Water is one of the most important molecules on our planet!

Water is:

Many issues involving water are essential to environmental understanding and management.

Natural Water Cycles

Hydrologic cycle

Water reservoirs:

The Earth-Hydrosphere System*

Earth area 5.1 x 1018 cm2
Oceans area 3.6 x 1018 cm2
Land area 1.5 x 1018 cm2
Atmosphere mass 52 x 1017 kg
Ocean Mass 13,700 x 1017 kg
Pore waters in rocks 3,200 x 1017 kg
Water locked in ice 165 x 1017 kg
Water in lakes, rivers 0.34 x 1017 kg
Water in atmosphere 0.105 x 1017 kg
Total stream discharge 0.32 x 1017 kg year-1
Evaporation = precipitation 4.5 x 1017 kg year-1

* Aquatic Chemistry, by Strumm and Morgan, Wiley Interscience press. 2nd ed. 1981, p7.

Distribution of Earth's Surface Water**

Oceans 9.5 x 1019 mol (>99%)
Lakes and Rivers 1.7 x 1015 mol
Atmosphere 7.2 x 1014 mol

** Environmental Chemistry, by Nigel Bruce, Wuerz Publishing ltd. p117, 1991.

Figure 2.1. The hydrologic cycle, quantities of water in trillions of liters per day.

Figure 2.2. Distribution of percipitation in the continental U.S., showing average annual rainfall in centimeters.

United States water use

1.48 x 1013 liters of water rainfall per day in the U.S.
1.02 x 1013 liters per day evaporate

Water available for use per day
4.4 x 1012 liters per day

U.S. use per day
1.6 x 1012 liters per day

1994 per capita use of water 600 liters per day
1900 per capita use of water 40 liters per day

Natural waters acquire unique chemical composition through many physicochemical processes;

Surface and ground water dissolve minerals and acquire unique characteristics depending where they are located and reflect the activity and geology that they contact.

Why is water a unique solvent?
Property Significance
Universal solvent Transport medium for nutrients and chemicals making aqueous medium the primary medium
Highest dielectric constant Ability to stabilize ionic charged species and keep them in solution
Highest surface tension Governs drop and surface phenomena and physiological control mechanisms
Transparent to Vis- and UV light Colorless, permits light for photosynthesis
Maximum density at 4 degrees C Ice floats, vertical circulation restricted in stratified bodies of water (thermocline)
Higher heat of evaporation Determines transfer of heat and water distribution between atmosphere and water bodies; 585 cal/g at 20 degrees C
Highest heat capacity (except ammonia) Stabilization of temperatures of organisms and geographical regions1 cal /g/deg
Highest latent heat of fusion (except ammonia) Temperature stabilized a the freezing point of water

Dielectric Constant Effect of Solvent

Dielectric Constant is the ability of a solvent to cause particles of opposite charge to separate and function independently.

Solvent D (Dielectric Const.)
Water 78.5
Methanol 32.6
Ethanol 24.3
Ammonia 22.4
Acetone 20.4
Chloromethane 12.6
Methylene chloride 9.1
Acetic Acid 6.2
Chloroform 4.8
Ethyl ether 4.3
Toluene 2.4
Benzene 2.3
Carbon tetrachloride 2.2

Water is the best solvent for the stabilization of charged particles and to provide for their independent action.

Ref. - further reading can be done in - J. S. Fritz "Titrations in Nonaqueous Solvents" Boston: Allyn and Bacon, 1973; I. M. Kolthoff et al., Treatise on Analytical Chemistry, 2nd ed., I. M. Kolthoff and P. J. Elving, Eds., Part I, Vol 2 Chapter 19. New York: Wiley, 1979.

Definitions:

Hydrology is -- The study of water

Limnolgy is -- the study of fresh water including rivers, lakes, and biological properties and physical and chemical properties

Oceanography is -- the study of oceans including physical and chemical characteristics.

Natural waters are sub-classified using physical and chemical characteristics

Natural surface waters have many identifications:
wetlands, lakes, streams, estuaries, brines, etc.

Autotrophic organisms - utilize solar energy to fix elements into living organisms (photosynthesis)

Heterotrophic organisms - use organic substances produced by autotrophic organisms as their energy source; Decomposers are a subclass of heterotropic organisms made up mainly of bacteria and fungi.

Productivity is the ability of a water system to support living systems.

Eutrophication is a condition where algae grows rapidly due to excess nutrients and reduced oxygen levels to a point that fish and other higher life forms cannot survive.

DO or Dissolved in oxygen content of the water a water - a quality parameter

BOD or Biological oxygen demand is the amount of O2 used when the organic mater in a volume of water is degraded biologically - a water quality parameter

Anthropogenic - originating from man or human endeavors

* Aquatic Chemistry, by Strumm and Morgan, Wiley Interscience press. 2nd ed. 1981, p9.

Thermal stratification is the result of several of waters unique properties acting simultaneously

Figure 2.3. Stratification of a lake.

Figure 2.4. Major aquatic chemical processes.

The hydrologic cycle: distribution of water among atmospheric, freshwater, and seawater reservoirs and fluxes between reservoirs. Units: fluxes in 106 km3/year; inventories in 106 km3. The atmospheric inventory is reported as the liquid equivalent of water vapor.

Other cycles in the Environment

The various spheres interact in many and various ways to exchange:

Figure 2.5. General cycle showing interchange of matter among the atmosphere, biophere, anthrosphere, geosphere, and hydrosphere.

Endogenic and Exogenic Cycles

Endogenic cycles - involving subsurface rocks

Exogenic cycles - involving surface soil and were interfaces of geosphere, atmosphere, hydrosphere and biosphere occure.

Table 2.2. Interchange of material among the possible spheres of the enviroment.

Figure 2.6. General outline of exogenic and endogenic cycles.

Schematic representation of the cycling of inorganic, organometallic and organometalloidal compounds in the environment.

Carbon Cycle

  1. Biomass Development (refereed to a carbon fixation)

    CO2 + H2O + Electro Radiation (Sun light) ----> Biomass (CH2O) + O2

  2. Biomass conversion back to CO2 through Degradation

    Aquatic - 7-8 mg of organic mater will stoichiometrically consume all the O2 in 1L of water.
    Atomosphereic - In air direct O2 from Atomosphere
    Aerobic respiration conditions:
    From {CH2O} + O2 + Bacteria ----> CO2 + H2O

    Organic mater decomposition is also a significant source of CO2 in aqauatic systems and in soil

    Anaerobic respiration conditions:
    From 2{CH2O} + Bacteria ----> CO2 + CH4

  3. Atomosphere and Hydrosphere (Solubilization)

    CO2 + H2O <----> HCO3- + H+ <----> H2CO3

    Sequestration in the hydrosphere of atomosphereic CO2
    example CO2(aq)+ Ca2+(aq)+ 2X- + H2O < ---- > CaCO3(s) + 2HX

Figure 2.7. The carbon cycle.

Nitrogen Cycle

Additonional References:

Sources of nitrogen

N2 cannot be used by plants or animals

Conversion from N2 to NH3, NH4+, NO2-, NO3-, is required

Why is Nitrogen important to life?

It is one of the fundamental building blocks in:

Proteins, Nucleic acids, DNA, RNA
Precursors to - Hormones, Vitamins, Coenzymes, Porphyrins, Pigments, and Neurotransmitters.

Without it, plants and animals cannot grow or carry on molecule building syntheses

Chemical process can be nitrogen limited

Only Some forms of Nitrogen can be used directly by biological systems

Ammonia (NH3) can be used by all plants and animals for conversion into nitrogen containing complex molecules.

N2 cannot be used by most higher biological systems

N2 has a triple bond with a bond energy of 940 kJ/mole

Remember normal chemical bonds, remember normal bond strengthes are:

Molecule Bond Bond Energy in kJ/mol
Methane H-CH3 438.4 ± 1
CH3-C6H5 317.1 ± 6.3
CH3-CH2CCH3 308.4 ± 6.3
Ethyl alcohol H-OC2H5 436.0 ± 4.2
F-CF2Cl 490 ± 25

Nitrogen fertilizer is frequently ammonia based and is prepared by catalytic hydrogenation of N2.

How then does the Nitrogen form distributed by nature N2 differe from the Nitrogen form destributed by Man or Anthropogenic Nitrogen?

Nitorgen Fixation

Bacteria must convert N2 to NH3 for plants

Conversion of N2 to ammonia (NH3) is a very energy expensive process biologically (or energy demanding industrially)
Breaking a 940 kJ/mole bond for 2NH3 formed

This process requires an enzyme system (Nitrogenase System).

It consists of two proteins, Fe4S4 iron-sulfur cluster, and a Mo cofactor

Thus the oxidation of N2 to NH3 requires:

{Note: Enzyme is inhibited by O2 and nodule on legumes exclude O2 while N2 fixation is accomplished. It is thought that if nodules exist they will be inhabited by these bacteria}

All plants and bacteria can reduce ammonia (NH3) to nitrate (NO3-)

Most plants and animals transform nitrate to ammonia using the same steps also:

Carried out by Nitrate Reductase which includes Fe2S2

Nitrogen Pathways Common in Life

Most plants, animals, and bacteria share ammonia utilization pathways

This is why when you provide a plant NO3- or NH3 directly they can readily use it.

Biochemical Axiom:
In biochemistry you may enter metabolic cycle with any intermediate in the reaction.

At pH 7, ammonia exists in ammonium ion form NH4+

Remember pH and the equilibrium of water?

How is Nitrogen Processed

All organisms take ammonia to glutamate or carbamoyl phosphate


Conversion is accomplished by

  1. Nitrogen fixing bacteria (ultimately NH3)
    Cyanobacteria - soil
    Rhizobium - plants

    Called "biological nitrogen fixation"

  2. lightning in the atmosphere (primarily N2O, NO)

Plants in which nitrogen fixing bacteria function

Other plants require water soluble forms of nitrogen to grow

Completeing the Nitrogen Cycle

Reduction from Soluble nitrogen to N2 is denitrification
many bacteria in decay perform this task

Usually - As plants and animals decompose, they contribute water soluble nitrates to the soil making it available to the next generation of plants and to other plants

Nitrogen depletion occurs when land is planted with soluble nitrogen depleting plants repeatedly.

Harvested and Removed - Anthopogenic intervention in Nitrogen Cycle


Where else can Nitrates and Ammonia go?

Describe the processes that may accomplish this.

Since fertilizer is a soluble form of nitrogen, it leaches sometimes deep into the soil or aquifers:

  1. deep into the soil (and into the aquifers)
    No plant growth takes place deep in soil without a rout to the Sun, Fungi and Bacteria may use it in these layers

  2. It may be transported away from the soil as runoff (into streams, rivers, oceans)

Figure 2.8. The nitrogen cycle.

A living audit of Nitrogen use?

In protein use per day for an average person

The half- life of a nitrogen atom in the body is 2 hrs. to 6 months depending on where it gets incorporated.

Why the difference?

In active chemistry, such as enzymes, molecules are stable for a few hours as a particular protein

In structural collagen or hair tissue, these structural materials are not renewed for longer times

Overall turnover of proteins and nitrogen seems to have a 1st order kinetic rate. That indicates that it is a random process. Why?

Since proteins are the chemical producers of the body and are damaged by chemical and physical use perhaps this is a quality control step to maintain structural integrity. DNA can be repaired but proteins are not once they are made.

What are the ramifications of this process?

Protein turnover also represents a route for cellular adaptation to altered environmental conditions.

Examples such as body adaptation to new foods, new life stile (more body smooth muscle when you are working hard over a period of time)

Other N2 process related to pollution

Burning in a furnace

NOx Air Pollutants
NO2 & N2O Emissions 1989 1980
North & Central Am. 21,600,000 22,300,000
Asia 1,400,000 ?
Europe ~15,000,000 ?
USSR 4,190,000 ?

Principle source of NOx compounds is from combustion processes:

Then NO combines with O2 in air to convert to NO and NO2 within a few hours under normal conditions after NO is fromed in furnace.

All Oxides of nitrogen with water form nitric acid HNO3
N2O, NO, N2O3, NO2, N2O4, N2O5

NOx's are produced and released into the air by the burning of fuels including:
Coal, Gas, Oil, Wood, etc. and increase with temperature

NOx Prevention

Primary method of prevention is reduced the temperature of the oxidation in the presence of Air and N2.

The oxidation reaction N2 + O2 <----> 2NO is very temperature dependent and is favored to the right at high temperatures.

Scrubbing with various bases can be used if the process permits.

NOxs are water soluble (that is why they are in acid rain)

Auxiliary references:

How Bacteria convert N2 to NH4+
Biochemistry, Stryer, Freedman, 1981, pg 486-488

Metabolism of Nitrogen Compounds: Principles of Biosynthesis, Utilization, turnover, and Excretion
Chapter 20 pages 670-704

Biochemistry, Mathews and van Holde, The Benjamin/Cummings Publishing Co., 1990

Sulfur Cycle

Like carbon and nitrogen, sulfur is made available to organisms largely in the form of inorganic compounds such as sulfates.

The process is mostly confined to plants and bacteria.

Higher mammals use complex sulfur containing molecules from food.

Two important animo acids, Cysteine and Methionine, contain sulfur.

Sulfur enters the atmosphere from many natural sources

1/3 of all sulfur and 99% of all Sulfur Dioxide (SO2) entering the atmosphere is anthropogenic.

Of the anthropogenic portion, 2/3's is from electric power production

In the atmosphere, sulfur dioxide is transformed to sulfur trioxide with molecular oxygen and then with water to sulfuric acid.

Figure 2.10. The sulfur cycle.

Outdoor Sulfur Air Pollutants

Pollution Emissions
Anthropogenic compositional alterations to the atmosphere:
From 1989 Compilation (from United Nations Reference)

SO2 Emissions in Metric Tons 1989 1980
North & Central Am. 20,700,000 23,900,000
Asia ? 1,263,000
Europe ~23,000,000 ?
USSR 9,318,000 12,800,000

Atmospheric Sources

Primary forms are SO2, H2S, in the gas phase and SO4-2 in the condensed phases. From the burning of sulfur containing fuels. From bacterial reduction of SO4-2 to H2S and sulfur containing proteins. Natural sources are volcanoes which produce large quantities of SO2 and biological processes.

Notes on significance:
SO2 and NO2 (NOx) in the presence of water contribute to acid precipitation (acid rain) and photochemical smog. Acid Rain adversely effects agriculture, forests, aquatic habitats, and the weathering of building materials. SO2 and NO2 aerosols impair visibility.

SO2 concentrations as low as 0.1-0.2 ppm can incapacitate asthma or emphysema patients.

SO2 combines with water to form sulfuric acid H2SO4

Prevention of Sulfur Pollution

  1. Primary methods of preventing SO2 is removal of "S " compounds prior to combustion of carbon or hydrocarbon "desulfurization" of Coal or Fuel Oil.

  2. Scrubbing (bubble through solution of calcium oxide CaO (lime) forming CaSO4)

Additional References:
In the Introduction to Env. Sci. text.
Living in the Environment, by Miller, 7th ed. Wadsworth Publishing Co. CA, 1992. Text pgs 98-99

The Phosphate cycle

Primarily obtained from geological sources for plants.

Primarily obtained in food for higher animals

It is like Nitrogen a fertilizer and therefore a source of run off and the other related mechanisms of nitrogen.

It is however a complexing agent unlike nitrogen compounds (except ammonia which is also a complexing form of nitrogen)

It is required for life and is the primary energy exchange medium as well as a fundamental building block of many important biological molecules.

Figure 2.9. The phosphorus cycle.

Oxygen Cycle deferred to chapter 9 and the atmosphere



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Revised 4/15/99.