Unit C - Water Systems on Earth Water, water, everywhere, Nor any drop to drink.
Chapter 7-The Water Cycle 7.1 – WATER IN OUR WORLD
Water Distribution • Water covers 71% of the Earth’s surface
Water Distribution • Most of Earth’s liquid water is salt water in the oceans.
Water Distribution • Fresh water- is water (liquid, solid or gas) that contains a low concentration of dissolved salts.
Salt Water • Oceans contain most of the world’s salt water. The salinity of ocean water is about 3.5% • Most of the salt in the water comes from land. As fresh water seeps through the soil, it dissolves some of the salt and other minerals we can’t taste the salt yet, but once the runoff (the fresh water going over the land) reaches the oceans it deposits the salt. Over millions of years the salt concentration in the oceans has built up to current levels.
Salt Water • Estuaries- are areas where rivers flow into an ocean. • Sometimes high tides cause ocean water to flow upstream into the river. This results in salt water mixing with fresh water. This mixed water is saltier than fresh water but fresher than salt water – it is called brackish water.
Fresh Water • Canada contains about 9% of the world’s fresh water supply although it only has 0.5% of the world’s population • Canada has many wetlands which: help filter and clean the water, and moderate water levels
The Three States of Matter • Water is the only substance on Earth that exist naturally in all three physical states; solid, liquid and gas
Water is always on the move. It is always changing its state and location The movement of water and its changing of states is known as the Water Cycle- the movement of water as it changes state over, on, and in Earth The Water Cycle
The Water Cycle • Heat energy from the sun causes water on Earth’s surface to change to water vapour in a process called Evaporation • Water can also evaporate from soil, plants and animals • As the air rises it cools. Cool air can not hold as much water as warm air. The cooled water vapour in the air becomes liquid again in a process called Condensation
The Water Cycle • Eventually so much water collects as clouds and the wind can no longer keep it aloft (floating). It then falls to Earth as Precipitation • Rain, hail, sleet, and snow are examples of precipitation • Sometimes snow and ice can turn directly into water vapour in a process called sublimation- change of state where a solid turns directly into a gas without first becoming a liquid
The Water Cycle • Liquid water flows along the surface of the ground (Runoff) and gathers in rivers, lakes and oceans • Wetlands are important reservoirs of water.
Types of Wetlands • Marsh-low-lying, treeless area of soft wet ground usually covered by water (fresh or salt) for part of the year. Grasses, cattails and other plants grow there.
Types of Wetlands • Swamp- low-lying, treed area of soft, wet ground covered with water (fresh or salt) for part of the year but contains many trees and bushes
Types of Wetlands • Bog- is dominated by mosses, which are wetland sponges
Groundwater • Groundwater is water that has soaked into the soil. • It passes through gravel, sand, soil and rock on its way back to rivers, lakes and oceans, or to longer term storage underground
Water • Water in vapour and liquid form can dissolve many substances. • This can be a problem because along with minerals and salts, pollutants and chemicals can also be transported by ground and surface water into lakes and oceans.
The Water Table • Water can be “sticky” that is, it shows an attraction to many other materials. This property is called Adhesion – the attractive forces between the particles of a fluid and the particles of another substance.
The Water Table • Water is composed of hydrogen and oxygen. Because of the way the atoms are arranged one end of a water molecule has a positive end and one has a negative end • This causes water molecules to act like tiny magnets and forms a cohesive force- the attractive force among particles of the same substance
Water in the Ground • When rain hits the ground, gravity causes it to sink. As it sinks, the water dissolves salts and minerals as it moves through the spaces between the soil particles. This process is known as Percolation.
Water in the Ground • As the water continues down through the ground, it eventually reaches a level where it will not go down any further. This is called the impermeable layer. Soil above this layer then becomes saturated with water. This is called the saturated zone. • The Upper layer of the Saturated zone is called the water table
Factors Affecting the Water Table • Amount of rainfall • If no little precipitation has fallen the water table can be depleted by capillary action • Capillary action happens because water is adhesive and cohesive
Human Activities • In urban areas water percolation does not happen as much as in other areas Why? • Urban areas are paved, so precipitation that falls in the city runs directly into the sewers and is emptied into stream and rivers without having a chance to become ground water.
7.5-The Power of Water • Sediment – Weathered pieces of rock that can be carried away by erosion
Weathering • Weathering- Weathering is the breaking down of rock into smaller and smaller pieces.
Weathering • There are different methods by which rocks can be broken into smaller and smaller pieces • Mechanical • Chemical • Biological – can be both physical and biological
Mechanical Weathering • Mechanical Weathering occurs when rock is physically broken down into smaller pieces. The “new material” is the same as the parent material
Mechanical Weathering • Ice Wedging – water gets inside tiny cracks of rocks and freezes. When water freezes it gets about 9% bigger. Over time this will split the rock
Chemical Weathering • Rain water is slightly acidic. Also water can dissolve other chemicals that can react with minerals in the rock causing chemical weathering
Erosion • Erosion is the movement of sediment from its place of origin • Erosion can be caused by • Gravity • Running water • Waves • Moving ice • wind
Erosion • Sediment gets picked up by rain or running water and eventually finds its way into a river • When the water is moving slow enough the sediments will settle to the bottom of the river in a process called DEPOSITION. • Heavier sediments settle first while light sediments take longer to be deposited
Erosion • Over time the deposited sediment can fill in lakes or can build up a delta at the mouth of a river • Delta-a flat area of land formed by sediment that has settled at the mouth of a river over many thousands of years
-recycle plastic-make sure garbage goes to the right place-make strict laws to help minimize waste-Mass clean up to help pick out the trash-Using an alternative to plastic. What Do We Do about it? Brainstorm
7.6 – The Human Side of Water Systems • Earth has a lot of people ( aprox. 6.8 billion) who need water for survival and recreation. Unfortunately our actions have not always have a positive impact on the water supply • WATER POLLUTION – any pollution that negatively affects the quality of water
Micro-organisms in Water • Coliforms (bacteria found in the intestines of animals) can cause a serious health issue. • Coliforms can be in high concentrations if raw or improperly treated sewage is discharged into the water. • Nausea, vomiting and diarrhea can result
Acid Precipitation • ACID PRECIPITATION – occurs when water vapour reacts with air borne pollutants, like sulfur dioxide and nitric oxide, to form an acid (sulfuric acid and nitric acid) • The water then condenses and falls to the Earth as acid rain or snow