water chemistry I - Oregon State...
Transcript of water chemistry I - Oregon State...
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Water Chemistry
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Major cations
Ca++
Mg++
Na+
K+
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Major anions
HCO3 -
CO3 - -
SO4- -
Cl -
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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
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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
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Salinity of the world's surface waters is determined by three major factors
Rock dominance
Atmospheric precipitation
Evaporation-precipitation processes
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Specific conductance
Specific conductance is a measure of the resistance of a solution to electrical flow
Specific conductance increases with increases in ionic concentrations
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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
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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)
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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
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Geological Sources
Most commonly as apatite - Ca5(PO4)3+
Phosphine gas - PH3
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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
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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
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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)
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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
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SRP and Orthophosphate
Orthophosphate (PO43-) is equivalent to
soluble reactive inorganic phosphorus
Only dissolved phosphate can be used directly for plant growth
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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
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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
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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
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Sediment to Water
Mineral-water equilibriaTurbulencePhosphorus-mobilizing bacteriaPseudomonasBacterium
Benthic algaeVascular macrophytes
Root uptakeLeaching from dead plants
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Sediment to Water
Burrowing activity and migration of benthic invertebrates
BioturbationSmall as related to other processes
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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
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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
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Nitrogen
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Nitrogen
Nitrogen gas - N2
Ammonia - NH3
Ammonium - NH4+
Nitrite - NO2-
Nitrate - NO3-
Organic N
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N2
NH4+ Amino Acids
Dissolved Organic N
NO2-NO3
-
Lysis, excretion
Amino Acid Synthesis
Ammonification
Nitrification
Nitrification
NitrateReduction
Denitrification
NitrogenFixation
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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
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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
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Nutrient Retention
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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
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Retention
Md = Mo * e-kd
Md = Mass at distanceMo = Mass at original locatione = Natural logarithmk = Instantaneous retention constantd = Distance downstream
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Retention
0
10
20
30
40
50
60
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0 5 10 15 20 25 30 35 40 45 50
Distance (m)
Md
0.1 0.05 0.01
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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
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Retention
-1
0
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0 5 10 15 20 25 30 35 40 45 50
Distance (m)
ln M
d
0.1 0.05 0.01
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Retention
Average travel distance = 1/k
Average travel distance ≈ Sw