Natural Waters

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Natural Waters

• Take a few minutes to talk about water
• Cycling between reservoirs (hydrologic cycle)
• What are the reservoirs of water on earth?
• Movement between reservoirs measured by flux ?
  simple flux mass / time
• Real flux ? mass unit area-1 time-1

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Time in a reservoir

• Steady State condition that reservoir sizes do
  not change
• Residence time amount of time material spends
  in a reservoir
• Steady state
• Residence time mass / flux __ time
• Residence time of water in ocean
• 1.4E21 kg / 4E17 kg/yr ? 104 10,000 years!

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Water and Gases

• Pure water (evaporation generally purifies water)
  interacts with gases in air
• Equilibrium between air and gases
• H2O CO2 ? H2CO3(aq)
• How do we determine conc. H2CO3(aq)??

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Diffusion, Fickian

• Diffusion from high to low levels..
• Where D is the diffusion coefficient, dc/dx is
  the gradient, and J is the flux of material

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Water particles

• Other Stuff in atmosphere
• anthropogenic gases SO2?
• Particles Fine minerals (dust from Africa
  crosses the ocean, volcanic particles cirle the
  planet)
• What about other stuff ? why does Lagavulin and
  Talisker have an iodine taste after it sits 12
  years in oak barrels?

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Rivers

• Once rain hits the earth, lets think about where
  it goes and what happens to it
• What about when it hits the ground?
• Chemical interaction?
• Physical interaction?
• What makes different rivers different in the
  dissolved chemistry and particles carried?

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Particulates in rivers

• Suspended load particles transported in the
  water
• Bed Load particles moved along th river bed

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Dissolved River water
River Ca2 Mg2 Na K Cl- SO42- HCO3- SiO2
Africa 5.7 2.2 4.4 1.4 4.1 4.2 26.9 12
N.Am (pol) 21.2 4.9 8.4 1.5 9.2 18 72.3 7.2
N.Am (nat) 20.1 4.9 6.5 1.5 7 14.9 71.4 7.2
How constant is some of this??? Is a river in
Quebec similar to one in Texas? What about the
winooski same in July as in February?
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Oceans

• Average depth of the oceans is 3730 meters, but
  we consider the top part somewhat separately-
  why??
• Thermocline T gradient change
• Pycnocline Density gradient change
• Chemocline Chemical gradient change

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Ocean Chemistry
Element Mg/kg molality
Cl- 19,350 0.556
Na 10,760 0.485
SO42- 2,710 0.0292
Mg2 1,290 0.0550
Ca2 411 0.0106
K 399 0.0106
HCO3- 142 0.0024
What about the speciation?
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Elements in the Oceans

• Split elemental abundances in the ocean into 3
  classes
• Conservative - constant
• Recycled used by organisms in photic zone
• Scavenged taken out by precipitation of small
  particles dont dissolve, settle out
• Where do major elements come from?
• Table 7-9

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Oxygen in the Ocean

• Oxygen is supersaturated in surface water
• WHY??
• Oxygen becomes depleted from consumption by
  organisms, goes back up some at the bottom (???)

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Ocean Chemistry reservoirs

• INPUT Precipitation, river drainage (dissolved
  and particulate), atmosphere (gases and
  particles) anything else??

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Ocean pH buffering

• What buffers pH in ocean waters??
• Are there any solids that can buffer pH?

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CCD Calcite Compensation Depth
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Evaporation

• Minerals that are very soluble only precipitate
  as more dilute waters evaporate, leaving behind
  an increasingly concentrated solution
• Ca2 SO42- 2 H2O ? CaSO42H2O

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Seafloor hydrothermal systems

• Spreading centers heat source drives convection
  cells, leach materials from country rock, spews
  out at fractures

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Groundwater

• Precipitation that does not run-off into rivers
  percolates into soils, sediments, and into
  basement rock fractures to become groundwater
• Water always flows down-hill
• Darcys Law describes the rate of flow
• where,Q volumetric flow rate (m3/s or
  ft3/s),A flow area perpendicular to L (m2 or
  ft2),K hydraulic conductivity (m/s or ft/s),l
  flow path length (m or ft),h hydraulic head
  (m or ft), andD denotes the change in h over
  the path L.

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Groundwater Chemistry

• Just like other waters, encounters minerals,
  gases, etc.
• Some key differences from other waters
• PCO2 variable respiration!
• Segregation of flowpaths in different units

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Lakes

• Lakes are stratified as well
• Epilimnion warmer, less dense upper layer
• Hypolimnion denser, cooler bottom layer
• Stratification changes seasonally due to surface
  water temperture being controlled by sun, air T
• Because the most dense water is at 4 C, as the
  surface water cools, water column ca overturn
  in spring as it warms, another turnover can
  happen!

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Nutrients

• Lakes are particularly sensitive to the amount of
  nutrients in it
• Oligotrophic low nutrients, low photosynthetic
  activity, low organics ? clear, clean
• Eutrophic high nutrients, high photosynthetic
  activity, high organics ? mucky, plankton /
  cyanobacterial population high
• Plankton growth
• 106 CO2 16 NO3- HPO42- 122 H2O 18 H
  trace elements light ? C106H263O110N16P1 138
  O2 (organic material composing plankton)
• This CNP ratio (106161) is the Redfield Ratio
• What nutrients are we concerned with in Lake
  Champlain?