Rivers

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Rivers
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River Water

• Water
• Suspended inorganic matter
• Sand, silt, clay
• Dissolved major species
• Elements with no gaseous phases in atmosphere
• Ca2, Na, K, Cl-, etc.
• Elements with gaseous phases in atmosphere
• SO42-, HCO3-
• Dissolved nutrient elements
• N and P
• Suspended and dissolved organic matter
• Trace metals
• Dissolved and suspended

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Source of River Water

• Direct precipitation
• Surface flow runoff
• Interflow flow through soil in stream valley
• Residence time in soils hours to 10s hours.
• Groundwater variable residence time in
  subsurface hours-millennia

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Stream Hydrographs

• Records stream flow (discharge) through time

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Major Rivers
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Suspended Matter

• Small particles carried by turbulence
• Generally less than 100 microns, but varies with
  water velocity
• At high velocities can carry 10s to 1000s mm
• At very low velocities can carry lt 10 microns
  (clay size)
• Colloids common

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Suspended Matter

• Colloids
• Suspension of solids in water, not solid, not
  solution
• Colloidal particles are charged double layer
• Clays a common constituent
• Cation Exchange Capacity
• Much of the humic matter in natural waters is
  colloidal
• 80 of the oxidizable carbon in raw domestic
  sewage is colloidal or larger.

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Colloids

• Much of the dissolved iron in rivers is
  colloidal
• Fe3 oxyhydroxides occur in colloidal form
  between pH 5-10.
• Both in surface and subsurface waters
• lt5 microns
• Can comprise up to 70 measured Fe in water.
• the colloidal iron found in many rivers has a net
  negative charge whereas should be positively
  charged
• the colloidal iron oxide is coated with humic
  matter and other dissolved organic matter.
• The excess negative charge on the organics
  confers a negative charge to the colloid.
• Can transport generally immobile trace elements
  and radioactive elements

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Colloids

• 3 main classes of colloids
• Hydrophilic colloids
• very large molecules or ions, large molecules
  such as proteins which interact strongly with
  water
• Hydrophobic colloids
• interact less strongly with water but are stable
  because the particles repel each other.
• clays
• Association colloids - typical of soaps
• Collections of ions and molecules which associate
  as micelles. The head groups interact strongly
  with the water whilst the hydrophobic tails group
  together away from the water.

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Colloids

• Colloidal material must first be aggregated
  (flocculated) to be removed from the system
• Colloids can be destabilized by
• compression of the double layer
• By increasing the dissolved salt content of the
  solution
• adsorption causing charge neutralization
• enmeshment in a precipitate

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Suspended Matter

• Controlled by
• Relief of the drainage basin
• Drainage basin area
• Amount of water discharge
• Climate
• Season
• Geology of the river basin
• Presence of lakes/reservoirs along river length

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Suspended Matter
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Human Influence

• Increases due to
• Deforestation and cultivation
• Overgrazing
• Construction
• Decreases due to
• Building of dams and reservoirs
• Bank stabilization of rivers
• Soil conservation practices
• The effect of European settlement of the U.S. has
  been to increase the sediment loss to the oceans
  by a factor of 2.6

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Chemical Composition of Suspended Matter

• Controlled by
• Climate
• Weathering patterns in the drainage basins
• Tropical rivers have high Al and Fe because
  particulate originate from lateritic soils
• Temperate and Arctic rivers have a suspended load
  close to average surface rock compositon

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River Water Chemistry

• Compared with sea water

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Chemical Classification of Rivers

• Gibbs (1970) Classification
• Precipitation Dominant
• Surface water chemistry controlled by Atmospheric
  Precipitation
• River water composition resembles rainfall
• Low TDS
• High Na relative to Ca
• High Cl relative to HCO3
• Tropical rivers

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Chemical Classification of Rivers

• Gibbs (1970) Classification (Cont.)
• Rock Dominant
• Surface water chemistry controlled by rock
  weathering
• TDS are intermediate
• Na/(NaCa) is low
• Cl/(Cl HCO3) is low
• Rock weathering supplies most dissolved salts
• Dissolution of CaCO3 dominates
• Includes most of the major rivers

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Chemical Classification of Rivers

• Gibbs (1970) Classification (Cont.)
• Evaporation crystallization Dominant
• Surface water chemistry controlled by evaporation
  and fractional crystallization
• Evaporation along stream distance controls
  concentration of salts
• Increasingly higher downstream
• Irrigation contributes significantly
• TDS are high
• Na/(Na Ca) is high
• Cl/(Cl HCO3) is high
• Rock weathering supplies most dissolved salts
• Rivers are in arid climates

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Chemical Classification of Rivers

• Stallard and Edmund (1983) classification
• Rock weathering dominates the composition of all
  rivers.

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Chemical Classification of Rivers

• Ternary plot from Berner and Berner (1996)

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The Amazon

• Illustrates the importance of relief
• In lowlands, only dilution of solutes acquired in
  Andes

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Seasonal Variation

• North Fork of the Shoshone River, WY

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Seasonal Variation

• Change in chemistry after a rainstorm
• North Fork of the Shoshone River, WY, July 20,
  1973
• Na, HCO3-, Ca2, and Mg2 increased during first
  11 hrs
• Leaching of highly soluble material in soils
• After 11 hrs, dilution
• K increased as runoff increased indicating
  leaching from leaves, pollen, and insects

Arrow shows point of peak flow
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Major Dissolved Components

• Cations
• Sodium
• Calcium
• Magnesium
• Potassium
• Silica
• Organic Matter

• Anions
• Sulfate
• Chloride
• Bicarbonate
• Nutrients
• Nitrogen
• Phosphorus

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Major Dissolved Components

• Sodium
• Sea salt (cyclic salt)
• Rainfall
• Dry deposition
• Dissolution of halite in bedded deposits and
  shales
• Weathering of Plagioclase feldspar
• Redissoluiton of saline crusts in desert basins
  (minor)
• Cation exchange of dissolved Ca2 with Na on
  detrital clay minerals
• Pollution
• Domestic and industrial sewage
• fertilizer
• Oil and gas well brines
• Mining
• Road salt
• Detergents
• Water softeners

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Major Dissolved Components

• Potassium
• Dissolution of sylvite in bedded deposits
• Weathering of orthoclase feldspar
• Cation exchange of dissolved Ca2 with Na on
  detrital clay minerals
• Pollution
• Domestic and industrial sewage
• fertilizer
• Oil and gas well brines
• Mining
• Biogenic element
• Used by growing vegetation
• Concentrated in leaves
• Increase in K during autumn when trees lose
  leaves and they degrade

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Major Dissolved Components

• Calcium and Magnesium
• Sea salt (cyclic salt)
• Rainfall
• Dry deposition
• Dissolution of CaCO3 and CaSO4
• Weathering of Calcic Plagioclase feldspar
• Mg from weathering of dolomite and ferromagnesian
  silicate minerals (olivine, pyroxene, amphibole,
  biotite)
• Pollution
• fertilizer
• Oil and gas well brines
• Mining
• Road salt

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Major Dissolved Components

• Chloride
• Sea salt (cyclic salt)
• Rainfall
• Dry deposition
• Dissolution of halite in bedded deposits and
  shales
• Thermal and mineral springs in volcanic areas
• Redissoluiton of saline crusts in desert basins
  (minor)
• Pollution
• Domestic and industrial sewage
• Chlorination of public water supply
• fertilizer
• Oil and gas well brines
• Mining
• Road salt

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Major Dissolved Components

• Bicarbonate (HCO3-)
• Dissolution of CaCO3
• Reaction of CO2 dissolved in soil and groundwater
  with carbonate and silicate minerals
• Silica (SiO2)
• As H4SiO4
• Weathering of silicate minerals
• Dependent on level of precipitation
• High precip high flushing and high removal of
  silica
• Low precip low flushing and little silica
  removal
• Biogenic
• Used by Freshwater (and saltwater) diatoms for
  test formation
• Removes silica from water

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Major Dissolved Components

• Sulfate
• Sea salt (cyclic salt)
• Rainfall
• Dry deposition
• Weathering of bedded gypsum and anhydrite
• Weathering of pyrite
• Volcanism
• SO2 gas
• Pollution returned as wet and dry deposition
• Industrial
• Auto/truck internal combustion
• Power plants burning fossil fuels
• Fertilizer
• Industrial and municipal waste

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Major Dissolved Components

• Organic Matter (Organic Carbon)
• dissolved (DOC)
• Wide range due to location (2-25 mg/L)
• particulate matter (POC)
• 1 suspended load
• In rivers with DOC gt TDS
• Chemistry dominated by humic and fulvic acid
  carboxyl groups
• ?inorganic cation charge gt ?inorganic anion
  charge
• Balanced by organic anions
• Fe and Al are mobile as organic complexes and
  colloidal oxyhydroxides
• Tend to be acidic

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Nutrients in River Water

• Nitrogen in Rivers
• Dissolved inorganic nitrogen (DIN)
• NH4 and NO3-, NO2-
• NO3 is most important
• it is most abundant, and directly taken up by
  plants
• NH3 and NO2- are quickly oxidized to NO3-
• - both of these are also toxic to most organisms,
  
• - and are usually found in minute concentrations
• Dissolved organic nitrogen (DON)
• amino acids, proteins, and urea
• complex, high molecular weight compounds
• Particulate nitrogen

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Nutrients in River Water

• Nitrogen (cont.)
• Dissolved pollutive nitrogen
• 1/3 to 2/3 DIN and DON are pollutive
• Point sources
• Municipal and industrial sewage
• Septic tanks
• Refuse dumps
• Animal feed lots
• Diffuse (non-point) sources
• Runoff from urban and rural settings
• Fertilized fields
• Pastures
• Yards and gardens
• Nitrogen fixing crops
• Storm water runoff
• Precipitation directly into lakes and streams
• Wet and dry deposition

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Nutrients in River Water

• Phosphorus
• No stable gas phase in atmosphere
• Limiting nutrient in plant growth
• Dissolved Phosphorus in rivers
• Inorganic
• Orthophosphate anions
• PO43-, HPO42-, H2PO4- (dissociated
  orthophosphoric acid)
• these are readily available to plants
• concentrations usually low in water 5-20 µg/l
• Polyphosphates- may be hydrolyzed to soluble
  orthophosphate form
• Sourced from
• natural weathering of phosphate rich minerals
• Accelerated dissolution due to human induced soil
  erosion
• Phosphate from fertilizers
• Soluble phosphate from detergents and domestic
  and industrial waste

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Nutrients in River Water

• Phosphorus
• Dissolved Phosphorus in rivers
• Organic
• Proteins
• Particulate inorganic and organic compounds
• large molecules that settle quickly and lost
  indefinitely in deep sediments
• or can be broken down by decomposition to usable
  PO4
• There is a seasonality to phosphate
  concentrations in water
• related to plant activity
• greater in summer than in winter therefore
  concentrations less in summer than winter
• fairly soluble in water,
• can tie up with Ca, Fe and Al and quickly settle
  out into deep sediments and therefore not
  available to plants

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