The Properties and Composition of Seawater--An “Elemental” Overview by malj

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									The Properties and Composition of Seawater:
         An “Elemental” Overview

                 Dave Cohrs
            Water Quality Manager
      National Aquarium in Baltimore, US
The Properties and Composition of Seawater:
         An “Elemental” Overview

    Water and the Hydrological Cycle
    Elemental Trends – The Composition of Seawater
    Sources of Constituents
    pH, Alkalinity, ORP
    Nutrients: Natural vs. Artificial Environments
    Chlorination and Ozonation
    Disinfection byproducts


                   1st AQUALITY Symposium, April 2 - 7, 2004, Oceanario de Lisboa, Portugal
                                 e-                             e-
                            e-                                       e-



              Water
                                                O
                                 H             105o            H
   H2O
   Asymmetrical polar structure = permanent dipole
   Highest heat capacity of all solids and liquids (except
    ammonia) 4.184kJ/mol
   Highest surface tension of all liquids
   Dissolves more substances, in greater quantities than any
    other liquid
     – Seawater contains ~3.5% dissolved substances
   Highly transparent
                          1st AQUALITY Symposium, April 2 - 7, 2004, Oceanario de Lisboa, Portugal
The Hydrological Cycle




     1st AQUALITY Symposium, April 2 - 7, 2004, Oceanario de Lisboa, Portugal
             The Hydrological Cycle

   (Water x 1015kg)
     – Rivers and Streams (1)
     – Soil Moisture and Seepage (70)
     – Salt Lakes and Inland Seas (104)
     – Freshwater Lakes (125)
     – Groundwater (8400)
     – Glaciers and Icecaps (29300)
   Total amount of Water on Land (38000)
   Total amount of Water in the Oceans (1322000)
   Total Water Supply (1360000)



                    1st AQUALITY Symposium, April 2 - 7, 2004, Oceanario de Lisboa, Portugal
               The Hydrological Cycle

 The Oceans contain 97% of the global water inventory
 Less than 1% is available for drinking
 Density of Freshwater = 1.00x103 kg m-3
 Density of Seawater = 1.03x103 kg m-3
 Salinity = Average Concentration of Dissolved Substances
   – Surface waters: salinities range from 33 to 37 mg kg-1
   – Average: 35 mg kg-1 (3.5% by weight)
   – Salinity is a function of density and temperature (oC)
   – The density of seawater normally increases with depth
   – Now measured as R = conductivity of seawater sample
                            conductivity of standard KCl solution
                             Where KCl solution = 32.4356 g kg-1


                      1st AQUALITY Symposium, April 2 - 7, 2004, Oceanario de Lisboa, Portugal
     The Composition of Seawater:
    It’s Elementary my dear Watson

 All of the naturally occurring elements
  are present in Seawater
                                                              H                H
 Water 96.5%                                                         O
 Everything Else 3.5%




                 1st AQUALITY Symposium, April 2 - 7, 2004, Oceanario de Lisboa, Portugal
            The Composition of Seawater

   Major constituents              H2O      Cl-
    – 11 Major Ions make up 99.9% of dissolved      Na+
    constituents by weight                             SO42-
    – >1mg L-1 Concentration
    – 21.9% Anions (Negatively Charged)
    – 12.6% Cations (Positively Charged)
                                                           Mg2+
    – Overall Salinity 34.482% (g kg-1 solvent)
 Minor constituents                                       Ca2+
 Trace constituents
                                                           K+
       F-     Sr2+      H2BO3-         Br-         HCO3-
                                                                                                                                       100000
The Composition of Seawater
                                                                                                                                       10000


     19000                                                                                                                             1000
          10500
                        2700
                                  1350
                                                                                                                                       100
                                                400 380
                                                                      140
                                                                                        65
                                                                                                                                       10
                                                                                                   8          4.6
                                                                                                                       1.2             1




                                                                                                                            Fluoride
                                                                                                                   Borate
                                                                                                       Strontium
                                                                                         Bromide
                                                                          Bicarbonate
                                                              Potassium
                                                    Calcium
                                        Magnesium
                             Sulfate
                    Sodium
         Chloride




                                                Major Constituents (mg kg-1)
                                       1st AQUALITY Symposium, April 2 - 7, 2004, Oceanario de Lisboa, Portugal
                                                                           Water
                                                                           ~97%


Trace Constituents
Minor Constituents

                             Chloride
                            54.995%

                                                                Sodium
                                                               30.392%              Major
                                                                                 Constituents
                                                   Sulfate
                Fluoride
                                                  7.815%
                0.003%
    Strontium
     0.023%
                                                              Magnesium
       Borate
                                                                 4%
      0.013%
                  Bromide                            Calcium
                               Bicarbonate Potassium
                  0.188%                    1.100%   1.158%
                                   1st AQUALITY Symposium, April   2 - 7, 2004, Oceanario de Lisboa, Portugal
                                 0.405%
                The Composition of Seawater

 Minor constituents
    – < 1 mg L-1 but >0.001 mg L-1 (= 1 ppb)
 Trace constituents
   – <0.001 mg L-1
 Other
   – Nitrogen, Silicon, Oxygen not included
          Nitrogen is mostly present as a gas (N2)
          O, Si considered non-conservative (they vary considerably)
    – Dissolved Organic Carbon
          Approximately 0.6mg L-1 in surface waters (Williams, Spotte)
             –Carbohydrates, phenols from algae, phytoplankton blooms
          Higher in Aquarium Systems
             – Yellow water
The Composition of Seawater                                                                                                                                               0.18
                                                                                                                                                                         0.16
                                                                                                                                                                         0.14
                                                                                                                                                                         0.12
                                                                                                                                                                         0.10
                                                                                                                                                                         0.08
                                                                                                                                                                         0.06
                                                                                                                                                                         0.04
                                                                                                                                                                         0.02
                                                                                                                                                                         0.00




                                                                                                                                                              Titanium
                                                                                                                                                  Manganese
                                                                                                                                       Vanadium
                                                                                                                             Arsenic
                                                                                                                    Copper
                                                                                                          Uranium
                                                                                                 Nickel
                                                                                      Aluminum
                                                                               Iron
                                                                  Molybdemum
                                                           Zinc
                                                  Barium
                                         Iodine
                            Phosphorus
                 Rubidium
       Lithium




                                                                Minor Constituents (mg kg-1)
                                                    1st AQUALITY Symposium, April 2 - 7, 2004, Oceanario de Lisboa, Portugal
              Aluminum Nickel Uranium Copper
               1.96% 1.37% 0.59% 0.59% Arsenic         Vanadium
                                             0.59%       0.39%
                  Iron
   Molybdemum                                               Manganese

                                                                                           Water
                 1.96%
      1.96%                                                   0.39%
      Zinc                                             Titanium
                                                        0.20%
                                                                                           ~97%
     1.96%
      Barium                                 Lithium
      5.87%                                  33.27%
                   Iodine
                  11.74%
                  Phosphorus
                     14%          Rubidium
                                  23.48%




Minor Constituents

                                Chloride
                               54.995%

                                                                                 Sodium
                                                                                30.392%           Major
                                                                                               Constituents
                                                                     Sulfate
                Fluoride
                                                                    7.815%
                0.003%
    Strontium
     0.023%
                                                                               Magnesium
        Borate
                                                                                  4%
       0.013%
                  Bromide                                 Calcium
                                    Bicarbonate Potassium
                  0.188%                         1.100%   1.158%
                                        1st AQUALITY Symposium, April            2 - 7, 2004, Oceanario de Lisboa, Portugal
                                      0.405%
                                                                                                           Tin
                                                                            Hafnium                     Cobalt
                                                                              Helium                     Silver
                                                                              Cerium                   Cesium
                                                                                                     Antimony
                                                                            Scandium
                                                                                                       Mercury
                                                                              Indium
                                                                                                       Krypton
                                                                            Tantalum                 Cadmium
                                                                           Dysprosium                Tungsten
                 Praseodymium                                                                             Neon
                                                                            Gadolinium                 Selenium
                                                                               Erbium               Germanium
                                                                            Ytterbium                     Xenon
                                                                            Samarium                  Chromium
                                                                              Thorium                       Lead
                                                                                                          Gallium
                                                                              Holmium
                                                                                                       Zirconium
                                                                            Ruthenium
                                                                                                         Bismuth
                                                                              Beryllium
                                                                                                     Lanthanum
                                                                               Thulium                    Yttrium
                                                                               Lutetium                  Thallium
                                                                            Protactinium                  Niobium
                                                                                Radium                        Gold
                                                                                 Radon               Neodymium
                                                                                                         Rhenium
                                                                                         1.00E-16
                                                                                         1.00E-15
                                                                                         1.00E-14
                                                                                         1.00E-13
                                                                                         1.00E-12
                                                                                         1.00E-11
                                                                                         1.00E-10
                                                                                         1.00E-09
                                                                                         1.00E-08
                                                                                         1.00E-07
                                                                                         1.00E-06
                                                                                         1.00E-05
                                                                                         1.00E-04
                                                                                         1.00E-03
                                                                                         1.00E-02
                                                                                         1.00E-01
                                                                                         1.00E+00
                                                                                                                 1.00E-06
                                                                                                                            1.00E-05
                                                                                                                                       1.00E-04
                                                                                                                                                  1.00E-03
                                                                                                                                                             1.00E-02
                                                                                                                                                                        1.00E-01
                                                                                                                                                                                   1.00E+00




1st AQUALITY Symposium, April 2 - 7, 2004, Oceanario de Lisboa, Portugal
                   Sources of Constituents

   Volcanic Activity/Atmospheric Interactions
    –   Gaseous Emission
           Chlorine (as Chloride) and other Halogens
           Sulfur
           Carbon Dioxide and Methane
   Activity on the Sea Floor
    –   Dissolution of minerals in rock of the oceanic crust from
        hydrothermal circulation
    –   Calcium, Magnesium & other Alkali Earth Metals (Group II)
    –   Organically-Rich Marine Sediments (Copper, Uranium, Zinc)
   Weathering of Igneous and Metamorphic Rock by rainfall
    and other mass movement of water on land


                             1st AQUALITY Symposium, April 2 - 7, 2004, Oceanario de Lisboa, Portugal
                   Sources of Constituents

   Major Constituents
    – Most behave conservatively
          SiO2 and Ca2+ are notable exceptions
          Bio-Unlimited Constituents (i.e. Sodium, Chloride)
          Bio-Intermediate Constituents
             – Depleted in surface waters, but never exhausted
   Minor and Trace Constituents
    – Unlike Major constituents, most Minors and Traces:
          Behave non-conservatively
          Concentrations are affected by biological or chemical processes
             – Depleted from or added to the water
          Toxic above certain concentrations
             – (See AQUALITY discussion on heavy metals by Conklin)


                             1st AQUALITY Symposium, April 2 - 7, 2004, Oceanario de Lisboa, Portugal
                   Sources of Constituents
   Gases
    – Solubility of gases increases with decreasing temperature
    – Nitrogen (N2)
        About 11 of the 11.5 mg L-1 total Nitrogen in seawater

    – Oxygen (O2)
        Surface waters are consistently supersaturated due to liberation of
          oxygen by phytoplankton and wave activity driving gases into solution
    – Carbon Dioxide (CO2)
        Present in seawater as carbonic acid, bicarbonate, and carbonate

        Only about 0.23 mg L
                               -1 at 24oC as gas

        Increasing atmospheric content during the last 60 years

    – Other Gases
        Sulfur Dioxide (SO2) Air to Sea [acid rain, vulcanism]

        Carbon Monoxide (CO) Sea to Air [microbial decomposition]

        Nitrous Oxide (N2O) Sea to Air [microbial decomposition]

        Methane (CH4) Sea to Air [anoxic conditions/microbial]

        Methyl Iodide (CH3I) Sea to Air [Phytoplankton/Anoxic conditions]

        Dimethyl Sulfide ((CH3)2S) Sea to Air [Phytoplankton/Anoxic conditions]
                             1st AQUALITY Symposium, April 2 - 7, 2004, Oceanario de Lisboa, Portugal
A Comparison of Seawater                                                          100000

to other waters                                                                   10000
(mg kg-1)
                                                                                  1000

                                                                                  100

                                                                                  10

                                                                                  1

                                                                                  0.1
                                                                    K+    Na+
                                               Cl-   Ca2+ Mg2+
                   SiO2   Br-   HCO3- SO42-

              Na+         K+      Mg2+        Ca2+       Cl-      SO42-     HCO3-         Br-      SiO2
Seawater      10500       350      1340       420      19000       2700         140       65        1.2
River Water    7           2        5          15         9        10           55         0        11
Rainwater      2          0.3      0.2        0.15        4        0.7          0.3        0        0
                                    1st AQUALITY Symposium, April 2 - 7, 2004, Oceanario de Lisboa, Portugal
                              pH of Seawater
• pH
   – Concentration of Hydrogen (Hydronium Ion)                                       H3O+
      – The “p” stands for Power
          – pH = - log10[H3O+]                                                                     e-
                                                                                                  e-
          – Example…pH 8.2
                   – 8.2 = - log[H+]
                   – - 8.2 = log[H+] (flip the sign and take Antilog)
                   – [H+] = 10-8.2 mol L-1                                              e- e-
                   – [H+] = 6.3 x 10-9 mol L-1
          – pH ranges from 7.7 to 8.3 in surface waters

 pH Scale is logarithmic




                                                                           e- e-
                                                                                         OH-
   -   At pH 7, there is 10x more H3O+(aq) than at pH 8
   -   Conversely, there is 10x more OH-(aq) at pH 8 than at pH 7
   -   10-14 = [H+][OH-]
   -   14 = pH + pOH                                                                    e- e-
   -   2H2O (l) = H3O+(aq) + OH-(aq)
                                 1st AQUALITY Symposium, April 2 - 7, 2004, Oceanario de Lisboa, Portugal
                      Alkalinity of Seawater
•  Formally, the net molar concentration of strong base cations
in excess of the net molar concentration of strong acid ions (in
terms of charge equivalents)
       – A = [Strong Base Cations] – [Strong Acid Anions]
       – A = ([Na+] + [K+] +2[Mg2+] + 2[Ca2+]) – ([Cl-] + [Br-] + 2[SO42-])
            – Seawater is electrically neutral
            – This works out to about 2 mol m-3
        – Therefore…
             – A = [HCO3-] + 2[CO32-]
             – A ≈ 2 mol m-3 throughout the oceans (A ≈ 140 mg kg-1)
        – K = [H3O+][HCO3-]
                 [CO32-]
        – [H3O+] = K [HCO3-]
                      [CO32-]
        Therefore the ratio of the concentration of bicarbonate and carbonate ions
        must control the hydronium concentration and pH! As the ratio increases,
        so does the pH.
                              1st AQUALITY Symposium, April 2 - 7, 2004, Oceanario de Lisboa, Portugal
                                pH & Alkalinity
H2O + CO2                   H2CO3            H+ + HCO3-                        2H+ + CO32-
100

          H2CO3
          (carbonic acid)
                                                                           CO32-
                                                                           (carbonate ion)

50

                                                             average pH
                                                             of seawater
                    HCO3-
                                                                normal pH range
                    (bicarbonate ion)
                                                                of seawater

 0
      4        5            6      7           8            9            10           11          12
                                               pH
                                 1st AQUALITY Symposium, April 2 - 7, 2004, Oceanario de Lisboa, Portugal
                         ORP of Seawater
   Oxidation-Reduction Potential
     – OILRIG (Oxidation is Loss of electrons, Reduction is Gain of
     electrons)
     – The oxidation state of elements with more than one valence state
     greatly affects their solubility
         – Oxidized form of Iron (III) Fe(OH)3 – very low solubility,
         suspended colloid
         – Reduced form Iron (II) Fe(OH)2 – more soluble
     – Therefore, for waters of High ORP:
         – Available Iron will be very low
         – This is true for Cobalt, Manganese
              – Precipitated as hydroxides or hydrated oxides
     – Biological significance where ORP varies dramatically

                             1st AQUALITY Symposium, April 2 - 7, 2004, Oceanario de Lisboa, Portugal
                           ORP of Seawater
   ORP of seawater
         – Very complex due to all of the redox couples present

     – Natural waters
         – In natural waters, redox reactions are usually quite different from
         what would be predicted based on thermodynamics (Horne 1965,
         Stumm and Morgan 1981).
         – Surface waters are oxygen rich – Oxidizing
         – Sediments, mangrove habitats, low oxygen, organics - Reducing
     – Aquarium systems
         – Generally considered to be a measure of the state of “cleanliness”
         – Use a platinum/combination electrode
         – Make sure the filling solution matches the ionic strength of the
         solution
         – Check against reference standards (Zobell’s or pH buffers with
         Quinhydrone)
         – 275 – 350mV is an acceptable “safe” range
                               1st AQUALITY Symposium, April 2 - 7, 2004, Oceanario de Lisboa, Portugal
                      Nutrients in Seawater
   Nutrients
          – Polyatomic compounds containing Nitrogen, Phosphorus, Silicon

      – Nitrogen
          – Ammonia (NH3+NH4+), Nitrite (NO2-), Nitrate (NO3-), N2
                – Nitrogen gas 11 mg L-1
                – [NH3+NH4+] + [NO2-] + [NO3-] = ≤ 0.5 mg L-1
      – Phosphorus
          – Phosphate (PO43- ) 0.06 mg L-1
      – The Magic Ratio
          – Nitrogen:Phosphorus 15:1 molar ratio
                – Same in both Tissue and Seawater
      – Nutrients are depleted in surface waters, increase with depth
      – Biologically limiting
                                1st AQUALITY Symposium, April 2 - 7, 2004, Oceanario de Lisboa, Portugal
        Nutrients in Aquarium Systems
- Ammonia (NH3+NH4+), Nitrite (NO2-)
    – typically very low concentrations in stable systems where
    filtration is adequate, well maintained
    – Toxic in relatively low concentrations
– Nitrate (NO3-)
    – Typically accumulates in fish or marine mammal systems
    – May be depleted in photosynthetically active systems (corals)
    – Biological effects at high concentration (much debate!)
        – Water exchanges
        – Denitrification systems (see Hignette, Mort, Aiken)
        – Algal turf scrubbing (Adey, et al)
        – Electrochemical reduction
– Phosphorus
    – Also can climb to undesirable levels, stimulating algal growth
                       1st AQUALITY Symposium, April 2 - 7, 2004, Oceanario de Lisboa, Portugal
            Chlorination and Ozonation
   Increasing ORP: Add an oxidant
    – Sanitization or sterilization
             – Mammal, marine mammal, or avian pools
             – Human/Animal interaction
             – Control of coliform and other bacteria
    – Improve clarity
    – Improve color
   Consider Bromine and Chlorine in Seawater
    – Bromine (as Bromide) 65 mg L-1
    – Chlorine (as Chloride) 19000 mg L-1
          Both species react with Chlorine (typically NaClO) or
           Ozone (O3) to form weak acids
             – Strong oxidizing power
             – Increased ORP
             – Side Effects
                         1st AQUALITY Symposium, April 2 - 7, 2004, Oceanario de Lisboa, Portugal
                Chlorination and Ozonation
   Inorganic Reaction Products of Chlorination
    – NaOCl + H2O<-> HOCl + Na+ + OH-
    – HOCl <-> OCl- + H+
        hypochlorous acid - hypochlorite
    – HOCl + Br -<-> HOBr + Cl-
        HOBr <-> OBr- + H+

        hypobromous acid - hypobromite

           – HOCl + OCl- = Free Chlorine
           – HOBr + OBr- = Active Bromine
    – Bromine (as bromide impurity) is sometimes restricted
      when selecting salts for seawater formulation to prevent
      unwanted reactions


                           1st AQUALITY Symposium, April 2 - 7, 2004, Oceanario de Lisboa, Portugal
                    Chlorination and Ozonation
   Inorganic Reaction Products of Ozonation
    –   O3 + Cl- <-> O2 + OCl-
    –   O3 + Br - <-> O2 + OBr -
    –   OCl- + Br - <-> OBr - + Cl-
    –   HOCl + Br -<-> HOBr + Cl-
          HOBr <-> OBr- + H+

    – Monochloramines
            NH3 + HOCl <-> NH2Cl + H2O
    – Mono and Dibromamines
            Monobromamines prevail at NH4-N >0.8mg L-1
            Bromine oxidation predominates in seawater so bromamines are
             favored



                               1st AQUALITY Symposium, April 2 - 7, 2004, Oceanario de Lisboa, Portugal
                Disinfection Byproducts
– Nothing is Free. Unfortunately, Blue Water has a price…
    – Disinfection byproducts can and do form during Chlorination and
    Ozonation
    – Dissolved organic substances
– Disinfection Byproducts
    –THM trihalomethanes. Known mutagens and carcinogens!
    – Humic and fulvic acids are precursors (cause yellow water)
        – Chloroform, Bromoform, Bromochloromethane,
        Dibromochloromethane
    – Packed column aeration for removal of volatile THM and NCl3
    – Bromate, Chlorate potential carcinogens
        – Regulated DBP in drinking water
        – Both species are stable and hard to get rid of, once formed


                        1st AQUALITY Symposium, April 2 - 7, 2004, Oceanario de Lisboa, Portugal
             Disinfection Byproducts

- Bromate and Chlorate
   – O3 + Br - <-> O2 + OBr   –

   – O3 + OBr – <-> 2O2 + Br      –

   – 2O3 + OBr – <-> 2O2 + BrO3       –


   – Sunlight induces conversion of up to 50% of OBr - to BrO3- in
   chlorinated seawater (Macalady et al. 1977)
   – Chlorate production favored in chlorinated natural seawater
   receiving strong sunlight (personal observation)
   – Bromate has been shown to be reduced to Br - by activated
   carbon (Marhaba, Medlar et al.)
   – USEPA D/DBP MCL in finished drinking water
       – Bromate to 10µg L-1
       – Chlorite to 1000µg L-1

                      1st AQUALITY Symposium, April 2 - 7, 2004, Oceanario de Lisboa, Portugal
          Thank you,
Enjoy the rest of the conference




         1st AQUALITY Symposium, April 2 - 7, 2004, Oceanario de Lisboa, Portugal

								
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