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20 Dec 2010
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Chapter 11: Freshwater Systems and Water Resources
-Only 2.5% of Earths water is freshwater
-Of that 2.5%, most is tied up in glaciers and icecaps
-Of the 1% that is surface water, most is in lakes and soil moisture
Rivers and streams wind through landscapes
-River and streams flow downhill, shaping landscapes
-A smaller river flowing into a larger one is a tributary
-The area of land drained by a river and all its tributaries is that river’s drainage basin or
-Areas nearest a river’s course that are flooded periodically are within the river’s
-Riparian (river side)
-Water of rivers and streams hosts diverse ecological communities
Wetlands include marshes, swamps, and bogs
-Wetlands: systems that combine elements of freshwater and dry land
-In freshwater marshes, shallow water allows plants to grow above the waters surface
-Swamps consist of shallow water rich in vegetation and can occur in forested areas
-Bogs are ponds thoroughly covered with thick floating mats of vegetation
-Wetlands help with the slowing of runoff, reducing flooding, recharging, and filtering
Lakes and ponds are ecologically diverse systems
-Littoral zone: edge of body water
-Benthic zone: extends along the bottom of the entire water body, from show to the
deepest point
-Limnetic zone: open portion of a lake or pond, away from shore
-Profundal zone: located below the limnetic zone, the volume of open water that sunlight
does not reach
-Oligotrophic lakes and ponds, which have low-nutrient and high-oxygen conditions, may
slowly give way to the high-nutrient, low-oxygen conditions of eutrophic water bodies
Groundwater plays key roles in the hydrologic cycle
-Groundwater makes up 1/5 of earths freshwater supply
-Groundwater is contained within aquifers: porous formations of rock, sand, or gravel that
hold water
-An aquifer’s upper layer, or zone of aeration, contains pore spaces partly filled with water
-In the lower layer, or zone of saturation, spaces are completely filled with water
-Boundary b/w there two zone is the water table
-Any area where water infiltrates Earths surface and reaches an aquifer below is an aquifer
recharge zone
-A confined aquifer, or artesian aquifer, exists when a water-bearing porous layer of
rock, sand, or gravel is trapped b/w upper and lower layers of less permeable substrate (often
clay)…water is under great pressure
-An unconfined aquifer has no such impermeable layer to confine it, so it water is under
less pressure
-Groundwater flows downhill and from areas of low pressure, emerging to join surface
water bodies at discharge zones
-Groundwater may remain in an aquifer for a long time…average age of groundwater has
be estimated at 1400 yrs, and some in ten of thousands of yrs old
Water is unequally distributed across Earth surface
-Main concentration of water resources in the united States is in Alaska
-People are not distributed across the globe in accordance with water availability…one
challenge has always been to transport freshwater from its source to where people need it
Climate change will cause water problems
Environment Canada reports that climate change is expected to affect freshwater and the
hydrologic cycle in Canada in four ways:
-The present mid-latitude rain belt will shift northward
-Snowmelt and spring runoff will occur earlier than at present
-There will be more evapotranspiration, which will start earlier and continue longer
-The interior continental region will experience drier summers
-It is estimated that 60% of the worlds largest 227 rivers (and 77% of those in North
America and Europe) have been strongly or moderately affected by artificial dams, canals, and
diversions, that is, the rerouting of water from its natural river channel by means of built
-1/3 of the worlds people are already affected by water scarcity (2006)
Water supplies our households, agriculture, and industry
-When we remove water from an aquifer or surface body water body and do not return it,
this is called consumptive use (i.e. agricultural irrigation)
-Nonconsumptive use of water does not remove, or only temporarily removes, water from
an aquifer or surface water body (i.e. hydroelectric dams)