Seawater and Its Constit

The Properties and Composition of The Properties and Composition of Seawater:Seawater:

An “Elemental” OverviAn “Elemental” Overviewew

Dave CohrsWater Quality Manager

National Aquarium in Baltimore, US

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

The Properties and Composition of The Properties and Composition of Seawater:Seawater:

An “Elemental” OverviAn “Elemental” Overviewew

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


WaterWater

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

ee-- ee-- ee--

ee--

105105oo

OO

HHHH


The Hydrological The Hydrological CycleCycle



(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)



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


The Composition of Seawater:The Composition of Seawater:It’s Elementary my dear WatsonIt’s Elementary my dear Watson

HH HH

OO

All of the naturally occurring elements are present in Seawater

Water 96.5% Everything Else 3.5%

ClCl--

The Composition of SeawaterThe Composition of Seawater

Major constituents – 11 Major Ions make up 99.9% of dissolved constituents by weight– >1mg L-1 Concentration– 21.9% Anions (Negatively Charged)– 12.6% Cations (Positively Charged)– Overall Salinity 34.482% (g kg-1 solvent)

Minor constituents Trace constituents

SOSO442-2-

BrBr--

MgMg2+2+

CaCa2+2+

KK++

SrSr2+2+ HCOHCO33--HH22BOBO33

--FF--

NaNa++HH22OO

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

SulfateMagnesium

CalciumPotassiumBicarbonate

BromideStrontium

BorateFluoride

1.2

4.68

65140

380400

13502700

1050019000

1

10

100

1000

10000

100000The Composition of The Composition of SeawaterSeawater

Major Constituents (mg kgMajor Constituents (mg kg--

11))


Sodium30.392%

Chloride54.995%

Sulfate7.815%

Magnesium4%

Calcium1.158%

Strontium0.023%

Fluoride0.003%

Bicarbonate0.405%

Borate0.013%

Potassium1.100%

Bromide0.188%

WaterWater~97%~97%

MajorMajorConstituentsConstituents

Minor ConstituentsMinor ConstituentsTrace ConstituentsTrace Constituents

The Composition of SeawaterThe 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


LithiumRubidiumPhosphorus

IodineBarium

Zinc

Molybdemum

Iron

Aluminum

NickelUranium

CopperArsenicVanadiumManganese

Titanium

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18The Composition of The Composition of SeawaterSeawater

Minor Constituents (mg kgMinor Constituents (mg kg-1-1))


Sodium30.392%

Chloride54.995%

Sulfate7.815%

Magnesium4%

Calcium1.158%

Strontium0.023%

Fluoride0.003%

Bicarbonate0.405%

Borate0.013%

Potassium1.100%

Bromide0.188%

WaterWater~97%~97%

MajorMajorConstituentsConstituents

Vanadium0.39%

Manganese0.39%

Titanium0.20%

Molybdemum1.96%

Aluminum1.96%

Iron1.96%

Nickel1.37%

Copper0.59%

Arsenic0.59%

Uranium0.59%

Zinc1.96%

Barium5.87%

Lithium33.27%

Rubidium23.48%

Phosphorus14%

Iodine11.74%

Minor ConstituentsMinor Constituents

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

HeliumCeriumScandium

IndiumTantalum

Dysprosium

Praseodymium

Gadolinium

ErbiumYtterbiumSamarium

ThoriumHolmiumRuthenium

BerylliumThuliumLutetium

Protactinium

RadiumRadon

1.00E-161.00E-151.00E-141.00E-131.00E-121.00E-111.00E-101.00E-091.00E-081.00E-071.00E-061.00E-051.00E-041.00E-031.00E-021.00E-011.00E+00

TinCobaltSilver

CesiumAntimony

MercuryKryptonCadmiumTungsten

Neon

SeleniumGermanium

Xenon

Chromium

LeadGallium

ZirconiumBismuth

Lanthanum

YttriumThalliumNiobium

Gold

Neodymium

Rhenium

1.00E-06

1.00E-05

1.00E-04

1.00E-03

1.00E-02

1.00E-01

1.00E+00

Tra

ce C

onstitu

ents (m

g kg

Tra

ce C

onstitu

ents (m

g kg

-1-1))


Sources of ConstituentsSources 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


Sources of ConstituentsSources 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)


Sources of ConstituentsSources 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]


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

0.1

1

10

100

1000

10000

100000

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

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

A Comparison of A Comparison of SeawaterSeawaterto other watersto other waters(mg kg(mg kg-1-1))


pH of SeawaterpH of Seawater

• pH– Concentration of Hydrogen (Hydronium Ion)

– The “p” stands for Power– pH = - log10[H3O+]– 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

– [H+] = 6.3 x 10-9 mol L-1

– pH ranges from 7.7 to 8.3 in surface waters

pH Scale is logarithmic- 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- 2H2O (l) = H3O+(aq) + OH-(aq)

HH33OO++

ee--ee--

OHOH--

ee- - ee--

ee- - ee--

ee- - ee

--


Alkalinity of Seawater 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[SO4

2-])– 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

-][CO3

2-]– [H3O+] = K [HCO3

-] [CO3

2-]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.


pH & AlkalinitypH & Alkalinity

100500456789101112pHnormal pH rangeof seawateraverage pHof seawaterH2CO3(carbonic acid)HCO3-

(bicarbonate ion)

CO32-

(carbonate ion)

H2CO3 H+ + HCO3- 2H+ + CO3

2-H2O + CO2


ORP of SeawaterORP 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


ORP of SeawaterORP 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


Nutrients in SeawaterNutrients 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


Nutrients in Aquarium SystemsNutrients 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


Chlorination and OzonationChlorination 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


Chlorination and OzonationChlorination 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


Chlorination and OzonationChlorination 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


Disinfection ByproductsDisinfection 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


Disinfection ByproductsDisinfection 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


Thank you,Thank you,Enjoy the rest of the conferenceEnjoy the rest of the conference

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Seawater and Its Constit

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