7/31/2019 02. Physics04

1/31

Physics and Ionic Content ofWater

2 September 2004

1. How does waters unusual temperature-density relationship

influence life in lakes?

2. What are the major substances dissolved in water?

3. How does the ratio of inertial forces to viscous forces

affect both water flow and how organisms experience their

environment?

7/31/2019 02. Physics04

2/31

Water has several unique propertiesthat make life in lakes possible

http://www.cdnarchitect.com/asf/enclosure_design_strategies/precedent_vs_innovation/images/waterspider.jpghttp://squam.boaters.home.att.net/images/squam/optimized_PC290070.JPG

7/31/2019 02. Physics04

3/31

Water molecules are dipoles:

d+

H H

O

d-

104.5

These hydrogen bonds form and break at a rate determined by

the temperature

And hydrogen bonding occurs:

7/31/2019 02. Physics04

4/31

Forms a tetrahedron when frozen

Kalff2002 Wetzel 2001

7/31/2019 02. Physics04

5/31

Density relationships

Density of ice is 0.9168 g/cm3at 0C, but water is 0.9999 g/cm3

As water is warmed from 0C, it increases in density until a

maximum of 1.000 is reached at ~4C (actually 3.94C).

Density of water is affected by pressure

Many lakes are too shallow for this to matter

Density of water is affected by salinity

7/31/2019 02. Physics04

6/31

7/31/2019 02. Physics04

7/31

An important consequence of hydrogen

bonding and the density relationships:

Ice floats

7/31/2019 02. Physics04

8/31

Other unique properties of water:

Water naturally occurs as a liquid, solid and gas

Water has a high specific heatthe amount of heat

in calories required to raise the temperature of 1 g

of water 1C

7/31/2019 02. Physics04

9/31

Water has a high surfacetensionmeasures the

strength of the surface film

www.wonderquest.com/ waterwalk-blueice-magneti...

Higher for any other liquidexcept mercury

Barrier to diffusion

Decreases with increasing

temperature

Can be disrupted byorganic compounds

Organisms live in and on

the surface film

http://www.wonderquest.com/waterwalk-blueice-magneticpoles.htmhttp://www.wonderquest.com/waterwalk-blueice-magneticpoles.htmhttp://www.wonderquest.com/waterwalk-blueice-magneticpoles.htmhttp://www.wonderquest.com/waterwalk-blueice-magneticpoles.htmhttp://www.wonderquest.com/waterwalk-blueice-magneticpoles.htmhttp://www.wonderquest.com/waterwalk-blueice-magneticpoles.htm

7/31/2019 02. Physics04

10/31

Ionic content of water:Water is a solvent for many ionic compounds

Salinitythe concentration of eight major ions (next slide)

Seawater = 32 g/L = ppt =

Freshwater < 3 g/L

Saline lakes = 18330 g/L

7/31/2019 02. Physics04

11/31

Principle dissolved substances (in order of abundance)

Cations Anions

Ca++ (Calcium) CO32- (carbonate)

Mg++ (Magnesium) HCO3- (bicarbonate)

Na++ (Sodium) SO42- (sulfate)

K+ (Potassium) Cl- (chloride)

7/31/2019 02. Physics04

12/31

Other substances are also present in fresh water at low

concentrations and have a negligible effect on salinity.

Some rare compounds are of great biological significance.

They are often referred to as Nutrients

PO43- (Phosphate)

NO3- (Nitrate)

SiO4- (Silicate)

7/31/2019 02. Physics04

13/31

Mechanisms controlling salinity:

1.Rock dominance

2. Atmospheric precipitation

3. Evaporation - precipitation balance

7/31/2019 02. Physics04

14/31

Saline Lakes formed in a closed basin when

evaporation exceeds inflow, yet that inflow issufficient to sustain a standing body of water.

Dominated by Na and Cl

Hard waters contain

large concentrations of

Ca and Mg salts

Soft waters water of

low salinity (dont have

many of the ions)

7/31/2019 02. Physics04

15/31

Water also dissolves gases

O2

CO2

N2

7/31/2019 02. Physics04

16/31

Explain the reasons for the shape of the

relationship between temperature and

density for water.

Why is the solid form of water (ice) lessdense than the liquid form?

What are 3 other properties of water that

are important to understand for limnology?

Why?

7/31/2019 02. Physics04

17/31

Dynamic Viscosityresistance of a liquid to motion

How to measure:

How much force is needed to move the plates?

Higher force, higher viscosity

7/31/2019 02. Physics04

18/31

Viscosity of water varies with temperature, warm water isless viscous than cold water

Viscosity at 0C = 1.792 x 10-3 kg/m/sViscosity at 30C = 0.801 x 10 -3 kg/m/s

The frictional resistance encountered by a swimming fish is

about 100 times greater than for organisms living in air

7/31/2019 02. Physics04

19/31

Forces acting on an organism in water:

1. viscosity

2. gravity

3. pressure4. motility

The relative impact of viscosity on the momentum of an

organism depends on:

the size of the organism

the speed of the organism

These determine relative contribution of viscous and inertial

forces

INERTIAL FORCES

VISCOUS FORCES

7/31/2019 02. Physics04

20/31

Inertial forces keep things going, viscous forces make things

stop

Gravity keeps pulling you downward

Pressure, in this case, is equal in all directions

Motility keeps you going

Viscosity determines how far you go

7/31/2019 02. Physics04

21/31

To determine relative importance of inertial forces to,

viscous forces use the ratio:

Inertial forces/Viscous Forces = Reynolds Number= Re

Re= ( U L) /

= density of the fluidU = Velocity of the organism (or current)

L = Length of the organism (or thickness of the water layer)

= viscosity

7/31/2019 02. Physics04

22/31

Small Re means that viscous forces dominate

A large Re means that inertial forces dominate

7/31/2019 02. Physics04

23/31

BrownianRe < 0.1

Depending on Re, organisms occupy one

of three realms

StokesianRe 0.1 low 100

ArchemedianRe > 500

7/31/2019 02. Physics04

24/31

BrownianRe < 0.1

Very small organism (e.g. phytoplankton) and

molecules

Viscous forces dominate

7/31/2019 02. Physics04

25/31

StokesianRe 0.1 low 100s

Stokes Law applies The terminal velocity of a

particle is proportional to 1/viscosity of water

Viscous forces still dominateif stop propelling,

stop moving

This influences the moving and feeding ofzooplankton

7/31/2019 02. Physics04

26/31

ArchemedianRe > 500

Inertial forces dominate

These organisms live in a turbulent environment

7/31/2019 02. Physics04

27/31

1 m 0.1 mm 1 cm 1 m 100 m

Re

0.000001

0.0001

0.01

1

100

10,000

1,000,000

Realms

Archimedean

Stokesian

Brownian

Hutchinson 1971

Phytoplankton

Zooplankton

Fish

7/31/2019 02. Physics04

28/31

Laminar flow is smooth and orderly,dominated by viscous forces (Re < 500)

Reynolds number also defines whether the

flow of water is laminarorturbulent

Turbulent flow contains a swirling of water and

chaotic eddies (Re > 2000)

7/31/2019 02. Physics04

29/31

Laminar flow is smooth and orderly,dominated by viscous forces (Re < 500)

Reynolds number also defines whether the

flow of water is laminarorturbulent

Turbulent flow contains a swirling of water and

chaotic eddies (Re > 2000)

7/31/2019 02. Physics04

30/31

Turbulent flow, not laminar flow,

is what mixes heat, gases,

nutrients etc. in the water

7/31/2019 02. Physics04

31/31

Terms to Know

hydrogen bonding

specific heat

surface tension

salinitynutrients

hard water

soft water

saline lakeviscosity

viscous force

inertial force

Reynolds number

Brownian RealmStokesian Realm

Archimedian Realm

laminar flow

turbulent flow