Nutrient Cycles Flashcards
How is Water required by all Life on Earth?
Solvent of life, Regulates Climate, Physical Processes, and Nutrient Cycles
Solvent of Life
Exists as solid, liquid, and gas
Physical Processes
Weathering and erosion of rocks and minerals
Nutrient Cycles
Ability to dissolve many substances
What is the Hydrologic (Water) Cycle
It describes the continuous movement of water on (surface), above (atmosphere) and below (groundwater) the Earth
Hydrology is the study of ___?
Water Cycle
How does the Mass of water on Earth Remain Constant?
water partitioned into the major reservioirs of ice, freshwater, saline water and atmospheric water is variable depending on climate
What are the Physical Processes in the Water Cycle?
Evaporation, condensation, Precipitation, infiltration, surface runoff, and subsurface flow
Evaporation
Trasnfer of water from the Earth Surface (liquid state) to the atmosphere (gaseous state)
- Evaporated water is in gaseous state outside of clouds
- 80% from ocean, 20% from land & plants (evapotranspiration)
- wind moves evaporated water around the globe (humidity)
- higher evaporation rates in warmer temperature with high solar energy
Transpiration (Evapotranspiration)
- evaporation of water into the atmosphere by plants
- through stomata of leaves
- accounts for 10% of total water in the atmosphere
- influences by leaf size, solar radiation, temperature, humidity, soil water supply
Condensation
- the change of water from its gaseous state to liquid state
- occurs in the atmosphere
- warm air rises, then cools, then water vapor condenses to liquid water droplets
- formation of clouds and fog
Precipitation
- Transport of condensed water from the atmosphere back to Earth’s surface
- Rain, hail, snow, sleet, fog drip
- Can vary by biome, year, topography
Infiltration/Seepage
- the flow of water from the ground surface into the ground (aquifer)
- once infiltrated, the water is stored as soil moisture or groundwater
- influenced by soil type, slope of surface
Runoff (Surface Runoff)
- movement of surface water (rivers, lakes, streams) on land to ocean
- consists of precipitation that neither evaporates, transpires, nor infiltrates the surface to become groundwater
- excess runoff can lead to flooding
- Runoff due to few major rivers ( 20% Amazon, 43% 50 largest rivers)
Groundwater (Subsurface) Flow
- flow of water underground in aquifers
- can return to surface as a spring or pumped
- moves downwards towards sea level by gravity
- moves slowly and is replenished slowly
What is Residence Time?
The average time that a water molecule spends in a reservoir
- its a measure of the average age of water in a reservoir
What percent of Earth’s water is freshwater?
2.5%
Why is Majority of Freshwater Inaccessible?
- ~99% of freshwater is in groundwater, ice, glaciers, permafrost
- many aquifers (groundwater) not connected to earth’s surface
- deep aquifers are not renewable by precipitation
- accessible (surface) groundwater is renewable, but turnover is slow (100-200 yrs)
Renewable Groundwater
- surface groundwater that is accessible by humans
- recharged by precipiation
- slow rate of recharge, long residence time
- overuse or quick depletion can cause shrinking/compaction of aquifer
- above ground alterations to streamflow, landscape can influence infiltration of precipitation into groundwater
- can be contaminated by chemicals, nutrients, bacteria
Oglala Aquifer, Great Plains, USA
- Accessible surface groundwater
- Largest aquifers (174,000 sq mi)
- irrigates 1/5 of cropland in U.S.
- drinking water for 1.9 million people
- recharged by precipitation, but arid land with impermeable soil/rock
- 60-70yrs have reduced by 9%
- contaminated with Nitrates
- 6,000 yrs. to replenish by rainfall
- lifespan estimated up to year 2028
Case Study: Aral Sea, Kazakhstan & Uzbekistan
- accessible surface water for humans
- previously 1 of 4 largest lakes in the world
- Shrinking since 1960’s
- Rivers diverted for irrigation
- Now 10% of size with desert remaining
- Remaining land not usable
- High salinity
- Fish kills
- Dust storms
What are Human Impacts on Water Cycle in the Tropics?
- most rain over the ocean & coastal areas is from evaporation from the ocean
- BUT in tropical rainforest, 50% of rain is from local evapotranspiration
- Immense implications for runoff, precipitation
