Transcript Slide 1

THE WATER CYCLE AND HUMAN USE
SUPPLIES OF WATER EXIST IN DIFFERENT
PARTS OF THE WORLD AS SURFACE WATER
AND GROUND WATER.
THESE SUPPLIES ARE BASED ON CLIMATE
AND NATURAL GEOGRAPHY.
THESE SUPPLIES CAN CHANGE BASED ON
CHANGES IN CLIMATE AND HUMAN
INTERVENTION.
FOR EXAMPLE, DURING THE LAST ICE AGE
MUCH OF AFRICA WAS UNDER A DROUGHT.
AREAS THAT WERE RAINFOREST BECAME
SAVANAH.
IN TURN, HUMAN INTERVENTION CAN
CHANGE WATER AVAILABILITY.
HUMANS HAVE HARVESTED SO MUCH
FIREWOOD IN SUB SAHARAN AFRICA THAT
THE DESERT HAS REPLACED MUCH OF WHAT
WAS ONCE GRASSLAND.
DEFORESTATION IS OCCURING IN THE
AMAZON BASIN. 50% OF THE MOISTURE IN
THIS AREA COMES FROM TRANSPIRATION OF
MOISTURE FROM TREES. DEFORESTATION
COULD RESULT IN THE AMAZON BECOMING
GRASSLAND IN A SHORT PERIOD OF TIME.
IN MANY AREAS OF THE WORLD, WATER IS
BEING PUPMPED OUT OF AQUIFERS FASTER
THAN IT CAN BE REPLINISHED BY RAINFALL
AND INFILTRATION.
THIS CAN QUICKLY RESULT IN WATER NOT
BEING AVAILABLE FOR ANY HUMAN USE IN
THOSE AREAS.
ANOTHER EXAMPLE GIVEN EARLIER WAS THE
ARAL SEA. SO MUCH WATER IS TAKEN FROM
RIVERS FEEDING THE ARAL SEA THAT THE
VOLUME HAS DRASTICALLY BEEN REDUCED. THE
OLD SEA BED IS DESERT, AND THE LAND
AROUND THE ARAL IS BECOMING COOLER AND
DRYER (MICRO CLIMATE CHANGE) DUE TO LOSS
OF WATER.
GROUNDWATER: THE WATER HELD IN THE
PORES OF SOIL AND ROCK.
AS YOU DID DEEPER, THE SOIL BECOMES
MOISTER.
THE WATER TABLE IS THE TOP OF THE
SATURATED ZONE.
THE WATER TABLE TENDS TO FOLLOW THE
TOPOGRAPHY OF THE LAND.
HOW DOES WATER BECOME GROUNDWATER?
FIRST, IT HAS TO SOAK INTO THE GROUND.
THIS HAPPENS WHEN IT RAINS.
SOME OF THE WATER SOAKS INTO THE
GROUND, AND SOME OF THE WATER
BECOMES RUNOFF.
RUNOFF IS DETERMINED BY THREE FACTORS:
1. AMOUNT OF RAIN
2. TYPE OF SURFACE
3. SLOPE OF LAND
THESE SAME FACTORS WILL DETERMINE HOW
MUCH WATER SOAKS INTO THE GROUND.
SOME SURFACES WILL BE MUCH MORE
PERMEABLE THAN OTHERS.
A PERMEABLE SOIL HAS PORES THAT ARE
CONNECTED THAT WATER CAN FLOW THROUGH.
A MATERIAL LIKE GRANITE WITH NO CRACKS
WOULD BE IMPERMEABLE.
IF YOU HAD PLENTY OF TIME AND DUG DOWN
INTO THE GROUND, THE SOIL WOULD GET
WETTER AND WETTER THE DEEPER YOU DUG.
IF YOU DUG DEEP ENOUGH, THE SOIL WOULD BE
SO WET THAT IT WOULD NOT HOLD ANY MORE
WATER.
WE SAY THAT THIS SOIL IS SATURATED.
THE TOP OF THE SATURATED ZONE IS THE
WATER TABLE.
IF THE GROUNDWATER IN THE SATURATED
ZONE COVERS A LARGE AREA, WE CALL THIS AN
AQUIFER.
SOME AQUIFERS ARE HUGE.
IDEALLY, IF YOU ARE DEPENDING ON
GROUND WATER FOR PERSONAL WATER
SUPPLY, YOU WOULD LIKE TO HAVE A WELL
DRILLED IN A VERY TRANSMISSIVE
GEOLOGIC FORMATION.
IF THE FORMATION IS NOT VERY
TRANSMISSIVE, A MUCH DEEPER WELL
WOULD HAVE TO BE DRILLED.
WATER HAS A VERY LONG RESIDENCE TIME
IN AQUIFERS.
WATER CAN REMAIN IN AQUIFERS FROM
THOUSANDS OF YEARS TO HUNDREDS OF
THOUSANDS OF YEARS.
WHAT THIS MEANS IS THAT POLLUTION AND
WASTES THAT HAVE BEEN DUMPED ON THE
GROUND IN THE LAST CENTURY MAY JUST BE
REACHING AQUIFERS.
A GOOD EXAMPLE OF AQUIFER
CONTAMINATION IS THE USE OF MTBE IN
GASOLINE AS A MEANS OF REDUCING
HYDROCARBON PARTICULATES AND SMOG.
PARTS OF CALIFORNIA ENDED UP WITH
GROUND WATER CONTAMINATION AS A
RESULT.
THE OGALLALA AQUIFER COVERS MOST OF THE
GREAT PLAINS AND EXTENDS FROM SOUTH
DAKOTA TO TEXAS.
THERE IS A LARGE AQUIFER UNDER MEXICO
CITY.
AQUIFERS SUPPLY WATER TO MANY PEOPLE IN
THE WORLD.
THE PROBLEM IS THAT IF YOU TAKE OUT WATER
FASTER THAN WATER GOES IN, YOU CAN DRAIN
THE AQUIFER.
THIS IS HAPPENING IN MEXICO CITY AND WITH
THE OGALLALA AQUIFER.
IN FLORIDA, SOME OF THE GROUND WATER
FLOWS THROUGH UNDERGROUND CAVES IN THE
LIMESTONE.
A LARGE PERCENTAGE OF FRESH WATER IS
TIED UP AS ICE.
ALMOST 90% OF THIS IS PART OF THE
ANTARTIC ICE CAP.
10% IS TIED UP IN THE GREENLAND ICE
SHEET.
THE REMAINDER IS IN GLACIERS.
GLACIERS AND SNOW CAPS PLAY A MAJOR
ROLE IN WATER SUPPLIES IN MANY PARTS
OF THE WORLD, ESPECIALLY ASIA AND
NORTH AMERICA.
FOR EXAMPLE, MUCH OF THE WATER IN
WESTERN U.S. RIVERS DEPENDS ON MELT
RUNOFF DURING SUMMER MONTHS.
INCREASE IN SALT LEVELS IN WATER
SUPPLIES CAN ALSO BE A PROBLEM.
IN ARID REGIONS, SUCH AS THE DESERT
SOUTH WEST, WATER USED FOR
IRRIGATION CAN EVAPORATE, LEAVING
SALT DEPOSITS BEHIND.
HIGH SALT LEVELS CAN KILL VEGETATION
AND CAUSE SOILS TO BECOME HARDER AND
MORE COMPACT.
GROUNDWATER IN COASTAL AREAS CAN
BECOME SALINE WHEN THE FRESH WATER
IS PUMPED OUT FASTER THAN IT CAN BE
REPLENISHED.
THIS CAUSES SALT WATER TO INTRUDE
FROM THE OCEAN AND FROM ESTUARIES.
THIS IS A PROBLEM IN EASTERN NORTH
CAROLINA.
Concern about aquifer depletion and salt
water intrusion.