1	Water All life is based on water. All actively growing living things are more than 50% water.
2	Reference Fresh Water by E.C. Pielou, 1998, University of Chicago Press Assigned Reading In addition to chapter 2, pages 1254- 1256 describes the global water cycle.
3	Life and Water Water is intimately involved in biological function at all levels from cellular reactions to the ecosystem. Hydrophilic versus hydrophobic
4	The Water Molecule Water = H₂O = H-O-H = 3D view Because oxygen is much heavier than hydrogen, H₂O is 89% oxygen by weight. The electrons in the bond are not shared equally. The oxygen atom has a partial negative electrical charge and both hydrogen atoms have a partial positive charge. Molecules with separation of electrical charge are said to be ‘polar’ molecules.
5	Hydrogen bonds: bonds between molecules The positive charge on H of one water molecule ‘bonds’ to the negative charge on O of different molecule. This attraction between water molecules is known as a hydrogen bond. The hydrogen bond is much weaker than a covalent bond.
6	Water as a Solvent Solvents allow materials (named solute) to mix completely (=dissolve). Ionic compounds, such as salt, almost always are soluble in water. Polar compounds typically readily dissolve in water and are said to be hydrophilic. Non-polar compounds dissolve only slightly in water and are called hydrophobic. Non-polar compounds often dissolve in other non-polar liquids.
7	Solubility of non-polar compounds Oxygen: only a small amount dissolves in water, saturation is about 16 x 10^-3g•l^-1. More oxygen dissolves in cold water than in warmer water. Carbon dioxide dissolves in readily water and forms carbonic acid, H₂CO₃. Nitrogen, N₂, is less soluble than oxygen. PCB and DDT are non-polar organic pollutants are only very slightly soluble in water, i.e. measured in ppb.
8	Ionization of water The water molecule, H-O-H, has a small probability of breaking into two pieces, H⁺ (the hydrogen ion) and OH^- (the hydroxyl ion). The product of the molar concentration of hydrogen ions and hydroxyl ions is always 10^-14. [H⁺]•[OH^-] = 10^-14. The pH is –(log [molar hydrogen ion concentration]). The pH of pure water is 7 as the concentrations of hydrogen and hydroxyl ions must be equal.
9	Acidity increases as pH decreases Acidity promotes many chemical reactions. Substances that increase the concentration of hydrogen ions are called acids. Your stomach is very acidic, pH = 1.5 [OH^-] is 10^-12.5 M as product of 10^-1.5& 10^-12.5 =10^-14. Carbon dioxide in atmosphere dissolves in rain giving it a pH of 5.6. Other gases (e.g. SO₂, N_xO) in air make the rain even more acidic.
10	Ice, water as a solid One unusual property of water is that ice is less dense (Density is mass per unit volume) than as a liquid. The fact that ice floats (ice is 11% less dense than 4° C water) is important in understanding the aquatic environment. If ice was more dense than water, deep lakes (in this part of the world) would have ice at the bottom all year long.
11	Specific Heat –melting & boiling At phase transitions adding heat does not raise temperature. Transition from ice to water takes a lot of energy without changing the 0° temperature. Melting takes 80 calories per gram. Transition from liquid water to water vapor takes even more energy. Evaporation takes 540 calories per gram. Remember 1 calorie = energy to raise 1 gram water from 14.5° C to 15.5° C.
12	Losses and Gains of Water Evaporation of water has a great capacity to cool the body. Sweating helps regulate body temperature by putting water where it can evaporate. Animals generate water as part of metabolism. Sugar + Oxygen → Carbon dioxide + water
13	The Earth’s Water Cycle Water is constantly cycling between the atmosphere and the earth’s surface. Energy from the sun evaporates water into the atmosphere. In terrestrial environments, plants suck water from the ground to the air, called transpiration. Water vapor in air condenses into droplets as the temperature drops. These drops return as precipitation, (rain or snow).
14	Water Balance in Chicagoland The yearly total precipitation averages 91.4 cm (36 inches). Precipitation during growing season averages higher than in the non-growing season, but… Evapotranspiration is higher than precipitation in the growing season and lower in the non-growing season, so wetlands usually have the least water in October/November and the most in April.
15	Quantities of Water Water on earth totals 1.4 x 10¹⁸ m³. Fresh water is only 2.6% of all water and most of it (70%) is in ice in Antarctica or deep groundwater which circulates slowly. Only 1.1 x 10¹⁵ m³ circulates rapidly. Residence time = Pool size/input (=output) rate
16	Residence Time
17	Water in air Water dissolves in air. Warmer air can hold more water vapor than cooler air. The relative humidity is the percent the actual amount of water in the air is to the maximum possible at that temperature. The dewpoint is the temperature at which the current humidity would be saturated.
18	Groundwater Groundwater is water in the soil and the rock of the earth. There is much more water in groundwater than there is in rivers and lakes. An aquifer is a groundwater resource with a lot of easily extractable water. Aquifers are ‘mined’ in the sense that after discovery, the output in greater than input.
19	The Great Lakes Lakes Superior, Michigan, Huron, Erie and Ontario contain about 18% of the world’s fresh water supply. Many fish species that were important in Lake Michigan 150 years ago are not found there now. New, abundant non-native species are called invasive species.
20	Vocabulary Acid Aquifer Density Dewpoint Evapotranspiration Groundwater Hydrogen bond Invasive species pH Polar/non-polar Relative humidity Residence time