Unit 4 12.net



Unit 7 Day 9

Freshwater resources

Freshwater systems

◆ Water may seem abundant, but drinkable water is rare

◆ Freshwater = relatively pure, with few dissolved salts

◆ Most is tied up in glaciers, ice caps, and aquifers

◆ As water is cycled it redistributes heat, erodes mountains, builds river deltas, maintains ecosystems and organisms

◆ It also shapes civilizations and political conflicts

◆ Surface water = on Earth’s surface

◆ 1% of freshwater

◆ Runoff = water that flows over land

◆ Water merges in rivers and ends up in a lake or ocean

◆ Tributary = a smaller river slowing into a larger one

◆ Watershed (drainage basin) = the area of land drained by a river system (river and its tributaries)

Water is renewed and recycled as it moves through the hydrologic cycle

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Lakes and ponds are ecologically diverse

◆ Lakes and ponds = bodies of open, standing water

◆ Littoral zone = region ringing the edge of a water body

◆ Rooted aquatic plants grow in this shallow part

◆ Benthic zone = extends along the bottom of the water body

◆ Home to many invertebrates

◆ Limnetic zone = open portion of the lake or pond where sunlight allows photosynthesis

◆ Profundal zone = water that sunlight does not reach

◆ Supports fewer animals because there is less oxygen

◆ Oligotrophic lakes and ponds = have low nutrient and high oxygen conditions

◆ Eutrophic lakes and ponds = have high nutrient and low oxygen conditions

◆ Eventually, water bodies fill completely in through the process of succession

◆ The largest lakes are known as inland seas

◆ Great Lakes, The Caspian Sea

◆ Wetlands = the soil is saturated with shallow standing water

◆ Freshwater marshes = shallow water

◆ Plants grow above the surface

◆ Swamps = shallow water in forested areas

◆ Can be made by beavers

◆ Bogs = ponds covered in thick floating mats of vegetation

◆ A stage in aquatic succession

◆ Wetlands are extremely valuable for wildlife

◆ They slow runoff, reduce flooding, recharge aquifers, and filter pollutants

◆ People have drained wetlands, mostly for agriculture

◆ Southern Canada and the U.S. have lost over half of their wetlands

◆ In 2006 the Supreme Court told the Army Corps of Engineers it must create guidelines to determine when wetlands are valuable enough to protect by law

◆ Groundwater = water beneath the surface held in pores in soil or rock

◆ 20% of the Earth’s freshwater supply

◆ Aquifers = porous, sponge-like formations of rock, sand, or gravel that hold water

◆ Zone of aeration = pore spaces are partly filled with water

◆ Zone of saturation = spaces are filled with water

◆ Water table = boundary between the two zones

◆ Recharge zone = any area where water infiltrates Earth’s surface and reaches aquifers

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◆ Confined (artesian) aquifer = water-bearing, porous rocks are trapped between less permeable substrate (clay) layers

◆ Is under great pressure

◆ Unconfined aquifer = no upper layer to confine it

◆ Readily recharged by surface water

◆ Groundwater’s average age is 1,400 years

◆ It may be tens of thousands of years old

◆ Groundwater becomes surface water through springs or human-drilled wells

◆ The world’s largest known aquifer

◆ Underlies the Great Plains of the U.S.

◆ Water is unevenly distributed in space and time

◆ Different areas possess different amounts of water

◆ People erect dams to store water

◆ Climate change will cause

◆ Altered precipitation patterns

◆ Melting glaciers

◆ Early season runoff

◆ Intensified droughts

◆ Flooding

◆ We have achieved impressive engineering accomplishments to harness fresh water

◆ 60% of the world’s largest 227 rivers have been strongly or moderately affected

◆ Dams, dikes, and diversions

◆ Consumption of water in most of the world is unsustainable

◆ We are depleting many sources of surface water and groundwater

◆ Proportions of these three types of use vary dramatically among nations

◆ Arid countries use water for agriculture

◆ Developed countries use water for industry

◆ Consumptive use = water is removed from an aquifer or surface water body and is not returned

◆ Irrigation = the provision of water to crops

◆ Nonconsumptive use = does not remove, or only temporarily removes, water

◆ Electricity generation at hydroelectric dams

◆ Rapid population growth requires more food and clothes

◆ The Green Revolution uses irrigation

◆ We use 70% more irrigation water than 50 years ago

◆ Irrigation can double crop yields

◆ 18% of land is irrigated but produces 40% of our crops

◆ Irrigation is highly inefficient

◆ Water evaporates in “flood and furrow” irrigation

◆ Over irrigation leads to waterlogging and salinization

◆ Reducing world farm income by $11 billion

◆ Wetlands are being lost as we divert and withdraw water

◆ Channelize rivers, build dams, etc.

◆ As wetlands disappear, we lose ecosystem services

◆ Filtering pollutants, wildlife habitat, flood control, etc.

◆ Many are trying to protect and restore them

◆ Groundwater is easily depleted

◆ Aquifers recharge slowly

◆ Used by one-third of all people

◆ As aquifers are mined, water tables drop

◆ Salt water intrudes in coastal areas

◆ Sinkholes = areas where ground gives way unexpectedly

◆ Aquifers can’t recharge Wetlands dry up

◆ Water for human consumption and other organisms needs to be:

◆ Disease-free

◆ Nontoxic

◆ Half of the world’s major rivers are seriously depleted and polluted

◆ They poison surrounding ecosystems

◆ Threatening the health and livelihood of people

◆ The invisible pollution of groundwater has been called a “covert crisis”

◆ Pollution = the release of matter or energy that causes undesirable impacts on the health and well-being of humans or other organisms

◆ Point sources = discrete locations of water pollution

◆ Factories, sewer pipes

◆ Addressed by the U.S. Clean Water Act

◆ Nonpoint sources = pollution arises from multiple inputs over larger areas (farms, city streets, neighborhoods)

◆ The major source of U.S. water pollution

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• Nutrient pollution from fertilizers, farms, sewage, lawns, golf courses leads to eutrophication

◆ Fertilizers add phosphorus to water, which boosts algal and aquatic plant growth

◆ Spreading algae cover the surface, decreasing sunlight

◆ Bacteria eat dead algae, reducing dissolved oxygen

◆ Fish and shellfish die

◆ Solutions include treating wastewater

◆ Reducing fertilizer application

◆ Using phosphate-free detergents

◆ When algae blooms occur because of nutrient pollution in water ways the effects can be devastating

◆ The bloom dies off then sinks to the bottom

◆ Decomposing bacteria then rapidly multiple to consume the algae

◆ The bacteria use the oxygen in the water for respiration

◆ The lake becomes hypoxic which destroys the animal live that depend on the oxygen in the water

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