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 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  ~10 4 =10,000 years!

Water and Gases Pure water (evaporation generally purifies water) interacts with gases in air: Equilibrium between air and gases: H 2 O + CO 2  H 2 CO 3(aq) How do we determine conc. H 2 CO 3(aq) ??

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

Water particles Other ‘Stuff’ in atmosphere: –anthropogenic gases: SO 2 ? –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?

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?

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

Dissolved River water River Ca 2+ Mg 2+ Na + K+K+ Cl - SO 4 2- HCO 3 - SiO 2 Africa N.Am (pol) N.Am (nat) 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?

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

Ocean Chemistry ElementMg/kgmolality Cl - 19, Na + 10, SO , Mg 2+ 1, Ca K+K HCO What about the speciation?

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…

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 (???)

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

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

CCD = Calcite Compensation Depth

Evaporation Minerals that are very soluble only precipitate as more dilute waters evaporate, leaving behind an increasingly concentrated solution Ca 2+ + SO H 2 O  CaSO 4 *2H 2 O

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

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 (m 3 /s or ft 3 /s), A = flow area perpendicular to L (m 2 or ft 2 ), K = hydraulic conductivity (m/s or ft/s), l = flow path length (m or ft), h = hydraulic head (m or ft), and D = denotes the change in h over the path L.

Groundwater Chemistry Just like other waters, encounters minerals, gases, etc. Some key differences from other waters: –P CO2 variable – respiration! –Segregation of flowpaths in different units

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!

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 CO NO HPO H 2 O + 18 H + + trace elements + light  C 106 H 263 O 110 N 16 P O 2 (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?