water composition & quality criteria

8/13/2019 Water Composition & Quality Criteria

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Water Composition and quality criteriaWater Composition and quality cr iteria

Composition of seawater, major and minor elements, dissolvedelements in seawater

Salinity, concepts, how to determined, salt balance.

Residence time

Composition of freshwater

Dissolved gases

Thermal and chemical stratifications

Nutrients status: Eutrophy, oligotrophy and dystrophy



Composition of Seawater

Seawater is composed of a number of dif ferent components that can bedivided into following phases:

1. Solids (materials that does not pass through a 0.45µm fil ter):

- Particulate organic matter (plant detritus) and

- Particulate inorganic matter (minerals detritus)

2. Gases:

- Conservative (N2, Ar, Xe) and

- Non-conservatives (O2 and CO2)

3. Colloids (passes through a 0.45µm filter, but is not dissolved):

- Organic and- Inorganic

4. Dissolved solutes:

- Inorganic solutes (1) Major (>1ppm) and (2) minor (<1ppm) and

- Organic solutes.



ConstituentConcentration

(ppt)Ratio of constituent/total salts

(%)

Chloride (Cl-)

Sodium (Na+)

Sulfate (SO42-)

Magnesium (Mg2+)Calcium (Ca2+)

Potassium (K +)

Bicarbonate(HCO3-)

Bromide (Br -)

Boric Acid (H3BO3)Strontium (Sr 2+)

Fluoride (F-)

---------------------

Total

18.98

10.556

2.649

1.2720.4

0.38

0.140

0.065

0.0260.013

0.001

------------------

34.482

55.04

30.61

7.68

3.691.16

1.10

0.41

0.19

0.070.04

0.00

--------------------------------------

99.99%

Major consti tuents in seawater



Table : Concentration of minor elements in Seawater

Element Symbol Concentrat ion (mg/L)

SiLi

Rb

P

I

N

Ba

Fe

Zn

Al

Mo

Cu As

I

Mn

3.00.17

0.12

0.07

0.06

0.05

0.03

0.01

0.01

0.01

0.01

0.0030.003

0.002

0.002



The physical properties of pure water and seawater are remarkably

similar with few exceptions. Some of those are as follows:

Property Pure water Seawater

Color

-Small quantities

- Large quantities

Clear

Blue-green because water

molecules scattered blue

and green wavelengths

best

Clear

Same as pure water

Odor Odorless Distinctly marine

Taste Tasteless Salty

pH 7.0 (neutral) 8.1 (slightly alkaline)

Density at 4oC 1.00g/cm3 1.028g/cm3

Freezing point 0oC -1.9oC

Boiling point 100oC 100.6oC



The table does not represent the last word in seawatercompositions.

Water flow across vegetation areas also dissolved variousorganic compounds and particulate organic matters both

organic and inorganic. Mixing well in surface runoff andenriched river water.

All those constituents finally deposited in to oceanic systemand constitutes seawater as complex media.



From table the ratio is:From table the ratio is:

Conc. K+Conc. K+

---------------------------------- = 0.380/34.482 = 0.011= 0.380/34.482 = 0.011

Total salinityTotal salinity

If salinity rise to 36If salinity rise to 36‰‰

Conc. of K+Conc. of K+

---------------------------------- = 0.011= 0.011

3636

So, Conc. of K+ = 0.011 x 36 = 0.396So, Conc. of K+ = 0.011 x 36 = 0.396 ‰‰ (by weight)(by weight)



The chloride ion in river originates mainly from the sea.

It leaves the ocean as an aerosol and carried in the atmosphere

to fall as rain and return to sea via rived.

In sea water chloride is the most abundant, but in river waterbio-carbonate is most abundant, chloride rank in 6th position.

Volcanoes produce large quantities of hydrogen chloride gas and the

high level of volcanic activity early in the Earth history is probably the

sources of majority of the chloride present in today’s ocean.



Table: Approximate average percentages by weight of the tenTable: Approximate average percentages by weight of the ten

most abundant elements in Earthmost abundant elements in Earth’’s crusts crust

ElementElement % by weight% by weight

SiliconSilicon 2828

Aluminum Aluminum 8.28.2

IronIron 5.65.6CalciumCalcium 4.24.2

SodiumSodium 2.42.4

PotassiumPotassium 2.42.4

MagnesiumMagnesium 2.02.0TitaniumTitanium 0.60.6

ManganeseManganese 0.10.1

PhosphorusPhosphorus 0.10.1



Operation ofOperation of hydrological cyclehydrological cycle provides most of theprovides most of the

dissolved const ituents in seawater dissolved constituents in seawater

Another important process that contribute in seawater Another important process that contribute in seawater

composition is:composition is: Hydrothermal ventHydrothermal vent circulation at thecirculation at the

ocean ridge crustsocean ridge crusts

Some of most abundant elements not appear at all inSome of most abundant elements not appear at all in

major ionic composition.major ionic composition.

The region lies in the degree of solubi lity and theThe region lies in the degree of solubi lity and the

chemical behavior of different elements when rocks arechemical behavior of different elements when rocks areweathering and resulting products carried by surfaceweathering and resulting products carried by surface

run off through river to sea.run off through river to sea.



Many of the commonest elements in rocks, such as silicon,Many of the commonest elements in rocks, such as silicon,

aluminium, and iron arealuminium, and iron are not solublenot soluble..

So, they transported and deposited mainly as solid particles ofSo, they transported and deposited mainly as solid particles of

sand and clay.sand and clay.

Sodium, calcium and potassium are relativelySodium, calcium and potassium are relatively solublesoluble andand

transported mainly in solution.transported mainly in solution.

Hydrothermal solution associated with sea floor spreading supplyHydrothermal solution associated with sea floor spreading supply

some elements to seawater solution (e.g. calcium, silicon,some elements to seawater solution (e.g. calcium, silicon,

manganese) and remove others from it (e.g. magnesium, sulfur)manganese) and remove others from it (e.g. magnesium, sulfur)

However, the relative amounts of dissolved consti tutes withinHowever, the relative amounts of dissolved consti tutes withinocean are controlled by complex and bio logical reactions inocean are controlled by complex and bio logical reactions in

seawater seawater



Definition: SalinityDefinition: Salinity

Originally salini ty was defined to the total amount ofOriginally salini ty was defined to the total amount of

dissolved materials in grams in one kilogram of seadissolved materials in grams in one kilogram of sea

water.water.

This is not useful because the dissolved materials isThis is not useful because the dissolved materials is

almost impossible to measure in practice. As volatilealmost impossible to measure in practice. As volatile

materials like gases difficult to measure.materials like gases difficult to measure.

If seawater evaporate to dryness chlorides are lost inIf seawater evaporate to dryness chlorides are lost in

the last stages of dryingthe last stages of drying



Concepts of salinity

Salinity is the total amount of dissolved material inSalinity is the total amount of dissolved material ingrams in one kilogram of sea water. Thus salinity is agrams in one kilogram of sea water. Thus salinity is adimensionless quantity.dimensionless quantity.

The variabili ty of dissolved salts is very small, so toThe variabili ty of dissolved salts is very small, so to

define salini ty it must be accurate and precise.define salinity it must be accurate and precise.

But the range of salinity for most of the oceans is withinBut the range of salinity for most of the oceans is wi thin3535‰‰..

The average salinity of seawater is S = 35, which meansThe average salinity of seawater is S = 35, which meansthatthat seawater is 3.5% salt and 96.5% Hseawater is 3.5% salt and 96.5% H22OO by weightby weight



Classification of water based on salinity (Fast 1986):Classification of water based on salinity (Fast 1986):

-- Freshwater less than 0.5Freshwater less than 0.5‰‰

-- Oligohaline 0.5 to 3.0Oligohaline 0.5 to 3.0‰‰

-- Mesohaline 3.0 to 16.5Mesohaline 3.0 to 16.5‰‰

-- Polyhaline 16.5 to 30Polyhaline 16.5 to 30‰‰

-- MarineMarine 30 to 4030 to 40‰‰-- Brine or hyperhaline more than 40Brine or hyperhaline more than 40‰‰

Brackishwater is in the range of 0.5 to 30Brackishwater is in the range of 0.5 to 30‰‰..

In dry season some of the shrimp farm in Ecuador andIn dry season some of the shrimp farm in Ecuador andPanama salinit ies are in the range of 40 to 60Panama salinit ies are in the range of 40 to 60‰‰



Salinity based on ConductivitySalinity based on Conductivity

Conductivity is a measure of the abili ty of water to conductConductivity is a measure of the abili ty of water to conduct

electricity.electricity.

Conductivity is due to the dissolved ions, which are conductor.Conductivity is due to the dissolved ions, which are conductor. So,So,an increasing conductivi ty reading signifies the increasingan increasing conductivity reading signifies the increasingconcentration of d issolved ions.concentration of d issolved ions.

The unit is the micromho per centimeter.The unit is the micromho per centimeter.

Distilled water 1Distilled water 1--22 µµmhos/cmmhos/cm

Freshwater 20Freshwater 20--15001500 µµmhos/cmmhos/cm

Seawater more than 2000Seawater more than 2000 µµmhos/cmmhos/cm

Conductivity increases with the increase of salinity.Conductivity increases with the increase of salinity.

Many instruments are design to read out both specific conductancMany instruments are design to read out both specific conductanceeand salini tyand salini ty



How is salinity determined?How is salinity determined?

11.. Gravimetric methods: Evaporate to dryness. First precipitation iGravimetric methods: Evaporate to dryness. First precipitation iss

CaCOCaCO33, fol lows by CaSO, fol lows by CaSO44, NaCl, K and Mg salts. Several problems, NaCl, K and Mg salts. Several problemsexist and tedious process.exist and tedious process.

2.2. Analyze al l major ions and sum. Problems: have to analyze 11 Analyze al l major ions and sum. Problems: have to analyze 11ions, some are difficult, cumulative errors are large.ions, some are difficult, cumulative errors are large.

3.3. Utilize theUtilize the ““ law of constant proportionslaw of constant proportions”” chlorinity approach:chlorinity approach:

Measure Cl% (which gives the sum of all halides: ClMeasure Cl% (which gives the sum of all halides: Cl-- + F+ F-- + Br + Br -- + I+ I--))by titration with AgNOby titration with AgNO33 to precipitate AgCl. The titration gives theto precipitate AgCl. The titration gives theg Cl equivalent in 1kg sea water.g Cl equivalent in 1kg sea water.

Ag Ag++

+ seawater = AgCl (s) + AgBr (s).+ seawater = AgCl (s) + AgBr (s).The Cl can be converted to salinity using the equation:The Cl can be converted to salinity using the equation:

S = 1.80655 x Cl, where Cl chlorinity define as the concentratiS = 1.80655 x Cl, where Cl chlor ini ty define as the concentration ofon ofchloride in SW.chloride in SW.

4. Conductiv ity: Use the equation as before4. Conductiv ity: Use the equation as before



5. Density: The measurement are normally made by passing water o5. Density: The measurement are normally made by passing water orr

sample through a vibrating tube encased in a constant temperatur sample through a vibrating tube encased in a constant temperatur ee

jacket . The density of the solution is proportional to the squar jacket. The density of the solution is proportional to the squar e of thee of theperiod of the vibration. Use the following equation:period of the vibration. Use the following equation:

S = 1.3343 (S = 1.3343 (pp--ppoo)10)1033 + 2.155306 x 10+ 2.155306 x 10--44 x [(x [ (pp--ppoo)10)1033]]22 – – 1.171160 x 101.171160 x 10--55 [([(pp--ppoo)10)1033]]33

Where,Where, ((pp--ppoo) = B (t) = B (t22 – –ttoo22), t and t), t and too are respectively the periods ofare respectively the periods of

vibration for the solution and water. The system can be calibratvibration for the solut ion and water. The system can be calibratededusing Nusing N22 and Hand H22O or standard seawater and HO or standard seawater and H22O. The instrumentO. The instrument

constant (B) is determined from this calibration.constant (B) is determined from this calibration.

6. Sound speed: Measurement of sound speeds (U) relatives to pur 6. Sound speed: Measurement of sound speeds (U) relatives to pur ee

water (Uo) the salinity can be determined as:water (Uo) the salinity can be determined as:

S = 0.91712 (US = 0.91712 (U – – Uo) + 7.670097 x 10Uo) + 7.670097 x 10--44 x (Ux (U – – Uo)Uo)22 – – 1.107557 x 101.107557 x 10--55 (U(U – – Uo)Uo)33

7. Refractive index7. Refractive index



Difficulties in dryness methodsDifficulties in dryness methods

The residue left after evaporation in gravimetric methodsThe residue left after evaporation in gravimetric methods

isis mixture of complex saltsmixture of complex salts , together with some water, together with some water

chemically bound to the solidschemically bound to the solids , plus a, plus a small amount ofsmall amount of

organic material.organic material.

The amount of water left behind can further be decreasedThe amount of water left behind can further be decreased

by drying the residual salts at high temperature. This leadby drying the residual salts at high temperature. This lead

to other problems, such as:to other problems, such as:

1. Decomposition of some salts (loss of water1. Decomposition of some salts (loss of waterand gaseous HCl from hydrous MgCland gaseous HCl from hydrous MgCl22))

2. Vaporization of decomposit ion organic matter2. Vaporization of decomposition organic matter

3. Expulsion of CO3. Expulsion of CO22 gases from carbonate salts.gases from carbonate salts.



Modern Salinometer are compact and rapid in operation,Modern Salinometer are compact and rapid in operation,

and can measures salinity toand can measures salinity to ±±0.001 or better.0.001 or better.

Conductivity sensors, have been incorporated intoConductivity sensors, have been incorporated into

-- in situin situ temperaturetemperature--salinity instrument for use insalinity instrument for use in

shallow water, andshallow water, and

-- conductivityconductivity--temperaturetemperature--depth (CTD) probes fordepth (CTD) probes foruse in the deep oceans.use in the deep oceans.

Because a salini ty value determined by conductivityBecause a salini ty value determined by conductivity

depends on the temperature and pressure at which thedepends on the temperature and pressure at which the

conductivity is measured.conductivity is measured.

It is advisable to calibrate the system using weightIt is advisable to calibrate the system using weight --diluteddiluted

seawater for better resultsseawater for better results



Precision in salinity determination by various methodsPrecision in salinity determination by various methods

1. Evaporation to dryness1. Evaporation to dryness ±± 0.010.01

2. Composition studies of major components2. Composition studies of major components ±± 0.010.01

3. Chlorinity3. Chlorinity ±± 0.0020.002

4.4. ConductivityConductivity ±± 0.0010.0015. Density5. Density ±± 0.0040.004

6. Sound speed6. Sound speed ±± 0.030.03

7. Refractive index7. Refractive index ±± 0. 050. 05



The Salt Balance: Addition and removalThe Salt Balance: Addition and removal

The salts of the ocean come from theThe salts of the ocean come from the::

Land through river Land through river Chemical reaction of sea water with sedimentsChemical reaction of sea water with sediments

Gases produced by volcanoesGases produced by volcanoes

Spreading centers of the mid ocean ridge and rise systemSpreading centers of the mid ocean ridge and rise system

During volcanic eruptionsDuring volcanic eruptions ““ sulfide and chloridesulfide and chloride”” gases are released,gases are released,dissolved in rain water and carries to ocean as Cldissolved in rain water and carries to ocean as Cl-- and SOand SO4422-- ions.ions.

These ClThese Cl -- and SOand SO4422-- ions are acidic, grinded down and dissolved theions are acidic, grinded down and dissolved the

rock over which it flows. It helps to liberate the other +ve ionrock over which it flows. It helps to liberate the other +ve ions suchs suchas, Naas, Na++, Ca, Ca2+2+ and Mgand Mg2+2+ from earth crust.from earth crust.

When flowing through the fractured crust becomes heated. HeatedWhen f lowing through the fractured crust becomes heated. Heatedreacted chemically with rock crust whereby copper, iron,reacted chemically with rock crust whereby copper, iron,manganese, zinc, potassium and calcium are dissolved in water manganese, zinc, potassium and calcium are dissolved in water



Salts are removed from sea water in a number of ways:Salts are removed from sea water in a number of ways:

Sea spray from wave and action is blown a shore deposited aSea spray from wave and action is blown a shore deposited afilm of salt on the landfilm of salt on the land

Shallow arm of sea may becomes isolated the water evaporatedShallow arm of sea may becomes isolated the water evaporatedand salt left behind to become land depositsand salt left behind to become land deposits

Salt ions react with each other to form insoluble products thatSalt ions react with each other to form insoluble products thatsettled to ocean floor settled to ocean floor

Biological process concentrated salt, which are removed withBiological process concentrated salt, which are removed withthe harvest of organisms.the harvest of organisms.

Other biological process removes calcium by incorporating itOther biological process removes calcium by incorporating itinto shells, silica is used to form hard parts of certain diatominto shells, silica is used to form hard parts of certain diatomss

Adsorption is most important single process of ion removal. Adsorption is most important single process of ion removal.



““ Tiny clay mineral particles, weathered from rock are brought toTiny clay mineral particles, weathered from rock are brought to

ocean by he river or the winds, bind ions and molecules to their ocean by he river or the winds, bind ions and molecules to their

surface by a process known as adsorptionsurface by a process known as adsorption””

The fecal pellets and skeleton left over of small organisms alsoThe fecal pellets and skeleton left over of small organisms also

act as adsorption surfaces. Calcium is removed rapidly from seaact as adsorpt ion surfaces. Calcium is removed rapidly from sea

water, forming l imestone and shells of marine organism.water, forming l imestone and shells of marine organism.

NaNa++ is moderately abundant in freshwater, but because it reactsis moderately abundant in freshwater, but because it reacts

slowly with other substances in sea water, it remains dissolvedslowly with other substances in sea water, it remains dissolved inin

ocean.ocean.



Residence time (RT)Residence time (RT)

The average time that the substances remains in solution in oceaThe average time that the substances remains in solution in oceans isns is

called itscalled its ““ Residence timeResidence time”” ..

Amount of substance in oceans Amount of substance in oceans

RT =RT = ----------------------------------------------------------------------------------------------------------------------------------------

Rate at which substance is added to or removed from ocRate at which substance is added to or removed from oceanseans

The RT of substance in ocean depends on how reactive it is withThe RT of substance in ocean depends on how reactive it is with thetheexisting marine environment.existing marine environment.

Compounds that are less reactive have a longer residence time. TCompounds that are less reactive have a longer residence time. Thehelong residence time leads to the availability of higher concentr long residence time leads to the availability of higher concentr ations ofations of

the dissolved substances.the dissolved substances.

Calculations suggest that shallow surface water resides in oceanCalculations suggest that shallow surface water resides in ocean forforperiod that average 100yrs, whi le deep water average between 100period that average 100yrs, whi le deep water average between 1000 to0 to2000yrs.2000yrs.



Table: Approximate Residence Time of Ions in the OceansTable: Approximate Residence Time of Ions in the Oceans

IonsIons Time in yearsTime in yearsChlorideChloride 100million100million – – infiniteinfinite

SodiumSodium 260 mil lion260 mil lion

MagnesiumMagnesium 22 million22 mill ion

PotassiumPotassium 11 million11 mill ion

SulfateSulfate 11 million11 mill ionCalciumCalcium 1 million1 million

ManganeseManganese 0.0014 mill ion (1400 yrs)0.0014 mill ion (1400 yrs)

IronIron 0.00014 mill ion (140 yrs)0.00014 mill ion (140 yrs)

Aluminum Aluminum 0.00010 mill ion (100 yrs)0.00010 mill ion (100 yrs)

Source: The WorldSource: The World’’s Oceans. Sverdrup, Duxbury and Duxbury,2005s Oceans. Sverdrup, Duxbury and Duxbury,2005



Dissolved matter in inland waters

Most inland water is classed as freshwater: by definition meanssalinity lower than 3ppt.

The concentration of solutes generally increases in river withdistance from the source and can vary in response to discharge,while freshwater lake becomes more solutes enriched with time.

The chemical composition of inland water is determinedparticularly by the catchments.

Rain bringing some inputs, but the area with hard rock and thinsoils adjacent to coast relatively unimportant.

Many constituents of fresh water are, however at much higherconcentrations then catchments weathering.



Table : Chemical constituents (mg/L) of rain water and river

Symbol Rainfall

(continental)

Rainfall (marine &

costal)

Rivers

Cl-

Na+

SO4-2

Mg+2

Ca

+2

K+

HCO3-

SiO2

0.2-2.0

0.2-1.0

1.0-3.0

0.05-0.5

0.2-4.0

0.1-0.5

0

0

1.0-10.0

1.0-5.0

1.0-3.0

0.4-1.5

0.2-1.4

0.2-0.6

0

0

3.4-7.0

3.2-7.0

3.5-15.1

1.4-5.2

5.3-24.2

1.0-1.6

26.7-80.1

6.8-16.3



The main differences is that HCOThe main differences is that HCO33-- is the main anion in river and has ais the main anion in river and has a

much higher concentration than Clmuch higher concentration than Cl--

CaCa2+2+ is the main cation in river water, followed by Nais the main cation in river water, followed by Na2+2+ , Mg , Mg2+2+ and K and K ++

The SiOThe SiO22 is predominantly in the Unionized form Si(OH)is predominantly in the Unionized form Si(OH)44 in most riverin most river



The relative composition of rivers entering the oceans ofThe relative composition of rivers entering the oceans of

various continents is shown as:various continents is shown as:



Dissolved Gases

The gases that composed the air is soluble in water, but solubilityis not in it proportion. Solubility of various gases in surface ofseawater at 0oC:

Nitrogen 14.0mg/LOxygen 8.0mg/L

Carbon dioxide 0.47mg/L Argon 0.36mg/L

O2 and CO2 are important as they are non-conservative and depleted orproduce with the depth.

Oxygen is important in water, for respiration and carbon dioxide, forphotosynthesis.

Both originate mainly from the atmosphere, but diffusion mixes gases veryslowly and physical mixing is required to ensure that they penetrate beyondthe surface level.



Dissolved Oxygen

The major sources of oxygen in water are from air and also from

photosynthetic activities.

Solubility of oxygen depends on temperature, pressure salinity and so ondepth.

There exist inverse relationship of temperature and solubility of oxygen asshown below:

Temperature (oC) Solubility (mg/L)0 8.010 6.3

20 5.230 4.3

1O2 solubility ∞

Temperature



Also with salinity solubility of O2 is inversely proportional

Thus, seawater contains approximately 20% less oxygen than fresh

water at an equivalent temperature and pressure.

Dissolved oxygen concentration at saturation may be calculated as:

CmSaturation (%) = ----------- x 100

CS /

Cm is measured dissolved oxygen concentration in mg/L.

TPCS / = CS x ----------

760TP = BP + HP, where BP is the total pressure at givendepth (mm Hg) and HP is the hydrostatic pressure (mm Hg)

HP = γ (Z), where γ is the specific weight and Z is the depth.



Transfer of oxygen between air and water is reversible process. Transferof oxygen from air to water occurs when water is unsaturated withdissolved oxygen and oxygen diffused from water to air when water

supersaturated with dissolved oxygen.

The driving forces causing net transfer of dissolved oxygen between airand water is the differences in oxygen tension.

Although dissolved oxygen diffuses from air to water, but biological

process are important than physical process to regulate oxygenconcentration in water.

Factors that control dissolved oxygen in natural water are:- Temperature- Light- Nutrients concentration- Species of plants/plankton- Abundance of plants/plankton-Turbulence or water mixing



Carbon dioxide

Carbon dioxide is subject to the same effect of temperature,pressure, salinity and depth as oxygen, but is considerably moresoluble in water because it combines with alkali metals to formbicarbonates and carbonates according to the reactions

CO2 + H2O H2CO3 H+ + HCO3- 2H+ + CO3

2-

Therefore, very little carbon dioxide gas is present in water.

Total dissolved carbon dioxide in oceans decreases with depth to

about 100m and then is fairly constant to the bottom.

This is because carbon uptake in the surface zone by biologicalactivity (Photosynthesis and skeleton production) while, in deepwater, lower rates of carbon uptake are balance by regenerationfrom decomposition of organic particles.



Thermal/chemical Stratification

Lakes share many physical characteristics with oceans,modified by their size and depth.

All but the shallowest lakes undergo stratification similar to

that in marine systems.

Life in lakes and larger ponds experiences seasonal shifts.

The heating and cooling of surface waters changestemperature and oxygen levels through out the basin.



With the onset of coolerweather, the temperature ofepilimnion drops until it is thesame as that of the hypolimnion.

Then the water of the enter lakeor begins circulating oxygen andnutrients.

This circulation, which recharges

oxygen and nutrients throughthe basin, is called the falloverturn.

Stirred by wind, the overturnmay last until ice forms.



Then comes winter, and the surfacewater cools to below 4oC.

It becomes lighter again and remainson the surface.

If winter is cold enough, surface waterfreezes, the process called winterstratification.

In winter supply of oxygen is usuallynot greatly reduced because bacterialdecomposition and respiration oforganisms are not so great at lowtemperature.

At low temperature water also holdsmore oxygen. But if ice form at thesurface, it prevents photosynthesis,resulting in oxygen depletion for theenter lake and winter kill of the fish.



In spring the ice melts and waterbecomes warmer, it becomesheavier and sinks to the bottom.

Thus, when the surfacetemperature rises to 4oC, thelake takes another deep breath,as it were the spring overturn.



Nutrients Status

A close relationship exists

between land and waterecosystems. Primarily throughthe hydrological cycle, onefeeds on the other.

The water carries it silt and

nutrients in solution. Humanactivities, including roadconstruction, logging, mining,construction and agricultural,add another heavy loaded siltsand nutrients, especially

nitrogen and phosphorus andorganic matter.

These inputs enrich aquaticsystems, a process calledeutrophication.



The term eutrophy (from the GreakThe term eutrophy (from the Greak eutrophoseutrophos,, ““well nourishedwell nourished””) means a) means a

condition of being nutrient rich.condition of being nutrient rich.

The opposite is oligotrophy, the condition of being nutrient pooThe opposite is oligotrophy, the condition of being nutrient poor.r.



Eutrophic Systems

A typical lake has high surfaceto volume ratio; that is, thesurface area is larger relative todepth.

An abundance of nutrients,especially nitrogen andphosphorus, stimulates a heavygrowth of algae and otheraquatic plants.

Increase photosynthesisproduction leads to an increasesre-generation of nutrients andorganic compounds, stimulatingeven further growth



Eutrophic condition

Phytoplankton concentrations in the warm upper layer of the water,

giving it a murky green cast.

The turbidity reduces light penetration and restricts biologicalproductivity to a narrow layer of surface water.

Algae, inflowing organic debris and sediment, and remains of

rooted plants drift to the bottom, adding to the highly organicsediments.

Bacteria partially convert this dead organic matter into inorganicsubstances.

The activities of these decomposers deplete the oxygen supply of the bottom sediments and deep water to the point at which thisregion of the lake cannot support aerobic life.

The number of bottom species declines, although the biomass andnumber of organisms remain high.



Oligotrophic System

Oligotrophic lakes have a low surface to volume ratio.

The water is clear and appears blue to blue-green in sunlight.

The epilimnion is cool, the hyperlimnion is high in oxygen, and

bottom sediments are largely inorganic.

The nutrient content of the water, however, is low; and althoughnitrogen may be abundant, phosphorus is highly limited.

With the additions of increasing quantities of nutrients by humanor natural way added to a lake or pond, it begins to change fromoligotrophic to metatrophic to eutrophic



Oligotrophic condition

Low availability of nutrients causes low productivity oforganic matter, particularly phytoplankton.

Low organic matter production leaves little fordecomposers, so oxygen concentration remains high in thehyperlimnion.

The lack of decomposable organic matter means lowbacterial populations and slow rates of microbialmetabolism.

Although the number of organisms in oligotriophic lakes andponds may be low, species diversity is often high.



Dystrophic system

Water bodies that receive large amounts of organic matter fromsurrounding land, particularly in the form of humic materials thatstain the water brown are called dystrophic (from dystrophsmeans ill nourished).

Productivity of such water bodies is low, only low inphytoplankton production.

Such types of water bodies generally have large productivelittoral zone, particularly those developed bog flora.

These zones are providing sources of both dissolved andparticulate organic matter.



QUESTIONS?QUESTIONS?

water composition & quality criteria

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