Chapter Twelve: Fresh Water, Oceans, and Coasts
Freshwater Systems
About 97.5% of Earth’s water resides in the oceans and is too salty to drink or to use to
water crops.
About 2.5% is considered fresh water, water that is relatively pure with few dissolved
salts
o Because most fresh water is tied up in glaciers, icecaps, and underground aquifers,
just over 1 part in 10,000 of Earth’s water is easily accessible for human use.
Water is renewed and recycled as it moves through the water cycle
o The movement of water in the water cycle creates a web of interconnected aquatic
systems that exchange water, organisms, sediments, pollutants, and other
dissolved substances.
Underground aquifers exchange water with rivers, ponds, and lakes through the
sediments on the bottoms of these water bodies.
Groundwater Plays Key Roles in the Water Cycle
Liquid water occurs either as surface water or groundwater.
Surface water is water located atop Earth’s surface and groundwater is water beneath the
surface held within pores in soil or rock
o Groundwater flows slowly beneath the surface from areas of high pressure to
areas of low pressure and can remain underground for long periods in some cases
for thousands of years.
, o Groundwater makes up one-fifth of Earth’s fresh water supply and plays a key
role in meeting human water needs
Groundwater is contained within aquifers: porous formations of rock, sand, or gravel that
hold water
o An aquifer’s upper layer, or zone of aeration, contains pore spaces partly filled
with water
o In the lower layer or zone of saturation, the spaces are completely filled with
water
The boundary between these two zones is the water table.
The largest known aquifer is the Ogallala Aquifer, which underlines the Great Plains of
the United States
Surface Water Converges in River and Stream Ecosystems
Surface water accounts for just 1% of fresh water, but it is vital for our survival and for
the planet’s ecological systems
Each day in the United States, 1.9 trillion L of groundwater are released into surface
waters- nearly as much as the daily flow of the Mississippi River
Water that falls from the sky as rain, emerges from springs, or melts from snow or a
glacier and then flows over the land surface is called runoff.
A smaller river flowing into a larger one is called a tributary
o The area of land drained by a river and all its tributaries is the river’s watershed
Landscapes determine where rivers flow, but rivers shape the landscapes through which
they run
, o Over thousands or millions of years, a meandering river may shift from one
source to another, back and forth over a large area, carving out a flat valley and
picking up sediment that is later deposited in coastal wetlands
Areas nearest a river’s course that are flooded periodically are said to be within the
river’s floodplain
Frequent deposition of silt from flooding makes floodplain soils especially fertile
o As a result, agriculture thrives in floodplains, and riparian forests are productive
and species-rich
Lakes and Ponds are Ecologically Diverse Systems
The largest lakes, such as North America’s Great Lakes, are sometimes known as inland
seas
Around the nutrient-rich edges of a water body, the water is shallow enough that aquatic
plants grow from the mud and reach above the water’s surface.
o This region, names the littoral zone, abounds in invertebrates- such as insect
larvae, snails, and crayfish- that fish, birds, turtles, and amphibians feed on.
The benthic zone extends along the bottom of the lake or pong, from shore to the deepest
point.
Many invertebrates live in the mud, feeing on detritus or on one another.
In the open portion of a lake or pong, far from shore, sunlight penetrates shallow waters
of the limnetic zone.
Below the limnetic zone lies the profundal zone, the volume of open water that sunlight
does not reach
, o This zone lacks photosynthetic life and it lower in dissolved oxygen than upper
waters
Oligotrophic lakes and ponds, which are low in nutrients and high in oxygen, may slowly
transition to the high-nutrients, low-oxygen conditions of eutrophic water bodies.
Freshwater Wetlands Include Marshes, Swamps, bogs, and Vernal Pools.
Wetlands are systems in which the soil is saturated with water and which generally
feature shallow standing water with ample vegetation.
In freshwater marshes, shallow water allows plants such as cattails and bulrushes to grow
above the water surface
Swamps also consist of shallow water rich in vegetation, but they occur in forested areas
Bogs are ponds covered with thick floating mats of vegetation and can represent a stage
in aquatic succession.
Vernal pools are seasonal wetlands that form in early spring from rain and snowmelt and
dry up once the weather becomes warmer.
Wetlands also provide important ecosystem services by slowing runoff, reducing
flooding, recharging aquifers, and filtering pollutants.
The Oceans
The vast majority of rivers empty into oceans, so the oceans receive most of the inputs of
water, sediments, pollutants, and organisms carried by freshwater systems.
Freshwater Systems
About 97.5% of Earth’s water resides in the oceans and is too salty to drink or to use to
water crops.
About 2.5% is considered fresh water, water that is relatively pure with few dissolved
salts
o Because most fresh water is tied up in glaciers, icecaps, and underground aquifers,
just over 1 part in 10,000 of Earth’s water is easily accessible for human use.
Water is renewed and recycled as it moves through the water cycle
o The movement of water in the water cycle creates a web of interconnected aquatic
systems that exchange water, organisms, sediments, pollutants, and other
dissolved substances.
Underground aquifers exchange water with rivers, ponds, and lakes through the
sediments on the bottoms of these water bodies.
Groundwater Plays Key Roles in the Water Cycle
Liquid water occurs either as surface water or groundwater.
Surface water is water located atop Earth’s surface and groundwater is water beneath the
surface held within pores in soil or rock
o Groundwater flows slowly beneath the surface from areas of high pressure to
areas of low pressure and can remain underground for long periods in some cases
for thousands of years.
, o Groundwater makes up one-fifth of Earth’s fresh water supply and plays a key
role in meeting human water needs
Groundwater is contained within aquifers: porous formations of rock, sand, or gravel that
hold water
o An aquifer’s upper layer, or zone of aeration, contains pore spaces partly filled
with water
o In the lower layer or zone of saturation, the spaces are completely filled with
water
The boundary between these two zones is the water table.
The largest known aquifer is the Ogallala Aquifer, which underlines the Great Plains of
the United States
Surface Water Converges in River and Stream Ecosystems
Surface water accounts for just 1% of fresh water, but it is vital for our survival and for
the planet’s ecological systems
Each day in the United States, 1.9 trillion L of groundwater are released into surface
waters- nearly as much as the daily flow of the Mississippi River
Water that falls from the sky as rain, emerges from springs, or melts from snow or a
glacier and then flows over the land surface is called runoff.
A smaller river flowing into a larger one is called a tributary
o The area of land drained by a river and all its tributaries is the river’s watershed
Landscapes determine where rivers flow, but rivers shape the landscapes through which
they run
, o Over thousands or millions of years, a meandering river may shift from one
source to another, back and forth over a large area, carving out a flat valley and
picking up sediment that is later deposited in coastal wetlands
Areas nearest a river’s course that are flooded periodically are said to be within the
river’s floodplain
Frequent deposition of silt from flooding makes floodplain soils especially fertile
o As a result, agriculture thrives in floodplains, and riparian forests are productive
and species-rich
Lakes and Ponds are Ecologically Diverse Systems
The largest lakes, such as North America’s Great Lakes, are sometimes known as inland
seas
Around the nutrient-rich edges of a water body, the water is shallow enough that aquatic
plants grow from the mud and reach above the water’s surface.
o This region, names the littoral zone, abounds in invertebrates- such as insect
larvae, snails, and crayfish- that fish, birds, turtles, and amphibians feed on.
The benthic zone extends along the bottom of the lake or pong, from shore to the deepest
point.
Many invertebrates live in the mud, feeing on detritus or on one another.
In the open portion of a lake or pong, far from shore, sunlight penetrates shallow waters
of the limnetic zone.
Below the limnetic zone lies the profundal zone, the volume of open water that sunlight
does not reach
, o This zone lacks photosynthetic life and it lower in dissolved oxygen than upper
waters
Oligotrophic lakes and ponds, which are low in nutrients and high in oxygen, may slowly
transition to the high-nutrients, low-oxygen conditions of eutrophic water bodies.
Freshwater Wetlands Include Marshes, Swamps, bogs, and Vernal Pools.
Wetlands are systems in which the soil is saturated with water and which generally
feature shallow standing water with ample vegetation.
In freshwater marshes, shallow water allows plants such as cattails and bulrushes to grow
above the water surface
Swamps also consist of shallow water rich in vegetation, but they occur in forested areas
Bogs are ponds covered with thick floating mats of vegetation and can represent a stage
in aquatic succession.
Vernal pools are seasonal wetlands that form in early spring from rain and snowmelt and
dry up once the weather becomes warmer.
Wetlands also provide important ecosystem services by slowing runoff, reducing
flooding, recharging aquifers, and filtering pollutants.
The Oceans
The vast majority of rivers empty into oceans, so the oceans receive most of the inputs of
water, sediments, pollutants, and organisms carried by freshwater systems.
