Transcript Water Cycle
Water Cycle Water Quality About the Hydrologic Cycle • Hydrology is the study of movements and characteristics of water. • The hydrologic cycle has a profound effect upon climate prediction. • Water is vital for life so we must understand where to find water and how water supplies cycle through the Earth. W h e r e ’s t h e W a t e r ? 97.5% 2.5% 1.7% 2.5% 0.77% 2.5% FIGURE 11.2 The distribution of water on Earth. [Data from J. P. Peixoto and M. Ali Kettani, “The Control of the Water Cycle.” Scientific American (April 1973): 46; E. K. Berner and R. A. Berner, Global Environment. Upper Saddle River, N.J.: Prentice Hall, 1996, pp. 2–4.] The Water Cycle http://www.enchantedlearning.com/wgifs/Watercycle.GIF Flows and Reservoirs • Precipitation: water vapor condenses into tiny drops that form clouds, eventually fall as rain or snow • Infiltration: when precipitation soaks into the ground through particles of soil or cracks • Runoff: precipitation that doesn’t infiltrate moves over the land surface, eventually collecting in streams and rivers • Evaporation/Transpiration: liquid water transforming into gaseous water (water vapor) from surface water (evaporation) or plants (transpiration) • Sublimation: solid water (ice) transforming directly into gaseous water (without becoming liquid) Water Quality • We will be going on a field trip to test water quality. • What is ‘Clean’ water? • Why is water quality important? • What impacts water quality? Water Quality Tests • • • • • • • • Temperature pH Dissolved Oxygen (DO) Biochemical Oxygen Demand (BOD) Nitrates Total Dissolved Solids (TDS) and Salinity Turbidity Total Coliform Bacteria Temperature • Water temperature changes much more slowly than air temperature. • How would water body size affect temperature? How about vegetation near the water? How about flowing vs. standing water? • Why do we care about temperature? – Warm water holds less oxygen, but produces conditions that require more oxygen. pH • A relative measure of water’s alkalinity/acidity. • Chemically a measure of the number of hydrogen ions. • pH scale is logarithmic, so substances at the far ends are extremely acidic or alkaline. pH • Natural factors that influence pH – Decomposing organic materials release carbon dioxide, creating carbonic acid. • Human factors that influence pH – Releases of sulfur dioxide, nitrogen oxides and carbon dioxide all can form acid rain. • Why should we care about pH? How does it influence water quality? Dissolved Oxygen (DO) • Water holds a reasonably large amount of dissolved oxygen, which is essential for life. • Dissolved oxygen is influenced by salinity, agitation and turbulence, temperature, minerals, plant life, and organic wastes. – How do you think these factors influence DO? Biochemical Oxygen Demand (BOD) • Decomposing organic materials consume oxygen. • High BOD indicates pollution. • Low BOD suggests good water quality. Nitrates • Nitrogen is an abundant element. • Nitrogen is considered a nutrient because it is essential for plant growth. • How could plant growth impact water quality? • Eutrophication is enrichment with nutrients. – Eutrophication can be both a natural and humaninduced phenomenon. Total Dissolved Solids (TDS) and Salinity • Water is a universal solvent, so it may contain a wide range of substances. – Examples include calcium, sodium, phosphorus, iron, etc. • Some solids in water are essential to maintaining health. • High concentrations may lower water quality by increasing turbidity. • Salinity is a measure of specific type of dissolved solid, namely, salts. Turbidity • Turbidity is a measure of how cloudy water appears. – It is a measure of how much light passes through the water caused by light scattering solid particles. • Do you think that if turbidity is low (water is clearer) that it is automatically healthier? Total Coliform Bacteria • Coliform bacteria is generally nonpathogenic and lives throughout the environment. • Fecal coliform lives in the intestines of warm blooded animals and helps to digest food. • The presence of fecal coliform indicates that pathogenic bacteria is present also. • Testing for specific pathogenic bacteria takes a lot of time and may be difficult. – How might we solve this problem? Water Quality • For many of the indicators we will be testing for there are national standards determined by the Environmental Protection Agency. • Water quality standards are based on the use. – Drinking water, recreation, and fishing each have different standards. • Do you think there is a magic formula that creates high quality water?