have depended on water for years, and this is evident in the way early settlements were located: near coasts and riverbanks
• Even today, humans still depend on water resources for food, water, transportation, religious, and recreational activities
• Human activities affecting water quality

  • Population growth
  • Migration from rural settlements to urbanized areas
  • Demands for greater food security and higher living standards
  • Increased competition
  • Pollution from factories, cities, and farmlands
• Other activities for water degradation

  • Sedimentation
  • Acid mine drainage
  • Improper waste disposal
  • Overexploitation of known water supplies
  • Responses to natural phenomenon
• The Republic Act No. 8041 of 1995 National Water Crisis Act addressed the Philippines' water problems through an integrated water management program and the development of new water resources and conservation of identified watersheds, among other provisions