The Water Cycle Water vapor was “out gassed” during Earth’s cooling process some 4.5 billion years ago. This volume of water has been recycled ever since.
What happens to precipitation that reaches the Earth’s surface? Water retention Infiltration Water is trapped on the Earth’s surface as snow or ice. Water “seeps” or infiltrates into the soil. Runoff Evapotranspiration Water moves across the surface of the Earth to a large body of water. Water is evaporated and/or transpired back into the atmosphere
What factors can affect the infiltration of water into the soil? Slope of the land The steeper the slope, the less likely water will infiltrate into the ground. Slope of the Land Rate of Infiltration
What factors can affect infiltration? Vegetation and Land Use Infiltration tends to be higher in areas where vegetation covers the soil (ie: grasses, shrubs, trees). Infiltration tends to be poor in areas where the land has been used by people (ie: compacted soil of farms and/or city landscapes covered by asphalt). Amount of land used by people Amount of vegetation Rate of Infiltration Rate of Infiltration
Soil Saturation Zone of aeration: Area of the soil in which space between soil particles is partially filled with air and partially filled with water. Water Table:The interface between the zones of aeration and saturation. Zone of saturation: Area of the soil in which all of space between soil particles is filled with water (GROUNDWATER).
As the ground becomes saturated with water, the water table rises. As the water table rises, the chance of water infiltrating the soil will decrease. Soil Saturation Soil Saturation Rate of Infiltration
Porosity Porosity: The amount of “open space” (pore space) between soil particles compared to the total volume of soil. If the amount of “pore space” between soil particles is high, then water will infiltrate the soil more easily. pore space Some soil types have a high porosity due to the size and shape of the soil particles. Porosity Rate of Infiltration
Factors that affect Porosity Shape Round soil fragments have a higher porosity than angular soil fragments. Round fragments High Porosity Angular fragments Low Porosity
Factors that affect Porosity Sorting Soil fragments that are roughly the same size and shape (sorted) will have a higher porosity than those that are not the same size and shape (unsorted). Sorted High Porosity Unsorted Low Porosity
Factors that affect Porosity Packing Soil fragments that are loosely packed will have a lot of pore space and will have a high porosity. Soil fragments that are compacted will have a small amount of pore space and will have a low porosity. Loose soil High Porosity Packed soil Low Porosity
Permeability Permeability: The ability of a material to allow a fluid to pass through it. Different soils have different levels of permeability – or the rate at which water can move through the soil. Which soil type do you think has the highest permeability? Sandy soil has the highest permeability.
Capillarity Capillarity: The upward migration of water in soil against the force of gravity. Capillarity is commonly found in soils with loosely packed, small particle size. The larger the particle size of the soil; the lower the rate of capillarity. Which soil sample below has the smallest particle size? The clay soil sample has the smallest particle size. The clay shows the best evidence of capillarity as seen by the highest upward rise of water in the sample. Capillarity Particle Size
What factors can affect the runoff of water on Earth’s surface? Rate of Precipitation Soil Saturation If the rate of precipitation is higher than the rate of infiltration, runoff will occur. If the soil is saturated with water, runoff will occur. Slope of the land Rate of Evapotranspiration If the slope of the land is steep, runoff will occur. If the rate of evapotranspiration is low, runoff will occur.