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Natural Waters

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. Time in a reservoir.

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Natural Waters

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  1. 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

  2. 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: 1.4E+21 kg / 4E+17 kg/yr  ~104 =10,000 years!

  3. 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)??

  4. 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

  5. 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?

  6. Rivers • Once rain hits the earth, let’s 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?

  7. Particulates in rivers • Suspended load – particles transported in the water • Bed Load – particles moved along th river bed

  8. Dissolved River water 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?

  9. 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

  10. Ocean Chemistry What about the speciation?

  11. 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 – don’t dissolve, settle out… • Where do major elements come from? • Table 7-9…

  12. 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 (???)

  13. Ocean Chemistry reservoirs • INPUT: Precipitation, river drainage (dissolved and particulate), atmosphere (gases and particles) – anything else??

  14. Ocean pH buffering • What buffers pH in ocean waters?? • Are there any solids that can buffer pH?

  15. CCD = Calcite Compensation Depth

  16. Evaporation • Minerals that are very soluble only precipitate as more dilute waters evaporate, leaving behind an increasingly concentrated solution • Ca2+ + SO42- + 2 H2O  CaSO4*2H2O

  17. Seafloor hydrothermal systems • Spreading centers heat source drives convection cells, leach materials from country rock, spews out at fractures…

  18. 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 • Darcy’s 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.

  19. 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

  20. 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!

  21. 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 C:N:P ratio (106:16:1) is the Redfield Ratio • What nutrients are we concerned with in Lake Champlain?

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