Lec 1a: Life in Water - Water Properties All life basically is aquatic –Life on Earth evolved in and is sustained by water –Terrestrial organisms maintain an internal aquatic environment for their organs and tissues 1 Determines human distribution and population sizes Water is both a renewable and a non-renewable resource Available fresh water is relatively scarce

Water Reservoirs (Horne & Goldman, 1994) Renewal Time ,000 yrs 12,000 yrs yrs 330 days 7-11 days 7 days 2

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Human Water Use Summary – Pressures on a Key Resource Only 1% of water in lakes, 0.01% in rivers –(as % of inland liquid water) 4 U. S. water use ~2000 m 3 / person /year –e.g. versus Israel ~500 m 3 / person / year Much water use for industry and irrigation, not just home use (Fig 1.3) Surface water provides majority of water (Fig1.4)

Factors Affecting Human Need for Fresh Water Population pressure and growth –Now approximately 6.6 billion humans –Human population doubling every 50 years 5 Development and Technology –New technologies in manufacturing and agriculture often result in increased per capita need for fresh water –Development often interferes with the water cycle (e.g., reduction of vegetation, paving, etc.) Pollution –Reduces amount of fresh water available for use

92% 5% 3% Sufficiency Stress Scarcity 58% 24% 18% Sufficiency Stress Scarcity World Population and Water Supply 1995 & billion billion How Many People Can The Earth Support? Joel Cohen. Norton, New York, pp. 6

Human-Biological Interactions in the Water Cycle Evaporation Surface runoff Deep storage Interception Transpiration Withdrawal from deep storage Factories Wells Reservoirs Agriculture Ground water 7

Water Properties Depiction of the three phases of water: steam, liquid water, and ice ©Time, Inc. All rights reserved. 8 (See Table 2.1 for a summary)

A. Basic Structure 1. Covalent bonding of 2H + O atoms 2. Polar-covalent bond 3. Inter-molecule attraction 4. H-bonds 9

B. Cohesion 1. Wave formation and other water movements 2. Distribution of heat, gases, nutrients, plankton, etc. 10

C. Surface Tension 1. Pressure needed to break surface 2. Only Hg is higher 3. Implications for organisms? -Related to what characteristics? 11

D. Liquid at ambient temperatures E. Low density solid (ice floats!) -Critical for life on earth F. High heat capacity -Specific Heat (also called Heat Capacity) calories required to raise 1 g H 2 O 1 O C (e.g. from 14.5 to 15.5 O C) - Exceeded only by Liquid NH Liquid H Heat transfer by water is very important 12

G. Good Solvent (for some things) Difference on land vs. water % of air as oxygen=21% Concentration=210 ml / L What about in water? (at 15 degC and 1 atm) Solubility of oxygen in water=34 ml / L Solubility of carbon dioxide in water=1019 ml / L ….Why the disparity? So, volume of oxygen at equil. with air:= 34.1 ml/L * 21% = 7.16 ml / L (30x less than air!) What is the effect of temperature on gas solubility? (in eq. with Atm) Water Temperature (deg C)ml / L (This is why hot water supposedly freezes more quickly than cold water) 13

Density Difference (x 10 5 / o C Lowering) T( o C) Temperature o C Density Liquid Ice % Density change H. Very viscous x more dense than air 2. Water Temperature - Density Relationship 14

Lake Thermal Profile - Time and Depth 15

Hensley Reservoir (Madera Co) JuneAugustDecember Oxygen Temperature 16

Relationships among Water Viscosity, Inertia, and Physical Parameters Hydrogen bonding becomes more important at smaller scales, altering both viscosity and inertia Viscosity is the resistance to change in form (internal friction) Inertia is the resistance of a body to a change in its state of motion Reynolds number incorporates both 17

Reynolds Number (Re) Inertia F i =  SU 2 Viscosity F v = µSU/L (decreases w/ temp) Re = F i /F v =  U L / µ µ = dynamic viscosity  = density U = velocity S = surface area L = length 18

Reynolds number for some organisms 19

Contrast of Properties Varied by Scale ParameterSmall organism (< 100 µm) Large organism (> 1 cm) ReLowHigh Viscosity (F u )HighLow Inertia (F i )LowHigh Body shapeVariableStreamlined Particle sinking ratesLowHigh Relative energy requirement for motility HighLow 20

Stokes Law Sinking rate of small spheres is a function of size and density of the sphere and viscosity and density of water 21 Stoke’s Law : where: g = gravitational acceleration (m / s 2 )  = coefficient of viscosity of the medium (kg/m/s) dens p = density of particle dens m = density of fluid r = radius of the particle Cells alter shape to change sinking rate (Melosira example)

Cell Morphology alters Sinking Rate 22

Water Chemical and Physical Properties Summary Hydrogen bonding High density, surface tension, heat of vaporization, heat capacity, liquid at earth’s surface, excellent solvent (important for weathering) Ions more soluble in warmer water, gasses less Unusual relationship between temperature and density Influence of water physical properties on organisms 23