earth 168

• What is laminar flow

  characterized by uniform fluid, has low Reynolds # (Re < 500), follows the banks
• point source vs non point source

  point: comes from a single place

  
  

  non-point: hard to address and identify, comes from many places
• what is turbulent flow

  Characterized by random (chaotic) motion and flow lines (Re > 2000)
• factors of laminar flow (including two important transport processes)

  Flows in smooth, parallel layers and lacks chaotic motion. Molecular diffusion. Groundwater lake sediments (ex)
• factors of turbulent flow

  Random, chaotic motion patterns. Turbulent diffusion. Lakes and rivers (ex)
• Reynold's #


  Re = uL/v where u - velocity, L = length, v = kinematic viscosity
• What is advection


  the movement of a solute by the fluid current
• Gradient transport


  movement of a solute from high to low concentrations caused by radon motions and the concentration gradient
• advection-diffusion equation**


  advection + diffusion - kC

  
  

  - consider flux into and out of a fluid parcel with x, y and z

  - let flux into out of parcel due to advection and diffusion (fick's first)

  - allow chemical reactions (1st order)

  - solve mass balance eq
• Dispersion


  the spreading of a solute caused by differential advection due to a gradient in current velocity (occurs in laminar and turbulent flow)
• what is fick's first law
• fick's second law


  relates molecular diffusion with concentration as a function of time and space, assumes ux = 0 and a conservative solute
• what do water quality decisions typically consist of

  field measurements and model output
• temporal functions


  continuous, intermittent, instantaneous (spill), most sources are intermittent
• spatial functions


  point source (ie waste water/industrial outfall, tributary) or non-point source (gas exchange, precipitation, dust, groundwater, etc).
• External sources


  temporal variations in both discharge rate and concentration, diurnal/weekly cycle
• what are system models

  based on mass balance approach, formally defines model parts and where constituent is, where it is going, how long it will take. lacks detail
• components of system model*


  system, reservoir, flux, source, sink, turnover time, budget, results of budget, cycle
• system


  part of the universe we are studying (ex CO2 in earth or water in lake)
• reservoir


  part of a system (subsystem) with common properties (M (kg) defines amount of material in reservoir)
• source


  flux into a reservoir (+Q)
• sink


  flux out of a reservoir (-Q)
• turnover time (mean residence time)


  average time a molecule spends in a reservoir (T = M/(sum source or sink))
• budget


  a balance sheet of all sources and sinks:

  - Source = sink, STEADY STATE

  - Source > sink, reservoir mass increase

  - Source < sink, reservoir mass decrease
• what does the result of the budget define?

  defines missing sources or sinks, ID major and minor sources/sinks
• cycle


  a system with two or more connected reservoirs
• when does a maximum concentration occur?

  when xmax = uxt
• where is most of the mass located in a normal function?

  +- 1 standard deviation
• what is a flux

  amount of material transferred between reservoirs per unit time (Q (kg/s) defines flux)
• mass balance equations


  change in M/ change of t = sum sources - sum sinks

  
  

  or = sum of sources - kM

  
  

  or = Q - kM, where k = 1/t

  
  

  or 3Q1 = Q2, 0.6Q1 = Q2 (when change in source loading occurs and Q = sum of sources)
• when does steady state occur?

  sum of M/sum of t = 0 or sources = sinnks
• what are results of the mass balance equation?

  if Q is constant and sum of sinks are proportional to M, the system will approach equilibrium
• history of gas transfer between the atmosphere and water interface

  old problem

  ; recognizes the rate limiting process is the transfer of gas through water boundary layer by molecular diffusion
• What is the equation that describes the unit flux of gas across the air-water interface


  q = kgtv(C - Ceq) where:

  
  

  kgtv is the gas transfer velocity and proportional to (Dm)^n

  
  

  Dm = molecular diffusion coefficient

  n = 1 for the stagnate film model

  n = 1/2 to 2/3 for surface renewal model
• How long does it take to reach steady state?

  3 tao or 3t
• Assumptions needed to test in Sutherland pond

  volume = constant, pond is well mixed, Qchem is a 1st order reaction
• What is Wtotal?


  the sum of the sources
• Concentration vs time


  Large sd = poorly mixed

  Small sd = well mixed
• what does wwtf stand for

  waste water treatment facility
• Sulfur bank mercury mine


  one of the largest in the US~5000 metric tons of Hg mined between 1870 and 1960

  
  

  water column and surface sediment Hg extremely high, likely that hg still being added into system