water chemistry i - oregon state...

Water Chemistry

Major cations

Ca++

Mg++

Na+

K+

Major anions

HCO3 -

CO3 - -

SO4- -

Cl -

Salinity

Salinity is the total ionic composition of water, expressed in terms of mg/l or meq/l

Total solids is a measure of salinity and is determined by evaporating water at 105°C and weighing the residue

Total dissolved solids is determined by filtering before evaporation

Water Hardness

Soft waters are low in salinity and are frequently derived from drainages of acidic igneous rocks

Hard waters are high in salinity and frequently drain areas of calcareous deposits

Salinity of the world's surface waters is determined by three major factors

Rock dominance

Atmospheric precipitation

Evaporation-precipitation processes

Specific conductance

Specific conductance is a measure of the resistance of a solution to electrical flow

Specific conductance increases with increases in ionic concentrations

Chemical Concentration

Mass concentration

Weight per unit volume w/v

Weight per unit weight w/w

If the density of the solution is one (as in water), the two expressions are identical

Origins and Distributions of Freshwater Organisms

There are greater numbers of species occurring in marine and fresh waters than in brackish watersAquatic bacteria, blue-green algae, algae, fungi, and protozoans are generallyeuryhaline (exhibit wide range of tolerance to salinity)

Origins and Distributions of Freshwater Organisms

Higher aquatic plants evolved terrestrially and invaded fresh water secondarily

Most higher freshwater animals evolved in marine environments

Most aquatic insects were originally terrestrial

Geological Sources

Most commonly as apatite - Ca5(PO4)3+

Phosphine gas - PH3

Sources for surface waters

Precipitation and falloutConcentrations are variableOften lower concentrations than nitrogenGenerally range from 30 ug/l to greater than 100 ug/lFallout as dust and fertilizers

Sources for lakes

GroundwaterConcentrations are generally lowOften less than 20 ug/l

Surface runoffSoil relatedOften a major source of inputRelated to soils, topography, vegetation cover, quantity of runoff, land use, and pollution

Sources for lakes

Phosphorus content of parent geology is highly variablePollution from detergents is a major source of phosphorus

Sodium pyrophosphates and polyphosphates are added to complex with cations and inactivate them to enhance cleaning action (related to hardness)

Forms of Phosphorus

Inorganic phosphorus (orthophosphate or PO43-)

Dissolved inorganic phosphorusParticulate inorganic phosphorusInorganic phosphorus is usually less than 5% of the total phosphorus content of a lake

Organic phosphorusDissolved organic phosphorusMajor form of total dissolved phosphorusParticulate organic phosphorus

SRP and Orthophosphate

Orthophosphate (PO43-) is equivalent to

soluble reactive inorganic phosphorus

Only dissolved phosphate can be used directly for plant growth

Abundance

Orthophosphates, polyphosphates, and higher phosphates form complexes, chelates, and insoluble salts with metal ionsExtent of complexation and chelationdepends on relative concentrations of phosphorus and metals

Abundance

Metal ions of micronutrients (Fe, Mn, Zn, Cu) are generally in equal or lower concentrations than phosphorus, therefore phosphorus can greatly affect their distributions

Metal-phosphate complexes are generally insoluble, therefore concentrations are reduced by complexation

Sediments

Concentrations of phosphorus often increase near sediments because of the effects of reduced oxygen concentration on redox potentialPhosphate concentrations are high in the interstitial water of the sediments (0.6 - 10.0 mg/l PO4-P)Because of exchange between sediments and overlying waters, there is little correlation between phosphorus content of sediments and productivity of the lake

Sediment to Water

Mineral-water equilibriaTurbulencePhosphorus-mobilizing bacteriaPseudomonasBacterium

Benthic algaeVascular macrophytes

Root uptakeLeaching from dead plants

Sediment to Water

Burrowing activity and migration of benthic invertebrates

BioturbationSmall as related to other processes

Uptake of P by algae

Luxury consumptionAll phytoplankton can take up more phosphate than is required for growth and store it within the cellPhosphate stored in the form of polyphosphate granules

Ability to use phosphates at low concentrationsThe growth constant (Ks) for phosphate is low

Uptake of P by algae

Alkaline phosphatase activityAlgae release the enzyme alkaline phosphataseThe enzyme cleaves the bond between PO43- and organic molecule, freeing phosphate for uptake Synthesis of enzyme is suppressed by high concentrations of phosphate

Nitrogen

Nitrogen

Nitrogen gas - N2

Ammonia - NH3

Ammonium - NH4+

Nitrite - NO2-

Nitrate - NO3-

Organic N

N2

NH4+ Amino Acids

Dissolved Organic N

NO2-NO3

-

Lysis, excretion

Amino Acid Synthesis

Ammonification

Nitrification

Nitrification

NitrateReduction

Denitrification

NitrogenFixation

Hypoxia in Gulf of Mexico

Zone was 20,000 km2 (7,728 mi2) in 1999Size of New JerseyZone was 4,000 km2 (1,545 mi2) in 2000Extended to depths of 100 ft

Redfield Ratio

Determined by ratio of N and P in cells

N/P atomic ratio

< 15 photosynthesis is N limited

> 30 photosynthesis is P limited

Nutrient Retention

Nutrient Cycling

Spiraling Length = Sw + Sp + Sc

S = Flux/Uptake

S = N * v / N * u

N = Standing stock (g/m)v = Velocity (m/s)u = Uptake rate (s-1)S = m

Retention

Md = Mo * e-kd

Md = Mass at distanceMo = Mass at original locatione = Natural logarithmk = Instantaneous retention constantd = Distance downstream

Retention

0

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20 25 30 35 40 45 50

Distance (m)

Md

0.1 0.05 0.01

Retention

•ln Md = ln Mo - kd

•Md = Mass at distance

•Mo = Mass at original location

•e = Natural logarithm

•k = Instantaneous retention constant

•d = Distance downstream

Retention

-1

0

1

2

3

4

5

0 5 10 15 20 25 30 35 40 45 50

Distance (m)

ln M

d

0.1 0.05 0.01

Retention

Average travel distance = 1/k

Average travel distance ≈ Sw